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ENWC314 book notes

by: Eden Tinkelman

ENWC314 book notes ENWC314

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the ecological world view book notes
Anastasia Chirnside, Joanna York
Class Notes
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This 22 page Class Notes was uploaded by Eden Tinkelman on Wednesday August 24, 2016. The Class Notes belongs to ENWC314 at University of Delaware taught by Anastasia Chirnside, Joanna York in Fall 2016. Since its upload, it has received 6 views. For similar materials see COMP TERRESTRIAL/MARINE ECOLOG in Ecology at University of Delaware.


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Date Created: 08/24/16
ENWC314 Book Notes Chapter 3: What Limits Geographic Distributions?  In the News o San Francisco Bay supports the largest and most important expanses of tidal mudflats and salt marches in the western United States  Many non-native species of plants and animals have been introduced to the bay, and some now threaten to cause fundamental changes in the bay’s tidal areas  One such species is the Atlantic salt march cordgrass  This cordgrass is likely to dominate tidal marches, cause the extinction of native tidal march plants, choke tidal creeks by its extensive growth and eliminate thousands of hectares of shorebird habitat  Cordgrass colonization could endanger threatened species that use existing tidal marsh habitats, including the rare California clapper rail and the salt-marsh harvest mouse  3.1 Dispersal often Limits on a Global Scale o to understand why species are found in particular places, and how their geographic ranges may shift in response to environmental changes, we need to know what factors set the limits to their ranges; how widely an introduced pest might colonize a new area and how climate change might affect the distributions of both common and endangered species o Types of Dispersal  Simplest explanation for why a species is not found in a particular area is that is has not been able to reach the area  The movement, or dispersal, of organisms can occur by two mechanisms  Diffusion is a common form of dispersal involving the gradual spread of a population across hospitable terrain. It results from the movement of many individuals over several generations  Jump dispersal is the movement of individual organisms across large distances, usually over unsuitable terrain, to a new area where they establish another population. This form of dispersal occurs in a short time during the life of an individual o The Spread of the Gypsy Moth, an Introduced Pest  The European gypsy moth is an example of a species that has spread by both mechanisms of dispersal  In 1868/1869, Ettiene Leopold Trouvelot brought some gypsy moth eggs from France to his home in Massachusetts; a few of the caterpillars that hatched from the eggs escaped  Gypsy moth caterpillars eat the leaves of a great variety of deciduous and coniferous trees  To curb the severe defoliation of deciduous trees caused by the caterpillars, Massachusetts initiated a control program in 1889 and by 1900 the severity of the outbreaks was reduced; this was eventually terminated by the state  The US Forest Service started placing traps laced with a pheromone along the expanding boundary of the moth’s range; these traps have slowed, but not stopped, the spread of the moth  One factor that may affect the spread of the gypsy moth is a disease caused by the fungus Entomophaga maimaiga, a widespread gypsy moth pathogen in Asia  Ecologists are now trying to predict how this fungal disease will influence the future range of the gypsy moth in North America  Gypsy moth problem illustrates three recurring themes in geographic ecology:  Species moved by humans can become serious pests after they are introduced  Governments often ignore the problem of introduced species in the early stages of introduction when the problem is often easiest to address  Pests spread by diffusion once they are established; gradual spread of introduced species may be slowed, but can’t easily be stopped o Aquatic Invasions  Many aquatic invasions have been assisted by humans  During the 19 century, aquatic organisms often arrived in foreign ports attached to the bottoms of ships, but this dispersal mechanism largely disappeared with the advent of antifouling paints and faster ships, which reduced the transit time during which organisms could attach to the ships’ hulls  Included in ballast water are large numbers of organisms of diverse species  The biological results of ship-assisted jump dispersal are significant  Chesapeake Bay now has 116 introduced marine species and San Francisco Bay has 212  The zebra mussel is one of the best-known examples of an aquatic species brought to North America in ballast water  Introduced aquatic species can also pose health risks to humans  Single-celled marine protists called dinoflagellates are transferred worldwide in ballast water; some dinoflagellates produce toxins that are accumulated by marine mollusks, which may be deadly to people who consume them  Cholera has also been found in ballast water  There are 2 ecological messages in these aquatic invasions:  Many of these introduced species were originally limited in their global distribution by distribution  Action is urgently needed to reduce the global transport of