Guilds and assembly rules in lawn communities

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Abstract
The community structure of 11 lawn sites in New Zealand and Fiji was examined in terms of guilds, seeking assembly rules based on guild proportionality.First, associations were analysed, using a new patch model which examined the mean of associations within patches of about 4 cm x 4 cm. As expected from the previously‐demonstrated existence of niche limitation at this scale in lawns, the majority of associations between individual species were negative. Even in a lawn only four months old there were significant associations (mostly negative, and one positive). At some sites those species with the most negative associations were those whose morphology might be expected to restrict co‐existence with other species.Much ecological theory is based on the assumption that there are limitations to coexistence, related to the resource usage of the species, such that species that are too similar in resource use are less likely to coexist. This theory was tested by looking for evidence of guild proportionality. We defined two guilds, graminoids and forbs. Using these guilds, three of the sites showed significant evenness in proportional representation from the two guilds in quadrats containing four species, i.e. there was less variation in the graminoid:forb ratio than expected on a random basis. Inclusion of species‐poor quadrats in a joint analysis over all richness categories overwhelmed this effect, though there was still a strong trend for two of the New Zealand sites: the two species‐rich grass lawns. Preliminary analyses of alternative guild delimitations gave no indication that other guild delimitations would have revealed stronger community structure. There was a strong and significant tendency in most sites for the graminoid guild to be more strongly represented in species‐poor quadrats, an effect caused by species frequencies.