Specific projects

While our primary motivation is theoretical, the active projects are a roughly equal split between theory, data analysis and experimental collaborations.


Statistical physics of resource competition

One classic way to link composition and function is provided by MacArthur's resource competition model from the late 60's. It was extensively studied for N = 1 and N = 2 resources, in particular by Tilman, who developed a highly influential geometric intuition.

In natural communities, however, the number of relevant metabolites is in the dozens. Remarkably, the high-diversity regime of the MacArthur model can be solved analytically, using methods of statistical physics of disordered systems. This exactly solvable model provides a rich platform to investigate the implications of high dimensionality for both ecological and evolutionary dynamics.

Tikhonov M, Monasson R (2017) Collective phase in resource competition in a highly diverse ecosystem. PRL
Tikhonov M, Monasson R (2018) Innovation rather than improvement: a solvable high-dimensional model highlights the limitations of scalar fitnessJ Stat Phys


Community-level competition

Natural microbial ecosystems do not just exchange members: they frequently come into contact as entire communities. For instance, think of a leaf falling on the ground, or a dog licking your hand. These events have been dubbed "community coalescence". A frequent, yet largely unstudied natural occurrence, they are expected to be an important factor shaping community structure, and are also of significant medical interest (e.g. fecal matter transplants are one of the few effective therapies against C. difficile infections). Interpreted as community-level competition, community coalescence is a very intriguing phenomenon also from a theoretical standpoint. 

In collaboration with Alvaro Sanchez (Yale) and Pankaj Mehta (Boston U), we are investigating community coalescence both theoretically and experimentally.

Rillig MC et al. (2015) Interchange of entire communities: microbial community coalescence. Trends Ecol Evo
Tikhonov M (2016) Community-level cohesion without cooperation. eLife
Goldford J, Lu N et al. (2017)
 Emergent simplicity in microbial community assembly. Science
Lu N et al. (2018) Cohesiveness in microbial community coalescence (bioRxiv)


Other projects

Other ongoing projects cover a diverse set of topics, including:

  • metabolically driven spatial assembly of multi-species consortia (see our paper in PNAS);
  • an intriguing exact mapping of MacArthur's resource competition onto learning theory;
  • a theoretical construct of "weakly structured" ecologies where the number of species is ill-defined.

We expect to develop additional collaborations with groups at the WashU medical campus and the Center for Genome Sciences & Systems Biology.