Environmental Niche Adaptation Revealed Through Fine Scale Phenological Niche Modeling

Aim Phenology, the temporal response of a population to its climate, is a crucial behavioral trait shared across life on earth. How species adapt their phenologies to climate change is poorly understood but critical in understanding how species will respond to future change. We use a group of flies ( Rhaphiomidas ) endemic to the North American deserts to understand how species adapt to changing climatic conditions. Here we explore a novel approach for taxa with constrained phenologies aimed to accurately model their environmental niche and relate this to phenological and morphological adaptations in a phylogenetic context. Taxon Insecta, Diptera, Mydidae, Rhaphiomidas Location North America, Mojave, Sonoran and Chihuahuan Deserts. Methods We gathered geographical and phenological occurrence data for the entire genus Rhaphiomidas , and, estimated a time calibrated phylogeny. We compared Daymet derived temperature values for a species adult occurrence period (phenology) with those derived from WorldClim data that is partitioned by month or quarter to examine what effect using more precise data has on capturing a species9 environmental niche. We then examined to what extent phylogenetic signal in phenological traits, climate tolerance and morphology can inform us about how species adapt to different environmental regimes. Results We found that the Bioclim temperature data, which are averages across monthly intervals, poorly represent the climate windows to which adult flies are actually adapted. Using temporally-relevant climate data, we show that many species use a combination of morphological and phenological changes to adapt to different climate regimes. There are also instances where species changed only phenology to track a climate type or only morphology to adapt to different environments. Main Conclusions Without using a fine-scale phenological data approach, identifying environmental adaptations could be misleading because the data do not represent the conditions the animals are actually experiencing. We find that fine-scale phenological niche models are needed when assessing taxa that have a discrete phenological window that is key to their survival, accurately linking environment to morphology and phenology. Using this approach, we show that Rhaphiomidas use a combination of niche tracking and adaptation to persist in new niches. Modeling the effect of phenology on such species9 niches will be critical for better predictions of how these species might respond to future climate change.