Biology 111 Chapter 31
Biology 111 Chapter 31 BIOL 111
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This 12 page Class Notes was uploaded by Megan Giesler on Sunday May 1, 2016. The Class Notes belongs to BIOL 111 at University of North Dakota taught by Christopher Felege in Spring 2016. Since its upload, it has received 19 views. For similar materials see Concepts of Biology in Biological Sciences at University of North Dakota.
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Date Created: 05/01/16
Biology 111: Concepts of Biology Chapter 31 31.1Ecology of Communities Community: Assemblages of populations of multiple species interacting with one another within a single environment Communities come in different sizes. Relationships and interactions between species form over time. o Coevolution Evolutionary change in one species results in an evolutionary change in another Ex: Hummingbird-pollinated flowers are usually red, a color that these birds can see, and the petals are recurved to allow the stamens to dust the birds’ heads. All species in a community possess adaptations suitable to the conditions of their particular physical environment. Ecosystem: Species interacting with each other and the physical environment If the physical environment changes, corresponding changes will occur in species and their relationships with each other. Extinction can occur when change is too rapid for suitable adaptations to occur. Community composition and diversity o Can compare communities based on species richness and species diversity o Species richness: species composition of a community Simply a listing of various species in that community Coniferous forest has a different species composition than a tropical rain forest Types and number of plants and animals also differ between the two Two communities differ in species composition and tropical rain forest supports more species (higher species richness) o Species diversity: goes beyond species richness to include species distribution and relative abundance o If a forest has 77 trees 76 poplar trees and 1 American elm—less diverse 36 poplar trees and 41 American elms—more diverse Same species richness—2 species Higher diversity value in 2example Ecological succession o Community species composition and diversity DO change over time o Change is slow so may not be noticeable for few decades o Natural forces (glaciers, volcanic eruptions, fires, hurricanes, and floods) are disturbances that can change the community o Ecological succession: more or less orderly process of community change Ecologists have model to explain why succession occurs and predict patterns Climax-pattern model o Climate of an area always leads to the same stable climax community o Specific assemblage of bacterial, fungal, plant, and animal species Two types of succession Primary succession o Occurs where soil has not yet formed o On hardened lava flows or bedrock scraped by glaciers Secondary succession o For example, begins in a cultivated field that is no longer farmed (soil already present) o Both types have a progression of species over time First species in an area undergoing primary or secondary succession are called opportunistic pioneer species o Small in stature, short-lived, quick to mature, and produce numerous offspring per reproductive event o First pioneer species are photosynthetic organisms like lichens or mosses Lichens are 2 organisms (fungal and algal partners) living as one organism o Pioneer herbivores and the carnivores follow Equilibrium species come later o Larger in size, long-lived, slow to mature, and produce few offspring per reproductive event Interactions in communities Competition o Between two species for limited resources has a negative effect on the abundance of both species Predation o Predator feeds on prey Parasitism o Parasite obtains nutrients from host but does not kill host Commensalism o One species benefits while the other is not harmed Mutualism o Two species interact so that they both benefit Ecological Niche Each species occupies a particular position in the community, both in a spatial and a functional sense Habitat o Spatially, species live in a particular area of the community, such as underground, in the trees, or in shallow water Functionally, each species plays a role, such as whether it is a photosynthesizer, predator, prey, or parasite Ecological niche of a species o Incorporates the role the species plays in its community, its habitat, and its interactions with other species o Includes the living and nonliving resources that individuals in the population need to meet their energy, nutrient, and survival demands Competition o Competition for resources contributes to the niche of each species and structures the community. o Competitive exclusion principle No two species can occupy same niche at same time 1930s experiments on two species of Paramecium in a test tube containing a fixed amount of food Although populations of each species survived when grown in separate test tubes, only one species, Paramecium aurelia, survived when the two species were grown together P. aurelia acquired more of the food resource and had a higher population growth rate than did P. caudatum Eventually, as the P. aurelia population grew and obtained an increasingly greater proportion of the food resource, the number of P. caudatum individuals decreased, and the population died out Niche specialization o Competition for resources does not always lead to localized extinction of a species. o Multiple species can coexist by partitioning resources. o Resource partitioning decreases competition between the species. When three species of ground finches of the Galápagos Islands live on the same