Changing wildlife: this article is part of a series looking at how key species such as bees, insects and fish respond to environmental change, and what this means for the rest of the planet.
We may lose a lot more than honey if bees are unable to cope with the changing climate and increasing demand for agricultural land.
Your morning coffee might be a thing of the past if bees disappear, and if coffee isn’t your thing, you undoubtedly eat many of the fruit and vegetables (and chocolate) that rely on bee pollination for survival.
In fact, the world’s 25,000 bee species are responsible for pollinating a third of the food humans eat. If we lose bees, then we risk the food security of ourselves, and all the other animals that depend on bee-pollinated crops for survival.
While European (managed) honey bees steal the limelight, other wild (non-honey) bees are just as important for pollinating crops and will also be impacted by climate change. Data from all over the globe suggest that both groups are in decline, but since we do not have a global integrated and complete monitoring system of bee populations, these data do not describe the full extent of the problem.
So how well equipped are bees to survive a warming climate, and is there anything we can do to help?
Bees and plants: it’s a long-term relationship
Bees and flowering plants share a long evolutionary relationship and depend on each other for survival. Plants provide bees with food and habitat, while the bees feeding on pollen and nectar provide the plants with pollination.
To orchestrate this beautiful exchange, plants and bees rely on environmental cues (such as temperature) to coordinate their seasonal activity. However, climate change can disrupt these relationships so that bee activity periods will no longer time with flowering periods. This will cause the bees to lose a food source and plants that fail to fruit, potentially leading to extinctions of both.
Some plant-bee relationships are highly specialised. These species have evolved together so closely that a plant can depend on a single bee species in order to reproduce and vice versa.
Bees in specialist plant-bee relationships (such as this one) are most susceptible to climate induced extinction, as the loss of one will inevitably lead to the loss of the other.
More generalist bee species, that can collect food from more than one plant species, may fare better than their specialist counterparts. As the climate changes, animals and plants evolve new genetic traits to adapt to the new environment.
However, when the environment changes at a faster pace than evolution can produce new traits, species that already have the physiological and behavioural abilities within its genetic code to cope with the changes will have an advantage.
A bee species that can already access more than one food source (such as the honey bee) can quickly adapt to changing plant communities and survive when other specialist species cannot.
‘Beehaving’ differently in the heat
Bee species that can alter their behaviour to cope with high temperatures (for example by changing their activity periods to avoid the hottest part of the day) will tolerate climate stress. But these adaptive capabilities have their limits.
Increasing heat waves can directly kill bees by overheating them and/or melting wax-based nesting structures. Drought can also kill bees indirectly, by causing dehydration or starvation through the death of food plants.
Alternatively, it is possible that bees will change their range in response to changing climactic zones. As one area gets too hot, the bees can move to more tolerable climatic conditions.
However, a study on bumble bees conducted in North America and Europe using data spanning the last century indicate that bumble bees do not move in a way that “tracks” warming. Rather, they stay in the same place despite the changing climate.
While most of us think bees live in colonies, most of the world’s bees are actually solitary. In solitary species, female bees generally live alone in nests they’ve built, in which they raise their offspring.
Most bee species are also fixed in their social structures, with some species living alone while others have varying degrees of social behaviour. However, a few native bee can change their social structure depending on the environment, so bees that are solitary in one set of environmental conditions are social under another. These socially flexible species may have surprising responses to climate change.
As the weather warms and growing seasons lengthen, socially flexible bees (such as some carpenter and sweat bees) may, eventually, switch permanently from solitary behaviour to social behaviour. However this may also decrease their ability to adapt.
Bee habitats are disappearing
While changing the climate, humans have also made dramatic changes to Earth’s landscapes. Increasing human population and our consequent demands for space to live and grow food has meant that more of the bees’ habitat has been changed into urban and intensive agricultural areas.
This has resulted in loss of habitat and food sources for the bees (as well as exposure to potentially harmful pesticides). Large areas of monoculture crops fragment vital bee habitats that are required for native bee food and nests. The crops may not provide a suitable food sources for certain bee species and generalist bee species such as the honey bee suffer compromised immunity when only fed one source of pollen.
Our agricultural pollination needs cannot be met with honey bee pollination alone, as native bees are often specialised pollinators for crops honey bees cannot pollinate. For example, the solitary alfalfa leafcutting bee pollinates alfalfa, an important crop for animal feed and a plant with a trip-mechanism that honey bees avoid. Furthermore, native and honey bees can work cooperatively to pollinate, producing the maximum crop yield required for efficient food production.
The problems with taking over bee habitats can be partly resolved by leaving adequate wildflower borders between fields and in urban areas. This can link habitats and food sources (such as Norway’s bee highway) so that bees can move across the entire landscape.
Bees are interpretive dancers
Just as plants and bees are codependent, we are dependent on their relationship for survival and must do our best to keep bees healthy, and this means more research about all aspects of the lives of wild bees including their influence on pollination. Without knowledge of how they live and their habitat needs, we cannot adequately protect them.
In the case of the honey bee, we can find out what food sources it prefers by asking the bees themselves. Honey bees perform a waggle dance to communicate the direction and distance of their preferred food source, and how much they like it (a honey bee dance is more “vigorous” when they really value a food source).
By interpreting the dance of the honey bee workers, and identifying the pollen on their legs to determine which plant they are dancing about, we can find out where and when they like to forage. This information on foraging behaviour can also be used as an indicator of the biodiversity in the area, and whether the landscape is healthy for bees.
The knowledge we gain from the bees can be used to help conserve them, and in turn, conserve ourselves.
Marianne Peso has previously received funding from the Australian Produce Council.