The Disassortative Pollen Flow Hypothesis proposed by Darwin postulates that the relative position of anthers and stigmas in distylous flowers enhances pollen flow between flowers of different morphs (legitimate pollination), in comparison to flow between flowers of the same morph (illegitimate pollination). In order to test this hypothesis, we measured pollen transport, mediated by a trained Copper-rumped Hummingbird (Amazilia tobaci), between flowers of the distylous Palicourea fendleri under laboratory conditions. In individual tests, we offered to the hummingbird a pollen donor flower and two emasculated recipient flowers in a controlled sequence. After each foraging bout, we counted the number of pollen grains transported from the donor flower to the stigmas of both recipient flowers. In agreement with Darwin's hypothesis, we found that hummingbirds transport pollen of "pin" flowers in significantly higher numbers to legitimate "thrum" stigmas, even if previously visiting a "pin" flower. However, "thrum" pollen was deposited in greater numbers on illegitimate "thrum" stigmas. We interpret this asymmetry largely as the consequence of floral morphology; pollen flow was greater between anthers and stigmas that exhibit greater spatial matching. In P. fendleri, the position of floral organs along the corolla tube does not always precisely correspond. In our experimental system, the probability that the pollinator extracts a pollen grain from the anther and the probability of self-pollination were both dependent on the type of floral morph. We discuss the relevance of the latter findings in relation to other studies of pollen flow in heterostylous species.

Spatial and seasonal patterns of seed removal by rodents, ants and birds were evaluated using seed-dish experiments in a Trachypogon savanna in Venezuela. Four-day experiments were conducted on three dates and at four different sites. Seeds from 10 native plant species representing a broad mass range were offered at densities equivalent to 3145 seeds m−2. We found that total seed removal and relative importance of granivorous groups varied widely among sites and dates. Rodents were the major seed predators in all the habitats, except for the savanna/forest border where birds dominated. Ants removed more seeds than birds, but since they preferred the smallest seeds, ants ranked last in mass removed. We found a temporally variable relationship between seed removal rates and seed rain or seed bank. We inferred monthly seed predation from seed-dish experiments as well as through the decline of the seed bank in the environment during the dry season, and compared both estimations to evaluate the suitability of the seed-dish technique for estimating granivory. We initially hypothesized that seed-dish experiments that emulate seed availability more closely may yield a better estimate of seed predation, but in fact, they may still overestimate granivory intensity.

Arbuscular mycorrhizal fungi (AMF) play a crucial role in ecosystem functioning improving plant nutrition and resistance to environmental stress. In La Gran Sabana (LGS), an upland belonging to the Venezuelan Guayana Shield, AMF are determinant for plant survival due to the acidic, sandy and oligotrophic nature of its soils. The vegetation is mainly constituted by savannas intermixed with forests, shrublands, meadows and palm swamps. In this region a high diversity of species of Gigasporacea has been found and four new species (S. spinosissima, S. crenulata, S. striata, S. tepuiensis), as well as others undescribed morphotypes, are considered endemics. Some ecological and historical factors that could be involved with the restricted distribution of these species were evaluated. The high endemism of plants and the particular edaphic conditions present in shrublands looks like the main drivers of the important diversification processes within Gigasporacea detected in this region. The monophyletic origin of some of these endemic Gigasporaceae suggest that their endemism could be the result of a process of in situ diversification combined with limitations for dispersal and/or establishment in other regions. These findings and the presence of a basal lineage for the family allows proposing LGS as an evolutionary hotspot for Gigasporaceae.