Research

(For a very non-technical, jargon-free description of my research, look over here!)

Environmental change is everywhere: from the rising and setting of the sun and the turning of seasons, to the profound ways that we humans are modifying our environment. Variation in abiotic and biotic conditions create complex challenges for living organisms. The traits of organisms – including their physiology and behavior, as well as their capacity to evolve – determine how they meet these challenges. Ultimately, this influences the ecology of populations, communities, and entire ecosystems. Through my research I seek to understand:

• Mechanisms that link organismal physiology to population, community, and ecosystem ecology (a.k.a. Trait-based ecology, see Kremer et al. 2016).
• Feedbacks between evolution, phenotypic plasticity, and ecological dynamics
• Consequences of global change for freshwater and marine ecosystems

As a quantitative ecologist, I use a combination of mathematical, statistical, and experimental approaches to pursue these questions. Most of my current projects involve phytoplankton, tiny photosynthetic organisms inhabiting lakes and oceans. I care deeply about advancing a strong, quantitative, and conceptually driven understanding of ecology: much of what I do focuses on developing and testing ecological theories using a combination of large data sets, diverse statistical tools, mathematics, and targeted experiments.

More specific summaries of major research areas follow:

1. Thermal ecology of phytoplankton
2. Competition, coexistence, and evolution in fluctuating environments.
3. Slow phenotypic plasticity and ecological dynamics
4. Effects of climate change on the ecology & evolution of plankton
5. Statistical ecology (or seeds, rats, flowers, and fish?)

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1. Thermal ecology of phytoplankton

As a result of rising temperatures, species distributions will shift pole-wards, leading to altered patterns of diversity across the world’s oceans (Thomas et al. 2012).

Temperature has a strong effect on the growth of phytoplankton. Species exhibit unimodal relationships between growth rate and temperature (thermal performance curves, or TPCs). Each species has an optimum temperature, where grows most quickly, and a finite range of temperatures over which it can grow at all (its thermal niche). But there is significant variation in these thermal traits among species. Over the last decade, I have been studying differences in thermal traits among different species, including how these differences: (i) affect the competition and coexistence of species, (ii)  relate to the evolutionary history, ecology, and spatial distributions of species, and (iii) evolve experimentally in laboratory experiments. Much of this work was inspired by ongoing collaborations with Mridul Thomas, as well as Elena Litchman and Chris Klausmeier.

See, e.g.: Thomas et al. 2012, Thomas et al. 2016, Kremer et al. 2017, Aranguren-Gassis et al. 2019

2. Competition, coexistence, and evolution in fluctuating environments.

When evolution is slow, divergent selection leads to two coexisting species with different trait attractors (A, B); but rapid evolution leads to trait convergence, supporting only on species (Kremer & Klausmeier 2013).

Organisms inhabiting fluctuating environments face several challenges. Traits that make a particular species well suited to one set of conditions may reduce its growth when conditions change. Evolution through selection can counteract these effects, allowing species to shift their traits (or strategies) for dealing with fluctuations in response to environmental change. Evolution can lead to differentiation and coexistence among species, supporting diversity, but sufficiently rapid evolution can also undermine coexistence based on temporal variability. This work is part of a broader study of how eco-evolutionary dynamics inform our understanding of communities, using adaptive dynamics and quantitative genetics approaches.

See: Kremer & Klausmeier 2013, BEACON blog post, and Kremer & Klausmeier 2017, Edwards et al. 2018

3. Slow phenotypic plasticity and ecological dynamics

Individuals with identical genotypes can express different phenotypes (traits) in different environments – think for example of a chameleon changing its skin color to match its surroundings. This phenomenon is known as phenotypic plasticity. It is often convenient to assume that plastic phenotypic changes happen faster than the environmental changes that elicit them. However, this is not always true. When traits change more slowly, complex interactions between past and present conditions arise, affecting basic ecological dynamics like population growth. With Sam Fey and David Vasseur, supported by a new grant from the National Science Foundation, I am studying how slow phenotypic changes affect our understanding of population and community ecology, using thermal acclimation in freshwater phytoplankton as a model system.

See: Kremer et al. 2018

4. Effects of climate change on the ecology & evolution of plankton.

Over most of the world’s oceans, climate change is driving increases in ocean temperatures and altering the availability of essential nutrients. Predicting the effects of these environmental changes on species distributions, community composition, and critical ecosystem functions is essential. I study how changing thermal regimes may redistribute species across the oceans. I am also investigating the role evolutionary adaptation may play in mitigating the effects of climate change. Empirically, we can use experimental evolution to investigate adaptation to elevated temperature under controlled laboratory conditions. Computationally, large scale Earth Systems Models (resolving ocean circulation, physics, and chemistry) offer a means of considering how evolution influences the response of planktonic communities to climate change, especially in novel high temperature environments  (Collaborative work with Charles Stock, David Vasseur, and Jorge Sarmiento).

See: Thomas et al. 2012, O’Donnell et al. 2018, Aranguren-Gassis et al. 2019

Over the next ~100 years, regions of the worlds oceans exceeding 31 C will increase (RCP 8.5 Scenario). These are regions where the functioning of current plankton populations may decline, without a rapid evolutionary response.

5. Statistical ecology (or seeds, rats, flowers, and fish?)

Ecologists and evolutionary biologists should be empowered to design experiments offering the strongest possible tests of their driving questions, rather than being constrained by the format of standard out-of-the-box statistical methods. To this end, I regularly engage in collaborations developing and applying techniques ranging from maximum likelihood analysis and nonlinear regression to hierarchical/generalized linear mixed models. Among other things, this has led to exciting and rewarding work on everything from seed dispersal by giant rats, to floral evolution, population genetics, the rescue of isolated fish populations, and the factors connecting diversity and ecosystem function.

See: Seltzer et al. 2015, Royer et al. 2016, Prunier et al. 2017, Bannar-Martin et al. 2017