Little and Large Herbivores as Indicators of Trophic Transfer: Do Trace Nutrients Drive Populations?
Abstract
Trace minerals, such as copper, iron, and zinc, are essential for reproduction, growth, and immunity of mammalian herbivores and the growth of their populations. I examined the relationship between supplies of essential minerals on the landscape and hepatic stores of those minerals in two wild herbivores to assess the effects of weather, soils, plants, animal attributes (i.e., sex), and population processes (i.e., density) on the transfer of trace minerals from soils to the animal. Soils, grasses, woody browse, hispid cotton rats (Sigmodon hispidus), and whitetailed deer (Odocoileus virginianus) were sampled across 19 study sites. Liver copper was < 5 µg/g at 13 % of sites for rats and < 20 µg/g at 58 % of sites for deer, which indicated regional limitations for copper in herbivore populations. Leaves of woody browse were higher in copper, lower in iron, and similar in zinc when compared with grasses. Available mineral concentrations of soils were positively related to liver copper and zinc in rats, which was consistent with the short lives and high productivity of these small granivores that rely on grasses. Significant interactions between soil concentrations and plant growing conditions (i.e., summer precipitation and temperature) affected liver iron and zinc in deer, which reflected the greater complexity of trophic transfers in large, long-lived, browsing herbivores. Population density affected liver concentrations of copper, iron, and zinc in both rats and deer.
Values for δC13 in heart muscle indicated a shift in diet with increasing density for deer but not for rats. My data indicate that supplies of essential trace minerals contribute to density dependence of herbivore populations. Local population density may therefore influence the prevalence of deficiency states and disease outbreak that exacerbate population cycles in wild mammalian herbivore populations.
Subject
copperdensity dependence
iron
mineral
Odocoileus virginianus
Sigmodon hispidus
trophic
zinc
Citation
Hollingsworth, Kaylee Ann (2019). Little and Large Herbivores as Indicators of Trophic Transfer: Do Trace Nutrients Drive Populations?. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /189057.