potentially harmful organisms in ballast water o Tree Recolonization at the End of the Ice Age  One of the spectacular colonizations began at the end of the last ice age, about 14000 to 16000 years ago  As glaciers retreated from Europe and North America, oaks and other temperate-zone trees expanded their range northwards  In diffusion, the migration rate of a species depends on the species’ reproductive rate and its average dispersal distance  The discrepancy between this distance and the observed expansion is called Reid’s paradox  Two possible explanations for Reid’s paradox have been suggested o A species’ migration rate depends more on extreme dispersal events than on average dispersal distance o An alternative explanation for Reid’s paradox is that a few trees may have exited in isolated pockets farther north during the ice age, and recolonization of northern Europe and North America may have originated from those trees rather than from southern populations o Island Colonization  The results of jump dispersal are seen most easily on islands, because all the organisms that colonize an island after it forms must do so across water  Colonization of an island by terrestrial plants and animals is determined largely by the island’s distance from the nearest mainland: more remote islands generally have fewer species  Natural catastrophes can create areas of new habitat within continents  Range limitation imposed by barriers to disposal is the basis for a country’s quarantine restrictions, which are an important part of the fight to contain invading species  Quarantine measures that restrict the importation of plant pathogens are critical to protect the agricultural crops of islands; quarantine practices remind us that pest species can move rapidly by jump dispersal  Essay 3.1 A Simple Model of Dispersal Movements o The simplest model of species migration is called the diffusion model, which is based on an equation that describes chemical diffusion  Skellam showed that if trees or other organisms migrate by diffusion, the distance they migrate can be calculated using the following equation:  Distance moved= DnSQRT(logR ) 0 o In practice, we must modify the diffusion model because all individual organisms don’t live for the same time or reproduce at the same rate, and some seeds or spores may be transported greater distances by birds or windstorms  3.2 Physical or Chemical Factors Usually Limit Ranges on regional and Continental Scales o Shelford’s law of tolerance states that the distribution of a species is controlled by the environmental factor for which the species has the narrowest tolerance; only one environmental factor limits a species at any given time  Ecologists need critical natural history information to isolate the physical and chemical factors that limit a species o There are three steps to determining whether an environmental factor limits the range of species:  Determine the stage of the life cycle that is most sensitive to the factor  Determine the physiological tolerance of that stage  Show that variations in the factor are within the tolerance limits of the species in its geographic range and that they exceed those limits outside its range o If the tolerance limits of a species are exceeded in certain sites, those sites can’t be colonized; of the species is transplanted there, it will not become established and will die out o The geographic limits of invertebrates and algae are often very sharply defined in the intertidal zone of rocky coastlines o No single factor determines geographic range o Range Extension via Adaption  In out analysis of range limitation by environmental factors, we have assumed that all individuals of a particular species have certain physiological tolerances built in; since species can undergo local adaptations, they aren’t genetically or physiologically uniform throughout their ranges  Common garden—an experiment where one or more organisms are moved from one environment to another environment  This allowed for the separation of phenotypic and genotypic components of variation among plants of the same species growing in different environments  Phenotype—observable physical or biochemical characteristics of an organism, as determined by both genetic makeup and environmental influences  Genotype—the genetic constitution of an individual organism  Is all of the variation within a species is phenotypic, then plants of that species should have the same characteristics when grown in a common garden; on the other hand, if all of the variation is genotypic, then plants should have the characteristics typical of the habitat where the seeds were obtained.  