Luis Diego Rios

Introduction: Female fecundity in dioecious plants is influenced by ecological factors that affect pollen and pollinator availability. A high flowering synchrony between sexes, an abundance of pollen donors and pollinators are expected to increase female reproductive success. Objective: To understand how fruit production is related to flowering phenology, sex ratio, abundance and proximity of reproductive males to focal pistillate plants, and pollinator abundance in the dioecious understory palm Chamaedorea pinnatifrons (Arecaceae). Methods: We followed the population flowering of the study species in a montane forest in Costa Rica during 2012. We correlated the number of fruits and fruit set from 115 inflorescences (74 plants) with the size of male and female neighborhoods surrounding focal plants, as well as with plant size and floral display (number of flowers per inflorescence). We estimated pollinator abundance by sampling thrips (Thysanoptera) from staminate inflorescences throughout the plant reproductive season. Results: Flowering was seasonal, with a high degree of overlap between the sexes. The sex ratio of reproductive plants did not significantly deviate from one (79 females and 88 males). Female reproductive success was not related to the abundance and proximity of pollen donors but was instead associated with plants possessing shorter stems, more leaves and flowers per inflorescence, and fewer female neighbors. Late-flowering inflorescences significantly produced more fruits and had a higher fruit set, which coincided with an increase in thrips abundance. Conclusions: We hypothesized that a higher floral display acts as a signal effect to attract pollinators, while larger inflorescences with more flowers can attract more insects, resulting in greater pollination success. Moreover, late-flowering inflorescences seem to benefit from the increase in pollinator abundance at the end of the flowering season. Pollination of C. pinnatifrons and other Chamaedorea species is highly dependent on thrips; as a result, the reproductive success of these palms is susceptible to fluctuations in pollinator population sizes.

Conspecific negative density dependence ( CNDD ) is one of the main mechanisms influencing diversity maintenance in tropical forests. Tropical highland forests, in contrast to most lowland forests, are commonly dominated by a few tree species, and testing the importance of density dependence effects on seedling establishment of dominant trees may provide insights on the mechanisms regulating population dynamics and forest composition of tropical highlands. We tested the effect of CNDD regulation on seedling survival and recruitment of Quercus costaricensis , a monodominant oak in the Talamanca highland forests of Costa Rica. We used Ripley's K and generalized linear mixed models to test the effects of conspecific density, distance to the nearest adult, density of Chusquea bamboo shoots, and herbivory on the annual survival probability of 3579 seedlings between 2014 and 2017. We did not find a significant effect of CNDD on seedling survival. However, bamboo density and herbivory both significantly decreased oak seedling survival. All seedlings had signs of herbivory and predator satiation may explain the lack of density dependent regulation in seedlings of this species. We argue that the lack of intraspecific density regulation at the seedling stage may contribute to explain the dominance of Q. costaricensis in the highland forests of Costa Rica. Local seedling dynamics of this endemic oak are instead regulated by herbivory and the density of Chusquea . Abstract in Spanish is available with online material.

Conspecific negative density-dependence(CNDD) is one of the main mechanisms proposed to regulate species coexistence. Tropical highland forests, in contrast to diverse lowland forests, are commonly dominated by a few tree species. Testing the importance of density-dependence effects on seedling establishment of dominant trees may provide insights on the mechanisms regulating population dynamics and forest composition of tropical highlands. We tested the importance of CNDD regulation on seedling survival and recruitment of Quercus costaricensi s, a monodominant oak in the Talamanca highland forests of Costa Rica. We used spatial statistics and generalized linear mixed models to test the effects of conspecific density, distance to the nearest adult, density of Chusquea bamboo shoots, and herbivory on the annual survival probability of 3538 seedlings between 2014 and 2017. We did not find any effect of CNDD on seedling survival. However, bamboo density and herbivory both significantly decreased seedling survival. All seedlings had signs of herbivory and predator satiation may explain the lack of density dependent regulation in this species. We argue that the lack of intraspecific density regulation at the seedling stage may explain the dominance of Q. costaricensis in the highland forests of Costa Rica. Local density of this endemic oak is instead regulated by herbivory and the density of Chusquea .

