1 Tahrcountry Musings: Habitat fragmentation, percolation theory and the conservation of a keystone species

Wednesday, April 06, 2011

Habitat fragmentation, percolation theory and the conservation of a keystone species

Habitat fragmentation, percolation theory and the conservation of a keystone species
Proceedings: Biological Sciences © 1998. The Royal Society

This paper is worth a read. The authors say sustainable forest–harvesting strategies may not be as successful as is currently thought. They also impute that habitat corridors, once thought of as the saviour for fragmented environments, may have a detrimental effect on population in certain cases.

Many species survive in specialized habitats. When these habitats are destroyed or fragmented the threat of extinction looms large. In this paper, the authors use percolation theory to consider how an environment may fragment. They then developed a stochastic, spatially explicit, individual-based model to consider the effect of habitat fragmentation on a keystone species (the army ant Eciton burchelli) in a neo tropical rainforest. The results point to the fact that that species may become extinct even in huge reserves before their habitat is fully fragmented. This aspect of the results of the study has important implications for conservation

The authors discuss the appropriateness of corridors.  They say for species that possess no `long-term memory’ corridors between reserves have to be sufficiently large so that the corridors can be found, and second they can be negotiated successfully. It is hard to lay down any minimum corridor size, since divergently shaped lattices and different models for local movements will yield different answers. The researchers say that there is a minimum corridor width between small reserves to ensure the persistence of a population. They observed persistence to be impossible if pockets of habitat are hard to find. Geometrically complicated reserves are of little use to the keystone species Eciton burchelli . A colony become strapped in a small pocket of rainforest, depleting its local resources and thus faces starvation. It could be possible for this situation to be repeated in a habitat corridor and an individual (with poor or no navigational skills) enters a corridor, wanders back and forth, depleting its resources, and therefore leading to starvation. A corridor that would suit one species might be detrimental to others.

On the whole this paper is very thought provoking.

No comments: