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Interspecific Plant Association as Influenced by Three Variables

Byer, Michael D.
Ecology 1970 v.51 no.1 pp. 103-112
Pteridium, biogeography, environmental factors, habitats, microrelief, rare species, stochastic processes, vegetation
Changes in interspecific association related to variation in quadrat size, position on a gradient, and abundance measure used in calculating indices yielded information about the nature and causes of this association, and results often corroborated one another mutually. Distribution of species along the gradient and interspecific association within gradient segments appeared to be continua, with varying steepness of transition. Strong association of some rare species suggested that they are highly specific ecologically and/or controlled by few factors. Association changes related to quadrat size suggested general grouping of species on two scales. Possibly, Pteridium and litter generate this grouping between patches where they inhibit plants generally. Weaker positive correlation of cover than of presence suggests unequal competitive restriction of plastic response within the patches of high cover formed by grouping. Large and abundant species in particular seem to inhibit others. Strong positive and negative association characterized heterogeneous habitats and vegetation, extreme habitats in which small environmental differences may be critical, species whose restricted distributions along the gradient may reflect narrow tolerances and consequent microsite specificity, and extremes of species' ranges along the gradient. At these extremes, species perhaps require specific uncommon microsites, and these requirements seem to be similar for species having similar distributions along the gradient. Weak species—environment correlation may reflect low variability of environmental parameters, strong correlation between the latter suggesting that few stochastic processes and complex interactions affect them. In a bog, the major patterning element seems to be hummock—hollow microtopography.