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Using an experimental approach, this study addresses the following two questions for the perennial herb Paeonia broteroi (Paeoniaceae) at a location in southeastern Spain. (1) What are the relative magnitudes of the effects of pollinators and herbivores (invertebrates and vertebrates feeding on flowers and developing fruits) on maternal fe- cundity (total seed production per plant)? (2) Are the effects of pollinators and herbivores on fecundity additive, or is there some significant interaction between them? A two-factor (‘‘Pollinators’’ and ‘‘Herbivores,’’ each with two levels, ‘‘present’’ and ‘‘excluded’’) ex- perimental design was used, with individual plants being treated as experimental units and maternal fecundity as the response variable. On average, the effects of pollinators and herbivores were of opposite sign and roughly similar absolute magnitude (—7.5 seeds per plant), thus approximately canceling each other. A significant interaction (non-additivity) between factors did exist, with plants exposed to pollinators experiencing a disproportion- ately higher incidence of herbivores than those from which pollinators had been excluded. This was mainly due to mammals browsing only on the larger fruits from flowers that had been exposed to pollinators. Only in the absence of herbivores did pollinators account for a significant amount of between-plant variance in maternal fecundity. It is concluded that the interaction between pollinators and herbivores will lead to variable, herbivore-dependent ‘‘opportunity for selection’’ (sensu Arnold and Wade 1984) on P. broteroi by its pollinators. Regional variation in herbivore incidence experienced by P. broteroi populations will pre- sumably generate local variation in the degree of adaptedness of the plant to its pollinators.

The groundlayer of an abandoned field was found similar to that in nearby foothill woodland, presumably the original vegetation of the field. By 1965, 27 years after abandonment, the annual species in the field were characteristic of ungrazed ranges. Thirteen perennial herb species were found in the field by 1944, 6 years after abandonment, and 26 were present by 1966. Although some of the perennial herbs were abundant, many required intensive searching to detect their presence. Woody plants were present but not abundant by 1966.

This paper isan effort to emphasize the force which insects may exert over the destinies of their plant hosts, and to reveal the pattern of such vegetational changes as have been experienced up to this time in the local areas of Chrysornela (Chrysolina) releases in California. The importation of these European beetles from Australia as a means of controlling Klamath weed (Hypericumt perforatum L.) has been reported by Smith ('47) and Holloway ('48). This perennial herb, often called common St. Johnswort, is a European plant extensively naturalized in the United States. It infests perhaps 400,000 acres of range land in California alone. The importance of controlling this noxious weed on range land has been covered by Sampson and Parker ('30) and many other authors. By far the greatest economic losses from this weed result from lowered carrying capacity of the ranges, due to its displacement of desirable forage plants. This plant has the interesting characteristic (U.S.D.A. Forest Service, '37) of containing a photosensitizing principle which causes blistering and loss of hair only in white-skinned (unpigmented) horses, cattle, and sheep if exposed to strong sunlight after eating the plant. Sick animals lose weight and in se