Seasonal consumption of Thamnochortus spicigerus (Restionaceae) by eland is associated with plant sex and nutrient status

Abstract

Historic distributions of large herbivores in the Fynbos Biome remain poorly described and, despite ongoing reintroductions, their dietary strategies and forage selection in the Fynbos Biome are understudied. We monitored an introduction of eland into Cape Flats Dune Strandveld vegetation, focusing on their impact on Thamnochortus spicigerus (Restionaceae), a dominant strandveld plant species. Over 3 years, eland feeding behaviour was recorded, and data were collected on plant height and inflorescence presence in both male and female T. spicigerus individuals, with and without exposure to eland herbivory. Samples of both restio sexes were collected for laboratory analyses to determine protein, moisture, fibre and dry matter contents during autumn and spring. Eland mostly fed on T. spicigerus in autumn, with very low feeding incidences during the remainder of the year. Browsing damage was strongly male-biased, with female plants showing little to no signs of herbivory. In autumn, plants tended to have lower contents of protein, fibre and dry matter, but higher moisture content than in spring. These effects were more pronounced for male plants than for female plants in autumn, providing a potential reason for male-biased feeding. This study demonstrates how sex-specific and seasonal variation in plant traits can shape herbivore foraging. We concluded that nutrient variation across seasons differs between T. spicigerus sexes and may influence eland foraging strategies. Furthermore, it raises the possibility that herbivore presence within the Fynbos Biome may have been influenced by seasonal changes in the palatability of plant species, an area for future research.