Complex networks of species interactions might be determined by species traits but also by simple chance meetings governed by species abundances. Although the idea that species traits structure mutualistic networks is appealing, most studies have found abundance to be a major structuring mechanism underlying interaction frequencies. With a well‐resolved plant–hummingbird interaction network from the Neotropical savanna in Brazil, we asked whether species morphology, phenology, nectar availability and habitat occupancy and/or abundance best predicted the frequency of interactions. For this, we constructed interaction probability matrices and compared them to the observed plant‐hummingbird matrix through a likelihood approach. Furthermore, a recently proposed modularity algorithm for weighted bipartite networks was employed to evaluate whether these factors also scale‐up to the formation of modules in the network. Interaction frequencies were best predicted by species morphology, phenology and habitat occupancy, while species abundances and nectar availability performed poorly. The plant–hummingbird network was modular, and modules were associated to morphological specialization and habitat occupancy. Our findings highlight the importance of traits as determinants of interaction frequencies and network structure, corroborating the results of a previous study on a plant–hummingbird network from the Brazilian Atlantic Forest. Thus, we propose that traits matter more in tropical plant–hummingbird networks than in less specialized systems. To test the generality of this hypothesis, future research could employ geographic or taxonomic cross‐system comparisons contrasting networks with known differences in level of specialization.

-(Functional morphology and ecology of tree species seedlings of the Ecological Station of Panga, Uberlândia, Minas Gerais). The seedling functional morphology classification was used to study 122 tree species occurring at the Ecological Station of Panga, Uberlândia, Minas Gerais. The tree species of three contiguous forest formations -gallery forest, semideciduous forest and "cerradão" -had their seedlings classified according to the position, texture and cotyledon exhibition. This study intended to verify if all the studied species would fit in a functional morphology classification system and if seedling morphology would have any relation with some ecological traits, such as successional group, type of dispersal, fruiting period, seed weight, habitat, sexual system, and root/stem biomass allocation. The species were subdivided into five categories: 63 species of the phanero-epigeal-foliaceous type (PEF), 20 phanero-epigeal-reserve type (PER), 10 phanero-hypogeal-reserve type (PHR), 28 crypto-hypogeal-reserve type (CHR) and only one species of the crypto-epigeal-reserve type (CER). The classification used was very effective, representing almost all the studied species. There were no significant relationships between functional morphology groups and type of dispersal, fruiting period, root/stem biomass or micro-habitat. On the other hand, significant relationships were found between successional groups, seed weight and sexual systems with seedling functional morphology categories. Pioneer species, mostly with small and light seeds, presented almost exclusively PEF seedlings, while shade tolerant climax species, which usually produce fewer and larger seeds with plenty of reserves, showed mostly CHR seedlings. This seedling type prevails also among the dioecious species. The results demonstrated that morphology has, at least in early stages, a determinant role in the processes of tree seedling establishment and development.Key words -cerrado, cotyledons, ecology, establishment, seedling RESUMO -(Ecologia morfofuncional de plântulas de espécies arbóreas da Estação Ecológica do Panga, Uberlândia, Minas Gerais). Realizou-se a classificação morfofuncional de plântulas de 122 espécies arbóreas da Estação Ecológica do Panga. Espécies de três formações florestais contíguas -mata de galeria, mata mesófila semidecídua e cerradão -tiveram suas plântulas classificadas segundo suas características cotiledonares de posição, textura e exposição. O estudo objetivou verificar se as espécies estudadas enquadravam-se no sistema de classificação utilizado e se existiria alguma relação entre os tipos morfofuncionais de plântulas com grupos sucessionais, síndrome de dispersão, peso das sementes, micro-habitat, sistemas sexuais, épocas de frutificação e relação entre a biomassa de raízes e partes aéreas. As espécies foram incluídas em cinco categorias, sendo 63 espécies do tipo fanero-epígeo-foliáceo (PEF), 20 fanero-epígeo-armazenador (PER), 10 fanero-hipógeo-armazenador (PHR), 28 cripto-hipógeo-armazenador (CHR) e apenas um...

