Lec 10.docx

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7 Feb 2013
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HOW DO SPATIALLY VARIABLE ENVIRONMENTAL INFLUENCE POPULATION DYNAMICS
Will not find individuals of a species everywhere within the area indicated on the map.-no
species not even the most abundant, is found everywhere within its mapped range
Populations are divided into separated, discrete subpopulations that live in distinct habitat
patches-areas of a particular kind of environmental that are surrounded by other kinds
Metapopulation: larger population to which such subpopulations belong
Rescue effect: immigrants may prevent declining subpopulations from becoming extinct
bay checkerspot butterfly example of metapop’n; caterpillars feed on specific plants, restricted
to outcrops of serpentine rock in California; during drought yrs, most host plants die early in
spring, before the caterpillar have developed far enough to be able to enter their resting stage
study-manipulated the habitat of tiny arthropods; created isolated patches of their habitat-
mosses growing on rocks-# of patches patches declined 40% in a yr; demonstrated that small
pop’n were more likely to become extinct than large pop’n; another experiment-created similar
patches connected by narrow corrioders of moss; a gap of 10 ,, was sufficient to reduce the
rescue effect for tiny organisms
populations of migratory species may be influenced by events on both teh breeding and
wintering grounds, as well as in the places where teh individuals stop to rest and feed during
migration
HOW CAN WE MANAGE POPULATIONS
both the total number of births and the growth rates of individuals tend to be highest when a
pop’n is well below its carrying capacity
pop’n that have a high reproductive capacities can persist even if harvest rates are high
in fast-reproducing pop’n, growth rates of individuals are often density-dependent
examples whales-2 reasons-whales reproduce low rates- distributed widely
at densities well below carrying capacity, pop’n typically have high birth rates and can therefore
withstand higher death rates that they can when they are closer to carrying capacity
when pop’n dynamics are influenced primarily by factors that operate in a density-dependent
manner, killing part of a pop’n reduces it to a density at which it reproduces at a higher rate;
reduce such a pop’n is to remove its resources, therby lowering the carrying capacity of its
environment
introduced predator or parasite simply fails to control its host; more serious consequences occur
when a species introduced to control an exotic pest not only attacks the pest species but also
destroys other species that are considered valuable
size of human pop’n contributes to most of the environmental problems we are facing today,
pollution, extinction
took more than 10, 000 years for earths pop’n of homo sapiens to reach one billion
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