Ecotones as refuges

In a recent Opinion piece in TREE entitled 'Agroforestry: a refuge for tropical biodiversity?', Bhagwat from the Oxford University Centre for the Environment and colleagues combine two ideas that have appeared on this blog: ecotones and refuges. They discuss the value of unprotected areas, specifically agroforestry systems- where trees and shrubs are grown in combination with crops- to the conservation of wildlife in human-dominated landscapes. Farms with trees can provide wildlife habitat outside of formally protected areas as well as connect reserves. As discussed in an earlier post, farms that attract wildlife could be viewed as having potential for agro-tourism and, if converting to agro-forestry would also mean decreasing crop losses, then such a scheme could be advantageous to farmers. What we need to learn is if the costs to farmers of having e.g. howling monkeys in their coffee plantations do not outweigh the benefits accrued from agroforestry, agrotourism and conservation. Ideas on how to evaluate such situations are needed, so post one here if you have one!

Habitat shifts and refuges

Animals world over are being affected by climate change and human disturbance. Many shift habitats and ranges for food, shelter, and reproduction. If they are unable to exploit an alternative habitat or one is unavailable, they may not survive. Habitats not easily accessed by humans and therefore not easily converted to agriculture may be particularly important now and in the future as 'refuges' for wildlife whose historical ranges and preferred habitats are threatened. I think there exist two such habitat types which make particularly good refuges for primates: mangroves and peat swamp forest. The use of mangrove has been called a 'survival adaptation' for the Senegal red colobus by researchers Galat-Luong and Galat (2005) and an upcoming article by Quinten and colleagues (from the Siberut Conservation Programme) reports high primate densities in peat swamp forest. Adapting to these wetland habitats must be challenging for primates: diets may be salty or high in tannins, locomotion can be tricky along mangrove prop roots, and tide levels change. But that even the 'specialist' colobines can exploit mangroves in Africa and peat swamp in SE Asia lends some hope that these relatively more extinction-vulnerable species will persist.

Why flexible 'specialists' can't be indicator species too

The capacity to shift habitat and diet by such supposed 'specialists' as red colobus makes me question the use of red colobus as indicators of forest health in some regions of Africa. Some primatologists claim that these behavioral adjustments of red colobus are temporary and that what we are seeing is a time lag between response and ultimate population crash. However, in some cases, extinction has long been forecasted and species persist. Many of them persist in altered landscapes - human-induced ecotones. The Zanzibar red colobus is one such species - an exceptional example of a species that ticks many of the vulnerability traits predisposing it to extinction (island endemism, fragmented habitat, persecution, specialized morphology) and yet adapts through innovative, flexible and opportunistic behavior.