Size matters: Nest colonization patterns for twig-nesting ants

Background/Question/Methods

Understanding the drivers of ant diversity and co-occurrence in agroecosystems is fundamental because ants influence food webs and are important predators in agroecosystems. Past studies have shown that multiple factors at the local and regional levels influence ant community assembly. However local factors, such as environmental variation, that act at the recruitment stage have been largely overlooked. We examined local ecological mechanisms that influence the structure of a twig-nesting ant community in coffee systems in Mexico. We investigated whether twig characteristics (nest size and diversity of nest sizes) and nest strata (shade tree or coffee shrub) affect occupation, species richness, and community composition of ants occupying twigs. We also examined preferences of ant species for nest size or strata. We conducted our study in a shaded coffee farm in Chiapas, Mexico between March and June 2012. Ant occupation of nests was studied by placing 6 artificial nests (bamboo twigs with different entrance sizes) on coffee shrubs and shade trees (of the genus Inga) either in diverse (one nest of each size) or uniform (six nests of the largest size) treatments, in 44 sites. We also characterized the vegetation (no. of trees, canopy cover and coffee density) in each site.

Results/Conclusions

We found 33 ant species that occupied 73% of nests placed. Strata and size did not influence the percent of occupied nests (P>0.05). However, mean species richness was significantly higher on plants with diverse nests (P <0.05). Community composition differed between coffee and shade trees (P<0.001), and between diverse and uniform size treatments on coffee shrubs (P<0.001), but not on shade trees (P=0.12) as shown by a NMDS and an ANOSIM. Individual species showed preferences for nest strata and size treatments. Camponotus atriceps, Camponotus striatus and Pseudomyrmex gracilis preferred coffee nests (P<0.05), and Cephalotes basalis and Camponotus bretesi preferred tree nests (P<0.05). C. atriceps was more abundant in uniform nests (P<0.05), and C. striatus and P. gracilis were more abundant in diverse nests (P<0.05). Moreover, individual ants were more abundant in certain sized nests. Our results indicate that twig-nesting ants are nest-site limited in this habitat and quickly occupy artificial nests of varying sizes. Further, individual ant species do respond to differences in nest diversity and size and these differences in nest size promote diversity on individual coffee plants and trees.