Linking landscape‐scale differences in forage to ungulate nutritional ecology

Abstract

Understanding how habitat and nutritional condition affect ungulate populations is necessary for informing management, particularly in areas experiencing carnivore recovery and declining ungulate population trends. Variations in forage species availability, plant phenological stage, and the abundance of forage make it challenging to understand landscape-level effects of nutrition on ungulates. We developed an integrated spatial modeling approach to estimate landscape-level elk (Cervus elaphus) nutritional resources in two adjacent study areas that differed in coarse measures of habitat quality and related the consequences of differences in nutritional resources to elk body condition and pregnancy rates. We found no support for differences in dry matter digestibility between plant samples or in phenological stage based on ground sampling plots in the two study areas. Our index of nutritional resources, measured as digestible forage biomass, varied among land cover types and between study areas. We found that altered plant composition following fires was the biggest driver of differences in nutritional resources, suggesting that maintaining a mosaic of fire history and distribution will likely benefit ungulate populations. Study area, lactation status, and year affected fall body fat of adult female elk. Elk in the study area exposed to lower summer range nutritional resources had lower nutritional condition entering winter. These differences in nutritional condition resulted in differences in pregnancy rate, with average pregnancy rates of 89% for elk exposed to higher nutritional resources and 72% for elk exposed to lower nutritional resources. Summer range nutritional resources have the potential to limit elk pregnancy rate and calf production, and these nutritional limitations may predispose elk to be more sensitive to the effects of harvest or predation. Wildlife managers should identify ungulate populations that are nutritionally limited and recognize that these populations may be more impacted by recovering carnivores or harvest than populations inhabiting more productive summer habitats.

A global comparison of the nutritive values of forage plants grown in contrasting environments

“…This dataset demonstrates that these decisions are crucial. Lower nutritive value diets can lead to higher mortality rates, lower pregnancy rates, production of fewer offspring and a higher risk of predation (Proffitt et al 2016). An analysis of 77 mammalian herbivores showed that larger animals better tolerate diets of lower nutritive quality because they can consume a greater volume of vegetation without increasing the efficiency of digestion (Müller et al 2013).…”

To forage or flee: lessons from an elk migration near a protected area

“…The size of the effect depends on the difference in the quality and availability of forage between origin and destination ranges, and the ability of individuals to replenish stores thereafter. This is much more difficult for ungulates in temperate regions in fall and winter than in spring and summer and thus the early-fall migration strategy could negatively impact pregnancy rates and calf survival in PAgroup elk (Cook et al 2004, Tollefson et al 2010, Hurley et al 2014, Proffitt et al 2016). Fig.…”

“…, Proffitt et al. ), few studies have considered fall migration and the tradeoffs of forage and risk during that time period, likely because of the difficulties posed by the protracted and asynchronous nature of autumnal events (Gallinat et al. ).…”

“…Despite the known importance of autumn nutrition as a driver of overwinter survival and fecundity (Cook et al 2004, Tollefson et al 2010, Hurley et al 2014, Proffitt et al 2016, few studies have considered fall migration and the tradeoffs of forage and risk during that time period, likely because of the difficulties posed by the protracted and asynchronous nature of autumnal events (Gallinat et al 2015). Snow depth and cold temperatures are the main identified drivers of autumn migration (Nelson 1995, Mysterud 1999, Monteith et al 2011, Jones et al 2014), but these variables do not fully account for the wide variation in the timing of summer-winter range migration (~July-December for recent studies in the northern hemisphere, Mysterud et al 2011, Bischof et al 2012, Rivrud et al 2016.…”

Assessing Nutritional Condition of Mule Deer Using a Photographic Index

“…Nutritional ecology, the study of the relationship between animals and their environment through nutritional interactions, has important implications for wildlife management and conservation (Parker et al 2009). Nutrition influences many aspects of animal life history, including pregnancy, reproductive success, juvenile growth and survival, and adult survival (Keech et al 2000, Cook et al 2004, Monteith et al 2014, Duquette et al 2015, Proffitt et al 2016). Understanding patterns of nutritional availability can improve inferences about effects of various limiting factors on population dynamics including disease, predation, climate, seasonal change, and habitat loss (Haskell and Ballard 2004, Long et al 2014, Monteith et al 2014, Downs et al 2015, Eacker et al 2016).…”