PARENT SESSION
Oral Session # 53: Herbivory IV: Communities, Populations, and Genetics.
Presiding: JA Rudgers
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 103.
Herbivory, male and female fitness and compensation in an annual plant.
Mariano, Nestor1, Dirzo, Rodolfo2, 1 Dept. Ecologia, Ceamish, Cuernavaca, MOR2 Instituto de Ecologia, Unam, DF
ABSTRACT- Plants responses to herbivory range from undercompensation to overcompensation. Such flexibility of responses is possible by the plant's modular structure. However, few studies of herbivory have analyzed changes in the demography of plant parts, which in turn determines the plant's photosynthetic capacity to maintain growth and reproduction. Such quantitative dynamics may be reflected in qualitative changes in resource allocation to male and female structures in order to maintain fitness in cosexual species. We analyzed such effects using artificial herbivory treatments (control, 25%, 75% leaf area removed) on a monoecious annual plant, Cucurbita sororia , under greenhouse conditions. We measured leaf natality, mortality and longevity, number of male and female flowers, flower size, pollen production and number of aborted male flowers. Our demographic analyses showed that plants with moderate herbivory (25%) increased leaf natality and longevity, yet, mortality was not affected. Under intense herbivory (75%) leaf standing crop diminished due to increased mortality and reduced longevity; unexpectedly, leaf natality was unaffected. Although herbivory reduced overall flower production and effects were exacerbated in female flowers, moderate damage did not affect male flower production. Increased herbivory leads to an increase in the number of male aborted flowers and, under heavy herbivory, those flowers that did not abort took longer to develop. Pollen production/flower was affected only under intense herbivory, while corolla size was affected by both levels of herbivory. Considering effects on both growth and reproduction, we found that defoliation leads to a negative relationship between leaf natality and male flower production. Defoliation had a greater impact on the more costly sexual function. In contrast, the greater allocation to male function seems to lead to a relaxation of the tradeoffs between growth and reproduction. This may be a mechanism to compensate for the negative effects of herbivory on plant fitness.
Key words: fitness, demography, herbivory, compensation