Topic 14 - Logistic Growth (BIOL 2300)

T/F: open populations grow when: b+i (inputs) > d+e (outputs)

true

what factors reduce inputs relative to outputs

1. biotic - interactions among organisms (e.g. competition (intraspecific), predation)

• intensity of reduction is related to the density of ind.s = density-dependent

2. abiotic - fluctuations in environmental conditions (e.g. temp)

• intensity of reduction is unrelated to the density of ind.s = density-independent

• biased - reduce fitness (selection for favorable traits) , biased - random mortality (no selection for favorable traits, e.g. severe storms)

factors that limit population growth (b,d,r) as population size increases (at higher N)

• intraspecific competition increases (limited resources)

• predator density increases (higher risk of predation)

• parasite density (higher risk of parasitism)

• disease (higher rate of disease transmission)

density-dependence

may reduce growth, survival and reproduction of ind.s in a pop., thereby affecting population growth through b and d (R) with increased crowding

primary underlying assumption - logistic model of population growth

factors limiting population growth exert stronger effects on b and d as a pop. grows (population growth is density-depended)

K = carrying capacity

population size (N) that the envr. can carry or support

T/F: logistic model des not represent the quantitative dynamics of natural populations

true

• K changes with varying environmental conditions → K constantly changes

T/F: logistic model does represent qualitative dynamics of natural populations

true

• population sizes below K increase towards K

• population sizes above K decrease towards K

density-dependent factors

tend to bring populations under control and maintain their size close to K

• caused by biotic factors (e.g. competition, predators, parasites, disease)

density-independent factors

tend to reduce populations far below K and initiate periods of population recovery 

• caused by abiotic factors (e.g. temperature, water)

• e.g. thrips