The relationship between morphological variability and biotic environmental heterogeneity was studied in a pasture population of Trifolium repens L. It had been argued that the unexpectedly high levels of variation in T. repens could be maintained by diversifying selection. The mosaic of neighbours (perennial grasses) with which T. repens co-exists constitutes a prominent element of biotic patchiness that may lead to sorting among T. repens genotypes on the basis of neighbour-specific compatibilities.
A variation study was conducted on a set of 400 individuals of T. repens collected on a neighbour-specific basis from a 43–year-old pasture and grown for over 2 years under common garden conditions. Variation in a set of 12 morphological characters was assessed after 4 months and again after 27 months. After 4 months′ growth, a significant proportion of this variation was accounted for by the neighbour with which the individuals of T. repens had been growing in the pasture. The actual amount of variation accounted for, however, was low (6-19%).
When the same characters were assessed after 27 months, none of the neighbour-specific differences in morphology were retained. It is concluded that the original results reflected developmental differences carried over from the pasture, and that diversifying selection is not of importance in the maintenance of morphological variation in this population.