Disentangling the drivers of deer diet composition in subtropical Nepal: the role of plant apparency and nutritional quality among growth forms and vegetation types

Résumé fourni par la source

Being medium-sized mammals, deer species (Cervidae) are expected to feed on relatively nutritious plant species. Variation in plant apparency (i.e., relative cover), plant growth form and vegetation type may further influence deer foraging behaviour. However, it is still poorly known how these drivers of herbivory rank in importance. Therefore, based on a conceptual framework integrating plant apparency and leaf traits, we addressed the following questions: a) how does deer herbivory relate to plant apparency, growth forms, and vegetation types? b) How does plant nutritional quality relate to deer herbivory at a given apparency? We investigated these questions in lowland Nepal, a critical habitat for the conservation of tigers and their main prey (deer), during the cool dry winter season, in contrasting vegetation types (grassland, riverine forest, mixed forest, and sal forest). We showed that while deer fed on a diverse array of plants, the probability of herbivory related positively with species apparency irrespective of growth form or vegetation type. In contrast with our expectations, we showed that the probability of herbivory increased with higher leaf structural defences and lower nutritional quality, but tannin content showed no relationship with the probability of herbivory. Specifically, relatively abundant grasses, with high fibre and lignin but low nutrient content, were eaten preferentially, across all vegetation types, even when accounting for apparency. However, this preference may be driven by lower predation risk during grassland management. Additionally, plant litter from the canopy (senesced or fresh) formed a substantial input to the deer’s diet that is not commonly accounted for in feeding behavioural research. Contrary to general belief, our findings also showed that forests generally serve as a paramount food reservoir for South Asian deer in addition to grassland, with implications for vegetation management policies.

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