Range shifts and emergence phenology advances in odonates (dragonflies and damselflies) are interrelated across Europe and North America

Background/Question/Methods

Unprecedented rates of climate change, land use change and land use intensification profoundly alter biological communities and increase species extinction rates. Insects are thought to be at considerable risk, but how species respond may lessen risks of extirpations. Insects show varying degrees of spatial and temporal responses to climate change, but there remain critical gaps in understanding how these strategies relate to each other, and whether ecological traits can be used to identify threatened species. In this work, we ask: do species that shift their northern range boundaries northward also show greater phenology shifts? Further, do biological traits predict range shifts at species’ northern range limits, and do similar biological traits that predict range expansions also predict shifts in species emergence phenology? We assembled approximately 2 million georeferenced observations of European and North American odonate species to answer our questions using both Bayesian and frequentist statistics. We assessed range and phenological shifts of European and North American odonate species between two time periods (1980-2002 and 2008-2018) to measure the strength and direction of the association between both responses. Trait-based predictions were tested to explain mechanisms underlying range and phenology shifts.

Results/Conclusions

We uncovered a significant relationship between range and phenology shifts and found that these responses converge across continents. Species shifting their northern range limits towards higher latitudes also tend to advance their emergence phenologies over time. We also discovered that mechanisms underlying spatial responses are not related to ecological traits, but to the geographic position of species ranges. Widespread and southern species tend to shift their range limits more strongly towards higher latitudes compared to northern species. Exposure to higher rates of temperature change and climate variability in northern latitudes may contribute to the cause of this finding. In contrast, phenological changes are related to only one ecological trait, breeding habitat type, but the effect size is strong. Lentic species (i.e. fast moving water dwelling species) and habitat generalists tend to advance their emergence phenologies more strongly than lotic species (i.e. slow moving water dwelling species). Oviposition, body size, flight duration, and geographic characteristics of species ranges were not related to phenological shifts. While species traits have been abundantly studied for their potential in identifying species threatened by climate change, we show that they cannot be used reliably across taxa for this purpose. This raises concern in identifying threatened species.