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Organisms and Environments

by: Oma Larkin

Organisms and Environments BIOL 116

Marketplace > University of Idaho > Biology > BIOL 116 > Organisms and Environments
Oma Larkin
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This 66 page Class Notes was uploaded by Oma Larkin on Friday October 23, 2015. The Class Notes belongs to BIOL 116 at University of Idaho taught by Staff in Fall. Since its upload, it has received 21 views. For similar materials see /class/227886/biol-116-university-of-idaho in Biology at University of Idaho.


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Date Created: 10/23/15
Protists Clues to the Evolutionary History of Eukaryotes Eukaryotes Appear Early in the Fossil Record Eukaryotes all cells have membrane bound nucleus Mm organelles cytoskeleton first appeared at least 21bya Origin a solar system and Earth Mullicellulav Singlecaned Eukaryotes Atmospheric oxygen cnrlynuhl Pmlsnn Educamn Incquot Puhllshmu as Benlzmn Currmlnus The vast majority of organisms that we are familiar with are eukaryotes including plants animals and fungi But what exactly is a eukaryote The term eukaryote is derived from the Latin words for true nucleus eu true karyo nucleus This refers to the fact that all eukaryotic cells contain a membranebound nucleus In addition eukaryotic cells also contain various organelles such as mitochondria and plastids and a cytoskeleton Essentially the cells ofeukaryotes are more compartmentalized and structured versions oftheir distant prokaryote relatives The oldest known fossils ofeukaryotic organisms have been dated at about 21 billion years ago But how did eukaryotes evolve from their prokaryotic ancestors and how did early singlecelled eukaryotes give rise to the vast diversity of eukaryotes that are on our planet In this lesson and the next we will discuss the leading hypotheses proposed to answer these questions and briefly introduce the protists the organisms living today that most closely resemble the earliest eukaryotes As you progress through this lesson keep in mind what the conditions on earth were like during the early history ofeukaryotes During this period there existed only microscopic life forms in the oceans large multicellular organisms did not exist and land had not yet been colonized In essence this means that many evolutionary opportunities existed for growth diversi cation and specialization Because ofthis we see a great diversity in growth forms and reproductive and metabolic strategies in the early eukaryotes and in their descendants present on Earth today mu Evolution of Eukaryotic Cells Infolding of plasma membrane gave rise to nuclear membrane Golgi apparatus endoplasmic reticulum Endosymbiosis gave rise to mitochondria plastids Ancasimt helemtmplllc wkmom It is likely that the various structures inside of eukaryotic cells originated in at least two different ways Some structures appear to have developed by an infolding and pinching off ofthe cell membrane The nuclear membrane Golgi apparatus and endoplasmic reticulum most likely developed in this way Other structures such as mitochondria and plastids originated when ancestral eukaryotic cells engulfed free living bacteria Rather than being digested however these bacteria somehow persisted as symbionts inside of the eukaryotic cell This theory of endosymbiosis is supported by many lines of evidence including the fact that mitochondria and plastids contain chromosomes and ribosomes very similar to those of bacteria and still divide independently oftheir eukaryotic hosts by binary fission It is also believed that mitochondrial endosymbiosis occurred prior to plastid endosymbiosis as all eukaryotic cells have mitochondria while only some such as plants and algae have plastids Early Growth Forms 3 Earliest eukaryotes were 39 singlecelled Multicellularity arose from simple cell attachments 39 filaments 39 colonies Euglena a singlecelled VOIWXY a COIONial alga alga pimrus University Dr Wscunsin Elnard ur Ra The earliest eukaryotes were probably singlecelled like their prokaryote progenitors However in numerous cases it appears that singlecelled organisms became attached to each other in small colonies or filaments Over time certain cells of these colonial or filamentous forms became specialized to perform specific roles for the organism In turn it is likely that these rudimentary groupings of cells eventually evolved into true multicellular organisms with differentiated cells and tissues It is interesting to note that the entire spectrum of this evolutionary history is still present in today s eukaryotic organisms In extant lineages one can find single celled organisms such as those of marine plankton colonial and filamentous organisms both with and without cell specialization and multicellular organisms which may contain simple or highly complex tissues The Protists Fungi animal and plant lineages All other eu karyotic lineages are considered protists Now that you have a basic understanding of the evolutionary trends in early eukaryotes you might be interested to learn about the lineages arising from these organisms and the present day representatives of the early eukaryotes Historically this group of organisms has been referred to as the protists The protists as a group represent all eukaryotes that are not clearly classified as plants animals or fungi However as you can see here the protists are not a monophyletic group This artificial group then while including the oldest lineages of eukaryotes also includes the closest relatives of plants animals and fungi V thin the protists there are both familiar organisms such as the kelps seaweeds and amoebas and less familiar organisms such as the slime molds Let s take a brief look at the protist groups that represent the closest living relatives of plants fungi and animals Green Algae Closest Relatives of the Plants Vllmiplanlm WW Green algae share features with plants a i chloro h Ilsaandb a gt fg cellulose In cell m 19 amplyquot swam mummyquot walls starch inside plastids sporopollenin Green algae WWW FEE cwyngvt VezrsonEdmrtim he mishaps BenPrwn Emmrgs The green algae represent over 10000 different species of protists In form they are very diverse including unicellular colonial sheetlike filamentous and multicellular organisms All green algae however share numerous similarities such as the presence of chlorophylls a and b in their chloroplasts cell walls that contain cellulose and the usage of starch as a storage compound inside of plastids These characteristics are also shared with land plants and particularly when found in multicellular forms suggest that green algae and terrestrial plants are very closely related The Charophycean green algae in fact are considered the closest living relatives of land plants These algae share other specific characteristics with this group For example the structure of flagellated sperm cells found in some land plants closely resembles that found in Charophyceans In addition some members of the Charophyceans have sporopollenin in their spore walls just as land plants do As the tree of life is continuously updated with new information some researchers have suggested that the plant kingdom should be expanded and renamed to include some or all of the green algae You can see two possibilities here listed as the Streptophyta and the Viridiplantae While these issues are still under debate at the very least they underscore the great similarities found between the green algae and the land plants Chytrids are considered the most ancient lineage of fungi 39 spores have single posterior flagella Zygniiiycota Glnmemmylmta Ascomycala aaaiiiiaiiiycaia E canyniini Pezsnn Enumiiiin Incquot Puhllshlnu as Benjzmln cumninns Current research indicates that the Fungi originally evolved from a unicellular flagellated protist In part this evidence is based on the fact that the most ancient members of the Fungi often called the Chytrids still possess unicellular agellated spores The oldest fossilized fungi found so far date to around 400 million years old However molecular analyses suggests that fungi may have diverged from their protist ancestors at a much earlier date perhaps as long as 15 billion years ago One extant group of protists the Choano agellates is considered to be very similar to the protist relatives ofthe Fungi However as we will see on the next slide the Choanoflagellates are actually more closely related to animals 80 while animals and fungi share protist relatives that were physically similar these groups diverged independently of one another and from different protist ancestors Choanoflagellates Relatives of Animals Some researchers would group the Fungi Animals and Choano agellates together as a single group the Opisthokonta Fungl g Fungi Choanollagallaias The Choanoflagellates are a relatively small group of singlecelled organisms numbering around 150 species These tiny organisms while easy to overlook represent the closest living relatives of animals The relatedness of the Choanoflagellates to the animals is in part based on the presence of a collar of tightlypacked microvilli surrounding a single posterior flagellum These characteristics are very similar to a number of primitive animal cells In fact the Choanoflagellates are nearly indistinguishable in form and function from the collar cells of sponges which represent some of the most primitive living animals Further some Choanoflagellates are colonial during part of their life cycle and exhibit some cellular differentiation Similar to the classifications of green algae and plants some researchers have suggested lumping the choanoflagellate protists together with their close eukaryote relatives the fungi and animals This group while not widely accepted is called the Opisthokonta This name means literally posterior flagella The Protists E In the following lesson you will learn even more about the fascinating protists You now know that this group is interesting because of its close relationship to the plants animals and fungi However you will shortly discover that the protists are worthy of study