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