Heliconia acuminata reproductive success is independent of local floral density

Abstract

Reproductive plants in tropical forests are patchily distributed, with some in large aggregations of reproductive consepecifics while others are relatively isolated. This variation in floral density is hypothesized to have a major effect on plant reproductive success, since individuals in higher density neighborhoods can attract more or higher quality pollinators. We experimentally tested this hypothesis with populations of the understory herb Heliconia acuminata in central Amazonia. We created replicated plots in which reproductive plant density spanned the range of naturally occurring floral neighborhood size, then measured three surrogates of plant fitness in focal plants in each array. There was no significant difference between any of the three floral neighborhood treatments in total seed production, fruit set, or the number of seeds produced per fruit. Pollinator visitation rates to plants in all treatments were extremely low, with many plants not visited at all during the observation period. This could be because H. acuminata's hummingbird pollinators are unable to find the widely scattered reproductive plants, however this hypothesis appears unlikely. Instead, natural flowering plant densities may simply be below the threshold value at which neighborhood effects become important, even in "high-density" aggregations. Nutrient limitation, selective fruit abortion, and reproduction via male rather than female function may also be playing a role. We argue the absence of neighborhood effects may be a general phenomenon in central Amazonian forests, though additional experiments with other plant-pollinator systems are needed to determine the extent to which this hypothesis is supported. KEY WORDSPhaethornis, resource limitation, pollinator limitation, transplants O sucesso reprodutivo de Heliconia acuminata é independente da densidade floral local. RESUMO Plantas reprodutivas em florestas tropicas são distribuidas em manchas, com algumas em grandes agregações coespecíficas e outras relativamente isoladas. A hipótese é que esta variação na densidade de flores em um local tem um grande efeito no sucesso reprodutivo de plantas, já que indivíduos em agregações maiores poderiam atrair mais polinizadores ou polinizadores de melhor qualidade. Esta hipótese foi testada na Amazônia central com populações da erva de sub-bosque

Effects of forest fragmentation on the seedling recruitment of a tropical herb: assessing seed vs. safe‐site limitation

“…However, positive density dependence may be indicative of favorable conditions for establishment or increased pollinator visitation (Feinsinger et al 1986(Feinsinger et al , 1991, thereby confounding biotic and abiotic drivers of seedling establishment. However, previous research at the site has demonstrated that H. acuminata reproductive success is independent of local flower density (Bruna et al 2004). This allows us to interpret positive density dependence with established plants as a proxy for habitat favorability, an approach often used in plant ecology (e.g., Iverson and Prasad 1998).…”

Low plant density enhances gene dispersal in the Amazonian understory herb Heliconia acuminata

“…Visitation rates by pollinators are low (median = 0.182 visits/hour per plant), with hummingbirds failing to visit 28% of the observed plants (Bruna et al . ). These low visitation rates, coupled with the results of hand‐pollination studies, suggest fruits resulting from self‐pollination are extremely unlikely.…”

“…Here, we use a hierarchical Bayesian approach to quantify the contributions of pollen and seed movement to gene dispersal in Heliconia acuminata L. C. Richard (Heliconiaceae), an understory herb pollinated by hummingbirds (Bruna et al . ), whose seed is dispersed by manakins and thrushes (Uriarte et al . ).…”

Propuesta de incorporación de plantas del género Heliconia sp. como estrategia de conservación y manejo sustentable de sistemas cacaoteros y cafetaleros del Sur del Lago de Maracaibo y Valle del Mocoties, Venezuela

“…Aunque la autoincompatibilidad en las especies de heliconias es muy conocida (Kress, 1983;Bruna et al, 2004;Meléndez-Ackerman et al, 2008) y puede estar limitando su éxito reproductivo, por el bajo porcentaje de autopolinización, nosotros encontramos que un número importante de flores maduras se transforman en frutos inmaduros pero es muy bajo el que lo hace en frutos maduros (entre el 16,8 y 26,3%).…”

“…Algunos autores que han reportado resultados similares, plantean la posibilidad de que la baja producción de frutos maduros puede ser una limitación en la repartición de los recursos de los fotoasimilados (Bruna et al, 2004). Pensamos que al alimentarse de partes concretas de las flores, la fauna hospedada no permite la formación de frutos, y/o que al hacerlo de partes o de la totalidad del fruto inmaduro, no se obtiene al final frutos maduros como lo sugieren Fontenelle et al (2012) y Missagia y Alvez (2017.…”