Thread by @ManuSaunders

Great new study from Germany showing how insect pollinator diversity & pollination varies between urban & rural systems. Interesting how media reports have portrayed the results… nature.com/articles/s4146…

“Plants Benefit From More Bees, Especially Bumble Bees”

“Flowering plants are better pollinated in urban than in rural areas.”
scitechdaily.com/surprisingly-p…

“Flowering plants are now better pollinated in urban areas compared to rural ones, a new paper reports. But it’s likely because insects are struggling in the countryside.”
zmescience.com/science/pollin…

The stories seem to be getting some of their text from press releases
eurekalert.org/pub_releases/2…

So what did the study show?

The authors used a neat study design to test how urban vs rural environments influenced pollinator communities & potential pollination services. They paired similar urban & rural sites & conducted the same methods at each
nature.com/articles/s4146…

They surveyed insect diversity at each site using standard methods, focused on Diptera (flies), Hymenoptera (bees, wasps, ants), Coleoptera (beetles), & Lepidoptera (moths & butterflies). These 4 groups of insects are known to be important pollinators

The authors tested pollination services by placing potted plants of red clover at designated locations at each site. They documented visitors to the plants and measured seed set to calculate the ‘pollination service’ metric.

This is a great scientific study based on standard methods. But it is not evidence that ‘pollination works better in cities’!

This study shows us that urban sites in Germnay have lower insect species richness. Richness of all groups except Hymenoptera, especially bees, was higher at rural sites compared to urban sites

Pollination of the experimental red clover plants was higher in urban sites. But...visitation was mostly from bees, which were also more common in urban sites. When comparing all insect visitors across the studied groups (see above), there was no difference

Pollination of the experimental red clover plants was higher in urban sites. But visitation was mostly from bees, which were also more common in urban sites. When comparing all insect visitors across the studied groups (see above), there was no difference

From the paper: “While Diptera and Lepidoptera were more diverse in rural areas, Hymenoptera diversity was higher in urban areas”

From the paper: “Our data suggest that Hymenoptera may be more resilient to urbanisation compared to these other three major flying insect orders, or less resilient to the rural environment dominated by agricultural land use.”

So what does the paper tell us? Flower-rich urban environments can support insects that depend on flowers, i.e. bees (solitary and social). The results of the pollination experiment need to be taken with caveats

All pollinators, including bees, don’t just need flowers…Pollinating insects, which include flies, beetles, bees, wasps, moths, butterflies, [& many others] need multiple resources...incl. (but not limited to) flowers, carrion, water, wood, soil, stone etc.

Importantly, bees are not the only pollinators. There’s a reason the authors focused on flies, beetles, bees/wasps, moths/butterflies…every plant requires different types of pollination & these insect groups include the most important pollinators annualreviews.org/doi/10.1146/an…

Importantly #2: #ecosystemservices (as claimed) must be measured via human benefits. Pollination ES measured with crop yield & quality. In urban environments, experimental plant used by this study (red clover) is often considered a weed

(Ecologically, red clover is not always a weed...but these complexities need to be addressed in any discussion of #ecosystemservices)

nutshell:

Insect diversity does not mean increased pollination services.

Insect diversity is important for lots of reasons, not just pollination.

Urban environments can support lots of biodiversity, as long as we manage those environments to ensure diversity thrives.