Population Ecology: Growth and Regulation, Dynamics

Question 1

Define exponential growth.

Answer 1

the change in the size of a population of a species with continuous reproduction by a constant proportion at each instant in time; human populations have exceeded the exponential growth expected to be seen in nature

Question 2

What are the determinants of population size?

Answer 2

birth, death, immigration, and emigration

Question 3

Define and provide an example of discrete growth. What additional factors contribute to discrete growth?

Answer 3

discrete growth: populations without overlapping generations (semelparous insects that reproduce at end of lifecycle)
initial population size and net reproductive rate; if R0 > 1, then population becomes larger; if R0 < 1, then population becomes smaller

Question 4

Define continuous growth. What additional factors contribute to continuous growth?

Answer 4

continuous growth: populations with overlapping generations; results in exponential growth; future population size and population growth time can be predicted; depends on r (intrinsic rate of increase) and N (population size)

Question 5

What are density-independent and density-dependent factors? Provide examples of both.

Answer 5

density-independent factors: their effects are independent of the number of individuals in the population (i.e. annual rainfall and temperature trends impact the population size of thrip bugs per rose bush)
density-dependent factors: dependent of the number of individuals in the population; cause a change in birth, death, or dispersal rates (i.e. food scarcity, competition, disease)

Question 6

Define logistic growth. What additional factors contribute to logistic growth? Provide an example.

Answer 6

logistic growth: density-dependent population growth; k = carrying capacity = maximum number of individuals of a population that can be sustained in the long-term; birth and death rates become constant, little or equal migration (i.e. harbor seals, sheep)

Question 7

Describe the relationship between exponential and logistic growth.

Answer 7

as the number of individuals in a population increase, then there will be a larger deviation between exponential and logistic growth

Question 8

Define population dynamics and provide an example.

Answer 8

how population abundances change over time (i.e. an outbreak of mountain pine beetles has killed lots of trees, impacting species composition of forests and increasing co2 emissions)

Question 9

Describe types of population growth fluctuations. Provide examples.

Answer 9

outbreaks - occur when there are short time periods where populations have access to grow exponentially due to suddenly favorable conditions (i.e. cockroaches, mountain mine beetle)
cycles - patterns of fluctuation with nearly constant periods of alternation in high and low abundances (i.e. lemming abundance tends to rise and fall every 4 years due to predation from stoats and changes in food supply)
delayed density dependence - the delays in the effect of population density on population size; dependent on intrinsic rate of increase (r) and the length of the time lag

Question 10

What threats make smaller populations at a greater risk of extinction? Provide an example for each.

Answer 10

1. genetic factors - genetic drift reduces allele diversity and may cause harmful alleles to become fixed within a population
   inbreeding depression - the reduced survival and fertility of offspring of related individuals
   (i.e. biting flies drastically reduced population of lions and caused inbreeding)
2. demographic factors - demographic stochasticity - chance influences that determine whether individuals survive and reproduce
   allee effect - how demographic stochasticity reduces population growth rates when population density is decreasing (i.e. poaching has caused a drop in sumatran rhino population size, which leads to extreme difficulty finding mates and loss of genetic diversity through inbreeding)
   environmental variation - environmental stochasticity - unpredictable fluctuation in environmental conditions (i.e. extinction in heath hen from habitat destruction)

Question 11

Define metapopulations.

Answer 11

metapopulations - group of spatially separated populations of the same species that interact at some level; habitat fragmentation disrupts gene flow and increases chance of extinction: better chance at survival when they are close enough to interact with one another (i.e. northern spotted owl thrives in old-growth forests)

Question 12

Define competition, interspecific competition, and intraspecific competition.

Answer 12

competition - an interaction between individuals in which each is harmed by their shared use of a resource that limits their ability to grow, survive, or reproduce
interspecific - competition between individuals from different species
intraspecific - competition between individuals from the same species (i.e. sexual selection)