Paul A. Opler

Dioecism in tropical forest trees.

The existence of dioecism among angiosperms is universally acknowledged, yet is poorly understood both from the ecological and evolutionary points of view. The reason for this hiatus might be that some have believed the relative proportion of dioecious taxa to be low (Yamplosky and Yamplosky, 1922; Lewis, 1942), while others have felt that since the number of seed-bearing individuals is halved in a dioecious population its evolution is an unlikely and perhaps inconsequential event (HeslopHarrison, 1972). However, recent studies have reported a large proportion of dioecious tree species in tropical forests (Ashton, 1969; Bawa, 1974; see also Tomlinson, 1974); this indicates that the incidence and importance of dioecism may have been underestimated in the past. These new data are significant in at least one other respect. Dioecious (and monoecious) flowers in temperate plants are presumed to have evolved in response to selective pressures favoring wind-pollination (Grant, 1951; Stebbins, 1951), yet windpollination is probably either absent or uncommon in tropical forests (Whitehead, 1969; see also Daubenmire, 1972). Here we present an overview of the adaptive and evolutionary significance of dioecism in general and its expression in certain tropical forests in particular. We first present data on the frequency of dioecious species in a lowland tropical semi-deciduous forest in Costa Rica, then proceed to an examination of available information on

The Butterflies of Costa Rica and Their Natural History: Papilionidae, Pieridae, Nymphalidae.

The Description for this book, The Butterflies of Costa Rica and Their Natural History, Volume I: Papilionidae, Pieridae, Nymphalidae, will be forthcoming.

SEX RATIOS IN TROPICAL FOREST TREES

Sex ratios of dioecious plants often depart significantly from unity (Correns, 1922; Dzhapardize, 1967; Godley, 1964; Pauley and Mennel, 1957; Rathore, 1969). Explanations for these deviations have usually been sought in the genetics of sexdetermination (for a review see Westergaard, 1958; Lloyd, 1974). However, biased sex ratios may also have an ecological basis, and thereby have important implications for the reproductive ecology of the subject plants. Yet, relatively few studies have considered the ecological aspects of deviant sex ratios (Harris, 1968; Lloyd, 1973; Lloyd and Webb, 1977; Putwain and Harper, 1972). Here we present data on the sex ratios of 23 species of tropical forest trees and attempt to explain these ratios with respect to certain ecological factors. Our study may be considered noteworthy because most previous studies of sex ratios in dioecious species have been conducted on plants of temperate regions. Since dioecism is more common in tropical than in temperate ecosystems (Bawa and Opler, 1975; see also Ashton, 1969; Tomlinson, 1973), studies of sex ratios in tropical trees should contribute significantly toward an understanding of deviant sex ratios in flowering plants.

Taxonomic isolation and the accumulation of herbivorous insects: a comparison of introduced and native trees

Abstract. 1 Evidence from leaf‐mining insects on Fagaceous hosts suggests that range expansions of insects onto introduced trees often involve species that feed on native hosts closely related to the introduced host. 2 An examination of the herbivorous entomofauna of British trees illustrates that the size of the entomofauna is partially determined by the taxonomic isolation of the host tree.

Why Are Pistillate Inflorescences Of Simarouba Glauca Eaten Less Than Staminate Inflorescences

MEWALDT, L. R. 1964a. Effects of bird removal on a winter population of sparrows. Bird-Banding 35:184-195. ---. 1964b. California sparrows return from displacement to Maryland. Science 146:941-942. NILES, D. M., S. A. ROHWER, J. A. JACKSON, AND J. D. ROBINS. 1969. An observation of midwinter nocturnal movement and tower mortality of tree sparrows. Bird-Banding 40:322-323. ROHWER, S. 1975. The social significance of avian winter plumage variability. Evolution 29:593610. ---. 1977. Status signaling in Harris sparrows; some experiments in deception. Behaviour 61:107-129. ROHWER, S., S. D. FRETWELL, AND R. C. TUCKFIELD. 1976. Distress screams as a measure of kinship in birds. Amer. MidI. Natur. 96:418--430. ROHWER, S., AND F. C. ROHWER. 1978. Status signaling in Harris sparrows: Experimental deceptions achieved. Animal Behav. (in press).

The Butterflies of Kenya and their Natural History

This is the most complete and detailed book ever written on a significant portion of the East African butterfly fauna. Torben Larsen is eminently qualified to write such a work because he is well familiar with butterflies of the African continent; he has written books previously on the butterflies of Lebanon, Arabia, Egypt, and Jordan.