Browsing by Author "Gottleuber, Peter"

Amazonian rainforests are among the most species-rich terrestrial habitats on Earth. The aim of this study was to analyze phylogenetic diversity (PD) patterns of orchid bee assemblages along a latitudinal gradient of 15 degrees from northern Peru to central Bolivia and to relate them to climatic factors and geological history. We expanded an existing phylogeny of orchid bees and analyzed the PD of 15 orchid bee assemblages along a latitudinal gradient using mean pair-wise phylogenetic distance. The resulting pattern was correlated to climatic factors and elevation. We found a hump-shaped pattern of PD that peaked in central Peru and decreased towards the equatorial and especially towards the southern, subtropical sites. The decrease in PD towards higher latitudes is a common pattern found in many taxa, which in our case correlates with increasing climatic seasonality. However, the decrease towards the equatorial sites is unusual and may be related to a particular historic event: the northern sites with low PD are situated in the area of the former Lake Pebas, which covered western Amazonia until 3 mya. After the lake disappeared orchid bees mainly belonging to two distantly related species groups apparently colonized the region and diversified, which led to the comparatively low observed PD. In contrast, in central Peru, no in situ radiations were detected, hence the assemblages were composed of species from diverse phylogenetic lineages. Additionally, we identified multiple phylogenetically independent radiations of regionally restricted Euglossa species along the latitudinal gradient that, according to a published, dated phylogeny, diversified roughly 3-1 mya. The hump-shaped latitudinal pattern of PD of the orchid bees of western Amazonia thus appears to have resulted from a preponderance of early divergent lineages in central Peru and of young radiations from distantly related clades colonizing higher latitudes, possibly triggered by historic climate fluctuations and major geological events.

Tropical forests are known for their diverse insect fauna. We aimed to determine the effect and relative importance of latitude, elevation and climatic factors affecting species richness and turnover in euglossine bee assemblages along a gradient of 18A degrees A latitude from tropical rainforests to subtropical, deciduous dry forests in Peru and Bolivia. Sixteen forest sites were sampled during the dry season. Variance partitioning techniques were applied to assess the relative effects of the spatial and environmental variables on species richness and composition. Furthermore, we conducted a Species Indicator Analysis to find characteristic species for the biogeographic zones. There was a significant decrease in species richness towards the subtropical area. The best predictors of species richness were precipitation and its consequences on soil properties as well as temperature seasonality. The abundance of euglossines was most closely related to precipitation and soil-pH, but the causal links of abundance to these factors is unclear since soil-pH itself is correlated to a drastic turnover of vegetation structure. Based on the analysis of assemblage composition we propose three different assemblages with a transitional zone at the southern tropical area. The biogeographical distribution of euglossine bees along our study transect appears to be primarily related to climatic conditions and does not reflect the common subdividion of Amazonia into drainage systems.

Orchid bees are an important group of specialized insect pollinators in the Neotropics. Male orchid bees are attracted by a wide range of aromatic substances often produced by flowers. Previous studies found that in some species the males change their aromatic preferences between seasons. In our study we documented seasonal changes of aromatic preferences in five euglossine bee assemblages along a 380-km-long seasonality and precipitation gradient and related them to climatic factors. We found that the proportion of species per site showing changes in their aromatic preference between seasons increased with climatic seasonality towards the south. Those species mainly belong to the genus Euglossa, subgenus Euglossa. We conclude that climatic seasonality mainly affects the orchid bees via the turnover of the aromatic substances provided by the plants. Further, we suggest that the ability to change the aromatic preference between seasons could be interpreted as a phylogenetic pre-adaptation that enabled some species to colonize climatically strongly seasonal habitats.