Population Ecology and Community Interactions

        Ecology - the study of interactions between organisms and between organisms and their
        physical environment; the study of an ecosystem

        Ecosystem - community and its environment; all the biotic and abiotic components and their
        intricate interactions

        Habitat - living space of a population

        Population - a group of individuals all of the same species in the same location at the same time;
        a gene pool

        Community - the populations of all the species in a given place at a given time

        Biosphere - thin shell around the surface of earth where all life exists

        Niche - with respect to a particular species/population, all the physical and biological
        conditions/characteristics of the environment in which the species/population lives
        and reproduces

    Population dynamics - includes size, density and rate of growth

            -size is the actual number of individuals
            -density is the number per unit area; distribution may be uniform, random or clumped population
            -growth rate = (births + immigration) - (deaths + emigration)
            -exponential (such as doubling) growth
            -biotic potential - maximum growth rate if no environmental limits
            -limiting factors - density dependent and independent
            -carrying capacity - maximum number of individuals of a population that can be sustained over a
                    long period of time in a particular ecosystem
            -logistic growth - a natural fitting to the carrying capacity; generally an "S" shaped curve
            -zero population growth - birth rate = death rate

Human population growth rate in 1998: 287,670 new humans per day (11,990 per hour, 200 per minute,
3.3 per second)

        history - large rate jump at agricultural revolution and industrial revolution (page 819)

        Why is human population able to grow so rapidly?
                new habitats
                increased carrying capacity
                fewer limiting factors

Species interactions in a community

        commensalism - one benefits while the other neither gains nor is harmed
        mutualism - both benefit
        symbiosis - obligate or near obligate mutualism
        interspecific competition - both disadvantaged (distinct from intraspecific competition that
                involves members of the same species)
        predation and parasitism - one benefits while the other is harmed; steady state or cyclical balance
                in the interaction; extinction not likely

Gause’s principle of competitive exclusion - two competing species cannot long coexist in the same
ecological niche; eventually, one will exclude the other

Resource partitioning - a slight difference in mechanisms of access to a particular resource results in
non-exclusion in what appears to be the same niche

Defense mechanisms

        physical - thorns, armadillo plates, etc.
        chemical - skunk spray, plant toxins, etc.
        behavioral - baring teeth, puffing up, etc

        Mullerian mimicry - advertising a dangerous characteristic
        Batesian mimicry - not dangerous but advertising as if dangerous

Unnatural species introductions and their consequences

        Natural dispersal or migration is usually slow/gradual. Jump dispersals are longer, quicker
        dispersals. Unnatural (human caused) jump dispersals can and usually do have negative
        consequences.

        Japanese beetle - arrived from Japan in 1911; primarily to east coast; most likely on imported
        flowers; unintentional; defoliate many native US plants

        Water hyacinth - arrived from Suth America in 1884; all over US, but primarily in the south;
        intentional; clogs aquatic systems and shades native aquatic plants

        Carp - arrived from Germany in 1887; in most US fresh water systems; intentional; displaces
        native fish and disrupts aquatic plants, negatively impacting waterfowl populations

Ecological succession - sequence of populations in a community towards a climax community (a
balanced or equilibrium community in which relative population size of each species remains about
the same)

        Primary succession - sequence in a location not previously occupied by a community; initial
        colonization by pioneer species

        Secondary succession - sequence in a location previously occupied by a community; previous
        community significantly disrupted or destroyed