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Wild bees and the flowers they pollinate are disappearing together

21 July 2006

The diversity of bees and of the flowers they pollinate, has declined significantly in Britain and the Netherlands over the last 25 years.

This is according to research led by the University of Leeds and published in Science today (21 July 2006). The paper is the first evidence of a widespread decline in bee diversity.

Concerns have been raised for years about the loss of pollination services, but until recently most of the evidence has been restricted to a few key species or a few focal sites. To test for more general declines, an international team of researchers from three UK universities (Leeds, Reading and York) and from the Netherlands and Germany compiled biodiversity records for 100s of sites, and found that bee diversity fell in almost 80% of them. Many bee species are declining or have become extinct in the UK.

Lead author, Dr Koos Biesmeijer from the University of Leeds said, "We were shocked by decline in plants as well as bees. If this pattern is replicated elsewhere, the 'pollinator services' we take for granted could be at risk. And with it the future for the plants we enjoy in our countryside."

Pollinators are essential for the reproduction of many wild flowers and crops. Co-author Simon Potts (of the University of Reading) said, "The economic value of pollination worldwide is thought to be between £20 and 50 billion each year."

The team examined pollinator and plant data, collected by professional and volunteer researchers and naturalists in Britain and the Netherlands, comparing records from before and after 1980.  The results showed bee diversity had declined consistently in both countries, whereas the diversity of hoverflies (another group of pollinating insects) stayed roughly constant in Britain, but increased in the Netherlands.

Loss of bee diversity in itself might not be too worrying, so long as other surviving insect pollinators are similar, and capable of pollinating the same flower species. However, this is not the case. The research found for both bees and hoverflies, the 'winners' and 'losers' were consistently different; insects which pollinate a limited range of flower species or which have specialised habitat needs were most often lost. Overall, a small number of common generalist pollinators are replacing a larger number of rarer specialist species.

Stuart Roberts from the University of Reading pointed out: "In Britain, pollinator species that were relatively rare in the past have tended to become rarer still, while the commoner species have become even more plentiful. Even in insects, the rich get richer and the poor get poorer." 

There have been parallel shifts in the plant world, with the plants that depend on pollination by bees disappearing too.

Dr Bill Kunin, coordinator of the project at the University of Leeds explained, "We looked at plant changes as an afterthought, and were surprised to see how strong the trends were.  When we contacted our Dutch colleagues, we found out that they had begun spotting similar shifts in their wildflowers as well."

In Britain, where bee diversity has fallen and hoverflies have at best held steady, there have been declines in 70% of the wildflowers that require insects for pollination. However, wind-pollinated or self-pollinating plants have held constant or increased.

The pattern is slightly different in the Netherlands, where bees have declined on average but hoverfly diversity has increased. In that country there has been a decline in plants that specifically require bees for pollination, but not in plants that can make use of other insect pollinators. Thus the plant declines closely mirror those of the pollinators. 

This difference between the countries suggests the declines in pollinators and plants are causally linked. Researcher Dr Ralf Ohlemüller from the University of York explained, "The parallel declines of wildflowers and their pollinators seem too strong to be a coincidence."

The research can't tell us whether the bee declines are causing the plant declines, or vice versa, or indeed whether the two are locked in a vicious cycle in which each is affecting the other.  It's also not clear as of yet what the ultimate causes of the declines are, although land use change, agricultural chemicals and climate change may be important factors. The researchers hope to clarify these issues with follow-up studies.

Dr Biesmeijer said, "Whatever the cause, the study provides a worrying suggestion that declines in some species may trigger a cascade of local extinctions amongst other associated species."

The research may not yet prove a global decline in pollination, but in two countries at least there is strong evidence that both wild pollinators and the wildflowers that they visit are in serious trouble.

Further information

Koos Biesmeijer
University of Leeds
Tel: 0113-3432837 (work)
Tel: 0113-2263507 (home)
Mob: 07979287867

Lead author with good overview of all aspects of the study.

Stuart Roberts
University of Reading and Bees Wasps, and Ants Recording Scheme
Tel: 0172 2320072 (home)
Tel: 0118 378 8964 (work)
Mob: 0779 947 2746

Wild bee ecology and conservation in UK and throughout Europe.

Mike Edwards
Hymettus Ltd., the Aculeate Conservation Group
Tel: 01730 810482

Wild bee ecology and conservation in UK.

Bill Kunin
University of Leeds
Tel: 0113 3432837 (work)
Tel: 0113 266 2891 (home)
Mob: 0787 563 7334 (mobile)

Team leader; Plant ecology, pollination, and landscape ecology.

Simon Potts
University of Reading
Tel: 0118 378 6154 (work)
Mob: 0790 9977 618 (mobile)

Plant-pollinator interactions, economic value of pollination.

NERC Press Office
Natural Environment Research Council
Polaris House, North Star Avenue
Swindon, SN2 1EU
Tel: 01793 411561
Mob: 07917 557215

Notes

1. The research was in part funded by the Natural Environment Research Council (NERC).

Examples of declining bees and plants

Scabious bees and Field Scabious are declining
Field scabious (Knautia arvensis) provides pollen and nectar to a wide range of insects. One visitor, the scabious bee, Andrena hattorfiana, raises her young exclusively on pollen from this plant. Our study shows that both species have recently declined in Britain and the Netherlands. Field scabious is still common, but much less so than several decades ago. In addition, grazing and early cutting of hay meadows makes that field scabious often does not reaches the flowering stage. This may be a major cause of the decline of the scabious bee.

The absence of the bee may also play a role in the decline of the plant. The bee has been shown, in a Swedish study, to be a more effective pollinator of field scabious than other bees and hoverfly visitors.  The good news is that adequate habitat management can help the declining bee and its food plant.

The story is even more complex. A parasitic wild bee, the scabious cuckoo bee, Nomada armata (a UK BAP species), is completely dependent on the scabious bee as a host, and is also declining.

Bees specialized on wild peas are having a hard time
It has been suggested that the decline of various bumblebee species has been caused, in part, by the decreased use members of the pea family as fodder for farm animals. Our analysis shows that other species of wild bees that specialize on pollen collection from wild peas are also declining. As an example, the longhorn bees (Eucera nigrescens, Eucera longicornis) have all but disappeared. Eucera nigrescens has become extinct in the UK and is very rare in the Netherlands. This may be a result of a decline in some of their food plants (vetches, vetchlings and clovers).

Press release: 46/06

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