in their own right due in part to a notable diversity in reproductive strategies life cycles and modes of nutrition as well as for the important roles they play in food chains and the global carbon cycle Community Ecology Part 2 Community Dynamics mun mum mmquot tabularkm l f I quot7 0W3 9 MT i m Afood Chain Mood web amp The feeding relationships among organisms called the trophic structure exert a strong influence on the interactions of the organisms within a community The diagram on the left illustrates how the primary producers organisms that can use the sun s energy to fix carbon form the basis of typical food chains In this rather linear relationship each subsequent consumer eats and obtains energyfrom the previous organism as energy is transferred up the food chain Food webs on the other hand are interconnected and can be quite complex in nature The food web shown on the right illustrates the interconnections between different food chains Linkages between species are varied and there is generally more than one connection to another species Keep in mind that there are limits to the number of linkages within a given community with most food chains involving five or fewer links from the primary producer to the topmost consumer You will learn more about food chains and food webs in the lesson Dynamics of an Ecosystem Disturbances High level Leave completely different ecosystems in wake Intermediate Opens up new niches without destroying existing species increases diversity 39 Low level Dominant species continue decreases diversity Vhata nymmum momquot 9 n the previous lesson we studied interactions between species and the oLtcomes based on those interactions What happens though when the environment is calling the shots when changes or disturbances occur within the established environment Environmental disturbances can come in many forms drought ood fire and even through human impact First let s talk aboLt the different levels of disturbances high low and moder e Fl ods re clearcutting these highlevel d39stu ces are nown to decrease species diversity leaving different e osystems in their wake These kinds of disturbances generally involve both high intensity andor high frequency or instance a flood could wipe o l pecies wi hin one community located along a riverbank Frequent flooding along the same riverbank will drastically change the nown community decreasing both genetic and species variability e are many instances owever where a highlevel disturbance is n ssary For example the lodgepole pine foun much of the West requires re to propagat dyi e the species intense heat from the re releases the Mth previous re suppression plans even small res were extinguished as quickly as possible sti ing the germination and subsequent growth of young trees Lowlevel disturbances also decrease species diversity by allowing dominant species to continue The disturbances are not enough to clear areas where the less competitive species can survive reproduce and t rive n seed The one kind of disturbance that can actually increase species diversity is the moderatelevel or intermediate disturbance Intermediate disturbances are severe enough to open habitats for less competitive species to take hold yet not too severe to overstep the environmental tolerances of the species already living there H a Human Disturbances Growth of the human population continues to put pressure on the environment mm sulumumnpmmn use 7 mm mm man so mu mu a m w WWW Humans impact their environment in many ways You may have heard a story on the nightly news about coyotes or moose wandering into a town and getting into people s garbage With current rates of population growth these incidents will continue most likely with more frequency in the future Clearing of lands through farming logging or mining impacts species diversity within those communities These activities diminish resources available to species located within the community or kill organisms by pollution disruption of habitat disruption of interaction networks and so on Succession clockwise from upper right glacier to lichens to fireweed to spruce forest What happens Wnen a community has been devastated by a largescale disturbance such as glacial retreat A process called ecological succession comes into play and begins with pioneer species continuing through a sequence from primary succession to mature or old growth communities often called climax communi ies Pioneer species mosses and lichens in ourglacier example begin growing in the newly formed lifeless area of the retreating glacier helping produce soil and causing other changes that allow other species to inhabit this changing community Grasses and small shrubs begin to move in next reducing the pioneer species and changing the community even further The dominant species in a particular community changes overtime In our glacial retreat example mosses fireweed and cottonwood dominate as pioneer species Which are then replaced with dense stands of alder after a few decades The alder are eventually overgrown by spruce trees which form a dense forest Which is subsequently invaded by hemlo k ultimately forming a sprucehemlock forest This sprucehemlock forest takes about 300 years to achieve Environmental Changes with Vegetation OPioneeralder stages eTrahsition eSpruce stage 00 01 D Total nitrogen in topsoil glm2l18 in profile a 3 O C l I l 50 100 150 200 Estimated surface age years cwmme Pearson summon in wbllshlnvasae lzmlnmmming 1 As the community continues to change through time the soil also plays a large role in dictating which vegetative species grow within a particular community Soil pH changes from basic to acidic with the arrival of vegetation Nitrogen from the air is also fixed by symbiotic bacteria into certain species This nitrogen fixation ability helps increase the fertility of the soil allowing new species to thrive in this environment As you can see from this slide soil nitrogen is very low early in succession and increases dramatically in the transition stage Finally it levels off as the climax spruce community takes over Interaction of Organisms with Environments Distribution of organisms depends on a complex interplay between the environment abiotic and the species living within it biotic Remember that although we have been talking specifically about the vegetation there are other changes that are occurring at the same time In addition to soil nitrogen soil pH changes with the kinds of plants that are dominant at any one time At the same time animal populations within the community have changed We learned in the previous lesson that community interactions may either increase or decrease species survival This lesson teaches usthat environments also interact with organisms Although environ mental factors can be harsh for some species over time organisms can modify an environment significantly making it hospitable for a growing number of species The Fundamentals of Evolution Notes Evolution Simple or Complicated 2m I39 7 A simplified outline for the history of l life on Earth r39l 39 Just how complex i 11 I am rs this history WEEquot rm Wquot m t Notes If evolution seems to you a very complicated process take heart you39re right However the fundamental concepts of evolution are really pretty simple In fact much of evolution can be summed up as follows 1 the physical and behavioral characteristics of organisms determine how they interact with their environment and so how well they are able to suwive and reproduce 2 physical and behavioral characteristics are largely determined by the DNA of organisms and so are heritable 3 DNA through mutation and recombination changes over time and successive generations therefore the physical and behavioral characteristics of different types of organisms are also apt to change over time We can define evolution then as a change in the heritable characteristics of organisms over time Furthermore the pathways that evolution takes are a result of the differential suwival and reproductive rates of different organisms which in turn are largely based on the interplay of hereditary characteristics and the changing environment of organisms At a fundamental level then evolution isn39t so complicated after all Published by Articulate Presenter wwwarticulatecom A Second Pattern of Evolution V this node represents the common ancestor ofrats and mice 39 Change occurs along lineage I as a result lineages have their own unique characteristics s Notes In a sense evolution follows two very basic patterns To illustrate these patterns let s take a look at a phylogenetic tree The tree shown here represents the diversi cation over time ofa single ancestral lineage into several extant currently existing groups of organisms includ39 39 ertebrates shown here as ies cartilagino shes amphibians birds u ns rats and mice On the tree we see e common ancestor or ancestral lineage of all of the extant organisms represented as the vertical line at the base ofthe tree In other words this is the trunk of the phylogenetic tree The currently existing groups of organisms are located at the ends ofthe branches of the tree At the nodes or branching points a hypothetical common ancestor of two lineages split to form the two lineages At these nodes then speciation occurred during which one original species split to form two new species which in turn gave rise to new linea es You ma also refer to this process as the splitting of a lineage This is one ofthe fundamental patterns of evolution On our tree for example you can see that the rat and mou e share a relatively recent common ancestor represented by the node that splits to each of the rat and mouse branches Most li ely this ancestor had de nite physical similarities to both rats and mice but was not identical to either At some point this ancestral species split and gave rise to two new species both of which became new lineages and which led to the development of rats and mice Take a moment to look at other nodes on the tree to determine whose ancestors they represent Notes Also on our tree the lines arising 39om each node represent a second major pattern of evolution