Plant protein and secondary metabolites influence diet selection in a mammalian specialist herbivore

Abstract

For herbivores, nutrient intake is limited by the relatively low nutritional quality of plants and high concentrations of potentially toxic defensive compounds (plant secondary metabolites, PSMs) produced by many plants. In response to phytochemical challenges, some herbivores selectively forage on plants with higher nutrient and lower PSM concentrations relative to other plants. Pygmy rabbits (Brachylagus idahoensis) are dietary specialists that feed on sagebrush (Artemisia spp.) and forage on specific plants more than others within a foraging patch. We predicted that the plants with evidence of heavy foraging (browsed plants) would be of higher dietary quality than plants that were not browsed (unbrowsed). We used model selection to determine which phytochemical variables best explained the difference between browsed and unbrowsed plants. Higher crude protein increased the odds that plants would be browsed by pygmy rabbits and the opposite was the case for certain PSMs. Additionally, because pygmy rabbits can occupy foraging patches (burrows) for consecutive years, their browsing may influence the nutritional and PSM constituents of plants at the burrows. In a post hoc analysis, we did not find a significant relationship between phytochemical concentrations, browse status and burrow occupancy length. We concluded that pygmy rabbits use nutritional and chemical cues while making foraging decisions.

Keywords: foraging; monoterpenes; nutrition; pygmy rabbit; sagebrush.

Fig. 1

A) Average crude protein (%, ± SE) and B) artemiseole (µg/g dry weight, ± SE) between browsed (closed circles) and unbrowsed plants (open circle) on burrows that have been occupied by pygmy rabbits for short (1–2 years) and long (6–7 years) amounts of time in October 2009 at the Leadore site in Idaho. Crude protein (%) for short occupancy, browsed: 13.22 ± 0.41; short occupancy, unbrowsed: 12.71 ± 0.29; long occupancy, browsed: 13.66 ± 0.33; long occupancy, unbrowsed: 12.32 ± 0.31. Artemiseole (µg/g dry weight) for short occupancy, browsed: 5444.77 ± 550; short occupancy, unbrowsed: 6502.81 ± 537; long occupancy, browsed: 544 6441.15 ± 481; long occupancy, unbrowsed: 7796.31 ± 658.