Too many honey bees (on the town)?

Synopsis : Honey bees compete with native bees. What number of hives are too many, leading to harm to native bee populations? In all probability fewer than you suppose.

Introduction

A number of years in the past I visited Montréal to talk at a global symposium. It was a giant convention with a really busy programme however I nonetheless managed to sneak away and see town. We had per week or so of beautiful Indian summer time climate so I walked nearly in every single place; alongside the banks of the St Lawrence and Prairies Rivers, via the Botanic Gardens and the Mount Royal Park.

Montréal Olympic stadium from the Botanic Gardens

In the event you’ve not been I can advocate it.

Nonetheless, I didn’t see a single honey bee.

I wasn’t particularly trying for honey bees, however beekeepers have a tendency to note this stuff.

On reflection that wasn’t too stunning. At the moment there have been simply a few hundred hives inside the metropolis, which covers an space of 430 km² .

I did see monarch butterflies (Danaus plexippus) within the gardens, stocking up on nectar earlier than beginning their migration again to Central Mexico.

Monarch butterfly, Montréal Botanic Gardens

This was early October. Had there been a lot of honey bees in Montréal I’d have anticipated to see them on the identical asters, competing for the nectar with the butterflies, piling within the shops earlier than the approaching winter.

And competitors isn’t at all times an excellent factor.

Save the bees

Scientists have lengthy been conscious of the significance of pollinators (a lot of that are bugs) and the worldwide decline of insect populations. The function of bugs, and the significance of conserving them is usually a troublesome factor to ‘promote’ to most of the people.

They’re typically perceived as wriggly, creepy-crawlies, which may sting … urgh!

With out public help many conservation tasks will fail.

Growing public consciousness and related conservation measures, for instance banning pesticide gross sales by backyard centres, is required and a mixture of ‘model consciousness’, a widespread fondness for honey and (inevitably) sloppy journalism implies that honey bees (Apis mellifera) have develop into the poster lady for insect pollinators.

Save the bees …

’Save the bees’ as a slogan is a gross oversimplification of ’improve the quantity and variety of bugs pollinators within the surroundings’ and is often taken to imply – or interpreted as – ‘promote honey bees’.

In the event you’re inquisitive about seeing simply how biased this protection is I like to recommend Smith and Saunders (2016) who collated press articles on pollinators (in Australia) and quantified the completely different species featured. The title of their paper neatly defines the issue:

Honey bees: the queens of mass media, regardless of minority rule amongst insect pollinators

The beekeeping ‘explosion’

Partly as a consequence of this media protection there was an explosion of curiosity in honey bees and beekeeping over the past 10-15 years … and plenty of new beekeepers.

Since over 80% of Canadians reside in city areas a major proportion of those new beekeepers – and their hives – are in cities and cities.

Between 2013 and 2020 the variety of hives in Montréal elevated from 283 to ~3000.

Conveniently – for this put up and the paper (MacInnes et al., 2023) on which it’s based totally – there was an intensive survey of Montréal’s city bees in 2013 (Normandin et al., 2017). By repeating the survey in 2020 it was doable to find out the affect of the rise in city honey bees on wild bees and among the flowers on which each rely for pollen or nectar.

This ‘earlier than and after’ examine confirmed that the introduction of huge numbers of hives cut back wild bee species richness and pollen availability.

“Too many honey bees” … maybe not what you anticipated in a beekeeping weblog 😉 .

Testable hypotheses

The MacInnes examine had three targets, to:

Study the species richness and composition of untamed bee communities alongside a gradient of honey bee abundances

Assess the affect of honey bee abundance on floral useful resource (pollen) availability

Examine the richness and composition of the wild bee communities earlier than and after the massive improve within the honey bee colonies in Montréal

The 2918 hives in Montréal should not evenly distributed . The situation of some had been recognized, however within the absence of that info it needs to be inferred by the frequency of honey bees sampled particularly areas … if there are many honey bees it’s cheap to imagine that hive density inside foraging distance is larger than in areas the place there are fewer honey bees.

