No recent temporal changes in body size of three Danish rodents

Abstract

We used museum collections to study temporal trends of possible changes in skull size, body mass and body length in three species of rodents in Denmark. Skulls of adult Microtus agrestis, Apodemus flavicollis and Apodemus sylvaticus, collected between 1895 and 2004, 1847 and 2002, and 1895 and 2002, respectively, were measured and data on body mass and length were taken from the museum registers. Principal component (PC) analysis was used to combine data of the four skull measurements taken. We tested the relationship of sex, latitude, longitude, month and year of collection to PC1 by a General Linear Model (GLM). PC1, body length and body mass of M. agrestis significantly increased from west to east. In addition, PC1, body mass and body length of M. agrestis declined from summer (August) through autumn and winter to spring (March), probably due to the decline in food availability towards winter. None of the other factors examined (sex, latitude and year) were significantly related to body size. PC1 of A. flavicollis and A. sylvaticus was not significantly related to any of the environmental factors examined.

Widespread recent changes in morphology of Old World birds, global warming the immediate suspect

“…In recent decades, rapid morphological change has been documented in many animal species (Gardner et al., 2011; Sheridan & Bickford, 2011). The direction and significance of these trends are equivocal for mammals (Meiri et al., 2009; Riemer et al., 2018; Teplitsky & Millien, 2014; Yom‐Tov, 2003; Yom‐Tov & Yom‐Tov, 2004, 2005, 2012; Yom‐Tov et al., 2012), but birds seem to tend towards size reduction (Yom‐Tov, 2001; Yom‐Tov et al., 2002, 2006; Yom‐Tov & Yom‐Tov, 2006). Several studies have suggested that reductions in size are common, general or even near universal (Gardner et al., 2014; Ryding et al., 2021; Salewski et al., 2010; Van Buskirk et al., 2010; Weeks et al., 2020).…”

Post-weaning growth of endemic Iberian wild rabbit subspecies, Orycto lagus cuniculus algirus, kept in a semi-extensive enclosure : implications for management and conservation

“…These problems are transversal to most repopulating programmes and body fitness conclusions drawn from these facilities should be addressed with care (Ryman and Laikre, 1991). Moreover, although conditions present at the enclosure were similar to the surrounding habitat, natural settings are always difficult to simulate in enclosures; for example, stress associated with predation, which might reduce fitness and general weight (Yom-Tov et al, 2012), was never a problem at our site, as no predators were able to enter. Likewise, food availability in a very small enclosed area could pose a setback to maintaining individuals in a healthy environment, as the home range of free-living individuals of high density populations is wider (≈ 7000 m 2 in Devillard et al, 2008) than the 1300 m 2 available at all times in our enclosure.…”

Life history and habitat do not mediate temporal changes in body size due to climate warming in rodents

“…A similar trend was reported in Eastman et al (2012) , Nengovhela, Baxter & Taylor (2015) , Ozgul et al (2010) , Pergams & Lawler (2009) , with either decreases, increases and no changes reported ( Table S3 ). Changes in body size have been attributed to differing factors such as global warming, increased food availability, snow melt, longer growing season ( Eastman et al, 2012 ; Nengovhela, Baxter & Taylor, 2015 ; Pergams & Lawler, 2009 ; Smith, Browning & Shepherd, 1998 ; Villar & Naya, 2018 ; Yom-Tov & Yom-Tov, 2004 ; Yom-Tov et al., 2012 ) with some of these studies providing support for Bergmann’s clines. As clarified by Blackburn, Gaston & Loder (1999) , Bergmann’s Rule was originally applied to closely related species, but as noted by James (1970) it was later adapted to apply to ‘races of a species’ (see Mayr, 1956 ).…”

“…Six cranial variables were taken to measure skull size by AN with ©TESA digital calipers to the nearest 0.01 mm: greatest length of skull (GLS), nasal width (NAW), braincase width (BW), zygomatic width (ZYW), interorbital constriction (IOC) and the maxillary tooth row length (MXTRL) ( Taylor & Kumirai, 2001 ). We used principal component analysis (PCA) to combine the information of the six skull measurements (log transformed to standardize contribution of different variables) into a single variable for each species (PC.1, Delcros, 2012 ; Yom-Tov et al., 2012 ). This is because all of our six cranial variables were related to each other and PC.1 reflected a measure of size as indicated by the variable component loadings ( Fig.…”

“…Studies that tested temporal changes in body size in rodents were included. In total, ten published studies were investigated (i.e., Eastman et al, 2012 ; Koontz, Shepherd & Marshall, 2001 ; Nengovhela, Baxter & Taylor, 2015 ; Ozgul et al, 2010 ; Pergams & Lawler, 2009 ; Pergams et al, 2015 ; Smith, Browning & Shepherd, 1998 ; Villar & Naya, 2018 ; Yom-Tov & Yom-Tov, 2004 ; Yom-Tov et al., 2012 ) (References in Table S3 ). Apart from three species in which the studied time span was seven years ( Dipodomys merriami ; Koontz, Shepherd & Marshall, 2001 ), eight years ( Neotoma albigula ; Smith, Browning & Shepherd, 1998 ) or 32 years ( Marmota flaviventris ; Ozgul et al, 2010 ), all of the other above studies covered a time-span of >50 years (50–106 years).…”