A combination of phenotypic and genotypic determination should produce intermediate characteristics  Ecotype—a distinct form or race of a plant or animal species occupying a particular habitat o Impacts of Rapid Climate Change  Earth’s climate is warming and is expected to become more variable over the next century; one way to predict how these climate changes may affect species’ geographic ranges is to examine what has happened in temperate regions since the end of the last ice age  Temperate-zone trees in the northern hemisphere started migrating northwards when the continental glaciers began to retreat about 14,000 to 16,000 years ago  According to the models, southern forest types will move north as the potential ranges of all temperate-zone trees expands northwards; these changes will happen only if trees can colonize new areas with sufficient speed  Climate change is happening too quickly for trees to disperse by natural mechanisms alone  The effects of climate change will not appear immediately; long-lived species, such as trees, will survive for many years their present ranges  As the climate changes, they will reduce their seed production and finally be unable to produce viable seedlings  Many lines of evidence link global climate shifts during the last 50 years with a variety of biological changes  Life-cycle events are strongly affected by temperature  For most plants and animals that have been studied, these events have been occurring progressively earlier over the last half-century; over the same period, the geographic ranges of 99 species whose ranges are well known have shifted toward the poles an average of 6 km per decade  The impact of climatic warming is established without a doubt for many species, with the largest effects occulting in temperate and polar regions  Climatic change will also have impacts in mountainous regions; most mountains have a tree line—an upper limit to the distribution of forests  As global warming proceeds, trees will colonize the higher levels and alpine tundra species may be lost if the zone disappears entirely; reduced precipitation in mountains will affect aquatic organisms by reducing stream flows and raising water temperature  Essay 3.2 Bioclim—Computer Software For Predicting Potential Geographic Ranges of Organisms o Well-developed computer programs, such as BioClim or CLIMEX, can be used to predict the potential ranges of species whose ranges are limited by climate o These programs use two approaches to make their predictions  One approach, used for species whose present geographic ranges are well documented, is to construct a predictive model based mainly on rainfall and temperature readings taken inside and outside the species’ ranges  The second approach is to construct a predictive map based on the specific climatic factors that are known to limit each species’ range o The second approach was applied to the red fire and Solenopsis invicta  This species’ range seems to be limited in cold areas by low winter soil temperature and in dry areas by low rainfall  3.3 Predators, Diseases, Parasites, and Competition can Limit Ranges on a Local Scale o Limitation by Predators  The best illustrations of range limitation by predators are cases in which introduced predators have severely affected native prey species  Other examples of predator0related range changes have resulted from the elimination of predators o Limitation by Diseases  A large proportion of the bird species that were once endemic (found nowhere else) to the Hawaiian Islands have become extinct in historical times  one major factor in their extinction is introduced diseases, like avian pox  a second wave of extinction in Hawaiian birds began in the early 1900s and was probably the result of avian malaria  most introduced bird species occupy lower elevations, and so does the main malarial vector  the roles of predators and diseases in the geographic ecology of plants and animals have been studied far less than their potential importance warrants  essay 3.3 o the emergence of new infectious diseases is one of the major problems of our times and a good example is the West Nile virus  West Nile virus is carried by mosquitoes and infects birds as its primary host o in June 1999, a large number of dead and dying crows were found; by autumn, 62 people had become infected with West Nile virus  in humans, the virus causes symptoms ranging from mild illness to encephalitis and meningitis  prior to 1999, there had been only a few sporadic outbreaks of infection by the virus in humans o since the mid-1990s, West Nile virus has become more virulent—killing birds and horses in eastern Europe, Israel and now North America; a new variant of the virus seems to have evolved and is responsible for these recent severe outbreaks o West Nile virus has spread very rapidly in North America  By 2003, in the US there were more than 4,000 cases cases of West Nile virus infection in humans, and 263 were attributed to the virus, many in elderly people  There have been only a few cases of West Nile virus detected in birds in Canada, and most of the human cases were Canadians who had visited parts of the US known to harbor the virus o The West Nile virus story is typical of many newly emerging diseases: a sudden dispersal of a known pathogen from an area where it has existed for many years causing relatively little damage to people or other animals, followed by a burst of mortality in new hosts that are not adapted to the pathogen  Humans typically acquire these diseases as incidental hosts, rather than as the primary target of the pathogen o Part of the solution to the problem of newly emerging diseases lies in preventing jump dispersal  Quarantine procedures prevent many of these undesirable introductions, but, because of increased travel and trade, countries are being bombarded with possible introductions of potential pathogens ENWC314 chapter 1 book notes  In The News o Emperor penguins in Adelie Land, Antarctica, have been declining in numbers for the last 50 years  They are now about half as abundant as they