Early successional colonizers both facilitate and inhibit the late successional colonizers in communities of dung-inhabiting insects

The influence of early arriving species on the establishment and activity of later ones (the priority effect) is a key issue in ecological succession. Priority effects have been extensively studied in communities subject to autotrophic succession (plants, sessile animals), but only sporadically studied in communities subject to heterotrophic succession (e.g. dung or carrion inhabiting communities). We studied the influence of early successional colonizers on late successional colonizers by manipulating the successional processes in cow dung pats via delaying, and thus lowering, colonization by early successional insects. The decreased activity of early successional insects did not affect the species richness of late successional insects, but it did lead to increased abundance of colonizers. Late successional coprophagous beetles were facilitated by early successional species while larvae of late successional coprophagous flies were inhibited, presumably, by the larvae of early successional flies. We therefore propose that both facilitation and inhibition have a role to play in the heterotrophic succession of coprophilous insects. In addition, facilitation and inhibition among taxa seems to reflect their evolutionary relationships, with facilitation being prominent between phylogenetically distant lineages (early successional Diptera and late successional Coleoptera), and inhibition being more common between closely related lineages (early vs. late successional Diptera). These patterns are strikingly reminiscent of the situation in the autotrophic succession of plants.