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Ecology

Ecology. Lecture 9 Ralph Kirby. The struggle for Existence. Remember Population Interactions Neutral 0 0 Mutualism + + Competition - - Note interspecies competition Seek a common resource in short supply Food; Living space; etc

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Ecology

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  1. Ecology Lecture 9 Ralph Kirby

  2. The struggle for Existence • Remember Population Interactions • Neutral 0 0 • Mutualism + + • Competition - - • Note interspecies competition • Seek a common resource in short supply • Food; Living space; etc • See squirrels, mice, deer, various birds competing for acorns • Model One. Two forms • Exploitation • Interference • Model Two. Six forms • Consumption • preemption\ • Overgrowth • Chemical interaction • Territorial • encounter

  3. Consumption • Utilization of a shared resource by 2 species • Preemption • Occupation of a site by 1st organism stops occupation by 2nd organism • Usually sessile organisms • Overgrowth • Where organism covers another preventing access to a resource • Light in rain forest • Chemical interaction • Release of toxin to kill competing organisms • Antibiotics in soil by Streptomyces • Territorial • Behavioral exclusion of 1st organism by 2nd organism defending territory • Encounter • Non-territorial encounters cause a negative effect on one or both species • Lion and wild dogs over a antelope kill

  4. Mathematical approach • N: population size • t: time • K: carrying capacity • r: rate of increase • αN1and βN2:effect of interspecific competition, namely, where α and β per capita effects of competition • Species 1 • dN1/dt = r1N1((K1-N1-αN2)/K1) • Species 2 • dN2/dt = r2N2((K2-N2-βN1)/K2) • No interspecific competition, then α and β are 0 and normal growth to carrying capacity • Interspecific competition is density dependent

  5. (a) Species 1 alone or no competition (b) Species 2 alone or no competition (c) Species 1 inhibits growth of species 2 and latter goes extinct (d) Species 2 inhibits growth of species 1 and latter goes extinct (e) Unstable situation, both inhibit in a density dependent manner. Depending on initial density, either can make other extinct (f) Each species inhibits its own population growth more than competitor. Neither can eliminate competitor Diagonal lines are zero growth isoclines

  6. Laboratory experiments to verify Lotka-Volterra Equations • Two Paramecium • One with higher rate of growth • Extinction of slower grower • With different food supplies • Coexistence • Two Diatoms • Require silica in water for growth • Adequate silica • Coexistence • Inadequate silica • One goes extinct

  7. Competitive exclusion principle • Two species possessing exactly the same ecological requirements cannot coexist • One species must go extinct • Not normal situation • Immigration • Use of other resources • No selection • No changes in the environment • Thus most of the time species can coexist

  8. Thus if environment varies • Then competition varies • See secondary succession success in graph • Also moisture • Grass species southern African savanna • Species change • 1971 to 1981 • Low rainfall in 1971-1973 • This is the norm

  9. Systems are not simple one resource situations • Usually competition for more than one resource • Territorial defense against wide range of other species • Plants • Monoculture • Root competition • Skeleton weed reduce by 35% • Shoot competition • Skeleton weed reduced by 53% • Root and shoot competition • Skeleton weed reduced by 69% • Thus clover superior to skeleton weed for all resources

  10. Effect of interspecific competition across an environmental gradient • Note changes in response when in mixture

  11. Similar effect for summer annuals and moisture gradient • Also happens in nature with water, anoxia and salt stress in a salt marsh • Chipmunks • Alpine • Cold tolerant • Lodgepole • Most aggressive • Needs shade • Yellow Pine • aggressive • Least • Heat tolerant

  12. For competing species to all survive • Partitioning of resources • Cat species in Israel • Cats with larger canines can kill bigger prey • Note regular spacing of sizes • Therefore distinct prey groups

  13. Evolution is thus affected by competitionSelection causes changes in resource utilization

  14. See finches on Galapogos islandsBeaks of same species are different when they compete

  15. Fundamental Niche • Where species can exist with no competion • Realized Niche • Niche utilized under competition • See cattail in water depth experiment • See two models for species competition • Compression • Splitting to suboptimum periphery

  16. See effect of environmental gradients • Note effect of competitive release

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