Prey analysis in the diet of some ponerine ants (Hymenoptera : Formicidae)and web-building spiders (Araneae) in coffee plantations in Chiapas, Mexico

A census of the prey captured by seven common web-building spiders (Cyclosa caroli, Gasteracantha cancriformis, Leucauge mariana, L. venusta, Anelosimu s jucundus, Achaearanea tesselata, and an undetermined species of Linyphiid ae) and two dominant ponerine ant species (Ectatomma ruidum and E. tubercul atum) was carried out over a two-year period in different coffee plantation s, in the Mexican state of Chiapas. A total of 4,334 prey items were recove red, of which near to 70% were identified to family level and classified ac cording to their feeding habits. For each of the predators, the bulk of the prey belonged to the four most abundant orders of insects (Hymenoptera, Di ptera, Homoptera and Coleoptera) known to be associated with Neotropical co ffee plantations. The comparison by computed coefficients of both diet breath and diet overla p indicated some degree of similarity between the two ant species, and betw een the six spider species. Moreover, spiders that used webs that function in a similar manner as insect traps (both araneids and the tetragnathid on one side, both theridiids and the linyphiid on the other side) showed more similar diets. Each predator appeared to have an unique feeding niche withi n the coffee agroecosystem for all of the 28 comparisons made between pairs of species, diet overlap (C) values were far lower than the theoretical Va lue of +1 corresponding to complete overlap. Each species also differed in its response to prey availability although the frequency of predation on mo st types of prey appeared to be positively correlated with their relative a bundance in the biotope. This correlation was especially obvious within the Hymenoptera. Of the 159 families identified, 30 (38.1% of all the identified prey) were recognized as containing species known to be pests of coffee plants. Herbiv ores, detritivores and polyphagous arthropods constituted the major part of prey for ants and spiders alike (82.9% of all identified prey for the web- building spiders against 89.9% for the ponerine ants), while only 11.9% of all identified prey corresponded to families that are beneficial (from an a gricultural view point) as predators, parasitoids, or possible pollinators. These results, along with the absence of serious native coffee pests in th e study area, confirm the beneficial economic impact of web-building spider s and carnivorous ants as generalist predators in Neotropical coffee agroec osystem.