Lecture 5 ecology

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Environmental Science
Environmental Science 1021F/G
Marnie Branfireun

ES1021F Lecture 5 October 12, 2011 ECOLOGY: From Individuals to the Biosphere Ecology Ecology is the study of the relationships of organisms and their environment It is a core subject area of environmental science Humans have unique and powerful capabilities, but are nevertheless dependent on the environment to supply all vital resources The sustainability of the human economy is fundamentally an ecological issue Ecology is studied at several hierarchical levels: Individual organisms, which are discrete, genetically unique entities Populations, or groups of individuals of the same species that can potentially interbreed with each other Species, consisting of one or more interbreeding populations that, in aggregate, are reproductively isolated from other such groups Communities, consisting of populations of various species that co-occur at the same time and place Landscapes and seascapes, which are spatial integrations of various communities over large areas The biosphere, consisting of all life and ecosystems on Earth Resources and Stressors Many environmental influences are resources that organisms can exploit to achieve productivity and to reproduce themselves Others influences are stressors that constrain productivity and reproductive fitness, such as: Inadequate nutrients or toxic chemicals Disturbances Biological stressors such as competition, predation, or disease All species have evolved unique solutions to coping with environmental opportunities and constraints faced during their evolutionary history For the purposes of studying the diverse life histories of species, ecologists have reduced the complexity by identifying broader strategies One scheme, mostly applied to animals, groups species as having life-histories that are: K-selected longer-lived species that produce relatively few offspring but invest heavily in each one to improve their likelihood of survival Are better suited to stable, infrequently disturbed habitats, where competition is a powerful influence on productivity, fitness, and community organization ES1021F Lecture 4 October 5, 2011 r-selected shorter-lived species that produce numerous small offspring that have a low chance of survival but a wide dispersal ability for colonization of new habitats Are adapted to dealing with frequent disturbances and temporary resource opportunities Population growth and constraints on population size A population changes in size according to the following equation: P = BR DR + IR ER P = change in population BR = birth rate DR = death rate IR = immigration rate ER = emigration rate If the population is closed, then P = BR DR The maximum possible rate of population growth depends on biological attributes of a species, such as its fecundity and maturation time this sets the intrinsic rate of population growth Usually, however, environmental constraints mean that population growth is less rapid than is biologically possible Resources may be limiting Competition may be intense There may be disturbances or diseases ES1021F Lecture 5 October 12, 2011 Populations change over time Under ideal conditions a population may level off at an abundance that can be sustained by the ability of the environment to provide resources this is known as the carrying capacity Other outcomes are also possible, including an over-shoot of carrying capacity This may cause damage to the environment and to resources needed by a species The resulting biological effects could include starvation or a disease epidemic, leading to a rapid population decline called a crash
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