Trees Increase Ant Species Richness and Change Community Composition in Iberian Oak Savannahs

Abstract

Iberian man-made oak savannahs (so called dehesas) 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 dehesas with nearby treeless grasslands to assess the effects of oaks on ant communities. Formica subrufa, 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 dehesas and grasslands, as expected in areas with a Mediterranean climate. Within dehesas, 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 dehesas. 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 dehesas; within grasslands, they offer an additional microhabitat for species that would otherwise be scarce or absent.

Diversity and assembly composition of arboreal ants in a west African humid forest‐savannah mosaic

“…Indeed, the fact that an ant species is dominant in one habitat and not in another could be related to the specific environmental conditions of each habitat (plant richness, plant composition, tree density, herbaceous cover, shade or canopy cover, temperature and relative humidity, etc). See (Gaytán et al, 2021) for tropical forests and (Mhlanga et al, 2022; Vasconcelos et al, 2019) in savannah for studies.…”

Which Factors Favour Biodiversity in Iberian Dehesas?

“…The presence of trees on open grasslands is also a positive factor for diversity in ants [43,44], coleoptera and diptera [45][46][47][48][49]. Ant species richness and Shannon diversity tend to increase in areas under Q. rotundifolia canopies as a consequence of the shade effect, as tree size plays an important role in the density of ground ant nests.…”