Agriculture and the exploitation of natural resources have transformed tropical mountain ecosystems across the world, and the consequences of these transformations for biodiversity and ecosystem ...functioning are largely unknown
. Conclusions that are derived from studies in non-mountainous areas are not suitable for predicting the effects of land-use changes on tropical mountains because the climatic environment rapidly changes with elevation, which may mitigate or amplify the effects of land use
. It is of key importance to understand how the interplay of climate and land use constrains biodiversity and ecosystem functions to determine the consequences of global change for mountain ecosystems. Here we show that the interacting effects of climate and land use reshape elevational trends in biodiversity and ecosystem functions on Africa's largest mountain, Mount Kilimanjaro (Tanzania). We find that increasing land-use intensity causes larger losses of plant and animal species richness in the arid lowlands than in humid submontane and montane zones. Increases in land-use intensity are associated with significant changes in the composition of plant, animal and microorganism communities; stronger modifications of plant and animal communities occur in arid and humid ecosystems, respectively. Temperature, precipitation and land use jointly modulate soil properties, nutrient turnover, greenhouse gas emissions, plant biomass and productivity, as well as animal interactions. Our data suggest that the response of ecosystem functions to land-use intensity depends strongly on climate; more-severe changes in ecosystem functioning occur in the arid lowlands and the cold montane zone. Interactions between climate and land use explained-on average-54% of the variation in species richness, species composition and ecosystem functions, whereas only 30% of variation was related to single drivers. Our study reveals that climate can modulate the effects of land use on biodiversity and ecosystem functioning, and points to a lowered resistance of ecosystems in climatically challenging environments to ongoing land-use changes in tropical mountainous regions.
Species' functional traits set the blueprint for pair-wise interactions in ecological networks. Yet, it is unknown to what extent the functional diversity of plant and animal communities controls ...network assembly along environmental gradients in real-world ecosystems. Here we address this question with a unique dataset of mutualistic bird-fruit, bird-flower and insect-flower interaction networks and associated functional traits of 200 plant and 282 animal species sampled along broad climate and land-use gradients on Mt. Kilimanjaro. We show that plant functional diversity is mainly limited by precipitation, while animal functional diversity is primarily limited by temperature. Furthermore, shifts in plant and animal functional diversity along the elevational gradient control the niche breadth and partitioning of the respective other trophic level. These findings reveal that climatic constraints on the functional diversity of either plants or animals determine the relative importance of bottom-up and top-down control in plant-animal interaction networks.
The effect of biodiversity on ecosystem functioning is increasingly well understood, but it has mainly been studied in small‐scale experiments of plant‐based ecosystem functions. In contrast, the ...relevance of biodiversity for animal‐mediated ecosystem functions like seed dispersal still poses an important gap in ecological knowledge. In particular, it is little understood how avian diversity affects frugivory rates, one of the most important parameters of seed dispersal rates, along large environmental gradients. Even less is known about the environmental context dependence of the frugivore–frugivory relationship. We used artificial fruits to analyze experimentally how the abundance and richness of three avian frugivore guilds (with incrementally more stringent classifications of frugivory) contributed to frugivory rates across 13 different habitat types along an elevational gradient from 870 to 4550 m a.s.l. at Mt Kilimanjaro, Tanzania. We further investigated how environmental context, in terms of local vegetation structure and natural fruit availability, modified the relationship between frugivores and frugivory rates. Our results demonstrate that the positive effect of avian diversity on frugivory rates holds along a large elevational gradient. We found marked differences in frugivory rates among the 13 habitat types, which were strongly related to the abundance and richness of obligate frugivorous birds. Vegetation structure had no significant effect on frugivory rates. An intermediate abundance of natural fruits enhanced frugivory rates, but this effect did not alter the positive frugivore–frugivory relationship. These results emphasize the fundamental importance of obligate frugivore diversity for frugivory rates and suggest that the positive effect of biodiversity on ecosystem functioning holds along large environmental gradients.
AIM: Understanding how species respond to climate and land use change is of prime importance for biodiversity conservation. However, studies using historical, empirical data to understand species ...responses to climate change and anthropogenic habitat disturbance remain scarce, especially for tropical mountain ecosystems. Here, we compare historical to recent mist net data to study changes in abundance of forest understorey birds along two elevational gradients. LOCATION: Mount Kilimanjaro, Tanzania. METHODS: We investigate patterns of understorey bird abundance along elevational and disturbance gradients on two slopes of Mt. Kilimanjaro between 1991 and 2011. To understand species responses to climate change and disturbance, we use a trait‐based approach. Specifically, we test whether and how species' traits (temperature, habitat and dietary preferences) affect species responses to environmental change. RESULTS: We found that over the 20‐year time interval, mean minimum temperature increased across all sites along the elevational gradient, while levels of habitat disturbance remained similar. Mean abundance of understorey bird species increased significantly, especially at higher elevations and on the southern slope. Temporal increases were not related to species' temperature preferences and were detected for habitat generalists as well as herbivorous and omnivorous species, but not for forest specialists and insectivores. MAIN CONCLUSIONS: Our results suggest subtle effects of climate change on bird abundances which would not have been detectable if we had examined elevational range shifts or changes in species richness. Both warm‐ and cold‐adapted species appear to have benefited from increases in minimum temperatures at high elevations. This was not the case for forest specialists and insectivores which remained stable between sampling periods. This demonstrates that different groups of birds vary in their response to ongoing climatic changes. Our results underline the importance of tropical mountain ecosystems not only as global biodiversity hotspots, but also as safe havens for biodiversity in the face of global climate change.
Consolation payments have been introduced as an important mitigation measure for avoiding human-carnivore conflicts. However, few studies have assessed their impact on changing people's behaviors ...toward wild predators. Here, we used questionnaires to assess people's behaviors toward livestock predation before and after the introduction of consolation payments in three villages near the Tarangire-Manyara Ecosystem, Tanzania. Findings revealed that people's behaviors toward wild predators changed after the introduction of consolation payments; from hunting/killing the predator after livestock predation to reporting the incident to game scouts. To enhance the sustainability, adequacy, and effectiveness of consolation payments, we recommend regular revision of consolation regulations.
Many experiments have shown that biodiversity enhances ecosystem functioning. However, we have little understanding of how environmental heterogeneity shapes the effect of diversity on ecosystem ...functioning and to what extent this diversity effect is mediated by variation in species richness or species turnover. This knowledge is crucial to scaling up the results of experiments from local to regional scales. Here we quantify the diversity effect and its components-that is, the contributions of variation in species richness and species turnover-for 22 ecosystem functions of microorganisms, plants and animals across 13 major ecosystem types on Mt Kilimanjaro, Tanzania. Environmental heterogeneity across ecosystem types on average increased the diversity effect from explaining 49% to 72% of the variation in ecosystem functions. In contrast to our expectation, the diversity effect was more strongly mediated by variation in species richness than by species turnover. Our findings reveal that environmental heterogeneity strengthens the relationship between biodiversity and ecosystem functioning and that species richness is a stronger driver of ecosystem functioning than species turnover. Based on a broad range of taxa and ecosystem functions in a non-experimental system, these results are in line with predictions from biodiversity experiments and emphasize that conserving biodiversity is essential for maintaining ecosystem functioning.
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