Hippopotamus (H. amphibius) diet change indicates herbaceous plant encroachment following megaherbivore population collapse.

Megaherbivores (>1000 kg) are critical for ecosystem health and function, but face population collapse and extinction globally. The future of these megaherbivore-impoverished ecosystems is difficult to predict, though many studies have demonstrated increasing representation of C3 woody plants. These studies rely on direct observational data, however, and tools for assessing decadal-scale changes in African ecology without observation are lacking. We use isotopic records of historical common hippopotamus (Hippopotamus amphibius) canines to quantify herbaceous vegetation change in Queen Elizabeth National Park, Uganda following a period of civil unrest and poaching. This poaching event led to population collapse of two threatened African megaherbivore species: hippopotamus and African elephants (Loxodonta africana). Serial carbon isotope ratios (δ(13)C) in canine enamel from individuals that lived between 1960-2000 indicated substantial increases in C3 herbaceous plants in their diet (<20% C3 in the 1960s to 30-45% C3 in the 80s and 90s), supported by other observational and ecological data. These data indicate megaherbivore loss results in succession of both woody and herbaceous C3 vegetation and further reaching effects, such as decreased grazing capacity and herbivore biodiversity in the area. Given multiple lines of evidence, these individuals appear to accurately capture herbaceous vegetation change in Mweya.

Energy costs of reproduction in the djungarian hamster Phodopus sungorus under laboratory and seminatural conditions.

The aim of this study was to obtain ecologically relevant data on the rates and efficiencies of energy allocation to reproduction and to determine how laboratory data compare with data obtained under 'seminatural' conditions. Using the tritiated water (HTO) method we measured average daily metabolic rates (ADMRs) in Phodopus sungorus reproducing females over the whole period of pregnancy and lactation and in nonreproducing ones, under both laboratory and 'seminatural' conditions.Taking the difference in total energy expenditure between reproducing and nonreproducing females as the additional energy requirement for reproduction, it was found that the absolute energy expenditure for reproduction was independent of the experimental conditions used. For the production and nursing of one litter, Djungarian hamsters metabolized an additional 20.9 MJ kg-1 in the laboratory, i.e. a 37% increase over normal maintenance expenditure, and 22.6 MJ kg-1 under seminatural conditions, i.e. a 24% increase. The efficiency of litter production was estimated as 18.3% in the laboratory and as 16.4% under seminatural conditions. The differences between the two experimental conditions were not significant.