Unformatted text preview: If N is = in 2 populations,
the one with the greater r will grow faster Figure 53.7 (Campbell 9th ed) 25 Logistic Growth
Exponential growth is unrealistic since resources are not unlimited! • More individuals means less resources per individual
• At some N there is not enough resources for individuals to live.
• The max pop size that the environment can support = carrying capacity (K)
Carrying capacity (K)
is a specific population size!!!
As N approaches K,
pop growth rate slows down
• Fewer resources/ ind
= < healthy thus:
> deaths
< births
When N reaches K,
pop growth stops (dN/dt = 0)
Figure 53.9 (Campbell 9th ed) 26 Logistic vs Exponential Growth Exponential: The larger N, the faster the population grows (i.e. dN/dt increases)
Logistic  At low N, like exponential, population growth rate increases as N increases;
 BUT as N approaches carrying capacity (K) the growth rate slows down;
 Once N reaches K, the population stops growing (i.e. growth rate (dN/dt = 0) Logistic growth can be
modeled mathematically
Logistic growth =
Exponential growth + an extra term (K N)
dN rN
dt
K
Figure 53.9 (Campbell 9th ed) 31 The Logistic Model is Density Dependent
densitydependent  birth & death rates change with density
due to variety of biotic / abiotic factors Competition for food, water, space, light, mates etc can increase with increasing N 32 The Logistic Model is Density Dependent
densitydependent  birth & death rates change with density
due to variety of biotic / abiotic factors Disease prevalence can increase with increasing N 33
• Densityindependent factors
can alsoenvironment alter birth and death ratesgrowth
affect population (& thus λ or r)
Changes in the w/o regard to – population alter
densityindependenttheFactors thatsize birth & death rates regardless of N
(e.g. high/low temp, heavy rain, drought, fire, wind, toxin)
(usually abiotic but…) 43 SKIP
• Logistic growth: Know what logistic growth is and how it differs
from exponential growth but do not need to know the model.
• Table 53.3
• Section 53.4 (11791181)
• Figure 53.15 (1182)
• Population Dynamics and Figures 53.18 – 53.21 (11851187)
• The Global Human Population
and Figure 53.23 (11871188)
• Infant mortality and Figure 53.25 (1189)
• Global carrying Capacity and Figure 53.26 (11901191) 45 NEXT
Chapter 54: Community Ecology...
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 Fall '10
 WOO
 Ecology, Demography, Population Ecology, per capita, population size

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