Estimating Mineral Requirements of Wild Herbivores: Modelling Arctic Caribou (Rangifer tarandus granti) in Summer

Abstract

Mineral requirements are poorly described for most wildlife. Consequently, the role of forage minerals in movement and productivity are poorly understood for sedentary and migratory ungulates, such as reindeer and caribou (Rangifer tarandus). We applied estimates of maintenance, lactation, body mass change, and antler growth to production curves (body mass, daily intake, and milk yield) for female caribou to calculate their mineral requirements over summer. The total requirements (mg or g·d^-1) were divided by the daily intake (kg·d^-1) to estimate the minimum concentration of minerals required in the diet (mg or g·kg^-1) to balance demand. The daily requirements (mg·d^-1) of all minerals increased from parturition to the end of summer. The minimum dietary concentrations (mg·kg^-1) of macro-minerals (Ca, P, Mg, Na, K) declined as food intake (kg·d^-1) increased over summer. The minimum dietary concentrations (Fe, Mn, Cu, Zn) were heavily influenced by body mass gain, which increased through late lactation even though food intakes rose. Our modeling framework can be applied to other wild ungulates to assess the impacts of changing forage phenology, plant community compositions, or environmental disturbances on movement and productivity.

Keywords: factorial model; nutritional ecology; production; reproduction; ungulate.

Figure 1

Flow diagram for estimating the mineral requirements and the minimum dietary concentrations for lactating female caribou in three stages: daily attributes of caribou; specific requirements; and projected daily requirements for minerals.

Figure 2

Model inputs for estimating requirements of female caribou from parturition through 120 days of lactation. Body mass (kg), milk yields (kg·d⁻¹), temperature (°C), and dry matter intake (kg·d⁻¹) were derived from measures of captive caribou in interior Alaska.

Figure 3

Minimum dietary concentration (dry matter basis) of Ca, P, and Mg calculated for lactating caribou with factorial relationships for domestic ungulates. S = sheep model projection, G = goat model projection, D = dairy cattle model projection, C = beef cattle model projection, H = horse model projection. Solid lines represent the regression of all species projections used for each element.

Figure 4

Minimum dietary concentration (dry matter basis) of Na and K calculated for lactating caribou with factorial relationships for domestic ungulates. S = sheep model projection, G = goat model projection, D = dairy cattle model projection, H = horse model projection. Solid line represents the regression of species projections used for each element.

Figure 5

Minimum dietary concentration (dry matter basis) of Fe, Mn, Cu, and Zn calculated for lactating caribou with factorial relationships for domestic ungulates. S = sheep model projection, G = goat model projection, D = dairy cattle model projection, H = horse model projection. Solid line represents the regression of species projections used for each element.