Putting a price on pollinators

Bees are important, the argument goes, because they flit about from flower to flower, picking up pollen from one plant and inadvertently depositing it on another. In other words, they facilitate plant sex. And plant sex is how you get fruits and nuts…lots of the tasty things we humans like to eat. If the bees disappear, so too do apples and avocados and pecan pie.

This sort of argument relies on a concept known as “ecosystem services,” a concept that’s become increasingly important in divisive discussions regarding biodiversity conservation. Some conservationists insist that biodiversity and nature ought to be conserved for its own sake; others argue that a more effective strategy is to calculate the economic impacts biodiversity conservation would have. Armed with that sort of information, it may then become easier to motivate conservation-related policies. In other words, conservation for our sake.

Writing in the journal Nature Communications this week, a massive group of researchers led by David Kleijn of the Netherlands-based Center for Ecosystem Studies, come down clearly on the “for its own sake” side. But they do it by taking an empirical look at how an ecosystem services approach plays out when considering pollinators.

Kleijn and his colleagues point out that when the economic benefit from ecosystem services is the primary factor driving conservation-related policies, then the most cost-effective approach is to conserve the subset of species that provides the largest return in the shortest amount of time possible. And what that means in the real world – a world in which any given ecosystem is dominated by only a few species that would respond favorably to any given conservation measure – is that only the most dominant species would benefit from an ecosystem services approach, leaving the rare, more threatened species behind. If their suspicions were true, then an ecosystem services approach to biodiversity conservation would be, at best, incomplete.

The researchers rounded up data already collected from 90 different studies on five different continents, comprising nearly 1,400 agricultural crop fields and the bees that pollinated them. They found that wild bees contributed more than $3,000 per hectare (100 hectares equals 1 square kilometer) to the production of insect-pollinated crops. That’s roughly equivalent to the economic value of managed, domesticated honey bee colonies ($2,913 per hectare). On the face of it, the conservation of wild bees would seem to be a no-brainer. It’s good for biodiversity and good for agriculture. However, a closer look revealed that not all wild bees are created equal.

When the researchers combined the information from all 90 studies, they had data on a total of 73,649 bees of 785 different species. But that’s only 12.6% of the known wild bee species in the parts of the world in which those studies took place. In other words, conservation efforts directed at the wild bees that visit agricultural crop fields would completely miss nearly 90% of the world’s bee biodiversity!

Even more striking, when the researchers only looked at those bee species that comprised at least 5% of the bees that visited any given field, they only accounted for 2% of regional bee biodiversity. That 2% accounts for nearly 80% of all the agricultural pollination accomplished by wild bees.

Additional analyses verified that those dominant species on agricultural fields were also the most common species found in each region. Or, put another way, threatened species were least likely to be observed visiting crops. It turns out that’s because threatened species are more likely to be foraging specialists and less likely to take advantage of crop fields to find their own food.

It is evident that wild bees provide critical services to human societies thanks to their pollination efforts; their economic impact is, after all, on par with that of domesticated honey bees. But Kleijn’s study highlights the reality that a scant few of the most common species provide the vast majority of pollination services, with the most threatened species contributing the least, when it comes to agriculture. “Thus, a strictly ecosystem-service-based approach to conservation would not necessitate the conservation of threatened species,” he and his colleagues conclude.

On the other hand, many studies have found that more diverse pollinator communities tend to provide more effective pollination. Kleijn and his colleagues concede that more diverse bee communities could provide “insurance effects” to stabilize pollination services over time. If some important species decline, others could step in. Even in their own data, large contributions to pollination by any given species were typically limited to specific years, crops, or sites. To maintain stable ecosystem services year after year, it might then be prudent to conserve a broader set of bee species than just those that are currently dominant. However, they also point out that such an argument still only applies to those species that are willing to visit crop plants in the first place, and nearly nine for every ten bee species were never found in the crop fields included in this study.

Taken together, this study suggests that ecosystem services are not sufficient to motivate policies aimed at promoting bee biodiversity, which is perhaps surprising since pollination is one of the most obvious ecosystem services that there is. That’s not to say that ecosystem services can never be a useful tool in the conservationist’s toolbox. Instead, the researchers argue that the “benefits of biodiversity should…not be used as the sole rational for biodiversity conservation.” Instead, they say that such an approach needs to be complemented by the same sorts of moral arguments we use to motivate actions like taking care of the elderly or preserving important artworks…at least, if voters, policymakers, and landowners are to find value in conserving those species with “no clearly defined economic value” to human society. – Jason G. Goldman | 17 June 2015

Source: David Kleijn et al. (2015). Delivery of crop pollination services is an insufficient argument for wild pollinator conservation. Nature Communications 6, 7414. DOI: 10.1038/ncomms8414.

Header image: A wild bee visits a flower, via shutterstock.com