Relevant Degree Programs
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Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - Nov 2020)
A central goal of ecology is to understand what drives the abundance, distribution and diversity of life on Earth. For centuries, biologists have been addressing these questions from a variety of perspectives, and yet we still lack a coherent and mechanistic understanding of what drives these patterns. One process that is shared by all of life on Earth is metabolism. The development and testing of metabolic scaling theory (MST), which formalizes relationships between body size, temperature and metabolism, has revealed remarkable generality in the way that organisms respond to the environment. In spite of extensive documentation of cross-species metabolic patterns, we still lack evidence for how metabolic constraints propagate from the fine to the broad organizational scales. The large gap in our understanding at the level of populations presents a critical challenge for MST. I have combined theory, experiments and data synthesis to test the metabolic underpinnings of biodiversity and its implications for human well-being. Results showed that the temperature-dependence of population dynamics can be predicted from the temperature-dependence of individual metabolism, thus lending strong support for the role of energetic constraints in governing population growth and abundance. Further, I showed that variation in ecologically important traits such as body size has important implications for the nutritional value of aquatic species assemblages, thus linking the processes that structure ecosystems with the benefits they provide. This approach has revealed that understanding what generates and maintains aquatic biodiversity has direct and immediate consequences for human well-being.
Temperature influences biological processes at all levels of biological organization. As such, temperature is a fundamental abiotic variable affecting ectotherm fitness. As human induced climate change persists, the need to understand biological responses to temperature has never been more pressing. One consequence of rapid climate change is an increase in the frequency and intensity of heat waves. Despite substantial interest in the physiological effects of heat stress, it is less clear how individual responses to extreme heat events influence population-level responses such as persistence and population growth. Energy balance is a unifying concept that integrates the effect of temperature across scales. The Energy Limited Tolerance to Stress (ELTOS) framework links physiological models of temperature and oxygen availability to dynamic energy budgets in order to predict the effect of stress on individual reproduction and population growth. Drawing on the ELTOS framework, I tested three critical predictions about individual thermal experience, and how the influence of heat stress scales up from physiological to individual to populations, utilizing the splash pool copepod, Tigriopus californicus. In Chapter 2, I tested the prediction that aerobic energy production declines with increasing heat wave intensity and duration, and that individual reproduction declines similarly. In Chapter 3, I tested the assumption that short-term impacts of heat waves on individual reproduction have persistent effects on longer-term population dynamics. In Chapter 4, I tested for an effect of spatial variation in thermal history on subsequent heat wave survival. Together, these tests provide a comprehensive examination of ELTOS predictions of biological responses to heat waves across scales. My data are consistent with ELTOS predictions that heat wave intensity affects energy balance and subsequent individual reproductive effort. However, I did not find consistent patterns of population dynamics over both short and longer-term time scales. The opposing effect of temperature on different life-history traits that occur over different time-scales likely underlies differences in the effect of short-term heat wave effects on population dynamics over short and longer time periods. Lastly, I found that spatial variation in thermal history, particularly recent heat accumulation, explains reduced survivorship during experimental heat waves.
Networks of Marine Protected Areas are implemented to conserve fish populations, yet their effectiveness is rarely comprehensively examined or adaptively managed. In this dissertation, I evaluate a network of Rockfish Conservation Areas (RCAs) implemented to reverse population declines of inshore Pacific rockfishes (Sebastes spp.). First, I used SCUBA surveys to examine patterns of Black Rockfish abundance compared to spatial and temporal variability in recruitment to determine how recruitment influences population density in and around a RCA. Habitat variables such as complexity and rocky substrate predicted adult Black Rockfish abundance while recruitment did not. Next, I surveyed the fish communities of 35 RCAs and adjacent unprotected areas using a Remotely Operated Vehicle (ROV). Habitat features such as percent rocky substrates and depth influenced the density of Quillback (S. maliger), Yelloweye (S. ruberrimus), Greenstriped Rockfishes (S. elongatus), Kelp Greenling (Hexagrammos decagrammus), Lingcod (Ophiodon elongatus) and all inshore rockfishes combined, while reserve status did not. The results give little indication that demersal fish populations have recovered inside the RCA system. I used aerial observations of recreational fishing from surveys before, during and after 77 RCAs were established and found there was no evidence of a change in fishing effort in 83% of the RCAs. Compliance was related to the level of fishing effort around the RCA, the size and perimeter-to-area ratio of RCAs, proximity to fishing lodges and the level of enforcement. Non-compliance in RCAs may be hampering their effectiveness and impeding rockfish recovery. Lastly, I modeled rocky reef habitat using Random Forest Classification to assess habitat in the RCAs. I combined three habitat metrics with data on compliance, RCA size, rockfish bycatch, and connectivity into a single Conservation Score. The Conservation Score is related to the log reserve ratio, a measure of relative abundance, for Quillback Rockfish. RCAs with low Conservation Scores are not likely to be effective and managers should evaluate the reasons for low scores and address reserve shortcomings in an adaptive spatial management framework. Education and enforcement efforts are critical to the recovery of depleted fish stocks. Continued monitoring and evaluation of the RCAs is essential to rockfish conservation.
