Temporal Shifts and Cactus-Beetle Networks in an Intertropical Semiarid Zone in Mexico.

Cactus-dominated semiarid scrubland covers 40% of Mexican territory. This ecosystem is highly dynamic and undergoes drastic changes caused by seasonality. These temporal changes influence saprophagous insect communities associated with Cactaceae species. In this study, we analyzed the beetle community associated with decayed cactus species at the Barranca de Metztitlán Biosphere Reserve in central Mexico. We compared the diversity and composition of beetle communities in rainy and dry seasons; moreover, the network architecture of cactus-beetle interactions was examined. High dominance and abundance were detected in rainy assemblages, whereas the dry season had less abundance but more ecological diversity. A nested structure was found between individual cactus species and beetle species, as well as in an intrapopulation network between fragments of the columnar cacti Isolatocereus dumortieri (Scheidw.) Backeb. (Cactaceae), and beetle species for both seasons (rainy and dry). This finding shows more generalist than specialist beetle species inhabiting cactus species. Further research is still needed to understand whether the presence of these beetle species is determined by microhabitat conditions or the abundance of prey associated with decayed cacti. This is the first step in untangling the complex interactions among cactus-beetle species involved in the decomposition process of cacti in semiarid environments. This study provides evidence of temporal shifts in abundance and diversity patterns of these beetles associated with decayed cacti; furthermore, we did not detect an influence of seasonality on the structure of cactus-beetle interactions.