by Jennifer Opel, Bayreuth University
When a tree is surrounded by many similar individuals, its mortality increases, which is probably caused by specialized pathogens or herbivores. This effect occurs in forests all over the world, but is more pronounced in rare tropical tree species, which could contribute to the astonishing tree species diversity of tropical forests.
This was discovered by a team of 52 scientists led by Lisa Hülsmann, Professor of Ecosystem Analysis and Simulation at the University of Bayreuth, and Florian Hartig, Professor of Theoretical Ecology at the University of Regensburg. Their paper is published in the journal Nature.
How tropical forest communities can support hundreds of species without one species becoming dominant and others going extinct has puzzled ecologists over centuries.
More than 50 years ago, ecologists Daniel Janzen and Joseph Connell hypothesized that the stable climatic conditions in the tropics allow pathogens to specialize more strongly on individual tree species, causing trees to grow less and die more frequently when surrounded by other trees of the same species—a reaction called density dependence.