islands, their beak sizes differ, and each feeds on a different-sized seed. When the finches live on separate islands, their beaks tend to be the same intermediate size, enabling each to feed on a wider range of seeds. Character displacement often is viewed as evidence that competition and resource partitioning have taken place. Mutualism o Symbiotic relationship in which both members benefit o Recognized to be at least as important as competition in shaping community structure o Relationship between plants and pollinators o Lichens—fungal and algal partners living together Can live on rocks since fungal partner leaches minerals valuable to algal partner and algal partner photosynthesizes to provide food for both o In western U.S., branches and cones of whitebark pine are tuned upward (seeds do not fall to the ground when cone opens) Clark’s nutcrackers eat the whitebark pine seeds and store them in the ground Birds are critical seed dispersers for the tree Grizzly bears find seed stores and eat them Whitebark pine seeds do not germinate unless exposed to fire Without fire, the whitebark pine population decreases along with Clark’s nutcracker and grizzly bear populations Community stability o Fragile web of interdependencies o Keystone species: some communities have one species that stabilizes the community and holds the web together Not always the most numerous organism Loss of keystone species can lead to extinction of other species Bats are keystone species in tropical rainforests Pollinators and dispersers of seeds When bats are killed off, trees fail to reproduce Grizzly bears in the northwestern U.S. Disperse thousands of berry seeds in one dung pile Keep herbivore populations under control Native versus exotic species Native species o Indigenous to an area and have evolved in that particular community Exotic species o Non-native species, intentionally or accidentally introduced to an area by humans o Introduction disrupts community Exotic species populations may grow exponentially if they are better competitors or lack a natural predator or disease Myrtle tree was introduced to Hawaii from Canary Islands o Myrtle tree has mutualistic bacteria that fixes nitrogen so it out competes native vegetation 31.2 Ecology of Ecosystems Ecosystem is more inclusive than a community Includes interactions with physical environment that include both biotic AND abiotic factors How an organism acquires food o Autotroph o Heterotroph Autotrophs o Take in only inorganic nutrients 2CO and minerals) and an outside energy source to produce organic nutrients o Called producers because they produce food o Photoautotrophs are photosynthesizers Use energy of the sun Algae and green plants Release O2to atmosphere as byproduct o Chemoautrophs Some bacteria obtain energy by oxidizing inorganic compounds such as ammonia, nitrites, and sulfides Energy source to synthesize organic compounds Found in caves and hydrothermal vents along deep sea oceanic ridges Heterotrophs o Need a source of preformed organic nutrients o Release CO2to atmosphere o Called consumers because they consume food o Herbivores graze on algae or plants. Zooplankton, caterpillars, giraffes o Carnivores eat other animals. Primary, secondary, and tertiary consumers Tertiary consumers are top predators o Omnivores eat both plants and animals. Humans o Consumers Primary consumer—caterpillar or giraffe Secondary consumer—praying mantis Tertiary consumer—cheetah Decomposers o Heterotrophic bacteria and fungi o Break down organic matter including animal waste o Very valuable service o Release inorganic nutrients that are taken up by plants once more o Detritus Remains of dead organisms plus bacteria and fungi aiding in decay Energy flow and chemical cycling Living components of ecosystems process energy and chemicals. Energy flow through an ecosystem begins when producers absorb solar energy. Chemical cycling begins when producers take in inorganic nutrients from the physical environment. Producers convert solar energy and inorganic nutrients into chemical energy in the form of organic nutrients. Energy flows through the ecosystem because organic nutrients pass from one component of the ecosystem to another. Eventually energy dissipates into the environment as heat. The vast majority of ecosystems cannot exist without a continual supply of solar energy. Only a portion of the organic nutrients made by producers is passed on to consumers. o Plants use organic molecules to fuel their own cellular respiration. Only a portion of nutrients consumed by lower-level consumers (herbivores) is available to higher-level consumers (predators). Elimination of feces and urine or death of organisms does not mean organic nutrients are lost from an ecosystem. o Nutrients available to decomposers o Convert organic nutrients back into inorganic nutrients for release into soil or atmosphere Of the food eaten by an herbivore, o Some is never digested and eliminated as feces o Of the assimilated energy, a large proportion is used for the production of ATP. Which also produces heat o Only energy converted into body weight or additional offspring is available to carnivores. Energy flow Food web o Interconnecting paths of energy flow between components of an ecosystem Grazing food web: begins with plants o Caterpillars and other herbivorous insects feed on the leaves of trees. o Other herbivores (mice, rabbits, and deer) also feed on leaves. o Birds, chipmunks, and mice feed on fruits and nuts of trees. Omnivores because they also eat caterpillars and insects o All provide food for carnivores Detrital food web: begins with bacteria and fungi o Detritus is food for larger organisms. o Shrews and salamanders can become food