Does dispersal influence the strength of intraspecific competition in a stream salamander?

Abstract

Metacommunity ecology emphasizes the role of dispersal in linking local processes across space. Competition is one such local process that can be affected by dispersal. Dispersal can influence intraspecific trait variation, thereby affecting the strength of intraspecific competition and, consequently, the relative importance of intra‐ versus interspecific interactions. Prior research has shown that spring salamanders, Gyrinophilus porphyriticus, self‐organize within streams by a common trait (body condition) and that dispersal and gene flow along streams vary with slope. Building on this prior work, we tested how dispersal influences the strength of intraspecific competition via one of two spatial mechanisms: (1) spatial sorting of individuals by traits that affect competitive performance or (2) variation in gene flow resulting in evolutionary divergence of traits affecting competitive performance. To test these alternative mechanisms, we conducted a mesocosm experiment with spring salamanders from downstream and upstream sites of streams with low and high rates of dispersal and gene flow. Spatial patterns of intraspecific competitive performance differed significantly in the low‐ and high‐dispersal streams. In the low‐dispersal stream, downstream individuals were better intraspecific competitors than upstream individuals, whereas the opposite was true in the high‐dispersal stream. These differences support the spatial sorting mechanism, reinforcing direct dispersal data showing that high‐performance individuals are more likely to move upstream in the high‐dispersal stream and to remain downstream in the low‐dispersal stream. To our knowledge, this is the first time that spatial sorting has been explicitly identified as contributing to the strength of intraspecific interactions. Our study underscores the importance of integrating natural rates of dispersal into mechanistic experiments to understand spatial variability in the strength of intra‐ and interspecific species interactions.

Elevated temperatures alter competitive outcomes and body condition in southern Appalachian salamanders

“…To evaluate performance of individuals among mesocosm treatments, we used differences in the scaled mass index preand post-experiment referred to as body condition (Peig & Green, 2009;Davenport & Lowe, 2016). We assessed the significance of our treatments using a linear mixed model implemented in R using the lme4 package with our random effect being an individual's mesocosm number (R Core Team 2013; Bates et al, 2015).…”

Evidence for asymmetric competition among headwater stream vertebrates

“…These types of streams are amenable to replication and allow researchers to isolate mechanisms of coexistence within stream communities (Resetarits, 1991). Similar systems have been used in prior experiments involving fish and salamanders (Resetarits, 1995a;Lowe et al, 2004;Davenport & Lowe, 2015). Twelve recirculating systems were constructed using fiberglass enclosures (Red Ewald, Inc., Karnes City, TX) and plastic sumps (Sterilite Corp., Townsend, MA, 68.14 l plastic vessel).…”

“…Briefly, SMI Hydrobiologia (2016) 772:207-213 209 accounts for the scaling relationship between mass and length and more accurately depicts changes in organisms' energy reserves (Peig & Green, 2009, 2010. This measure has been used in prior experiments with stream vertebrates as a direct measure of competition (Resetarits, 1995b;Davenport & Lowe, 2015). From this point forward, we referred to scaled mass as body condition.…”

Selecting for invasive tendencies: the evolution of morphological, physiological, and movement behaviour traits associated with dispersal

“…Many invasive species (including amphibians, birds, fish, and insects) have been found to exhibit certain traits that assist in their dispersal ability, and rapid phenotypic change occurs at expanding range edges (Llewelyn et al 2010;Berthouly-Salazar et al 2012;Laparie et al 2013;Myles-Gonzalez et al 2015;Davenport & Lowe 2016). As climate change and anthropogenic disturbance of natural systems continues, the importance of understanding biological invasions grows, therefore elucidating the impact of evolutionary processes in the spread and ecological impact of invasive species is a vital component of this understanding (Colautti & Lau 2015).…”

“…Natural selection is the conventional mechanism for evolutionary change, whereby individuals that have traits better suited to their local environment will have a fitness advantage (Darwin 1859). Both of these evolutionary mechanisms are prevalent in shaping traits that are associated with accelerating range expansion in invasive species, including birds (Berthouly-Salazar et al 2012), toads (Shine et al 2011;Lindström et al 2013), fishes (Rehage & Sih 2004;Myles-Gonzalez et al 2015), salamanders (Lowe & McPeek 2012;Davenport & Lowe 2016), mites (Van Petegem et al 2015;2016a), and insects (Piiroinen et al 2011;Laparie et al 2013). Understanding trait evolution is a pre-condition for elucidating factors that contribute to shifts in the distributions of invasive species; such shifts have potentially dire consequences for the ecology of native species and the conservation of natural environments (Colautti & Lau 2015).…”