Changes in the Diet and Body Size of a Small Herbivorous Mammal (Hispid Cotton Rat, Sigmodon Hispidus) Following the Late Pleistocene Megafauna Extinction
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University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Faculty Publications in the Biological Sciences Papers in the Biological Sciences 12-2019 Changes in the diet and body size of a small herbivorous mammal (hispid cotton rat, Sigmodon hispidus) following the late Pleistocene megafauna extinction Catalina P. Tomé University of New Mexico, [email protected] Emma A. Elliott Smith University of New Mexico, [email protected] S. Kathleen Lyons University of Nebraska - Lincoln, [email protected] Seth D. Newsome University of New Mexico, [email protected] Felisa A. Smith University of New Mexico, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/bioscifacpub Part of the Animal Sciences Commons, Biodiversity Commons, Biology Commons, and the Population Biology Commons Tomé, Catalina P.; Elliott Smith, Emma A.; Lyons, S. Kathleen; Newsome, Seth D.; and Smith, Felisa A., "Changes in the diet and body size of a small herbivorous mammal (hispid cotton rat, Sigmodon hispidus) following the late Pleistocene megafauna extinction" (2019). Faculty Publications in the Biological Sciences. 755. https://digitalcommons.unl.edu/bioscifacpub/755 This Article is brought to you for free and open access by the Papers in the Biological Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications in the Biological Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 42 1–16 ECOGRAPHY Research Changes in the diet and body size of a small herbivorous mammal (hispid cotton rat, Sigmodon hispidus) following the late Pleistocene megafauna extinction Catalina P. Tomé, Emma A. Elliott Smith, S. Kathleen Lyons, Seth D. Newsome and Felisa A. Smith C. P. Tomé (http://orchid.org/0000-0001-8508-7202) ✉ ([email protected]), E. A. Elliott Smith, S. D. Newsome and F. A. Smith, Dept of Biology, Univ. of New Mexico, Albuquerque, NM 87131, USA. – S. K. Lyons, School of Biological Sciences, Univ. of Nebraska-Lincoln, Lincoln, NE, USA. Ecography The catastrophic loss of large-bodied mammals during the terminal Pleistocene likely 42: 1–16, 2019 led to cascading effects within communities. While the extinction of the top consumers doi: 10.1111/ecog.04596 probably expanded the resources available to survivors of all body sizes, little work has focused on the responses of the smallest mammals. Here, we use a detailed fossil record Subject Editor: Jessica Blois from the southwestern United States to examine the response of the hispid cotton rat Editor-in-Chief: Miguel Araújo Sigmodon hispidus to biodiversity loss and climatic change over the late Quaternary. Accepted 15 November 2019 In particular, we focus on changes in diet and body size. We characterize diet through carbon (δ13C) and nitrogen (δ15N) isotope analysis of bone collagen in fossil jaws and body size through measurement of fossil teeth; the abundance of material allows us to examine population level responses at millennial scale for the past 16 ka. Sigmodon was not present at the cave during the full glacial, first appearing at ~16 ka after ice sheets were in retreat. It remained relatively rare until ~12 ka when warming tempera- tures allowed it to expand its species range northward. We find variation in both diet and body size of Sigmodon hispidus over time: the average body size of the population varied by ~20% (90–110 g) and mean δ13C and δ15N values ranged between −13.5 to −16.5‰ and 5.5 to 7.4‰ respectively. A state–space model suggested changes in mass were influenced by diet, maximum temperature and community structure, while the modest changes in diet were most influenced by community structure. Sigmodon maintained a fairly similar dietary niche over time despite contemporaneous changes in climate and herbivore community composition that followed the megafauna extinc- tion. Broadly, our results suggest that small mammals may be as sensitive to shifts in local biotic interactions within their ecosystem as they are to changes in climate and large-scale biodiversity loss. Keywords: biodiversity loss, climate change, late Quaternary Introduction Large-bodied mammals play a critical role within communities and ecosystems. Either directly or indirectly, they influence soil and vegetation structure and composition, nutrient cycling and other biogeochemical processes, and especially, the distribution –––––––––––––––––––––––––––––––––––––––– © 2019 The Authors. Ecography published by John Wiley & Sons Ltd on behalf of Nordic Society Oikos www.ecography.org This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 1 and abundance of other mammals (Ripple et al. 2015, of flora and fauna across North America at both regional and Malhi et al. 2016, Smith et al. 2016a). The loss of apex con- continental scales (Prentice et al. 1991, Graham et al. 1996, sumers can lead to cascading effects, changing community Whitlock and Bartlein 1997, Lyons 2003, 2005, Blois et al. structure and species (Estes et al. 1998, 2011, Schmitz et al. 2010, Gottfried et al. 2012, Cotton et al. 2016). 