Pollination Ecology Of Two Species Of Elleanthus (orchidaceae): Novel Mechanisms And Underlying Adaptations To Hummingbird Pollination.

Relationships among floral biology, floral micromorphology and pollinator behaviour in bird-pollinated orchids are important issues to understand the evolution of the huge flower diversity within Orchidaceae. We aimed to investigate floral mechanisms underlying the interaction with pollinators in two hummingbird-pollinated orchids occurring in the Atlantic forest. We assessed floral biology, nectar traits, nectary and column micromorphologies, breeding systems and pollinators. In both species, nectar is secreted by lip calli through spaces between the medial lamellar surfaces of epidermal cells. Such form of floral nectar secretion has not been previously described. Both species present functional protandry and are self-compatible yet pollinator-dependent. Fruit sets in hand-pollination experiments were more than twice those under natural conditions, evidencing pollen limitation. The absence of fruit set in interspecific crosses suggests the existence of post-pollination barriers between these synchronopatric species. In Elleanthus brasiliensis, fruits resulting from cross-pollination and natural conditions were heavier than those resulting from self-pollination, suggesting advantages to cross-pollination. Hummingbirds pollinated both species, which share at least one pollinator species. Species differences in floral morphologies led to distinct pollination mechanisms. In E. brasiliensis, attachment of pollinaria to the hummingbird bill occurs through a lever apparatus formed by an appendage in the column, another novelty to the knowledge of orchids. In E. crinipes, pollinaria attachment occurs by simple contact with the bill during insertion into the flower tube, which fits tightly around the bill. The novelties described here illustrate the overlooked richness in ecology and morphophysiology in Orchidaceae. This article is protected by copyright. All rights reserved.

Nectar Robbery By A Hermit Hummingbird: Association To Floral Phenotype And Its Influence On Flowers And Network Structure.

Interactions between flowers and their visitors span the spectrum from mutualism to antagonism. The literature is rich in studies focusing on mutualism, but nectar robbery has mostly been investigated using phytocentric approaches focused on only a few plant species. To fill this gap, we studied the interactions between a nectar-robbing hermit hummingbird, Phaethornis ruber, and the array of flowers it visits. First, based on a literature review of the interactions involving  P. ruber, we characterized the association of floral larceny to floral phenotype. We then experimentally examined the effects of nectar robbing on nectar standing crop and number of visits of the pollinators to the flowers of Canna paniculata. Finally, we asked whether the incorporation of illegitimate interactions into the analysis affects plant-hummingbird network structure. We identified 97 plant species visited by P. ruber and found that P. ruber engaged in floral larceny in almost 30 % of these species. Nectar robbery was especially common in flowers with longer corolla. In terms of the effect on C. paniculata, the depletion of nectar due to robbery by P. ruber was associated with decreased visitation rates of legitimate pollinators. At the community level, the inclusion of the illegitimate visits of P. ruber resulted in modifications of how modules within the network were organized, notably giving rise to a new module consisting of P. ruber and mostly robbed flowers. However, although illegitimate visits constituted approximately 9 % of all interactions in the network, changes in nestedness, modularity, and network-level specialization were minor. Our results indicate that although a flower robber may have a strong effect on the pollination of a particular plant species, the inclusion of its illegitimate interactions has limited capacity to change overall network structure.

Nesting behavior of the swallow-tailed hummingbird, Eupetomena macroura (Trochilidae, aves)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

The dawn lek of the Swallow-tailed Hummingbird

We studied the lek behavior of the Swallow-tailed Hummingbird (Eupetomena macroura) in an urbanized area in S (a) over tildeo Paulo state, Southeastern Brazil. During the 22-month study we identified a total of 26 lekking territories in one lek that covered an area of approximately 12 ha. The lek was active throughout the year; the number of singing males per morning ranged from 6-15. The abandonment of territories and the establishment of new ones caused continuous rearrangement of lek boundaries. Lekking territories had a mean size of 217 m(2) and were separated from each other by 24-120 m. on average, males started singing 27 min before sunrise and kept singing for 17 min. At the end of this period and after a few minutes of silent perching, they abandoned their lekking territories until the next morning. During the singing period. males spent 72-100% of the time inside their territories. The lek behavior of E. macroura is unusual compared to other lekking hummingbirds because of the short daily period of lekking, restricted to just before Sunrise. Since males and females of E. macroura possibly defend feeding territories throughout the rest of the day, the short lekking period may represent a tradeoff between two different time budget pressures from lekking and feeding activities.