Faunal isotope records reveal trophic and nutrient dynamics in twentieth century Yellowstone grasslands

Abstract

Population sizes and movement patterns of ungulate grazers and their predators have fluctuated dramatically over the past few centuries, largely owing to overharvesting, land-use change and historic management. We used d C and d15 N values measured from bone collagen of historic and recent gray wolves and their potential primary prey from Yellowstone National Park to gain insight into the trophic dynamics and nutrient conditions of historic and modern grasslands. The diet of reintroduced wolves closely parallels that of the historic population. We suggest that a significant shift in faunal d15 N values over the past century reflects impacts of anthropogenic environmental changes on grassland ecosystems, including grazer-mediated shifts in grassland nitrogen cycle processes.

A wolf in fox's clothing? Using stable isotopes to quantify ecological replacement

“…Prior to the introduction of sheep, upland geese were the primary terrestrial grazers in the Falklands, so limits on their distribution by FIWs were likely to have had cascading effects on vegetation, nutrient cycling, avian nesting habitat, and so on. (Fox-Dobbs et al, 2012). We presume that SAGFs may have similar effects on those islands where they are present but further study would be required to confirm this.…”

“…Previous studies have compared past to present day isotopic niches of members of the same or similar species (Chamberlain et al, 2005;Fox-Dobbs et al, 2012;Newsome et al, 2010) but as far as we are aware, this is the first study to explicitly compare isotopic niches between an extinct species and a potential ecological replacement. Given the burgeoning interest in ecological replacement as a conservation tool (Falcón & Hansen 2018;Griffiths et al, 2011;Seddon et al, 2014), we foresee that similar studies will become more common.…”

“…Previous studies have compared past to present day isotopic niches of members of the same or similar species (Chamberlain et al, 2005;Fox-Dobbs et al, 2012;Newsome et al, 2010) but as far as we are aware, this is the first study to explicitly compare isotopic niches between an extinct species and a potential ecological replacement.…”

“…Given that many species, especially predators, impact ecosystems through their diet, we suggest that one way of doing this is to compare the volume and overlap of dietary niches of extinct taxa and their potential ecological replacements. Stable isotope ratios in the tissues of consumers predictably reflect those in their food (Phillips et al, 2014) so one indirect but tractable way of doing this is to quantify isotopic niche volume and overlap using modern and historical tissue samples (Chamberlain et al, 2005;Fox-Dobbs, Nelson, Koch, & Leonard, 2012;Newsome et al, 2010). To exemplify this approach, we consider whether nonnative South American grey foxes (Lycalopex griseus, hereafter SAGF) act as de facto ecological replacements for extinct Falkland Island wolves (Dusicyon australis, hereafter FIW; Figure S1, Table S3).…”

Niche convergence suggests functionality of the nocturnal fovea

“…Within the Philippines, the δ 15 N values of O. megalotis (mean: 7.04 ± 2.3‰) were ca. 2.22‰ greater than those of T. syrichta (mean: 4.82 ± 1.9‰), indicating significant 15 N-enrichment (Wilcoxon W = 239, p = 0.008; Figure 5 ); however, the samples from T. syrichta collected in 2010 exhibited systematically low δ 15 N values, perhaps due to recent anthropogenic changes to the landscape (e.g., Fox-Dobbs et al, 2012 ). When we calculated the mean of these samples, log-transformed all δ 15 N values, and controlled for specimen year in a general model, there was no statistical difference between O. megalotis and T. syrichta ( t = –0.28, p = 0.781).…”