Dispersal barriers and climate determine the geographic distribution of the helicopter damselfly Mecistogaster modesta

Abstract

1. Species? ranges are typically constrained by the interplay of physical barriers todispersal, environmental requirements such as suitable climatic conditions andbiotic constraints such as from predation or competition. However, teasing apartthe relative importance of these constraints in determining species distributionsstill represents a major challenge for ecologists.2. The Neotropical damselfly Mecistogaster modesta (Coenagrionidae: Odonata)inhabits wet and moist forests in mainland Central America and north-westernSouth America. This habitat specialist spends its larval development exclusivelyin tank bromeliads, where it acts as a keystone predator within the aquatic foodweb. Although tank-forming bromeliads occur from the southern United Statesthroughout most of South America, M. modesta is absent from the Caribbeanislands and South America south-east of the Andes mountain chain.3. We employed species distribution models to explore the relative importance ofphysical barriers (Andes mountain range and oceanic barriers), climate (meanannual temperature and annual precipitation) and biotic interactions (competitionfrom other bromeliad-dwelling odonates) in limiting the geographic distributionof M. modesta.4. We found that dispersal barriers strongly limit the geographic distribution ofM. modesta. In addition, its range is restricted by low temperatures and low precipitation.Competition from other bromeliad-dwelling odonates was not importantin limiting the damselfly?s range. Because of the physical barriers todispersal, M. modesta does not occupy its full potential geographic range. Specifically,our model predicted suitable habitat on the Caribbean islands and throughoutmost of South America, where the species is currently absent.5. These findings have important conservation implications, particularly as the aridificationof rainforests and subsequent localised extinctions due to climate changecontinue. On the other hand, the species may respond to warming temperaturesby tracking climate to higher elevations, with subsequent effects on na?ıve highelevationbromeliad food webs. An upwards migration could also increase theprobability of M. modesta overcoming the dispersal barrier presented by theAndes, enabling the damselfly to invade large areas of suitable habitat in SouthAmerica.