Moose selection for resource stoichiometry

Herbivores consider the variation of forage qualities (nutritional content
and digestibility) as well as quantities (biomass) when foraging. Such
selection patterns may change based on the scale of foraging, particularly
in the case of ungulates that forage at many scales. To test selection for
quality and quantity in free-ranging herbivores across scales, however, we
must first develop landscape-wide quantitative estimates of both forage
quantity and quality. Stoichiometric distribution models (StDMs) bring
opportunity to address this because they predict the elemental measures
and stoichiometry of resources at landscape extents. Here, we use StDMs to
predict elemental measures of understory white birch quality (% nitrogen)
and quantity (g carbon/m2) across two boreal landscapes. We analyzed GPS
collared moose (n = 14) selection for forage quantity and quality at the
landscape, home range, and patch extents using both individual and pooled
resource selection analyses. We predicted that as the scale of resource
selection decreased from the landscape to the patch, selection for white
birch quantity would decrease and selection for quality would increase.
Counter to our prediction, pooled-models showed selection for our
estimates of quantity and quality to be neutral with low explanatory power
and no scalar trends. At the individual-level, however, we found evidence
for quality and quantity trade-offs, most notably at the home range scale
where resource selection models explain the largest amount of variation in
selection. Furthermore, individuals did not follow the same trade-off
tactic, with some preferring forage quantity over quality and vice-versa.
Such individual trade-offs show that moose may be flexible in attaining a
limiting nutrient. Our findings suggest that herbivores may respond to
forage elemental compositions and quantities, giving tools like StDMs
merit towards animal ecology applications. The integration of StDMs and
animal movement data represents a promising avenue for progress in the
field of zoogeochemistry.