Generalization prevails in flower-animal interactions, and although animal visitors are not equally effective pollinators, most interactions likely represent an important energy intake for the animal visitor. Hummingbirds are nectar-feeding specialists, and many tropical plants are specialized toward hummingbird-pollination. In spite of this, especially in dry and seasonal tropical habitats, hummingbirds may often rely on non-ornithophilous plants to meet their energy requirements. However, quantitative studies evaluating the relative importance of ornithophilous vs. non-ornithophilous plants for hummingbirds in these areas are scarce. We here studied the availability and use of floral resources by hummingbirds in two different areas of the Cerrado, the seasonal savannas in Central Brazil. Roughly half the hummingbird visited plant species were non-ornithophilous, and these contributed greatly to increase the overall nectar availability. We showed that mean nectar offer, at the transect scale, was the only parameter related to hummingbird visitation frequency, more so than nectar offer at single flowers and at the plant scale, or pollination syndrome. Centrality indices, calculated using hummingbird-plant networks, showed that ornithophilous and non-ornithophilous plants have similar importance for network cohesion. How this foraging behaviour affects reproduction of non-ornithophilous plants remains largely unexplored and is probably case specific, however, we suggest that the additional energy provided by non-ornithophilous plants may facilitate reproduction of truly ornithophilous flowers by attracting and maintaining hummingbirds in the area. This may promote asymmetric hummingbird-plant associations, i.e., pollination depends on floral traits adapted to hummingbird morphology, but hummingbird visitation is determined more by the energetic "reward" than by pollination syndromes.

Aim: Among the world's three major nectar-feeding bird taxa, hummingbirds are the most phenotypically specialized for nectarivory, followed by sunbirds, while the honeyeaters are the least phenotypically specialized taxa. We tested whether this phenotypic specialization gradient is also found in the interaction patterns with their floral resources.Location: Americas, Africa, Asia and Oceania/Australia. Methods:We compiled interaction networks between birds and floral resources for 79 hummingbird, nine sunbird and 33 honeyeater communities. Interaction specialization was quantified through connectance (C), complementary specialization (H 2 0 ), binary (Q B ) and weighted modularity (Q), with both observed and null-model corrected values. We compared interaction specialization among the three types of bird-flower communities, both independently and while controlling for potential confounding variables, such as plant species richness, asymmetry, latitude, insularity, topography, sampling methods and intensity.Results: Hummingbird-flower networks were more specialized than honeyeaterflower networks. Specifically, hummingbird-flower networks had a lower proportion of realized interactions (lower C), decreased niche overlap (greater H 2 0 ) and greater modularity (greater Q B ). However, we found no significant differences between hummingbird-and sunbird-flower networks, nor between sunbird-and honeyeaterflower networks.

Rubiaceae contains the largest number of distylous species in the Angiosperms, but the evolution and control of distyly is poorly understood in this group. Atypical distylous populations and species have been described in this family and associated with disturbance, pollination failure and impaired reproductive success. Some of these atypical taxa belong to Psychotria, the largest genus in the family. In the present study, we investigate the pollination and breeding biology of Psychotria carthagenensis Jacq., a widely distributed species that has been described as typically distylous. Fieldwork was carried out mainly at the Panga Ecological Station, in Uberlândia, MG, Brazil. We carried out phenological observations, floral biology studies and hand pollination experiments within the Panga Ecological Station population. We complemented these data with herbarium and field surveys from elsewhere in Brazil. The studied population bloomed at the beginning of the rains (September-December). The main pollinators were Bombus and small Halictidae bees. The Panga Ecological Station population presented pinmonomorphism with only two thrum individuals in more than 100 flowering individuals surveyed. Hand pollinations at the Panga Ecological Station showed self-compatibility and intramorph compatibility. Typical distyly and isoplethy were found in other areas and both morphs appeared in herbarium material. However, pin-monomorphism was also observed elsewhere in Brazil. Typical distyly, pin-monomorphism and homostyly observed concurrently in Brazilian populations of P. carthagenensis indicate that alternative reproductive strategies, probably favoring selfing, appear to have developed independently in this species.