Plant size variation and vertebrate herbivory: winter wheat grazed by rabbits.
In field trials in Silwood Park, Berkshire, UK in 1982-85, wheat cv. Hustler was subjected to no grazing or to several regimes of grazing by rabbits. Shoot-weight distributions of ungrazed plants changed significantly over the course of the growing season, with sized inequality between plants increasing rapidly at first, peaking in mid-winter, and remaining high thereafter. Variance: mean relationships for shoot-wt distributions conformed to Taylor's Power Law throughout the growing season, becoming Poisson by harvest time. Continuous rabbit grazing reduced mean plant size and consistently increased size inequality. The largest plants in populations grazed in winter and then allowed to recover were typically larger than the largest plants from ungrazed populations. This was probably due to a reduction in competition from mortality caused by grazing. Total grain yield per unit area was never increased by grazing. Weight distributions of grazed populations tended to show increased skewness and kurtosis compared with ungrazed populations. There was no evidence for bimodality, but platykurtosis was frequently observed.