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Social Science
Human Geography
Population Geography
Biology 53.2
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Gravity
Terms in this set (20)
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Exponential model describes
population growth in an idealized, unlimited environment.
Reasons unlimited growth does not occur in nature
individuals have access to fewer resources as a population grows
Why do ecologists study populations in ideal and unlimited environments, despite the limitations?
To reveal how fast populations are capable of growing and the conditions under which rapid growth might actually occur
Per capita rate of increase
r = b-m
Population ecologists are most interested in this. Difference between birth rate and death rate.
If r is positive, then growth!
If r is negative, then decrease!
Change in population size
= births + immigrants entering the population - deaths - emigrants leaving the population
∆N/∆t = B-D
B = number of births in the population
∆N = Change in population size
∆t = time interval appropriate to the life span or generation time of the species.
D = the number of deaths (not to be mistaken for D that stands for delta in my notes)
Per capita birth rate
number of offspring produced per unit time by an average member of the population.
B=bN
b = per capita birth rate
B = number of births in the population
N = total population size.
Used to calculate the expected number of births per year in a population of any size.
per capita death rate
m, for mortality
calculate the expected number of deaths per unit time in a population of any size
D = mN
Birth and death rates can be calculated from
estimates of population size and data in life tables and reproductive tables
∆N/∆t = bN-mN
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Rewriting the equation for change in population size
∆N/∆t = rN
Zero population growth (ZPG)
Occurs when the per capita birth rate and the per capita death rate are equal (b = m, r = 0)
Limitation of the equation (∆N/∆t=rN)
Often for one year
Does not include immigration or emigration
Most ecologists use differential calculus
As ∆t becomes shorter, the discrete r approaches the r.inst in value
Exponential population growth
occurs when r.inst is greater than zero and is constant at each instant in time.
Increases at a constant rate, resulting eventually in a J-shaped curve when population size is plotted over time.
Under ideal conditions, the per capita rate of increase may assume
the maximum rate for the species, denoted as r.max
Although the maximum rate of increase is constant, the population accumulates more new individuals per unit of time when it is large than when it is small
This is because population growth depends on N as well as r.inst. And larger populations experience more deaths and more births than smaller ones growing at the same per capita rate.
J-shaped curve of population growth is characteristic of
-exponential population growth
-Species introduced to a new environment
-Species that experienced drastic reductions in population size because of a catastrophic event
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