Environmental carry-over effects drive context dependent competitive dynamics

Background/Question/Methods

Developmental plasticity in response to variable habitat quality is a common source of individual and cohort level phenotypic variation. When habitat quality then changes, such as when individuals disperse to new patches, the phenotype induced by their development habitat can carry-over with them and influence population level performance in the new habitat. We hypothesized that these carry-over effects could also influence community dynamics since traits that influence population performance likely relate to competitive ability. We tested this hypothesis using the classic Tribolium castaneum and T. confusum competition study system with two habitat types known to have different qualities (high and low quality) that lead to carry-over effects important for population dynamics. We generated carry-over effects by independently manipulating the habitat quality each competitor experienced during their development and the habitat quality in the patch where competition then occurred. Using the Tribolium system allowed us to set up initial density gradients for the competitors based on previous work showing density-dependence in competitive outcomes based on initial densities. By following the dynamics of competition for six months this design allowed us to estimate how carry-over effects influence the strength and dynamics of competition leading to coexistence or exclusion.

Results/Conclusions

Carry-over effects of past habitat quality had strong, but context dependent, impacts on competitive interactions between the two species. Within low quality habitats, which species was the dominant competitor after six months and the rates of exclusion of T. castaneum at high competitor densities depended on carry-over effects of the colonizing beetles developmental habitat. Thus carry-over effects led to very different dynamics at the same starting densities in the same current habitat. However, carry-over effects were more subtle and clearly less important for driving competitive dynamics in high quality habitat. This indicates that carry-over effects of past habitat quality can have profound, but highly context dependent, effects on the dynamics and outcome of competition and coexistence over many generations. Given that a majority of examined species show the potential for strong developmental plasticity, carry-over effects could be a common driver of variation in community dynamics and invasion success across natural landscapes with variable habitat quality.