If we think that the definition of the niche is 'the relationship between an organism and its environment' then the niche concept is probably pretty important in ecology. Together with Jon Chase, we've tried to resurrect the concept after it had a rough period in the 1970-90s. Our central premise was that the relationship had two parts; one the effect of the organism on the environment and the other the response of the organism to the environment. Like many things in life, relationships are best when they go both ways! We still think this approach is central to thinking about ecology and use this approach throughout our work. Some key publications include:
Leibold, M.A. 1995. The niche concept revisited: mechanistic models and community context. Ecology 76:1371-1382 (Special Feature: Concepts Section).
Leibold, M.A. 1998. Similarity and local coexistence of species from regional biotas. Evolutionary Ecology 12:95-110.
Chase, J.M. and M.A. Leibold. 2003. “Ecological Niches”, U. Chicago Press.
Leibold MA. 2008. Ecology – Return of the Niche. Nature 454:39-40
Food webs and the joint action of 'top-down' and 'bottom-up' interactions in ecosystems:
During my dissertation I was inspired by two important lines of work that seemed disjunct; the study of competition for resources studied using zero-net-growth isoclines as developed especially by David Tilman (ZNGIS), and the study of food chains to study biomass relations among trophic levels as developed especially by Lauri Oksanen. I have worked to combine these two in simple food web models that we called 'keystone predation' and others have called the 'diamond food web'. This approach showed that there could be interactions between the within- and the between-trophic level interactions that could explain key features of ecosystems. Especially important was that this could resolve the interaction between 'bottom up' effects (driven by the supply of abiotic resources that fuel food webs) and 'top-down' effects (driven by the distribution and control of top trophic levels in food webs.
Diversity along productivity gradients:
The food webs models (above) predict interesting patterns about biodiversity and composition. One of the more intriguing ones is the prediction that species richness might show a unimodal (humped) relationship with ecosystem productivity. Of course it isn't the only hypothesis that predicts this relationship (there seem to be at least 12 others!). But these models also make related predictions about regional diversity and about 'beta-diversity' (how much species composition differs from one place to another) and 'turnover' (how much species composition changes with time at a single place). We think that food web interactions are the only models that predict that the unimodal curve is related to simultaneous monotonic increases in regional diversity, beta-diversity, and turnover. And it seems that these relationships are true at least in freshwater ecosystems. Interesting, but maybe more needs to be done on this question.
The most exciting set of ideas I have worked with came from a working group (sponsored by NCEAS) I co-organized (with Jon Shurin and Bob Holt) on metacommunities. It started as a simple way of thinking about the role of dispersal in regulating community assembly from a regional biota to structure at a local scale but has since expanded hugely. It has now taken a life of its own as a driving concept in modern ecology. Some key publications include:
Leibold, M.A., M. Holyoak, N. Mouquet, R.D. Holt, D. Tilman and 7 others. 2004. The metacommunity concept: a framework for large scale community ecology? Ecology Letters 7:601-613.
Leibold, M.A. and T.E. Miller. 2003. From metapopulations to metacommunities. In I. Hanski and O. Gaggioti (eds). Ecology, Genetics, and Evolution of Metapopulations.
Holyoak, M., M.A. Leibold, N. Mouquet and R.D. Holt. 2005. Metacommunities: a framework for large scale community ecology. In Holyoak, Leibold and Holt (eds). Metacommunity Ecology: Emerging views of community structure and dynamics above the local scale. University of Chicago Press.
Leibold MA. 2011. The metacommunity concept and its theoretical underpinnings. In: Scheiner, SM and Willig MR (eds). The Theory of Ecology.
Leibold MA and Chase JM. 2017. Metacommunity Ecology. Princeton Monographs in Population Biology. Princeton University Press, Princeton, N.J.
Niche evolution in metacommunities (especially involving Daphnia):
Most community ecologists are happy to ignore evolution. You can't really blame them, since community ecology is complicated enough as it is. Many also take solace in thinking that niche differences within species are small compared to niche differences between species. However, I've always wondered just how true this is. My early work with adaptive population differentiation in Daphnia showed that niche evolution could be pretty big. Since then we have continued to work on both theory and experimental studies of niche evolution and been especially interested in how this worked in a multipatch metacommunity where metapopulation evolution could interact with species interactions.