Influence of climate, weather and floral associations on pollinator community composition across an elevational gradient

Insect pollinators, which are ectothermic, are especially sensitive to
abiotic conditions, which often drive predictable patterns of pollinator
species turnover along environmental gradients. However, pollinator
activity is also reliant on suitable biotic conditions, such as the
presence of host plants. High-elevation environments provide a useful
setting to examine the relative contribution of abiotic and biotic factors
in shaping species interactions as they are often characterised by strong
environmental gradients over short geographic distances. Here, we examined
pollination interaction networks across an elevational gradient from
930-2000m a.s.l. in southern Australia, to determine the underlying
patterns of pollinator activity and their interactions with flowers. The
interaction frequency of Diptera increased at high elevations, while the
interaction frequency of Hymenoptera and Coleoptera decreased. We provide
evidence that this elevational pattern of activity is partly driven by
floral associations, with interactions dominated by Hymenoptera-attracting
plant families at lower elevations (Proteaceae, Fabaceae) and a
Diptera-attracting family at high elevations (Asteraceae). Pollinator
activity was also influenced by weather conditions, with reduced activity
for all three orders at lower temperatures, and Diptera active across the
broadest range of temperature, humidity, and wind conditions. We suggest
that changes across elevation gradients in pollinator community
composition are driven by both direct responses to abiotic conditions such
as temperature, as well as the elevational distribution patterns of
associated flowering plants. Despite these distinct shifts in the
composition of the pollinator assemblage with elevation, the pollination
network structure was stable across the elevational gradient, with
moderate levels of specialisation and low levels of connectance and
nestedness present across the gradient. By considering both abiotic
conditions and biotic processes, our results provide insight for
predicting the impacts of upslope vegetation shifts on pollinator
communities in the face of climate change.