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This 5 page Class Notes was uploaded by Amanda Notetaker on Saturday April 30, 2016. The Class Notes belongs to 012 at University of Vermont taught by Dr. Hill in Fall 2016. Since its upload, it has received 23 views. For similar materials see Exploring Biology in Biomedical Engineering at University of Vermont.
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Date Created: 04/30/16
CH. 43 Interactions Diversity-Stability: Greater amount of diversity à Greater stability - Controls dominance of any single species - Redundancy forms in system allowing for quick fixes when problems arise Interspecific Interactions: between individuals of different species - Affects each life history (survival/reproduction) - Determines fitness: one’s contribution to population growth rate Competition (-,-) Consumer-Resource Interactions (+,-) Ex: Predation, herbivory, parasitism Mutualism (+,+) Ex: Plants and pollinating or seed-dispersing animals; humans and gut bacteria Commensalism (+,0) Ex: Cowbirds follow cattle foraging on insects from the vegetation Amensalism (-,0) Types of Competition: Interspecific: members of diff species decrease each others fitness being that they require same resources - Can affect species distributions /restrict habitats where species live o Realized niche: actual species’ use of resources (as constrained by interactions w/ other species) o Fundamental niche: potential resource space (usually w/ lower competition) - Competitors presence always reduces population growth rate - When 2 competitors coexist, they achieve lower carrying capacities than when alone - One competitor can drive the other extinct Intraspecific: among individuals of same species - Increased population density à Decreased growth rate - Value of r is not fixed in either case b/c individuals are constantly interacting within population Exploitative: Individuals consume abundance of a resource to a point that others cannot persist - Indirect competition being that it occurs through shared resource Interference: Competitors defend resources, without immediately consuming them - Direct competition Apparent: Species negatively effect each other involving an enemy (predator, parasi te, herbivore) The Role of Resources Resource: anything consumed/used to improve growth rate - Ecological/Abiotic factors that cannot be consumed are NOT resources - Interspecific Competition: (Competitive exclusion) Two species compete for single limiting resource, the species that persists is the one that can drive down the abundance of that resource to the lowest level o One group grows slower, but does not necessarily decline - Interaction among resources: Increase in one resource can have a great er effect on a population when there is also an increase in another resource Leibig’s Law of the Minimum: Populations increase until the supply of the most limiting resource prevents them from increasing further (Limiting reagents!) Limiting Resource: shortest in supply relative to demand - Can be sunlight, space, as well as food Darwin: Competition between related species is most intense b/c they have consume similar resources - For related species that compete strongly, natural selection should favor differences in habitat use - Competition can also be intense among distantly related species that consume common resource à causes one group to find new resource for survival Rarity Advantage: Species has growth advantage when at low er density than competitors; Prevents species from decreasing to zero - Results in coexistence - Intraspecific competition > interspecific competition - Resource Partitioning: competing species use different resources causing intraspecific competition > interspecific o If difference in resource use is sufficiently large, competing species can coexist o Can foster mutualistic relationships o Temporal: Feeds during different times of day/year Interactions à Evolution - Intraspecific competition à increase carrying capacity through stabilizing natural selection - Interspecific competition à resource partitioning/coexistence - Consumer-Resource Interactions à Evolutionary Arms Race o Prey evolve better defenses while predators evolve better offenses; neither gaining advantage over other - Mutualisms à Conflict of interest o Species benefit others not out of altruism, but out of own self-interest o Results in “biological barter”: exchange of resources/services o Some unstable ones à consumer-resource interactions Consumer-Resource Interaction Webs Food Webs: shows who eats who Trophic Levels: feeding interactions; determines flow of resources through a community Primary Producers (Autotrophs): converts NRG/inorganic materials into organic compounds for consumption Heterotrophs: NRG by breaking organic compounds assembled by other organisms Primary Consumers (Herbivores): eat primary producers Secondary Consumers (Carnivores): eat herbivores Tertiary Consumers (Carnivores): eat secondary consumers Omnivores: feed from multiple trophic levels Decomposers: feed on waste products/dead bodies of others Trophic Cascades: Altering the abundance of one species affects entire web ( Muir Effect) Non–Target Effect: Other species than expected/intended are also directly affected Indirect Effect: Target of a species indirectly affects population of another species; “middle man” Conservation Ecology: avoids the loss of elements of a web of interactions Restoration Ecology: Provides guidance for restoring los t elements of a web Invasive Species: A species accidentally/deliberately introduced into a region where natural enemies are absent à rapid reproduction/spread - Likely to have negative effects on native species that lack adaptations to compete with