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Expert Q&A: Jeff Ollerton

The University of Northampton’s Jeff Ollerton is an expert on the ecology, evolution and conservation of plant-pollinator interactions. He shares insight into the diversity and importance of pollinators as well as advice on incorporating pollinator habitat protection and restoration in planning and design work.

Jeff Ollerton is Professor of Biodiversity in the Department of Environmental and Geographical Sciences at the University of Northampton. He works mainly, though not exclusively, on plant-pollinator relationships, pollinator diversity, plant reproductive biology, and the evolution of flowers.

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About how many of the world’s insect species are pollinators?

One of the first attempts to answer that question was in a paper published in 2015 by Carl Wardhaugh [of the University of South Bohemia and the Czech Academy of Sciences] entitled “How many species of arthropods visit flowers?” He reviewed literature, discussed the question with experts, and estimated that about 30% of arthropod species regularly visit flowers. That is over 350,000 described species. (There are one million described insect species; estimates for the number of undescribed species vary from five to 100 million.)

But not everything that visits a flower acts as a pollinator. Factors like an insect’s size, morphology, behavior, and hairiness can make a difference in its effectiveness as a pollinator. For example, there are 20,000 species of bees worldwide and all visit flowers, but not all of them are good pollinators. So the percentage of insects that pollinate [as opposed to just visiting flowers] is probably more like 20% or 10%.  But the short answer is, of course, that we just don’t know!

Pollen-coated thistle long-horned bee (Melissodes desponsa,) ©USGS

Honeybees and monarch butterflies get a lot of press. What can you tell us about some of the lesser known, but equally important insect pollinators?

I just mentioned that there are 20,000 species of bees. There are many Diptera [fly] families with thousands of species that pollinate. For example, there are somewhere around 6,000 species of hoverflies (Syrphidae), and many of them visit flowers. There are wasps, several families of beetles, some mosquitoes, and of course, butterflies and moths. There are birds such as honeyeaters, and mammals such as bats. And there are some strange pollinators. For example, crickets actually act as pollinators for some orchids.


Hoverfly (family Syrphidae) on lemon balm (Melissa officinalis)

How important is insect pollinator diversity to terrestrial ecosystems?

Plants and pollinators sit right at the heart of most terrestrial ecosystems. Flowering plants are far and away the most diverse and abundant plants on the planet. Until quite recently, we didn’t have a very good estimate of the proportion of flowering plants that require animals (both insects and vertebrates) as pollinators. We did the first rigorous calculation of a figure to address that question. Our study, which was published in 2011 in the journal Oikos, found that 87. 5% of flowering plants [i.e., 308,000 species] require animal pollinators. This percentage increases quite steeply from the temperate zone, where 70-75% of flowering plant species require animal pollination, to the tropics, where in many places, it is over 90%. That gives you a sense of the ecological importance of pollinators.

What would happen if those pollinators all went extinct? It’s a very unlikely scenario.  But if it ever occurred, for some of those plants, those with the ability to self-pollinate, it wouldn’t make a lot of difference in the short term. But in the long-term, we would certainly lose a significant portion of plant diversity because many plants cannot self-pollinate and those that can would ultimately decline in abundance and diversity because they do not produce as many seeds when they self-pollinate and there could be genetic problems due to inbreeding.

A fly on a buttercup at high altitude

Bee (genus Melissodes) on sunflower (genus Helianthus)

Can you talk about mutualism in the pollinator/plant relationship?

A mutualistic interaction is any kind of interaction between two or more species in which each species benefits. Most plant/pollinator relationships are mutualistic in the sense that the plant offers a reward—usually nectar or pollen. Sometimes it is another kind of reward. With some high altitude/latitude flowers, the reward can actually be heat, because the flowers are warmer than the surrounding air temperature. In some tropical plant species, the reward can be a sticky resin, which bees collect and use to make nests.

Pollinators are also responsible for the production of seeds and fruits which are consumed by other animals, and those animals are in turn consumed by predators. The flower visitors themselves are also taking a significant amount of energy directly from the pollen and nectar they consume, and that energy flows through the ecosystem. So pollinators are critical to how most terrestrial ecosystems function.

What does a functioning community of insect pollinators look like?

