Metapopulations Flashcards
Define a metapopulation.
A group of spatially separated populations of the same species that interact at some level.
What are ‘patches’?
Areas of actual or possible occupation. Patches may be filled or awaiting to be recolonized by the metapopulation.
There are 4 characteristic spatial structures of metapopulation. What are they?
- Classic
- Core-satellite
- Patchy
- Non-equilibrium
Explain the structure of a classic metapopulation.
There are multiple patches with low-level connectance. Some patches are occupied and some await re-colonisation.
Explain the structure of a core-satellite metapopulation.
There is a large mainland population with many smaller ‘sinks’. The sinks are likely to go extinct and need constant re-colonisation from the mainland.
Explain the structure of a patchy metapopulation.
Lots of dispersal between many smaller patches. All patches are always occupied.
Explain the structure of a non-equilibrium metapopulation.
There are lots of isolated patches but no dispersal, leading to extinction.
What are ‘patches’?
Areas of actual or possible occupation. Patches may be filled or awaiting re-colonisation by the metapopulation.
If metapopulations inhabit discrete patches, is there a high risk of extinction?
Yes: migration and re-colonisation is essential for maintaining metapopulations.
What kind of landscapes do metapopulations inhabit?
Dynamic, heterogenic landscapes.
Metapopulations are said to have asynchronous dynamics. Why?
Because patches are constantly going extinct then being recolonized.
Levins in 1970 came up with the following equation for patch extinction:
E = eP
Explain the terms.
E = patch extinction e = extinction rate P = proportion of occupied patches
Levins in 1970 came up with the following equation for colonisation:
C = mP(1 - P)
Explain the terms.
C = colonisation m = migration rate P = proportion of occupied patches
The two equations by Levin in 1970 can be combined into:
dP/dt = mP(1 - P) - eP
What does this equation convey?
dP/dt = no. of patches occupied at a certain time, which is patch colonisation minus extinction rate.
At equilibrium what does dP/dt equal?
0
When dP/dt = 0 you can multiply out the equation and get 1 - e/m = P^. What is P^?
Proportion of colonised patches at equilibrium.
There are always some empty patches. True or false?
True.
When is there extinction?
When e = m.
Why is metapopulation theory useful in conversation?
Just because a patch is not currently being occupied doesn’t mean it won’t be in the future, thus it should be conserved.
If there is a high rate of colonisation, what can be said about extinction rate?
It is low.
What does it mean to say a patch is occupied?
There is at least 1 individual living there.
What are some assumptions about patches? List 4.
- Patches are the same size
- Patches are equally connected
- Extinction in each patch is independent and constant
- Dispersal is constant and not a function of population size
What can be said about all the patch assumptions?
They are unrealistic.
If a patch is smaller we assume there are less individuals living there than in a larger patch. True or false?
True.
Which is more affected by demographic stochasticity, small or large populations?
Small.
Which is more affected by demographic/environmental stochasticity, small or large populations?
Small.
Nearest neighbour analyses can be performed on metapopulations to assess inter-patch relations. What information would this tell us?
Spatial distribution, e.g. average inter-patch distance etc.
Some patches stay unoccupied. Why?
Limited dispersal.
Habitat heterogeneity may reduce the probability of patch extinction. How?
In a small patch the habitat is less likely to be variable, thus any stochasticity will affect the whole area. In a larger patch there is likely to be heterogeneity, and stochasticity will not affect the whole area, leaving refuges for organisms to persist in.
The same environmental conditions can have varying effects on organisms in different life stages. Give an example of this.
Bush crickets:
Juvenile crickets need high vegetation to protect them from the sun. Older crickets need lower levels of vegetation because it retains water, and wet conditions lower fecundity.
Connectivity has a threshold. In a fragmented landscape what happens to levels of dispersal?
Dispersal is greatly reduced.
Connectivity has a threshold level. If it falls below this level, there is no connectivity. True or false?
True.
What is percolation theory? Explain it in the context of connectivity.
Seeks to explain why populations clump in random environments. Percolation theory often comes into play when there is a fragmented landscape, reducing connectivity and leading to extinction of patches, thus the ones that are left are clumped together.
What is an ‘edge habitat’?
The edges of the patches. The habitat on the edge will be different to that in the centre.
What effect does habitat loss have on edge habitat?
Habitat loss increases edge habitat.
Define the edge effect.
Edge habitat is often lower in quality than core habitat. For example organisms may need a large radius of territory but if they live on the edge of the patch then this is not possible.
There is higher mortality and turnover in edge habitat than core habitat. True or false?
True.
Give an example of higher mortality in an edge habitat.
Trees are more exposed and more likely to be brought down in storms or exposed to herbivores.
Is there more or less edge habitat in an irregular-shaped patch?
More edge habitat.
