The intricate lives of bees

The intricate lives of bees

These are some of the questions that Assistant Professor Kristian Trøjelsgaard attempts to answer through his work at the Section of Biology and Environmental Science at the Department of Chemistry and Bioscience at Aalborg University.

- “The overall topic of my research is ecological networks, which is a way of characterizing the interactions between species or individuals. One example of this is pollination networks. In this type of network, a number of plants are pollinated by a variety of species; at our latitudes this is primarily done by insects, but in other places it may also be birds, bats and various mammals. We depict these ecosystems as networks because it enables us to map out the interactions: Which plant is being pollinated by whom? And which plants do the different pollinators depend on for their lives?” Kristian Trøjelsgaard explains and adds:

“You can compare it to Facebook, where you can see who is friends with whom, who interact a lot, and how the overall network is structured. We actually use a lot of tools and concepts from Social Science in order to analyze ecological networks. They let us see which plants are highly important and which pollinators are crucial in order to make the network function.”


Understanding how these ecological networks function also means trying to predict the consequences if one or more of the plants or pollinators were to disappear from the network. “We aim to understand how each ecological network is structured and what makes them either robust or sensitive to disturbances. What happens if we lose a species – if we remove a nodal point from the network, so to speak?  Will it all fall apart, or can the ecological society still exist? And to do that, we need to know the specific function of each species in that community, including which other species – plant, insect or animal – it interacts with” Kristian Trøjelsgaard explains.

- “I am currently working with data from the Galapagos Islands where I look at the impact that invasive pollinators like the honeybee have on the indigenous ecological networks. Islands are particularly vulnerable to invasive species, and what the data show is that the impact on the ecological networks varies markedly from island to island. In some cases, they are hardly affected at all – in other words the indigenous species still play the central roles in the network – but in other cases, the invasive species have influenced the ecological networks to such an extent that even if we had unlimited resources and wanted to restore them to their original structure, this would be impossible because the invasive species now play an important role for the system to work” he adds.


The data from the Galapagos Islands was sent to Kristian Trøjelsgaard for analysis from some of his international research colleagues, but he himself can also be found out in the field gathering empirical data. He is currently working on another major project focusing on monitoring and modelling the foraging of bumblebees in order to find out how they navigate the landscape where they forage. “Our experiments consist of catching the bumblebees and placing a tiny number on their backs before releasing them again. In addition, we have assigned a number to all the flowers and plants in the specified area – a field of approximately 75X75 meters – and then we have actually followed these numbered bees across the field and registered how they move from flower to flower” Kristian Trøjelsgaard says.

“For the bees, every plant is a resource where they can get either pollen or nectar. And for the plants, the bees serve to transport pollen from one plant to the next. We had a theory that the bees do not just move around randomly, and that is exactly what we see: They use the landscape deliberately; they remember which direction they are coming from and where they are going” Kristian Trøjelsgaard explains.

- “We can also see that they choose the shortest route from one flower to the next. They don’t just fly randomly from one flower to another, or a long distance away even though such plants might be more rewarding in terms of the number of flowers. In other words, they fly a very deliberate route and potentially expend the smallest possible amount of energy” he adds.


While the research into the foraging patters of bumblebees is still at the relatively small scale of a single field, the researcher hopes that it will become an important piece in a much bigger puzzle in the future.

- “Estimates show that approximately 87 % of all flowering plants depend on insects or other animals for their pollination. Also crops that we use here in Denmark, including rapeseed and a variety of fruit crops, depend on animal pollination. Although some crops may be capable of giving a certain yield even if they are not pollinated, they will often give a significantly higher yield if they are properly pollinated” Kristian Trøjelsgaard explains. In some cases, domesticated pollinators – most famously the honeybee – are released to perform the pollination of crops. However, wild pollinators have been shown to be more efficient – and provide a better yield.

- “Pollination is crucial for natural and wild ecological systems, but they are also crucial for some agricultural crops. Add to that the fact that many pollinators are under pressure from climate changes, the use of pesticides, various diseases and general agricultural intensification, and we have a situation where increased understanding of these pollinators is critical, both from nature’s perspective and in a commercial context” Kristian Trøjelsgaard says and adds: “If I dare to dream about the future use of my research, it could be incorporated when Denmark or the EU initiate activities for the restoration of natural habitats. A better understanding of how bumblebees move – not just from flower to flower but at a larger scale from hive to foraging fields – will enable us to say, ‘We know they have a preference for doing this, so let’s utilize that knowledge when we plan our habitats.’ And we could even plan the landscape in such a way that we place orchards in between habitats that are tailored to wild pollinators.”

In that way, the behavior of the bumblebees becomes a part of an even larger ecosystem that also includes humanity and our network of cities, roads, huge grain fields and other anthropogenic, modified landscapes.

- “My interest in the bees stems from an interest in nature. In order to understand what is going on in nature, we need to focus not on each species in isolation but the species in unison with all the other species they interact with. And just as we have to look at nature in such a holistic way, we also need to include the way we interact with nature and the ecological communities in which they, and we, are part, if we are to fully understand the species around us” Kristian Trøjelsgaard finishes.