Stefano Allesina, Ph.D. Visiting Assistant Professor Department of Ecology & Evolution Computation Institute Office: | Phone: | Fax: | email: Subjects: I am interested in the application of network theory to biology, with a focus on food webs, the networks describing who eats whom in the ecosystem.

Research Interests

I am interested in the application of network theory to biology, with a focus on food webs, the networks describing who eats whom in the ecosystem. The main themes I've been working on are the following:

Ecological networks: dynamics and consequences of structure

The past decade has seen the rapid proliferation of network research, including the revitalization of studies on food webs and ecological networks. New techniques and applications have been published at a rapid pace, with hundreds of publications in ecological journals addressing network properties. Fundamental questions underlying these efforts fall into two general categories: (a) how the network structure of ecosystems constrains their dynamical properties, and (b) how properties of ecosystems influence the formation and evolution of these networks. I am particularly intrigued by the persistence of ecological systems and the ways in which these complex, adaptive systems are able to resist perturbations. While some ecosystems are long-lasting, others experience rapid collapse. What are the determinants of these variations?

The assembly and disassembly of ecological networks

It is much easier to estimate the population size of a species than to quantify its importance in maintaining ecosystem's functions. This simple consideration is reflected in the ecological management of biodiversity, where conservation efforts are typically appropriated to rarer species rather than to those possessing the greatest strategic value. From a network perspective, the importance of a species in an ecosystem has been measured by quantifying the effect of its loss on ecosystem structure and the persistence of other species. This approach defines the branch of food web theory concerned with the robustness of networks. I've been working on models for ecosystems collapse and on methods for the identification of critical species in ecosystems.

Characterizing ecological networks

Many different types of networks share similar properties: for example, two nodes (colleagues in a collaboration network, proteins in a protein-interaction
network) are reachable from each other via a few links (smallworld); the number of interactions is distributed in a power law fashion (scale-free); and nodes tend to form cliques of highly connected subnetworks (clustering). These types of networks span from email contacts to authorship graphs, from genomics to sociology. Unfortunately, ecosystems differ in important ways and do not typically conform to structural categories defined for other systems. A major challenge is to quantify and qualify the differences and similarities that ecosystems exhibit in comparison with other types of networks.

Simple models for food web structure

A central problem in ecology is determining the processes that shape food webs. The topology of these networks is a major determinant of ecosystems' dynamics and is ultimately responsible for their responses to human impacts. Several simple models have been proposed for the intricate food webs observed in nature. We recently showed that the main models proposed so far fail to fully replicate the empirical data, and we developed a likelihood-based approach for the direct comparison of alternative models based on the full structure of the network. I am currently working on slightly more complicated models that yield better AIC values and are able to replicate the data. My current focus is on the role of body size in determining feeding relations and on the role groups and clusters of species play in shaping the networks.

Recent Selected Publications

Allesina, S., Bodini, A., Pascual, M., 2008. Functional links and robustness in food web. Phil. Trans. Royal Society B in press.

Allesina, S., Alonso, D., Pascual, M., 2008. A General Model for Food Web Structure. Science 320(5876):658-661.

Lafferty, K.D., Allesina, S., et al. 2008. Parasites in food webs:the ultimate missing links. Ecology Letters 11:533-546

Allesina, S., Pascual, M., 2008. Network structure, predator-prey motifs, and stability in large food webs. Theoretical Ecology 1(1):55-64.

Peacor, S.D., Allesina, S., Pascual, M., Riolo, R.L., 2006. Phenotypic plasticity increases species coexistence by altering fitness surface. PLoS Biology 4(11): e372.

Bondavalli, C., Bodini, A., Rossetti, G., Allesina, S., 2006. Detecting stress at the whole ecosystem level. The case of a mountain lake: Lake Santo (Italy). Ecosystems 9(5):768-787.

Allesina, S., Bodini, A., 2004. Who dominates whom in the ecosystem? Energy flow bottlenecks and cascading exctinctions. Journal of Theoretical Biology 230(3):351-358.