Ecologists have long struggled to explain why tropical forests have so many different species of trees. One dominant theory to emerge contends that each plant has a specialist natural enemy that helps keep populations of that plant in check — and allows others to thrive.
A new study by Yale researchers finds that this phenomenon, known as the Janzen-Connell hypothesis, does indeed promote coexistence of tropical species — except when it doesn’t.
Writing in the journal Ecology Letters
, they note that there can be large disparities in the extent to which different species are susceptible to these natural enemies. Using a theoretical model — as well as through analysis of data collected on Barro Colorado Island in Panama — they show that these disparities can a create a competitive advantage for some species that may make communities less
stable rather than more stable.
“Our analysis suggests that the natural enemies on this island may actually be harming the ability of many species to survive rather than uniformly helping species co-exist,” said Simon Stump
, a postdoctoral associate at the Yale School of Forestry & Environmental Studies (F&ES). “This finding calls into question – or at least adds a significant caveat — to a major hypothesis in community ecology. At the very least it suggests that other explanations may be needed.”