Paradise Lost? Loss of large fruit-eating birds threatens tropical forests

More than 90% of tropical trees rely on fruit-eating animals, especially birds, for the dispersal of their seeds. Adding to previous evidence, new research shows that large birds are more important than small and medium-sized birds for plant regeneration. "Especially large fruit-eating birds are declining due to habitat loss and hunting in the tropics. This is likely to cause a poor regeneration of some plant species. It may bring about profound change to the tropical forest as we know it." warns Marcia Muñoz, Senckenberg Biodiversity and Climate Research Centre.

Muñoz and her team conducted a study on fruit removal and seedling recruitment in a tropical forest. It showed that large-bodied bird species weighing up to 1400 grams contributed more to fruit removal than small-bodied species. Large birds have higher energy demands and are able to eat a wider spectrum of fruit sizes than small birds. This relates to another important observation -- some large-seeded plants can only be dispersed by large birds.

From the plants' perspective, the scientists found that fruits with small seeds were more frequently eaten than large fruits as they were more accessible to all birds from the forest. "This means if large birds become extinct in a tropical forest, not only the large-seeded plant species, but also the small-seeded plant species lose important dispersers," says Muñoz.

In the process of forest regeneration, fruit removal is followed by seedling establishment. Plants with large and heavy seeds recruited more seedlings than plants with light seeds. Large-seeded plant species thus compensated their lower dispersal rate because they had a competitive advantage over small-seeded species and could better tolerate low light or other hazardous conditions.

"Our results highlight that plants with large seeds are particularly successful in tropical forests and contribute an important part of their diversity. So if we are to conserve this diversity, we need to protect large fruit-eating animals that are crucial for the maintenance of these ecosystems," says Matthias Schleuning, a researcher at Senckenberg and senior author of the study.

The study was carried out in two adjacent protected areas of tropical forest on the eastern side of the Colombian Andes. Researchers recorded the removal of about 17,000 fruits by birds and measured the most important characteristics of birds and plants, such as body size or seed mass. In addition, the researchers counted how many seedlings of each plant species established at their study sites.

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Materials provided by Senckenberg Research Institute and Natural History Museum. Note: Content may be edited for style and length.[1][2]


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