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Transcript
Ecology and People (BIOL 120) Ecology an Introduction Critical Factors and Tolerance Limits Lecture 3 !Von Liebig proposed the single factor in shortest supply relative to demand is the critical determinant in species distribution. Today’s Outline Critical Factors and Tolerance Limits Adaptation Natural Selection = Evolution Speciation Ecological Niche Species Interactions Succession Introduced Species and Community Change "Shelford later expanded by stating each environmental factor has both minimum and maximum levels, tolerance limits, beyond which a particular species cannot survive. 1 Critical Factors and Tolerance Limits 2 Adaptation ! Interacting factors often determines biogeographical distribution. !For some organisms, there may be a specific critical factor that mostly determines abundance and distribution. !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. !Explained by process of evolution. 3 4 Natural Selection Speciation !Influences: !Natural Selection - Members of a population best suited for a particular set of environmental conditions survive and reproduce more successfully than competitors. "geographical isolation "selective pressure "Alternatively, isolation of population subsets, preventing genetic exchange, can result in branching off of new species that coexist with the parental line. "Acts on pre-existing genetic diversity. "Limited resources place selective pressures on a population. 5 6 1 Evolution Ecological Niche Definition: The scientific theory that explains how random changes in genetic material and competition for scarce resources cause species to change over time. !Divergent Evolution ! Habitat " Place or set of environmental conditions where a particular organism lives. ! Ecological Niche " The total set of environmental factors that determines species distribution. ! Fundamental Niche !Look different - Act different " Full range of resources or habitat a species could exploit if there were no competition with other species. !Convergent Evolution ! Realized Niche !Look alike - Act alike… but aren’t alike " Resources or habitat a species actually uses. 7 Resource Partitioning 8 Species Interactions !Law of Competitive Exclusion !A predator is an organism that feeds directly upon another living organism, whether or not it kills the prey in doing so. !One will either migrate, become extinct, or partition the resource and utilize a sub-set of the same resource. "Prey most successfully on slowest, weakest, least fit members of target population. !Reduce competition, population overgrowth, and stimulate natural selection. 9 10 Keystone Species Competition !Keystone Species !Interspecific !Intraspecific "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. "Often intense due to same space and nutritional requirements. !Territoriality - Organisms defend specific area containing resources, primarily against members of own species 11 12 2 Symbiosis Defensive Mechanisms !Symbiosis - Intimate living together of members of two or more species. "Batesian Mimicry - Harmless species evolve characteristics that mimic unpalatable or poisonous species. "Mullerian Mimicry - Two unpalatable species evolve to look alike. "Commensalism - One member benefits while other is neither benefited nor harmed. !(_+) "Mutualism - Both members benefit. !(++) "Parasitism - One member benefits at the expense of other. !(-+) 13 Abundance and Diversity 14 Communities in Transition !Ecological Succession !Abundance "Primary Succession "Total number of organisms in a community. !A community begins to develop on a site previously unoccupied by living organisms. !Diversity "Secondary Succession "Number of different species, ecological niches, or genetic variation. !An existing community is disrupted and a new one subsequently develops at the site. 15 16 Introduced Species and Community Change Ecological Succession !If introduced species compete more successfully than native populations, the nature of the community may be altered! ! Ecological Development - Process of environmental modification (facilitation) by organisms. ! Climax Community - Community that develops and seemingly resists further change. "Human history littered with examples of problematic introduced species. " Equilibrium Communities (Disclimax Communities) Never reach stable climax because they are adapted to periodic disruption. !Can you think of examples? 17 18 3