Characterising food web responses to climate change using a combination of traditional and molecular tools

Abstract

Freshwater ecosystems are considered hot spots for biodiversity and provide a wide range of ecosystem services for human beings. A variety of natural and anthropogenic stressors are now threatening the stability and prosperity of these ecosystems. In particular, climate change and pollution are the main stressors impacting all freshwater ecosystems on Earth. In this mix of multiple stressors, climate change is already having profound impacts, and is predicted to result in large-scale population collapses, species range shifts, and local species extinctions, as well as altered ecosystem properties. Scientists have spent considerable efforts in recent years investigating how these perturbations might impact food web structures and dynamics to predict potential future scenarios, but much of this work has been hindered by the slow pace of data generation using traditional techniques. Thus, there is a need to adopt and develop new approaches that can answer questions and generate data at a much higher pace. Molecular tools can address this issue by generating millions of DNA sequences in a short period of time with the potential to build food webs in a very reliable way. Therefore, a detailed understanding of food webs and their interactions is critical to predict what effects climate change will have in the near future, and we need to find faster and cheaper ways of building the necessary evidence base. This will ultimately improve our ability to forecast how communities and ecosystems will respond to global change and anticipate which species (and systems) are more likely to deteriorate under these new conditions. In this thesis, I have used a combination of traditional and molecular tools to characterize the diet of a widely distributed generalist predator. DNA sequencing revealed a higher number of links compared to traditional microscopy, but protocols need to be refined to accurately quantify each link. In addition to this, I carried out two sets of laboratory experiments to quantify warming impacts on freshwater invertebrate interactions. Functional response experiments showed increased feeding rates with warming, while qPCR was not able to detect changes in DNA retention time in predator gut contents.