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General patterns among coexistence mechanisms? A research program.

Coexistence of multiple species is one of the central problems of community ecology.  We all know of many different ecological systems where the diversity of species found living together is bewildering.  However, models of species interactions suggest that coexistence of these species (in the strict ecological sense) is extremely difficult and requires very particular conditions.

I have just begun a new project to take an empiricist’s approach to understanding theoretical mechanisms of coexistence.  In this project,  I am examining models of various types of species interactions in various configurations of communities to explore exactly what is necessary for coexistence.  Coexistence has a very particular definition that is much more restrictive than the common-place meaning of the word.  To a community ecologist, coexistence means that some ecological mechanism promotes the long-term persistence of multiple species.  It does not simply mean that they are found living together.  Thus, the central question in this work asks what is required for multiple species to live together indefinitely in various types of community configurations.

The first step in this project was to consider basic resource competition – in other words, two or more consumers feeding on a single resource – to see what conditions may permit more than one consumer to coexist with the resource.  Spoiler alert: it is possible!!  However, I’ll wait until a later post to explain how it’s possible.

This project will explore predator-prey interactions, resource competition and mutualisms, and build ever more complicated ecological systems to explore how various mechanisms might interact to promote or inhibit coexistence.

The central focus of this work is to search for commonalities and organizing principles across the myriad mechanisms that have been proposed to promote coexistence.  Once these generalities have been identified, I hope to then extend a proposal for how ecologists might attack the analysis of coexistence mechanisms in the field.



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1 Comment

  1. We also try to explain coexistence mechanisms. We are sure that coexistence mechanisms of species competing for one resource may be simple if they are mechanistic.

    We think that the main problem of theoretical ecology is about the competitive exclusion principle. The lack of strong proof or disproof of this principle makes difficult any further investigations. The Lotka-Volterra model predicts stable coexistence of two species when, for both species, an interspecific competition is weaker than intraspecific one. This interpretation follows directly from the Lotka-Volterra model. However, the further interpretation of this interpretation, known as the competitive exclusion principle has no rigorous justification under itself. The problem is that the Lotka-Volterra model is phenomenological (descriptive, nonmechanistic, black-box) as it based on differential equations [1] and, therefore, no physical insight is available.

    The Unified Neutral Theory of Biodiversity was proposed as an alternative to niche theory. But Stephen Hubbell’s model of neutrality is also the black-box model as it based on probability theory. More of all it is not even a null model [2]. It is just a statement of ignorance about which species can succeed and why [2].

    1 Tilman D., The Importance of the Mechanisms of Interspecific Competition, The American naturalist, 129 (1987) 769-774
    2 Clark, J. S. The coherence problem with the Unified Neutral Theory of Biodiversity. Trends in Ecology & Evolution. 27, 198-202, doi:10.1016/j.tree.2012.02.001 .

    Vyacheslav L. Kalmykov,
    Lev V. Kalmykov,

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