PS 19-189 - Importance of sexual and clonal reproduction for population dynamics of a neotropical understory herb in high and low light

Background/Question/Methods

It is unclear how variation in light availability within forest understories influences the population dynamics of clonal herbs. In forest understories, many herbs produce both sexual and clonal offspring and are found across the light gradient from open canopy tree fall gaps to shaded closed canopy. In this study we investigate the population dynamics of the Neotropical understory herb Calathea marantifolia at different points along the light gradient to understand how light influences population growth. Demographic data (growth, survival and reproduction) of individuals were recorded in eight plots (four high light and four low light) in Corcovado National Park, Costa Rica from August 2004 until March 2007 (N = 2168). We collected data for six census intervals, including three August-to-March and three March-to-August seasonal periods. As a first step in understanding the contribution of sexual and clonal reproduction to population growth, we used these data to parameterize an integral projection model of structured population dynamics for a single season. We evaluated the contribution different sized individuals for population growth using sensitivity and elasticity analyses as well as a life table response experiment (LTRE).

Results/Conclusions

Using the data from first seasonal period only, we found the rate of population growth (λ) was much faster in high light (λ = 1.33) compared to low light (λ = 1.25). LTRE analysis revealed that this difference in λ was primarily due to greater survival and growth at larger sizes and to a lesser extent increased clonal reproduction in high light. Removing sexual reproduction from the model reduced λ dramatically in both high (0.32 reduction in λ) and low light levels (0.21). Conversely, removing clonal reproduction from the model resulted in only a modest decreased in λ in both high (0.05) and low (0.02) light levels. The single season analysis suggests that population dynamics of C. marantifolia differs greatly between light levels and that sexual reproduction contributes greatly to λ. A more complex picture of their contribution to long run population dynamics is revealed when we parameterize each census interval separately and create appropriate temporal sequences that include both seasonal and inter-annual variability.