Behavioural and morphological traits influence sex-specific floral resource use by hummingbirds

Research on resource partitioning in plant-pollinator mutualistic systems
is mainly concentrated at the levels of species and communities, whereas
differences between males and females are typically ignored. Nevertheless,
pollinators often show large sexual differences in behaviour and
morphology, which may lead to sex-specific patterns of resource use with
the potential to differentially affect plant reproduction and
diversification. We investigated variation in behavioural and
morphological traits between sexes of hummingbird species as potential
mechanisms underlying sex-specific flower resource use in ecological
communities. To do so, we compiled a dataset of plant-hummingbird
interactions based on pollen loads for 31 hummingbird species from 13
localities across the Americas, complemented by data on territorial
behaviour (territorial or nonterritorial) and morphological traits (bill
length, bill curvature, wing length and body mass). We assessed the extent
of intersexual differences in niche breadth and niche overlap in floral
resource use across hummingbird species. Then, we tested whether floral
niche breadth and overlap between sexes are associated with sexual
dimorphism in behavioural or morphological traits of hummingbird species,
while accounting for evolutionary relatedness among the species. We found
striking differences in patterns of floral resource use between sex.
Females had a broader floral niche breadth and were more dissimilar in the
plant species visited with respect to males of the same species, resulting
in a high level of resource partitioning between sexes. We found that both
territoriality and morphological traits were related to sex-specific
resource use by hummingbird species. Notably, niche overlap between sexes
was greater for territorial than nonterritorial species, and moreover,
niche overlap was negatively associated with sexual dimorphism in bill
curvature across hummingbird species. These results reveal the importance
of behavioural and morphological traits of hummingbird species in
sex-specific resource use and that resource partitioning by sex is likely
to be an important mechanism to reduce intersexual competition in
hummingbirds. These findings highlight the need for better understanding
the putative role of intersexual variation in shaping patterns of
interactions and plant reproduction in ecological communities.