19 June 2008

Forest butterflies of West Africa: still hanging on today, but where will they be tomorrow?

Larsen, T.B. (2008). Forest butterflies in West Africa have resisted extinction… so far (Lepidoptera: Papilionoidea and Hesperioidea). Biodiversity and Conservation DOI: 10.1007/s10531-008-9399-z

In this recently published paper, Torben Larsen cautiously presents good news for African biodiversity conservation in general and for butterfly conservation in specific: 97% of all butterfly species ever recorded in 4 western African countries—where the tropical rainforests have been extensively decimated—were still present during the period 1990-2006.

Although most people, including myself, would associate butterflies with sunny meadows full of wild flowers, the dense tropical forests of Africa harbor hundreds of species of butterflies. In fact, the 1,000 or so species known from west Africa comprise ~5% of the world total of approximately 20,000 described species of butterflies.

According to the paper:

Butterflies are a major, integral part of the forest ecology. They are important specialized herbivores. They play a role in pollination of many plants. They are important prey to a varied assemblage of predators (rodents, birds, lizards, chamaeleons, mantids, assassin bugs, wasps, ants, robber-flies, dragonflies, crab-spiders, and orb-spinning spiders). They are hosts to a plethora of parasites and parasitoids, some of which are themselves subject to hyper-parasitism. Many Lycaenidae live in complex and curious symbiotic relationships with ants. The web of life that surrounds butterflies is so varied and so complex that it seems safe to say that when essentially all butterflies still survive, this will be true also for much of the rest of forest biodiversity.
What this means is that butterflies are a good biodiversity indicator group. If most butterflies species are still surviving, this presumably indicates that the remaining forest ecosystems are, at least for the time being, still functioning and their constituent species are also still surviving.

Obviously, the continuing survival of the butterflies and all other forest species ultimately depends on the continuing existence of the remaining forests as well as smaller woodland fragments, including the traditional “sacred groves”, riverside forests and even plantations, that serve as stepping stones for continued gene flow between forest populations.

Torben’s analysis covered the countries of Sierra Leone, Liberia, Ivory Coast (Côte d'Ivoire) and Ghana. Forest destruction appears to have accelerated after the independence of these countries at various times during the last century. According to the figures in the paper, Ivory Coast, which became independent in 1960, provides a tragic example: the country's forest cover went from ~175,000 km2 in 1966 down to 31,000 km2 in 1987.

The ultimate cause behind all of this, something most conservationists seem to be afraid to accept publicly, is, of course, the seemingly unstoppable growth in human population. There will be no relief in sight until there is less of us.

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