PARENT SESSION
Oral Session #101: Plant-Animal Interactions.
Presiding: S. Faeth
Friday, August 9. 9:00 AM to 12:00 PM. Coconino Meeting Room, TCC.

Phenology and seed consumption in wild rice.

Ng, Melody^*,1, Andow, David¹, ¹ University of Minnesota, St. Paul, MN

ABSTRACT- The timing of plant development, especially of such critical events as budburst, flowering, and seed set, can influence pollination, seed predation, herbivory and seed dispersal. Reproductive synchrony is generally believed to decrease resource consumption through predator satiation. It can actually lead to different levels of consumption, however, depending on characteristics of the resource and the consumer, and coincidence of these interacting species in time. A mathematical model and field observations will illustrate this phenomenon. Univoltine Apamea apamiformis moths oviposit in female wild rice (Zizania palustris) florets when stigmas are exserted. Larvae feed solely on wild rice seeds, and can cause major seed loss. Natural stands of wild rice in Minnesota flower asynchronously, which, we have hypothesized, decreases seed predation. While moths are ovipositing only for about three weeks, flowering lasts over six weeks. Early and late-developing plants were predicted to suffer less seed consumption than plants that flowered in mid-summer when moths were active. Plants that were manipulated to delay development, but still flower during the moth oviposition period, did not differ from controls in the number of eggs present or the number of seeds eaten. Plants that developed very late in the summer had few moth larvae on them, but also produced fewer seeds; they were likely pollen limited. Because wild rice germination is strongly influenced by light while moth eclosion depends on temperature, the timing and degree of coincidence of seeds and their consumers may change yearly, which may promote plant reproductive asynchrony.

KEY WORDS: phenology, reproductive synchrony, seed predation, wild rice (Zizania palustris)