change within a lineage over time During this process a lineage diverges or ecomes more different from its ancestor overtime Also a lineage becomes more different 39om its sister lineage with which it shares a mmon ancestor If we a ain exam39ne rats and mice from the same ancestor were produced by the splitting ofthe ancestral species most likely were not identical to either rats or mice It is more likely that signi cant changes occurred overtime within the lineages leading to ra s and mice resulting in their current physical characteristics In addition change within a lineage typically leads to diversi cation ofthat lineage The mouse lineage for example includes all species ofmice both extant and Published by Articulate Presenter wwwarticuatecom extinct that have ever existed the rat lineage includes all extant and extinct species of rats Rates of Evolution I Time is an integral f evolution I Why might different organisms evolve at di erent rates u Notes A third facet of evolution which bears consideration and that can be noted on our phylogenetic tree is time Regardless of the type of organism signi cant evolutionary change 0 39n y cases hun thou ccurs over time dreds sands or even millions of years It is merou such as the environm nt in which they are found their overall body plan and the longevity and reproductive rates of the members ofthe lineage Evolu on at a Slow Pace nkgos I Members ofthe Ginkgo lineage have changed very little over millions ofyears Lem m may mm mm mm s n m Vamuene m la Notes Let s take two types of organisms as contrasting exam les the ink as also known as the maidenhairtrees and the cichlid shes of Lake ictoria Africa According to the current fossil record G 39nkgo the maximum amount of d ty was reached during the cretaceous period 14465 million Ginkgo biloba It would appear then that the ginkgo lineage in particular the Ginkgo genus has c very little over many millions of years 0 39 s39 e ow e he is likely that ecological factors such as environmental constraints have played a role Published by Articulate Presenter wwwarticulatecom Ra id 5 eciation Lake Victoria Cichlids N0tes Compared to the ginkgos the cichlid fishes of Lake Victoria display a very different evolutionary history The cichlid fishes of Lake Victoria include over 500 endemic species in other words over 500 species found nowhere else in the world Based on geologic evidence the Lake Victoria basin was formed around 750000 years ago The development of over 500 species in just threequarters of a million years alone is itself representative of a much greater rate of cichlid 39 39 39 39 39 evolution than we find in the ginkgos However recent 4 molecular evidence strongly suggests that the 500 cichlid species in Lake Victoria actually evolved in a much shorter period of time somewhere on the order of 100000 years In fact this is one of the most rapid rates of speciation known for any vertebrate organism What led to this rapid rate of speciation Again it is impossible to know for certain all of the factors influencing this rate of evolution However it is very likely that this radiation was strongly affected by the diverse and previously unoccupied habitats available to these fish as they colonized Lake Victoria from surrounding waters Lake Victoria cichlids have evolved at a very rapid rate for vertebrates at Notes As we noted at the beginning of this lecture evolution and the history of life are at the same time both immeasurably complex and fundamentally simple Organisms develop diversify and go extinct over time The History and the Future of Life Elucidating the quot history of life is a great challenge 3 U 3539 T bUt UHderStandinQ due to interactions between their hereditary this history Will characteristics and their environment It is impossible help us better to predict what pathways evolution will take in the understand how future and a great challenge to elucidate exactly what the world works pathways evolution has taken in the past However by utilizing various resources such as the fossil record today 4 molecular and morphological data and even current ecological data we are able to gain a growing insight into the fascinating history of life and a better understanding of how life works today Published by Articulate Presenter wwwarticulatecom The Fossil Record Bangun youmu V uymmgwr hwy lumpqr In mum wanme Fem unalan m vpublishingax mlzmincummlng As we consider the diversity of organisms found here on Earth today we have to delve into the history of the Earth and its organisms to understand how they are related to each other We will be thinking about life that existed hundreds of millions or even billions of years ago not necessarily familiar territory for biologists However it is important to understand how the physical processes that have shaped the Earth through time have also impacted the evolution of living things Living organisms in turn have had a profound impact on the Earth itself All of these processes have left records in the rocks but if we are to interpret the information contained in the rocks it is important to understand some ofthe principles of how rocks and fossils are formed am The Principle of Superposition First of all the vast majority of historical information we have regarding living things comes from sedimentary rocks Many sedimentary rocks were deposited by water Think about the silt and sand that flow down the Mississippi River Over time these products of erosion are being deposited in layers in the Gulf of Mexico As those deposits are buried compacted and cemented together they will eventually turn into layers of sandstone and shale This process is called lithification When we see ancient rock formations of sandstone and shale that look like those along the Mississippi delta we applythe idea of uniformitarianism to postulate that those ancient rocks were deposited in a similar river delta system Uniformitarianism is the idea that the same types of processes that we observe on Earth today have been at work throughout geologic time Getting back to the layers of sand and silt being deposited at the mouth of the Mississippi the principle of superposition states that the layers on the bottom of a sedimentary sequence are olderthan the layers on the top If fossils the preserved remnants of living organisms are incorporated into those sediments as they are being deposited the principle of superposition will apply to them too In other words the fossils in the layers of rock at the bottom of the sequence are older than the fossils in the layers at the top of the sequence my Using Fossils to Correlate Rock Layers 39 Some species of Brachiopod bivalves were abundant throughout but largely restricted to the Paleozoic era Their presence immediately restricts the possible age of a layer of rock mm by m mm Vaselk Humbaldt 5m many 4 The principle of superposition allows us to put together a relative time scale We can determine what came rst second and third Paleontology the study of fossils gives us some other useful tools Using fossils gives us the possibility of correlating sedimentary layers over large distances For example some fossils known as index fossils are found in rocks all over the world and allow us to place all of those rocks in the same time period These types of correlations are vital to putting together the geologic time scale that geologists and biologists use my Radiometric Dating my my my 40 10000 years 235 Lead 207 100 my 14 14 years Source After Odin 1982 As important as the relative time scale is however it still doesn t tell us the absolute age of rocks or fossil organisms To determine absolute ages we use radiometric dating Radioactive isotopes of elements such as uranium potassium rubidium and carbon have very predictable decay rates Half of the parent isotope decays to the daughter isotope in a set time period termed the halflife By measuring the amount of parent isotope and the amount of daughter isotope found in a particular mineral it is possible to say how old the rock containing the mineral is Thistable shows some isotopes commonly used for radiometric dating along with their half lives and effective age ranges The age of a sedimentary rock can not be determined directly When layers of volcanic rocks or volcanic ash and dust are interspersed with other sedimentary rocks however the dateable minerals in those volcanic rocks allow us to put limits on the ages of the sediments The Geologic Time Scale Cenozoic Mesozoic Pu Cambrian Mesozoic Era Cenozoic Precambrian Period Quaternary many crewman Jurixxk Epoch Ream Flam vimquot Min any 2m Palm Age mullahs11mm lmMal mm H k w humanswear 539 Apel39lke anaesle ofhumaus appeal a manned Mlallan almammalsand anglcspemu as Onglnx Mummy pnmmgmupmwdndln a 5 Wm do him mmuwg quotmm plimxlangms armsappeavminygmupsufn inkms lndudrngmundlnuuur nugaammalelnnuand a pm Cmmmxemmnml Gymnaxb rmsmmlnueixdominanrplanindlnouursdomlnale ngplinulgymnnspevmxldom elindxmpe 39 an m mmils a m numb oxygen in Incumullltng m mmmye cram hull knew lpmlmym Arapmximm timzufuvlgln gram Through a lot of hard work painstaking fossil and rock correlations and radiometric dating geologic time scales like the one shown here can be produced see where some of the major life forms appeared ourished and in some cases disappeared we can begin to understand some of the evolutionary patterns that form the basis for our classification of organisms The hiatus in this sequence of rocks could represent millions of years of erosion Once rocks are eroded away it may be impossible to reconstruct what is missing Both the amount of sediment and the fossils preserved in them are gone forever it With this background on sedimentary rocks and how they are correlated and dated let s think a little more about what is actually recorded in the fossil record First of all the sedimentary rock record is neither continuous nor complete At any given time at any given point on the earth sedimentation erosion or neither is occurring When we look at a sequence of sedimentary rocks we need to be able to recognize when sedimentation has been continuous and when it has been interrupted by non