What are the type, direction, and strength of species, community, and ecosystem responses to warming in aquatic mesocosm studies and their dependency on experimental characteristics? A systematic review protocol

Background Mesocosm experiments have become increasingly popular in climate change research as they bridge the gap between small-scale, less realistic, microcosm experiments, and large-scale, more complex, natural systems. Characteristics of aquatic mesocosm designs (e.g., mesocosm volume, study duration, and replication) vary widely, potentially affecting the magnitude and direction of effect sizes measured in experiments. In this global systematic review we aim to identify the type, direction and strength of climate warming effects on aquatic species, communities and ecosystems in mesocosm experiments. Furthermore, we will investigate the context-dependency of the observed effects on several a priori determined effect moderators (ecological and methodological). Our conclusions will provide recommendations for aquatic scientists designing mesocosm experiments, as well as guidelines for interpretation of experimental results by scientists, policy-makers and the general public. Methods We will conduct a systematic search using multiple online databases to gather evidence from the scientific literature on the effects of warming experimentally tested in aquatic mesocosms. Data from relevant studies will be extracted and used in a random effects meta-analysis to estimate the overall effect sizes of warming experiments on species performance, biodiversity and ecosystem functions. Experimental characteristics (e.g., mesocosm size and shape, replication-level, experimental duration and design, biogeographic region, community type, crossed manipulation) will be further analysed using subgroup analyses

Species diversity and environmental variability: patterns and processes of lacustrine fish community responses in a variable world

Thesis (Ph.D.)--University of Washington, 2015Ecosystems are heterogeneous on multiple scales of space and time, and this variation in abiotic and biotic features confronts organisms with complex challenges. Climate change signals are also often heterogeneous across these scales, and it is important to understand how climate plays out over the landscape due fine-scale variability in habitat. In addition, the temporal scale over which species respond to environmental change may vary across taxa, presenting an opportunity for mismatches in ecological relationships. To date, much work has focused on climate change effects on primary and secondary production in lakes, but mechanisms and community-level processes for higher trophic level organisms remain less clear. This dissertation aims to reveal patterns and processes of fish individual and community responses to environmental change on multiple time scales. In Chapter 1, I developed a bioenergetics model for the threespine stickleback to define ecological demands of this fish under a range of temperatures, indicating that this fish has a different thermal optimum than sympatric fishes. This physiological diversity has possible implications for community composition. Chapter 2 examined the intersection of seasonal variability and life history diversity, and showed that the timing of seasonal lake productivity varied widely across years and that sockeye salmon fry with more protracted migration experienced higher overall survival. Chapter 3 contributes to our understanding of how spatial variability can affect the way that fish communities change over time, and showed that, within a single lake, community change varied by fine-scale location and depended on species-specific responses to temperature. In Chapter 4, we asked how climate-driven changes in lakes can influence phenology and expression in a species trait. These results showed that reproduction in fish is closely linked to physical lake changes. As a whole this research illustrates that lacustrine fishes can be highly susceptible to changes in the environment. However, the responses that we observed depended upon physiological or life history diversity among and within species and diversity within habitats, and upon the scale at which changes are observed in the environment. My hope is that this dissertation will contribute to the understanding of the role of biological diversity in explaining ecosystem processes and observed changes to the environment

Data from: A multi-decade experiment shows that fertilization by salmon carcasses enhanced tree growth in the riparian zone

As they return to spawn and die in their natal streams, anadromous, semelparous fishes such as Pacific salmon import marine‐derived nutrients to otherwise nutrient‐poor freshwater and riparian ecosystems. Diverse organisms exploit this resource, and previous studies have indicated that riparian tree growth may be enhanced by such marine‐derived nutrients. However, these studies were largely inferential and did not account for all factors affecting tree growth. As an experimental test of the contribution of carcasses to tree growth, for 20 yr, we systematically deposited all sockeye salmon (Oncorhynchus nerka) carcasses (217,055 individual salmon) in the riparian zone on one bank of a 2‐km‐long stream in southwestern Alaska, reducing carcass accumulation on one bank and enhancing it on the other. After accounting for partial consumption and movement of carcasses by brown bears (Ursus arctos) and variation in salmon abundance and body size, we estimated that 267,620 kg of salmon were deposited on the enhanced bank and 45,200 kg on the depleted bank over the 20 yr, for a 5.9‐fold difference in total mass. In 2016, we sampled needles of 84 white spruce trees (Picea glauca) the dominant riparian tree species, for foliar nitrogen (N) content and stable isotope ratios (δ15N), and took core samples for annual growth increments. Stable isotope analysis indicated that marine‐derived N was incorporated into the new growth of the trees on the enhanced bank. Analysis of tree cores indicated that in the two decades prior to our enhancement experiment, trees on the south‐facing (subsequently the depleted) bank grew faster than those on the north‐facing (later enhanced) bank. This difference was reduced significantly during the two decades of fertilization, indicating an effect of the carcass transfer experiment against the background of other factors affecting tree growth