The geographic range areas of plant and animal species vary across twelve orders of magnitude and the range sizes of congeners that utilize the same general habitat can vary widely, spanning 2-3 orders of magnitude. The factors that determine range size and the reasons for such broad variation across species is a fundamental question in ecology and one with important consequences for conservation. Range size is a strong predictor of extinction risk, and the factors controlling range size may also influence the extent to which species are able to shift their distributions in response to climate change. Using data from several species of libellulid dragonflies, we examined how four factors hypothesized to be related to range size were correlated with species range areas across North America. These factors include niche breadth (larval distribution across a local habitat gradient), body size, extinction-colonization dynamics, and dispersal behavior all of which were measured at a local scale. Range area was estimated using OdonataCentral, a compilation of data on species distributions, while local scale data were taken from a long-term survey of ponds in and around the E.S. George Reserve (ESGR) in southeast Michigan and an experimental assessment of dragonfly dispersal behavior within the ESGR.
Results/Conclusions
Data from the local scale were predictive of the size of species’ ranges at the continental scale. One aspect of niche breadth, the range of habitat permanence across which species occur, was positively related to range size. However, the breadth of larval distributions across different top predator communities was unrelated to range size. Body size, including total body size and relative wing size, was also unrelated to species range areas. There was mixed evidence for a positive correlation between local colonization and extinction rates and range size. This relationship was found in the majority of species but there were outliers to this pattern. A striking finding was that dispersal (distance and rate) measured at the level of a single landscape was significantly positively related to range size across North America. Taken together these results indicate that niche breadth across a gradient of habitat permanence, rates of extinction and colonization, and dispersal behavior are all positively correlated with and may predict species’ continental scale range sizes. The connection between species’ local scale distributions, mobility, and continental range size support the use of range size as a tool in assessing species resilience to local or regional environmental change.
