Small and declining populations Flashcards Preview

Ecology > Small and declining populations > Flashcards

Flashcards in Small and declining populations Deck (22)
Loading flashcards...

What is the MVP?

Minimum Viable Population, defined as the critical threshold beneath which a population is ensured to decrease in size until extinction.


What are deterministic changes?

Predictable changes to the population size.


What are stochastic changes?

Inherently random changes to population growth.

More likely to cause extinction.


What is demographic stochasticity?

Random variations in birth and death rates that occur in populations from year to year.

Can have a major effect on small populations, if individuals happen to have unusual values for a demographic trait.

Example - sex ratios.


What is environmental stochasticity?

Any fluctuation in the physical environment and the biotic, such as predators, parasites and competitors.

Can affect the whole population and isn't dependent on density. More likely to cause extinction as doesn't require a small population.


How does inbreeding depression affect small populations?

Increased probability of mating with a close relative. Results in a higher probability that any gene will be homozygous. This can lead to lower fitness in the case of deleterious recessive mutations.

Can be avoided in populations where the size decreases slowly as natural selection will eliminate the deleterious recessive alleles from the gene pool.


How does genetic drift affect small populations?

Alleles can be lost by chance. This is a big issue in small populations as mutations are less likely to occur and so the rate of loss of variation to drift is larger.

Big threat to species survival if the environment changes as natural selection can't act as quickly.


What is the effective population size?

The number of individuals in a population who contribute offspring to the next generation.


How can behavioural problems lead to extinction in small populations?

Allee effect.
In animals that hunt in packs. Widely dispersed animals might not find mates.


Define extinction vortex?

Forces affecting small populations that cause them to spiral into a vortex of increasingly smaller populations.


Example of a persisting small population?

Isolated Pacific Island has about 20 pairs of Socorro Island Hawk.

Likely to have been this size throughout its entire history of several thousand years.


What is a Population Viability Analysis?

A species specific method of risk assessment frequently used in conservation biology.

Defined as the process that determines the probability that a population will go extinct within a given number of years.


What circumstances can lead to small populations persisting?

Immigration can increase genetic diversity.


Main drivers of extinction?

Habitat destruction/fragmentation
Harvesting (over-exploitation)
Chains of extinction
Climate change
Introduced species


Biggest threat to bird species?

Habitat change and loss is the main threat to 75% of the 1100 threatened species.


Potential responses to climate change?

Plasticity to adapt in situ
Evolution to adapt in situ
Shift their distributions
Shift their phenology (timing of biological events).


How can declining populations be identified?

Demographic surveys - is the population size declining?

Distribution surveys - is the area taken up by the population declining?


Demographic surveys?

Measure the population size over time. Need to distinguish declines from normal stochastic variation.

Population cycles may be driven by predator prey interactions.

Important to study over a long time period.

Takes a lot of time and effort.


Example of a distribution survey?

Every 10km square in Britain was surveyed for the presence or absence of species in the early 1970s and late 1980s.


Issues with distribution surveys?

There may be a time lag before declines in size are translated to declines in distribution - happened with an arctiid tiger moth.


How can spatial patterns in species distribution reveal biodiversity change?

Declining populations show sparse, fragmented distributions for their distribution size, reflecting the extinction process.

Expanding species show denser, more aggregated distributions, reflecting colonisation.

Can be used to assess relative levels of threat facing different species which lack other forms of data.


An example of how extinction can be avoided?

Lord Howe Woodhen.

Population restricted to 10 pairs on two remote high mountains after formerly ranging over the entire island.

Low productivity and adult survival on the tops of mountains.

Pigs were eating eggs and chicks.

Removed pigs and introduced 50-60 pairs.

Habitat is now saturated.