Habitat diversity increases species diversity: theoretical models against patterns in nature

The number of different species living on islands nearly always increases with habitat diversity, and most importantly never decreases, according to a new study published in The American Naturalist.

Joaquín Hortal, Kostas Triantis, Shai Meiri, Elisa Thébault and Spyros Sfenthourakis carried out a review of empirical evidence using data from several archipelagos worldwide, and theoretical modeling techniques. The results showed that the more different habitats there are on an island, the more species live on it. The paper's authors say this result is important for conservationists, as it suggests that they should try to conserve as many different types of habitats as possible, as opposed to concentrating their efforts on large areas of few kinds of habitat.

The new study was led by a multidisciplinary team of researchers working at the NERC Centre for Population Biology of the Imperial College London, the University of Oxford and the University of Patras, Greece.

The team's findings contradict a theoretical study published last year by another team of scientists, which predicted that the relationship between the number of habitats on an island and the number of species inhabiting it would be hump-shaped. That is, that species numbers would increase with the increase of habitat types but beyond a certain number of habitats, the extent of some of them will be too small to host many species, and therefore the total number of species will decrease.

Lead author Dr Joaquín Hortal from Imperial College London says that the previous study's theoretical models were flawed, creating results that did not reflect observations in the natural world:

"The previous theoretical model contained the unrealistic assumption that all species are extreme habitat specialists, able to occupy only one type of habitat. Once we altered the model to reflect the fact that most species can establish populations in more than one habitat, our numerical simulations were much closer to the patterns observed in Nature, based on either simple parameters or on real data of isopod crustaceans from the Aegean islands," he said.