Metapopulations Flashcards
What is exponential growth in populations
Populations can initially grow exponentially when resources are unlimited. However, this growth slows as density dependence kicks in, causing the population to approach a carrying capacity
What causes population sizes to fluctuate around the carrying capacity
Environmental stochasticity - random changes in environmental conditions - causes populations to vary in size around the carrying capacity
What is demographic stochasticity
Random chance variations in births and deaths in very small populations. It can act alongside environmental stochasticity to influence population size
What happens to population sizes in fragmented landscapes
As landscapes become fragmented, patches shrink in size. Smaller populations in these patches are more prone to extinction due to environmental and demographic stochasticity, genetic effects, and Allee effects
What are Allee effects
Allee effects occur when populations are so small that individuals have difficulty finding mates or cooperating, reducing survival and reproduction
What is a key process that can allow fragmented populations to persist
Dispersal. Movement of individuals between patches allows extinct populations to be recolonised and is crucial for long-term persistence
How does a species’ dispersal ability affect its survival in fragmented landscapes
If a species can disperse well, it can recolonise empty patches more effectively and is more likely to survive in a fragmented landscape
What is a metapopulation
A group of spatially separated populations of the same species that interact through colonisation and extinction; often described as a “population of populations
What does the Levins Metapopulation Model describe
The proportion of occupied patches increases with higher colonisation rates and lower extinction rates
What are correlated population dynmaics and why are they important
When populations experience similar environmental conditions, they may fluctuate in sync. This increases the risk of simultaneous extinction across a landscape
How does dispersal influence metapopulation dynamics
Dispersal allows recolonisation of empty patches, reducing the likelihood of long-term extinction. However, distant patches are harder to colonise
How does patch size affect extinction rates
Larger patches are less likely to experience extinction due to supporting more stable populations
What happens when populations are uncorrelated
They are less likely to go extinct at the same time, decreasing the risk of overall extinction in the metapopulation
Why is environmental stochasticity dangerous at the landscape level
If ES is widespread, it can simultaneously affect multiple populations, increasing the risk of landscape-level extinction
What four factors help maintain metapopulation persistence
- Minimising extinction rates
- Maximising colonisation rates
- Conserving empty habitat patches
- Reducing population synchrony
What are patchy populations
A form of population where individuals are spread across patches, but functionally it acts as one population. Colonisation far exceeds extinction, so extinction is not a major concern
What is the mainland-island metapopulation model
A system with one large “mainland” population and several smaller “island” populations. The mainland population is stable and supplies immigrants to the islands, which are more prone to extinction
In the mainland-island model which population should be prioritised for conservation
The mainland population, because it serves as a source of immigrants and is less likely to go extinct
What is the source-sink dynamic
A large, high-quality habitat (source) produces excess individuals that migrate to lower-quality habitats (sinks), which cannot sustain populations without immigration
What happens to sink populations without immigration
They decline and eventually go extinct because local reproduction is not enough to sustain them