deposition or erosion Once a sequence of rocks has been eroded away during a time that the area was above sea level it and any information it contained about life during that time is lost forever In addition there are thousands of feet of sedimentary rocks below the earth s or ocean s surface in many areas around the world Until these sediments are uplifted to a place where we can see them and study them we can only get glimpses ofthe fossils they contain if we drill through them for some reason The geologic record and thusthe fossil record is incomplete and not always exposed for us to see my Preferential Preservation of Organisms 39 Ifthis coral reef community was buried which organisms would most likely be preserved It turns out that more things are missing Let s think a little bit about taphonomy or how organisms are preserved when they are buried What types of organisms are most likely to be preserved as fossils Certainly organisms with hard parts shells or bones and those that live in aquatic environments are the most i ey to be preserve art is reason we ave some very complete records ofthe evolution of several marine shelled animals Almost any kind of an organism from insects in amber to plants in shale to dinosaurs in tar pits to shells in sandstone can be preserved under the right conditions but there is a de nite bias towards aquatic organisms with hard parts Consider a coral reef community like the one pictured here lfit were buried either quickly by a huge mud ow or slowly as 39 over it wha g 39 e most likely to be preserved Corals aar sh clams snails and other organisms with lots of hard parts would almost certainly be represented Fish would probably contribute some of their bones to the fossil record as they died and sank into the sediment While shark teeth are quite common in the fossil record the cartilaginous skeletons of sharks are not so easily preserved What about the symbiotic algae that are intimately associated with the coral Would octopi worms or sea slugs be preserved Would bacteria or seaweed be included in the record lfyou were to nd this buried community millions ofyears om now wou you be a le to reconstruct the entire ecosystem that had existed there How would ou know how differe 39 39 39 some organisms that probably lived there but weren t preserved ow would you go about reconstructing the paleoecology from what you could observe Interpreting ancient environments quot 39 quot 39 39 L a 1000piece jigsaw rom e puzzle is supposed to look like when you only have 50 or 75 ofthe pieces quotmmquot The E evolutionary bush of the horse muman lem39lon 5mm Meganppm mnmnwu Wanmu 25ml AutumnHum l I l onmm 3 9 MW ma mum anlhcrlum SaintIrma mpalmmnum Em39m a Man in sum P quot quot quot g 4 223 Q Used by permissun ur In addition to helping us understand ancient environments and ecosystems fossils can show us how organisms have evolved through time Careful study ofthe lineage of modem horses shows a highly branched succession ofdifferent forms The horses we know today represent one branch of this tree Many of the phylogenetic trees we will be using in this course have been reconstructed by comparing fossil morphological anatomical and molecular data 1 7 W u u hvmmiissan aweser Edumtian lnc Emilia 3 Whatevertheircauses major extinction events are usually followed by rapid radiations of new forms of organisms u sea by Permissan m Peamn Edumtian lnc The fossil record also records several major extinctions throughout the history of life In fact most ofthe major boundaries in the geologic time scale are placed at points where mass extinctions profoundly changed the character of the flora and faunafound in the rocks Postulated reasons for mass extinctions range from asteroid impacts to widespread volcanism to glaciation to global warming to species competition While it is likelythat different mass extinctions had different causes one common observation following mass extinctions isthat new forms of the survivors rapidly radiate intothe niches left behind bythe organisms that went extinct Even with our current knowledge ofthe geologic time scale and our ability to date rocks and fossils using relative and absolute methods we are still missing a lot of the pieces of the puzzle Debate continues over things like the extinction of the dinosaurs the exact movement of the continents the changing composition of the atmosphere through time and the mechanisms of climate change Although more types of data are being used to understand different aspects of the earth through time we will probably never be able to say with certainty This is how it happened Not without a time machine anyway Distribution of Organisms Factors Affecting Distributions Ecology is generally defined as the study of the interactions between organisms and their environment In essence though the question that ecology as a science attempts to answer is what factors control the distribution of organisms on our planet The answer to this question of course can be as complicated or as simple as one can imagine depending at what level it is pursued In general much research in ecology is done at or near the level of the ecosystem which is defined as an interacting community of organisms and the environment in which they live Ultimately though the answers provided by this research help us to better understand the complete distribution of organisms in the earth s biosphere In this lesson we will briefly discuss some of the factors that can affect the distribution of organisms on our planet In the following two lessons you will learn about how the different regions of our planet are broadly classified using both biotic and abiotic factors Factors Affecting Distribution Kangarooskm 1 5 Distribution is affected by biotic and abiotic factors 39 example red kangaroo distribution in Australia Ehsmania Canvmc Pearson Education in nubllxhlnu 3 mmquot Cummwg Many factors affect the distribution of organisms In general these factors fall into two categories biotic factors and abiotic factors Biotic factors pertain to organism activity that affects the environment andor the distribution of other organisms Abiotic factors on the other hand are nonbiological influences on an organism s environment such as temperature substrate type pH or oxygen levels For example consider the red kangaroo This species is distributed over the continent of Australia but is not found in equal densities on all parts of the continent Biotic factors such as the presence ofthe appropriate forage grasses and abiotic factors such as the presence of local water sources both play important roles in the kangaroo s distribution Let s take a look on the next few slides at some other examples of how biotic and abiotic factors can affect the distribution of organisms Many organisms migrate seasonally to reach suitable habitat migration and habitat selection greatly in uence distribution Breeding range at Pacllic golden plnver managing E Emtztztszr m Kllzf gtl z39pm Downyin Penman Edunallon in Jubllsnll m a Emlzmin cumming Annual migration routes of the Pacific golden plover 41 The interaction between biotic and abiotic factors plays a role in the distribution of organisms An organism s behavior can greatly affect where it is found at certain times of the year Migratory organisms such as many birds some mammals and some insects travel hundreds to thousands of miles every year between the seasonal habitats in which they live and reproduce Often these travels are based on the location of suitable habitats for the organism at given times of the year or in certain stages of the organism s life cycle In many cases biotic factors such as the presence of food organisms in different areas at different times of the year strongly affect migratory patterns However note again that abiotic factors such as temperature or water availability also play significant roles affecting the survival of the migratory species and its food supplies Abiotic Factors Affect Distributions 39 On a global scale air circulation patterns are quite predictable New 39 greatly influence distribution of organisms and 39 over time Global air circulation m Abiotic factors as just mentioned also play important roles in the distribution of organisms Physical factors arch as day length and sunlight intensity temperature substrate type topography and wind patterns help de ne environments and so greatly in uence the types of organismsthat can live in them For example on a global scale the air circulation and wind patterns of our planet are very predictable As you can see from the illustration here air masses circulate regularly between zero and thirty degrees latitude thirty and sixty degrees latitude and sixty and ninety degrees latitude in both the northern and southern hemispheres Air circulation patterns and water circulation patterns cwpled with the rotation and orbit of the earth help maintain relatively stable climatic patterns in different regions of the earth This in turn helps maintain fairly stable environments over time Abiotic Factors Creating Climates Rain shadows 39 air picks up water while traveling over ocean or lake 39 loses water as it is forced up mountain 39 inland side of mountains experiences dry air East direction L l nnnnnnnnnnnnnnnnnnn 9 ll As you may have noticed from the previous slide abiotic factors as well as biotic factors tend to work in concert ratherthan individually Another example of this is the phenomenon of rain shadows These areas are affected by prevailing wind patterns topography and latitude among other things Rain shadows often occur in the vicinity of oceans or other large bodies of water which are bordered by mountain ranges Prevailing wind patterns carry air masses across the body of water during which time the air picks up moisture from the water As the air moves onto land the wind direction forces it up into the mountains toward higher elevation and cooler temperatures This results in the moisture condensing out of the air and falling as rain and snow on the coastal side ofthe mountain range As the air continues to travel inland across the mountains it loses more and more moisture