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Introduction
Understanding the dietary ecology of biotic organisms, both today and in the past, is critical to current species management and conservation efforts. A powerful tool used to make conservation decisions in the face of ongoing climate change is bioclimatic envelope models, which predict an organism's future distribution (e.g., Araújo and Townsend Peterson 2012). However, these models make a critical assumption that "what an animal does today an animal will do tomorrow," also known as niche conservatism. Niche conservatism can also be defined as the capacity of a species to retain components of its fundamental niche over time (Hadly et al. 2009) or the phenomenon that enables species to persist in ecological environments over time (Wiens and Graham 2005). Regardless of the precise definition, assuming that niches are static over time may not be valid, even over short time spans. While recent reviews reveal that "niche conservatism" is generally widespread (e.g., Wiens and Graham 2005; Losos 2008; Peterson 2011), even over deep time (Hadly et al. 2009; DeSantis et al. 2012a), the majority of these studies focus on assessing an organism's niche based on range areas or characteristics of those occupied ranges (as broken down to temperature and precipitation, in most cases). However, studies of mammalian dietary niches over time have demonstrated a mixture of results, with some taxa maintaining static dietary niches (e.g., like tapirs, also referred to as "living fossils"; DeSantis and MacFadden 2007) and others shifting their diets with changing climatic conditions like interglacial warming during the Pleistocene (DeSantis et al. 2009). This dietary plasticity documents the adaptability of mammalian dietary behavior in response to available resources (and potential biotic interactions) and falsifies the idea that dietary niches are conserved over time. Therefore, examining whether and how dietary niches are conserved over time is critical to assessing the scientific foundation upon which conservation decisions are made, including how much confidence we put in bioclimatic envelope models that assume niche conservatism.
An underutilized but valuable model organism for testing dietary niche conservatism is the spotted hyena (Crocuta crocuta). While C. crocuta is now largely restricted to sub-Saharan Africa, the ranges of Pleistocene cave spotted hyenas (C. crocuta spelaea...