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BMEN 515 Lecture Notes - Guppy

Biomedical Engineering
Course Code
BMEN 515
William Huddleston

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Ecologists usually measure the densities of organism in terrestrial
environments as the number of individuals per unit of area
For species whose members differ markedly in size, such as plants and
animals, the percentage of ground covered or the total mass of individuals
may be more useful measures of density than the number of individuals
most accurate way to determine the density and structure of a pop’n is to
count every individual and note its location
estimating pop’n densities is easiest for sedentary organisms
only need to count # of individuals in a sample of representative habitats and
extrapolate the counts to entire ecosystem
counting mobile organisms is much more difficult b/c they move into and out
of census areas
involves capturing, marking ,releasing-after having time to mix with the
unmarked individuals, another sample is taken-proportion of individuals in
new sample that is marked can be used to estimate the size of the pop’n
using the formula
m2/n2=n1/N n1=# of marked in first sample
n2=total # of individuals in 2nd sample
m2=# of marked in second sample
N= estimated size of total pop’n
estimates of total pop’n size will be inaccurate if marked individuals learn to
avoid traps or leave study area
ecologists use estimates of pop’n densities to estimate the rate at which
births, deaths and movements take place in a pop’n and study how rates are
influences by environmental factors
the number of individuals in a pop’n at given time is equal to the # present at
some time in past plus the # born between then and now, minus the # tht
died, plus the # that immigrated into teh pop’n, minus the # that emigrated
life table-created by tracking a group of individuals born at the same time
(cohort) and determining the # that are still alive at later dates (survivorship)
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