Wild bees again

old fashioned urban beekeeping woman 1883

An 1883 Urban Beekeeper from AJ Cook’s Bee-keeper’s Guide

A few days ago, I wrote a snarky blog entry about one researcher’s efforts to alert us to a hazard of urban beekeeping. It is Dr Cartar’s contention that keeping bees in an urban environment robs wild native bees of food, which in turn threatens their survival.

I agree with some of the Calgary professor’s position – but I’ve not actually studied the subject in detail as Dr Cartar has. We agree that honey bees are an imported species – they are not native to North America – and thus they disrupt the natural ecological balance established by millions of years of evolution on our continent. We also agree that honey bees sometimes take nectar and pollen produced by native (and invasive) flowers that wild bees may have eaten. But I’m not sure about the severity of the problem. Nor do I know much about Dr Cartar’s premise that forage competition is the primary threat to native bees.

Research and evidence exists to show that the loss of habitat (nesting sites) in urban settings have jeopardized wild native bees, probably more than interspecies competition for food from honey bees. At this time, I think that urban honey bee keepers should be encouraged as these people are often great advocates for maintaining nesting sites and good pasture for wild bees. You can read our difference of opinion in more detail in the June 12 blog entry on this page.

When warranted, I sometimes publish letters received from informed sources. I feel that Dr Cartar deserves the opportunity to answer some of my missives, so with his permission, the bulk of his letter to me follows:

Dear Ron,

“The point of my “every joule of honey in their jars….is a joule robbed from native bees” quote is simple. At equilibrium, the density of native bees tends to be most determined by flower availability (that is, the nectar and pollen available). More flowers = more bees, in general. This is the essence of competition, and is readily observable in nature. Bee populations build up (or get smaller) based on floral availability. And the converse is true, but over longer scales (because most bees are annuals, and most flowers are perennials; more on this later). Think of this as a game of musical chairs: native bee abundance is (on average) in proportion to the chairs in the game (i.e., the flowers). Then somebody brings in a large number of players (a colony of honey bees), but there’s no change in the number of chairs. And these introduced, non-native honey bees have little chance of failing, because their keeper usually feeds the colony when foraging is insufficient to colony needs.
What you’ve done is stack the game of musical chairs against native bees, with an expected outcome (loss of local bees). Hence, “every joule of honey is robbed from native bees”…

“But there are exceptions to this too-simplistic characterization. As I noted in my email to you, in some years, bad weather (often in spring) removes many of the bees, so there’s little competition, and flowers get insufficient pollination service from natives. I see this in one year in 5 or 6, locally. In these cases, nectar accumulates in flowers. Flowers age and drop off without producing seed. You’d think that in this circumstance, adding honey bees would have little impact on natives. But the outcome depends on amount. As noted in the paper I emailed you, honey bees prefer to forage near their colony (but will fly far if necessary). So the addition of a honey bee colony, will greatly deplete nectar and pollen rewards in the local area (others have documented this, where the depletion of floral rewards makes their use by other bees unprofitable). Hence, even in the case where flowers are super-abundant relative to native bees, adding honey bees can easily push out the natives
who previously had more food than they knew what to do with. This is not an empirical observation, just one that seems reasonable. The observation that honey bees deplete flowers to levels that make them unprofitable to local native bees is reasonably well established…

“Another exception of note is that, for some flower species, the joules available depend on the rate of visitation. In these species (which are not typical), flowers resorb nectar that is accumulating unharvested, and/or produce more nectar when it is harvested more rapidly. In this case, floral rewards depend on visitation, suggesting that then number of chairs in my musical chairs analogy might change. But again, these effects are easily dominated by the sheer density of honey bees in a colony, so adding honey bees is likely to hurt natives…

“Of course, other factors determine abundance of native bees. You correctly point to one: nesting habitat. But to make the argument persuasive, you need to point to evidence of nest site limitation of population abundance in the literature. I’ve noted that abundance of floral resources is the single best predictor of bee abundance, and this obtains at 2 levels: bees visiting flowers, and bee reproductive success. To be complete, the other determinants of local population size are diseases, predators, and parasites. Along with nest sites, all of these should operate in a density-dependent manner. But don’t assume that nesting resources limit bees in Calgary, when there is such heterogeneity in human structures (bare ground for hole-diggers, tubes for cavity-nesters, vole nests and unprotected insulation for bumble bees)…

“I’m not deliberatley picking on urban beekeepers, and admire them for embracing a truly fascinating insect. I share that admiration and fascination. I’m just pointing out that ANY honey bee colony, given its enormous size (relative to local densities of native bees) and propensity for local foraging, has the potential to have big negative impacts on the local native bees. The overall impact would depend on the number of these colonies added. So one colony is too many, at least for the locals. Urban beekeeping is not a win-win (beekeeper gets free honey, plants get pollinated), unless you ignore the displaced native bees. My suggestion: DO feel guilty about keeping non-native bees, but keep your fascination with bees! Instead, consider accommodating native bees. The Xerces society provides a wonderful web resource for how to begin in this endeavour.

“Introduced, managed honey bees have negative effects, in all sorts of ways, on native bees (especially when the native bees are honey bees, like in Europe). If scientific evidence still matters in decision-making (an increasingly dubious preposition in recent years in Canada), then it’s unlikely that an urban (or rural) honey beekeeper will have no local negative effects on native bees. And the extent of the problem will increase with each increase in the extent of urban and rural honey beekeeping…

“Just because everything we do (short of suicide) has negative effects on our environment should not make us throw in the towel, and ignore the environment. Let’s be mindful of what we do, and embrace our love of and fascination with insect pollinators. Instead, let’s channel and extend that affection and fascination to our neglected native bees. When you notice native bees, and their amazing diversity, your fascination will be well-rewarded.”

Cheers, Ralph

About Ron Miksha

Ron Miksha is a bee ecologist working at the University of Calgary. He is also a geophysicist and does a bit of science writing and blogging. Ron has worked as a radio broadcaster, a beekeeper, and Earth scientist. (Ask him about seismic waves.) He's based in Calgary, Alberta, Canada.
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3 Responses to Wild bees again

  1. Pingback: Should a “Bee City” Ban Honey Bees? | Bad Beekeeping Blog

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