Refuge availability and within species differences in cannibalism determine population variability and dynamics

Background/Question/Methods

Theoretical studies show that both cannibalism and intraspecific resource competition can have major effects on population dynamics. Cannibalistic intensity, offspring size, harvesting and refuge availability are all important factors affecting the interplay between cannibalism and competition and hence the dynamics. We studied two populations of the common guppy (Poecilia reticulata)that differed in their cannibalistic voracity as well as offspring size. We manipulated the availability of refuges for juveniles and harvesting intensity of large adults to investigate how these factors influenced the dynamics of the two populations.

Results/Conclusions

Overall population dynamics was affected by the origin of the founder populations and the population with a higher cannibalistic propensity and smaller offspring exhibited higher population variability. Both populations displayed cannibal-driven cycles with repression of recruitment when no refuges were present. Harvest of large cannibalistic females destabilised the dynamics and also caused extinctions of several populations without refuges.  The presence of refuges reduced cannibalism and stabilised the dynamics in both populations. However, when refuges were present there was evidence of another type of cycle with shorter cycle period and synchronised peaks in density of vulnerable juveniles and cannibals. We suggest that increased number of refuging juveniles led to intensified resource competition in the population with competition driven cohort cycles as a result. The harvest yield was low in the refuge treatments as few females grew large due to resource competition, leading to a small impact of harvesting in these treatments.