Unformatted text preview: a “per capita death rate”
e.g.
So:
B = bN [( 0.034) (1000) = 34 births in total population]
D = dN = [(0.016) (1000) = 16 deaths in total population] ∆N
= B – D+ I – E
∆t ∆N
= bN  dN
∆t Per capita rate of increase 20
Let:
B = births
D = deaths N = population size
t = time ∆N
=B–D
∆t Let:
r=b–d
= per capita rate of increase
= rate of net reproduction per individual
= prob an indiv. will give birth – their prob of dying When:
r = 0, population size stable (ZPG) (b=d)
r > 0, population is increasing in size (b>d)
r < 0, population is decreasing in size (b<d)
r is the per capita rate of increase
whereas dN/dt is the growth rate of the population ∆N
= bN  dN
∆t ∆N
= (b – d)N
∆t ∆N
= rN
∆t dN
= rN
dt Exponential growth rate Exponential Growth 21 Population growth is unrestricted
Occurs when there are infinite resources
and no environmental change
As population size (N) gets larger
the population growth rate (dN/dt) increases
(i.e. the curve gets steeper)
But the population growth rate
depends not only on N but also on r
dN/dt = rN r = per capita rate of increase = b – d
dN/dt = population growth rate
N = population size
Figure 53.7 (Campbell 9th ed) 22 Exponential Growth
Population growth rate depends on BOTH r and N
dN/dt = rN So an increase in either r or N can
increase the population growth rate
(i.e. the growth curve gets steeper)
If r is = in 2 populations,
the one with the >N will grow faster...
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 Fall '10
 WOO
 Ecology, Demography, Population Ecology, per capita, population size

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