Microbial ecology and evolution

a) Marine microbes: We are currently involved in several projects related to the lower trophic levels of the marine food web; mostly, phytoplankton and/or marine viruses. We are interested in understanding how the microbial ability to react during ecological time to environmental changes (i.e. phenotypic plasticity) affects the species distribution and dynamical interactions in the short (ecological timescale) and the long term (evolutionary timescale).

To that end, we have developed models that allow us to understand the ecological and evolutionary implications of such plasticity. For example, the implications of phytoplankton regulation of their nutrient-uptake capacity and rate in response to changes in nutrient availability, which also influences their cellular elemental ratio. We have also explored the implications of changes in viral traits that occur after changes in the physiological state of the microbial host.

Past and present collaborators and co-authors include Simon Levin from Princeton, Steve Allison and Adam Martiny from U.C. Irvine, Mike Lomas from Bigelow, and Elena Litchman and Chris Klausmeier from Michigan State University.

b) Bacterial spatio-temporal patterns: With Ricardo Martinez-Garcia from Princeton, Carey Nadell from Dartmouth, and Knut Drescher from the Max Planck Institute for Terrestrial Microbiology, we are using physics observables to understand the ecological and evolutionary implications of the biofilm matrix (which allows cells to stick together) during the initial stages of the colonization of different environments. To that end, we combine our experimental observations with toy models that allow us to explore environments beyond the constraints imposed by laboratory conditions.

Catastrophic shifts and emergent patterns

In a clear example of how physics concepts can help understand better the ecology of an ecosystem, we use the theory of phase transitions to study whether real ecosystems undergo a catastrophic regime shift (a sudden irreversible change from one state to another, e.g. vegetation to desert), or a more avoidable and smoother continuous one. Importantly, such transitions can be evidenced by significant qualitative changes in, e.g. vegetation spatial distribution, and influence the resilience and robustness of the ecosystem. We use data we take in the field to inform theoretical models with which we study the associated emergent patterns and potential transitions.

We are interested in a variety of systems but, currently, we focus mainly on vegetation dynamics and how the interactions with resources or fauna may alter the expected spatio-temporal patterns and transitions. We are also working on finding ways to actually transform these transitions, which can help design policies to manage natural resources aiming at avoiding sudden collapses, or design restoration strategies.

Collaborators and co-authors in these projects include Simon Levin, Corina Tarnita and Robert Pringle from Princeton, Efrat Sheffer from the Hebrew University of Jerusalem, and Miguel A. Muñoz from University of Granada.

Marine food webs

Food webs are a graphic representation of the trophic relationships between species present in an ecosystem. Most of the time, food webs are modeled from a static perspective, which overlooks the high dynamic character of those trophic interactions. My collaborators and I aim to develop simple yet realistic dynamic models that improve our understanding of important ecological and evolutionary aspects of the marine food web.

We aim at devising models at an intermediate level of complexity, between the very simple but unrealistic and unstable typical predator prey model, and the very complicated and extremely data-expensive physiologically-structured models. As an example, we are developing a model to study how the most important commercial fish species in the Barents Sea will react to different future scenarios (e.g. changes in fishery management, climate change, or catastrophic events like oil spills). We consider that both the ecology and evolution of the different species present in the food web, and therefore account for potential eco-evolutionary interactions.

Collaborators include Mia Eikeset from the Center for Ecological and Evolutionary Synthesis (Norway), and James Watson from Oregon State University. These projects have been funded through the on-going international initiative GreenMar.

Interactions ecology-evolution

Common to all the topics above is the fact that ecology and evolution interact to shape ecosystems. In the case of microbes, their short generation time and vast offspring number make it easy to observe mutations occurring at the ecological timescale. In the case of the marine food web, the fact that there are so many timescales present across trophic levels ensures that the evolution of some organisms of that network will influence the ecological relationship with others.

We are currently involved in several projects in which we try to understand the consequences that eco-evolutionary interactions have for the focal system. Some of those projects are listed above. Others aim to explore the links between micro- and macro-evolution (e.g. to what extent the former allows us to understand and predict the latter), as part of an ambitious international research initiative led by Nils Ch. Stenseth, from the Center for Ecological and Evolutionary Synthesis (Norway).