Biological Communities and Species Interaction

1. Biological Communities and Species Interaction

2. Important Concepts: • Critical Environmental Factors • Adaptation • Natural Selection • Speciation • Ecological Niche • Population Dynamics • Community Properties • Succession • Introduced Species

3. Types of Species Interactions • Competition • Predation – Trophic levels • Mutualism • Community Structure • Succession

4. Critical Environmental Factors • Single factor in shortest supply relative to demand is the critical determinant in species distribution. • Each environmental factor has both minimum and maximum levels, tolerance limits, beyond which a particular species cannot survive. • No humans permanently above 5 km

5. Tolerance Limits

6. Limits of Range • Physical Barriers • Oceans (humans, cattle egrets, marsupials) • Mountains (house finch) • Ice (humans in the Americas) • Climatic • Altitude • Food • Water • Competitors

7. Expanding Human Range

8. Critical Environmental Factors • For many species, the interaction of several factors, rather than a single limiting factor, determines biogeographical distribution. • Altitude = oxygen, temperature, food • May be a specific critical factor that mostly determines abundance and distribution. • Species requirements and tolerances can also be used as useful indicators. • Environmental indicators

9. Adaptation Adaptation is used in two ways: • Individual (moving from Alabama to Wisconsin) • Population (evolution)

10. Natural Selection • Natural Selection - Members of a population best suited for a particular set of environmental conditions survive and produce offspring more successfully than their competitors. • Acts on pre-existing genetic diversity. • Limited resources place selective pressures on a population.

11. Speciation • Given enough geographical isolation or selective pressure, members of a population become so different from their ancestors that they may be considered an entirely new species. • Alternatively, isolation of population subsets, preventing genetic exchange, can result in branching off of new species that coexist with the parental line.

12. Divergent vs. Convergent Evolution • Divergent Evolution - Mutations and different selective pressures cause populations to evolve along dissimilar paths. • Convergent Evolution - Unrelated organisms evolve separately to cope with environmental conditions in the same fashion. • Look alike - Act alike • Usually means some physical basis

13. Ecological Niche • Habitat - Place or set of environmental conditions where a particular organism lives. • Ecological Niche • Role a species plays in a biological community (e.g. large grassland herbivore) • Total set of environmental factors that determines a species’ distribution. • Generalists - Broad niche • Specialists - Narrow niche • When generalists and specialists collide, generalists usually win.

14. Competition

15. Law of Competitive Exclusion • No two species will occupy the same niche and compete for exactly the same resources for an extended period of time. • One will either migrate, become extinct, or partition the resource and utilize a sub-set of the same resource. • Given resource can only be partitioned a finite number of times.

16. Resource Partitioning

17. Predation • Feeds directly upon another living organism, whether or not it kills the prey in doing so. • Mosquitoes prey on humans • Prey most successfully on slowest, weakest, least fit members of target population. • Reduce competition, population overgrowth, and stimulate natural selection. • Co-evolution (arms race)

18. Co-Evolution and Disease • If a disease kills too quickly, it can’t spread • Disease can moderate while host becomes more resistant (measles) • Disease can be lethal but messy (cholera, ebola) • Disease can be lethal but slow-acting (AIDS)

19. Keystone Species • Keystone Species - A species or group of species whose impact on its community or ecosystem is much larger and more influential than would be expected from mere abundance. • Large predators • Critical food organisms (bamboo and pandas) • Often, many species are intricately interconnected so that it is difficult to tell which is the essential component.

