Plants use advertising-like strategies to attract bees with colour and scent


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A honeybee (left), a scarab beetle (middle), and a fly (right) feeding on flowers of the white rock rose in a Mediterranean scrubland.
Aphrodite Kantsa., Author provided

Aphrodite Kantsa, University of the Aegean and Adrian Dyer, RMIT University

Watching plants and pollinators such as bees can teach us a lot about how complex networks work in nature.

There are thousands of species of bees around the world, and they all share a common visual system: their eyes are sensitive to ultraviolet, blue and green wavelengths of the light spectrum.

This ancient colour visual system predates the evolution of flowers, and so flowers from around the world have typically evolved colourful blooms that are easily seen by bees.

For example, flowers as perceived by ultraviolet-sensitive visual systems look completely different than what humans can see.

However, we know that flowers also produce a variety of complex, captivating scents. So in complex natural environments, what signal should best enable a bee to find flowers: colour or scent?

Our latest research uncovered a surprising outcome. It seems that rather that trying to out-compete each other in colour and scent for bee attention, flowers may work together to attract pollinators en masse. It’s the sort of approach that also works in the world of advertising.




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Daunting amount of field work

Classic thinking would suggest that flowers of a particular species should have reasonably unique flower signatures. It makes sense that this should promote the capacity of a bee to constantly find the same rewarding species of flower, promoting efficient transfer of pollen.

So a competition view of flower evolution for different flower species with the same colour – for example purple – would suggest that each flowering plant species should benefit from having different scents to enable pollinator constancy and flower fidelity. By the same logic, flowers with the same scents should have different colours so they’re easily distinguished.

To know for sure what happens requires a daunting amount of field work. The challenges include measuring flower colours using a spectrophotometer (a very sensitive instrument that detects subtle colour differences) and also capturing live flower scent emissions with special pumps and chemical traps.

A wild bee of the genus Anthophora upon making the decision to visit the flowers of purple viper’s bugloss, in a Mediterranean scrubland in Greece.
Aphrodite Kantsa.

At the same time, in order to record the actual pollinator “clientele” of the flowers, detailed recordings of visits are required. These data are then built into models for bee perception. Statistical analyses allow us to understand the complex interactions that are present in a real world evolved system.

Not what we thought

And what we found was unexpected. In two new papers, published in Nature Ecology & Evolution and in Nature Communications, we found the opposite to competition happens: flowers have evolved signals that work together to facilitate visits by bees.

So flowers of different, completely unrelated species might “smell like purple”, whilst red coloured species share another scent. This is not what is expected at all by competition, so why in a highly evolved classical signal receiver has this happened?

The data suggests that flowers do better by attracting more pollinators to a set of reliable signals, rather than trying to use unique signals to maximise individual species.

By having reliable multimodal signals that act in concert to allow for easy finding of rewarding flowers, even of different species, more pollinators must be facilitated to transfer pollen between flowers of the same species.




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Lessons for advertising

A lot of research on advertising and marketing is concerned with consumer behaviour: how we make choices. What drives our decision-making when foraging in a complex environment?

While a lot of modern marketing emphasises product differentiation and competition to promote sales, our new research suggests that nature can favour facilitation. It appears that by sharing desirable characteristics, a system can be more efficient.

This facilitation mechanism is sometimes favoured by industry bodies, for example Australian avocados and Australian honey. En masse promotion of the desirable characteristics of similar products can grow supporter base and build sales. Our research suggests evolution has favoured this solution, which may hold important lessons for other complex market based systems.

A successful colour–scent combination targeted at attracting bees can be adopted by several different plant species in the same community, implying that natural ecosystems can function as a “buyers markets”.




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We also know from research that flowers can evolve and change colours to suit the local pollinators. Colours can thus be changed by flowers if instead of bees pollinating flowers, flies, with different colour perception and preferences, dominate the community.

These findings can also prove useful for identifying those colour-scent combinations that are the most influential for the community. This way, the restoration of damaged or disrupted plant-pollinator communities can become better managed to be more efficient in the future.

The ConversationWhen next enjoying a walk in a blooming meadow, remember plants’ strategies. The colourful flowers and the mesmerising scents you experience may have evolved to cleverly allure the efficient pollinators of the region.

Aphrodite Kantsa, Postdoctoral Researcher, University of the Aegean and Adrian Dyer, Associate Professor, RMIT University

This article was originally published on The Conversation. Read the original article.

Birdbath, food or water? How to attract your favourite birds to your garden


Grainne Cleary, Deakin University

This summer, when a rainbow lorikeet or kookaburra comes to visit your home, what will you do? Will you offer them a slice of apple, or simply watch until they take flight?

It brings many people joy to provide food and water for birds, to encourage them to stay a while and be given the chance to observe them more closely. But some people are reluctant to interact with birds in this way because they’re worried it might damage the birds’ health.

In contrast with other countries, little research has been done on the effects of feeding birds in Australia. As a result, there are no established guidelines around how to feed and provide water for local birds.

Kookaburra having a snack.
Photo supplied by Wanda Optland, provided by author.

That’s why we ran the Australian Bird Feeding and Watering Study. We asked nearly 3,000 people to monitor the birds that visited their feeding areas and birdbaths. We wanted to know if there was a difference in the species that visited different types of gardens.

We examined the numbers and types of birds visiting:

  • birdbaths where no food was provided
  • birdbaths where food was provided
  • bird-feeders where birdbaths were provided
  • places where only food was provided.