were in the 1960s  Like all scientists, ecologists begin with observations—in this case annual counts of penguins in one colony for 50 years  Next, ecologists suggest ideas to explain the observations and look for additional data to see if these ideas are correct  1.1 interaction between species determine where organisms live and how many live there o ecology—scientific study of the interactions that determine the distribution and abundance of organisms  some interactions are between diff species  other interactions are between organisms and factors in the physical environment, including temp and precipitation o distribution—where organisms are found o abundance—how many organisms live in a given place  distribution and abundance of many species vary in space o ecology and environmentalism  world ecology was first used by German zoologist Ernst Haeckel ith1866, and it came into wider use in the last half of the 19 century  in the public mind, the word ecology came to mean everything and anything about the environment, esp. human impact on the environment and its social ramification  ecology deals with the interrelations of all organisms; while it includes humans as a very significant species by virtue of their impacts, ecology is not solely concerned with humans  environmental study—analysis of human impacts on the physical, chemical, and biological environment of Earth  much broader than ecology because it integrates ecology, geology, climatology, sociology, economics, anthropology, political science and philosophy  has led to environmentalism—a social movement whose agenda for political and social change is directed toward minimizing human impacts on Earth  ecology should be the foundation for environmentalism  we are constrained by principles of ecology when we alter the environment  many ecologists work hard in the political area to achieve the social goals of environmentalism o ecological systems  ecology is the science that examines the relationships between all the animals, plants, fungi, and microbes on Earth  these organisms interact in ecological systems, which include all the organisms in an area as well as their non-living (abiotic) environment  essential message of ecology is that changing one component in an ecological system usually changes others  humans are a dominant species in the world today, and ecology is concerned with how humans interact with all others kinds of organisms  of all the sciences, ecology is one of the closest to our daily lives  1.2 ecology’s foundation in natural history goes back more than 2000 years o roots of ecology lie in natural history; primitive tribes, which depended on hunting, fishing, and food gathering, needed detailed knowledge of where and when they could find their food  establishment of ag. Depended on an increased understanding of the practical ecology of plants and domestic animals; early naturalists knew that a major constraint on animal populations is their food supply, and that predators and disease could also have a significant impact o the balance of nature  ecological harmony was a guiding principle basic to the ancient Greeks’ understanding of nature—the concept of the balance of nature is at least 2000 years old  providential design, which held that nature is designed to benefit and preserve each species, which was implicit in the writings of Herodotus and Plato  when outbreaks of some populations did occur, they were usually explained as divine retribution for the punishment of evildoers  each species had a special place in nature, and extinction did not occur because it would disrupt the balance and harmony in nature o applied ecology  many of the early developments in ecology came from the applied fields of ag and fisheries, long before the word ecology was coined  in subsequent years, an increasing knowledge of insect parasitism and predation led to many such introductions all over the world in efforts to fight ag pests—a branch of applied ecthogy we now call biological control  by the 17 century, some Icelandic fisheries started to fail; but it was only during the 20 century, with the development of motor-powered fishing vessels, that industrial fishing and sustained over-fishing became rampant, leading to the collapse of the northern cod stocks and many other fish species  ecology has blossomed, providing an increasing understanding of our world and how humans affected ecological systems  1.3 ecologists study biological interactions from the level of the individual to the entire biosphere o biological systems can be analyzed at different levels, ranging from molecules to ecosystems, defined largely by size—levels of integration  biological processes in each level of integration involve the level immediately below, so there is a natural hierarchy that is assumed in this pattern o 6 levels of integration:  biosphere/ecosphere—an aggregation of landscapes to include the whole-earth ecosystem  landscapes—groups of ecosystems typically at a larger spatial scale  ecosystems—consist of communities and their physical environment  communities—groups of species that live in the same area, so they include many populations  populations—groups of individuals if a single species  individual organisms  each level of integration involves a separate and distinct set of attributes and problems o density—number of individuals per unit area