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Chapter 53: Community Ecology Trophic Structure, Predation, and Competition.

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Presentation on theme: "Chapter 53: Community Ecology Trophic Structure, Predation, and Competition."— Presentation transcript:


2 Chapter 53: Community Ecology Trophic Structure, Predation, and Competition

3 Assemblage of populations of various species living close enough for potential interaction Symbiosis Predation Competition Herbivory Disease

4 2 species competing for same resource can’t coexist in same place at same time Competitive Exclusion Principle Sum of species’ use of biotic & abiotic resources Resource partitioning: differentiation of niches, so similar species coexist in same community Ecological Niche More divergent characteristics in sympatric populations of 2 species than in allopatric populations of same species sympatric: geographically overlapping, need diff. niches to survive; allopatric: separate, can have same niches Character Displacement

5 +/- interaction; predator kills & eats prey +/- interaction; herbivore eats plant, kills it PredatorPrey Have senses that enable them to locate prey Self-defense mechanisms: camouflage, bright coloration, mimicry Herbivore Plant Have special sensors to recognize appropriate food Chemical weapons/ thorns protect them +/- interaction; one organism (parasite) gets nourishment from other organism (host), which is harmed endoparasite Live within host’s body ectoparasite parasitoidism Feed on external surface of host Insect lays eggs in/on living host, leaving the larvae to feed on body, and kill it

6 Inflict lethal harm, can limit populations Pathogen: disease-causing agent; unlike parasite: microscopic, lethal; +/- interaction +/+ interaction; both species help each other +/0 interaction; 1 species benefits, & the other is not affected; hard to find true example in nature Total # of different species Variety of diff. kinds of organisms that make up the community Proportion each species represents of total individuals in the community

7 Feeding relationships between organisms Food Chain: Eventually to decomposers Energetic Hypothesis: length of food chain is limited by inefficiency of energy transfer along chain Dynamic Stability Hypothesis: long food chains are less stable than short food chains; population fluctuations at lower levels are more profound at higher levels, causing potential extinction of high level predators Food Web: food chains are linked together; 1 species, such as plant, is eaten by several species

8 Biomass: total mass of all individuals in a population Dominant species Species that: collectively have highest biomass OR most abundant Keystone species Not necessarily abundant; exert strong control on community by their ecological roles Ecosystem engineers “foundation species”; facilitators; cause physical changes that benefit community, by increasing survival and reproduction

9 Mineral nutrients control community organization; nutrients control plant #’s, which control herbivore #’s, which control predator #’s Predation controls community organization; predators control herbivores, which control plants, which control nutrient levels Model of community organization FishAbundantRare ZooplanktonRareAbundant AlgaeAbundantRare Biomanipulation Polluted State Restored State


11 Primary Succession: occurs in virtually lifeless area, with no organisms or soil; only autotrophic prokaryotes are present Secondary Succession: occurs where an existing community was cleared by disturbance, that leaves soil intact; first plants to recolonize: grow from wind-blown/animal-borne seeds Geographic Location Size Tropical habitats have the most species; tropical habitats are older (long growing season), and greatest evapotranspiration Greater area=more diverse habitats, more species

12 New Species Immigration Rate Species Extinction Rate Influenced By: Island Size Island’s Distance from Mainland # of Species Already Present new colonizers: unlikely to reach small island = low immigration rate, high extinction rate (less resources) Islands near mainland: high immigration rate, low extinction rate (new colonizers sustain presence of species) # Species Extinction rate (competitive exclusion) immigration rate (those reaching island are less likely to represent species not already there)

13 States that species are found in the same area simply because they happen to have similar abiotic requirements Integrated Hypothesis (Clements) Individualistic Hypothesis (Gleason) Describes a community as an assemblage of closely linked species, locked into association by mandatory biotic interactions These interactions cause the community to function as an integrated unit

14 **Walker agrees with Gleason Rivet ModelRedundancy Model Suggests: most of the species in a community are associated tightly with particular other species in a web of life **the Ehrlich’s agree with Clements Exact opposite of the rivet model Suggests: species in a community are redundant; species operate independently, & aren’t affected if one species increases/decreases Ex. – if one pollinator disappears, then another species will do the job

15 DDT and other toxins, when in tissues and fats of an organism, can accumulate and be passed onto the next level of the food chain, affecting many organisms. Rachel Carson states in Silent Spring that the concentration of DDT in a low level organism’s fat is a lot lower than that of a higher level organism on the food chain If phytoplankton is infected Zooplankton & other primary consumers, secondary consumers, etc. are affected Everything occurring at low food chain levels is magnified at high food chain levels, causing possible extinction of top level predators

16 Similar effect of DDT; If organism is affected by pollution, it can spread through food chain, greatly affecting top-level predators If water is polluted and filled with garbage, the fish living there drink bad water and aren’t getting the right nutrients Make fish sick, and all those who eat them: fish’s predators, fish’s predators’ predators, and even human who eat fish for dinner **If one organism is infected by either DDT, pollution, or by several other possibilities, the harms done to that animal certainly don‘t stop there**

17 The spraying will cover the soil and the nutrients it contains. The producers absorb the DDT and are eaten by the consumers. The predators will continue to consume the DDT laden prey, accumulating the DDT in their body fats. imbalance of predators to prey will cause the ecosystem to go out of balance DDT Impacts Predation The reduction of 4 th level predators, for example, will cause: overabundance of the 3 rd level prey, which consume so much 2 nd level prey Decrease 2 nd level prey, so there’s not as many organisms to eat primary producers

18 As the environment becomes increasingly warmer each year, organisms might not be able to adapt or migrate to other areas The introduction of organisms disrupts and changes the ecosystem of the environment. This migration will bring new predators and new prey, which would alter the trophic structure. Altering the trophic structure would change the predator- prey relationships; the top level carnivores may not be the top level carnivores anymore, having an effect like the top-down model Effects of Global Warming on Predation If organisms die, their predators would starve, and there would be an increase in the dying organisms’ prey

19 DDT Affects Competition DDT can increase competition  DDT may kill many organisms of a species that two other species compete for.  Because the resource is in short supply, interspecific competition between the two competing species will increase, hurting both species eventually eliminating one of the two competing species (competitive exclusion).

20 DDT can also lessen competition Biological Magnification DDT’s concentration with each link in the food chain. By eating DDT-contaminated food, DDT accumulates in carnivores, which may be enough to kill the carnivores. Reproduction Rates DDT influences reproduction rates Ex.: Eagles in Silent Spring by Rachel Carson -DDT stored in eagles’ fatty cells cause the deposition of calcium in their eggshells to be hindered. DDT Affects Competition less competition among remaining carnivores for resources. Less carnivores; some organisms’ populations from lower trophic levels (top-down model), providing more of those organisms for the surviving carnivores (more food for them). Weak eggs, so many parent eagles accidentally crushed the egg during incubation; some eggs also didn’t hatch eagle population; the population of eagles’ prey increased, so competition for those prey isn’t as intense.

21 Global Warming’s Impact on Competition Some organisms may not be able to adapt fast enough to the rapidly changing conditions of the world Species may become extinct; its predators may starve/be eliminated & its prey is more abundant Some organisms may adapt well to the new conditions caused by global warming Have edge over other species to get resources, reproduce rapidly; lead to local elimination of interior competitor (not able to obtain resources) Survivors reproduce, pass genes onto offspring; over evolutionary time, may evolve to new species If species is extinct or adapts, a competitor is still eliminated, leading to less competition for resources

22 A.P. Biology Pd. A 9/15/08

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