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

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
Two types of speciation:
allopatric - due to geographic separation
sympatric - does not require geographic separation

13. Reproductive Isolating Mechanisms
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
bioremediation

15. Evolution and Religion
evolution as “God’s tool”
“missing links”
molecular support
intelligent design
punctuated equilibrium
scientific theory

16. 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

17. 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.

18. Resource Partitioning

19. SPECIES INTERACTIONS
A 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

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

21. 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

22. 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

24. Defensive Mechanisms
Batesian Mimicry - Harmless species evolve characteristics that mimic unpalatable or poisonous species.
Mullerian Mimicry - Two unpalatable species evolve to look alike.

25. 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.

27. 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.

28. Community Structure
ecological structure - patterns of spatial distribution of individuals and populations within a community
random distribution
clustered/clumped distribution - for protection, mutual assistance, reproduction, access to resources
uniform distribution - often the result of competition
Distribution can be vertical as well as horizontal.

30. 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.

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

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. 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.

35. 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 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

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