Trees Increase Ant Species Richness and Change Community Composition in Iberian Oak Savannahs
Álvaro Gaytán | José L. Bautista | Raúl Bonal | Gerardo Moreno | Guillermo González-Bornay
Iberian man-made oak savannahs (so called <i>dehesas</i>) are traditional silvopastoral systems with a high natural value. Scattered trees provide shelter and additional food to livestock (cattle in our study sites), which also makes possible for animals depending on trees in a grass-dominated landscape to be present. We compared <i>dehesas</i> with nearby treeless grasslands to assess the effects of oaks on ant communities. <i>Formica subrufa</i>, a species associated with decayed wood, was by far the most abundant species, especially in savannahs. Taxa specialized in warm habitats were the most common both in <i>dehesas</i> and grasslands, as expected in areas with a Mediterranean climate. Within <i>dehesas</i>, the number of species was higher below oak canopies than outside tree cover. Compared to treeless grasslands, the presence of oaks resulted in a higher species richness of aphid-herding and predator ants, probably because trees offer shelter and resources to predators. The presence of oaks changed also the species composition, which differed between grasslands and <i>dehesas</i>. In self-standing scattered oaks, ant communities did not differ between the trunks and soil below canopies. These results stress the conservation value of trees in <i>dehesas</i>; within grasslands, they offer an additional microhabitat for species that would otherwise be scarce or absent.
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