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Title: Wildlife Management - Population Growth and Regulation
Description: These notes cover topics related to measuring growth rates of populations of wildlife. They include many of the important equations for wildlife managers to assess the numerical status of wildlife populations. These notes were used for Wildlife Management at American Public University.
Description: These notes cover topics related to measuring growth rates of populations of wildlife. They include many of the important equations for wildlife managers to assess the numerical status of wildlife populations. These notes were used for Wildlife Management at American Public University.
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Rate of increase
growth increment – net number of individuals added over the year to a population
growth rate – net number of animals added, divided by numbers present at the
beginning of the time interval
Nt+1 = Ntλ = Nter
o Geometric rate of increase where Nt is the population size at time t, Nt+1 is the
population size a unit of time later, e is the base of natural logs taking the
value 2
...
g
...
g
...
5W-0
...
The geometric model can be translated into the exponential model Nt = N0λermaxt
The theory of population limitation and regulation
Populations have inputs of births and immigrants and outputs of deaths and emigrants but for
simplicity just use births B and deaths D
If either the proportion of the population dying increases or the proportion being born
decreases as population density increase then these changes are density dependent and the
underlying causes of changes in these rates are density-dependent factors
Births and deaths as a proportion of the population can be related to the instantaneous birth
and death rates as:
o Nt+1 – Nt = B – D
o Instantaneous rate of increase (r) is given by r = b – d
o The finite rate of increase (R) is given by λ = Nt+1/Nt = er
o Therefore eb-d = (Nt+1/Nt) = (B – D+Nt)/Nt
o If d=0, D= 0 then:
o Eb = (B+Nt)/Nt = (1 +(B/Nt)) and b = (ln(1+(B/Nt))
o Similarly if b = 0, B=0, and D/nt is much less than 1
o d = ln(1+ (D/Nt))
o If B and D fall in the range of 0 – 20% of the population then b and d are nearly linear on
N and they remain approximately linear even if B and D are 20 – 40% of N
...
If the
density-dependent factor becomes stronger, the slope becomes steeper and K drops
...
Both density-dependent and density-independent factors
affect the equilibrium population size and thus are both limiting factors
...
Regulation is the process whereby a density-dependent factor tends to return a population to
its equilibrium
Mortality factors that respond after a delay are delayed density-dependent factors (lag time)
Predators can have a depensatory or inverse density-dependent effect – they take a
decreasing proportion of the prey population as it increases, allowing it to increase faster as it
becomes larger
...
o One of the equilibrium points that a population tends toward through densitydependent effects from lack of food, space, cover, or other resources
o If the environment changes briefly, it deflects the population from achieving its
equilibrium and produces random fluctuations around that equilibrium
o Long-term environmental change can affect resources and alter K
Economic CC – the population that produces the maximum offtake (sustained yield) – livestock
carrying capacity – this population level is well below carrying capacity – for a population
growing logistically it = ½ K
Other types of CC – the number of lions on a Kenya farm or the number of wolves on a
Wyoming ranch
...
g
...
When the rate has slowed so that borths and deaths are equal, K has been reached
...
It arises because the population
grows so fast that it tends to overshoot K, a process known as overcompensation
...
For some
populations with lower rates of increase, the pattern of fluctuation will be cyclical rather
than deterministic chaos, but the underlying cause is still overcompensation
...
This
includes both removal of a resource (consumption use of food e
...
) or occupation of a resource
(pre-emptive use as in nesting sites)
Interference competition – direct interaction of individuals through behavior: e
...
exclusion of
some individuals through territories, displacement of subordinates by dominants
Direct measures of food shortage – measuring food supplies
Indirect measures – body condition
Interactions of food, predators, disease
o Can be synergistic interactions with predation and disease
o Animals may later behavior when food becomes difficult to find in safe areas and
animals search increasingly in areas where they are at risk of predation (Lima and Dill
1990, McNamara and Houston 1987) (predator-sensitive foraging) and such behavior
can result in increased predation well before starvation takes effect (Sinclair and Arcese
1995)
o Disease can also interact synergistically with food as pathological effects suddenly
become apparent at certain stages of undernutrition (Ch 11) (wood bison switch from
high-density, food-regulated state to low-density predator-regulated when diseases (TB,
brucellosis) affect the population (Rettie and Messier 2004)
Title: Wildlife Management - Population Growth and Regulation
Description: These notes cover topics related to measuring growth rates of populations of wildlife. They include many of the important equations for wildlife managers to assess the numerical status of wildlife populations. These notes were used for Wildlife Management at American Public University.
Description: These notes cover topics related to measuring growth rates of populations of wildlife. They include many of the important equations for wildlife managers to assess the numerical status of wildlife populations. These notes were used for Wildlife Management at American Public University.