Relationships between size, biomass allocation, reproduction, and survival in Triglochin palustris:: implications for the effects of goose herbivory

Triglochin palustris (arrowgrass) on the Yukon-Kuskokwim Delta reproduces primarily vegetatively, and is heavily grazed by geese. To link effects of herbivory on individuals to population-level effects, we examined relationships between plant size or biomass allocation and survival or reproduction by matching more than 400 individuals into groups and sequentially harvesting individuals from each group. We compared size and biomass allocation for nonreproductive plants and plants with either or both modes of reproduction in exclosed plots, and examined effects of clipping leaves or inflorescences in flowering and nonflowering plants. Survival and vegetative reproduction increased with plant size, particularly bulb size, but was unrelated to biomass allocation. Very small plants do not reproduce, very large plants produce both flowers and stolons, and intermediate sized plants produce either flowers or stolons. Inflorescences require greater biomass investment than stolons, resulting in decreased allocation to all vegetative plant parts except roots. Plants that produce flowers seldom regenerate overwintering bulbs on the parent plant, indicating a trade-off with survival. Geese may decrease flowering by reducing plant size and consuming inflorescences. Flowering plants have much higher rates of herbivory than other plants, suggesting that increased risk of herbivory results in low rates of flowering.