20. Competition • Interspecific - Competition between members of different species. • Intraspecific - Competition among members of the same species. • Often intense due to same space and nutritional requirements. • Territoriality - Organisms defend specific area containing resources, primarily against members of own species. • Resource Allocation and Spacing

21. Mutualism Intimate living together of members of two or more species. • Commensalism - One member benefits while other is neither benefited nor harmed. • Cattle and Cattle Egrets • Symbiosis - Both members benefit. • Lichens (Fungus and cyanobacterium) • Parasitism - One member benefits at the expense of other. • Humans and Tapeworms

22. Commensalism: Epiphytes:

23. Symbiosis - Lichens

24. Defensive Mechanisms • Batesian Mimicry - Harmless species evolve characteristics that mimic unpalatable, dangerous or poisonous species • Viceroy and Monarch butterfly • Mullerian Mimicry - Two unpalatable species evolve to look alike • Bees and Wasps • Camouflage • Advertising and warning (coral snake) • Attracting prey, pollinators, mates, etc.

25. Abundance and Diversity • Abundance -Total number of organisms in a community. • Diversity - Number of different species, ecological niches, or genetic variation. • Abundance of a particular species often inversely related to community diversity. • As general rule, diversity decreases and abundance within species increases when moving from the equator to the poles.

26. Productivity • Primary Productivity - Rate of biomass production. Rate of solar energy conversion to chemical energy. • Net Primary Productivity - Energy left after metabolism • Highest in rain forest, estuaries, reefs • Decreases toward poles • Open oceans very low

27. Trophic Level (Food Chain) • A pond • Phytoplankton • Zooplankton • Small Fish • Larger Fish • Higher predators (birds, mammals) • Organisms are at same trophic level if they get their food from similar sources

28. Trophic Level (Food Chain) • A forest • Decaying organic matter • Insects • Small mammals and birds • Higher predators (owls, foxes, bears) • A Pasture or Grassland • Grass • Herbivore • Higher predators

29. Trophic Level (Food Chain) • At each level, some matter goes into biomass • Most goes into energy and metabolism • Hence each level needs about 10x as much energy, has fewer individuals • Bio-Accumulated chemicals get more abundant higher up the food chain

30. Food Requirements • Warm-blooded organisms require more food than cold-blooded • Predator/prey ratio higher for cold-blooded • Indication that some dinosaurs may have been warm-blooded • Large organisms eat less in proportion to their mass than small ones • Shrew: 100%+ per day • Human: 1% per day

31. Improbable Movie Biology • Things that eat people (Morlocks, The Time Machine) • Really huge carnivores (The Phantom Menace) • Huge carnivores in empty environments (Empire Strikes Back, Return of the Jedi) • Ultra-voracious carnivores (Jaws, Alien, Anaconda, Jurassic Park)

32. Complexity and Connectedness • Complexity - Number of species at each trophic level, and the number of trophic levels, in a community. • Diverse community may not be complex if all species are clustered in a few trophic levels. • Highly interconnected community may have many trophic levels, some of which can be compartmentalized.

33. Resilience and Stability • Constancy (Lack of fluctuation) • Inertia (Resistance to pertubation) • Renewal (Ability to repair damage) • MacArthur proposed complex, interconnected communities would be more stable and resilient in the face of disturbance. • Controversial

34. Edges and Boundaries • Edge Effects - Important aspect of community structure is the boundary between one habitat and others. • Ecotones - Boundaries between adjacent communities. • Sharp boundaries - Closed communities • Indistinct boundaries - Open communities

35. COMMUNITIES IN TRANSITION • Ecological Succession • Primary Succession - A community begins to develop on a site previously unoccupied by living organisms. • Pioneer Species • Secondary Succession - An existing community is disrupted and a new one subsequently develops at the site.

36. Terrestrial Primary Succession

37. Ecological Succession • Ecological Development - Process of environmental modification (facilitation) by organisms. • Climax Community - Community that develops and seemingly resists further change. • Equilibrium Communities (Disclimax Communities) - Never reach stable climax because they are adapted to periodic disruption.

38. Introduced Species • If introduced species prey upon or compete more successfully than native populations, the nature of the community may be altered. • Human history littered with examples of introducing exotic species to solve problems caused by previous introductions. • Mongoose and Rats in Caribbean

39. Summary: • Critical Environmental Factors • Adaptation • Natural Selection • Speciation • Ecological Niche • Population Dynamics • Community Properties • Succession • Introduced Species