Analysis of Two-Phase Pattern in a Mesquite Grassland, Texas

Whittaker, R; Gilbert, L; Connell, J

(1) Species-presence and cover were recorded in a strip transect of 107 1 × 1-m quadrats in mesquite grassland in Texas. (2) Reciprocal averaging (RA) was used to ordinate the quadrats and species along a first axis which was related to pattern differentiation within the community, from the shaded centres of the shrub patches to the grass-dominated matrix. In this community, with a rich flora and a well-defined pattern, the profile of first-axis RA scores along the transect effectively revealed patch intensity and boundaries. (3) The relative discreteness of patches was revealed by mean RA score-differences for successive quadrats of 5.0 in the grassland, 11.3 in the shrub patches and 24.7 in the transitions between. A weak periodicity at a scale of 13-14 m was shown by maximum quadrat similarity (minimum RA score-difference) for comparisons between pairs of quadrats at different distances along the transect. Pattern diversity, in the sense of within-community differentiation, was calculated from the first eigenvalue of RA as about two half-changes. (4) Species-RA scores and apparent distributional centres were dispersed along the first axis of the RA ordination rather than forming distinct groups. Spectral analysis and other measures of species contagion, period and association supplemented the RA information on species-relationships, but were less effective than RA in characterizing the community pattern.

Analysis of Two-Phase Pattern in a Mesquite Grassland, Texas

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