Chapter 11: Population Growth

in presence of abundant resources

populations can grow at geometric or exponential rates, but cannot continue indefinitely

unlimited resources leads to

max reproductive rate leads to pop. growth accelerates

geometric population growth

pop. growth in which generations do not overlap and successive generations differ in size by constant ratio

(pulsed reproduction)

geometric population growth equation

Nt = N0λ^t

(Nt = # of individuals at any time

N0 = inital number of individuals

λ = geometric rate of increase

t = number of time intervals or generations)

exponential population growth

pop. growth in which generations overlap and the per capita rate of increase (r) is constant

exponential population growth equation

Nt=Noe^rt

(Nt = # of indiv. at any time

N0 = inital number of individuals

r = per capita rate of increase

t = number of time intervals or generations)

exponential growth in nature

natural populations may grow exponentially for short period of time when resources are abundant

(ex: Scots pine: pollen in lake sediments showed following colonization, population grew exponentially for 500 years)

exponential growth is important process in

establishment of new environments, during favorable env. conditions, recovery from exploitation (or other threats)

logistic population growth

pop. growth that occurs when resources are limited and produces a sigmoidal (S-shaped) curve

pop. size stabilizes at carrying capacity (K)

logistic population growth equation

dN/dt= rmaxN(1-N/K)

(dN/dt = # individuals per unit time

rmax = intrinsic rate of increase

N = pop. size

K = carrying capacity)

density-dependent factors

biotic factors that limit pop. growth and are influenced by pop. density

tend to regulate a pop. at relatively constant size near K

ex: competition, disease, predation

density-independent factors

abiotic factors that limit pop. growth and are not influenced by pop. density, unpredictable

ex: weather events, habitat destruction, etc