Evolution, Biological Communities, and Species Interactions

1. Evolution, Biological Communities,and Species Interactions

2. Outline • Evolution and Speciation • Species Interactions • Community Properties • Communities in Transition • Introduced Species and Community Change

3. Definitions • evolution – • genetic changes within a population over time • natural selection – • differential reproductive success • mutations – • random changes in DNA • adaptation – • genetic trait that confers a selective advan- tage in a given environment

4. Critical Limits • Von Liebig proposed the single factor in shortest supply relative to demand is the critical determinant in species distribution. • Shelford later expanded by stating each environmental factor has both minimum and maximum levels, tolerance limits, beyond which a particular species cannot survive.

5. Tolerance Limits Tolerance Limits – for every environmental factor, an organism has maximum and minimum levels beyond which it can’t survive. Answers: What are the unique factors that limit growth of a population?

6. Critical Limits • For many species, the interaction of several factors, rather than a single limiting factor, determines biogeographical distribution. • For some organisms, there 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

7. Variation • Four conditions are necessary for evolution to occur • 1. variation in traits in a population • 2. traits must affect reproductive success • 3. traits must be inheritable • 4. some selective pressure must favor these traits differentially

8. Selective Pressure • Environmental factors that favor survival and increase reproductive success of some individuals over others can lead to evolution. • Natural selection modifies populations so that they are better suited to their environment.

10. resource partitioning - groups of individuals become specialized to utilize sub-sets of the same resource • radiative evolution - divergence from common ancestor into two or more species

11. Reproductive Isolation • Isolation prevents gene flow between members of a species

12. Two types of speciation: • Allopatric: • due to geographic separation

13. Reproductive Isolating Mechanisms • Sympatric - does not require geographic separation • mechanical - structural differences • temporal - different timing for breeding • behavioral - courtship displays • ecological - different ecological roles

14. Evolution at Work • Artificial selection • Pesticide and antibiotic resistance

15. Ecological Niche • Habitat – • Place or set of environmental conditions where a particular organism lives. • Ecological Niche – • Description of the role a species plays in a biological community, or the total set of environmental factors that determines species distribution. • Generalists – • Broad niche • Specialists – • Narrow niche

16. Resource Partitioning • 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.

17. Resource Partitioning

18. SPECIES INTERACTIONS Predator • is an organism that feeds directly upon another living organism, whether or not it kills the prey in doing so. • Prey most successfully on slowest, weakest, least fit members of target population. • Reduce competition, population overgrowth, and stimulate natural selection. • Co-evolution

19. Co-Evolution

20. 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. • Often, many species are intricately interconnected so that it is difficult to tell which is the essential component.

22. 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

23. Symbiosis • Symbiosis – • 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 • Mutualism – • Both members benefit. • Lichens (Fungus and Cyanobacterium) • Parasitism – • One member benefits at the expense of other. • Humans and Tapeworms

25. Defensive Mechanisms • Batesian Mimicry – • Harmless species evolve characteristics that mimic unpalatable or poisonous species.

26. Mullerian Mimicry • Two unpalatable species evolve to look alike. • Two or more harmful species, that are not closely related and share one or more common predators, have come to mimic each other's warning signals. • Ex. Heliconius butterflies Perhaps one of the most well-known examples of mimicry, the viceroy butterfly (top) appears very similar to the noxious tasting monarch butterfly (bottom). Although it was for a long time purported to be an example of Batesian mimicry, it has recently been discovered that the viceroy is actually just as unpalatable as the monarch, making this a case of Müllerian mimicry.[8]

27. COMMUNITY PROPERTIES • Primary Productivity – • Rate of biomass production. Used as an indication of the rate of solar energy conversion to chemical energy. • Net Primary Productivity - Energy left after respiration.

29. 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.

30. Community Structure

31. Complexity and Connectedness • Complexity • Number of species at each trophic level, and the number of trophic levels, in a community.

32. 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

33. Edges and Shapes

34. Ecogical Succession: Primary Succession

35. Primary Succession

37. Secondary Succession

38. Secondary Succession

39. Disclimax communities/Equilibrium communities

41. 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.

42. Ecological Succession • 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.

43. Introduced Species and Community Change • 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

44. Summary • Evolution and Speciation • Species Interactions • Community Properties • Communities in Transition • Introduced Species and Community Change