for aboveground animals linking the detrital and grazing food webs. Trophic levels and ecological pyramids o Food chain Diagrams that show a single path of energy flow in an ecosystem o Trophic level Level of nourishment within a food web or chain st 1 level—producers 2 ndlevel—herbivores rd th 3 (and 4 ) level—carnivores Food chains are short, because energy is lost between trophic levels. o In general, only about 10% of the energy of one trophic level is available to the next level. o Explains why few carnivores can be supported in a food chain o Ecological pyramid depicts energy losses between tropic levels Chemical cycling Biogeochemical cycles: pathways by which chemicals cycle within ecosystems o Involves both living (producers, decomposers, consumers) and nonliving (inorganic nutrients, atmosphere) components Two types of cycles o Sedimentary Chemical is absorbed from the sediment by plant roots, passed through the food chain, and eventually returned to the soil by decomposers o Gaseous Element returns to and is withdrawn from the atmosphere as a gas Cycles may involve o Reservoirs: source normally unavailable to organisms o Exchange pool: source from which organisms generally take elements o Biotic community: consists of autotrophic and heterotrophic species of an ecosystem that feed on each other Phosphorus cycle o On land, slow weathering of rocks adds phosphates (PO 4-and HPO )4to the soil Also runs off into aquatic systems o Producers use phosphates in a variety of molecules Phospholipids, ATP, nucleotides Decomposition of plant and animal materials makes phosphates available o Phosphates usually a limiting inorganic nutrient in ecosystems Limits plant growth and primary productivity Transfer rate o Amount of nutrient that moves from one component of the environment to another within a specified amount of time o Human activities change transfer rates. o Humans mine phosphate ores and use them for fertilizer, animal feed supplement, and detergents. o Animal wastes from livestock, lawn fertilizer, and sewage discharge from cities adds excess phosphates to nearby waters. o Eutrophication Over-enrichment of a body of water causing an algal bloom When algae die and decay, oxygen is consumed, causing fish kills. Nitrogen cycle o Nitrogen gas (N 2 comprises 78% of the atmosphere by volume. Plants cannot take up nitrogen gas. Plants rely on various bacteria to make nitrogen available. o Plants take up ammonium (NH ) 4nd nitrate (NO ) 3 from the soil. Incorporate it into amino acids and nucleic acids o Nitrogen fixation changes N to ammonium. 2 o Nitrification produces nitrates. o Denitrification converts nitrates to N . 2 o Human activities alter transfer rates by producing fertilizers from2N . o Nitrate leaching can lead to eutrophication. o To cut back on fertilizer rates, it may be possible to engineer soil bacteria with increased nitrogen fixation rates or farmers could grow legumes that increase the soil nitrogen content. Carbon cycle o Organisms in both terrestrial and aquatic ecosystems exchange carbon dioxide with the atmosphere. o On land, plants take up carbon dioxide from the air and incorporate it into organic nutrients. Aerobic organisms release carbon dioxide as a waste product. o In aquatic ecosystems, exchange of carbon dioxide with the atmosphere is indirect. Carbon dioxide combines with water to form bicarbonate ion (HCO3). Algae incorporate it into organic nutrients. Respiration also releases carbon dioxide (that becomes bicarbonate ion in water). o Living and dead organisms contain organic carbon. Reservoir for carbon cycle If dead plant and animal materials fail to decompose they may be transformed in fossil fuels. Most fossil fuels formed during Carboniferous period 286–360 MYA. Human activities o Transfer rates of carbon dioxide due to photosynthesis and respiration should be about even. o Humans burning fossil fuels and destroying forests are adding more carbon dioxide to the atmosphere. o Greenhouse effect: response to greenhouse gases absorbing and reradiating heat back to the Earth 31.3 Ecology of Major Ecosystems Biosphere: Encompasses all the ecosystems on planet Earth and final level of biological organization Aquatic ecosystems o Freshwater ecosystems Standing water—lakes and ponds Running water—rivers and streams o Saltwater (marine) ecosystems Ocean is a marine ecosystem that covers 70% of Earth’s surface Terrestrial ecosystems (biomes) o Temperature and rainfall define the biome o Contains communities adapted to regional climate Tundra o Northernmost biome o Permafrost persists even during summer in tundra; prevents large plants from becoming established Taiga o Very cold northern coniferous forest Temperate grasslands o Receive less rainfall than temperate forests (in which trees lose their leaves during the winter) and more water than deserts, which lack trees Temperate forests Deserts Savanna o Tropical grassland with alternating wet and dry seasons Tropical rain forests o Occur at the equator o Have a high average temperature and greatest amount of rainfall of all biomes o Dominated by large evergreen, broad-leaved trees Primary productivity Rate at which producers capture and store energy as organic nutrients over a certain length of time One way to compare ecosystems Influenced by temperature, moisture, and nature of soil In terrestrial ecosystems o Lowest in high Latitude tundra and desert o Highest at equator Tropical rain forests In aquatic communities o Largely dependent on availability of inorganic nutrients o High in estuaries, swamps, and marshes o Open ocean between desert and tundra o Coral reefs equivalent to tropical rain forests
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