Alternative classifications in the intrinsic guild structure of a New Zealand tussock grassland

Guild structure was determined in the inter-tussock vegetation of a New Zea land grassland. Twenty-one sites were sampled by shoot presence/absence in 10 x 10 cm quadrats, for all macroscopic plants. Using these data, intrinsi c guilds were derived (intrinsic guilds are those that are defined by the o bserved restrictions on species co-occurrence, not by a priori characters). Such guilds were found by heuristic searches for the guild classification that was optimal, as measured by an index of community structure, RV The op timisation was for minimum RVgp , i.e. maximum guild proportionality, relat ive constancy in guild representation. One hundred searches were carried ou t on the data, each starting from a different initial random configuration. When the quadrats were split at random into an Optimisation subset and a T est subset, a guild classification that showed significant guild proportion ality in the Test subset was found in a significantly greater number of sea rches than expected by chance (28 out of 100). The ten of those 28 classifi cations that gave the tightest community structure comprised three groups. Further optimisation of representatives of these groups using the whole dat aset confirmed that the community contained at least two genuinely independ ent, alternative guild classifications. It is concluded that two or more gu ild classifications can exist within the same set of species in a community . These classifications can be orthogonal in the sense that they are unrela ted to each other and operate simultaneously. Attempts to correlate the dem onstrated guild membership with known characteristics of the species showed some, but limited, relation to growth form/height.