Mineral constraints on arctic caribou (Rangifer tarandus): a spatial and phenological perspective

Abstract

Abstract. Arctic caribou (Rangifer tarandus) have the longest terrestrial migration of any ungulate but little is known about the spatial and seasonal variation of minerals in summer forages and the potential impacts of mineral nutrition on the foraging behavior and nutritional condition of arctic caribou. We investigated the phenology, availability, and mechanistic relationships of calcium, phosphorus, magnesium, sodium, potassium, iron, manganese, copper, and zinc in three species of woody browse, three species of graminoids, and one forb preferred by caribou over two transects bisecting the ranges of the Central Arctic (CAH) and Western Arctic (WAH) caribou herds in Alaska. Transects traversed three ecoregions (Coastal Plain, Arctic Foothills and Brooks Range) along known migration paths in the summer ranges of both herds. Concentrations of mineral in forages were compared to estimated dietary requirements of lactating female caribou. Spatial distribution of the abundance of minerals in caribou forage was associated with interactions of soil pH and mineral content, while temporal variation was related to plant maturity, and thus nitrogen and fiber content of forages. Concentrations of sodium were below caribou requirements in all forage species for most of the summer and adequate only on the Coastal Plain during the second half of summer. Phosphorus declined in plants from emergence to senescence and was below requirements in all forages by mid-summer, while concentrations of copper declined to marginal concentrations at plant senescence. Interactions of sodium with potassium, calcium with phosphorus, and copper with zinc in forages likely exacerbate the constraints of low concentrations sodium, phosphorus, and copper. Forages on the WAH contained significantly more phosphorus and copper than forages collected on the CAH transect. We suspect that migrations of caribou to the Arctic Coastal Plain may allow parturient females to replenish sodium stores depleted by foraging inland through the long arctic winters, while also extending the availability of adequate phosphorus, if animals are able to selectively track emerging waves of forage.

Trace mineral supplies for populations of little and large herbivores

“…Juknevičius and Sabienė [ 79 ] had similar results for agricultural plants, indicating that mineral content varied with plant species and Family. Oster et al [ 10 ] demonstrated that even the same species of plant contained different concentrations of minerals over the course of the growing season, depending on location. This demonstrates the complexity of trophic transfer of nutrients beginning at the soil-plant interface within the rhizosphere, which is further complicated by differences among species and the functional responses of the animal to plant growth.…”

“…Assessing trace minerals in the body of herbivores can be done for the short-term (weeks) by examining plasma samples, or for the long-term (months or years) with liver and bone samples [ 8 , 9 ]. Liver mineral concentrations indicate dietary supplies, as well as the rate of use of liver stores, over a season, which captures the changes in trace mineral concentrations of individual plant species over the growing season [ 10 ]. Liver mineral concentrations may not indicate forage selection of herbivores but ratios of the stable isotopes of carbon (δ 13 C: δ 12 C) and nitrogen (δ 15 N: δ 14 N) can track forage selection in animals [ 11 ].…”

Causes and short‐term consequences of variation in milk composition in wild sheep

“…What generated these biological associations is unknown, but all these markers were also repeatable among mothers. Temporal variation in nutrient availability partly explains associations among minerals, and between mass gain and minerals found in the forage of migrating caribou (Oster, Barboza, Gustine, Joly, & Shively, 2018). For instance, P and K are associated with photosynthetic parts and decline as plants senesce, while Ca, Fe and Zn are tied to structural components and may increase in concentration with plant senescence (Oster et al, 2018).…”

“…Temporal variation in nutrient availability partly explains associations among minerals, and between mass gain and minerals found in the forage of migrating caribou (Oster, Barboza, Gustine, Joly, & Shively, 2018). For instance, P and K are associated with photosynthetic parts and decline as plants senesce, while Ca, Fe and Zn are tied to structural components and may increase in concentration with plant senescence (Oster et al, 2018). Individuals would integrate, through changes in body mass and composition, temporal variation in nutrient content; associations between milk nutrients could similarly be explained, but perhaps only the most stable macro-or micronutrients would show associations at the individual level.…”

Evaluating the use of hair as a non-invasive indicator of trace mineral status in woodland caribou (Rangifer tarandus caribou)

“…Similar effects of mineral imbalances are assumed to occur in wild ungulates and, additionally, imbalances in trace minerals may contribute to population declines [ 1 , 7 , 8 ]. Constraints on dietary trace mineral access by caribou may even influence migration patterns, reproductive success, and calf survival [ 9 ]. Excessive amounts of some trace minerals, as well as heavy metals such as cadmium and lead, are toxic in domestic and wild ungulates, and can cause clinical disease, reduced immune function, and even impaired fecundity and population productivity [ 3 , 5 , 10 ].…”