"Tree species do not respond to deforestation in the same manner or with the same intensity," Daniel Montoya Terán of the University of Alcalá in Spain told environmentalresearchweb. "Although a few species respond positively to deforestation, habitat loss has overall negative effects on species. The way a tree is dispersed is a key trait. Although there is a large variation among species within each of the functional groups that we consider – wind-dispersed trees and animal-dispersed trees – we can significantly conclude that animal-dispersed trees are on average more robust to habitat loss."
Montoya says that animal dispersal helps physically isolated forest patches to be connected demographically. According to metapopulation theory, regional habitat loss not only removes biodiversity held in the lost habitat but also reduces the occurrence of species in the remaining habitat.
Montoya and colleagues from the University of Alcalá, Spanish National Research Institute for Agricultural and Food Technology, and Microsoft Research Cambridge, UK, looked at the relationship between local forest cover and 34 native tree species and eight exotic species in 89,365 sites across peninsular Spain. Twenty-four of the species showed a negative response to decreased forest cover.
"Scientific literature in ecology emphasizes the role of mutualist interactions – dispersal, pollenization – in creating and mantaining biodiversity," he said. "We also provide evidence that one kind of mutualist interaction, i.e. dispersal of seeds by animals, may also confer robustness to perturbations such as habitat loss and prevent collapse of biological communities. These results have implications for conservation practice."
Montoya says that wind-dispersed species are more vulnerable to deforestation if, and only if, animal dispersers exist in the ecosystem. Equally, if animal dispersers are extinct, then animal-dispersed trees cannot disperse their seeds and create new generations of individuals. "Therefore, animal-dispersed trees are most vulnerable to deforestation in the absence of animal dispersers," he explained. "So protecting plant-animal interactions must be a cornerstone of conservation policy because it enhances biodiversity and increases resistance to perturbations."
For the future, Montoya says that studies should take account of interactions between different factors affecting the dispersal process, such as seed size and the size of the dispersing animal. He believes it’s also important to research the phenomenon for different latitudes and climate conditions to find out to what extent the results can be generalized.
"Finally, more studies on the response of animal dispersers to habitat loss are very important," he said. "To date, it is known that higher trophic [food-chain] levels are more vulnerable to habitat loss. But this has been explicitly reported for predators, not mutualists. Studies of the effects of habitat loss on mutualist animals should be conducted."
The researchers reported their work in Science.