(Hylemya Sp.). I

International Association for Ecology Oviposition Choices by a Pre-Dispersal Seed Predator (Hylemya sp.). I. Correspondence with Hummingbird Pollinators, and the Role of Plant Size, Density and Floral Morphology Author(s): Alison K. Brody Source: Oecologia, Vol. 91, No. 1 (1992), pp. 56-62 Published by: Springer in cooperation with International Association for Ecology Stable URL: http://www.jstor.org/stable/4220031 . Accessed: 29/09/2011 14:38 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Springer and International Association for Ecology are collaborating with JSTOR to digitize, preserve and extend access to Oecologia. http://www.jstor.org Oecologia ( 1992) 91:56-62 ~ZZ-Z-?- Oecologia ? Springer-Verlag 1992 Oviposition choices by a pre-dispersal seed predator {Hylemya sp.) I. Correspondence with hummingbird pollinators, and the role of plant size, density and floral morphology Alison K. Brody Department of Entomology University of California Davis, CA 95616, USA, and the Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA Received July 15, 1991 / Accepted in revised form February 21, 1992 Summary. Although the importance of pollinators has that may use floral traits in locating hosts and subse- most often been examined in the evolution of floral quently affect floral evolution. Pollinators and florivores characters, seed predators may also play a role in shaping are likely to interact in affecting floral evolution. In floral evolution. In this study, I examined the role of particular, the effects of seed predators that use floral interplant distance, plant size, and flower morphology on cues and ultimately consume potential offspring (i.e., Ipomopsis aggregata'^ (Polemoniaceae) attractiveness to seeds) and pollinators may interact in affecting floral a pre-dispersal seed predator, Hylemya sp. (Anthomyii- traits. To date this interaction has been little studied. In dae) and to hummingbird pollinators. The attractiveness comparison to hundreds, if not thousands, of references of /. aggregata individuals to Hylemya was nonlinearly on the interactions between pollinators and host plants related to interplant distance in experimental arrays. (for reviews see Faegri and van der Pijl 1978; Real 1983; Clumped and highly dispersed plants were preyed upon Jones and Little 1983), the interaction between seed more frequently than those at intermediate distances. I predators and pollinators in affecting floral evolution has found no relationship between interplant distance and received relatively little attention (Beattie et al. 1973; visitation rates by hummingbird pollinators in these ex- Zimmerman 1980a; Augsburger 1981 ; Hainsworth et al. perimental arrays. However, in natural populations stud- 1984; Campbell 1991). Pollination ecologists have ad- ied, clumped plants were more frequently approached by dressed the question of how plants attract pollinators, hummingbirds than those growing more widely disper- and have studied the variety and sequences of behaviors sed. Display size was unrelated to visitation by Hylemya that pollinators exhibit in searching for floral rewards on inflorescences I clipped and maintained as "large", (see Jones and Little 1983; Waser 1983 for reviews). We "small" and "control". Display size was also unrelated know much less about how seed predators locate hosts. to the total number of visits by hummingbird pollinators Host finding is certainly a multi-level process occur- to each of these experimental plants, however "large" ring at several spatial scales. The cues that govern host display plants were more likely to be visited first in any finding and utilization by both pollinators and seed given visitation sequence. Of various morphological predators can conveniently be broken down into those measurements, corolla length showed the strongest pos- that attract animals to a given patch, to an individual itive correlation with Hylemya egg presence. To the ex- plant, and to flowers on that individual. tent that plant spacing and morphology is correlated Host density, or interplant distances, may affect with pollinator visits and ultimate seed set, Hylemya movement rates to and within a local population (Evans could be choosing flowers optimally, and playing a role 1983; Karieva 1982, 1983, 1985; Bergelson and Karieva in the evolution of floral traits. 