Habitat conservation alters the settling pattern but not its influence on the reproduction of Mallard

Background/Question/Methods

Understanding the ecological factors driving reproduction is one of the essential tasks in population ecology. Large-scale patterns of reproduction in the North American Mallard (Anas platyrhynchos) population are driven by their settling patterns, wetland habitat conditions, and density dependent processes. However, recent large-scale environmental and habitat changes may have altered the historical relationships governing mallard recruitment. Our objective is to examine the relationship between the reproduction of mid-continent Mallard population and recent distributional shifts in relation to environmental change and land use. We developed a hierarchical Bayesian modeling framework to estimate Mallard reproductive rates from parts collection and band-recovery data with explicit linkages to settling patterns and environmental and land use information. Settling patterns were indicated by mean latitude of Mallard distribution, which was weighted by their breeding population size, and land use was indicated by the area enrolled in Conservation Reserve Program. Candidate models including the additive or interactive effect of settling pattern and land use were considered. DIC and WAIC values were used to select the model with the best goodness of fit while accounting for model complexity. The posterior parameter estimates of the best model were then examined.

Results/Conclusions

The model that included the effect of settling pattern but not land use showed that Mallard reproduction was slightly higher (posterior mean: 0.04, 95% credible interval: -0.07, 0.14) when they settled in more northern latitudes. However, when land use was included in the model, it was revealed that Mallard reproduction was much lower (posterior mean: -0.17, 95% credible interval: -0.35, 0.01) when they settled in the north, except that mid-continent Mallard tended to settle in the more southern portion of their distribution since 1993. The change of their settling pattern was seven years after the first enrollment of Conservation Reserve Program. As a matter of fact, the model including the additive effect of settling pattern and Conservation Reserve Program enrollment with five-year lag had the best model fit among all candidate models, according to WAIC values. Model selection based on DIC values showed a similar pattern. Thus our results suggest that Conservation Reserve Program practices may have altered the settling pattern of mid-continent Mallards, but not the relationship between settling pattern and reproduction.