Anthropogenic-induced shifts in climate and natural landscapes can be perilous for freshwater organisms due to their specific niche requirements and physiological constraints. Reductions in the availability of suitable habitat for these species may shift ecological communities and lead to stronger interactions between organisms that require similar resources. In headwater streams, salamanders and crayfish often consume the same prey items and utilize the same interstitial spaces. Considering these similarities, it is likely both compete for interstitial spaces, especially when resources are limited. Yet, little is known about species interactions among stream salamanders and crayfish in the southern Appalachians. Therefore, we conducted a 3x2 factorial artificial stream experiment where we manipulated species identity (1) two salamanders, 2) one salamander, one crayfish, or 3) two crayfish) and refuge density (low or high) to investigate how the strength of interactions varied between black-bellied salamanders (Desmognathus quadramaculatus) and Appalachian brook crayfish (Cambarus bartonii). We hypothesized that 1) crayfish presence would negatively affect salamander growth and survival due to aggressive encounters, 2) the strength of interactions would be intensified with fewer spatial refuges, and 3) the degree of cohabitation would be lower between crayfish and salamanders than between conspecifics.
Results/Conclusions
Our results indicate that significantly higher occurrences of cohabitation between salamanders and crayfish occurred when the refuge density decreased in comparison to other treatment levels (F2,154 = 1.97; P = 0.049). The distances between individuals was not significantly affected by subject identity or refuge density (F5,176 = 0.289; P = 0.919). Changes in growth were not significantly affected by any of our treatments. Overall, our results indicate that a reduction in refuge density translates into a higher probability of cohabitation between the two different species than within the same species. Our results also suggest a growth trade-off may not exist even in environments where interstitial refuges are limited. The strength of intraspecific interactions may be stronger than interspecific interactions in some headwater stream communities where refuge space is limited. Further studies on how cohabitation and interactions are affected by the abiotic environment (e.g. stream flow) and the influence of top predators is a logical next step for understanding and predicting future community changes.