L19: Fragmentation Flashcards
What is fragmentation?
Habitat fragmentation is the process by which habitat loss results in the division of large, continuous habitats into smaller, more isolated remnants (Fahrig 2003). Also known as fragments or habitat islands.
What are the effects of habitat loss and fragmentation?
1) Reduction in: total area, resources, productivity
2) Local extinctions?
3) Changes to environmental characteristics and edge effect
4) Isolation of small populations (reduced genetic variability)
What are metapopulations?
Group of populations that are separated by space but consist of the same species.
These spatially separated populations interact as individual members move from one population to another.
When do metapopulations occur?
When a habitat is fragmented.
For example, wetlands across the landscape but also as a result of human activities.
What does the amount of movement a population can achieve following fragementation depend on?
The distance. etween neighbouring patches and how far and fast the individual can move.
What are the three types of metapopulation models?
1) Basic model
2) The source sink metapopulation model
3) Landscape metapopulation
What is the basic metapopulation model?
Assumes that all habitat patches are equal in quality and that the habitat matrix between patches is inhospitable.
A metapopulation persists because of a balance between colonization and extinctions in some habitat patches.
What is the source sink metapopulation model?
Builds on the basic mdoel but incorporates the fact that habitat patches differ in quality.
High quality are known as sources (high number of individuals that can disperse).
Low quality patches are known as sinks because they produce few individuals that can disperse.
What is the landscape metapopulation model?
Even more realistic because it knowledges that both the patches and the habitat matrix can vary in quality.
What happens to the population in a basic metapopulation model?
A population that is divided into several subpopulations, each occupying a distinct patch.
It is assumed that these habitat are of equality and with same subpopulation size, and that each subpopulation supplies the same number of dispersers to other patches.
What is the equation for the proportion of occupied patches when at equilibrium?
P = 1 - (e/m)
e = Fix probability of each patch becoming unccopied (subpopulation going extinct) ni a given time. m = fix probability that each unoccupied patch could be colonised.
Metapopulations and conservation
1) Relevant for the conservation of species around the world as humans continue to fragment terrestrial and aquatic habitats.
2) Relevant to preserve large fragments of habitat whenever possible because populations in large habitats are less likely to go extinct.
3) When we can only preserve small fragments, we must ensure that individuals can disperse to and from them so they can be colonized, which can help prevent small, declining subpopulations from going extinct.
In terms of biodiversity conservation what’s better regarding reserve size?
Larger reserves are better than small.
In terms of biodiversity conservation what’s better regarding number of reserves?
One large reserce is better than a few small ones of the same total area.
In terms of biodiversity conservation what’s better regarding reserve proximity?
Several reserves close together are better than several reserves far apart.
