Total Rewiring, Total Turnover, and Traits
As fish species’ traits may have high plasticity (Frimpong & Angermeier 2010), detecting relationships between traits and fish interaction dynamics can be an especially arduous task. Furthermore, given that rewiring can be both an active and/or passive process, it is perhaps especially difficult to identify key traits describing their ability to rewire. For example, a predator will actively rewire when it switches a prey item, whereas its prey passively rewires in response. In this case, we do not expect the predator and prey to exhibit the same traits. As traits related to the passive andactive process of rewiring likely differ, we do not expect to find a very strong relationship between any single trait and the total number of rewirings.
The significant relationship we found between the total number of rewirings and the interaction between the maximum length of a species and its piscivore status likely captures traits associated withactive rewiring. Indeed, larger species of piscivores generally do consume a larger range of prey size than their smaller counterparts (Gaeta et al. 2018). In addition, when holding maximum length constant, we also captured a significant negative relationship between piscivore status and the total number of rewirings indicating that overall non-piscivores have a higher total number of rewirings. This negative relationship may be in part due to many smaller non-piscivorespassively rewiring with a few larger key predators. Additionally, as our network captures more than food web dynamics, this negative relationship may also be capturing rewiring due to competition and other biological interactions. If this is the case, lower trophic levels may be more heavily competing with different species for space and food across seasons whereas piscivores may maintain competitive interactions with the same species year-round.
Interestingly, all species that contributed to species turnover and thus the total number of species turnover interactions, were those that also preferred large rivers. Given this, we strongly suspect that these fish may be seasonally migratory species. Regarding the total number of species turnover interactions, we were unable to find a specific trait that explains its variability. However, we found that Micropterus salmoides explained almost 25% of the total number of species turnover interactions. This result is not surprising as this species has been shown to exhibit trophic plasticity allowing them to be a successful invasive species even in stable food webs (Almeida et al. 2012).