Evolutionary and ecological response of pocket gophers (Thomomys talpoides) to late-Holocene climatic change

Abstract

Late-Holocene evolutionary and ecological response of pocket gophers (nomomys hlp&s) and other species to climatic change is documented by mammalian fossils from Lamar Cave, a palaeontological site in northern Yellowstone National Park. Pocket gophers illustrate ecological sensitivity to a series of mesic to xeric climatic excursions in the sagebrush-grassland ecotone during the last 3200 years, increasing in abundance during mesic intervals, and declining in abundance during xeric intervals. Four other small mammal taxa (Microhis sp., Peromyscus maninrlohis, Neotoma cinerca and Spennophilus annutus) also show response to climatic change, increasing or decreasing in abundance in accordance with their preferred habitat requirements. To determine evolutionary response to climate, two craniodental characters for the northern pocket gopher (nomays hlpodes) are investigated in modern representatives within a 4 0 0 h radius of Lamar Cave and then tracked through the time spanned by the fossils. One morphologic character shows that variation in body size, primarily a plastic response to the environment, demonstrates few taxonomically consistent patterns of geographic variation across 39 modern localities. In contrast, the other character indicates genetic relatedness within subspecies. Stasis in the genetically controlled character indicates that the same subspecies of pocket gopher ( E talpodcs hellus) has occupied northern Yellowstone for at least 3200 years. However, E t. tmcllus does show plastic response to climatic change because pocket gophers during the Medieval Warm Period were smaller than at any other time spanned by the deposit. I997 The Linncan Society of London

Geographic Variation in Populations of Microcebus murinus in Madagascar: Resource Seasonality or Bergmann's Rule?

“…Though the argument is based on energy requirements to maintain normothermy in cold climates, the same pattern might arise as a response to stressfully high temperatures. In woodrats and pocket gophers the tolerance of high temperature decreased with increasing body mass (Hadley, 1997;Smith et al, 1995). As a consequence significant changes in body mass occurred at very small changes of ambient temperatures of just a few degrees C during the Holocene (Brown and Lomolino, 1998), which matches the findings of Godfrey et al (1999) for Malagasy lemurs.…”

“…It is unclear whether the increase in body mass toward lower temperatures is an adaptation to conserve energy in a cooler climate because of lower surface-to-volume ratios (adaptations to the cold: the original argument for Bergmann's rule), or whether smaller animals have an evolutionary advantage over larger species at higher temperatures (adaptations to high temperature: Hadley, 1997;Smith et al, 1995). In any case the patterns in body mass variation are consistent with the idea that adaptations for temperature regulation are important for mouse lemurs and are reflected in their body mass.…”

A spatio-temporal decrease in molar size in the western European house mouse

“…In northern America, Smith et al (1995) recorded a decrease in body mass of the woodrat since the 20 last millenia, correlated with an average increase in temperature. At a higher resolution, Hadly (1997) showed that the pocket gopher increased in size during the Medieval Warm Period, and attributed this change to a plastic response. Our sampling was not sufficiently distributed through time to detect such short term changes.…”

Niche shifting in response to warming climate after the last glacial maximum: inference from genetic data and niche assessments in the chisel-toothed kangaroo rat (Dipodomys microps)

“…responded to cooling climate during glacial periods by increasing their body mass (Bergmann's Rule) instead of shifting their distributions to lower latitudes or altitudes as would be predicted if their climatic niches remained conserved (Smith & Betancourt, 2003). Consequently, one could ask, why are some taxa or populations capable of shifting their niches to novel conditions (Hadly, 1997;Smith & Betancourt, 2003) while others respond to an environmental change by tracking the conditions to which they are already adapted (Parmesan et al, 1999;Pounds et al, 1999)? Vrba (1992) proposed that taxa capable of utilizing alternative environments are most likely to persist through environmental changes.…”