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.

Keywords: Carrion; Competition; Insect succession; Necrobiome; Temporal partitioning.

Fig. 1

Bar plot of mean (± S.E.) number of eggs laid by adult a Chrysomya rufifacies and b Calliphora stygia on kangaroo mince with no larvae present (control), 2-day-old heterospecific larvae present (+ 2 day old) or 4-day-old heterospecific larvae present (+ 4 day old)

Fig. 2

Effects of priority effect treatments on larval survival to adulthood relative to the control (0R + 0S; no priority effect in a heterospecific mass) within three different larval densities for a Chrysomya rufifacies and b Calliphora stygia. Priority effect treatments within heterospecific masses is on the y-axis, with numbers representing age of larvae (0, 2 or 4 days old) and letters representing species (R = C. rufifacies and S = C. stygia). Conspecific mass consisting of only one species is the bottom tick of the y-axis (0R only for C. rufifacies conspecific mass and 0S only for C. stygia conspecific mass). Significant effects (shown in bold) are denoted by 95% CIs that do not cross zero, which represents the control for priority effect (grey dotted line). Effect sizes are derived from GLMs

Fig. 3

Effects of priority effect treatments on development time to adult eclosion relative to the control (0R + 0S; no priority effect in a heterospecific mass) within three different larval densities for a Chrysomya rufifacies and b Calliphora stygia. Priority effect treatments within heterospecific masses is on the y-axis, with numbers representing age of larvae (0, 2 or 4 days old) and letters representing species (R = C. rufifacies and S = C. stygia). Conspecific mass consisting of only one species is the bottom tick of the y-axis (0R only for C. rufifacies conspecific mass and 0S only for C. stygia conspecific mass). Significant effects (shown in bold) are denoted by 95% CIs that do not cross zero, which represents the control for priority effect (grey dotted line). Effect sizes are derived from GLMs

Fig. 4

Effects of priority effect treatments on adult fitness (body mass (mg)) relative to the control (0R + 0S; no priority effect in a heterospecific mass) within three different larval densities for a Chrysomya rufifacies and b Calliphora stygia. Priority effect treatments within heterospecific masses is on the y-axis, with numbers representing age of larvae (0, 2 or 4 days old) and letters representing species (R = C. rufifacies and S = C. stygia). Conspecific mass consisting of only one species is the bottom tick of the y-axis (0R only for C. rufifacies conspecific mass and 0S only for C. stygia conspecific mass). Significant effects (shown in bold) are denoted by 95% CIs that do not cross zero, which represents the control for priority effect (grey dotted line). Effect sizes are derived from GLMs

Fig. 5

Conceptual diagram of larval density effects on conspecific masses of a C. rufifacies and b C. stygia larvae. The effect of different combinations of priority effects and larval density effects is also displayed for heterospecific masses: c C. rufifacies arriving first at low larval densities, d C. stygia arriving first at low larval densities, e C. rufifacies arriving first at high larval densities and f C. stygia arriving first at high larval densities. Coloured arrows represent changes relative to the 0 + 0 control for survival (survival to adulthood), development speed and fitness (body mass). Green up arrows = increased survival rate, faster development speed (quicker) and increased fitness, and vice versa for red down red arrows. Grey dashed lines represent no effect