1987). The presence of neighboring conspecifics can affect arrival and tenure times within a patch of hosts - - Key words: Pre-dispersal seed pr?dation Pollination (Evans 1983; Bach 1980). One would predict that a - - Floral display Plant spacing Hylemya sp. denser host stand would attract more visitors (Moore 1978; Evans 1983) although this is not always the case (Moore 1978). Insects may respond primarily to within- plant (e.g., pod or flower production) characteristics, The evolution of floral traits conventionally has been and/or to local densities (Evans 1983). viewed as a function of plant attractiveness to pollina- Once in a patch, an animal must choose an individual tors. However, pollinators are not the only organisms plant. Large individuals may be most apparent, and thus Current address and address for offprint requests: The Rocky Moun- most attractive. The role of floral display size has been tain Biological Laboratory Crested Butte, CO 81224, USA addressed primarily in relation to pollinator attraction 57 (Willson et al. 1979; Pyke 1981; Zimmerman 1980b; color (Elam and Linhart 1988), flare of the corolla, and level of Thomson 1988; Schemske 1980). Hummingbirds stigma exsertion; the latter may determine a flower's relative invest- ment in male and female function 1989b; and preferentially visit many-flowered inflorescences of Ipo- (Campbell Campbell Waser 1989). The primary pollinators of /. aggregata are broad- mopsis aggregata (Pyke 1981) and birds may skip over tailed hummingbirds {Selasphorus platycercus Swainson) and ru- small in favor of to the next plants flying large plant fous hummingbirds {Selasphorous rufus Gmelin) (Waser 1978) al- (Campbell and Waser 1989). Inflorescence size may also though small insects play some role in pollinating this species as well affect movements between and within individuals. Al- (Waser 1978; Brody unpub. data). though more flowers may be visited on a many- versus In the vicinity of the Rocky Mountain Biological Laboratory, where this was /. is at few-flowered inflorescence, per-flower visitation rates study undertaken, aggregata pollen-limited, least in some parts of the flowering season and/or in some years may be similar (Schmid-Hempel and Speiser 1988). (Hainsworth et al. 1985; Campbell 1991). Pollen limitation is im- inflorescences be favored an increase Large may through portant in assessing the effects of choices made by seed predators in male reproductive effort through pollen export (e.g., for the following reason. If plants are not pollen limited, and all are Queller 1985), but may show little or no relationship to likely to attract sufficient numbers of pollinators to ensure a full pollen donation (Geber 1985; Schmid-Hempel and complement of seeds, then selection will not act through female function on the characters most attractive to Speiser 1988; Campbell 1989a). With notable exceptions pollinators. Thus, there would be no reason for seed predators to be "choosy" if all (Willson and Rathcke 1974; Queller 1985; Schmid- flowers have an equal probability of producing seeds. Hempel and Speiser 1988; Thomson 1988), the conse- Ipomopsis aggregata is preyed upon by an anthomyiid fly of size for and seed quences display pollination pr?dation {Hylemya sp.) which lays its eggs under the sepals and whose larvae have only rarely been experimentally tested. burrow into the ovary and eat the developing ovules. Normally, a Flower morphology may affect movement of animals single egg is laid on each flower, however clutches of two eggs are foraging among individuals; pollinators preferred large sometimes laid under the same sepal. A single larva normally con- sumes all of the seeds in a given fruit, a larva flowers of Raphanus sativus (Stanton and Preston 1988) although occasionally will emerge from a fruit before consuming all seeds. The larvae exit and Polemonium viscosum (Galen and Stanton, 1989), through the ovary wall and drop to the ground, where they pupate. and with flowers were over-visited in com- plants large Adult females do not pollinate the flowers. parison to those with smaller flowers (Galen and Stanton 1989). After arrival on a host, the role of variation in flower morphology within a plant on pollinator or preda- Interplant distance (density) and display size tor behavior has received much less attention. Using an artificial array of plants, I manipulated interplant distance The of this was to examine cues used purpose study to simulate clumps of different densities. In addition, I manipulated by a predispersal seed predator (Hylemya sp. Antho- flower number on plants within the density (distance) treatments. myiidae) in its selection of oviposition sites on Ipomopsis Plants were potted after bolting but before initiation of

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