Reciprocal intraguild predation and predator coexistence

Abstract

Intraguild predation is a mix of competition and predation and occurs when one species feeds on another species that uses similar resources. Theory predicts that intraguild predation hampers coexistence of species involved, but it is common in nature. It has been suggested that increasing habitat complexity and the presence of alternative food may promote coexistence. Reciprocal intraguild predation limits possibilities for coexistence even further. Habitat complexity and the presence of alternative food are believed to promote coexistence. We investigated this using two species of predatory mites, Iphiseiodes zuluagai and Euseius concordis, by assessing co-occurrence in the field and on arenas differing in spatial structure in the laboratory. The predators co-occured on the same plants in the field. In the laboratory, adults of the two mites fed on juveniles of the other species, both in the presence and the absence of a shared food source, showing that the two species are involved in reciprocal intraguild predation. Adults of I. zuluagai also attacked adults of E. concordis. This suggests limited possibilities for coexistence of the two species. Indeed, E. concordis invariably went extinct extremely rapidly on arenas without spatial structure with populations consisting of all stages of the two predators and with a shared resource. Coexistence was prolonged on host plant leaves with extra food sources, but E. concordis still went extinct. On small, intact plants, coexistence of the two species was much longer, and ended with the other species, I. zuluagai, often going extinct. These results suggest that spatial structure and the presence of alternative food increase the coexistence period of intraguild predators.

Keywords: Jatropha curcas; biological control; bistability; extinction; population dynamics; predator‐prey interactions; stage structure.

Figure 1

(a) Numbers of dead juvenile E. concordis (mean ± SE) after 48 hr in the presence or absence of ample pollen and in the presence or absence of adult I. zuluagai. (b) Oviposition rates (mean ± SE) after 48 hr of the adult I. zuluagai in the same experiments. Letters inside the bars indicate significant difference among treatments (contrasts after GLM)

Figure 2

(a) Numbers of dead juvenile I. zuluagai (mean ± SE) after 48 hr in the presence or absence of ample pollen and in the presence or absence of one adult female E. concordis. (b) Oviposition rates (mean ± SE) after 48 hr of the adult E. concordis in the same experiments. Letters inside the bars indicate significant difference among treatments (contrasts after GLM)

Figure 3

(a) Numbers of eggs (mean ± SE) produced by (a) adult female predatory mites I. zuluagai when feeding on juvenile E. concordis, and by (b) adult female predatory mites E. concordis when feeding on juvenile I. zulugai. Adult females of both species were allowed to feed on the juveniles of the other species for 2 days, but only oviposition rates of the second day were included to avoid effects of previous diet. Different letters inside the bars indicate significant differences between treatments

Figure 4

Mean total (all stages) numbers of mites (mean ± SE) of I. zuluagai (triangles) and E. concordis (circles). Populations of both species were started with 10 adult females and were allowed to grow on pollen for 6 days. Subsequently, populations of the two species were released on the same arena either with (drawn lines) or without (interrupted lines) pollen as a shared food source. See text for further explanation

Figure 5

Mean ± SE numbers of adults of E. concordis (a) and I. zuluagai (b) per plant. Populations of both species started with 10 adult females and were allowed to grow on pollen for 6 days. Both species were either released on the upper leaf (Same leaf, diamonds) or one of the species was released on the upper leaf and the other one leaf down (E. concordis up and I. zuluagai up). (C) Only individuals of I. zuluagai were released. See text for further explanation. The letters in the legend show significance of differences among treatments for E. concordis (contrasts after lme). Treatments did not differ significantly for I. zuluagai

Figure 6

Mean numbers of eggs (open circles), immatures (open diamonds), adults (open triangles), and total mites (closed circles) of E. concordis (a and b) and I. zuluagai (c and d) per leaf, either alone (a, c) or together with the other species (b, d). Populations of both species started with 10 adult females and were allowed to grow on pollen and honey for 6 days. Subsequently, populations of the two species were released on the same leaf or on different leaves, in all cases with pollen and honey as food. Letters to the left of the total curves indicate a significant difference between the total numbers in the mixed and single populations. For reasons of clarity, SE are only shown for total numbers