1. Biological Communities and Species Interaction
Chapter 4
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

2. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Outline:
Critical Environmental Factors
Ecological Niche
Population Dynamics
Community Properties
Succession
Introduced Species
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

3. Critical Environmental Factors
The nutrient in the shortest supply is the critical factor or critical determinant
Analogous to limiting reactant in chemistry
Shelford - each environmental factor has both minimum and maximum levels, tolerance limits, beyond which a particular species cannot survive.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

4. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Tolerance Limits
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

5. Critical Environmental Factors
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.
Environmental indicators are organisms or physical factors that serve as a gauge for environmental changes/conditions.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

6. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

7. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

8. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Competition
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

9. 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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

10. Resource Partitioning
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

11. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
POPULATION DYNAMICS
Predation - 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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

12. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

13. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Competition
Interspecific - Competition between members of different species
Snake and owl competing for mice
Bears and eagles for salmon
Intraspecific - Competition among members of the same speices
Bears competing for salmon
Both are in the same community
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
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

14. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Symbiosis
Symbiosis - Intimate relationship among members of two or more species.
Commensalism – relationship in which one member benefits and the other is neither harmed nor helped
Moss on trees
Mutualism –both species benefit
Bird and hippo; bacteria (e. coli) and humans
Parasitism - One species benefits at the others expense.
Humans and ringworm, tapeworm
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

15. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Defensive Mechanisms
Batesian Mimicry - Harmless species evolve characteristics that mimic unpalatable or poisonous species.
Coral snake and King snake
Mullerian Mimicry –both are unpalatable or poisonous or some other defense mechanism and they resemble each other.
Brightly colored frogs are poisonous
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

16. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

17. 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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

18. 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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

19. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

20. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Edges and Boundaries
Edge Effects –boundary between two habitats
Ecotones –boundaries between two communities
Forests/grassland
Sharp boundaries - Closed communities
Indistinct boundaries - Open communities
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

21. COMMUNITIES IN TRANSITION
Ecological Succession
Primary Succession – the ecological succession that begins in an area where no biotic community previously existed
Pioneer Species lichens, mosses
Secondary Succession –on a site where an existing community has been disrupted
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

22. Terrestrial Primary Succession
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

23. 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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

24. Invasive (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.
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

25. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.
Summary:
Critical Environmental Factors
Ecological Niche
Population Dynamics
Community Properties
Succession
Introduced Species
Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.