This was a fun collaboration that started a few years ago when I was postdoc in the Rader Lab. It originated with an idea I proposed one day in a lab meeting to test a common assumption about pollinators: that flies are more common pollinators than bees when it’s cold.
This is one of those anecdotal assumptions that any pollination ecologist ‘knows’ is very likely true, based on what we see in the field and what we know about relevant ecology. There are localised studies that show these patterns occur at particular times and places, but when you need a general reference to cite, there is very little evidence at the global scale to support a general pattern.
So a group of us decided to test this by collating as many publicly available plant-pollinator network datasets we could find. There are a lot of cool studies that have collated plant-pollinator networks from around the world to test for general patterns in network structure and species richness. However, these mostly test for patterns at the network level – all pollinator nodes are grouped together as one type of node.
We were more interested in an overlooked aspect of plant-pollinator network ecology, i.e. whether the network roles of different pollinator taxa vary between climate zones. We focused on the four main insect pollinator orders (Hymenoptera, Diptera, Lepidoptera and Coleoptera) and to test these relationships, we used Köppen–Geiger climate zones, which represent biome distributions and combine complex climate gradients and vegetation patterns into simple, ecologically meaningful categories.
Our results show empirical evidence that climate strongly influences the network roles of different pollinator groups. In the tropical climate zone, network interactions were dominated by bees and non-syrphid Diptera. Arid zones were dominated by Hymenoptera (bees and non-bees) and non-syrphid Diptera. Temperate networks were dominated by bees, and continental and polar zone networks were dominated by bees and Diptera (Syrphidae and non-syrphids).
These results give empirical support to the hypothesis that flies may be more important pollinators in cold weather and cooler climate zones. But, more importantly, we show an important link between climate and plant-pollinator networks at the global scale. We hope our results initiate further exploration of how the multivariate climate space influences network structure and the functional roles of pollinator insect species!
© Manu Saunders 2023
