BIO205H5 Lecture Notes - Isotopes Of Hydrogen, Electronic Tagging, Guppy

10 views6 pages
Published on 23 Jul 2012
of 6
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
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)
used to predict future trends in pop’n
study of the seed-eating cactus finch-210 birds that hatched in 1978, followed
until 1991, only 3 alive; mortality rates high during first yr then dropped for
several yrs, then increase later; survival of birds depends on seed production
which is related to rainfall
graphs are helpful for highlighting important changes in pop’ns
survivorship curves fall into 3 patterns:
omost individuals survive for most of their potential life span and die
about the same age
oprobability of surviving to the next yr is abt the same over most of the
life span once individuals are a few months old
oproduce a large # of offspring, each of which receives little investment
of energy
high death rates of young individuals are followed by high survival rates
life history: describes how organism allocates its time and energy among the
variance activities that occupy its life
female rockfish continue to grow throughout their lives; larger females are
much more productive than smaller females b/c the # of eggs a female
produces is proportional to her size; older, larger females produce eggs with
larger oil droplets-provide energy to newly hatched-grow faster and survive
guppies living in predator-free areas upstream from those waterfalls have low
mortality rates; those that live below the falls have high mortality rates; david
reznick reared 240 guppies from high-predation and low predation sites;
supplied some with plentiful food and others with limited; where no predators
were present, guppies from high-predation sites matured earlier, reproduced
as the # of individuals in a pop’n increases, the # of new individuals added per
unit of time accelerates, even if the rate of increase expressed on a per
individual basis-per capita growth rate-remains constant- exponential