Top-predators as biodiversity surrogates? Clarifying some issues
August 9, 2007 6:13 am Press releasesTop predators may be good biodiversity indicators if they are highly specialized in their habitat and food requirements, if they are sensitive to human disturbance and if they have a small range. There are few examples of such predators (some raptors are among them), and often include highly threatened species; concentrating conservation efforts on them is well justified. But many top predators are wide ranging generalist species that are not sensitive to habitat disturbance; if they occur everywhere, even in degraded habitats where sensitive species cannot longer occur, how can one use them to distinguish areas of high species richness?
Also, there are areas of high diversity that have no or few top predators. For example, several important biodiversity hostspots of conservation priority at a global scale, such as the Succulent Karoo and the Fynbos in South Africa, or Madagascar, could not have been detected with the aid of top predators occurrence, as these places have few of them, and mostly generalist. And yet, these are places that burst in diversity of endemic species, species that are found there and nowhere else.
It is clear that top predators won’t work everywhere and that any top predator cannot be assumed to be a good biodiversity indicator.
But most importantly, the point we wanted to make with our article was not about top predators being good or bad indicators of areas of high diversity of other species. Instead, we questioned their use in modern conservation approaches. We work with what is called systematic conservation planning. These are methods that help us make cost-efficient decisions, and are applied to select networks of conservation areas instead of single protected sites. For solutions to be efficient, it means that we often need to identify the minimum number of sites that all together include all species in the region. Such sites may not be the richest in species number, but they are rich in disctinct sets of species. I explain it with one example. Imagine we have to chose among the three following sites: A) has a large number of species B) is identical to A, C) is a site with slightly less species than A and B, but a completely different set of them. If we want to protect all the species with the minimum number of sites, it is obvious that we need 2 sites, and we need to include site C in the solution, the poorest in species number. Our question to the top predator dilemma was, do top predators work in such context? We don’t know it, as it has not been tested. Systematic conservation planning is being applied worldwide (including the hotspots above mentioned), often at large scales for which there is not enough data to identify the best set of sites to protect. The search for a group of species that would help us identifying important areas that complement each other has been a rather frustrating one, with just few promising cases, and too many flawed analyses that do not allow us to generalize. Ours, was a call for more careful research in this area. Too simple conservation messages may lead to mistakes that may be very expensive to correct for, making systematic conservation-planning decisions less cost-efficient. [see News/Press release]