Habitat requirements and ecological niche of two cryptic amphipod species at landscape and local scales

Abstract

Cryptic species are phylogenetically diverged taxa that are morphologically indistinguishable and may differ in their ecological and behavioral requirements. This may have important implications for ecosystem services and conservation of biodiversity. We investigated whether two ecologically important cryptic species of the freshwater amphipod Gammarus fossarum (types A and B) are associated with different habitats. We collected data on their occurrence at both the landscape scale (large watersheds) and at the local scale (river reach) to compare macro‐ and microscale environmental parameters associated with their presence. Analysis of the landscape scale data showed that occurrence of types A and B differ with respect to watershed and river size and, interestingly, human impact on river ecomorphology. Whereas type B was mainly found in less forested areas with higher human impact, type A showed the opposite occurrence pattern. Analyses of the local scale data suggested that habitats occupied by type A were characterized by larger gravel, larger stones and less macrophytes than habitats occupied by type B. The landscape and local data set showed contradicting patterns with regard to stream size. Overall, the observed differences between the two types of G. fossarum most likely reflect ecological differences between them, but alternative explanations (e.g., historical colonization processes) cannot be completely ruled out. Our study underlines that common cryptic species can differ in their ecology and response to anthropogenic influence. Such differences in habitat requirements among difficult‐to‐identify taxa present a challenge for biodiversity and ecosystem management. Our results emphasize the importance of conservative and precautionary approaches in maintenance of habitat diversity and environmental heterogeneity.

Lessons from the macroinvertebrates: species‐genetic diversity correlations highlight important dissimilar relationships

“…S2), which likely reflects colonisation history (dispersal), or natural selection due to limiting environmental factors upstream. These findings suggest that G. fossarum and other Amphipoda species may be affected by different local selective pressures compared to EPT species, either through differences in niche occupancy (e.g., Eisenring et al, 2016) or strong competitive exclusion. This may account for our positive a-SGDC between Amphipoda species and G. fossarum A and null or negative a-SGDCs for all other comparisons.…”

“…These findings suggest that G . fossarum and other Amphipoda species may be affected by different local selective pressures compared to EPT species, either through differences in niche occupancy (e.g., Eisenring et al ., ) or strong competitive exclusion. This may account for our positive α‐SGDC between Amphipoda species and G .…”

“…Gammarus fossarum is an ecologically important amphipod complex that has colonised the Rhine drainage since the Pleistocene (Müller, ). We chose to measure genetic diversity (using microsatellites) of these two species (Altermatt, Alther & Mächler, ; Eisenring et al ., ), as they are important for ecotoxicology, biodiversity and are relatively widely distributed, which is a precondition for obtaining genetic data from many populations in a given study. In contrast, many EPT species are only found at a few sites (1 to 10 sites), which limits large‐scale genetic studies across many populations and across environmentally diverse systems, including the Rhine river network, which is the focus of this study.…”

Cryptic species as a window into the paradigm shift of the species concept

“…Assuming that cryptic species significantly overlap in their ecological niche space, niche differentiation cannot explain their coexistence (Chesson, 2000). Several studies addressed this issue using various model organisms, including rotifers (Montero-Pau, Ramos-Rodr ıguez, Serra, & G omez, 2011;Ortells, Gomez, & Serra, 2003), nematodes (De Meester, Derycke, Bonte, & Moens, 2011;De Meester et al, 2016;Derycke et al, 2008), different amphipods (Cothran, Henderson, et al, 2013;Cothran, Noyes, & Relyea, 2015;Cothran, Stiff, Chapman, Wellborn, & Relyea, 2013;Dionne, Vergilino, Dufresne, Charles, & Nozais, 2011;Eisenring et al, 2016;Fi ser et al, 2015;Wellborn & Cothran, 2004), chironomids (Pfenninger & Nowak, 2008), bugs (Saleh, Laarif, Clouet, & Gauthier, 2012), bumble bees (Scriven, Whitehorn, Goulson, & Tinsley, 2016), fig wasps (Zhang, Lin, & Hanski, 2004) and bats (Ashrafi, Beck, Rutishauser, Arlettaz, & Bontadina, 2011;Nicholls & Racey, 2006;Rutishauser, Bontadina, Braunisch, Ashrafi, & Arlettaz, 2012). These studies unveiled emerging commonalities in co-occurrence patterns and unsolved issues with important implications for nature conservation.…”

Fluvial network topology shapes communities of native and non‐native amphipods

“…It has been shown in various studies of aquatic invertebrates, including amphipods, that specific environmental factors are also important drivers of community structure (e.g., Eisenring et al. , Kaelin and Altermatt ). However, the past focus on environmental factors has only let to a partially satisfying explanation of community dynamics, and the inclusion of network components has been acknowledged more recently (Tonkin et al.…”