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Experimental Ecology

Biology Master, ENS
Year : M2
Semestre : S1
ECTS : 3
Responsable : Silvia De Monte
Autres enseignants : Corina Tarnita (Princeton University, USA), Rob Pringle (Princeton University, USA), Paul Rainey (New Zealand Institute for Advanced Studies), Jean-François Le Gaillard (CEREEP-Ecotron IleDeFrance), Sandrine Adiba (EEM, IBENS)
Type d’enseignement : cours
Volume horaire : 30h

Aims :The course provides an overview of mechanistic approaches to the dynamics of biological populations. The accent will be set on theoretical models and their qualitative and quantitative test.

Theme :The course presents a series of topics in ecology and eco-evolutionary dynamics.
Focusing primarily on quantification and prediction of ecological determinants, the course will discuss the correspondence between theoretical predictions and observations derived from controlled experiments.
The teaching will be complemented by a hands-on experience on microbial populations, in the form of simple experiments conducted on paradigmatic bacterial organisms.

Organisation :
Morning : Introduction to the course (Silvia De Monte), Presentation of ecological and evolutionary experiments conducted on the bacterium P. flurescens (Paul Rainey)
Thanks to their fast demographical dynamics, microbial populations allow to explore ecological and evolutionary processes in real time, and to perform experiments in controlled environmental conditions. The bacterium Pseudomonas fluorescens allowed the reproduction in the lab of evolutionary phenomena such as adaptive radiation, the evolution of bet-hedging responses to changing environments, and shifts in the level of selection. I will discuss their observation and their ecological and genetic underpinnings.
Afternoon : Planning an experiment with P. fluorescens (Sandrine Adiba, Silvia De Monte, Paul Rainey).

Morning : Causes and consequences of spatial patterning at different scales (Corina Tarnita and Rob Pringle).
Self-organized spatial vegetation patterning is widespread and has been described using models of scale-dependent feedback between plants and water on homogeneous substrates. As rainfall decreases, these models yield a characteristic sequence of patterns with increasingly sparse vegetation, followed by sudden collapse to desert. Thus, the final, spot-like pattern may provide early warning for such catastrophic shifts. In many arid ecosystems, however, termite nests impart substrate heterogeneity by altering soil properties, thereby enhancing plant growth. In addition, due to competition for resources, termite mounds are also spatially patterned. We show that termite-induced heterogeneity interacts with scale-dependent feedbacks to produce vegetation patterns at different spatial grains. Although the coarse-grained patterning resembles that created by scale-dependent feedback alone, it does not indicate imminent desertification. Rather, mound-field landscapes are more robust to aridity, suggesting that termites may help stabilize ecosystems under global change. Furthermore, the spatial patterning induced by termite mounds scales up to the rest of the ecosystem and increases its productivity.
Afternoon : Setting up an experiment with P. fluorescens (Sandrine Adiba, Silvia De Monte, Paul Rainey).

Morning : Ecology and evolution of social behavior : from multicellularity to eusociality (Corina Tarnita).
Recent work suggests that risk-spreading (bet-hedging) strategies that reduce the temporal variance in fitness at the expense of a lowered average fitness may have been among the earliest evolutionary solutions to life in fluctuating environments : dormancy versus dispersal, persistence versus normal growth, and exploitation versus exploration are well established in ecology. I will discuss how bet hedging in variable environments is likely to have shaped transitions to sociality. I will give examples from all major groups in which social behavior has been studied — vertebrates (cooperatively breeding birds), invertebrates (ants and spiders) and microbes, with a particular focus on the social slime molds Dictyostelium discoideum.
Afternoon : Follow up of the experiment with P. fluorescens (Sandrine Adiba, Silvia De Monte, Paul Rainey) ; Game theory lab : The mathematics of social behavior (Corina Tarnita)

Morning : Food webs and other species interactions in real ecosystems (Rob Pringle).
I will discuss two large scale experimental manipulations and what they teach us about species interactions, from food webs to mutualisms and niche partitioning. One experiment is an herbivore exclusion in the African savanna ; the other is an experimental manipulation of species composition in a Bahamas island system.
Afternoon : Follow up of the experiment with P. fluorescens (Sandrine Adiba, Silvia De Monte, Paul Rainey).

Morning : Challenges and contributions of the experimental approach in ecology (Jean-François Le Gaillard).
The dependence of ecosystem properties on the scale of observation poses significant challenges to the experimental testing of general theories. Lab-scale investigations are indeed insufficient explore the structural and dynamical complexity of natural ecosystems, that are characterized by the interplay of multiple actors involving different spatio-temporal scales. In this lecture, I will discuss how the reach of controlled experiments on ecosystems can be enhanced by the use of large-scale infrastructures, such as the Ecotron-Ile de France, and how these tools can be used to test theoretical prediction, with the aim of increasing the predictive power of ecological models.
Afternoon : Analysis of the result of the experiment with P. fluorescens (Sandrine Adiba, Silvia De Monte, Paul Rainey).