Population Dynamics within Ecosystems Flashcards
im gonna eat you like a butterfly eats ur mum (12 cards)
Demography
Demography is the name we give
to the study of vital statistics that
affect population size.
There are four primary ecological events that determine
population size:
Birth rates
Death rates
Immigration rates
Emigration rates
Immigration:
The movement of individuals into the population.
Emigration:
The movement of individuals out of a population.
Equation that represents this change in population size:
Change in population size=(birth + immigration) - (deaths + emigration)
Exponential growth:
When exponential growth is observed, the
population’s growth rate rapidly accelerates or
increases over time.
Bacteria grown in a laboratory provide an
excellent example of exponential growth. Bacteria
reproduce by binary fission (splitting in half), and
the time between divisions is about 20 minutes.
Exponential growth is not a very
sustainable or realistic model
within the real world as it
depends on infinite amounts of
resources, such as food.
Even growth of bacteria in the
lab will slow down eventually, as
they start to compete for space
and food, exhausting both.
Logistic growth
A more realistic in the real
world is known as logistic
growth. The population can
increase rapidly at first, but
then starts to plateau (flatten
out) as resources are limited
and competition increases.
This creates an S-shaped
curve
The population size at which
the curve levels off, which
represents the maximum
population size a particular
environment can support, is
called the carrying capacity
(in other words, the
sustainable capacity of a
given environment).
As populations approach their carrying capacity,
individuals start to die because of insufficient
resources. They may also emigrate to find areas with
more space and resources.
Limiting factors
Limiting factors: Any form of biotic or
abiotic factors within an ecosystem that
prevent the population from growing
any larger
Example: 100 grey kangaroos may live
in an ecosystem that has enough water,
shelter and space to support 200 grey
kangaroos, but if there is only enough
food for 100 grey kangaroos, the
population will not grow any larger.
Apart from food, there are other factors that can limit
population growth such as:
shelter (for example, owls that rely on hollows in trees will
search new locations for nesting spots)
the number of predators
availability of water
the balance of male and female numbers
the presence of diseases
Quadrats
A quadrat is a tool used to
record the abundance or
density of a particular
species in a study area,
without needing to count
every organism.
For example, a quadrat can be used to help count the
population size of plants, slow-moving animals and
marine algae. Using quadrats, the population number
and density of each species can be estimated.
Quadrant equation
Total population = Average number per quadrant x Total area being studied/Area of quadrant
Capture-Mark-Recapture
Measuring the population size of fast moving animal species is
sometimes difficult. Therefore, a more appropriate way of
measuring population size, rather than setting up quadrats or
individually counting all the individuals within the species.
Is a method for estimating animal population sizes that
involves capturing, tagging, releasing and recapturing a
sample of the animal.
A sample of the species is captured
(maybe about 100 individuals).
These individuals are tagged or
marked in an inconspicuous way, and
then released.
Sometime later, another sample of the
same size is captured from the
population.
Ecologists count how many marked
individuals are in the second sample
and then this information is used to
find an estimate of the population size
using the following equation:
Capture-Mark-Recapture equation?
N/M=n/m
N= Population estimate
M= Number of animals captured and marked in the first sample
n= Number of animals captured in the first sample
m= Number of n that were already marked
