Assessment of Dietary Composition and Forage Selection in Black Rhinoceros (Diceros bicornis) Across Greening Onset Using Faecal Metabarcoding: Implications for Carrying Capacity Assessment and Adaptive Management
Author
Husted, Niels Søborg
Term
4. term
Education
Publication year
2026
Submitted on
2026-05-31
Abstract
This thesis investigates how the critically endangered black rhinoceros (Diceros bicornis) uses forage resources across a seasonal transition from dry to green conditions (greening onset) in Olifants West Nature Reserve, South Africa. Using faecal environmental DNA (eDNA) metabarcoding, the study reconstructed diet composition at genus and species level and integrated these data with vegetation availability obtained from field-based plant surveys and remotely sensed landscape productivity measured by the Normalised Difference Vegetation Index (NDVI). Molecular sex determination was also attempted to explore potential sex-specific dietary partitioning. The results revealed a pronounced shift in diet composition after greening onset that was strongly associated with increasing NDVI, while overall dietary richness remained stable. This indicates a replacement of forage items rather than a broadening of dietary niche, with graminoids becoming a major component of the post-greening diet. Forage use was not proportional to plant availability: several dominant plant genera in the environment were underutilised, whereas less abundant genera were actively selected, suggesting selective feeding based on forage quality and preferred vegetation traits. Exploratory clustering analyses further suggested possible dietary partitioning among individuals during the resource-limited pre-greening phase, although sex determination could not be robustly validated to confirm sex-specific patterns. Overall, the study demonstrates that faecal eDNA metabarcoding offers a high-resolution tool for quantifying seasonal dietary dynamics and forage selection in managed black rhinoceros populations, thereby improving the assessment of habitat carrying capacity and supporting adaptive conservation management in fenced and semi-fenced reserves.
Denne afhandling undersøger, hvordan den truede sorte næsehornsart (Diceros bicornis) udnytter føderessourcer over en sæsonovergang, hvor vegetationen skifter fra tør til grøn (greening onset), i Olifants West Nature Reserve i Sydafrika. Med udgangspunkt i DNA-metabarcoding af fækalier blev næsehornenes kost sammensat på arts- og slægtsniveau og sammenholdt med data om planteforekomst fra vegetationsoptællinger samt fjernmålt landskabsproduktivitet baseret på Normalised Difference Vegetation Index (NDVI). Derudover blev molekylær kønsbestemmelse forsøgt inddraget for at afdække mulig kønsspecifik ressourceopdeling. Resultaterne viste et markant skift i diætsammensætning efter greening onset, tæt knyttet til stigende NDVI, mens det samlede antal fødearter i kosten forblev stabilt. Dette peger på en udskiftning af fødeemner frem for en egentlig udvidelse af diætens bredde, hvor især græsser fik en langt større betydning i den grønne periode. Næsehornene udnyttede heller ikke vegetationen proportionalt med dens forekomst: flere dominerende plante-slægter blev underudnyttet, mens mindre udbredte slægter blev aktivt valgt, hvilket tyder på selektion baseret på fødekvalitet og præfererede plantestrukturer. Eksplorative klyngeanalyser indikerede desuden mulig diætisk opdeling mellem individer i den ressourcebegrænsede tørre fase, men kønsbestemmelsen kunne ikke valideres tilstrækkeligt til klare konklusioner. Samlet demonstrerer studiet, at fækal eDNA-metabarcoding kan anvendes som et højopløseligt redskab til at beskrive sæsonmæssig diætdynamik og fødevalg hos sorte næsehorn og derved styrke vurderingen af habitatets bæreevne og grundlaget for adaptiv forvaltningspraksis i indhegnede eller semifræhegnede bestande.
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