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Rationale: Stable isotope analysis (SIA) of whiskers has been used to identify temporal feeding habits, intra-population diet variation, as well as individual dietary specialisation of marine and terrestrial carnivores. However, the potential of the method to disclose such dietary information for large wild felids is hampered by lack of information on species-specific whisker growth rates, whisker growth patterns and whisker-diet trophic discrimination factors (TDFs). Methods: Whisker growth rates and growth patterns were measured for four lions (Panthera leo) and one leopard (Panthera pardus) held at the National Zoological Gardens, Pretoria, South Africa. Actively growing whiskers of the felids were 'marked' four times over 185 days using 13 C-depleted, C3 -based giraffe (Giraffa camelopardalis) meat. The periods with low δ13 C values, identified following serial sectioning of the regrown whiskers at 1 mm intervals and isotopic analysis, were then correlated to specific giraffe meat feeding bouts and hence growth periods. δ13 C and δ15 N whisker-diet TDFs were estimated for five lions whose diet remained consistent over multiple years. Results: The whisker growth rates of three lionesses and the leopard were similar (mean = 0.65 mm day-1 ), despite species, sex and age differences. There was a decrease in whisker growth rate over time, suggesting a non-linear whisker growth pattern. However, linear and non-linear growth simulations showed slight differences between the two growth patterns for the proximal ~50 mm of whiskers. δ13 C and 15 N lion whisker-diet TDFs were also similar amongst individuals (mean = 2.7 ± 0.12 ‰ for δ13 C values and 2.5 ± 0.08 ‰ for δ15 N values), irrespective of age and sex. Conclusions: The whisker growth rate and δ13 C and δ15 N lion whisker-diet TDFs obtained in this study can be applied in future studies to assign dietary information contained in analysed felid whiskers to the correct time period and improve deductions of prey species consumed by wild felids. [ABSTRACT FROM AUTHOR]

Nile crocodiles undergo a three to five order of magnitude increase in body size during their lifespan. This shift coincides with a change in resource and habitat use which influences the strength, type and symmetry of interactions with other species. Identifying size-specific crocodile groups displaying similar traits is important for conservation planning. Here, we illustrate how stable carbon (δ13 C) and nitrogen (δ15 N) isotope analysis of scute keratin, together with breakpoint modelling analysis can be used to characterise ontogenetic niche shifts. Using a sample set of 238 crocodiles from the Okavango Delta, Botswana (35–463 cm total length), we found prominent size-related changes in the scute keratin δ13 C and δ15 N profiles close to 40 and 119 cm snout-vent length. The first shift corroborated the findings of a traditional stomach-content study conducted on the same population at the same time, and the second conformed to known crocodile ecology. This approach can be used as a first approximation to identify size-specific groups within crocodile populations, and these can then be investigated further using isotopic or other methods. [ABSTRACT FROM AUTHOR]

1. A long-term (13-year) data set, based on > 4000 kills, was used to test whether a sympatric group of large predators adheres to the theoretical predictions that (1) mean prey body size and (2) prey diversity increase as functions of predator body size. 2. All kills observed by safari guides are documented routinely in Mala Mala Private Game Reserve, South Africa. We analysed these records for lion (Panthera leo, Linnaeus), leopard (Panthera pardus, Linnaeus), cheetah (Acinonyx jubatus, Schreber) and African wild dog (Lycaonpictus, Temminck). Males and females of the sexually dimorphic felid species were treated as functionally distinct predator types. Prey types were classified by species, sex and age class. 3. Prey profiles were compared among predator types in terms of richness and evenness to consider how both the range of prey types used and the dominance of particular prey types within each range may be influenced by predator size. No significant size-dependent relationships were found, so factors separate from or additional to body size must explain variation in prey diversity across sympatric predators. 4. A statistically strong relationship was found between mean prey mass and predator mass (r² = 0.86, P = 0.002), although pairwise comparisons showed that most predators killed similar prey despite wide differences in predator size. Also, minimum prey mass was independent of predator mass while maximum prey mass was strongly dependent on predator mass (r² = 0.71, P = 0.017). The ecological significance is that larger predators do not specialize on larger prey, but exploit a wider range of prey sizes. [ABSTRACT FROM AUTHOR]