Spatial and temporal variability in summer diet of gray wolves (Canis lupus) in the Greater Yellowstone Ecosystem

Abstract

The role of predation by large carnivores in suppressing prey populations and structuring ecosystems is highly debated, calling for a detailed understanding of carnivore diets. Wolves (Canis lupus) roam across three continents and persist throughout widely different ecosystems. Their diet is flexible and may vary spatially as well as seasonally, which requires analysis of diet on different spatial and temporal scales. Few studies have investigated the summer diet of wolves, which is more variable, consists of smaller prey, and requires different methods than studying their winter diet. To better understand the summer diet of wolves, we combined three independently collected wolf scat data sets from three distinctly different portions of the Greater Yellowstone Ecosystem: Yellowstone National Park (2009), Grand Teton National Park (2003 – 2009), and the Absaroka-Beartooth Wilderness (2009 – 2010). These areas represent different ecological conditions and management regimes, which may impact wolf diet. We estimated relative biomass and compared occurrence of different prey species among packs, years, as well as the three regions. In total, we analyzed 1,906 wolf scats and found that neonate cervids, adult elk, and adult deer were the most important prey species in the summer diet of the wolves. We found dietary variation among packs residing in the same area, as well as across years. The occurrence of neonate cervids displayed the most variation, and low occurrence of this prey type often was associated with a more diverse diet. Wolf packs within the national parks had a higher occurrence of medium-sized prey (~ 50 – 70 kg) and lower occurrence of small-sized prey (≤ 20 kg) compared to wolves in the Absaroka-Beartooth Wilderness. These results demonstrate flexibility in summer diet across packs, years, and between regions within the Greater Yellowstone Ecosystem.

Moose in wolf diets across northeastern Minnesota

“…Wolf diet estimates can be affected by temporal variation, inter‐pack collection, and age class (Gable et al 2017 a ). In a wolf scat study in the Greater Yellowstone Ecosystem during 2003‐2010, wolf diet composition varied among packs in the same area and across years, with the most variable prey item being the number of neonate cervids (Lodberg‐Holm et al 2021). Food availability per wolf and the amount of prey lost to scavengers decreases with larger pack size (Schmidt and Mech 1997, Peterson and Ciucci 2003).…”

“…The moose population estimate in northeastern Minnesota (1854 Ceded Territory) ranged from 2,760-4,350 during 2012 to 2020, or 0.18-0.28 moose/km 2 (DelGiudice 2020). Deer densities in the study area ranged from 0.4-7/km 2 (Lenarz 2011). Mean wolf density in Minnesota in 2012 to 2013 was 3.1 wolves/100 km 2 , with a mean pack size of 4.3 wolves (Erb and Sampson 2013).…”

Variation in adult and pup wolf diets at natal den sites is influenced by forest composition and configuration

“…These results contrast with other studies that showed more diverse wolf diets in the summer than in winter (Peterson & Ciucci, 2003; Spaulding et al, 1998) and which may also include a greater proportion of small‐bodied prey items (Mysłajek et al, 2019; Newsome et al, 2016; Stahler & Smith, 2006). Summer dietary diversity may increase as a result of wolves' restricted movements around den and rendezvous sites (Mech & Boitani, 2003; Newsome et al, 2016) in combination with lower availability or vulnerability of ungulates (Lodberg‐Holm et al, 2021; Paquet & Carbyn, 2003; Peterson & Ciucci, 2003; Spaulding et al, 1998).…”

“…The capacity of the habitat surrounding the den site to support prey species is therefore important for providing foraging opportunities for wolves and to promote efficient prey acquisition (Harrington et al, 1983). Variation in diet among wolf packs even in adjacent home ranges is likely influenced by differences in prey availability and abundance in each pack (Gable et al, 2017; Lodberg‐Holm et al, 2021).…”

“…Variation in diet among wolf packs even in adjacent home ranges is likely influenced by differences in prey availability and abundance in each pack (Gable et al, 2017;Lodberg-Holm et al, 2021).…”