Are less species enough? – Bee diversity or key pollinators
Last week, I gave some inspiration for helping pollinators and what is important beyond flowers. But on the other side – do we need all the 20,000 species of bees? Wouldn’t it be enough to know the key pollinators and to manage them? You may already know what my answer to this is. No. Fortunately, this has more reasons than just my preference for diversity. My first objection would be, that we don’t know how to define these key species. The standard answer from most people would be: the honey bee! But, this is not true. We have more and more evidence that it needs pollinator communities to get the best pollination.
Only this week at a conference in Berlin I heard the argument that honey bees have the big advantage of being present in big numbers already in early spring. They overwinter as a colony, right? So there are numerous foragers flying out as soon as the first flowers begin to bloom. Hearing this, I always wonder, if these persons ever stood in an apple orchard while it is flowering. In a study I did three years ago in UK (in Herefordshire), we hardly observed honey bees in the orchards. Even where honey bee colonies stood within, there were very few in the apple flowers. The main flower visitors were mining bees.
Beyond my personal observations, there is increasing evidence that pollinator communities work best together. For example, this is well studied in almonds.
Why there is no “one fits it all” key pollinator species
So why did honey bees not visit the apple flowers in the mass they were expected to? Well, there were several reasons. First of all, the days were still quite cool when the the apple trees began to flower. Honey bees like it warm, they fly out much later than, for instance, bumblebees or several solitary bee species. Secondly, there were also oil seed rape fields nearby, dandelions in the neighbouring greenland etc. Honey bees like diversity, too. They will explore the surroundings and decide themselves what they like best in that moment. In another study a single flowering cherry tree was buzzing with bees, while the oilseed rape we were observing was much less interesting. Also generalistic bees have preferences, depending on what they need in a single situation.
But there is another argument why it is difficult to determine key pollinators for a certain crop. And it is easy and complex at a time: conditions change. At a regional scale like that study in Herefordshire, the different orchards we surveyed had a different compostion of pollinator species. There were different microclimates, more or less structures like hedgerows, single trees or adjacent meadows. The soil quality may change, the exposure to the sun or the diversity and abundance of wild flowers. All this influences the pollinator community and their activity on the orchard. On the orchards with many different structures we found more pollinator species and in a higher abundance.
And now expand these differences we detected in Herefordshire to a larger scale: the “Altes Land” in Germany, Normandy in France or Southern Tyrol in Italy to name other big apple regions. The number of differences grows, also in management practices, size of the orchards, apple varieties etc. Further expand it to other pollinator-dependent crops: almonds, oilseed rape, sunflower… And now to wild plants. And the poor honey bees shall do pollination all alone?
Diversity creates diversity
That something has been believed for long time doesn’t mean that it is true forever. Having new data and insights, scientists must review their statements. Concerning pollinators, there is increasing evidence that more pollinators do a better job. This includes bees, but also other pollinators like hoverflies. In addition, honey bees are not even the key pollinators in food crops.
There is also another aspect in this: not all flowers are the same. They have different structures, have to be “handled” differently. They have different sizes, different colours, different flowering periods. How could you define “key pollinators” with all these differences?
Not all bees can handle all these differences. Perhaps they are too small to open a flower that needs some weight to reveal the nectar and pollen reward. Perhaps their tongue is too short to get the nectar at the end of a long spur. They may not change enough between different plants to meet the need for cross pollination. There are so many factors to consider for optimal pollination. The mass of honey bees does not compensate all these elements. Quantity doesn’t equal quality.
Coming back to the initial question: do we need all bee or even pollinator species? Yes, we do. From the egoistic point of view to ensure our food security and quality. But also from a broader perspective if we recognize the intrinsic value of diversity. Pollinator diversity and plant diversity are closely linked. Beyond that, there are also birds that feed on the seeds, small mammals that need nest building material, parasites that live on all these species and regulate their populations… Key pollinators? No, diversity is key.