Alfredo Cascante-Marín

Evaluating factors that predict the structure of a commensalistic epiphyte-phorophyte network.

A central issue in ecology is the understanding of the establishment of biotic interactions. We studied the factors that affect the assembly of the commensalistic interactions between vascular epiphytes and their host plants. We used an analytical approach that considers all individuals and species of epiphytic bromeliads and woody hosts and non-hosts at study plots. We built models of interaction probabilities among species to assess if host traits and abundance and spatial overlap of species predict the quantitative epiphyte–host network. Species abundance, species spatial overlap and host size largely predicted pairwise interactions and several network metrics. Wood density and bark texture of hosts also contributed to explain network structure. Epiphytes were more common on large hosts, on abundant woody species, with denser wood and/or rougher bark. The network had a low level of specialization, although several interactions were more frequent than expected by the models. We did not detect a phylogenetic signal on the network structure. The effect of host size on the establishment of epiphytes indicates that mature forests are necessary to preserve diverse bromeliad communities.

Neither insects nor wind: ambophily in dioecious Chamaedorea palms (Arecaceae).

Abstract Pollination of Neotropical dioecious trees is commonly related to generalist insects. Similar data for non‐tree species with separated genders are inconclusive. Recent studies on pollination of dioecious Chamaedorea palms (Arecaceae) suggest that species are either insect‐ or wind‐pollinated. However, the wide variety of inflorescence and floral attributes within the genus suggests mixed pollination mode involving entomophily and anemophily. To evaluate this hypothesis, we studied the pollination of Chamaedorea costaricana,C. macrospadix,C. pinnatifrons and C. tepejilote in two montane forests in Costa Rica. A complementary morphological analysis of floral traits was carried out to distinguish species groups within the genus according to their most probable pollination mechanism. We conducted pollinator exclusion experiments, field observations on visitors to pistillate and staminate inflorescences, and trapped airborne pollen. A cluster analysis using 18 floral traits selected for their association with wind and insect pollination syndromes was carried out using 52 Chamaedorea species. Exclusion experiments showed that both wind and insects, mostly thrips (Thysanoptera), pollinated the studied species. Thrips used staminate inflorescences as brood sites and pollinated pistillate flowers by deception. Insects caught on pistillate inflorescences transported pollen, while traps proved that pollen is wind‐borne. Our empirical findings clearly suggest that pollination of dioecious Chamaedorea palms is likely to involve both insects and wind. A cluster analysis showed that the majority of studied species have a combination of floral traits that allow for both pollination modes. Our pollination experiments and morphological analysis both suggest that while some species may be completely entomophilous or anemophilous, ambophily might be a common condition within Chamaedorea. Our results propose a higher diversity of pollination mechanisms of Neotropical dioecious species than previously suggested.

Complex phylogeographic patterns indicate Central American origin of two widespread Mesoamerican Quercus (Fagaceae) species

The northern Neotropical region is characterized by a heterogeneous geological and climatic history. Recent studies have shown contrasting patterns regarding the role of geographic elements as barriers that could have determined phylogeographic structure in various species. Recently, the phylogeography and biogeography of Quercus species have been studied intensively, and the patterns observed so far suggest contrasting evolutionary histories for Neotropical species in comparison with their Holarctic relatives. The goal of this study was to describe the phylogeographic structure of two Neotropical oak species (Quercus insignis and Quercus sapotifolia) in the context of the geological and palaeoclimatic history of the northern Neotropics. Populations through the distribution range of both species were collected and characterized using nine chloroplast DNA microsatellite loci. Both oak species showed high levels of genetic diversity and strong phylogeographic structure. The distribution of genetic variation in Q. insignis suggested an influence of two major barriers, the Isthmus of Tehuantepec and the Nicaraguan Depression, while Q. sapotifolia exhibited a genetic structure defined by the heterogeneity of the Chortis highlands. The haplotype networks of both species indicated complex histories, suggesting that colonization from the Sierra Madre de Chiapas to central Mexico and from the north of the Nicaraguan Depression to the Costa Rican mountains may have occurred during different stages, and apparently more than one time. In conclusion, the phylogeographic structure of Neotropical oak species seems to be defined by a combination of geological and climatic events.

Lack of negative density-dependence regulation in a dominant oak tree from a neotropical highland forest

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 costaricensis, 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.

High selfing capability and low pollinator visitation in the epiphyte Pitcairnia heterophylla (Bromeliaceae) at a Costa Rican cloud forest

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 (SCIf = 0.77), capable of autonomous pollination (AFIf = 0.78), and non-agamospermous (AGf = 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.

Late flowering and low synchrony with males enhance female reproductive success in the dioecious palm Chamaedorea pinnatifrons

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.