Quality of agroecological matrix in a tropical montane landscape: Ants in coffee plantations in southern Mexico

Conservation efforts in fragmented landscapes frequently focus on characteristics of the habitat fragments. We propose that the matrix within which habitat fragments occur is of equal importance and focus on quality of the matrix as an interesting variable. We studied ground-foraging ants in isolated montane forest fragments in the matrix of coffee agroecosystems of southwestern Chiapas, Mexico. We sampled the ants, with tuna fish as bait, in plots at various distances from a forest fragment (2-750 m) on two farms, one an organic farm with considerable shade, the other a conventional farm with only spotty shade. Each plot contained a grid of 49 (7 x 7) or 100 (10 x 10) baits. The species richness of ground-foraging ants was not significantly different between the forest fragment and the high-quality matrix, but it was significantly lower in the low-quality matrix than in the forest. Furthermore, species richness decreased with distance from the forest fragment in both matrix types. However, the rate of decrease in species richness was greater in the conventional farm (poor-quality matrix) than in the organic farm (high-quality matrix), suggesting that the quality of the agricultural matrix is important for the conservation of ant diversity.