How do living systems change in changing environments?

What do these changes mean for human well-being?

Understanding our changing biosphere requires connecting our fragmented knowledge of biological process across scales. My research advances a solution to this challenge by studying the processes that unite all of life on Earth – the metabolic processes by which living systems uptake, store and convert energy, matter and information from their environments to grow and persist. The goals of my research are 1) to identify the mechanisms by which biodiversity influences human well-being; and 2) to predict biological responses to environmental change at multiple scales. I use a broad quantitative and empirical toolkit, working across sub-disciplines and combining theoretical, experimental and comparative analyses with the aim of generating a more predictive understanding of biospheric change and implications for human well-being.

Identifying the mechanisms by which biodiversity influences human well-being

There is increasing concern that the global biodiversity crisis may directly harm human well-being. Yet operational measures of human well-being based on biodiversity have been difficult to implement, despite the strong links between biodiversity and ecosystem function known from ecological theory. My work is among the first to bridge the gap between biodiversity theory and human health by extending statistical and theoretical approaches from ecosystem science to human nutrition science in the context of seafood. With this novel approach, I am generating a mechanistic understanding of the consequences of biodiversity change for human well-being.

For many of the world’s seven billion people, food security is a benefit provided by aquatic ecosystems, and a large variety of wild species are still consumed even though biodiversity is declining worldwide. We used biodiversity-ecosystem functioning theory to test whether biodiversity directly enhances nutritional benefits at global and local scales, by collating and synthesizing nutritional traits of 801 aquatic species. We found that it does, particularly for essential micronutrients, such as calcium and zinc, with the potential to combat the problem of micronutrient deficiencies (‘hidden hunger’) in coastal communities.

Bernhardt, J.R and M.I. O’Connor, 2021. Aquatic biodiversity enhances multiple nutritional benefits to humans. PNAS. [bioRxiv preprint]

Predicting biological responses to environmental change at multiple scales

Effects of rapid metabolic trait evolution on species coexistence

A major challenge for ecology and evolution is to understand how biodiversity is maintained despite the tendency for competition to select for a single best competitor. The strength of competition is a key determinant of biodiversity, and may thereby impact ecosystem functioning. While it is well known that evolution can drive character displacement when species compete for nutritionally substitutable resources, we still do not know what facilitates or constrains adaptation of resource competition traits when limiting resources are non-substitutable (as in essential nutrients). Using a combination of experimental evolution, whole-genome re-sequencing, and competition experiments, we demonstrated that rapid evolution of metabolic traits (e.g. minimum resource requirements, R*) can alter competitive outcomes on ecological timescales and that improvements in resource requirements for different resources were positively associated (i.e. no detectable trade-offs), possibly owing to common metabolic pathways associated with essential resources.

Bernhardt, J.R., Kratina, P, Pereira, A, Tamminen, M., Thomas, M.K.T, and A. Narwani, 2020. The evolution of competitive ability for essential resources. Philosophical Transactions of the Royal Society B. [code and data]

Life in fluctuating environments

A major unknown dimension of global change is how environmental change is altering the informational milieu of living systems. Many organisms maintain steady internal conditions required for physiological functioning through feedback mechanisms that allow internal conditions to remain near a set point. However, living systems, ranging from phytoplankton cells to trees, persist in fluctuating environments not only by responding to change after it has occurred, but also by anticipating change through a variety of ecological and evolutionary cue and signal-based mechanisms. These feedforward mechanisms, in contrast to feedback mechanisms, allow biological systems to prepare or prime themselves for environmental change so that they can adaptively buffer or exploit expected environmental change.

Drawing on concepts from systems biology, physiology and evolutionary biology, we have developed a new framework for understanding how living systems deal with environmental variability which builds upon commonly studied feedback processes to incorporate a range of anticipatory, cue-based feedforward mechanisms, such as phenology. All living systems exploit the information in correlated environmental conditions to predict future environments through feedforward mechanisms. Explicitly considering feedforward processes may dramatically change our predictions of responses to global environmental change.

Bernhardt, J.R., O’Connor, M.I., Sunday, J.M and A. Gonzalez. Life in fluctuating environments. 2020. Philosophical Transactions of the Royal Society B. [code and data]

Scaling individual metabolism to populations and communities

The temperature dependence of highly conserved subcellular metabolic systems affects ecological patterns and processes across scales, from organisms to ecosystems. However, a major gap in our knowledge of how temperature-dependent subcellular metabolism may constrain higher level ecological processes has been at the level of populations. Using theory and experiments, we performed the first critical test of the hypothesis that temperature effects on subcellular metabolism constrain the dynamics of populations and their equilibrium abundance, making a fundamental advance in our understanding of how metabolic constraints shape population responses to changing environments.

Bernhardt, J.R., Sunday, J.M. and M.I. O’Connor, 2018. Metabolic theory and the temperature-size rule explain the temperature dependence of population carrying capacity. The American Naturalist. [data]

Predicting population growth in fluctuating environments

Predicting biological responses to global change requires explicitly confronting role of natural environmental variability at various timescales. Using experiments and a synthesis of thermal niches from 98 phytoplankton species, we showed that thermal variability drives systematic differences between the fundamental thermal niche and the realized thermal niche, advancing the way in which thermal performance curves are used to understand organismal fitness and species distributions in fluctuating environments.

Bernhardt, J.R., Sunday, J.M., Thompson, P.L. and M.I. O’Connor 2018. Nonlinear averaging of thermal experience predicts population growth rates in a thermally variable environment. Proceedings of the Royal Society B. [link][data][code]

Causes and consequences of temperature-dependent body size

The temperature size-rule (TSR), which describes a decrease in body size with increasing temperature is one of the most widely-documented temperature-related patterns among ectotherms; so widely observed as to be dubbed ‘a third universal response to warming’. To date, no complete explanation has been found for why the temperature-size rule should be so commonly observed and should persist after initial temperature changes. I am testing hypotheses about the mechanisms underlying the TSR in Daphnia pulex.