Friederike Gebert is a postdoc working in tropical entomology at the University of Würzberg. Her recent work, published in the Journal of Biogeography, focuses on understanding the patterns and drivers of dung beetle distribution along an elevational gradient on Mt. Kilimanjaro. From the collection of dung beetles to the measurement of mammal dung resources, Friederike provides an insider look into the study of two very different but functionally related groups of organisms on the highest free-standing mountain in the world.
Friederike whilst setting up a pitfall trap at the base of Mt. Kilimanjaro at 870m asl on a study plot located in the savannah
Institution: University of Würzburg, Department of Animal Ecology and Tropical Biology
Current academic life stage: Postdoc
Research interests: I am interested in tropical entomology and in the impact of elevation and land use on species’ distributions, traits, and ecosystem services.
Current study system: Currently, I am studying dung beetles and mammals on Mt. Kilimanjaro, Tanzania. The fascinating thing about my research is that I combine the study of two very different, yet closely functionally related groups of organisms on the highest free-standing mountain in the world to investigate the drivers of biodiversity along elevational gradients. Both dung beetles and mammals are of immense importance in ecosystems, the former because they provide many ecosystem services related to dung decomposition, and the latter because they turn over high amounts of biomass and provide an array of services from pollination to the maintenance of habitat heterogeneity.
Recent paper in Journal of Biogeography: Gebert F, Steffan-Dewenter I, Moretto P, Peters MK. (2020) Climate rather than dung resources predict dung beetle abundance and diversity along elevational and land use gradients on Mt. Kilimanjaro. Journal of Biogeography, 47(2):371–381. https://doi.org/10.1111/jbi.13710
Motivation for the paper: The distribution of species along mountains has fascinated biologists for more than two centuries. Even though the patterns of species diversity along elevational gradients are well described, the drivers behind them remain controversial until today. Many hypotheses are discussed, a general disagreement being whether energy-related or climate-related drivers are more important. I wanted to contribute to this current discourse on the predictors of biodiversity by investigating the patterns and drivers of ectothermic organisms—dung beetles—along a huge elevational gradient on Mt. Kilimanjaro. One shortcoming of studies investigating the importance of energy versus the importance of temperature in driving biodiversity gradients is that often, energy resources are not directly measured. Instead, primary productivity is used as a proxy for resources. However, most organisms use specific food resources which may not be represented accurately by primary productivity. Therefore, we tried to measure the energy resources available for dung beetles in the field.
(A) The study system: Mt. Kilimanjaro – this photograph was taken at 1600m from the research station, Nkweseko, which served as the base for the dung beetle study. It shows the south face of Kibo, the summit of Mt. Kilimanjaro at 5895m. Nkweseko research station is located in the cultivated zone of Mt. Kilimanjaro inside the coffee-banana belt. The predominant form of cultivation here is traditional agroforestry of the Chagga people, which is called Chagga homegardens. (B) Here you can see very rich lower montane forest. This beautiful valley is located at 1600m and, unfortunately, is not part of Mt. Kilimanjaro National Park. Therefore, logging is commonplace and a threat to the preservation of this remarkable area. Here, two study plots were located. (C) Here you can see a camera trap set up in the forest. (below) A part of our collection. In total, we collected 10432 dung beetles belonging to 135 species.
Key methodologies: We used baited pitfall traps to collect dung beetles. For measuring dung resources available for dung beetles, we calculated mammal defecation. To get the mammal data, we installed camera traps on the same 66 study sites along an elevational gradient of 3.6km on Mt. Kilimanjaro on which we collected dung beetles. We then estimated mammal defecation from mammal biomass data. To the best of our knowledge, this is the first study to accurately measure the amount of dung resources available for dung beetles. Apart from dung resources, we also investigated the impact of temperature, precipitation, land use and area on dung beetle species richness and abundance by means of path analysis.
A graph illustrating the drivers of dung beetle species richness and abundance. While dung beetle diversity is impacted by climate (temperature and precipitation), the main predictor for mammals (here represented as the dung resources) is net primary productivity, demonstrating the contrasting drivers of endothermic and ectothermic diversity.
Unexpected challenges: Since dung beetles rely upon mammalian dung as a food source for both adults and larvae and are thus closely functionally related to mammals, we expected mammalian dung resources to be one major driver of dung beetle diversity on Mt. Kilimanjaro. As we tried our best to have a good measure of dung resources for dung beetles, we were surprised to find that dung resources did not play a role in predicting dung beetle diversity. Since most dung beetles are active during the rainy season, I mainly collected dung beetles during the period of the long rains on Mt. Kilimanjaro. Because of muddy roads and paths, it was not always easy to reach the study plots and we had to overcome challenges like trees blocking the road or cars stuck in the mud.
Major result and contribution to the field: We found that even though we tried to meticulously measure the actual dung resources available for dung beetles, temperature was the major driver of dung beetle diversity on Mt. Kilimanjaro. This study shows that along huge environmental gradients, temperature is the main driver of diversity for ectothermic organisms. However, when we looked at the drivers of mammals, which are endothermic, we found that energy resources were the most important drivers. To conclude, our study is an important contribution to the current debate on the drivers of biodiversity as it illustrates that the drivers for montane diversity depend on the thermoregulatory strategy of organisms. Furthermore, our finding that dung beetle diversity is driven by temperature has important implications for biodiversity conservation in the context of climate change, as rising temperatures may have negative repercussions on dung beetles and their associated ecosystem services.
What are the next steps? The next step in this research is to look at the ecosystem services provided by dung beetles to investigate whether climate or biodiversity is more important in shaping ecosystem services along environmental gradients.
If you could study any organism on Earth, what would it be and why? In ecology, we are always in search of general patterns. I especially like organisms that make us question the concept of generality and make us acknowledge that there are always exceptions to the rule, which is one of the most intriguing features of studying biodiversity. That is why, even though I am actually an insect person, I would love to study the Grasshopper Mouse (Onychomys sp.). This mouse is so special because, in contrast to other rodents, it relies on a carnivorous diet and even feeds on scorpions and snakes, being immune to their venom. And since I am an old Dracula fan, I love the fact that this mouse is nocturnal and howls to the moon like a proper werewolf mouse!
Any other little gems you would like to share? During my research on Mt. Kilimanjaro, we collected a total of 80,000 film snippets from camera traps. Whilst most of the videos showed moving grass in the savannah, around 1600 videos did actually show mammals. Our biggest mammal highlight was that we filmed the elusive antelope species Abbott’s Duiker (Cephalophus spadix) for the first time on Mt. Kilimanjaro. This antelope is endemic to Tanzania and only occurs on few isolated mountain massifs. Up to now, the distribution of this species on Mt. Kilimanjaro has not been known – now our research suggests that Mt. Kilimanjaro might be a stronghold for this species. What’s cool is that we were the first ever to film an Abbott’s Duiker pair and a male trying to mate.
(left) Alpine Helichrysum scrub vegetation at 3800m. (right) The highest study plots were located at 4500 m.