Lecture Eight - Metapopulations Flashcards
Why do species have patchy habitat distributions?
Because resources and conditions are naturally patchy, or patchiness is increased by human activity.
What is habitat loss?
Reduction in overall area of particular habitat type or for particular species.
What is habitat fragmentation?
Increased isolation of habitat patches.
Give the size of a hectare in metres.
100 metres by 100 metres.
10,000 metres cubed.
Give the reduction in heathland in Dorset from the 18th to the late 20th century.
From 40,000 hectares to less than 6,000 hectares.
Describe the fragmentation of heathland habitat in Dorset compared to 2 years prior.
10 times as many habitat patches as 200 years prior.
What is the percentage decline in total area of heathland in Dorset?
85%
What is the name given to the hostile landscape in between habitat patches?
The Matrix
Describe three things that happen when habitat area declines.
- Local population density changes, because habitat is less suitable for a species.
- Local population size decreases, because reduction in variability of resources.
- Rates of immigration and emigration change, due to isolation and reduced change of successfully moving to a new habitat.
What kinds of habitat are more subject to edge effects?
Smaller patches of habitat
What is meant by edge effect?
At the edge of a habitat, organisms can experience
- Altered climate and environmental conditions
- Increased incursion of predators and competitors.
What happens to emigration rate in a habitat with a larger edge:area ratio?
Emigration rate increases.
Give two consequences of reduced population size.
- More at risk from Environmental Stochasticity
- More at risk from Demographic Stochasticity
What is stochasticity?
Chance events
What is demographic stochasticity?
Random variation over time in sex ratio, genotype, and phenotype, affecting birth and death rates.
(Variation within dynamics of the population)
Give an example of demographic stochasticity.
If one clutch contains only females, it is more likely to have a major effect on very small populations.
What is the Extinction Vortex?
Progressive decline in size until population extinction.
What are the genetic consequences of a small population?
- Increase in effects of genetic drift
- Increase in inbreeding depression
When might a habitat still be suitable for future occupation after local extinction of a species?
If extinction is caused by stochasticity.
Give a species that was experimentally introduced to empty but suitable habitats.
Silver-studded Blue Butterfly, in North Wales
What is a metapopulation?
An assemblage of local populations, a “population of populations”, that is linked by dispersal.
What causes an increase in metapopulation size?
Increased colonisation rate
What causes a decrease in metapopulation size?
Increased extinction rate
What is colonisation?
Dispersal to empty habitat followed by successful breeding.
What is the Rescue Effect, described by Brown & Kodric-Brown?
When immigration into a small population at risk of extinction rescues that population from extinction.
What is the threshold level of fragmentation?
The Minimum Viable Metapopulation Size
What kind of species show metapopulation dynamics?
Species with
- High habitat specitivity
- Small body size
- Shorter generation time
- High rate of population increase
Name at least three species that show evidence of metapopulation dynamics.
- Furbish’s Lousewort
- American Pika
- Nuthatch
- Two-coloured bush cricket
- Glanville Fritillary
- Silver-studded Blue
Give five pieces of evidence for metapopulation dynamics.
- Extinctions
- Colonisations
- Existence of empty but suitable habitat
- Effects of area and isolation on occupancy in habitat patches
- Habitat networks unoccupied below threshold area of habitat
Describe the observations in Edith’s Checkerspot in California.
- Populations in forest and rocky outcrops use different host plants
- When clearing populations went extinct, outcrop populations survived
