Protecting Our Pollinators.

Could better agri-management save the country's Bumblebees?

Imagine that all the supermarkets closed their doors for two weeks every month. Even if you were careful with rationing, the lack of fresh food for that fortnight would be a major issue. With no fresh vegetables or meat, you would struggle to maintain a balanced diet if at all. This is the situation that the UK's pollinators, the most important group of animals in Britain, are experiencing each year: severe food shortages when demand is high, but supply is starvingly low. Scientists are now coming to the rescue with new research that has identified when these 'hunger gaps' occur and what can be done to help. A Bumblebee takes flight after pollinating a flower.

Pollinator species like Bees, Birds and Bats are a crucial part of almost all ecosystems on the planet. These tiny, yet significant animals influence every flowering plant in the world, which in turn prevent soil erosion, increase carbon sequestration and produce countless fruits, vegetables and nuts for our consumption. Moreover, pollinators are responsible for 75% of the crops that we produce each year: that's over 1,200 different plants which accounts for one out of every three bites of food! In monetary value, pollinators add an astonishing £170 billion to the global economy each year.

Wild pollinators are limited by both floral nectar and pollen resources. Unfortunately, many pollinator species are experiencing a crisis of food shortages when these resources naturally run low during the flowering season. Not only do these 'hunger gaps' mean that individual animals become temporarily starved, but interruptions of just 15 days in these natural reserves can severely affect colony development, especially in Bumblebees.

Recently, researchers from the University of Bristol have looked at how we can identify these phenological, i.e. seasonal/cyclical, natural resources as well as what the best strategy would be to help keep the pollinators' food supply consistently high when there is a natural depletion of nectar. Considering that 70.8% of the UK's large-coverage land is used for agriculture, this investigation could play a crucial role in protecting our pollinators.

The research team, led by PhD student Tom Timberlake, set out three objectives: 1) Measure the phenology of nectar resources throughout the flowering season; 2) Compare those measures to the demands of the common farmland Bumblebee to see when there are 'hunger gaps' and; 3) Identify which habitats and plants are available that could be used when there are severe food shortages.

Between 2016 and 2017, the researchers surveyed four medium-sized farms in Somerset, south England, that were "broadly representative of the wider landscape." One of the challenges with scientific research regarding the phenology of flowering plants is based in methodology - it is difficult to effectively study a large amount of land whilst keeping a consistently high resolution of data within any reasonable time period. Therefore, the scientists used a "dual approach, whereby one site was sampled intensively to capture the fine-scale temporal variation in flowering phenology and three other sites were sampled less intensively to capture the spatial variation." Impressively, the researchers collected data from nearly half a million individual floral units and counted a staggering 176 different flowering plant species over the two years.

The team found that "the strong seasonality of nectar supply did not synchronise well with the sugar demands". This meant that bumblebees did indeed experience periods of time during the flowering season when their natural food supply was not as readily available as they required. In fact, there were "alternating periods of nectar deficit and surplus". In layman's terms, there may be enough sugar being produced to sustain a colony at one time, but that period is going to be followed by a noticeable "hunger gap".

For example, in early March the queen bee emerges meaning that the demand for nectar is extremely high; however, the natural supply is at its lowest: so much so that the scientists estimated that over 1Km2 of land, only 19 queen bumblebees can survive. This does not even account for the young that each of these queens will produce or any of the other competing pollinator species within that 1Km2 of farmland.

Unfortunately, these fluctuations in nectar supply may a crucial limiting factor in the survival of pollinator populations. The largest and most significant 'hunger gaps' identified in this research fell between late February and late March, June and between August and September.

The researchers found that the different habitats found on farmland "differed greatly in their pattern of nectar production but tended to complement each other's nectar supply." The scientists discovered that the differences in flowering phenology caused pollinators to travel between habitats, following the food supply as it changes, similar to how shoppers would travel between aisles in a supermarket. Unfortunately, climate change is altering the flowering phenology of many plant species. Therefore, monitoring how the pollinators' food supply alternates throughout the year will become even more important as climate change accelerates.

This research has important implications for how agricultural land in the UK is managed. The scientists recommend that plant species that flower during these identified 'hunger gaps' should be used to maintain a continuous and a sustainable supply of nectar for pollinators. As the scientists pointed out, "we have demonstrated why the timing of these resources may be an important factor driving this limitation" - it is now up to the agriculture industry to act.

Pollinators are the key component in both Britain's ecological makeup and our agriculture industry; without them, we would see severe food shortages ourselves. This research has provided crucial evidence for when these animals need our help the most in the year. Gaps in the supply of nectar and other resources may be a natural occurrence; however, we could have a vital role to play in protecting our pollinators if we can improve the management of our farmlands.

Author: Thomas Llewellyn

Reference:
Timberlake, T.P., Vaughan, I.P. and Memmott, J., 2019. Phenology of farmland floral resources reveals seasonal gaps in nectar availability for bumblebees. Journal of Applied Ecology.