The role of arrival phenology and size-mediated priority effects for species interactions in simple food webs

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 often determines the type and strength of interactions. 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. 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 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 final biomass and survival for both B. nebulifer and H. versicolor.  However, the specific effects of the predator on each of these two prey species depended upon the arrival time of the prey relative to the predator.  Furthermore, these arrival time-specific effects of predator on prey were contingent upon whether a prey species co-occurred with the other prey species. This suggests that differences in relative arrival time can lead to size-mediated priority effects that alter predator-prey interactions, and the consequences of these priority effects for prey also depend on the competitive interactions with other species.  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 these differential phenological shifts can result in interaction mismatches, which could affect population dynamics, community structure, and ecosystem functioning.