A functioning ecosystem involving pollinators would be one where there is a significant diversity of pollinators, because pollinator numbers will naturally fluctuate between years. There will also be pollinators that will match the flowering time of the plants in the community. Diversity provides a form of ecological insurance. If some groups of pollinators decline or go locally extinct, there are always other pollinators which can take their place.

How much do we know about the global status of insect pollinator diversity? What are the major challenges to getting a clearer picture?

We know an awful lot, but there’s also an awful lot that we don’t know. We have a good sense of the diversity in certain areas of the world, such as northern Europe and parts of North America. There are, however, large parts of the world for which we have a much poorer sense of pollinator diversity. If you were to map the coordinates of places on the planet where there have been intensive studies of pollinators undertaken, you’d see a big mass of data points in northern Europe and in the USA, a lot in Central America, and some in parts of South America, such as Brazil and Argentina. There would also be a cluster of data points in some areas of South Africa and Australia. But over most of Africa, and over large parts of Asia, there are no data. There are, however, increasing numbers of studies coming out of China and Japan at the moment. But it is important to bear in mind that for most of this work, it’s a single snapshot in time. We don’t know that much about how diversity changes over time. That’s because historically, people were interested in understanding the number of species in an area. They’d go into an area, take specimens, and leave.

Where we do have data related to insect pollinators, is it being shared, and is there uniformity in the way it is collected?

More and more data is now being shared, and that has been driven by the requirements of journals and public funding bodies. There is still an issue with regard to standardization of how data is collected, however. You have to tailor your specimen and data collection methods to the particular group of pollinators and type of habitat you’re looking at. Collecting pollinators and studying pollination in open grassland is very different from doing the same kind of work in high canopy tropical rainforest, for instance.

Some flowering plants are actually “cheaters” that fool the insects into visiting the flowers. For example, there are several groups of plants, from unrelated families, which produce flowers that smell like rotting flesh, feces, fermenting fruit, etc. They are pollinated by flies which are fooled into thinking they’re visiting a nutritious substrate on which they can lay eggs. In those cases, the flower is tapping into a very deep, hard-wired behavior of the insect, but the pollinator gets no reward.

My favorite example of these are various genera that are collectively called “stapeliads,” members of the plant family Apocynaceae, so they are related to the milkweeds on which monarch butterflies feed. The stapeliads are mostly succulent plants and are widely distributed in semi-arid areas across Africa and parts of Asia.  There’s at least 500 species in this group and all of them (as far as we are aware) are fly pollinated, by a wide range of different types of flies.

Stapelia flavopurpurea

Can you tell us about the difference between plant species that are considered “generalists” when it comes to pollinators, and those that are exclusively mutual with specific pollinators (and give an example of each)?

There is actually a continuum, from plants that specialize just on a single pollinator, to plants that have hundreds of pollinators. A good example of plants in North America which have many types of pollinators are many of the milkweeds (Asclepias). Milkweed is known for attracting monarch butterflies (which lay eggs on the plant, which is then fed upon by caterpillars) but some of the very common, widespread milkweed species have hundreds of reported pollinator species.

At the other end of the continuum, there are plants that are pollinated by just one hummingbird species, or single bee species. When plants are specialized on a single pollinator, that pollinator is usually not specialized on that plant. This makes good ecological sense. If you are a plant and you specialize on something which is specialized on you, in effect you double your chance of going extinct. The only examples which buck that trend are some of the fly pollinated plants I mentioned earlier and things like figs and fig wasps and yuccas and yucca moths. Many species of fig are pollinated by a single species of fig wasp. Those fig wasps in turn complete the whole of their life cycle on those figs. That relationship has been very successful, and has persisted for a long time, but it isn’t representative of the majority of interactions between plants and pollinators.

You were involved in research published in the journal Science in 2014 which looked at bee and wasp species which had gone extinct in the UK. Your research showed that the main period of species loss followed changes to agricultural policy and practice just after World War I. Why is this finding important, and what can we learn from it?

It is important to set the historical context for ecological and conservation questions, and to understand when things started to happen and what the main drivers were. In relation to the loss of habitat and species diversity in the UK, the perceived wisdom was that most of the changes were driven by government concerns over food security during and just after World War II. This led to agricultural intensification, with increased uses of technologies around fertilizers, pesticides, and herbicides, and [the conversion of] marginal land to cultivation. Our research showed that the British government and agricultural community had actually gone through a very similar process of concerns about food security, which in turn drove agricultural policies, during and after the First World War as well. Our research pushed back the beginning of that process by a whole generation. It really started in the 1920s, and it was linked with technological developments like the Haber Process, which meant that large amounts of inorganic nitrogen fertilizer could be manufactured, so farmers didn’t have to leave fields [fallow] for a year or two to build up fertility. All of these things resulted in the loss of habitat, plant diversity, and pollinators.

