E5 Flashcards
What is an ecological fact of life?
N t+1 = N + B - D + I -E
N = number of individuals of a species
t = time
B = births
D = deaths
I = immigrations
E = emigrations
How are populations open and dynamic entities?
Individuals can move from one pop to another. Pop size can change from one time period to the next, pops exhibit a wide range of growth patterns including exponential growth, logistic growth, fluctuations, and regular cycles. These four patterns are not mutually exclusive, and a single population can experience each of them at different points in time.
What happens with exponential growth in a new area?
If conditions are favourable in new areas. The pop may grow exponentially until density-dependent factors regulate its number
What species typically colonise new geographic regions?
Cattle egret, by long distance or jump dispersal events. Then, local populations expand by short distance dispersal events.
What is logistic growth?
Some population reach a stable size that changes a little over time, such pops first increase in size then fluctuate by a small amount around what appears to be the carrying capacity.
What are patterns of pop growth?
Plots of real populations rarely match the logistic curve exactly. Logistic growth is used to broadly indicate any population that increases initially then levels off at the carrying capacity. In the logistic equation K is assumed to be constant. K = population size for which birth and death rates are equal. Birth and death rates do vary over time so carrying cap fluctuates
What are population fluctuations?
A rise and fall in population size over time.
What are population cycles?
Some populations have alternating periods of high and low abundance at regular intervals. E.g. rodent pops, predation can drive pop cycles.
What is delayed density dependence?
Can cause populations to fluctuate in size. E.g. when a predator reproduces more slowly than prey. The effects of populations density often lag time of delay. The number of individuals born in a given time period is influenced by populations densities that were present several time periods ago. If predator pop is small initially, the prey population may increase, and as a result the predator population increases, but with a time lag. Large numbers of predators may decrease the prey population, then, the predator decreases again. Populations cycles.
What factors drive pop extinction?
Predictable factors, fluctuations in pop growth rate, pop size, chance events. Risk of extinction increases greatly in small populations
What is population extinction?
Chance, genetic, demographic, environmental events can play a role in making small populations vulnerable to extinction.
What is genetic drift?
Chance events influence which alleles are passed on to the next generation. Can cause allele frequencies to change at random from one generation to the next in small populations. Drift reduces the genetic variation small populations, has little effect on large populations.
What three reasons make small populations vulnerable to effects of genetic drift?
Loss of genetic variability reduces the ability of a population to respond to future environmental change.
Genetic drift can cause harmful alleles to occur at high frequencies.
Small populations show a high frequency of inbreeding which increases frequency of homozygotes including those that have two copies of a harmful allele, which can lead to reduced reproductive success.
What is demographic stochasticity?
Chance events related to the survival and reproduction of individuals. Has greater effect of wiping out small populations
What are allee effects?
Population growth rate decreases as population density decreases ; individuals have difficulty finding mates at low population densities. In small pops, allee effects can cause the population growth rate to drop, which causes the population size to decrease even further