Due to this fact, by sampling wild bee numbers and species throughout a variety of various websites, in addition to counting honey bee numbers, it was doable to find out whether or not the presence of honey bees influenced the presence, quantity and inhabitants make up of different bees.

Equally, by evaluating the 2020 knowledge with the 2013 survey it was doable to find out the affect of the city-wide 10-fold improve in honey bee numbers.

Competitors between bee species – at the least on this case – is exploitative.

One bee species exploits a useful resource that’s wanted by one other bee species. The obvious issues they compete over are the floral assets – pollen and nectar – produced by crops within the space. It’s doable to measure pollen abundance and nectar quantity (and sugar focus, although this could not change in response to bee numbers) and, on this examine, pollen was quantified to see if areas with excessive numbers of honey bees had much less pollen.

Examine design

I’m not an ecologist so am unqualified to correctly decide the examine however – to my unqualified eye – it appears to be like fairly cheap. The paper is freely obtainable so decide for your self . Sampling was carried out at 15 well-spaced websites throughout Montréal, in forage-rich areas comparable to group gardens, cemeteries and nature parks. Excessive decision satellite tv for pc mapping was used to quantify herbaceous cowl and impervious surfaces (concrete, buildings). Bees had been collected utilizing pan traps utilizing a standardised sampling process for the areas of the traps, their separation, the period of trapping and the forms of day on which trapping was carried out.

A few of Montréal’s impervious surfaces

For instance, you can’t meaningfully evaluate 3 hours of trapping on a moist April afternoon with 6 hours on a stunning late summer time day. Good foraging days had been chosen in June, July (twice), August and September.

Along with pan traps, aerial trapping (think about enthusiastic PhD college students prancing round swishing butterfly nets) was additionally carried out in parallel, with samples from every website/date pooled for counting and subsequent identification.

Lastly, the similar sampling websites had been used as had been chosen within the 2013 survey (although I feel there have been a few extra websites used as effectively) to permit related comparisons earlier than and after the inflow of honey bees.

A couple of definitions

Honey bees … you already know what these are 😉 .

All different bee species had been thought of ‘wild bees’ i.e. unmanaged, although they acknowledge some Bombus species are managed for pollination companies, however did/couldn’t distinguish these from free-living Bombus.

Inside these wild bees the authors recognized ‘native’ and ‘unique’ bees; the latter (~12% of the full) being launched via the actions of man.

The wild bees recognized had been additionally separated into two teams – giant and small – based mostly upon the inter-tegula span (ITS). That is the gap between the tegulae on the wing bases, and is an excellent indicator of physique mass and wing musculature which, in flip, is a predictor of foraging vary. Bees with a low ITS are small, mild and solely forage over quick distances .

Bee communities (i.e. X% of species A, Y% of species B, Z% of species C, remembering the group may comprise a number of dozen species) had been characterised utilizing plenty of statistical strategies that I’m additionally not certified to evaluate correctly (although I’ve printed a number of papers utilizing among the strategies cited … 😉 ). Go on, ’fill your boots’ … try the paper and resolve whether or not Shannon-Wiener or Simpson’s variety indices are the fitting ones to make use of. These strategies are pretty commonplace and have been utilized to the evaluation of bee communities in earlier research, so let’s assume they’re OK.

Pollen evaluation of white clover (Trifolium repens) was additionally carried out. Not all bees use this as a pollen useful resource, however many bees do. Pollen was ethanol extracted, stained and counted beneath a microscope (think about unenthusiastic PhD college students going cross-eyed with boredom … and cursing their supervisor 😉 ).

Wild bee richness and honey bee abundance

Richness is a measure of the variety of species and therefore variety of the wild bee inhabitants. The speculation was that richness would scale back as honey bee numbers elevated if there was competitors between the bees for limiting assets.

