Mechanisms of species coexistence in a lawn community: mutual corroboration between two independent assembly rules

Mason, N.W.H. and Wilson, J.B. (2006) Mechanisms of species coexistence in a lawn community: mutual corroboration between two independent assembly rules. Community Ecology, 7 (1). pp. 109-116. ISSN 1585-8553

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Abstract

Assembly rules are measures of community structure that link observed patterns with ecological processes, and as such may help to elucidate the mechanisms by which species coexist. We apply two approaches to a lawn community - limiting similarity and guild proportionality - hoping that agreement between them might give robust conclusions. We tested for agreement between these two assembly rules using functional characters that are related to two aspects of species function - light capture and response to defoliation. We combined point quadrat data and a null model approach to test for limiting similarity - a tendency for species differing in functional characters to co-occur more often than expected at random - in turves extracted from the lawn community. Examining the variance in the characters of the species co-occuring at each point, evidence for limiting similarity was found for mowing removal (the proportion of leaf area removed in mowing events). There was greater variation between the species co-occurring at a point than expected at random (i.e., under an appropriate null model). However, no such evidence was found for characters related uniquely to light capture, such as specific leaf area and pigment concentrations. In a previous study in the same community, “intrinsic” guilds had been determined from co-occurrences within the lawn community and from a competition experiment, as those effective in determining species assembly and co-existence. These intrinsic guilds are shown by t-test to differ in the proportion of their biomass removed in mowing (MRI), which is of course related to the height at which their leaf area is held. However, again no differences were seen in characters related uniquely to light capture. Thus, the two different approaches to assembly rules - guild proportionality and limiting similarity - agree that differences in response to mowing are responsible for species co-existence in the lawn community. The agreement between these two approaches, tested on independent datasets of quite different type from the same community, gives possibly the strongest evidence so far that niche differentiation may be responsible for local co-existence in plant communities. However, although MRI is related to this co-existence the lack of correlation with light-capture characters leads to speculation that the effects might be via the below-ground behaviour of the species.

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