Plant‐Animal Interactions and Fruit Production in a Neotropical Herb: A Path Analysis

Abstract

We used path analysis to estimate the direct and indirect effects of antguards, an ant—tended herbivore, and pollinators, on flower and fruit production in Calathea ovandensis, a neotropical herb. The natural variation in these plant—animal interactions was quantified for individual plants in Veracruz, Mexico in 1984 and 1985. We conclude that variation in plant—animal interactions has significant, and complex, effects on flower and fruit production in this species. Antguards had a positive direct effect on flower number in both years, and because of the positive effect of flower number on fruit number, had a positive indirect effect on mature fruit number. The herbivore had a negative direct effect on flower number and mature fruit number in both years. Thus, direct and indirect effects contribute to the large negative effect of herbivores on mature fruit number. The composition of the pollinator community was very different in the two years, with a marked increase in the number of visits by efficient pollinators in 1985. This change was reflected in between—year differences in the effects of pollinators on number of initiated fruits. In 1984, pollinators had no significant effect on initiated fruit number, while the two pollinators that increased in abundance in 1985 had significant effects on initiated fruit number in that year. These results are consistent with experimental data for 1985, which indicate that supplemental pollination causes a significant increase in the number of fruit initiated. While pollinators may limit the number of fruit initiated in some years, our observational and experimental data suggest that number of mature fruits is primarily limited by resources, not by pollination.