And that’s precisely what was seen.

Honey bee abundance and wild bee richness.

These graphs plot honey bee numbers (horizontal) towards a measure of species richness (vertical), with every dot being a distinct pattern website/sampling date. The overlaid strong line and shaded blue area represents a greatest match and 95% confidence restrict respectively.

Because the line slopes down from left to proper (a unfavourable slope) it signifies that elevated abundance of honey bees ends in decreased species richness within the wild bee inhabitants throughout Montréal (left hand graph). Massive bees and Bombus (bumble bees, that are very giant bees) had been unaffected by honey bee abundance (not proven), however small wild bees (proper hand graph) decreased considerably.

The wild bee group make up – the vary of species and the variety of every – is barely harder to clarify. Basically websites with excessive numbers of honey bees had been extra related to one another of their wild bee communities. Websites with low or medium ranges of honey bees had been extra various. This implies that solely some wild bees can compete within the face of excessive honey bee abundance.

The affect of beekeeping on wild bee communities

Unsurprisingly, in mild of the outcomes introduced above, the ten-fold improve in honey bee hive numbers in Montréal between 2013 and 2020 additionally negatively impacted wild bee richness.

Honey bee will increase from 2013 to 202 and wild bee richness

These graphs plot the distinction in honey bee numbers at every sampled website between 2013 and 2020 (horizontal axis) versus wild bee richness. The strong black line represents the very best match of the scattered knowledge factors having taken under consideration different variables comparable to sampling interval, floral richness, floral density and the quantity of impervious surfaces and herbaceous forage.

Once more, the downwards (unfavourable) slope of the road as honey bee abundance will increase signifies that wild bee group richness decreases if there are extra honey bees about. As earlier than, this was not seen in giant wild bees or Bombus, however was vital in small wild bees.

If there are will increase of generalist bees – comparable to honey bees – within the surroundings, the expectation could be that forage crops, like white clover, could be depleted of pollen and nectar … this was the subsequent factor that was examined.

Extra honey bees = much less pollen 🙁

White clover was broadly distributed throughout the pattern websites. It’s also a flower that a variety of completely different bees can entry for ‘assets’ (pollen and nectar) … no want for a extremely lengthy tongue, or sturdy jaws to chop via the edges of the florets.

Simple pickings for plenty of completely different bees.

Except there are considerable numbers of honey bees within the surroundings.

Pollen availability is decreased the place honey bees are considerable

The residual pollen on white clover considerably decreased with rising abundance of honey bees. With lower than 20 honey bees detected at sampling websites, every clover flower contained ~24,000 pollen grains. With numbers over 20 honey bees the quantity dropped to ~14,500.

This lower was unrelated to different variables examined e.g. the numbers of Bombus at every sampling website.

The idea right here is that the elevated numbers of honey bees exploit the obtainable pollen to the detriment of different bees that will in any other case forage on clover.

Is all of it dangerous information?

Sadly, sure.

I feel that this is likely one of the higher research of honey bee competitors with wild bee populations that I’ve learn .

It’s price noting among the limitations of the examine.

There was no sampling early within the season. The dimensions of honey bee colonies in April/Might most likely makes them fearsome opponents when put next with solitary queens rising after a winter’s hibernation. It’s possible that omission of early season samples underestimates the unfavourable affect of honey bees on wild bee populations.

Though the one variable measured that influenced wild bee richness was honey bee abundance, maybe the previous declined due to modifications in an unmeasured variable. For instance, maybe the floral variety/group dramatically modified between 2013 and 2020. This knowledge wasn’t collected in 2013 (however was in 2016) nevertheless it appears unlikely that it might be dramatically completely different.

Botanic gardens and concrete planting often comprise giant quantities of unique flowers i.e. non-native. Since native wild bees have co-evolved with native flowers, this unique planting is often thought of to learn unique bees extra.

