Effects of plant size, leaf herbivory, local competition and fruit production on survival, growth and future reproduction of a neotropical herb


Carol C. Horvitz (fax: 305-284-3039; E-mail: carolhorvitz@miami.edu)


1 The effects of natural variation in herbivory, local competition, plant size, and fruit production on next year’s growth, survival and inflorescence production of individuals in natural populations of Calathea ovandensis were estimated during 5 years.

2 For each year, we estimated path coefficients (by standardized multiple regression analysis) for the direct effects of predictor variables on demographic rates. Separate analyses were performed for each life-history stage: seedlings, juveniles, pre-reproductives and reproductives, for a total of 55 analyses. Emergent patterns for stages were evaluated (Fisher’s combined probability test) by combining years. To determine significance of effects in single years, we calculated table-wide probabilities for each stage across multiple years (Bonferroni sequential test). Emergent patterns for years were also evaluated (Fisher’s combined probability test) by combining stages.

3 Survival of seedlings was positively affected by plant size and negatively affected by local competition. Survival of juveniles was positively affected by plant size, but not by other factors. Survival of large stages was not generally affected by any of the factors.

4 Relative growth rates of all stages were negatively affected by plant size; larger plants grew more slowly than smaller plants. Additionally, growth rate of juveniles was negatively affected by local competition, whereas growth rate of reproductives was positively affected by reproduction.

5 Next year’s inflorescence production was positively affected by plant size for both pre-reproductive and reproductive stages. For reproductives, it was additionally positively affected by current fruit production.

6 Analysis of differences among years showed that herbivory negatively affected both survival and growth in 1985, but not in other years, whereas local competition negatively affected survival in 1983 and growth in 1984.

7 Effects of biotic interactions varied among stages and through time. The large effects of competition on seedlings and juveniles was as expected, but the small effect of herbivory on small plants was surprising as was the striking temporal variation in its effect and its impact on large plants.