Forests, Functions, and Food Webs : Riparian processes through an ecological and molecular lens

Abstract: Riparian systems are critical ecological interfaces that have a significant impact on the surrounding aquatic and terrestrial ecosystems. The riparian and surrounding systems have significant roles in regulating energy flow, providing essential nutrients, and supporting unique species, making them important for ecosystem function. Both the aquatic and terrestrial ecosystems are reliant on the reciprocal exchange of energy subsides to maintain productive and stable food webs. Retention of forested buffers along streams during tree felling operations is a common management technique used to protect aquatic resources and conserve the surrounding ecosystem processes. Measuring the effects of forestry practices on the function and food webs of riparian predators is vital to making forest management decisions that strengthen and protect these fundamental services. Insight into predator function and predator-prey interactions using powerful molecular techniques can further the understanding of these complex systems and help to mitigate the effects of forestry practices.This thesis explores the functional diversity, food webs, and predator-prey interactions in riparian systems impacted by forestry felling practices. I have studied the effects of clear-cutting and forested buffer zones on riparian functional diversity through the assessment of functional richness and redundancy of spider and plant communities. In addition, I have both validated and used stable isotope analysis and DNA metabarcoding to investigate the primary food sources and prey choices of riparian predators. Riparian buffer size had no direct effect on the functional richness or redundancy of riparian spiders and vascular plants. However, riparian buffer variables such as canopy closure, buffer density, and vegetation coverage did have direct impacts on both spider and plant function. Most riparian spiders and brown trout received a significant majority of their food source from the terrestrial environment and the presence or absence of a riparian buffer did not effect this outcome. However, web-weaving spiders in unbuffered systems were more likely to exploit aquatic resources as a primary food source. Overall, the responses of predator function and food webs to forestry practice are site-specific.