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McGill University
Biology (Sci)
BIOL 240
Christa Scholtz

Competition is widespread because all species share resources  Resources sharing influences the abundances and distributions of species only if individuals reduce the ability of others to access resources, either by interfering with their activities— interference competition—or by reducing the available resources –exploitation competition.  Intraspecific competition—competition among individuals of the same species—may result in reduced growth and reproductive rates form some individuals, may exclude some individuals from better habitats, and may cause the deaths of others. o Is a primary cause of the density-dependent birth and death rates.  Interspecific competition—competition among individuals of different species—affects individuals in the same way; a superior competitor can prevent all members of another species from using a habitat competitive exclusion  COMPETITION MAY RESTRICT SPECIES’ HABITAT USE: competition among sessile animals may also restrict their habitats distribution.  COMPETITION MAY RESTRICT SPECIES’ RANGES: a species can restrict the range of another species by reducing populations of shared prey to such low levels that the other species cannot persist. Commensal and amensal interactions are widespread  Amensalisms are widespread and inevitable interactions. Most organisms participate in mutualistic interactions. How Do Species Interaction Cause Trophic Cascades?  A progression of indirect effects across successively lower trophic levels  trophic cascade. One predator can affect many different species  Trophic cascades may have effects across multiple and very different ecosystems because individuals of many species move from one habitat type to another. Keystone species have wide-ranging effects  A species that exerts an influence out of proportion to it abundance is called a keystone species; may influence both the species richness of communities and the flow of energy and materials through ecosystems.  Keystone species are not necessarily predators. A plant species that serves as food for many different animals can also be a key stone species. How Do Disturbances Affect Ecological Communities?  Disturbance is an event that changes the survival rate of one or more species in an ecological community; may remove some species from a community, but may open up space and resources for other species.  Keystone species generate disturbance, so do physical events. Succession is a change in a community after a disturbance  Change in composition of an ecological community following a disturbance is called succession.  Prim
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