I wrote about the design of our study several weeks ago here.
In light of experimental research on how collective foraging in honeybee
colonies enables them to mobilize to
good resources and also explore
less rewarding ones at low risk to the colony, we were interested in
comparing the foraging strategies of honeybees and other pollinators in the
coastal sage scrub habitat in which honeybees seem to struggle during summer
drought when few flowers are blooming. Honeybees differ from other pollinators
found in the region in three important ways that could affect their foraging
strategy: they are not
native to the region and thus not adapted to regional blooming periods,
they live in colonies rather than as solitary individuals, and they use a
complex communication system to share information about resources. We observed
pollinator foraging at three pairs of patches of California buckwheat, each
pair consisting of a ‘large’ and ‘small’ patch; the patches were also at various
stages of flowering. We anticipated that the information-sharing honeybees
would be able to concentrate their foraging efforts on the most rewarding
resources – the ‘large’ patches – but also that their large colony size would
enable some foragers to keep tabs on increasingly less rewarding – senescing – resources. It’s
easy to imagine how these behaviors would help honeybees in their native
habitat where flowers were highly variable in day-to-day value, but do they
confer the same advantages in an ecosystem with one dominant, dwindling
resource?
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| Honeybee foraging on buckwheat |
We saw that honeybees did indeed visit ‘large’ patches per
flower more frequently than ‘small’ patches, while other pollinators visited
each equally. Previous research on the honeybee waggle dance indicates that
this communication system – in which a bee returning from foraging dances to relay information
about a resource’s location to other bees – is used to recruit many foragers to
the best resources. This result suggests that some variable related to patch
size – maybe the proximity of neighbor flowers once one is found, or total
amount of potential nectar/pollen available – is one way that honeybees
determine resource quality. In the regional context, it does make sense that honeybees
forage this way: patches offering many inflorescences close together should
give a greater
net reward than small patches that require more searching and flight time
per unit of energy gain.
But what if it actually takes more time to locate flowers
that have nectar on large patches? As senescence increases, the number of
flowers still producing nectar decreases, meaning a bee would have to check
many flowers before finding a good one. We observed several patterns of
senescence: sometimes one inflorescence had both fully blooming and fully
senesced spots; sometimes inflorescences were alternately blooming or senesced;
sometimes all inflorescences on a plant declined together. In any of these
cases, it seems like a bee would have to do more work to find a flower, making
the resource less valuable to the colony.
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| In the plant pictured at the top, all flowers in all inflorescences seem to decline at the same rate; in the bottom image, each inflorescence consists of some blooming and some senesced flowers. |
But we observed that honeybees visited senescing resources
pretty persistently – patches that were more than 80% senesced still saw many
honeybee visits (certainly more visits than the average at ‘small’ patches).
Meanwhile, other pollinators seemed to quit foraging at senescent resources –
although that could also be attributed to the ends of their foraging seasons,
in synchrony with the end of the buckwheat blooming season. Regardless, it
looks like honeybees continue to visit resources that are declining in value,
even when doing so is probably not energetically favorable.
While exploring less rewarding resources would have often
been a high benefit, low-risk behavior in honeybees’ native tropics (where
nectar rewards frequently oscillate), it’s probably very costly here. The
buckwheat will pretty predictably decline in value without peaking again until
the next blooming season, so continuing to check for peaks in rewards will
never result in the great benefit it did in their native habitat. All this
seems to suggest that ‘exploratory’ foraging is a maladaptive behavior in this
context. Though honeybees are flexible foragers in an environment characterized
by lots of variability and day-to-day change, that versatility does not
necessarily predict their ability to do well in many types of environments.
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| Manually counting buckwheat flowers [1] |
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| Many buckwheat flowers... [1] |
This project gave us some good insights into how pollinators with different evolutionary histories survive in this environment, but it left me with more questions than answers – how do honeybees assess resource quality? I know they don’t painstakingly count all those thousands of flowers by hand like I did. Why wouldn’t the honeybees just stop foraging if it became too costly? What are the advantages and disadvantages of solitary or colonial living in different kinds of changing environments? More research on the behavior of pollinators in diverse habitat types will be useful in exploring these questions and coming up with others.
One current challenge faced by biologists looking to
interpret results like ours is a lack of collected long-term,
geographically diverse data that require time and diligence to record. I
still can’t shake the feeling that although my clipboard and data sheets and
other tools have fooled some into thinking I’m a scientist, all I really did
was count flowers and bees – some elevated version of the backyard
caterpillar-rearing I did as a child. We’re often taught that STEM exists on an
intellectual plane far above the capabilities and understanding of ‘normal’
people, and it’s true that the learning curve for many scientific skills is
steep. But I think that any curious and willing person like myself might be
surprised by how naturally ‘science’ comes to those eager to learn; all the
jargon and technology can be deceptively insulating. You don’t become a
scientist when you wear the right spectacles and know hundreds of equations and
vocabulary terms by heart; it happens when you form questions and
problem-solving methods based on the knowledge we already have so that it can
be built upon, and pursue that knowledge with integrity and hard work. And
there is so, so much I don’t know – I have to ask my lab colleagues daily for
help with software they could probably operate in their sleep. But scientific
pursuit, at least for me, isn’t about getting good at knowing everything; it’s
about getting good at learning.
Citizen science – when interested citizens come to see
themselves as scientists – offers high-quality,
long-running research across many different environments that will be of
great help in contextualizing research like ours on how organisms with various
evolutionary histories fare in different places so we can predict and
understand how environmental change will affect ecosystems. People who are
actively engaged in what’s going on in the natural world around them – whether
formally affiliated with a research institution or not – can contribute
important information and ideas by getting involved with citizen
science networks.
Further reading
Al Toufailia, Hasan, Christoph
Grüter, and Francis L.W. Ratnieks. “Persistence to Unrewarding Feeding
Locations by Honeybee Foragers (Apis Mellifera): The Effects of Experience,
Resource Profitability and Season.” Ethology 119, no. 12 (December 1,
2013): 1096–1106. http://onlinelibrary.wiley.com/doi/10.1111/eth.12170/abstract
Rivera, Michael D., Matina
Donaldson-Matasci, and Anna Dornhaus. “Quitting Time: When Do Honey Bee
Foragers Decide to Stop Foraging on Natural Resources?” Frontiers in Ecology
and Evolution 3 (May 19, 2015): 50. http://dx.doi.org/10.3389/fevo.2015.00050
More citizen science
networks and project descriptions:
Media credits:
[1] Images copyright of Harvey Mudd College
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