An artificial habitat facilitates a climate-mediated range expansion into a suboptimal novel ecosystem

Abstract

As the geographic ranges of tropical species and ecosystems continue to shift poleward with climate change, it is critical to prediction and management to identify factors that facilitate these expansions. This is especially true for range shifts that involve the decoupling of a shifting species from its historic ecosystem and the colonization of an ecosystem that it has not previously inhabited (i.e. is novel to the shifting species). In cases where the colonized ecosystem is suboptimal for the shifting species, stepping stone refuges may play a critical role in facilitating further expansion. Here we document the facilitation of the northward range expansion of the mangrove tree crab ( Aratus pisonii ) into the previously uninhabited salt marsh ecosystem by artificial boat docks. While the cold tolerance of crabs did not differ between habitats, they were found on docks 36 km and 22 km further north than elsewhere in the salt marsh after the winters of 2016-‘17 and ‘17-’18, respectively. This extended range-edge appears to be a result of docks within the salt marsh acting as a stepping stone refuge by providing this historically tropical species with a relatively warm thermal refuge during the winter that mitigates seasonal population die-backs exhibited elsewhere at the range-edge. Further, population abundances were higher on docks at the range-edge than in the surrounding salt marsh. While artificial habitats often favor the expansion of non-indigenous species, our results demonstrate the facilitation of a native species’ range shift into a suboptimal ecosystem which it has not previously inhabited. The potential for analogous and refuge habitats, artificial or otherwise, to increase the rate and success of range shifts could be critical to the fate of many current and future range shifting species.

An artificial habitat increases the reproductive fitness of a range-shifting species within a newly colonized ecosystem

“…The importance of these effects to the reproductive potential of the population is not yet known. At the extreme range edge, there may be a source-sink dynamic with docks acting as a source, especially after winter die-offs 23 . Even in areas of the salt marsh ecosystem where populations are firmly established, the higher reproductive potential of crabs on docks may allow them to have a disproportional impact on the population and may serve to accelerate repopulation after an extreme event, such as a tropical storm 25 or an extreme winter 23 .…”

“…Given the importance of reproduction to colonization success 10,11 and the relatively small area of analogous habitats within colonized ecosystems, individuals occupying analogous habitats could play vital roles in the persistence and continued expansion of shifting species. Habitat analogues may even accelerate the rate of expansion through the production of more and/or higher quality offspring, an effect that could be enhanced if the habitat also allows for increased geographic penetration into the colonized ecosystem 23 . Thus, understanding the role of analogous habitats will be critical for the management and prediction of range-shifts.…”

Contrasting signatures of introgression in North American box turtle (Terrapenespp.) contact zones

“…These can allow species to disperse northward in response to climatic conditions, but do not necessitate complete continuity between patches. Recent research in the Gulf Coastal Plain serves as a proof-of-concept, with latitudinal range shifts being successful despite artificially-created refuge habitat that is both sub-optimal and previously uninhabited by the focal species (Cannizzo & Griffen 2019).…”

Microclimate and resource quality determine resource use in a range-expanding herbivore

“…At ecological margins, warming also increases the distribution and connectivity of microhabitats that are suitable for egg-laying [21]. Microclimatic variation could thereby drive range expansion at a faster rate than ambient temperatures would predict, and may account for recent range expansions by temperature-sensitive species across previously unsuitable landscapes [11,54,55]. Behavioural thermoregulation in ectotherms (e.g.…”