Density dependence Flashcards
(9 cards)
Define density dependence
Density dependence is the phenomena by which demographic processes, such as dispersal, growth, fertility and mortality, change as population density and crowding increase. It results in a net decrease in population growth rate.
How does density dependence effect dispersal?
Density dependence increases the dispersal rate, probability of dispersal behaviour and, in some species, the proportion of morphs / phenotypes specialised for dispersal (density dependent phase polyphenism). However, this is only while environmental tolerances and physical restrictions allow it.
How does density dependence effect individual growth?
Density dependence decreases individual growth rates and may cause reduction of body size due to intraspecific competition for food selecting for these traits. Competition for limiting resources increases with population density increase.
How does density dependence effect fertility?
Density dependence decreases fertility due to intraspecific competition leading to females producing fewer young, taking more time to reproduce or lowering population turnover rate (by spending more time looking after their young before reproducing again).
How does density dependence effect mortality?
Density dependence increases mortality due to intraspecific competition leading to decreased food resources per individual, increased aggression and increased transmission of disease. This may affect different demographic groups differently.
Define ‘r’ when modelling population change
r is the intrinsic rate of natural increase; it is what controls the rate of exponential growth ( dN/dt = rN ). It is related to R but is used when we use differential equations.
Define ‘K’ when modelling population change
K is the carrying capacity; it is what controls the rate of logistic growth ( dN/dt = rN[ (K - N)/K ] ). It is the upper limit of population size in a particular environment, where growth rate becomes 0 and birth rate and death rate become equal.
What are r-selected species?
r-selected species have traits such as fast reproduction, low parental care and short life-expectancy, which allow them to be favoured when environments are empty, transient or unpredictable. r-selection is expected where survival and reproduction are not limited by competition.
What are K-selected species?
K-selected species have traits such as slow reproduction, high parental care and long life-expectancy, which allow them to be favoured when environments are stable, competitive or close to carrying capacity. K-selection is expected where survival and reproduction are limited by competition.
