Spatiotemporal pattern of specialization of sunbird-plant networks on Mt. Cameroon.

Differences in interaction specializations between nectarivorous birds and plants across continents serve as common examples of evolutionary trajectory specificity. While New World hummingbird-plant networks have been extensively studied and are considered highly specialized, knowledge on the network specialization of their Old World counterparts, sunbirds (Nectariniidae), remains limited. A few studies from tropical Africa indicate that sunbird-plant networks are rather generalized. Unfortunately, these studies are limited to dry seasons and high elevations at the tree line, environments where niche-based hypotheses also often predict lower resource partitioning. In our study, we explored the specialization of sunbird-plant networks and their spatiotemporal variability on Mt. Cameroon (Cameroon). Using a combination of automatic video recordings and personal observations, we constructed eight comprehensive sunbird-plant networks in four forest types at different elevations in both the dry and wet seasons. As reported in previous studies, the montane forest plants, birds and whole networks were highly generalized. Nevertheless, we observed a much higher specialization in forests at lower elevations. Except at the lowest altitude, the wet season was also characterized by higher specialization. While less specialized flowering trees dominated in the dry season networks, more specialized herbs and shrubs were visited by birds during the wet season. As our findings do not support the generally accepted assumption that Old World bird-plant networks are rather generalized, we need further studies to understand the differences in bird-plant specializations on individual continents.

Spatial scaling of plant and bird diversity from 50 to 10,000 ha in a lowland tropical rainforest.

While there are numerous studies of diversity patterns both within local communities and at regional scales, the intermediate scale of tens to thousands of km2 is often neglected. Here we present detailed local data on plant communities (using 20 × 20 m plots) and bird communities (using point counts) for a 50 ha ForestGEO plot in lowland rainforest at Wanang, Papua New Guinea. We compare these local diversity patterns with those documented in the surrounding 10,000 ha of lowland rainforest. Woody plant species richness was lower within 50 ha (88% of 10,000 ha richness), even when both were surveyed with identical sampling effort. In contrast, bird communities exhibited identical species accumulation patterns at both spatial scales. Similarity in species composition (Chao-Jaccard) remained constant while similarity in dominance structure (Bray-Curtis) decreased with increased distance between samples across the range from < 1 to 13.8 km for both plant and bird communities. The similarity decay was more rapid in plants, but in both cases was slow. The results indicate low to zero beta-diversity at the spatial scale represented here, particularly for birds but also for woody plants. A 50 ha plot provided a highly accurate representation of broader-scale diversity and community composition within 10,000 ha for birds, and a relatively good representation for woody plants. This suggests potential for wider generalization of data from ForestGEO plots which are almost always locally unreplicated, at least for those in lowland tropical forest.

The drivers of avian-haemosporidian prevalence in tropical lowland forests of New Guinea in three dimensions.

Haemosporidians are among the most common parasites of birds and often negatively impact host fitness. A multitude of biotic and abiotic factors influence these associations, but the magnitude of these factors can differ by spatial scales (i.e., local, regional and global). Consequently, to better understand global and regional drivers of avian-haemosporidian associations, it is key to investigate these associations at smaller (local) spatial scales. Thus, here, we explore the effect of abiotic variables (e.g., temperature, forest structure, and anthropogenic disturbances) on haemosporidian prevalence and host-parasite networks on a horizontal spatial scale, comparing four fragmented forests and five localities within a continuous forest in Papua New Guinea. Additionally, we investigate if prevalence and host-parasite networks differ between the canopy and the understory (vertical stratification) in one forest patch. We found that the majority of Haemosporidian infections were caused by the genus Haemoproteus and that avian-haemosporidian networks were more specialized in continuous forests. At the community level, only forest greenness was negatively associated with Haemoproteus infections, while the effects of abiotic variables on parasite prevalence differed between bird species. Haemoproteus prevalence levels were significantly higher in the canopy, and an opposite trend was observed for Plasmodium. This implies that birds experience distinct parasite pressures depending on the stratum they inhabit, likely driven by vector community differences. These three-dimensional spatial analyses of avian-haemosporidians at horizontal and vertical scales suggest that the effect of abiotic variables on haemosporidian infections are species specific, so that factors influencing community-level infections are primarily driven by host community composition.

Differences in Nectar Traits between Ornithophilous and Entomophilous Plants on Mount Cameroon.

Despite a growing number of studies, the role of pollinators as a selection agent for nectar traits remains unclear. Moreover, the lack of data from some biogeographic regions prohibits us from determining their general importance and global patterns. We analyzed nectar carbohydrate traits and determined the main pollinators of 66 plant species in the tropical forests of Mount Cameroon (tropical West Africa). The measured nectar traits included total sugar amounts and proportions of sucrose and hexoses (i.e., glucose and fructose). We report the nectar properties for plants visited by five pollinator groups (bees, butterflies, moths, hoverflies, and specialized birds). Our results indicate that, rather than specific evolution in each of the five plant groups, there was a unique nectar-trait evolution in plants pollinated by specialized birds. The ornithophilous plants had a higher proportion of sucrose and produced larger sugar amounts than the plants pollinated by insects. We also demonstrated a significant phylogenetic signal in the nectar properties in some lineages of the studied plants.

Ecological fitting is a sufficient driver of tight interactions between sunbirds and ornithophilous plants.

Plant-bird pollination interactions evolved independently on different continents. Specific adaptations can lead to their restriction when potential partners from distant evolutionary trajectories come into contact. Alternatively, these interactions can be enabled by convergent evolution and subsequent ecological fitting.We studied the interactions between New World plants from the genus Heliconia, Asian plants of genus Etlingera and African sunbirds on a local farm in Cameroon. Heliconia spp. evolved together with hummingbirds and Etlingera spp. with spiderhunters -an oriental subgroup of the sunbird family.Sunbirds fed on all studied plants and individual plant species were visited by a different sunbird spectrum. We experimentally documented a higher number of germinated pollen grains in sunbird-visited flowers of Etlingera spp. For Heliconia spp., this experiment was not successful and pollen tubes were rarely observed, even in hand-pollinated flowers, where enough pollen was deposited. The analyses of contacts with plant reproductive organs nevertheless confirmed that sunbirds are good pollen vectors for both Heliconia and Etlingera species.Our study demonstrated a high ecological fit between actors of distinct evolutionary history and the general validity of bird-pollination syndrome. We moreover show that trait matching and niche differentiation are important ecological processes also in semi-artificial plant-pollinator systems.

Plumage iridescence is associated with distinct feather microbiota in a tropical passerine.

Birds present a stunning diversity of plumage colors that have long fascinated evolutionary ecologists. Although plumage coloration is often linked to sexual selection, it may impact a number of physiological processes, including microbial resistance. At present, the degree to which differences between pigment-based vs. structural plumage coloration may affect the feather microbiota remains unanswered. Using quantitative PCR and DGGE profiling, we investigated feather microbial load, diversity and community structure among two allopatric subspecies of White-shouldered Fairywren, Malurus alboscapulatus that vary in expression of melanin-based vs. structural plumage coloration. We found that microbial load tended to be lower and feather microbial diversity was significantly higher in the plumage of black iridescent males, compared to black matte females and brown individuals. Moreover, black iridescent males had distinct feather microbial communities compared to black matte females and brown individuals. We suggest that distinctive nanostructure properties of iridescent male feathers or different investment in preening influence feather microbiota community composition and load. This study is the first to point to structural plumage coloration as a factor that may significantly regulate feather microbiota. Future work might explore fitness consequences and the role of microorganisms in the evolution of avian sexual dichromatism, with particular reference to iridescence.