Functional traits predict whether butterfly species track their fundamental niches

A species’ ability to colonize habitat patches and expand its range is likely determined by its population growth rate and dispersal ability, though examining this hypothesis has been difficult due to a lack of natural history data. As climate change shifts functional niches poleward, and species’ face higher risks of extinction at their equatorial range limits, understanding species’ range shift abilities is becoming increasingly important. One way to determine how well a species can shift or expand its range is to compare the species’ realized niche to its fundamental niche. Here we ask whether the realized niche of butterfly species exhibiting strong dispersal abilities and high population growth rates is closer to their fundamental niche than those of poor dispersers with low growth rates.

We used 400,000 observations of over 60 North American butterfly species to calculate species-specific population growth rates at small population sizes, reflecting conditions of small colonizing populations at range edges, and obtained expert-based measures of dispersal ability for each species. Using these data, combined with key environmental measurements, we modelled differences in fundamental vs realized niches.



Preliminary results show that species with high population growth rates and strong dispersal abilities have realized niches that more closely match their fundamental niches; these species may more easily shift and expand their ranges with climate change. Poor dispersers with low population growth rates are less able to expand their realized niches to fill their fundamental niches, and should be prioritized for conservation interventions.