The result is that the inland side of the mountain range and following areas tend to lose water to the now dry air rather than gain water from rain These dry areas are in the shadow of the coastal rains This phenomenon is responsible for the weather patterns of among other areas the states of Washington and Oregon If you travel from one side ofWashington or Oregon to the other you will notice that the eastern and central areas of each state are quite dry on average while the coastal areas are quite wet Introduced species may become established in new areas Historical distributions influence present distributions Purple loose strifean introduced invasive plant species 7amp3 A third influence on the range of organisms somewhat beyond biotic and abiotic factors is historical distribution Simply put some organisms are found in area because that is Where they evolved For example if we look again at the distribution of the red kangaroo we can see that this type of organism is found only in Australia and nowhere else in the world Evidence from the fossil record and the geologic history of Australia strongly suggest that the red kangaroo evolved from its marsupial ancestors after Australia had become physically isolated from the other continents As a result of this and because the red kangaroo had no way of moving from the Australian continents to other continents the distribution of this organism is restricted to only Australia This is not to say that organisms that historically have been present only in one area cannot persist in other areas The history of life on earth has been continuously marked with introductions of various organisms into new habitats and environments perhaps never more frequentlythan in the last several hundred years In some cases such introductions are failed experiments and the introduced organism is not able to persist in its new environment In other cases the introduction is able to maintain small but stable populations in its new area In yet other instances introductions may become what we term invasive and quickly dominate new environments The Distribution of Organisms The major biomes of our planet Now that you have the basic idea of what types of factors influence the distribution of organisms lets take a look at some of the major environment types found on our planet These largescale ecosystems called biomes will be discussed in the following two lessons Distribution of Organisms Aquatic Biomes As you learned in the previous lesson the distribution of organisms is affected by both biotic and abiotic factors When the distribution of organisms is viewed in a global context it is possible to divide the biosphere into a relatively small number of consistent ecological associations or biomes In general biomes are classified as one of several major types of aquatic or terrestrial ecological associations Aquatic biomes include all of the aquatic regions of our planet such as the various regions of the oceans and freshwater lakes and rivers Terrestrial biomes include all of the surface land areas of our planet such as the deserts tundra grasslands and forests In this lesson we ll investigate the major aquatic biomes In the following lesson you will be introduced to several of the major terrestrial biomes The Major Aquatic Biomes aes 39 Iers s aries Ahyssalzona Coralreets Serials pelagic E n erial zone Pelagic zone my p mmmm1 mumnmmm As you can see the aquatic regions on our planet are roughly divided into several major biomes including freshwater lakes rivers estuaries intertidal zones coral reefs and abyssal zones Of these biomes by far the most extensive is the oceanic pelagic zone or the open sea which covers nearly 70 of the earth s surface In contrast some other biomes in particular the coral reefs occupy a much smaller portion of the earth s surface but hold a relatively much higher level of organismal diversity Freshwater and marine biomes are generally distinguished from each other by their salt concentrations Freshwater biomes typically have salt concentrations of less than one 1 while marine biomes average around 3 salt concentration Estuaries are found where fresh and saltwater biomes meet for example where a river flows into the ocean Stratification of Aquatic Biomes Strati cation is common in aquatic habitats particularly with regard to light and temperature lnlenl al zen LlIIara a Zonallcn in a lake in Marine zonallnn mm mm mum ler mmng zs enlrmncumlrgs Aquatic biomes are usually stratified with respect to light availability due to the light absorbing properties of water Photic zones in which light penetrates sufficientlyto support photosynthesis exist in the upper levels of bodies of water Aphotic zones on the other hand in which light is largely excluded exist below the photic zones For example the oceanic photic zone extends from the surface down to about 200 meters Within this zone one finds much of the life which is normally associated with the oceans including most fish and marine mammal species most marine algae and plankton and ecosystems such as coral reefs and kelp beds Below 200 meters in the oceans life is fairly sparse and is often concentrated around thermal andor chemical energy sources such as deep sea vents or dead sunken organisms Also as a result of light absorption in the upper layers of bodies of water surface waters tend to be much warmerthan deeperwaters Thus most bodies of water are also stratified by temperature in addition to light availability In many cases a relatively sharp gradient exists that separates warmer surface waters from colder deeper waters This gradient is referred to as a thermocline Now let s take a more detailed look at some of the world s aquatic biomes starting with some of the marine biomes Intertidal Zones Zone between high and low tide 39 found globally mm mm mm m wnrurrrnn EHllm mmm Intertidal zones are defined as ocean shoreline between high and low tide Intertidal zones are typically submerged and exposed by fluctuating ocean waters twice daily 80 in a sense this biome is both terrestrial and aquatic depending on the time of day The organisms inhabiting an intertidal zone face several challenges including the daily changes in water availability and the associated fluctuations in temperature and sunlight as well as the pounding wave action characteristic of ocean shorelines Substrate which can vary from rock to sand to mud also plays a significant role in determining which types of organisms can inhabit a particular intertidal zone In general it is common to find more diverse plant and animal communities in rocky intertidal zones as compared to sandy or muddy intertidal zones This is largely due to the fact that the rocky substrate is more secure and less apt to change allowing various plant and animal species to become securely established It is common to find various species of marine algae such as sea grass and rockweed various marine animals such as crabs sea anemones mollusks starfish and some fish as well as associated plankton in intertidal zones Coral Reefs 39 Found in warm shallow tropical waters biologically diverse 3 Coral reefs are often referred to as the tropical rain forests of the ocean dueto the astounding diversity of life associated with them Corals form the foundation of this biome In addition to coral reefs are inhabited by a tremendous diversity of life forms These life forms include for instance various algae and plankton including symbiotic photosynthetic algae living within the cells of the coral marine invertebrates such as sea anemones shrimp and lobsters and marine vertebrates such as fish and eels Coral reefs are strongly affected by light and oxygen availability as well as temperature Because of this coral reefs are found only in certain shallow waters between 30 north latitude and 30 south latitude In addition the sensitivity of coral reef systems to their immediate environment makes these systems very delicate and prone to serious disturbance by pollution global warming and mechanical disruption The Abyssal Zone 39 Deep ocean oor many species concentrated around hydrothermal vents The abyssal zone consists of the deepest regions of the ocean floor well below the photic zone As a result of the lack of light penetration and the depth of these regions organisms living in the abyssal zone are adapted to life without light at fairly cold temperatures around 3 C and extremely high pressures In addition organisms largely depend on marine snow the slow and consistent fall of organic material from surface waters for carbon and energy In certain areas of the abyssal ocean superheated chemicalrich solutions are released from volcanic vents providing energy to support small but diverse ecosystems These fairly recently discovered deepsea hydrothermal vents support some of the most interesting assemblages and interactions of life found on our planet In general the deep ocean floor is not particularly overflowing with life In a sense it is not totally different from terrestrial deserts large stretches of fairly lifeless surface with the occasional oasis such as the deep sea vents supporting a higher concentration of organisms A diversity of life including bacteria that utilize chemical compoundsfor energy tubeworms marine arthropods and various fish are associated with the deep sea vents Photosynthetic organisms of course a e conspicuously absent from the abyssal zone communities as there is no Iig ht to su pport them Seasonal turnover affects temperature and oxygen distribution my mm L av l Amm n mm mm mum m wnnnvinn EHllm mmm While aquatic biomes cover around 70 of the earth s surface only about 3 ofthis area is found as freshwater However a great portion of life s diversity has evolved to Ltilize this relatively small percentage of available water Freshwater biomes are typically classi ed as lakes wetlands and rivers and streams Let s rst take a look at freshwater lakes and some of their characteristics As with the oceans freshwater lakes are generally strati ed with respect to sunlight availability and temperature In temperate areas most lakes emerience a seasonal event called turnover During