So our study was significant not only because it was the first assessment of pollinator extinctions at the country level for any country in the world, but it also extended our historical understanding of these processes.

Do you think that extension of historical understanding helps inform or drive further reform in industrial agriculture?

I’d like to think it could. It certainly adds to the evidence base of understanding what we’ve lost in terms of biodiversity. It also tells us something about what could potentially happen in the future if agriculture continues to intensify, or if we introduce new agricultural technologies.

Land use change, particularly related to agriculture, is cited as a leading driver of insect pollinator decline. Is this mainly because of the resulting habitat loss? 

It’s loss of habitat, and it’s also changes in the way the existing habitat functions ecologically. We know, for instance, that using lots of fertilizer in grasslands will ultimately change the composition of the grasslands. You may not lose the habitat as such—it’s still grassland—but the ecological nature of that habitat changes fundamentally from a species-rich grassland in which pollinators can thrive to a species-poor grassland in which pollinators struggle to find somewhere to live.

In your opinion, what stressor presents the next greatest threat to insect pollinators?

Changes in habitat will continue to be a problem into the future. In Britain at the moment, there are no habitats that can’t be destroyed or developed under some circumstances. We have multiple levels of supposed legal protection, but there are always exceptions. One of the big debates in conservation in the UK is the idea of biodiversity offsetting. That is a dangerous road to go down because it implies that we can replace habitat that may have been present hundreds of years with newly built habitat. If someone were to propose bulldozing Stonehenge because we can build a new one in another part of Britain to offset the loss, the British public would rightly be outraged. When developers are allowed to destroy areas of ancient woodland, there is much less of an outcry.

Have studies been done to compare, in terms of ecological function, newly created pollinator habitat vs. existing, native pollinator habitat?

Not much work has been done in a formal way with relation to biodiversity offsetting. There has been work done that looks at the more general question of how restoration of habitats can affect pollinator diversity. A couple of my research students published a series of papers over the last few years where they have been comparing the biodiversity on restored landfill sites with biodiversity in nearby nature reserves. In the case of pollinators, the diversity in the restored landfill sites is equally high and sometimes exceeds that of the nature reserves, but what you get is a rather different mixture of pollinators. You may have just as many species, but it’s a different diversity. This suggests to me that areas like these restored landfill sites, on a landscape scale, are contributing to overall diversity. But what you don’t want to do is replace a local nature preserve with a landfill!

In July of 2015, a study was published in the journal Science which showed that climate change was not shifting, but shrinking (from the south) the range of bumblebees in North America and Europe. What do we know about the impact climate change is having and will have on other insect pollinators?

For bumblebees, which are adapted to relatively cool conditions, increasing regional temperatures could have a significant effect. In Europe, we now have a Bumblebee Risk Atlas, which shows the way in which the local diversity and abundance of even some of our very common bumblebees are likely to [be reduced] by the end of this century-even to the point where large swaths of Europe and Scandinavia will no longer be suitable for those once common bumblebees.

What do you think is the most pressing need for research related to pollinator protection?

The most pressing needs at the moment are around long-term monitoring of pollinator populations–understanding pollinator diversity and abundance in time and space. There is lots that we in Britain don’t know about where pollinators are actually found, which habitats are the most diverse, what the spatial relationships of those habitat are, and how we can link those habitats together to better ensure that there is a continuum of diversity across whole landscapes. We also need to know more about pollinator diversity and abundance in parts of the world where we don’t have good data – which is most of it!

While we wait for this research, where/what do you think is the most urgent need for insect pollinator habitat restoration?

There is some very interesting work showing the benefits to agricultural pollination to having just relatively small fragments of habitats intermingled into the agricultural landscape. For example, there is work going on in California looking at restoration of hedgerows and other habitat within almond plantations, and how those habitats can attract and support pollinators.

