Poor soils and density-mediated body weight in deer: forage quality or quantity?

摘要

Cervid studies have demonstrated body weight and lactation may be limited in areas with poor-quality soils, with the underlying mechanism often attributed to poor forage quality resulting from poor soil quality. However, if highly nutritious foods are produced but in limited quantities, selective foraging may alleviate nutritional stressors associated with poor soil productivity when adequate quantities of high-quality forage are obtained. We tested whether poor soil productivity limits forage from being high quality or conversely limits the abundance of high-quality forages. To do so, we determined whether nutrient concentrations in selected and non-selected forages on our poor soil study site met the nutritional requirements of lactating white-tailed deer Odocoileus virginianus assuming adequate amounts of forage are obtained. Also, we compared body weight of yearling males at a high density (13–17 deer km-2) and low density (3–5 deer km-2), because previous studies concluded soils on the study site were too poor for morphometrics (e.g. body weight) to be density-mediated. Deer selected plant species from each of five forage classes that would meet their nutritional requirements (i.e. assuming adequate forage intake) but also selected for different nutrients across forage classes. Phosphorus was limited in most forages, but deer selected forages that met P-requirements 10 times more than expected. We demonstrated body weight was 7.3% greater when deer density was low than high. Contrary to previous reports from poor productivity soil regions, deer on our study site should be able to meet lactation requirements when the quantity of high-quality forage is not limiting, and similarly body weight should be density-mediated. Hence, management strategies that alter the amount of forage per animal (i.e. decreasing animal density and/or increasing forage abundance) are viable options to promote desirable ungulate morphometrics in poor soil regions.