turnover a combination of temperature change and seasonal winds in the fall and spring cause the water ofthe lake to circulate leading to mixing of the surface and deeper waters As a result temperature and oxygen availability become fairly uniform throughout the lake during these times of year Seasonal turnover has signi cant impacts on the behavior and distribLtion patterns of organisms within freshwater lakes Lakes and the organisms that live in them are also greatly affeded by chemical factors such as nutrient availability pH salinity as well as oxygen availability Lake may be classi ed according to their production of organic matter Lakes that tend to be rich in nutrients and organic matter and generally deficient in oxygen are referred to as eLtrophic On the other hand deep clear lakesthat are nLtrientpoor and oxygen rich are referred to as oligotrophic In any case it is common to find a diversity of life associated both directly and indirectly with freshwater lakes ranging from plankton to diverse plant and algal species to numerous terrestrial and aquatic invertebrate and vertebrate animals Wetlands Shallow seasonally inundated with water As opposed to lakes wetlands are often inundated with water seasonally rather than yearrou nd and are typically not as deep on average as are lakes However wetlands are still able to support aquatic plant life during part or all of the year Included in the definition of wetlands are swamps marshes and bogs Which extend the range of wetlands to every continent except Antarctica Wetlands also serve important ecological roles such as acting as natural filtering systems for nutrients and even pollutants and of course providing habitat for various types of organisms As with lakes diverse life is found directly or indirectly associated with wetlands including plankton plants fungi and invertebrate and vertebrate animals Rivers and Streams 39 Characterized by continuous current 39 More even distribution of temperature and oxygen ll Finally rivers and streams represent another important freshwater biome Found on all continents and at all elevations rivers and streams support many different types of life but provide some different challenges and opportunities than do lakes and wetlands Primarily rivers and streams differ from lakes and wetlands because they have current Current in turn results in regular changes in the physical structure of the underwater environment and leads to more even distribution of oxygen temperature and nutrients Rivers and streams are also quite variable in terms of their physical characteristics Some such as many high mountain streams are fastmoving with cold clear water rocky or sandy substrates high oxygen levels and low nutrient content Others such as many lowland rivers are sluggish turbid muddybottomed waters with an abundance of organic material and relatively low oxygen levels The Distribution of Organisms Em WW mm mum m wnlmvmn EHllm m Now that you ve gained a littlefamiliarity with the earth s major aquatic biomes in the next lesson you will learn about some of the major terrestrial biomes which characterize the land surfaces of our planet The Cambrian through Ordovician Periods Ecology and Major Evolutionary Breakthroughs Notes 39 History of life marked by importantevents origin of life evolution of photosynthesis appearance of multi cellular organisms Cambrian explosion others Notes The fossil and geologic records tell a story of continuous evolutionary change over nearly four billion years However there are a number of key events in the history of life that stand out in their significance perhaps more than others For instance the fossil and geologic records suggest that life itself originated on Earth around 39 billion years ago evidence suggests that photosynthesis evolved perhaps as long as 35 billion years ago and the first simple multicellular eukaryotes likely arose between 12 and 15 billion years ago Another significant series of events occurred between 542 and 444 million years ago During this time period called the Cambrian and Ordovician Periods many lineages of animals appear in the fossil record for the first time In fact nearly half of all extant animal phyla appear for the first time in the fossil record during the first half of the Cambrian period Because of this great and relatively rapid diversification of animal phyla in the fossil record this time in Earth39s history is often referred to as the Ca mbrian explosion The Cambrian period 542488 mya and the subsequent Ordovician period 488444 mya thus featured many important evolutionary events The Cambrian Earth 39 Cambrian earth different than today s earth continents clustered in rlolvma L mu r nymml warns F gunman mahumszn mu subltropical areas expanses of warm shallow ocean 7 warmerglobal i w V A temperatures Continental locations drring the Cambrian period Notes During the Cambrian period the earth was in some respects very different than today For instance the cortinents were in very different positions Most land masses were found in tropical and subtropical regions and several were clustered into a large area called Gondwana The geographic location of the large land masses affected their climates likely resulting in the melting of previously existing glaciers and in turn rising sea levels This would have created large areas of warm shallow ocean waters In addition overall global temperatures were likely warm as the tropical land masses deflected warm tropical ocean currerts Published by Articulate Presenter wwwarticulatecom Cambrian Explosion Phy 39o I Possible abiotic causes of the Cambrian explosion end of severe ice age li l Iii l Factors The aPpEaiance mmaiuv animal linEaEEsinihECambiiaiipEiiud I to the northern and southern regions of the earth As a result of these factors there was a great increase in the amount fma ine environment available for organisms as compared to the immediately preceding portion of the Precambrian period To some degree this great increase in available environment played a role in the Cambrian explosion iaiigii Notes In addition to the roles played by the positions ofthe continents there were likely several other physical factors leading to the a parent Cambrian emlosion One hypothesis the snowball Earth hypothesis considers evidence suggesting the Earth may have emerienced a severe and longlasting ice agejust prior to the Cambrian period from around 750 to 580 million years ago According to some data this ice age so vere tha the oceans may have nearly frozen solid Of course this would have greatly impacted life multicellular forms of life and causing man t es of 39 39 39 ould w opportunities for ecological and evolutionary radiation Other hypotheses not mutually exclusive of each other or the snowball Earth hypothesis consider different factors For example an increase in atmospheric oxygen concentrations was correlated with the end of the glacial period just prior to the Cambrian During the Cambrian oxygen levels rose to around 610 of current levels and likely provided enough oxygen to meet the requirements of lar er multicellular organisms thereby allowing the possibility that such organisms could evo ve Also during the Cambrian the continents were shi ing their positions very rapidly This continental movement helped contribute to the emansion of shallow marine habitats as well causing a release of nLtrients from the earth s crust due to disruption of the ocean oor 39t changing ocean currents and volcanic actiVI y Published by Articulate Presenter wwwarticulate com Cam n Explosion Biological Factors I Possible biotic factors in the Cambrian xplosion immems used to foi m diverse S eis 39 diversification of predators evolution of Hox genes Omanist and Ecui oicaiieialiunships diinsi u inthe Ca n Notes There are also several biological factors that contribLted to the Cambrian explosion For example some types of nutrients released by continental shifting were utilized to form the earliest shells of inverte es Once the ability to form shells evolved a wide diversity of shelled invertebrates evolved relatively rapidly allowing shelled organisms to diversify and specialize The development of protective shells in turn likel also helped drive the evolLtion and diversi cation of predatory animals 2 EL Evidence also suggests that homeobox containing genes Hox genes evolved during the Cambrian period This type of ene found in most animals as well as other multicellular eukaryotes contribLtes to the developmental plasticity of organisms MLtations in these genes likely played a signi cant role in the diversity of body forms that evolved during the Cambrian and subsequent periods Thirdly ecosystems were relatively simple at the start ofthis period yet geographically immense It should not be too surprising then that rapid diversification occurred on a global level as new evolLtionary 39 ovations could quickly benefit organisms and spread throughout populations presented to Cambrian organisms w boundless As one might emec the Cambrian period has been described as a period of reat emerimentation in multicellular life forms This is particularly true as it seems only a portion of lineages 39 Xplosive period survived into subsequent n In all the ecological and evolLtionary opportunities ere s 3 O 3 5 m In time periods such as the OrdoVIcIa Skeletoiis Notes The major animal lineages that appear during the Cambrian period including those still represented on earth today are largely de ned by their body plans played important roles in the evolution of animals including the following 1 true tissues 2 digestive tracts 3 symmetrical body shapes 4 segmentation 5 skeletons On the phylogenetic tree on this slide you can see in which animal lineages some of these features occur While at least some of the features listed here appear sparingly in the fossil record prior to the Cambrian Published by Articulate Presenter wwwarticulate com period they are noteworthy here because they appear with great frequency and in many lineages for the rst time in the fossil record during the Cambrian period 0rdo aaners ca on 39 Ordovician alsoa eriod of great diversi