Of the 120 bee species recognized, 15 had been unique. Nonetheless, the 13 species lacking from websites the place honey bees had been most considerable had been all native bees.

The introduction of huge numbers of ‘unique’ honey bees was notably detrimental to native wild bee populations slightly than different unique bees. Small native bees (~60% of all species) had been probably the most adversely affected. That is possible attributable to their very restricted foraging vary (100’s of metres, slightly than kilometres).

’Secure’ colony densities

Within the conclusion of the paper the authors briefly talk about the honey bee ‘carrying capability’ of an surroundings i.e. the variety of colonies that may be launched with out detrimentally affecting native bee populations.

This carrying capability will range in accordance with the floral assets obtainable and – though not mentioned – is not going to be fixed all through the season.

Honey bees lower floral assets obtainable (crimson shaded space)

Complete pollen/nectar availability (blue line) varies through the season . Growing numbers of honey bees in an surroundings (crimson shaded space) successfully cut back what is offered. 

However it is a gross oversimplification … it assumes that every one floral assets are equal. Generalists can exploit all these assets.

Some bees are specialists; rising, maturing, mating, laying and dying through the flowering of a single species or genus of crops (cyan line). If honey bees can use the identical useful resource, notably if it flowers when there’s a scarcity of different forage, it may severely restrict what is offered for the specialist native bee.

MacInnes et al., cite two research which recommend that 3 or 3.5 hives per km² is the precautionary really useful colony density that reduces unfavourable interspecies interactions (Steffan-Dewenter and Tscharntke, 2000; Torné-Noguera et al., 2016).

I’ve learn these two papers and neither are research of city bee populations – one is on the thyme- and rosemary-rich scrubland within the Garraf Pure Park (Barcelona) , the opposite on the calcareous grasslands round Göttingen in Germany. Neither satisfied me that the recommended 3-3.5 hives/km² had been based mostly upon proof that essentially made them ‘transferrable’ to different environments.

However let’s assume that they’re …

Environmental colony densities

The 2918 colonies in Montréal had been unfold inconsistently round 430 km² i.e. a colony density approaching 7 hives/km². Keep in mind, there could have been undocumented hives that will improve this quantity.

I’m unaware of significant obtainable equal knowledge on hive densities within the UK.

The Nationwide Bee Unit (NBU) preserve a document of apiary and hive numbers of registered beekeepers (assuming data are up-to-date) however – irritatingly – solely publish the apiary numbers. Once you register an apiary you may see the quantity however not location of different apiaries inside 10 km.

Beebase reveals the ‘density’ of apiaries inside 10 km

I’ve had apiaries the place the NBU “<10km apiary quantity” is as little as 1 (distant west coast) or as excessive as 275 (Midlands). My present apiaries on the east coast have ~60 apiaries inside 10 km.

A circle of radius 10 km covers an space of 314 km² . Assuming you already know the apiary numbers , what number of hives would there must be in every apiary to provide a density of three or 3.5/km²?

Apiary quantity and hive density desk

Don’t belief my maths (!) however I feel the figures above are right.

My Midlands apiary, with 275 different apiaries inside 10 km would have been in an space with over 3.5 hives/km² if the opposite apiaries contained a mean of ~4 hives every. Primarily based upon my wanderings across the Warwickshire fields I’ve often estimated that rural apiaries truly common ~5 hives every.

Test your NBU Beebase-registered apiaries. What number of different apiaries are there inside 10 km? Do your bees forage in an surroundings with hive numbers above or under 3.5/km² ?

How about city apiary and hive densities?

That is getting foolish …

I did a fast verify of apiary numbers in London, Cardiff, Glasgow and Edinburgh. Central areas in Cardiff, Glasgow and Edinburgh had 196, 144 and 210 apiaries respectively inside 10 km.

Maybe wrongly I’ve at all times assumed that hive numbers per apiary are much less in city than in rural areas.

Persons are busy working, gardens are small, balconies are cramped and who needs to hold 36 supers onto a flat roof?