or volume; this property that can’t be attributed to a single individual o biodiversity—number of species; at the community level but not at the population level o reductionist—approach to science that reduces a problem at one level of integration to a series of problems at lower levels o holistic—encompassing higher levels  1.4 like other scientists, ecologists make observations, form hypotheses, and test predictions o essential features of the scientific method are the same in ecology as in other sciences; an ecologist begins with a problem, which is often based on observations of natural history o accurate natural history is a prerequisite for all ecological studies, because if a problem is not based on correct observations, all subsequent stages will be useless o hypothesis—a statement of cause and effect; a statement that offers an explanation for some observation  several answers might be possible, and several alt. hypotheses can be proposed to explain the observations o scientific law—a universal statement that is so well supported by experiment observations that everyone accepts it as part of the scientific background of knowledge. There are many laws in physics, chemistry and genetics, but few in ecology o principle—a statement that is universally accepted because it is mostly a definition, or an ecological translation of a physical or chemical law o theory—an integrated and hierarchal set of experimental hypotheses that together explain a large number of scientific observations. The theory of evolution by means of natural selection is perhaps the most frequently used theory in ecology o model—a verbal or mathematical statement of a hypothesis. Often the words model and hypothesis are used interchangeably o experiment—a test of a hypothesis that involves observation of the system in question. It may also include some manipulation of the system. The experimental approach is known as the scientific method o fact—a specific truth pertaining to the natural world. Some observations are faulty, so an observation is not automatically a fact o predictions and experiments  predictions follow logically from a hypothesis, and the more predictions a hypothesis makes, the better it is  predictions from simple hypotheses are often straightforward; every hypothesis must predict something and forbid other things from happening  every hypothesis should have a list of observations that are consistent with it and a list of observations that are not consistent with it  experiments can be manipulative or natural  the protocol for the experiments and the type of data to be obtained are called the experimental design  a successful experiment produces data that allow the researcher to either reject or tentatively accept the tested hypothesis; a hypothesis that is tentatively accepted may be rejected later if the data from another experiment do not support it o complexity in ecology  the complexity of systems often makes it challenging to apply the scientific method  systems in which many factors operate together are difficult to analyze, and require ecologists to formulate complex hypotheses; not matter how complex a hypothesis is, it must make predictions that can be tested by experimentation o ecological truth  to a scientist, truth consists of correspondence with the facts  arguments start when the inferences are drawn from whole sets of facts  many ecological ideas are at an incomplete stage because there has not been enough time, money, or personnel to test such general hypotheses sufficiently; like other scientists, ecologists must deal with the problem of uncertainty  the resolution to this problem in ecology and in many other areas of natural science has been the precautionary principle, which may be expressed as ‘look before you leap’ or ‘an ounce of prevention is worth a pound of cure’  the central ideas of the precautionary principle are to do no harm to the environment, to take no actions that are not reversible and to avoid risk as much as possible  ecological truth is never obvious in complex environmental issues and emerges more slowly than we might like; our knowledge obtained by the scientific method is always incomplete and science is a never-ending quest  Essay 1.1 How to Read Scientific Literature o The most important thing is t read critically and there are a few pointers for help  What is the question? This should be explicitly stated early in the paper  What are the proposed explanations for this problem? List the hypotheses that are possible explanations. There must be at least two alternative hypotheses that make different predictions  What observations or data would favor one hypothesis over the others? There must be some possible observations that would contradict each of the hypotheses  How were data collected in study?  What are the results of the study? Do they fit one hypothesis better than another? Are the results cleat and conclusive, or are they inconclusive?  What should be done next? Because science is an endless process, all research should lead to more hypotheses and more experiments, and good scientific papers end with suggestions for what should be done next  Essay 1.2 Science and Values in Ecology o Science is thought by many people to be value-free, but this is certainly not the case  Values are woven all through the tapestry if science  All applied science is carried out because of value judgments  Medical research is a good example of basic research applied to human health that virtually everyone supports  Weapons research is carried out because countries wish t be able to defend themselves from military aggression  Should conservation biologists be objective scientists studying biodiversity or should they be public advocates for preserving biodiversity?  