Lost Bumblebees of Denmark

research blogging iconOne of the really cool things about Entomology is there are a lot of opportunities for longitudinal studies. For hundreds of years, bug nerds have been routinely killing and preserving the subjects of their studies, so we have a nice historical record to make comparisons with.

A new paper in PLOS came out recently that did a nice job of reproducing the sampling methods of a bee study from 80 years ago–and the results are a bit depressing.

I’ve covered before the importance of native pollinators, and bumble bees provide important pollination services to crop plants–in this study, red clover. Red Clover is a great pick for a pollination study, since it is self-incompatible–in other words, it can’t fertilize itself, and is dependent on pollinators to move pollen around for any reproduction.

The investigators were interested in seeing how bumble species might have changed over time because of changes in climate, tilling practices, and overall landscape changes.   They managed to find plots to survey that were remarkably like the initial 1930′s study, and started catching bumblebees.

The news isn’t good.

The 1930 study identified 12 species of bees as common in fields of clover; 5 of them were not detected at all in this modern survey.  The bumblebee species that vanished were also what is called “long-tongued” species.   Bumble bees occupy a special pollination space, since as bigger animals, they have longer tongues.  This lets them work flowers that smaller honeybees can’t reach into.

Bumble bees also are able to forage at low temperatures, and can buzz pollinate.  (Some plants only release their pollen when they are vibrated at specific frequencies.)

Bumbles are critical to what are called “ecosystem services,”–the stuff we get for free just for living on Earth.  Like pollination of our food crops by wild pollinators, which in the US is valued around 6 billion dollars.

When you look at the graphs, it’s pretty clear–the number of species and the frequency (commonness) of species declined. As best I can tell from the paper, it seems to me that the modern researchers actually sampled more intensively than in the past.  Here’s what the authors have to say:

“For long-tongued species, abundances of queens was found to decline an order of magnitude from the 1930′s to the present, corresponding to a dramatic decline in effective population sizes. Findings of the present study are strong and direct evidence of local changes in species richness and abundances.”

Yikes.  But, you may be thinking, so what? Some bumblebees went away.

I can’t tell you what the consequences of this change will be, but I can tell you I am fairly sure it won’t be a good thing. I think Aldo Leopold said it best:

Only those who know the most about it can appreciate how little we know about it. The last word in ignorance is the man who says of an animal or plant: “What good is it?”  If the land mechanism as a whole is good, then every part is good, whether we understand it or not. If the biota, in the course of aeons, has built something we like but do not understand, then who but a fool would discard seemingly useless parts? To keep every cog and wheel is the first precaution of intelligent tinkering.

Citation:

Dupont YL, Damgaard C, & Simonsen V (2011). Quantitative Historical Change in Bumblebee (Bombus spp.) Assemblages of Red Clover Fields. PloS one, 6 (9) PMID: 21966445

4 thoughts on “Lost Bumblebees of Denmark

  1. Interesting study. Thanks for posting it. They sampled almost three times as many workers and almost five times as many queens as the 1930′s study and at two sites,not just one island site, so unless the earlier workers had a bias for rarer bees or the 2008-2009 summers were unusually cool (which would affect the late-emergers more), the conclusions seem robust. Good example of why you need to know what you had before you can tell if it has changed.

    I guess the good news is that the overall abundance of bumble bees wasn’t down significantly and the short-tongued species seem to be producing lots of queens (mid-season peak in Fig. 2), although these could be augmented by escapes from domesticated colonies (mostly B. terrestris and other Bombus (Bombus) I would guess). But if I were worried about native plant conservation in Denmark, I would find this paper distressing. Bombus pascuorum seems to be the only long-tongued species around to service plants with a long corolla tube.

    I suspect land use changes have had the most drastic effects on the bees, including things like eliminating hedgerows and the like for increased efficiency and conversion of meadows to farmland. I wonder if the long-tongued species are able to use urban gardens as refugia? That would be nice, but I’m not sure it would be of much use to plants in reserves.

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