Priority effects and density promote coexistence between the facultative predator Chrysomya rufifacies and its competitor Calliphora stygia

Abstract

Highly competitive ephemeral resources like carrion tend to support much greater diversity relative to longer-lived resources. The coexistence of diverse communities on short-lived carrion is a delicate balance, maintained by several processes including competition. Despite this balance, few studies have investigated the effect of competition on carrion, limiting our understanding of how competition drives coexistence. We investigated how priority effects and larval density influence coexistence between two blowfly species, the facultative predator Chrysomya rufifacies and its competitor Calliphora stygia, which occupy broadly similar niches but differ in their ecological strategies for exploiting carrion. We examined how adult oviposition, larval survival, developmental duration, and adult fitness were affected by the presence of differently aged heterospecific larval masses, and how these measures varied under three larval densities. We found C. rufifacies larval survival was lowest in conspecific masses with low larval densities. In heterospecific masses, survival increased, particularly at high larval density, with priority effects having minimal effect, suggesting a dependency on collective exodigestion. For C. stygia, we found survival to be constant across larval densities in a conspecific mass. In heterospecific masses, survival decreased drastically when C. rufifacies arrived first, regardless of larval density, suggesting C. stygia is temporally constrained to avoid competition with C. rufifacies. Neither species appeared to completely outcompete the other, as they were either constrained by density requirements (C. rufifacies) or priority effects (C. stygia). Our results provide new mechanistic insights into the ecological processes allowing for coexistence on a competitively intense, ephemeral resource such as carrion.

The ephemeral resource patch concept

“…Thus, increased species richness and abundance, and subsequent priority effects, can be beneficial for some species through facilitation (Komo et al ., 2019), while being detrimental for other species through increased competition or predation (Brundage, Benbow & Tomberlin, 2014; Dawson et al ., 2022 a ). Generalist consumers, such as the Australian carrion muscid Australophyra rostrata (Dawson, Barton & Wallman, 2020; Dawson et al ., 2022 b ), may be able to tolerate a broad range of species compositions, whereas specialist consumers often depend on the presence/absence of certain species (i.e. arrival before predators or competitors, or after mutualists) to enhance their chances of survival (Morais et al ., 1995; Brundage et al ., 2014; Dawson et al ., 2022 a ).…”

Response of adult carrion beetlesNecrodes littoralis(L.) (Staphylinidae: Silphinae) to selected cadaveric volatile organic compounds: laboratory and field tests

“…Their occurrence is spatially unpredictable, and for this reason carrion insects must rely on olfactory systems, which are effective over long distances. Moreover, carrion is frequently bulky, highly nutritious and ephemeral, causing intense competition among its users (4, 5). Carrion insects need to locate it quickly to maximize the chance for reproductive success.…”