The influence of climatic seasonality on the diversity of different tropical pollinator groups.

Stefan Abrahamczyk,Yuvinka Gareca,Michael Kessler,Jürgen Kluge,Steffen Reichle,Jerome Chave

doi:10.1371/journal.pone.0027115

Abstract

Tropical South America is rich in different groups of pollinators, but the biotic and abiotic factors determining the geographical distribution of their species richness are poorly understood. We analyzed the species richness of three groups of pollinators (bees and wasps, butterflies, hummingbirds) in six tropical forests in the Bolivian lowlands along a gradient of climatic seasonality and precipitation ranging from 410 mm to 6250 mm. At each site, we sampled the three pollinator groups and their food plants twice for 16 days in both the dry and rainy seasons. The richness of the pollinator groups was related to climatic factors by linear regressions. Differences in species numbers between pollinator groups were analyzed by Wilcoxon tests for matched pairs and the proportion in species numbers between pollinator groups by correlation analyses. Species richness of hummingbirds was most closely correlated to the continuous availability of food, that of bees and wasps to the number of food plant species and flowers, and that of butterflies to air temperature. Only the species number of butterflies differed significantly between seasons. We were not able to find shifts in the proportion of species numbers of the different groups of pollinators along the study gradient. Thus, we conclude that the diversity of pollinator guilds is determined by group-specific factors and that the constant proportions in species numbers of the different pollinator groups constitute a general pattern.

Highlights

Animal pollination is one of the key ecosystem services in natural habitats as well as in many agricultural systems [1,2]
We found that the species number of butterflies and hummingbirds increased from south to north towards the equator, which corresponds to the well-known latitudinal gradient of species richness in these groups [17,20]
Bees are known to be more species rich in warm and dry regions than in the wet tropics [22,23]. The causes determining these richness patterns are still unclear and may involve a variety of current ecological and historical factors. Among the former, we hypothesized that food availability should be more closely related to species richness of our study groups than purely climatic factors

Summary

Introduction

Animal pollination is one of the key ecosystem services in natural habitats as well as in many agricultural systems [1,2]. Our study was directed at addressing this knowledge gap by exploring the relations of the diversity between the three main diurnal pollinator groups (bees and wasps, butterflies, hummingbirds) to climatic factors as well as to flower number and food plant diversity along a natural gradient of precipitation and climatic seasonality in tropical and subtropical Bolivian forests. This region, located at the southern margin of the Amazon basin presents a good opportunity to assess how pollinator assemblages change along a climatic gradient mimicking the changes predicted for the decades [37]. Towards areas with lower climatic seasonality, pollinator assemblages include a higher proportion of hummingbirds and their food plants relative to insect pollinators and their food plants

Materials and Methods

Results

Discussion