Specialists and generalists fulfil important and complementary functional roles in ecological processes

D. Matthias Dehling, Irene M.A. Bender, Pedro G. Blendinger, Katrin Böhning-Gaese, Marcia C. Muñoz, Eike Lena Neuschulz, Marta Quitián, Francisco Saavedra, Vinicio Santillán, Matthias Schleuning, Daniel B. Stouffer

The Crested Quetzal (Pharomachrus antisianus) plays an important role for the dispersal of plant species in the montane rainforests along the Andes.
The Crested Quetzal (Pharomachrus antisianus) plays an important role for the dispersal of plant species in the montane rainforests along the Andes.

Different species eat different types of food, and therefore each species plays a different role in the ecosystem. For instance, one animal species may feed on other animals, another may consume and disperse the fruits of a plant, and another may pollinate flowers. Some species, called “generalists”, eat many different types of food or food items that are also eaten by many other species. Other species, called “specialists”, eat a smaller variety of food or an unusual type of food that is eaten by few other animals.

Since specialists feed on food items that few other species feed on, they might fulfil an important role in an ecosystem. On the other hand, if specialists only eat a small number or variety of food items, then their role in the ecosystem might be less important. In this study, we wanted to find out if specialists are more important for an ecosystem than generalists.

We studied fruit-eating birds in seven different sites in the South American Andes. First, we recorded which fruits each bird species eats. We then compared the set of fruits that one bird species eats with the sets of fruits that all the other bird species eat. We then classified a bird as a specialist (1) if it eats only a small variety of fruit or (2) if it eats unusual types of fruit that few other birds eat. Likewise, we classified a bird as a generalist (1) if it eats a large variety of fruit or (2) if it eats common types of fruit that many other birds eat. We also determined how important a bird species might be for the ecosystem. For this, we determined how much a bird species contributes to the total dispersal of the fruits of all plant species. We also determined the birds’ potential importance by how much the set of fruit that it eats overlaps with the sets of the other bird species.

We found that both specialists and generalists fulfil important roles for the dispersal of plants. Specialists are important because they eat fruits that few other birds eat, and the sets of fruits that they eat overlap little with the sets of fruit that other birds eat; generalists are important because they eat a wide variety of fruit, including both common and unusual types of fruit.

We also found that birds that mostly eat unusual types of fruit tended to eat a small variety of fruits, and that species that eat a large variety of fruit tended to eat more common fruits. However, some bird species ate both a large variety of fruit and unusual types of fruit. Those species might be especially important for the ecosystem. Finally, there were some bird species that ate only a very small variety of fruit, but those fruits were eaten by no other bird species. These birds also fulfil important roles that might easily be overlooked.

Read the article in full here.

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