The preservation of biodiversity is a value that often conflicts with other values  Scientists have a duel role  Firstly, they carry out objective science that collects data and tests hypotheses about ecological systems  Secondly, they can also have a role as advocates for particular policies that attempt to change society, such as the use of electric cars to reduce air pollution  Science is a way of knowing—a method for determining the principles by which systems operate  Scientists assume that once we know these scientific principles we can devise effective policies to achieve social goals  All members of society collectively decide on what social goals we will pursue  There will always be a healthy tension between scientific knowledge and public policy in environmental matters because there are always several ways of reaching a particular policy goal  1.5 lyme disease illustrates the complex interactions in ecosystems o first described in 1977 in Connecticut, Lyme disease is now spreading from east to west across North America o the disease is caused by the transmission of bacteria, called spirochetes, from ticks to humans; when a tick infected with spirochetes bites a person, the spirochetes enter the person’s bloodstream  the spirochetes do little harm to the ticks, but in humans they can cause severe damage to the nervous system, heart, eyes, and joints o after passing through a small nymphal stage, in which they feed on the blood of small rodents and birds, deer ticks reach a size at which they feed mainly on white-tailed deer; in their second year of life, they reach sexual maturity and drop off deer to lay their eggs in the forest floor o interaction webs  ecologists typically try to summarize such connections in an interaction web  an interaction web is a boxes-and-arrows diagram of all the relationships between species in an ecosystem  interaction webs have two simple rules for their construction:  arrows indicate ecological interactions; AB means species A affects species B  type of interaction is indicated by a plus or a minus sign o complex interactions in lyme disease  if mouse numbers increase, ticks have more mice on which to feed so tick numbers can increase  more mice may increase acorn production by decreasing gypsy moth numbers  when acorns become abundant, white-tailed deer are attracted to the forest in the short tern, and over the long term there is a loss of forestry understory, so that songbirds may produce fewer young  ecologists need to know by how much the numbers of organisms in interaction webs have changed  many things are connected in ecological systems, and the ecologist’s job is to uncover both the direct connections and the hidden, indirect connections; the best approach is to assume that there are more connections between species than are immediately obvious  many errors in the management of agriculture, forests, fisheries, and wildlife have been made by assuming too few connections between species; in ecology it’s important to recognize that we do not know everything about natural systems  1.6 ross river fever illustrates how humans and ecosystems are interconnected o ross river virus is the most common mosquito-borne pathogen in Australia, affecting more than 5000 people annually; this virus is found only in Australia and New Guinea and is common in all states  the wet season increases the abundance of mosquitoes that carry the virus, which has been recorded from 42 different species of 7 different genera of mosquitoes o ross river virus produces a variety of symptoms that can last for 6 months or more; fever and rash are common, as well as arthritis of all joints, resulting in persistent fatigue o most infections occur in people between 20 and 60 years old, and are rare in children o mosquitoes carry Ross River virus and the virus reservoirs appear to be mainly kangaroos and wallabies  virus reservoirs are animals that carry the disease in their blood, but are often not harmed very much by the virus; mosquitoes pick up the virus when the feed on a reservoir host and can then potentially carry it to people o in eastern Australia up to 89% of kangaroos and wallabies tested had antibodies against the Ross River virus, indicating that they had been infected at some time in the past o marsupials seem to be the main reservoir of the virus, and placental mammals like cats and dogs do not seem to be good hosts; horses tested positive to the viral antibodies o infected humans can be significant amplifiers of the virus, and this has caused a movement of the disease from Australia to the Pacific Islands o the ecological significance of diseases such as Ross River fever depend on a variety of species interactions, and these interactions are rarely simple o ecological world view—an ethical viewpoint that is infused with an appreciation of basic ecological science, and it often differs from the view of many business people, engineers and other scientists; it’s part of a