Lifetime Impacts of Herbivory for a Perennial Plant

In spite of widespread interest in the impact of herbivores on plants, few studies have addressed the lifetime consequences of attack for perennial plants. I have addressed this issue by studying the interaction between dwarf fireweed, Epilobium latifolium, and its principal herbivore in south—central Alaska, Mompha albapalpella (Momphidae Lepidoptera). Fireweed is a long—lived, clonal herb that grows as clumps of connected shoots, and suffers from chronic attack by Mompha. I used a Markov Process (transition matrix) model, in combination with 3 yr of experimental data, to simulate expected changes in size and fecundity for clumps growing under different frequencies and intensities of damage. These analyses indicate that fireweed suffers fairly little reduction in growth from low intensity attacks, even if these attacks are quite frequent, but that high intensity attacks suppress growth even at very low frequencies. Damage greatly reduces seed production and also increases the inequality of seed output from different clumps. Because the patterns in which damage is meted out are crucial in determining herbivory's effects, kniwong only average amounts of tissue loss will be insufficient to predict the impacts of herbivory. My results show that short—term impacts of herbivory canopy simply be extrapolated to longer time spans; a quantitative, modeling approach is necessary to understand herbivory's complicated effects.