Why biologists set up coloured soup bowls on Kilimanjaro and how this helps them find out that bees still live at an altitude of 4,550 metres and other interesting facts: New findings in biodiversity research.
The detailed accounts Alexander von Humboldt (1769-1859) gave of his journeys already emphasised that biodiversity is not equally distributed on our planet. Whereas tropical rainforests exhibit a vast diversity in plant and animal species in a small area, moderate climate zones have less to offer with the variety of species decreasing towards the poles.
Why are the tropics so densely populated and the poles rather sparsely? Science has never been able to completely answer this question. To shed light on the issue, a team of the University of Würzburg's Biocenter has travelled to Mount Kilimanjaro in Tanzania, the highest free-standing mountain in the world (5,895 metres).
What makes Kilimanjaro interesting to research
What does Mount Kilimanjaro have to do with the biodiversity on our latitudes? "Quite a lot," says Professor Ingolf Steffan-Dewenter, head of the Würzburg Department of Animal Ecology and Tropical Biology: "When you climb a mountain, the temperature will drop with elevation at a rate of around six degrees Celsius per kilometre – that is about a thousand times faster than if you were moving from the equator towards the poles."
Other environmental factors that change only slowly along latitudes vary relatively quickly along differences in altitude – the productivity of ecosystems, for example. This makes high mountains virtual "experimental labs" that allow the factors determining biodiversity in our planet's climate zones to be studied at a small scale.
How to measure the diversity of wild bee species
The Würzburg scientists wanted to know which factors influence the diversity of wild bee species. Why wild bees of all species? "Wild bees are among the most important pollinators of our ecosystems. Their diversity in the tropics is still manageable for us. And their food resources, nectar and pollen, are defined quite clearly compared to other insects. This makes wild bees great subjects for study," bee expert Steffan-Dewenter explains.
The scientists used simple plastic soup bowls to determine the diversity of bee species at Mount Kilimanjaro. Sprayed with blue, yellow or white paint that reflects the light, the bowls attract bees which think they are flowers and fly right into the trap containing water and soap. The soap reduces the surface tension of the water so that the insects sink to the bottom of the trap.
"If you work in the tropics, the simplest methods are often the best," explains Andreas Hemp, an Africa specialist of the University of Bayreuth. "Expensive equipment cannot be left unattended, whereas painted bowls at best attract some curious schoolchildren."
Where the researchers set up the insect traps
The scientists installed the painted bowls at 60 study sites in total on Kilimanjaro three times in two years. Half of the sites were only accessible after hours of marching. The highest location was 4,550 metres above sea level, exactly at Mount Kilimanjaro's limit of vegetation.
"You tire more quickly at such heights," Alice Claßen, a doctoral candidate, recalls. "And what is more, the mean annual temperature up there is only about three degrees Celsius. The dry season was most challenging physically: on some days we had to carry the water for the traps up the mountain. This is only possible if you work in a team and with the help of great field assistants."
The painted bowls were left in their respective locations for 48 hours each. During that time, the researchers collected key data regarding temperature, precipitation, number of flowers and intensity of land use at the respective sites of study.
What the scientists found out
It was worth the effort: In the end, the research team successfully demonstrated that the biodiversity of bees declines continuously with increasing altitude. They were greatly surprised to find a specifically adapted species of apex-burrow bee (Lasioglossum, Halictidae) still living at an altitude of 4,550 metres.
So far biodiversity has been known to be regulated by resources and temperature. "The resources are like a cake," Marcell Peters, a Würzburg postdoc, explains: "The bigger the cake, the more individuals can feed on it and the bigger the populations that can be maintained. And the bigger the populations are, the smaller their risk of extinction is."
However, matters become more complicated when we look at the temperature. High temperatures as found in tropical zones increase the speed of speciation processes, for example, by increased rates of mutation or ecological mechanisms. But given the fact that Mount Kilimanjaro is rather young in geological terms, higher speciation rates there are insufficient to account for the whole pattern of biodiversity.
How the use of resources depends on temperature
The researcher demonstrated that it is actually the combination of temperature and resources that plays a major role: "We found temperature to have a significant impact on biodiversity which was regulated by an increase in the populations," Peters further. "Moreover, we were able to show that bees visit fewer flowers when temperatures are low than when they are high, even though flowers are abundant. Hence, temperature seems to regulate the accessibility of resources and is therefore more relevant than the availability of resources." Surprisingly, this mechanism has hardly been taken into account by previous explanation approaches.
What is true for wild bees should at least apply to other poikilotherms, too. But it is possible that the biodiversity of homoeothermic animals, too, which frequently feed on poikilotherms, is regulated by the temperature-dependent use of resources. Although these findings have not completely answered the question of which mechanisms are actually responsible for regulating biodiversity on Earth, they have enabled us to add another piece of the puzzle to the overall picture.
These research results have been produced within the scope of the research group "Kilimanjaro ecosystems under global change" funded by Deutsche Forschungsgemeinschaft (DFG); Professor Ingolf Steffan-Dewenter is the group's spokesman.
Classen, A., Peters, M. K., Kindeketa, W. J., Appelhans, T., Eardley, C. D., Gikungu, M. W., Hemp, A., Nauss, T. and Steffan‐Dewenter, I. (2015), Temperature versus resource constraints: which factors determine bee diversity on Mount Kilimanjaro, Tanzania? Global Ecology and Biogeography. doi:10.1111/geb.12286, published online January 19, 2015.
Alice Claßen, Department of Animal Ecology and Tropical Biology (Zoology III), University of Würzburg, Phone +49 931 31-82793, firstname.lastname@example.org
Prof. Dr. Ingolf Steffan-Dewenter, Department of Animal Ecology and Tropical Biology (Zoology III), University of Würzburg, Phone +49 931 31-86947, email@example.com
https://www.kilimanjaro.biozentrum.uni-wuerzburg.de Link to the homepage of the DFG research group "Kilimanjaro ecosystems under global change"
Robert Emmerich | Julius-Maximilians-Universität Würzburg
The balancing act: An enzyme that links endocytosis to membrane recycling
07.12.2016 | National Centre for Biological Sciences
Transforming plant cells from generalists to specialists
07.12.2016 | Duke University
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
07.12.2016 | Health and Medicine
07.12.2016 | Life Sciences
07.12.2016 | Health and Medicine