cation in pan due to 39 fuither increase iri shallow watei iiiaiiiie environments furtliei increase iii atmospheric oxygen levels lncieasing o levelslikely helped uiganismswnh Ealciiim shells such as these biachiupuds to become inure common in the Oiduvician Notes lfthe early Cambrian period was considered an evolLtionary explosion the Ordovician period may be 39 a series of strong a ershocks At the end ofthe Cambrian period for example there are around 150 animal families represented in the fossil record By the late Ordovician period however there are upwards of 400 animal families represented What led to this further increase in organismal diversity In large part many of the same factors that played a role in the Cambrian emlosion also played a role in Ordovician evolution For example ocean tha t pla et In fact t e continents were most completely flooded Of course this meant that shallow marine habitats were also more extensive than ever before providing many ecological opportunities for organisms n n Atmospheric oxygen levels also continued to increase and reached levels similar to current levels during this period It is likely that a threshold oxygen concentration 16 of current levels was surpassed durin vician allowin organisms to build heavily calci ed shells and skeletons for the rst time in the earth s history oglcal Factors 39 Several biotic fadors generated Ordovician 4 a diversi 5 a 7 iJ 39 ecoiogicai opportunity 19 7 from Cambrian extinctions mfgggg ii increasing complexity of ecosys ems appearance oiiawed predators Die diveise lt1 usystems cam rn nine Oiduvician and beyond Notes As with the Cambrian period there were several biological influences that helped increase diversity within the Ordovician period First a significant period of extinctions occurred at the end of the Cambrian period thereby opening up many opportunities for new types of organisms to evolve and diversify Second ecosystems continued to become more complex as 39sms be m specialized and emlor ches ncreasing complexity of ecosystems drove these same ecosystems to become yet more com lex at the same time resulting in the increased diversification of life 3m x In In addition jawed predators rst appear in the fossil Published by Articulate Presenter wwwarticulatecom record during the Ordovician period These increasingly ef cient redators may have rapidly driven the diversification of both the organisms o which they preyed and those they competed against amhrlanlordo I Marinealgae very diverse I I an S i l 39 WEI COlOHlZallOH Of land I ngi 39 l kely colonized land Wllh plants I l Notes Finally while the Cambrian and Ordovician periods are most often discussed in terms of animal evolLtion 39 39 to recognize that other groups such as er rotists plants and fungi were not just standIng still during these periods Important changes weretaking place in all of these groups bLt it is easy to overlook these events due to the exciting nature of 39 mlosion In addition the fossil record in general contains a relatively higher amount of information on animal evolLt39ont an he evolLtion of other types of organisms particularly during this time iod At least two examples of important evolLtionary events in other groups are worth noting here First the Ordovician period was a time of high diversity in marine algae In part this must have been due to the r valence of warm shallow marine habitats mentioned before Of course this would have had signi cant effects on other organisms as photosynthetic algae both produced oxygen and served as food rces for herbivorous animals Second the colonization of land by plants occurred during the Ordovician period It is also likely that fungi moved to land in association with the plants This in turn aved the wa for the increasing development of soils terrestrial habitats and the movement of animals from the oceans to land Arthropods appear to be the first animal group to colonize land eit land with plants or shortly therea er er moving onto Published by Articulate Presenter wwwarticulatecom Camh anOrdov Ecological Opportu 39 Several rrajor extinctions during these periods A quotquotquotquot opened up rrany opportunities 39 Cambrjan exlmctjons W jililliHJj i Them l 5 bath Expenennedmass mm on jkejv dueto gjaoanon Q Notes To nish it is important to reiteratethat in part adaptive radiations such as the Cambrian Explosion are due to ecological opportunities For example when an abundance of available niches exists it is more likely that new types of organisms will evolve over time to ll them Several major extinction events during the Cambrian and Ordovician periods opened up many such opportunities and this is partly why so many new lineages of organisms appear during these time periods As mentioned previously the Cambrian period itself was preceded by a severe ice age during which it is likely that many types of organisms went extinc As the ea 39 s warming period into the Cambrian and sea levels rose many new opportunities were opened up for organisms to take advantage of During the Cambrian period itself major extinctions may have been due to changes in oceanic con it39 ns r example changes in temperature and oxyge content due to upwelling of colder currents Toward the end of the Ordovician period it appears that another major event marking the end of the Ordovician period was the second larges extinction event in the history ofthe earth second only to the Permian extinction which will be discussed in a subsequent lesson Published by Articulate Presenter wwwarticuate com um Dynamics of Ecosystems Key Features of Ecosystem Dynamics H3 Heal Mlcmnanismi quotquotquot quot39 any ecosystem 623732 1 involve g 39 Energy Flow 39 Chemical recycling 4 4 Dashed line energy flow 3 fo39SoIarenevgy Solid line nutrient cycling wamvtef emsonEnumllun lm vubllmlnn Emzmlncummmgs Two key ingredients are essential in the maintenance of any ecosystem energy and inorganic elements Let s think about where they come from Most of the energy that enters an ecosystem is solar energy This light energy is converted to chemical energy by photosynthetic organisms also thought of as primary producers in an ecosystem Energy may also enter the food chain in the form of chemical energy For example in deep sea thermal vent communities primary producers derive energy by oxidizing compounds such as hydrogen sulfide and then use that energy to convert inorganic elements into organic compounds In either case energy is then passed on to the consumers in the form of organic molecules or is lost as heat Since the energy entering an ecosystem is ultimately lost as heat ecologists consider energy to flow through an ecosystem rather than be recycled in it On the other hand inorganic elements are persistent in an ecosystem in one form or another They move through the ecosystem in biogeochemical cycles These inorganic elements may be locked in an organism as part of organic molecules or be present in the atmosphere or in rocks The inorganic elements must be released into the ecosystem where producers can once again incorporate them into organic molecules Ecologists therefore consider inorganic elements to be recycled in an ecosystems Detritivores fungi and microorganisms involved in the decomposition of organic matter connect all levels in the ecosystem Both energy and inorganic elements move by the same pathway through an ecosystem primarily via photosynthesis feeding and decomposition 259 rm 0 snuimol mzmozsm n 5 In 15 20 25 gt 7 Mam 5 1quot ma pwuuwvn gm lyr Primary production Yevrejlnal Freshwater on continents UEd by Permissun Pearmn Educatiun inc Examine the figure shown here and note the different ecosystems listed on the left hand side Also note that on a global scale net primary production which represents the stored chemical energy available to consumers varies with the different ecosystems The oceans and tropical rain forest are the two largest contributors to the overall percentage of Earth s net primary production In the ocean the net primary production per unit area is much lower than most of the other ecosystems however the area covered by ocean is so vast that overall net primary production is large The opposite is true of algal beds and coral reefs These organisms have high primary production per unit area but overall they cover a small percentage of the Earth s surface am Limitations of Primary Production n ma 200 an sawmm Pearson Educmun in nuulahlnaus Benlummcummi39igs The figure shown here is representative of the net primary production for Earth based on data such as chlorophyll density that can now be collected by satellite One striking result is how unproductive most of the oceans are per unit area compared to tropical rainforest Another striking result is that the oceans are not uniformly productive Now let s think about why that occurs The equatorial regions of the planet receive the greatest intensity of light so one might expect them to have the highest productivity However when we study the figure shown here we note that some of the more productive oceans are away from the tropical belt so something other than light must be limiting primary production Nutrient enrichment experiments have shown that the availability of inorganic nutrients is more limiting to primary production in the ocean than light The nutrient that is most limiting in the photic zone is usually nitrogen or phosphorus However in some areas when both nitrogen and phosphorus are plentiful primary production is still limited For example in the Sargasso Sea iron a micronutrient was found to be the limiting factor for primary production Experiments have shown that iron is required by cyanobacteria to convert atmospheric nitrogen into nitrogenous compounds that can be used by phytoplankton for growth At this point you should be thinking to yourself but why are some areas of the ocean low in iron To answer this question you have to think back to the wind patterns around the globe Many of the micronutrients that are delivered to the ocean are blown from the land masses as dust Some areas of ocean such as the Sargasso Sea receive relatively little dust am Limitations of