Hedgerow adds pollinator habitat to agricultural fields

An interesting study by Lucas Garibaldi, which recently came out in the journal Science, looked at the importance of pollinator diversity to crop production and how proximity to native pollinator habitat can really increase the diversity of pollinators, which in turn can increase yields. Restoration within the agricultural habitat matrix is very important. It has benefits for nature conservation and ecosystem services associated with agriculture–it’s a win-win situation.

We know that towns and cities can support high diversity and abundance of pollinators. That has got to be important for urban agriculture, which is becoming increasingly important as our urban areas grow. But there is still a lot we don’t know, and this is an area where we need more research.

The University of Bristol coordinated a big urban pollinator study. (For details, see Inspiration: Promising Progress With Pollinator Habitat article in this issue). Other interesting work is going on in Canada and the USA so there’s a world-wide interest in this question.

What advice do you have for planners and designers who want to incorporate resilient pollinator habitat into their work?

Remember that pollinators are very mobile organisms. They can use landscapes at a quite a large spatial scale. One of my favorite statistics is that a worker bumblebee can travel three kilometers in 15 minutes. The bumblebees I see pollinating the plants in my garden here in Northampton may be nesting three kilometers away. Likewise, the bees that nest around my garden may be going to the agricultural fields around Northampton and pollinating crops out there. When we attempt to restore habitat for pollinators, we have to think in terms of those kinds of spatial scales.

We also have to remember that many pollinators need lots of different things from habitats, so we have to have a diversity of habitats across a landscape. It’s not just a matter of planting lots and lots of nectar- and pollen-rich flowering plants. We need old areas of woodland or hedgerow with appropriate nesting places for ground- and cavity-nesting bees. We need ponds and wetlands where hoverflies can lay eggs and where the larvae will develop. That is probably one of the reasons why some of our towns and cities are so good for pollinators: there is a high level of heterogeneity of habitats, particularly within gardens and parks.

Ground nesting bee making nest in soil

Many of our bees are ground nesting and tend to make their nests in relatively dry, poor, sandy soil—the kind of soil you might find around the base of trees in a park. Those are exactly the sort of areas where people like to put in a lot of flowering plants in the belief that they are doing something for pollinators. What they might be doing is planting on top of bee nests! Any kind of plan to restore habitat or put interventions in place for pollinators needs to assess the habitat beforehand and not just assume that because an area is devoid of vegetation or has poor quality soil it’s not important habitat.

Are tools available to help landscape planners and designers establish appropriate plant palettes when trying to maximize pollinator habitat within certain conditions?

In the UK, we have the Royal Horticultural Society’s Perfect for Pollinators plant list, which came out of a BBC television series in which I was involved. I’m sure there are similar regional resources. For people who want to plant in a particular area and include plants that support pollinators, the best thing to do is to go to the local plant nurseries in spring and summer and watch which plants are visited by pollinators. Let the behavior and habits of the pollinators themselves guide the choice of planting.

You are one of few scientists featured in Leaf Litter to maintain a blog. How important is public education when it comes to maintaining healthy, resilient pollinator communities?

BlogIn part, my blog is for other scientists who are interested in biodiversity, but it is also for my students and for the general public and conservation professionals and enthusiasts. Public education is very important in terms of offering ideas for practical action—things that can be done in gardens and urban areas—and also in terms of raising awareness among business leaders and politicians. Using blogs and social media to highlight things like the UK’s National Pollinator Strategy and Pollinator Awareness Week is important because many people won’t necessarily pick up that information from a newspaper or broadcast media.

The U.S. and England have, fairly recently, developed national strategies related to pollinators. Do national plans like this give you hope for pollinators?

They suggest to me that these questions are at least on the minds of politicians and policy makers. What is unclear to me is how those strategies will be operationalized and what resources will be put into place to make them work.  I am an optimist, but given the current economic problems in the UK, USA, and most of the world, I’m not convinced that there is the political will to [do something about pollinator protection].   I hope I’m wrong though.

The United Nations’ Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES), an initiative that has been running for a couple of years, is starting to gain momentum. The very first thing the IPBES will produce is a report on pollinators in an international context. We talk about national strategies; well, this report will provide a lot of impetus and an evidence base for international strategies as well. But again, a strategy is only as good as the underlying will and resources to make it happen.

Editor’s note: For information about the IPBES report (Thematic Assessment of Pollinators, Pollination and Food Production), which has been referenced in other sections of Leaf Litter, click here.

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