Caveats of using the species-area relationship for extrapolations on historical and future species numbers
Abstract
We compiled species lists of birds, reptiles and amphibians in Hungarian reserves, then used these data to estimate historical species richness of Hungary using the species-area relationship. We could reconstruct the situation in the 18th century, before large scale land transformations started. The species-area relationship was significant for the three studied classes, however, two (Anseriformes and Charadriiformes) of the five bird orders considered did not perform the expected relationship. We argue that in these orders the preference for wetland habitats masked the expected relationship. This result highlights the limits of using the slope of species-area relationship to assess threat; it is reliable only in taxa in which habitat preference varies largely. We estimated that one amphibian species, four reptile species, and 230 bird species have become extinct from Hungary during the last few centuries. However, an evaluation of extinction in the best-known taxon (Falconiformes) revealed only 14 potentially extinct species, in spite of the 23 species expected from our analysis. Therefore, we suppose that the present pattern of species richness in the reserves is still in the state of faunal relaxation. This result highlights the threat of further species extinction. Previous estimates of species richness using the species-area relationship are usually based on the assumption that the habitat archipelago is in equilibrium, which may not be true in most fragmented landscapes.
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