Primary Production n ma no cowIMO Pearson Education lm nummnw Benlummcvmmmgs Areas of ocean with high primary productivity are usually in the vicinity of upwellings where nutrients from the deeper water are circulated up to the photic zone These regions of high primary production are able to support larger fish populations Now let s give some consideration to terrestrial habitats and think about what limits primary productivity there When we study the relative rates of primary production of the land masses above we note that tropical forests are the main primary producer Desert regions such as those found in North Africa or the semi frozen tundra to the far north are low primary producers So what is limiting primary production in terrestrial areas If you said temperature and moisture are the most limiting factors to primary production in terrestrial ecosystems you would be correct The most productive areas have warm temperatures and moisture all year long optimizing plant growth Nutrient availability also affects plant growth but tends to be more localized As in marine ecosystems nitrogen is the limiting element for terrestrial plants since it is required in large amounts for normal growth and cell function Plant material eaten by caterpillar 200 J eeIIuIa 100 J 39 e Feces p rat on Warm owmgmc Pearson EuunlIon InL wbuwm as EMIzmm Cummmgs During primary production autotrophs convert solar energy to chemical energy which is then locked inside the plant as plant biomass increases In any ecosystem consumers eat the plant material that was produced as part of the food chain The chemical energy from the plant material is converted into new biomass in the consumer This phenomenon is called secondary production Let s consider a herbivore such as this caterpillar for our primary consumer We know that caterpillars eat a lot of plant material but everything that is eaten is not converted to new growth Undigested plant material is excreted in feces the energy it contains remains in the ecosystem where it is digested by detritivores The caterpillar continuously undergoes cellular respiration which consumes a good deal of energy most of which is lost from the ecosystem as heat Whatever energy is left over contributing to growth ofthe organism is known as the production efficiency In this case the production efficiency is 33200joules of energy or about 17 of food consumed is converted to new biomass Birds and mammals have low production efficiencies in the range of1 3 fish have a production efficiency around 10 Insects are more efficient at converting food to biomass with production efficiencies around 40 iFKLETAd39l 39i e cwmwapemm Eilumllon inn mummy HelilzminCummmg Now let s think about trophic efficiency or energy transfer from one trophic level to the next in a food chain In general trophic efficiencies range from 5 20 depending on the ecosystem and this loss is multiplied through thefood chain The figure above represents an idealized pyramid of net production with a trophic efficiency of 10 for each link in the food chain With a transfer of 10 of the energy consumed being passed to the next level then only 1010000J 01 of the net primary production is availableto the tertiary consumer Thetop consumer in an ecosystem is typically a larger organism and will need to consume many prey organisms in order to acquire enough energyto survive The ecosystem shown on this slide will support relatively few snakes compared to the number of field voles Now that you have the concept of energy flow through an ecosystem compare how humans can impact the dynamics of energy flow through an ecosystem if they consume their energy exclusively as primary consumers or secondary consumers Nutrient Cycling in Ecosystems Reservoir a Reservoir l Or anic materials unavailable as nutrient Fossil ilaliun organisms Coal all peat Respiration decomposition cretion Assimilationy photosynthesis Reservoir c Reservoir d lnorganlc Inorganic materials materials Weathering as nutrients rosion Atmosphere gt Minerals soil water Formation of in rocks sedimentary rock Used by Permission Pearson Education in The figure above shows a general model of nutrient cycling indicating the main reservoirs of elements and how they are transferred in an ecosystem Each reservoir is characterized by two features whether organic or inorganic molecules are present and if they are available to an organism Note that nutrients may be locked up as biotic or abiotic components The route a particular element takes through a biogeochemical cycle will depend on the element and the trophic structure of an ecosystem For example let s consider carbon Carbon is converted to organic molecules via photosynthesis and is consumed in the food chain so some carbon becomes locked up in the growing organism Feces and dead organic material are broken down into inorganic elements by decomposers releasing carbon molecules Both plants and animals undergo cellular respiration and release carbon dioxide back into the atmosphere This would be the local movement of carbon between reservoirs a and 0 Let s say this carbon exchange occurred during the early Carboniferous period in the great swamps of that time Some of the vegetation and dinosaurs became fossilized in sedimentary rock others were compressed into crude oil Those particular carbon molecules have moved from reservoir a to reservoirs b and d where they remain unavailable until some of them are released back into the atmosphere by the burning of fossil fuels Those molecules that are locked up in rock are released back into the ecosystem as the rock is weathered Tracing elements through a particular biogeochemical cycle is really not this straightforward since elements are exchanged between ecosystems but a general pattern of movement can be established Nitrogenfixing acteria in root nodules of 39 Iegumes and anaerobic bacteria and fungi may Nllrlfyrng yy bacteria Ammonlflcallon N rmw on Ammonium NHf Nitrogen xing soil bacteria Ni r ying ena cavnlvln PenisonEuuullon in publishingzs wlammcummmgs This figure shows a simple representation of nitrogen movement in an ecosystem The largest reservoir for nitrogen is the atmosphere which contains 80 nitrogen However plants are unable to convert this nitrogen gas into organic molecules Nitrogen fixing bacteria in the soil may be free living or have formed an association with the roots of leguminous plants These bacteria utilize the chemical energy in the triple nitrogen bonds producing ammonium ions in the process Ammonium ions are also produced as fungi and other microorganisms decompose organic material such as feces and dead plant and animal material in a process called ammonification Nitrifying bacteria in the soil convert the ammonium ions into nitrate ions in a process called nitrification Nitrate ions are more readily absorbed by plants than ammonium ions In wetland areas denitrifying bacteria use nitrate molecules for energy and in the process release nitrogen back into the atmosphere In plants nitrate and ammonium ions are assimilated into amino acids and proteins which in turn are consumed by animals The strong triple bond of atmospheric nitrogen can also be broken by natural processes such as lightening or by artificial means during fertilizer production You should also familiarize yourself with the water carbon and phosphorus cycles shown in yourtext book Disruption of Biogeochemical Cycles Farming and logging disrupt natural cycles Under natural conditions nutrients are recycled continuously within an ecosystem However biogeochemical cycles are often disrupted by human activities For example cultivation of land to grow annual crops such as wheat disrupts the nutrient balance in the soil As the Wheat grows nutrients from the soil are locked into the growing plant At harvest time many of the nutrients are removed from the area as the grain is shipped off for food and the straw is removed for animal bedding or some other purpose The remaining plant material is eventually broken down by detritivores recycling those nutrients Farmers often replenish the removed nutrients by adding fertilizer to the soil The removal of a large number of primary producers from an ecosystem will cause some disruption to nutrient cycles Biological Magnification Biological magnification of PCBs in the food web of the Great Lakes Concentration of PCBs Used by F39Ermissun Pearson Educatiun in The dynamics of an ecosystem is also disturbed when something is added to the ecosystem which was not there previously Often this is a man made phenomenon when synthetic toxins and chemicals find their way into an ecosystem Examples of toxins entering the environment are pesticides such as DDT or industrial chemicals such as PCBs These chemicals enter the food chain and as they are passed through the different trophic levels they often increase in concentration This phenomenon is called biological magnification Some of these chemicals are metabolized by organisms and the waste products are excreted from the body Others are stored in fatty tissue and retained in the consumer Organisms higher up the food chain eat a larger quantity of the organisms from lower trophic levels and therefore consume more of the chemicals when they are stored in the body tissues Concentrations in an organism may reach levels where they become disruptive to the life cycle This was the case in the 1950s with the pesticide DDT High concentrations of the chemical interfered with calcium deposition in eggshells resulting in weak shells and many birds were unable to incubate their eggs Magnification of industrial chemicals such as PCBs in biological organisms is a more recent discovery These toxins are now found in a wide range of organisms ranging from Orca whales in the Pacific Ocean to herring gull eggs in the Great Lakes Current research indicates that these toxins disrupt the endocrine system of animals including humans The long term effects are not yet known Many of these synthetic molecules cannot be broken down by microorganisms and so they persist in the ecosystem for years or even decades


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