movement that uses scientific insights in an effort to achieve sustainable development  Essay 1.3 What is an Ecological World View o Ecologists view the world in a particular way, and one of the reasons to study ecology is to learn about this world view; we can begin this quest by listing five principles that outline the ecological world view  You can’t alter just one component of an ecological system. It calls attention to the connections between species in ecological systems. On a practical level, this principle is why we require environmental impact statements for any major developments  Human actions can have long-lasting ecological impacts. Ecologists look at events from a long-term perspective. Ecological processes can have effects decades or centuries in the future  We can learn from history. It’s particularly suited to ecology because we tend to think that present environmental conditions are ‘normal.’ There is a hope that if we learn from history we can avoid repeating mistakes  Conservation is essential. Many of these species play important roles in the biosphere, and it’s in our selfish interest to protect them from extinction  Evolution continues. Evolution is the background for all ecological interactions ENWC314: Chapter 2 book notes  In The News o The red fire ant has invaded the southern US with devastating consequences  The red fire ant is particularly dangerous because it forms large colonies that quickly swarm and sting en masse when an animal disturbs their mound by walking on it  Farm animals and wildlife species are also killed by these ants o Reproductive success for these ants depends in high temperature and moderate rainfall o The red fire ant was inadvertently introduced to Brisbane, Australia in 2001, presumably in a container shipped from the southern US  Because fire ants are a serious environmental pest that could spread across the warmer regions of northern Australia, the federal and state governments have spent $175 million, and employed 650 people, over the past 6 years in an attempt to eradicate fire ants in the Brisbane area  Essay 2.1 Global Temperature and Precipitation o temperature and precipitation are not uniform over the Earth o temperature changes seasonally and from year to year, but average temperatures clearly vary with latitude o areas near the equator are much warmer than the polar regions  the major exceptions to this general rule are the mountainous regions on the continents  average annual rainfall shows a much more complex global pattern o there is a belt of high precipitation around the equator o  low precipitation around latitude 30 N and S is associated with the distribution of deserts around the world  mountains and highland areas intercept more rainfall and leave a ‘rain shadow’ on their leeward side o these global patterns of temperature and precipitation determine the geographic distribution of biomes with their accompanying organisms  2.1 All Species Have a Limited Geographic Range o biogeography—the branch of biology that deals with the geographical distribution of plants and animals o Biogeographical Realms  Biogeography is a discipline that spans geography, ecology, and geology to provide the historical background for the present distribution of like on the continents  We can divide the land areas of earth into 6 regions known as biogeographical realms which tend to contain different animals and plants  The boundaries of these regions are not sharp, and many species live in 2+ realms o Biomes and Floristic Regions  Earth’s surface can also be divided into biomes, which are major biotic communities that occupy large areas of land or water  Terrestrial biomes are characterized by a dominant vegetation type; the marine biome and the freshwater biome complete the global description of life on Earth  The graph reveals that the boundaries of terrestrial biomes are strongly affected by both temperature and precipitation  Floristic regions—any of six areas of the world recognized by plant geographers for their distinctive plant life  there are 14 floristic regions in North America o Spatial Scales  Terrestrial biomes and floristic regions are typically represented on maps with a large special scale  A typical spatial analysis of geographic ranges uses a grid system with equal-area units; if a species is present anywhere within a grid square, that square is considered to be occupied  2.2 Geographic Ranges can be Very Small or Very Large o the areas occupied a species vary by more than a million-fold o possibilities of range size pattern for a group of species:  few species have very large or very small ranges, while most species have ranges of intermediate size; this possibility would give a bell-shaped curve of range sizes  many species have large ranges (in other words, are widespread) and a few have small ranges  many species have small ranges and few have large ranges o Hollow Curve Pattern  Most species have small geographic ranges and only a few species have very large ranges  it seems to apply for all groups that have been studied o Rapoport’s Rule  Argentinean ecologist Eduardo Rapoport suggested that geographic ranges decrease in size from the poles to the equator  This generalization, now known as Rapoport’s rule, is supported by studies on trees, fish, reptiles, and many mammals from several continents  Ecological basis for Rapoport’s