BIOL 2010 Lecture Notes - Isotopes Of Hydrogen, Electronic Tagging, Guppy

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Published on 22 Aug 2012
York University
BIOL 2010
54.1 How Do Ecologists Study Populations?
Population consists of the individuals of a species within a given area
any given time, an individual organism occupies only one spot in space-
particular age and size
members are distributed over space, differ in age and size
age distribution of individuals in a pop’n and the way they are spread over the
environment describe its population structure
population density: number of individuals of a pop’n per unit of area
structure of a pop’n changes continually b/c of demographic events- births,
deaths, immigration, emigration
study of birth death and movement rates that create population dynamics
changes in pop’n structure and density) is known as demography
ecologists determine how many individuals are found in an area and where
they are located
individuals change their locations by migrating or dispersing
investigators need to be able to recognize and track individual animals
field studies of animals pop’ns require tagging or marking individuals in some
birds are marked by coloured bands on legs; butterflies coloured spots on
wings; bees-numbered tags on bodies; mammals-tags or dye on fur; plants-
tags on branch or nearby ground
microchips and other forms of electronic tagging are used on organism of all
molecular markers used to determine movement of individuals over long
one way – analyze the chemical composition of feathers that the birds molt as
they migrate south-can determine where they molted by evaluating hydrogen
isotopes in feathers b/c there is a strong latitudinal gradient in stable hydrogen
isotopes in precipitation
Most individuals molted their feathers close to the breeding ground
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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
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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