When we think of bees, we often think of flowers. The more flowers the better, right? Well, not exactly. Like us, bees need to consume specific nutrients in suitable amounts and combinations.
So, the mere presence of flowers doesn’t necessarily mean the bees are getting nutritionally adequate food.
This matters because climate change is altering both the quantity and nutritional composition of pollen and nectar. At the same time, what nutrition the bees need is likely shifting, too. This creates rapidly moving goalposts – it’s increasingly difficult for bees to find and consume the right nutrients they need to reproduce, develop and survive.
In our new paper published in Current Opinion in Insect Science, we argue these changes are unlikely to affect all bees equally. Currently, most of what we know about bee nutrition comes from highly social species such as honeybees or bumblebees.
Yet most bees, including many native Australian species, are solitary or communal (group living but with no queens and workers). They might experience the nutritional landscape and nutritional stress in very different ways.
Understanding these differences is crucial for predicting which bees are most vulnerable under climate change.
Alison Mellor, Invertebrates Australia
Not all bees will encounter nutritional stress
One way to better understand vulnerability to nutritional stress is to think about the traits that shape how different bees interact with their environments. These include:
- how far they can forage
- how flexible their diets are
- whether they live alone or in groups
- how large those groups tend to be.
These traits can influence whether bees even encounter nutritional stress in the first place.
For example, a species with a large foraging range and a broad diet might live in a nutritionally poor landscape, but still be able to travel far enough, or combine pollen from different flowers, to meet its nutritional requirements. In contrast, species with narrower diets or shorter foraging ranges might have fewer opportunities to balance their diets.
Native stingless bees, such as Tetragonula carbonaria, generally forage over shorter distances than honeybees. This could make them more dependent on the nutritional quality of nearby flowers and more vulnerable to a changing climate.
marielaurenceo/iNaturalist, CC BY-NC
Living in a group may help a little
Once nutritional stress occurs, other traits will determine how this stress is buffered and absorbed.
T. carbonaria, for instance, live in colonies with workers that collect food and share resources. This kind of social organisation can buffer short-term changes in the environment. Even if their foraging range is small, and one floral resource declines for a season, a colony might be able to shift foraging effort, draw on stored resources, or distribute food among nestmates and brood.
But despite potential buffering, poor nutrition can still impact social species. This can show up as fewer offspring, slower colony growth, smaller workers, weaker immunity, or reduced ability to cope with other stressors, such as heat or pesticides.
Solitary bees might have fewer safety nets
Solitary bees, by contrast, will likely face different problems when it comes to nutritional stress. Many native bees, such as blue banded bees (Amegilla chlorocyanea, pictured below), don’t benefit from the support of a colony.
A single female must find a nest, collect pollen, lay eggs and provide food for her offspring. Under predictable conditions, this can be a very effective way of interacting with the environment.
Alison Mellor, Invertebrates Australia
However, if the right flowers are missing, bloom too late, or produce pollen containing different nutrients to what the bee has evolved to expect, the effects could be more immediate: fewer nests, smaller offspring, fewer daughters and lower chance of survival.
In these species, the condition of one female can shape the next generation, so poor nutrition might lead to rapid population declines. This means the timing and quality of floral resources are likely to be especially important for many of our native bees.
How we can help our native bees
To accurately predict how species respond to climate change, future studies will need to connect floral nutrition with bee performance in real landscapes. Most importantly, we need to include a diverse range of bees with different social lives and traits in these studies.
For now, there are still practical steps we can take to support our native bees at home. Rather than simply planting more flowers, we need to be more deliberate about what we plant.
Carmen da Silva.
Native plants are of course important, but we should plant them in diverse mixes, to account for variability in nutritional availability and timing.
The same applies to nesting habitats. Many native bees will not use a hive or a bee hotel. Some need bare or lightly disturbed ground; others use stems, wood or existing cavities.
So avoid the urge to over-manage every patch of ground – leave some bare earth and dead branching stems in your roses and other plants. This will make your garden or landscape more useful to more bees, so we can help support them in this rapidly changing world.
