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Lecture 5

Environmental Science 1021F/G Lecture Notes - Lecture 5: Stone Age, Doubling Time, Interspecific Competition

Environmental Science
Course Code
Marnie Branfireun

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ES1021F Lecture 5 – October 12, 2011
ECOLOGY: From Individuals to the Biosphere
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
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