The coexistence of different species of large herbivores (ungulates) in grasslands and savannas has fascinated ecologists for decades. However, changes in climate, land‐use and trophic structure of ecosystems increasingly jeopardise the persistence of such diverse assemblages. Body size has been used successfully to explain ungulate niche differentiation with regard to food requirements and predation sensitivity. But this single trait axis insufficiently captures interspecific differences in water requirements and thermoregulatory capacity and thus sensitivity to climate change. Here, we develop a two‐dimensional trait space of body size and minimum dung moisture content that characterises the combined food and water requirements of large herbivores. From this, we predict that increased spatial homogeneity in water availability in drylands reduces the number of ungulate species that will coexist. But we also predict that extreme droughts will cause the larger, water‐dependent grazers as wildebeest, zebra and buffalo–dominant species in savanna ecosystems – to be replaced by smaller, less water‐dependent species. Subsequently, we explore how other constraints such as predation risk and thermoregulation are connected to this two‐dimensional framework. Our novel framework integrates multiple simultaneous stressors for herbivores and yields an extensive set of testable hypotheses about the expected changes in large herbivore community composition following climate change.

Citation: Kihwele, E. S., V. Mchomvu, N. Owen-Smith, R. S. Hetem, M. C. Hutchinson, A. B. Potter, H. Olff, and M. P. Veldhuis. 2020. Quantifying water requirements of African ungulates through a combination of functional traits. Ecological Monographs 90(2):Abstract. Climate and land use change modify surface water availability in African savannas. Surface water is a key resource for both wildlife and livestock and its spatial and temporal distribution is important for understanding the composition of large herbivore assemblages in savannas. Yet, the extent to which ungulate species differ in their water requirements remains poorly quantified. Here, we infer the water requirements of 48 African ungulates by combining six different functional traits related to physiological adaptations to reduce water loss, namely minimum dung moisture, relative dung pellet size, relative surface area of the distal colon, urine osmolality, relative medullary thickness, and evaporation rate. In addition, we investigated how these differences in water requirements relate to differences in dietary water intake. We observed strong correlations between traits related to water loss through dung, urine and evaporation, suggesting that ungulates minimize water loss through multiple pathways simultaneously, which suggests that each trait can thus be used independently to predict water requirements. Furthermore, we found that browsers and grazers had similar water requirements, but browsers are expected to be less dependent on surface water because they acquire more water through their diet. We conclude that these key functional traits are a useful way to determine differences in water requirements and an important tool for predicting changes in herbivore community assembly resulting from changes in surface water availability.

A study on seasonal variations in the abundance of Lesser Flamingo (Phoenicopterus minor) in relation to phytoplankton abundance in lake Manyara was conducted for a period of fourteen consecutive months (July 2007 to August 2008). The aim was to relate the temporal variability in the phytoplankton species abundance and diversity of the lake to the population size of the Lesser Flamingo. Lesser Flamingo population numbers were obtained from monthly ground surveys whereby the lake was subdivided into defined counting vantage points. Water samples for phytoplankton species composition and biomass analyses were taken to the University of Dar es Salaam for laboratory analysis. The flamingo population estimates ranged from 9319 in August 2007 to 640,850 in August 2008. The Lesser Flamingo populations showed that temporal fluctuations were related to the changes in the abundance and diversity of phytoplankton species. The occurrence of Arthrospira associated with the increase in the abundance of Lesser Flamingo. It was observed that changes in the Lesser Flamingo numbers were influenced by the changes in the abundance and availability of their preferred food. The results indicated that microalgae assemblage positively correlated with ammonium and nitrate which were also related to the abundance of lesser flamingo. The phytoplankton community was dominated by cyanobacteria particularly Arthrosipira fusiformis likely due to the high lake salinity and pH that limited the growth of other microalgae. Correlation analysis showed strong correlation between the Lesser Flamingo abundance with the concentration of nitrate and ammonium and between the number of Lesser Flamingo and the cyanobacterium Arthrospira.