them - May benefit some if they provide new resource CH. 44 Ecology Interactions Community: group of species that occur together in a geographic area - Depend on communities for natural resources/services - The species/their interactions determine how well it functions - Understanding them is necessary for conservation Community Structure: Components include… - Species Composition: the types of species in the community; changes over time/space - Number of different species - Abundance of each species Community Assembly: A species can only occur in a location if it’s able to colonize/persist there - Community = those species minus those that have gone extinct locally - Local Extinctions are due to: o Inability to tolerate local conditions o Lack of resource o Invasion by competitors, predators, pathogens o Too small of a population size; no reproduction Turnover in Species Composition: repeated patterns of spatial/temporal change Spatial: Environmental gradients (Latitude, ocean depth, temperature, moisture) due to differing tolerances of each species - Spatial turnover signals hard-to-see gradients - Habitat Structure: horizontal/vertical distribution of objects in a habitat Temporal: Extinction/Colonization: dispersal of new species can affect growth of native species Disturbances: event causing sudden environmental change - Succession: species replace one another in a relatively predictable sequence o Depends on variation in colonizing ability of dispersing species o Usually results in a community resembling original one o OR Ecological Transition: disturbance pushed system past threshold leading to distinctly different community - Environment in disturbed site changes over time Climate Change: geographic ranges of species changes with physical conditions Community Function: measured by the amount of energy/matter that moves in/out of the community over time Flux: flow rate; reflects exchange between community/its environment - Energy enters community through Primary Producers Gross Primary Productivity (GPP): energy captured/converted to chemical energy over time - Some captured energy is used by the primary producers, rest goes to primary consumers - Measured from rate primary producers take up CO during photo2ynthesis Net Primary Productivity (NPP): amt. of energy stored in primary producer tissues over time - Measured based on rate of CO uptake 2inus rate of its release during cellular respiration - Approximately change in biomass of primary producer per unit time BOTH reflect rate at which primary producers capture energy, rate at which they convert it to forms of energy available to other trophic levels Ecological Efficiency of Energy Transfer: % of energy in biomass of one trophic level that’s incorporated in next level’s biomass - Biomass of one trophic level is about 10% of that in the next lower level - The biomass produced by primary consumers measure how well they convert primary producer tissue into own tissue - Low efficiency of such energy transfers limits # of trophic levels in a community o Not all biomass at one level is consumed by next o Some ingested matter is indigestible/excreted as waste o Consumers/producers use the energy to fuel own metabolism and is not passed on Community structure affects community function Niche: determines function of a species in a community - Physical/biological environments in which species has + growth rate o Biological = predators, competitors, etc. - It’s functional role or “profession” defined by how it affects others o What resources it uses/what it produces from them o Determined by trophic interactions Species Diversity: influences community function - Species Richness: # species in a community - Species Evenness: similarity of abundances of the species in a community - Equal abundance of each species prevents dominance from occurring NPP increases as species richness increases: - “Sampling” Hypothesis: Communities with more species are more likely to include some “superspecies” that are good at their function, having strong influence on total community output - “Niche complementarity” Hypothesis: differences among species in how efficiently they use alternative resources under different conditions (resource partitioning); More rich community contains more representatives of different functional groups à more complete use of resources o Proven to be the explanation! Species Richness Varies based on Location - Latitude: Climate conditions are more stable in tropics than temperate o Greater species richness o Greater NPP due to abundant solar input - Island Biography: Richness is greater on larger islands closer to mainland o Rate at which new species arrive on island decreases as island fills with species à extinction rate increases o Species richness stops changing when colonization = extinction; Equilibrium species richness is represented by point where colonization/extinction rates intersect Strategies for Conserving Community Function Ecosystem Services: goods/services involve exchanges between communities & abiotic environment - Many ecosystems can provide more goods/services at a lower cost than artificial substitutes could - Community functions that deliver goods/services depend on species diversity Fragmentation of Habitats: once-continuous areas of natural habitat are reduced to scattered fragments or habitat islands within human-modified landscapes - Causes loss of species from communities/lower richness in fragments - Decreases total amount of habitat/size of habitat patches à decreased subpopulations - Patches become more isolated from each other - Human-dominated landscape between them serve as barrier to dispersal à decreased colonization rate
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