Lac Hertel

Fussmann Lab
Department of Biology

Brachionus logoParadox of the PlanktonBrachionus logo

Competitive coexistence under equalizing and stabilizing mechanisms

Asterionella formosa Asterionella formosa ©Michael Pedruski
The theme

Competitive coexistence provides an intriguing problem in biodiversity research. While much research has suggested that species should not be able to coexist with other species that have the same niche or are limited by the same resource, nature provides many examples of high levels of biodiversity even in habitats where there are relatively few niches or limiting resources. This discrepancy between prediction and observation is also known as the paradox of the plankton, and has posed one of community ecology's most challenging and rewarding problems.

Recently, a new theoretical framework has been introduced to address this problem, which considers competitive coexistence to be the product of both equalizing mechanisms (those mechanisms which reduce fitness inequality between competitors) and stabilizing mechanisms (those mechanisms which focus intraspecific competition relative to interspecific competition). It is our goal to create an experimental framework that allows us to manipulate the relative importance of equalizing and stabilizing mechanisms in competitive coexistence, and see how the two classes of mechanisms affect ecological and evolutionary dynamics.

the three competing diatom species The three competing diatom species © Michael Pedruski
The questions
  • Is it possible to apply niche concepts and theory towards the development of a non-niche structured community?
  • Is it possible to effectively control community dynamics using the concepts of fitness inequality and stabilizing mechanisms? Do these dynamics validate existing theory regarding fitness inequality and stabilization?
  • How does evolution proceed in communities that are maintained by differing relative contributions of equalizing and stabilizing mechanisms?
  • Can we apply the results derived in experimental conditions to nature?
diatom cultures in growth chamber Diatom cultures in growth chamber © Michael Pedruski
The system

To manipulate the relative importance of equalizing and stabilizing mechanisms we are working with a model system of freshwater phytoplankton (diatoms) under resource limitation. Historically diatoms were used extensively to test the resource competition model, and they continue to be a workhorse of community ecology experimental work. As a result, diatoms offer a well studied system in terms of required resources that has been extensively studied both in laboratory and field conditions, and is of ecological importance.

We intend to first map out fitness differences between diatom species over a temperature gradient, and then set up communities with varying levels of fitness inequality. Subsequently, we intend to introduce stabilizing mechanisms to our communities by creating metacommunities that allow diatoms to disperse between habitats that experience different environmental conditions (and therefore different selective regimes). Thus, by controlling temperature and dispersal rates we expect to be able to control both the amount of fitness inequality present in any given community, as well as the potential for stabilization to overcome that fitness inequality.


Fragilaria crotonensis Fragilaria crotonensis © Michael Pedruski
The people

This project is being undertaken by Michael Pedruski under the supervision of Prof. Gregor Fussmann and Prof. Andrew Gonzalez.


Tabellaria fenestrata Tabellaria fenestrata © Michael Pedruski
The funding

This project is funded through an NSERC PGS-D postgradute scholarship to Michael Pedruski.