Pollinators – including bees, flies, wasps, moths, butterflies and some nectar-loving birds – are a cornerstone of our natural environment.
By helping plants reproduce, they keep our ecosystems healthy and ensure we can grow vital food crops.
But climate change threatens the of these hard-working animals.
has focused on how temperature changes affect bees, finding that certain groups are more vulnerable to hotter temperatures.
But our shows rising carbon dioxide (CO鈧�) levels may also be putting pollinators – such as bees and hoverflies – at risk.
Larger bees are the most vulnerable. We found populations of big bees – including Bombus asiaticus and Xylocopa pubescens – were smaller and less genetically diverse in areas with high CO鈧�. Small-bodied pollinators, however, may actually do better in higher-CO鈧� environments.
A dire situation
In Australia and around the world, we are facing a . There are several reasons for this, including the loss and degradation of wild pollinator habitat, the introduction of the European honey bee and other invasive species, and the use of broad-spectrum pesticides.
But climate change – driven by human-made greenhouse gases including CO鈧� emissions – is another key factor. Australia contributes to higher CO鈧� levels as the second-largest in the world.
Elevated CO鈧� levels can affect pollinators by reducing is in flower pollen. Having more CO鈧� in our atmosphere may also change the chemical , for example reducing how much sugar it contains. Both factors influence how pollinators develop and survive.
suggests higher CO鈧� concentrations could impact how pollinators’ bodies function, for example by accelerating how quickly they .
What we studied
In our , we examined how bees and hoverflies coped with different levels of CO鈧� across 25 sites. This is the first time researchers have investigated how natural changes in CO鈧� levels affect pollinators.
While our study was conducted in Pakistan, it is relevant to pollinator networks in Australia and around the world, given that CO鈧� levels are rising globally. Importantly, we controlled for other factors that may affect the number and distribution of bees and hoverflies, including altitude, temperature, humidity and rainfall.
Our results suggest pollinators respond to variations in CO鈧� in different ways. Specifically, smaller pollinators may actually do better in higher-CO鈧� environments. In contrast, larger-bodied pollinators were less abundant in areas with more CO鈧�.
We identified Xylocopa and Amegilla bees, two genera found in Australia, as being particularly vulnerable to increased CO鈧� levels. Ceratina and Lasioglossum bees are two examples of smaller-bodied Australian genera that did well in higher-CO鈧� environments.
Why big bees matter
These findings are concerning for several reasons.
shows larger-bodied bees such as Bombus are already more vulnerable to climate change. This is because they tend to retain more heat and don’t cope as well in dry conditions. Big bees also have higher metabolic demands than smaller pollinators, meaning they need more resources to keep their bodies functioning.
Large bees are among our most . They typically carry and deposit more pollen than smaller-bodied pollinator species. They also fly longer distances, meaning they can transport seeds and pollen to help plants reproduce and to new places.
suggests flowers have even evolved to match pollinators with particular body sizes. We see this in Australia with Melastoma. This plant’s impressive flowers are most effectively pollinated by large pollinators such as Xylocopa bees, which use vibrations to release pollen from flowers.
So, what can we do?
Here are four practical ways we can help our larger pollinators thrive in a warming world.
- protect their habitat by preventing, for example to make room for more livestock farms
- ensure pollinators have access to wildlife corridors to help them move to areas that are naturally lower in CO鈧�, such as
- plant more, with some Australian examples being Eucalyptus, Corymbia, Angophora, Melaleuca, Banksia and Brachychiton
- maintain populations of larger-bodied bees by reducing other threats such as competition from , to ensure they have the to adapt to rising CO鈧� levels.
To protect our pollinators in a rapidly changing climate, we must act now. Ensuring their habitat remains intact and curbing our greenhouse gas emissions are vital first steps.
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