Testing 'Proportion of Females Calving' as an indicator for population-level reproductive performance for black rhinoceros ( Diceros bicornis )

• Published in: PeerJ (San Francisco, CA) Vol. 6; p. e5430
• Main Authors: Law, Peter R, Fike, Brad
• Format: Journal Article
• Language: English
• Published: United States PeerJ, Inc 15.08.2018; PeerJ Inc
• Subjects: Age; Annual variations; Black rhinoceros; Conservation Biology; Data processing; Demography; Diceros bicornis; Ecology; Feedback; Herbivores; Megaherbivores; Population; Population Biology; Population reproductive performance; Population studies; Rainfall; Stochasticity; Studies; Time series; Ungulates; Variation; Wildlife conservation; Zoology; South Africa; Population reproductive performance; Megaherbivores; Black rhinoceros
• ISSN: 2167-8359; 2167-8359
• DOI: 10.7717/peerj.5430

The proportion of females calving (PFC) each year has been employed as an indicator of population reproductive performance in ungulates, especially for species that breed annually, because it requires less detailed population data than inter-birthing intervals and age at first reproduction. For asynchronous breeders with inter-birthing intervals longer than a year such as megaherbivores, however, it is unclear how much annual variation in PFC is expected and whether false signals of density feedback or environmental influence might result from analyzing PFC data. We used census data from a well studied, closed, expanding population of black rhinoceros ( ) to study annual variation in PFC over 22 years. Our analysis of PFC data yielded no false signals of density feedback but weak evidence for an unexpected influence of rainfall. The PFC data exhibited considerable variation, which we attribute to autocorrelation in the time series of PFC data, 'demographic-founding effects', changes in stage structure, and demographic stochasticity, some of which the modelling of PFC appears to confuse with an influence of rainfall. We expect such variation to be common in introduced populations and to persist for some years, complicating the interpretation of PFC, though moving averages of PFC can help if employed cautiously. While our analysis does not undermine the possible utility of PFC, the analysis and interpretation of PFC values require care.