Pitcairnioideae is the second most diverse subfamily of bromeliads (Bromeliaceae), a group exclusive to tropical regions of the New World. Pitcairnioid bromeliads have floral traits assumed to promote outcrossing through biotic pollination systems; however, the reproductive biology of most of the species of this group has not been documented. Pitcairnia heterophylla is an epiphytic (seldom saxicolous) bromeliad occurring from Southern Mexico, into the Northern Andes. We studied the pollination and breeding system of P. heterophylla in an epiphytic population at a mountain forest in Costa Rica from January to April 2013. We performed hand pollination experiments (agamospermy, autonomous self-pollination, hand self-pollination and hand cross-pollination) on 89 flowers from 23 individuals (3–6 flowers per individual) in 2013 flowering season. Nectar production was measured on 18 unvisited flowers of six individuals with a hand-held refractometer. Simultaneously, floral visitors were recorded on eight individuals with trail cameras for a total of 918 hours (115 ± 52 hours per individual, mean ± SE). Under natural conditions, seed set (540.4 ± 55.2) was similar to manually selfed flowers (516.3 ± 41.5) and autonomously selfed flowers (521.1 ± 29.0), but lower to manually outcrossed flowers (670.2 ± 31.3). The flowers of P. heterophylla are self-compatible, capable of autonomous pollination, and non-agamospermous. Intrafloral self-pollination is facilitated by adichogamy and lack of floral herkogamy. The scentless red flowers of P. heterophylla with tubular corollas and nectar production suggested ornithophilic pollination which was confirmed by video recording of 46 hummingbird visits. The most common floral visitor was the short-billed hummingbird Lampornis calolaemus which accounted for 78 % of the visits. However, the visitation rate during the flowering season was low (0.6 visits per day per plant). Selfing in P. heterophylla might be explained as a mechanism of reproductive assurance and to reduce interspecific pollen flow with taxonomically unrelated plants.

Background: Dioecious species require a conspecific for sexual reproduction. As such, they demand a high level of flowering synchronization. In this scenario, phenology can deepen the effect of density, sex ratio, and distance over fruit production. Also, pollinator reliability can affect a species reproductive success (RS). Pollinator specialist depend on their few pollinators have a high population size; in contrast, generalist (pollinated by many taxa) can surpass this because of their condition. In this paper, we analyzed the effect of phenology, density, distance and pollinator abundance on the female RS of the dioecious palm Chamaedorea pinnatifrons (Palmae) at a cloud forest in Costa Rica. This palm is pollinated by wind and a single species of thrips (Thysanoptera: Thripidae) in a mixed pollination system. The pollination system seems to be highly specialized, as the thrips species has been recorded only in flowers of Chamaedorea Methods: In the 2012 season we monitored the phenology of a population (n = 88 males, 94 females) in a 40x40 plot. All individuals were sexed, mapped, had their height measured and number of leaves counted. RS was measured as the number of fruits/inflorescence and as fruit set. Generalized Linear Mixed Effects Model (GLMM) were used to test the effect of flowering time, distance to nearest male, density of males, number of flowers, height, number of leaves and number of flowers over the two response variables. We also estimated thrips population by sampling insects directly from staminate inflorescences in anthesis, from early March to mid-May (11 weeks, n = 33 inflorescences). Results: Flowering of C. pinnatifrons lasted five months: it began by early February, had a peak by early April, and ended by July. Mean fruit production was 99.7 (± 12.1 SE, min = 0, max = 735). The amount of fruits produced was significantly higher in inflorescences from individuals with shorter stems, had more flowers, a lower flowering synchrony with males and flowered late. Mean fruit set was 0.144 ± 0.016%. Fruit set was also significantly higher in inflorescences from lower stems, with lower male synchrony and flowered late. The mean amount of thrips sampled in staminate inflorescences increased 13-fold between early March (20.8 ± 10.6 thrips/rachillae) and mid-May (282.0 ± 74.4). Discussion: The higher RS of late flowering plants can be partially explained by the progressive increase in the population of pollinators. Our results in C. pinnatifrons seem to oppose recent analyses in that early flowering plants should be positively selected. A deeper understanding of a species pollination system is necessary to understand the strength of the agents of selection.

Most epiphytic bromeliads exhibit specialized pollination systems likely to promote out-crossing but, at the same time, possess floral traits that promote autonomous selfing. Adaptations that promote selfing in flowering plants with specialized pollination systems have been considered as a mechanism for reproductive assurance. In this paper, we analyzed the breeding system and pollinator visitation rate of the hummingbird-pollinated bromeliad Pitcairnia heterophylla in order to see if they fit such trend. We performed hand pollination experiments, video recording of floral visitors, and recorded floral traits in order to describe the reproductive and pollination system of the studied species in a cloud forest in Costa Rica. Results from the pollination treatments indicated that P. heterophylla is self-compatible (SCI _f = 0.77), capable of autonomous pollination (AFI _f = 0.78), and non-agamospermous (AG _f = 0.01). Floral traits, such as scentless red flowers, with tubular corolla and nectar production, suggested ornithophily which was confirmed by the video recording of Lampornis calolaemus (Trochilidae) visiting flowers. However, the visitation rate was low (0.6 visits day-1 per plant) based on 918 hours of video recording using trail cameras. We suggest that the high selfing capability of the studied population of P. heterophylla might be related to the low pollinator visitation rate. If low pollinator visitation is common among hummingbird-pollinated and epiphytic bromeliads, then selfing could be a widespread mechanism to enhance their reproductive success.