The early results from the winter stage of the Australian Bird Feeding and Watering Study suggest that if you provide food and water, you will get more birds in your garden. But the species you attract will depend on what exactly your garden has to offer.

Common bronzewings like to eat seeds.
Glenn Pure, CC BY-NC
Providing different combinations of food and water will attract different species.

Granivores

Granivores are seed-eating birds. They include species such as parrots, crested pigeons, sulphur-crested cockatoos, crimson rosellas and galahs.

Gang gang cockatoos refresh themselves in a garden.
Glenn Pure

We noticed a spike in the number of granivores in gardens where both food and birdbaths were provided. But when food was on offer, fewer granivores chose to use the birdbath. We don’t yet know exactly why this is, but it could be because these seed-eaters need less water, or they can get it more easily from other sources than they can food.

Also, most of the bird food sold in shops is seed-based. People who buy these products will naturally attract more seed-eating birds to their garden.

We were, however, surprised to see crested pigeons visiting gardens where food was provided. These birds are only recent urban arrivals, and were previously restricted to semi-arid environments as opposed to the more urban areas where most of our citizen scientists lived. But crested pigeons are very adaptable and now compete fiercely for food and territory with the introduced spotted dove in some Australian gardens.

Many people derive great joy from feeding Australian birds.

Nectarivores

“Small” nectarivores are nectar-eating birds that weigh less than 20 grams. The main birds in this group are New Holland honeyeaters, eastern spinebills and Lewin’s honeyeaters.

The early results of our study suggest small nectarivores prefer gardens with birdbaths more than their granivore and insectivore friends. In fact, it seems that these small nectarivores like birdbaths so much, they will choose birdbaths over food when both are provided.

“Large” nectarivores are nectar-eating birds that weigh more than 20 grams. These species including noisy miners, rainbow lorikeets and red wattlebirds – seem to prioritise food over birdbaths. This may be because they’re looking for a source of protein that they can’t easily find in their natural environment.

Rainbow lorikeets seem to prioritise food over birdbaths.
Photo supplied by Wanda Optland, provided by author.

Honeyeaters – such as Lewin’s honeyeaters, blue-faced honeyeaters and noisy miners – will forage on nectar but will eat insects as well. They switch from one to the other, but once they have found their meal they will defend it vigorously from other birds.

Honeyeaters will forage on nectar but will consume invertebrates as well.
Photo by Wanda Optland, supplied by author.

Insectivores

Insectivores feed on insects, worms, and other invertebrates. Some insectivore species include superb fairy-wrens, willie wagtails and grey fantails.

Insectivores are most attracted to gardens where both food and water are provided. While superb fairy-wrens were frequently found in gardens where food was provided, willie wagtails and grey fantails preferred to visit gardens where only water is provided.

The striated thornbill feeds mainly on insects.
Glenn Pure, CC BY-NC

Many people have told me how confident fairy-wrens and willie wagtails can become around houses and gardens. These tiny birds can be bold and aggressive, and can work together to get what they want. A mum and dad fairy-wrens will conscript their older children into looking after younger ones – and siblings who refuse to help find food and defend territory may even be kicked out of the family. So these tough breeds have a competitive advantage in their new urban environments, and aren’t afraid to mix with or even chase off bigger birds.

Fairy wrens can become surprisingly bold around gardens and houses.
Photo by Wanda Optland, supplied by author.
Bolder than they look – a fairy wren eats from a citizen scientist’s hand.
Peter Brazier

You may be wondering exactly what type of seed to put out to attract which granivore, or which meat attracts a carnivore like a Kookaburra. I’m afraid we can’t yet say for sure, as we are yet to analyse the data on this question. Watch this space.

We don’t yet know exactly what offering will attract which bird.
Janette and Ron Ford

Could birds become reliant on humans for food?

Many people worry that birds will become reliant on humans to provide food for them. But this mightn’t be as big a concern as we once though.

The birds turning up at feeding areas and birdbaths are species that are highly adaptable. Many Australian birds live long lives, and relatively large brains when compared to their European counterparts. Some experts have argued that some Australian birds have evolved a larger brain to cope with feast and famine conditions in the Australian environment.

White browed scrubwrens feed mostly on insects.
Glenn Pure, CC BY-NC

Many Australian bird species can switch easily between estates and gardens in one area, be semi-nomadic, fully nomadic or seasonally migratory. This ability to adapt and switch between diets makes Australian bird species very resourceful, innovative and adaptable.

Of course, Australia also has birds that have highly specialised diets or habitats, and they’re the ones usually most threatened or limited to one territory – birds like the regent honeyeater or ground parrot. In this study, we’re concentrating on birds that are adapting to urban areas and turning up at birdbaths and feeding areas in gardens.

A crested pigeon tucks in.
Brad Walker

Building our knowledge of bird feeding behaviour

We plan to develop guidelines around providing food and water for birds in a way that has the highest conservation value for our feathered friends. But before we can do that, we need more data from you.

So please take part in the summer stage of the study and pass the word around to others who may wish to be involved.

The summer survey will run for four weeks, beginning on January 30 2017. Visit feedingbirds.org.auto download the complete report on our early findings or to register to take part in our summer study.

Different species may congregate at a feeding spot.
Brad Walker

The Conversation

Grainne Cleary, Researcher, School of Life and Environmental Sciences, Deakin University

This article was originally published on The Conversation. Read the original article.