An anthropogenic habitat within a suboptimal colonized ecosystem provides improved conditions for a range‐shifting species

Abstract

Many species are shifting their ranges in response to the changing climate. In cases where such shifts lead to the colonization of a new ecosystem, it is critical to establish how the shifting species itself is impacted by novel environmental and biological interactions. Anthropogenic habitats that are analogous to the historic habitat of a shifting species may play a crucial role in the ability of that species to expand or persist in suboptimal colonized ecosystems. We tested if the anthropogenic habitat of docks, a likely mangrove analog, provides improved conditions for the range‐shifting mangrove tree crab Aratus pisonii within the colonized suboptimal salt marsh ecosystem. To test if docks provided an improved habitat, we compared the impact of the salt marsh and dock habitats on ecological and life history traits that influence the ability of this species to persist and expand into the salt marsh and compared these back to baselines in the historic mangrove ecosystem. Specifically, we examined behavior, physiology, foraging, and the thermal conditions of A. pisonii in each habitat. We found that docks provide a more favorable thermal and foraging habitat than the surrounding salt marsh, while their ability to provide conditions which improved behavior and physiology was mixed. Our study shows that anthropogenic habitats can act as analogs to historic ecosystems and enhance the habitat quality for range‐shifting species in colonized suboptimal ecosystems. If the patterns that we document are general across systems, then anthropogenic habitats may play an important facilitative role in the range shifts of species with continued climate change.

Individual Morphology and Habitat Structure Alter Social Interactions in a Range-Shifting Species

“…We measured the size of each crab (carapace width) to the nearest 0.1 mm and painted the back of each individual with a thin stripe of one of six colors of nail polish for identification. Previous work has shown no effect of more extreme marking (painting of the entire carapace with nail polish) on the behavior of this species [4,14]. Crabs were then allowed to acclimate for an additional 24 h before behavior was assayed (see below).…”

“…The climate-mediated northward range expansion of this historically mangrove-associated arboreal crab has recently resulted in its colonization of the salt marshes of Florida and Georgia [12]. The foundation species in the salt marsh, the grass Spartina alterniflora, differs greatly in structure from mangrove trees leading to the alteration of numerous aspects of this crab's ecology, including behavior [4,13,14]. However, A. pisonii are also found on artificial boat docks within the salt marsh.…”

“…Unlike S. alterniflora, which dominates the salt marsh ecosystem, docks provide a shaded habitat similar to the mangrove canopy and vertical pilings which resemble mangrove trunks. Further, docks mitigate many of the negative impacts this species experiences in the salt marsh, including behavioral changes [14]. Docks, while not themselves a foundation species, are a result of an allogenic ecosystem engineer (humans), which provides structure similar to autogenic engineers, thus altering the flow of resources [1].…”

“…However, claw size in crabs is highly plastic [28]. Many factors related to habitat type can alter claw size, including a more carnivorous diet [29], which A. pisonii experiences on docks [14]. Thus, differences in claw morphology between habitats must be considered to fully understand the impact of habitat structure on the ritualistic aggression behavior of this crab.…”

“…In particular, we expected that the minimal structure provided by marsh grasses would increase the likelihood of a competitor falling in water, thus increasing the riskiness of interactions, leading to a Diversity 2019, 11, 6 3 of 14 reduction in the incidence of ritualized aggression compared to other structure types. Further, we hypothesized that the relatively high rate of carnivory exhibited in the dock habitat [14] would lead to relatively larger claws resulting in a higher rate of victory over conspecific from the salt marsh and mangrove habitats, and that the victor of interactions between crabs from the marsh and mangrove would not be predictable by habitat of origin due to a lack of morphological differences.…”