Phenology of species interactions: Size-mediated priority effects and the dynamics of predator-prey systems in seasonal communities

Background/Question/Methods

Colonization history plays an important role in the assembly of ecological communities. This is because earlier-arriving species can influence subsequent establishment of other species (i.e., priority effects).  For example, differences between species in the timing of reproduction in a habitat can affect the point in development at which their offspring interact.  Development is generally concomitant with increases in body size, and relative body size determines the interaction type and strength. Previous work on priority effects has largely focused on the role of relative population densities, but little is known about the role of relative body sizes in mediating priority effects. In this study, we tested 1) whether relative arrival time affects the outcome of growing predator-growing prey dynamics, and 2) whether these dynamics are altered by competitive interactions among different prey species. To do this, we conducted a field mesocosm experiment using a dragonfly naiad predator (Erythemis simplicicollis) and two competing tadpole prey (Bufo nebulifer and Hyla versicolor). 

Results/Conclusions

Results of this experiment indicate that arrival time of a prey relative to a predator and the number of prey species present in a system can interact in complex ways to affect predator-prey dynamics. As expected, the presence of predators negatively affected both final biomass and survival for prey species.  However, the importance of arrival time differed between the two prey species and was altered by inter-specific competition. For B. nebulifer, arrival time had significant consequences, but these consequences were contingent upon the presence of H. versicolor. Survival and final biomass of H. versicolor, on the other hand, were relatively unaffected by arrival time, and this was true irrespective of the presence of B. nebulifer. Instead, the interaction of relative arrival time and competition significantly altered the emergence phenology (average time of metamorphosis) of H. versicolor. This suggests that relative arrival time can lead to size-mediated priority effects that alter predator-prey interactions. However, the consequences may only emerge in the context of complex food webs and depend on species specific life-history traits (e.g. competitive ability or degree of phenotypic plasticity).  Understanding the role of relative arrival time for species interactions is becoming increasingly important because global climate change is altering the timing of life history events, such as reproduction, but the magnitude of these phenological shifts differs among species. Our results indicate that this mismatch can result in interaction mismatches, which could affect population dynamics, community structure, and ecosystem function.