In the event you assume there are 3 hives per apiary in these cities then the hive densities are effectively under the recommended 3.5/km2 threshold.

However London is a distinct matter altogether.

I checked each outer and central London … each areas I used to be accustomed to. Outer London had 441 apiaries inside 10 km and the central location I selected had an eye-watering 719 🙁 .

Except these apiaries comprise just one or two hives every it’s possible that the three.5/km² hive threshold is exceeded.

In case you are an city beekeeper verify the apiary numbers the place your hives are registered. There might be appreciable geographic variation – even over fairly quick distances – relying what’s ‘in vary’.

Conclusions

As I’ve stated earlier than, beekeepers have a duty to their bees and to the surroundings during which we preserve bees.

If we behave in a manner that’s detrimental to the surroundings it’s going to, ultimately, be detrimental to our bees. However that egocentric justification shouldn’t be wanted … there must be no satisfaction in swamping an space with hives if it ends in the lack of native bees and different pollinators.

It appears as if this summer time has been poor when it comes to honey yields … not in every single place in fact, however in lots of areas. If our bees are struggling simply think about the affect the presence of our colonies are having on the native pollinators that they share the surroundings with.

And bear in mind, the surroundings is being depleted, denuded and degraded; hedges are being grubbed out, subject margins ploughed up, flower meadows transformed to silage manufacturing, pesticides are broadly used and native habitats are concreted over as city areas develop.

It’s already powerful on the market for the a whole bunch of different bee species which our bees now compete with.

In terms of enhancing pollinator numbers and variety, honey bees most likely aren’t the answer … however they could effectively be a part of the issue.

Notes

For these of you who’ve coastal or lakeside apiaries keep in mind that the NBU ’10 km radius’ most likely isn’t good sufficient to take the water under consideration. One among my east coast apiaries has about 130 km² of North Sea inside 10 km, nearly all of which seems to be devoid of bees of any type 😉 .

I’m conscious of the deficiencies in my apiary/hive density calculations and can return to this in some unspecified time in the future sooner or later. In the event you assume honey bees forage 2 km from the apiary, a big apiary (e.g. a shared or affiliation apiary) containing 25 hives will end in an area hive density of three.5/km². 

Excessive hive densities from overlapping apiary ranges … or simply large apiaries

However, if apiary ranges overlap and plant assets are inconsistently distributed (which they’re) then a lot decrease hive numbers may end in larger native hive densities. 

References

MacInnis, G., Normandin, E., and Ziter, C.D. (2023) Decline in wild bee species richness related to honey bee (Apis mellifera L.) abundance in an city ecosystem. PeerJ 11: e14699 https://peerj.com/articles/14699. Accessed June 6, 2023.

Normandin, É., Vereecken, N.J., Buddle, C.M., and Fournier, V. (2017) Taxonomic and useful trait variety of untamed bees in numerous city settings. PeerJ 5: e3051 https://peerj.com/articles/3051. Accessed August 17, 2023.

Smith, T.J., and Saunders, M.E. (2016) Honey bees: the queens of mass media, regardless of minority rule amongst insect pollinators. Insect Conservation and Range 9: 384–390 https://onlinelibrary.wiley.com/doi/abs/10.1111/icad.12178. Accessed August 16, 2023.

Steffan-Dewenter, I., and Tscharntke, T. (2000) Useful resource overlap and doable competitors between honey bees and wild bees in central Europe. Oecologia 122: 288–296 https://doi.org/10.1007/s004420050034. Accessed August 16, 2023.

Torné-Noguera, A., Rodrigo, A., Osorio, S., and Bosch, J. (2016) Collateral results of beekeeping: Impacts on pollen-nectar assets and wild bee communities. Fundamental and Utilized Ecology 17: 199–209 https://www.sciencedirect.com/science/article/pii/S1439179115001504. Accessed August 16, 2023.