Sunday, 3 June 2012

Little monkeys need lots of space

This charming little creature is a White headed marmoset or "Sagui" (Callithrix geoffroyi). Tolerant of humans, they are often seen by tourists and will readily take pieces of fruit in their little hands. Classified as Least Concern (LC) on the IUCN Red List and in appendix II of CITES, surely conservation is no problem? Well, more or less.

Historically many were taken from the wild as pets, their very tolerance of man acting against them. This is tightly controlled these days, but their numbers are still decreasing. In the 21st century loss of habitat is the major problem, or more specifically, fragmentation of habitat. You might think that 20 forests of 1 km sq.would hold the same number of monkeys as 1 of 20 km sq. Indeed, given that predators tend to require much larger ranges and so are less likely to occur in small pockets, you might assume there would be more monkeys. You would be wrong (Chiarello & de Melo, 2001). There are various reasons.

a) Long term of course, small populations lack enough genetic diversity to stay healthy, but there are more immediate reasons.

b) Small forest fragments tend to favour trees and shrubs which are forest edge species, with proportionally less canopy or forest interior species (Cardoso da Silva and Tabarelli, 2000). Unfortunately, these are the very ones that produce the most fruit. Thus small monkeys, which tend to need a lot of fruit, suffer accordingly. In the same way, large fruit eating birds like macaws and toucans tend to be absent from isolated forests less than 250 hectares (Willis 1979).

Our little saguis are quite adaptable, and eat a lot of tree gum and insects (and anything really), so suffer less than fruit eating specialists, but it still cuts down their options. And they have another problem.

c). Small fragments may have fewer large fragments, but they still have plenty of cats, either native or feral from surrounding farm and residential land. Saguis and other small monkeys are especially susceptible to cats. They do their best, mobbing them and screeching, but that's not always enough. As an aside, it has been shown that being part of a "mob" actually reduces rather than increases monkey stress - it is tempting to extrapolate that to humans!

Driving through a landscape of fields and copses may appear more "natural" than a prairie of wheat or sugar cane, and it is, but maybe not that much more.

Cardoso da Silva JM, & Tabarelli M (2000). Tree species impoverishment and the future flora of the Atlantic forest of northeast Brazil. Nature, 404 (6773), 72-4 PMID: 10716443
Chiarello, A.G., de Melo, F.R. (2001). Primate population densities and sizes in Atlantic forest remnants of northern Espirito Santo, Brazil. International Journal of Primatology, 22, 379-396.

Willis, E.O. (1979). The composition of avian communities in remanescent woodlots in southern Brazil. Papéis Avulsos de Zoologia, São Paulo, 33, 1-25. 

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