Identification of subpopulations of North American elk (Cervus elaphusL.) using multiple lines of evidence: habitat use, dietary choice, and fecal stable isotopes

Abstract

We used multiple lines of evidence to assess habitat selection, dietary choice, and nutritional outcomes for a population of North American elk (Cervus elaphus), confined to a relatively small and isolated landscape of public and private land in south-central Great Plains, USA. The area of suitable elk habitat was a topographically diverse matrix of mature oak savannah, C 4 -dominated grasslands, and C 3 -dominated agricultural fields surrounded by unsuitable lowlands fragmented by anthropogenic activities. We hypothesized that such disparity in habitat availability and quality resulted in subpopulation differences in the overall elk population. We used 3 methods to evaluate this premise: radiotelemetry to determine home range and habitat use, microhistology of plant fragments in feces to determine dietary selection, and fecal nitrogen (N) and stable isotope ratios of nitrogen (d 15 N) and carbon (d 13 C) to assess nutritional outcomes of habitat use and dietary choice. By comparing these 3 approaches, we wanted to determine if fecal indices alone could efficiently and accurately identify subpopulation structuring. Compositional analyses from radiotelemetry observations of 21 female elk identified 2 subpopulations that occupied relatively disjunct areas and showed differential preferences for forested and cultivated fields in summer but comparable preferences for cultivated fields in winter. A third unmarked subpopulation of elk was known to be largely confined to an adjacent wildlife refuge. Microhistological analyses of feces collected in all 3 areas highlighted distinct diets, outcomes of habitat occupation by the 3 subpopulations. Increased use of cultivated forages in winter was evident for 2 of the subpopulations, but the extent of use by elk was dependent on availability of cultivated forages in areas they occupied. The refuge subpopulation had no access to cultivated forage. Fecal N, fecal d 13 C, and fecal d 15 N supported the premise that the subpopulation with the greatest access to cultivated forages was on a higher nutritional plane than the other 2 subpopulations. Changes in fecal N, fecal d 13 C, and fecal d 15 N paralleled percentages of cultivated forages in the diets highlighting the utility of such fecal indices as supplemental to or surrogates for traditional methods of habitat use and dietary selection in free-ranging ungulates.

Individual-based seasonal habitat selection in a forest-dwelling population of reintroduced bison Bison bison

“…We would have overlooked this variation in habitat selection strategies, had we relied solely on a pooled RSF and not investigated individual behaviour. The variation that we uncovered in individual behaviour may indicate subpopulation structure, similar to that found in caribou Rangifer tarandus (Nagy et al 2011), Yellowstone bison (Olexa andGogan 2007, Halbert et al 2012) and elk Cervus canadensis (Walter et al 2010). However, we did not have data adequate to detect subpopulation structure, which may be defined by spatial distribution, social interaction, diet and habitat selection.…”

“…However, we did not have data adequate to detect subpopulation structure, which may be defined by spatial distribution, social interaction, diet and habitat selection. In the future, detection of subpopulation structure could be aided by analysis of a larger number of collared bison with simultaneously active collars (Nagy et al 2011), as well as dietary and genetic data (Walter et al 2010, Halbert et al 2012). Regardless, similar to other studies (Gillingham and Parker 2008, Nielsen et al 2009, Anderson and Johnson 2014), our analyses broadly demonstrate how habitat models estimated by pooling data from multiple animals may conceal individual behaviour, which may have implications for management decisions.…”

Isotopic nitrogen in fecal fiber as an indicator of winter diet in caribou and muskoxen

“…[28] With few exceptions, [53] feces from large herbivores have higher δ 15 N values than the diet (approx. 3-4‰ [6,7,10,22,23,27,51,54,55] ) with marked variation in the discrimination within and among species. [23] For captive northern ungulates in this study on formulated diets, estimates of fecal fiber-diet discrimination factors from the detergent-free fiber assay were similar to those observed in other ungulates: fecal fibers of reindeer/caribou and muskoxen had consistently higher values (3.6 ± 1.4‰ and 2.8 ± 0.5‰, respectively) over a range of dietary δ 15 N values.…”

“…Stable nitrogen isotope ratios (δ 15 N values) in excreta have been used to assess diets in primates, [1,2] black bears (Ursus americanus), [3] several African ungulates, [4,5] muskoxen (Ovibos moschatus), [6] elk (Cervus elaphus), [7] and small mammals. [8] Changes in δ 15 N values have also been used to evaluate trophic and ecological relationships in large mammalian predator-prey systems, [9] wild and domestic herbivores, [10][11][12] rodents, [13] grazing waterfowl, [14] and seabirds; [15] as well as the nutritional status in northern ungulates, [16][17][18] orangutans (Pongo pygmaeus), [19] and reptiles.…”

The prospects of poop: a review of past achievements and future possibilities in faecal isotope analysis

“…We summarise several applications below to highlight the types of spatial questions that can be addressed. Walter et al (2010) found that by combining faecal δ 13 C, δ 15 N and %N values with faecal microhistology, radiotelemetry, and observational data it was possible to track differences in habitat and resource use (including consumption of cultivated crops) by North American elk. Conversely, The prospects of poop Gustine et al (2012) found that faecal δ 15 N values were not particularly well suited for distinguishing populations of caribou (Rangifer tarandus) in Alaska.…”