Master's Student Supervision (2010 - 2018)
Warming can influence the rate of plant-herbivore interactions through direct effects on individual metabolism, resource use, and growth rates, and via indirect effects on the properties of plant resources and behavior of consumers. Through these processes, temperature can affect the structure and function of food webs, though whether these overall responses reflect primarily direct or indirect effects of temperature is unclear. To begin to address this problem, I quantified the effects of temperature and grazing on primary producer traits and relative abundance to understand how temperature directly and indirectly affects an important aspect of food webs: resource availability to herbivores. I hypothesized that warming would decrease the availability of edible resources to consumers through decreased abundance, body size and shifts among dominant functional groups, and that these effects would be strengthened in the presence of consumers. I tested this hypothesis in freshwater algal-grazer communities maintained across an 11°C temperature gradient over 11 weeks. I observed direct, positive effects of temperature on whole-system oxygen fluxes (i.e. through net primary productivity and ecosystem respiration), and direct negative effects on phytoplankton abundance and body size, with higher relative abundance of small phytoplankton. Herbivores drove shifts in phytoplankton size distributions across the temperature gradient through size-selective consumption of large phytoplankton. Warming shifted species composition among algae from plankton-dominated to periphyton-dominated assemblages, consistent with indirect effects of warming on competitive interactions. Taken together, shifts in abundance, body size and functional group dominance over the temperature gradient decreased the availability of preferred plant resources to filter-feeding zooplankton at warmer temperatures, which may alter food web structure and function, especially under increased grazing pressure. I conclude that resource-availability shifts are predictable with warming, and that temperature-dependent community theory can be expanded to include these indirect effects of temperature on species interactions.
The assembly and persistence of ecological communities is a phenomenon that occurs across large spatial and temporal scales. However, the relative effects of regional versus local processes on community structure are not well understood in marine ecosystems. In order to understand how scale can alter processes that drive variation in community assembly it is necessary to determine patterns of diversity across multiple scales. Here, I used invertebrate epifaunal communities in the foundation species Zostera marina to test 1) whether this marine community exhibits meadow-scale variability through time, and 2) whether we can identify patterns of connectivity and diversity within and among meadows in the same region. I found that seagrass epifaunal communities are variable in terms of their rarefied richness, alpha and beta diversity, and evenness among meadows. In addition, differences in these metrics were detected over the course of a summer season.
An animal's need to balance energy intake with predator avoidance results in trade-offs predicted by optimum foraging theory. These trade-offs may include reducing foraging activity if 1) perception of predation risk is high or 2) abiotic conditions are suboptimal for foraging. Human disturbances such as hikers can influence an animal's perception of predation risk, yet little is known about how hiking affects the foraging behaviour of species in the alpine zone. American pikas (Ochotona princeps) are small, food-hoarding mammals whose foraging ability is restricted by heat. If pikas' ability to forage is further decreased by hiking disturbance it could negatively impact their survival due to reduced food storage. To quantify the effect of hikers on foraging time, I evaluated multiple hypotheses of risk avoidance by simulating disturbance events for 48 pikas in Glacier National Park, BC. I assessed pikas' response to hikers using four indicators of risk behaviour: alert distance (DA), flight initiation distance (DF), exit delay (TE) and delay in return to forage (TR). To test if temperature or distance to trail was more influential to pikas' foraging activity, I conducted behavioural observations on 17 pikas. All simulated disturbance events elicited anti-predator response behaviours in foraging pikas, reducing time available to forage and increasing time spent alert and vigilant. Distance to trail was an important predictor of TE and TR. Pikas near trails (100 m away from trails, which lost an average of 13.2 (SE=1.7, n=16) minutes of foraging time per disturbance event. Temperature, not distance to trail, was the strongest predictor of pikas' foraging activity over a 4-6 hour period. This suggests that human disturbance may be partially mitigated by pikas' behavioural adaptation at less frequented sites. Monitoring pika populations near and away from trails would be well-advised given projected trends in warming climate and potential increases in hiking traffic.