Spatial population ecology Flashcards
What is habitat fragmentation?
Woodlands get fragmented in order to cultivate land.
However, habitats are also naturally fragmented, for example tree habitats. Lakes are also fragmented across a country.
Anthropogenic fragmentation is one of the main threats to biodiversity globally.
Populations in small fragments are inevitable small and therefore vulnerable to extinction due to demographic and environmental stochasticity.
On a landscape scale, small populations migrate between different sites to fill those which are left empty after extinction.
How does Pedicularis furbishae colonise new areas?
Has to constantly colonise new riverbanks until other species out compete it.
A meta population approach is appropriate.
Dispersal of seeds to new river banks is frequent.
Although the risk of extinction to each population is high, overall extinction is unlikely.
What is Levin’s meta population model?
Rate of change of occupied patches (p) = colonisation rate (c) - extinction rate (e)
Dp/dt = cp (1 - p) - ep
When dp/dt = 0:
p = 1 - e/c
So:
the higher the rate of colonisation and the lower the rate of extinction, the greater the proportion of patches occupied.
Define a meta population?
A 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.
Why is Levin’s model quite simplistic?
Assumed that patches are the same size.
Assumed number of patches are infinite.
Assumed the patches have the same probability of extinction and colonisation.
Importance of a core mainland island population?
Normally immortal, so what happens to the smaller populations doesn’t matter as much.
Applications of meta population models in conservation?
- predict time to extinction
- how many patches are needed for persistence
- explore alternative scenarios or habitat loss
- which patches to conserve or restore
- show the effects of habitat loss may be long delayed
- planning of re/introductions
Source sink and psuedo-sink dynamics?
N(t+1) = N(t) + births - deaths + immigrants - emigrants
Source: net exporter of individuals
Sink: only persists due to immigration from the source
Pseudo-sink: can persist without immigration
How can you identify the difference between a pseudo-sink and a sink?
Have to cut off the immigration to the population.
Example of a sink and source population?
Sea rocket found on beaches and dunes.
The beach populations act as a source and the plant would be absent from the dunes without this source of seeds.
Example of meta population conservation?
Silver spotted Skipper butterfly
Occurs in Britain on calcareous grasslands.
When myxomatosis killed rabbits in mid 50s, their habitat became overgrown as rabbits were no longer eating it.
Butterflies declined to 46 or lower localities in 10 refuge locations.
By 1982, rabbits had recovered and many former sites again seemed suitable but hadn’t been recolonised.
Between 1982 and 1991, number of habitat populations that were populated increased by 30% in the S & N Downs. Some of the populations were too far away to be colonised (10km).
Stepping stones were created to try and restore the butterflies.
As the climate warms, more habitats are available to colonise.
Problems with application of meta-population ideas to conservation?
- not all species occur as meta-populations
- draws attention away from single populations
- requirement for lots of data
- developers may use meta-population arguments to justify fragmentation
- what is good for one species doesn’t transfer to others
