Table 2.

Estimates of the relative roles of top-down and bottom-up forces in determining variation in the populations of O. brumata and T. viridana on five Q. robur trees from 1951 to 1966 in Wytham Woods, England

	Top-down (predation), %	Bottom-up (plant quality), %	Bottom-up (plant quantity), %	Total explained, %	Total unexplained, %
O. brumata	34.2	17.2	Negligible	51.4	48.6
T. viridana	Negligible	5.7	29.4	35.1	64.9

Estimates were derived from partitioning total population variance between tree and year effects, then assessing the relative roles of competition, host-plant phenology, and natural enemies in generating those tree and year effects (see text for details).