2000, Shurin et al. 2002, Dirzo et al. 2014, Ripple et al. Fluctuations in environmental temperature are known to 2014). For example, experimental removal of large-bodied influence the morphology and ecology of species (Bergmann mammals from plots across a variety of ecosystems has led 1847, Brown 1968, Andrewartha and Birch 1986, Gylnn to increased rodent abundance, likely because of alterations 1993, Smith et al. 1995, Ashton et al. 2000, Stenseth et al. of vegetation abundance and composition (Keesing 1998, 2002, Walther et al. 2002, Millien et al. 2006). Indeed, the Parsons et al. 2013, Galetti et al. 2015). While empirical stud- ecogeographic relationship between population and/or spe- ies demonstrate rapid responses by the small-bodied mam- cies body mass and temperature gradients is so well-character- mal community, the ultimate consequences remain unclear, ized it is termed Bergmann’s rule; the principle that within a since direct and indirect effects may take decades or longer genus, larger species are found in colder climates and smaller to be fully realized (Brown and Munger 1985, Smith et al. species in warmer ones (Bergmann 1847, Mayr 1956). 1997, Ernest et al. 2000, Brown et al. 2001). Thus, longer- Bergmann’s rule is well-supported for most mammals both term perspectives are essential for investigating the influence across time and space, suggesting environmental temperatures of biodiversity loss and predicting how such events may have a strong impact on body size evolution (Brown and Lee change the interactions and dynamics within an ecosystem 1969, Smith et al. 1995, Ashton et al. 2000, Gillooly et al. over evolutionarily relevant time scales (Smith et al. 2010, 2001, Freckleton et al. 2003, Millien et al. 2006, Smith Blois et al. 2013). Moreover, given the precarious state of 2008; but see: McNab 1971 and Blackburn et al. 1999). most megafauna today (Davidson et al. 2009, Ripple et al. Moreover, changes in body size have consequences because of 2015, Smith et al. 2016a), such studies are crucial for the allometric scaling of many life history and physiological effective management. processes such as metabolism, growth, reproduction, locomo- The late Pleistocene megafaunal extinction led to the tion, home range size and even the degree of consumption of loss of more than 70 species in North America, including plant fiber (McNab 1980, Peters 1983, Calder 1984, Justice all mammals weighing >600 kg (Martin and Klein 1989, and Smith 1992, Smith 1995). Thus, selection for a larger Lyons et al. 2004). The high degree of size-selective extinc- (or smaller) body size changes how animals interact with tion was unprecedented in the Cenozoic mammalian record and/or are impacted by their ecosystem (Damuth 1981, Peters (Alroy 1999, Smith et al. 2018), and likely had significant 1983, Calder 1984). This coupling of climatic change at the impacts on the community structure and function of sur- late Quaternary with the terminal Pleistocene megafauna viving animals (Smith et al. 2018). For example, extinct extinction likely led to substantial ecosystem alterations for species had significantly more ecological associations than surviving mammals. do modern species today, suggesting a more tightly orga- We assessed the relative importance of changes in cli- nized web of species interactions (Smith et al. 2016b). mate, resources and community structure on both diet and Thus, loss of megafauna at the terminal Pleistocene is body size of Sigmodon hispidus, a medium-sized herbivorous a good proxy for examining the consequences of mod- rodent, over the past 16 000 years. We employ stable isotope ern losses in biodiversity, which preferentially target analysis and measurements of fossil molars. We focused on Earth’s remaining large-bodied mammals (Davidson et al. an exceptionally well-stratified and radiocarbon dated fossil 2009, Smith et al. 2018). Here, we are particularly inter- record in the Edwards Plateau, Great Plains of Texas. In the ested in the influence of biodiversity loss on surviving late Pleistocene, S. hispidus, along with the greater mammal smaller-bodied mammals within the community. assemblage, lived among a diverse assemblage of megaherbi- Coinciding with the loss of biodiversity at the end of the vores, including mammoths, giant ground