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

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.

Multiple nutritional currencies shape pregnancy in a large herbivore

Nutritional condition embodies environmental conditions experienced by animals with survival and reproductive consequences. Body fat is often associated with ungulate fecundity; however, other nutritional currencies may limit fecundity. Using data from 129 moose (Alces alces (Linnaeus, 1758)) monitored over 429 moose-years, we examined the limiting role of multiple nutritional currencies on pregnancy rates while concurrently assessing the influence of age and prior reproduction. Females tended to be pregnant in successive years, suggesting differences in individual or habitat quality. However, probability of pregnancy declined with survival of calves from prior litters, indicating a reproductive cost to rearing offspring. Pregnancy was positively associated with serum iron (Fe), body fat, body mass, and serum protein. The best model predicting pregnancy included serum Fe, body fat, and age class, with serum Fe being the strongest single predictor. Moose with Fe concentrations considered deficient in cattle (Bos taurus Linnaeus, 1758) had pregnancy rates of 33%–35%, whereas 89%–91% of individuals with sufficient Fe were pregnant. We subsequently evaluated hypotheses concerning factors potentially limiting Fe concentrations, including Fe-deficient diet, chronic infection, parasitism, and malnutrition. The best supported hypothesis was energy and protein malnutrition constrained Fe stores. We conclude that subclinical anemia due to nutritional constraints can limit or indicate limits in moose fecundity.

Seasonality of honey bee (Apis mellifera) micronutrient supplementation and environmental limitation

Honey bees (Apis mellifera) obtain micronutrients from floral resources and "dirty", or turbid, water. Past research suggests that honey bees drink dirty water to supplement the micronutrients in their floral diet, however, there is no research that directly investigates how floral micronutrient content varies with water preferences, or how micronutrients in honey bees themselves vary seasonally. In this study, we used chemical analyses (ICP-OES) to investigate seasonal variation of micronutrients in honey bee workers and floral resources in the field. We found that honey bees likely use mineralized water to supplement their floral diet and may be limited by availability of calcium and potassium. Our results also suggest that honey bees may seasonally seek specific micronutrients, perhaps in preparation for overwintering.