This blog post is provided by Friederike Gebert from the University of Würzburg and tells the #StoryBehindThePaper for her article Primary productivity and habitat protection predict elevational species richness and community biomass of large mammals on Mt. Kilimanjaro which has been shortlisted for the 2019 Elton Prize.
Mountains are biodiversity hotspots and prior areas for conservation. Even though elevational gradients belong to the best described patterns in ecology, their drivers remain controversial until today. We wanted to contribute to this discourse by investigating the distribution and predictors of large mammals on Mt. Kilimanjaro, the highest free-standing mountain in the world. Despite their immense functional and cultural importance, so far, large mammals have been neglected in studies on elevational diversity patterns.
However, at the beginning of our research project on Mt. Kilimanjaro, we did not have mammals as focal organisms in mind, but a group of organisms that is very different, yet closely related to mammals: dung beetles. Dung beetles are important decomposers and are largely coprophagous, meaning they feed and nest in mammalian dung. Originally, we were particularly interested in the factors behind the patterns of dung beetle diversity on Mt. Kilimanjaro. Among other factors, we wanted to test the availability of resources as a driver of dung beetle diversity. This is where mammals first came into the picture – instead of taking primary productivity as a proxy for resource availability for dung beetles, as do most studies, we wanted to have an accurate measure of resources available for dung beetles. To this end, we recorded mammals with camera traps and calculated defecation from mammal biomass data. In the course of analysing the results for the dung beetle study, now published in the Journal of Biogeography, we realized that we obtained a very valuable mammal data set, which is why we decided to publish our results in the Journal of Animal Ecology.
For documenting mammals on Mt. Kilimanjaro, we put up five camera traps each on 66 study plots, spanning an elevational gradient from 870 m to 4500 m. The study plots represented the major natural and anthropogenic habitats that can be found on the southern slopes of the mountain. They ranged from habitats such as savannah and maize fields at low elevations over lower montane forest and Chagga homegardens at mid elevations, to Mt. Kilimanjaro National Park, which protects all habitats above 1800 m and encompasses several natural and disturbed forest habitats and afro-alpine shrub vegetation. The camera traps remained in the field for two weeks. We collected a daunting 80.000 film snippets, each lasting 20 seconds. I started by looking at the film snippets from the savannah and was on the verge of getting desperate because I had watched thousands of videos already just showing moving grass, without trace of any mammal, when I finally spotted the first baboon. In the end, around 1600 videos did actually show mammals. In total, we recorded 33 wild mammal species and five domestic mammals. Apart from camera traps, we also used transect walks to document mammal faeces – we reported 176 dung samples.
We recorded common species like the Common Duiker and the Zanzibar Syke’s Monkey, but also species such as the Eastern Tree Hyrax, the Lesser Kudu and the Plains Zebra, which are categorized as threatened, and the Leopard, which is listed as vulnerable. Our biggest highlight was that we filmed the Abbott’s Duiker for the first time on Mt. Kilimanjaro. The Abbott’s Duiker is an elusive montane forest species endemic to Tanzania; it is restricted to a few isolated mountains in East and South Tanzania and listed as endangered in the IUCN red list. Prominent features of this duiker are the glossy, nearly black colour and the russet tuft between the horns. The first photograph of this species was taken as recently as 2003 and in 2013, the first videos were shot in the Udzungwa Mountains, the southernmost block of the Eastern Arc Mountains. Previously, the distribution of the Abbott’s Duiker on Mt. Kilimanjaro was hardly known – in the present study, we filmed the Abbott’s Duiker on 105 occasions at eleven study sites, ranging in altitude from 1920 to 3849 m. This high occurrence of the Abbott’s Duiker makes us suggest that Mt. Kilimanjaro could be another stronghold of this species apart from the Udzungwa Mountains. We are very proud to be the first ever to film an Abbott’s Duiker pair and a male trying to mate.
We found that mammal diversity and community biomass showed a hump-shaped pattern along elevation with a peak at 2500 m. However, when we only considered protected study plots – two savannah study plots inside a game reserve and Mt. Kilimanjaro National Park – the distribution of mammal species richness shifted to a low-elevation plateau, peaking at 1500 m. This result was mainly caused by the largest mammals, like the Lesser Kudu and the Plains Zebra, which were absent from unprotected study plots and only occurred in protected areas. As potential drivers of mammal diversity, we considered temperature, resource availability, area and human impact. Mammal diversity at Mt. Kilimanjaro was mainly predicted by primary productivity – our measure of resource availability for mammals –, climate and the protection status of study plots. The former driver lends support to the ‘energy-richness’ or ‘species-energy hypothesis’, which states that highly productive ecosystems harbour abundant resources, so that more and larger populations can persist than in less productive ecosystems. While the effect of primary productivity on mammal diversity was direct, there was both a smaller direct and stronger indirect effect of temperature, mediated via resource availability. The latter driver, the protection status of study plots, has huge implications for conservation. Large mammals perform key roles in ecosystems and their loss from unprotected habitats, for example through habitat destruction, hunting and retaliatory killing, will likely have negative repercussions on species communities and mammal-mediated ecosystem services, such as the maintenance of habitat heterogeneity. From a conservation point of view, there is no alternative to the designation, maintenance and expansion of protected areas to preserve mammal diversity in the long term.