rule:  One explanation is the climatic variability hypothesis, which states that climate is more variable at high latitudes, and only organisms that tolerate this variability can live there  this hypothesis predicts that the climatic tolerance of terrestrial animals and plants should increase from the equator to the poles. This prediction hasn’t been tested  in the ocean, temperature variation in surface waters is highest in temperate zones and much lower near the poles and in the tropics  climatic variability hypothesis predicts that the temperature tolerance of surface marine fishes should be lowest in both polar and tropical waters  in deeper ocean waters, temperature variability is minimal, so the climatic variability hypothesis would predict no relationship between latitude and range sixe for deep-sea organisms  there are no data to test this prediction  Rapoport’s rule is a good illustration of how ecologists can apply the scientific method to develop explanations for patterns in natural systems  Ecologists describe the patterns clearly and accurately  They propose hypotheses to explain these patterns, and make predictions based on each hypothesis  If the observed data agree with the predictions of a hypothesis, they may conclude tentatively that the hypothesis is supported  They search for exceptions to the hypothesis and try to uncover reasons why there might be exceptions o Abundance Within Geographic Range  Species aren’t equally abundant in all parts of their geographic range; if environmental conditions within a species’ geographic range become less favorable from the center to the edges of the range, we would predict the abundance of the species to be highest near the center and lowest near the edges  Many additional species will have to be tested before we can accept this prediction as an ecological generalization  It would also suggest that nature reserves should be placed at the center of the range to protect more individuals per unit area and that central populations should be the focus of conservation efforts o Species that are more widespread are typically more abundant o One possible explanation for the correlation between abundance and range size is that species that can exploit a wide variety of resources become both widespread and common—generalists  Species that exploit only a few resources are called specialists and they have smaller ranges and are less abundant because they have strict requirements for food or shelter  Ecological specialization—how many species limit themselves to small diet- or habitat-niches, as a result of evolutionary trade-offs  2.3 A Sequence of Hypotheses Guides an Ecologist’s Analysis of What Limits Ranges o the hypothesis in the first step (DISPERSAL) is that the species is absent from an area because a barrier has prevented it from reaching the area  test this hypothesis with a transplant experiment—in which you move some individuals of that species into the area  if the transplanted individuals survive and reproduce, we may conclude that the environmental conditions in the area are adequate for the species and that its range is limited by a lack of dispersal  controls—transplants done within the normal geographic Range to reveal any effects due simply to handling and transplanting the individuals o if the species can’t survive and reproduce in the transplant areas, it’s clearly not limited by dispersal and we proceed to the next hypothesis: the species range is limited behaviorally or by habitat selection  species may be programmed to select a smaller range of habitats than they could theoretically occupy because of evolutionary constraints o more commonly, species that are not limited in their geographic range by dispersal or habitat selection may be limited by interactions with other species  these interactions may involve either the negative effects of predators, parasites, disease organisms or competitors, or the positive effects of interdependent species within the actual range  we can often determine whether interactions with other species limit the range of a species by performing a transplant experiment with a protective device, such s a cage that excludes suspected predators or competitors o if other species do not limit the actual range of a species, we are left with the final possibility that physical or chemical factors are responsible  the effects of physical and chemical factors on the survival, growth and reproduction of organisms are the subject of an entire discipline called physiological ecology o Liebig’s Law of the Minimum  Liebig’s law of the minimum—which states that the rate of any biological process is limited by a single factor that is least available, relative to an organism’s requirements  we must define the ecological tolerances of species to a whole array of potentially limiting environmental factors, a broadening of Liebig’s law that was first elaborated by Victor Shelford o Shelford’s Law of Tolerance  Shelford’s law of tolerance, which can be stated as follows: the distribution of a species is controlled by the environmental factor which the species has the narrowest tolerance  Young stages of organisms are often the most sensitive to environmental factors.  Consequently, we should test the most sensitive stage when we determine a species’ tolerance


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