Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Biological Communities and Species...

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

Biological Communities and Species Interaction

Chapter 4


Outline:

• Critical Environmental Factors• Ecological Niche• Population Dynamics• Community Properties• Succession• Introduced Species


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.


Tolerance Limits


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.


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.


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


Competition


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.


Resource Partitioning


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.


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.


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


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


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


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.


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.


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.



Edges and Boundaries

• Edge Effects –boundary between two habitats

• Ecotones –boundaries between two communities

• Forests/grassland

Sharp boundaries - Closed communities Indistinct boundaries - Open communities


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


Terrestrial Primary Succession


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.


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.


Summary:

• Critical Environmental Factors• Ecological Niche• Population Dynamics• Community Properties• Succession• Introduced Species

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