Why do Ant Species Occur in the Matrix and Not in the Forests? Invasion from Other Habitats or Expansion from Forest Gaps (Hymenoptera: Formicidae)

Abstract

In a fragmented Brazilian landscape, 24 species of ant, which are considered to be open-area specialists, occur exclusively in the pasture areas around the forest remnant (matrix). In this paper, we propose possible theoretical explanations for the occurrence of these exclusively matrix species, and suggest that these species originally occurred in forest gaps. We also determine whether these species occur in another type of open vegetation, the cerrado (Brazilian savanna). Ants were collected from ten forest gaps within three forest remnants. Ant species sampled in forest gaps were compared to ant species collected from the cerrado. The aim here was to determine whether there were any similarities between the two sets of species, and also to collect information about the origin of matrix ant species. In the forest gaps, we sampled 44 species of ant. Of these, 11 species were also found to occur in matrix areasand eight species in the cerrado vegetation. Two scenarios could explain this result: (I) exotic ant species of open biomes migrate to, and establish in, the matrix; or (II) the species that currently occur exclusively in the matrix areas are originally from forest gaps and have increased their distribution following the fragmentation event. We discuss reasons to support these scenarios as wellas their implications for other ecological and conservation processes.