@phdthesis{Njovu2019, author = {Njovu, Henry Kenneth}, title = {Patterns and drivers of herbivore diversity and invertebrate herbivory along elevational and land use gradients at Mt. Kilimanjaro, Tanzania}, doi = {10.25972/OPUS-17254}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172544}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2019}, abstract = {This thesis elucidates patterns and drivers of invertebrate herbivory, herbivore diversity, and community-level biomass along elevational and land use gradients at Mt. Kilimanjaro, Tanzania. Chapter I provides background information on the response and predictor variables, study system, and the study design. First, I give an overview of the elevational patterns of species diversity/richness and herbivory published in the literature. The overview illuminates existing debates on elevational patterns of species diversity/richness and herbivory. In connection to these patterns, I also introduce several hypotheses and mechanisms put forward to explain macroecological patterns of species richness. Furthermore, I explain the main variables used to test hypotheses. Finally, I describe the study system and the study design used. Chapter II explores the patterns of invertebrate herbivory and their underlying drivers along extensive elevational and land use gradients on the southern slopes of Mt. Kilimanjaro. I recorded standing leaf herbivory from leaf chewers, leaf miners and gall-inducing insects on 55 study sites located in natural and anthropogenic habitats distributed from 866 to 3060 meters above sea level (m asl) on Mt. Kilimanjaro. Standing leaf herbivory was related to climatic variables [mean annual temperature - (MAT) and mean annual precipitation - (MAP)], net primary productivity (NPP) and plant functional traits (leaf traits) [specific leaf area (SLA), carbon to nitrogen ratio (CN), and nitrogen to phosphorous ratio (NP)]. Results revealed an unimodal pattern of total leaf herbivory along the elevation gradient in natural habitats. Findings also revealed differences in the levels and patterns of herbivory among feeding guilds and between anthropogenic and natural habitats. Changes in NP and CN ratios which were closely linked to NPP were the strongest predictors of leaf herbivory. Our study uncovers the role of leaf nutrient stoichiometry and its linkages to climate in explaining the variation in leaf herbivory along climatic gradients. Chapter III presents patterns and unravels direct and indirect effects of resource (food) abundance (NPP), resource (food) diversity [Functional Dispersion (FDis)], resource quality (SLA, NP, and CN rations), and climate variables (MAT and MAP) on species diversity of phytophagous beetles. Data were collected from 65 study sites located in natural and anthropogenic habitats distributed from 866 to 4550 m asl on the southern slopes of Mt. Kilimanjaro. Sweep net and beating methods were used to collect a total of 3,186 phytophagous beetles representing 21 families and 304 morphospecies. Two groups, weevils (Curculionidae) and leaf beetles (Chrysomelidae) were the largest and most diverse families represented with 898 and 1566 individuals, respectively. Results revealed complex (bimodal) and dissimilar patterns of Chao1-estimated species richness (hereafter referred to as species diversity) along elevation and land use gradients. Results from path analysis showed that temperature and climate-mediated changes in NPP had a significant positive direct and indirect effect on species diversity of phytophagous beetles, respectively. The results also revealed that the effect of NPP (via beetles abundance and diversity of food resources) on species diversity is stronger than that of temperature. Since we found that factors affecting species diversity were intimately linked to climate, I concluded that predicted climatic changes over the coming decades will likely alter the species diversity patterns which we observe today. Chapter IV presents patterns and unravels the direct and indirect effects of climate, NPP and anthropogenic disturbances on species richness and community-level biomass of wild large mammals which represent endothermic organisms and the most important group of vertebrate herbivores. Data were collected from 66 study sites located in natural and anthropogenic habitats distributed from 870 to 4550 m asl on the southern slopes of Mt. Kilimanjaro. Mammals were collected using camera traps and used path analysis to disentangle the direct and indirect effects of climatic variables, NPP, land use, land area, levels of habitat protection and occurrence of domesticated mammals on the patterns of richness and community-level biomass of wild mammals, respectively. Results showed unimodal patterns for species richness and community-level biomass of wild mammals along elevation gradients and that the patterns differed depending on the type of feeding guild. Findings from path analysis showed that net primary productivity and levels of habitat protection had a strong direct effect on species richness and community-level biomass of wild mammals whereas temperature had an insignificant direct effect. Findings show the importance of climate-mediated food resources in determining patterns of species richness of large mammals. While temperature is among key predictors of species richness in several ectotherms, its direct influence in determining species richness of wild mammals was insignificant. Findings show the sensitivity of wild mammals to anthropogenic influences and underscore the importance of protected areas in conserving biodiversity. In conclusion, despite a multitude of data sets on species diversity and ecosystem functions along broad climatic gradients, there is little mechanistic understanding of the underlying causes. Findings obtained in the three studies illustrate their contribution to the scientific debates on the mechanisms underlying patterns of herbivory and diversity along elevation gradients. Results present strong evidence that plant functional traits play a key role in determining invertebrate herbivory and species diversity along elevation gradients and that, their strong interdependence with climate and anthropogenic activities will shape these patterns in future. Additionally, findings from path analysis demonstrated that herbivore diversity, community-level biomass, and herbivory are strongly influenced by climate (either directly or indirectly). Therefore, the predicted climatic changes are expected to dictate ecological patterns, biotic interactions, and energy and nutrient fluxes in terrestrial ecosystems in the coming decades with stronger impacts probably occurring in natural ecosystems. Furthermore, findings demonstrated the significance of land use effects in shaping ecological patterns. As anthropogenic pressure is advancing towards more pristine higher elevations, I advocate conservation measures which are responsive to and incorporate human dimensions to curb the situation. Although our findings emanate from observational studies which have to take several confounding factors into account, we have managed to demonstrate global change responses in real ecosystems and fully established organisms with a wide range of interactions which are unlikely to be captured in artificial experiments. Nonetheless, I recommend additional experimental studies addressing the effect of top-down control by natural enemies on herbivore diversity and invertebrate herbivory in order to deepen our understanding of the mechanisms driving macroecological patterns along elevation gradients.  }, subject = {Species richness}, language = {en} }