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

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

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

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. 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. Species requirements and tolerances can also be used as useful indicators.  Environmental indicators

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Adaptation Adapt is used in two ways:  Range of physiological modifications available to individual organisms.  Inheritance of specific genetic traits allowing a species to live in a particular environment. (Population level) - Explained by process of evolution

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

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.

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

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

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

Cunningham - Cunningham - Saigo: Environmental Science 7 th 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.  Co-evolution

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

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

Cunningham - Cunningham - Saigo: Environmental Science 7 th Ed. Defensive Mechanisms  Batesian Mimicry - Harmless species evolve characteristics that mimic unpalatable or poisonous species.  Mullerian Mimicry - Two unpalatable species evolve to look alike.

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

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

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

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

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

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

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