Effects of Local Plant Density and Incomplete Dichogamy on the Reproductive Success of the Rare Neotropical PalmGeonoma epetiolata

Abstract

Density dependent processes are known to influence reproduction and establishment of plant populations. In this study, we evaluated the effects of local density and sexual expression on the reproductive success of the rare palm species Geonoma epetiolata in Costa Rica. We classified individuals in two density categories based on distances to the two nearest neighbors and recorded the occurrence of sexual overlap on each individual. Overlap between pistillate and staminate flowers in monoecious plants allows geitonogamous pollination, potentially reducing dependence on mates for reproduction. We measured plant size and light availability, and evaluated the influence of these variables on pollination success, fruit production, fruit abortion and seed mass. Pollination success significantly increased with density but there was no effect of sexual overlap. In contrast, there was no effect of density on the probability of initiated fruit, and a negative effect on fruit set. Fruit abortion was lowest in isolated plants with no sexual overlap. Plant size and light did not contribute to variation in reproductive success. In conclusion, the pollination advantage of plants in dense neighborhoods does not compensate reproductive losses incurred by fruit abortion, possibly due to mating among genetically related individuals. Geonoma epetiolata is threatened by habitat loss and poaching of seeds for the horticultural market. High fruit abortion rates associated with density in G. epetiolata suggest that seed collections from the remnant wild populations of this palm species may cause bottlenecks that further threaten population viability.Abstract in Spanish is available in the online version of this article.

Fine-scale processes shape ecosystem service provision by an Amazonian hyperdominant tree species

“…Patterns of negative density-dependent fecundity as suggested here have also been reported for the understory palm Geonoma epetiolata 75 and the pioneer tree Cecropia obtusifolia 20 , but do not seem to be universal. Several studies did find evidence of negative effects on fruit production due to higher kinship in denser conspecific neighbourhoods but these were not strong enough to compensate for the positive effects on fecundity of increased crosspollination 21 , 29 , 30 .…”

“…The available studies in Neotropical species suggest that the nature of density-dependent fecundity might be related to the idiosyncrasies of each species’ reproductive biology. Positive density effects tend to be found in species with wind, 21 bird, or bat-dispersed seeds 29 , which can be more effective in long distance dispersal than in species where dispersal is largely controlled by gravity 75 , or by mammals with very short dispersal ranges such as Brazil nut. Stronger fine-scale population genetic structures are expected in species with limited seed dispersal, leading to stronger negative fine-scale distance-dependent fecundity.…”

Tropical Forest Fragmentation Affects Floral Visitors but Not the Structure of Individual-Based Palm-Pollinator Networks

“…In this case, small fragments where individuals are less visited by effective pollinators could exacerbate the amount of pollen and diversity of pollen donors transferred between flowers (less variance in the abundance of pollinators per flower). Also the density of reproductive individuals can lead to an increase of potential donors, and have a positive impact on pollination success, as showed for the Neotropical palm Geonoma epetiolata [ 78 ]. These fragmentation-related scenarios could have strong consequences on the maintenance of plant species if we consider breeding systems of plants, as well as size and mobility capacity of pollinators, with consequences on some attributes of performance of seedlings in forest remnants [ 79 ].…”