Morphological Adaptations for Digging and Climate-Impacted Soil Properties Define Pocket Gopher (Thomomys spp.) Distributions

Abstract

Species ranges are mediated by physiology, environmental factors, and competition with other organisms. The allopatric distribution of five species of northern Californian pocket gophers (Thomomys spp.) is hypothesized to result from competitive exclusion. The five species in this environmentally heterogeneous region separate into two subgenera, Thomomys or Megascapheus, which have divergent digging styles. While all pocket gophers dig with their claws, the tooth-digging adaptations of subgenus Megascapheus allow access to harder soils and climate-protected depths. In a Northern Californian locality, replacement of subgenus Thomomys with subgenus Megascapheus occurred gradually during the Pleistocene-Holocene transition. Concurrent climate change over this transition suggests that environmental factors – in addition to soil – define pocket gopher distributional limits. Here we show 1) that all pocket gophers occupy the subset of less energetically costly soils and 2) that subgenera sort by percent soil clay, bulk density, and shrink-swell capacity (a mineralogical attribute). While clay and bulk density (without major perturbations) stay constant over decades to millennia, low precipitation and high temperatures can cause shrink-swell clays to crack and harden within days. The strong yet underappreciated interaction between soil and moisture on the distribution of vertebrates is rarely considered when projecting species responses to climatic change. Furthermore, increased precipitation alters the weathering processes that create shrink-swell minerals. Two projected outcomes of ongoing climate change—higher temperatures and precipitation—will dramatically impact hardness of soil with shrink-swell minerals. Current climate models do not include factors controlling soil hardness, despite its impact on all organisms that depend on a stable soil structure.

Locomotory adaptations in entoptychine gophers (Rodentia: Geomyidae) and the mosaic evolution of fossoriality

“…Because both chisel‐tooth and head‐lift digging require extensive morphological specializations of the crania, the shape of the skull of rodents can be used to predict their burrowing capabilities (Marcy, Fendorf, Patton, & Hadly, ; Morgan, Verzi, Olivares, & Vieytes, ; Samuels & Van Valkenburgh, ). The proportions of the skull of rodents can also be used to differentiate among broad categories of locomotor habits (Bertrand, Schillaci, & Silcox, ; Marcy, Hadly, Sherratt, Garland, & Weisbecker, ; Verde Arregoitia, Fisher, & Schweizer, ).…”

“…Indeed, multiple studies have suggested the succession of dominant clades within the burrowing rodent guild to be a consequence of such ecological processes (Baskin, ; Calede et al, ; Hopkins, ; Samuels & Van Valkenburgh, ; Shotwell, ). There is also some evidence for these processes playing an important role in the distribution of modern burrowing rodents (Calede et al, ; Marcy et al, ; Marcy et al, ). We therefore analyzed the skull morphology of a suite of rodents from families including burrowing species that overlapped in time and space with the entoptychine species we studied (Table ).…”

Pocket gopher (Thomomys talpoides) soil disturbance peaks at mid-elevation and is associated with air temperature, forb cover, and plant diversity

“…However, compared to climate and plant biotic factors, their influence on gopher disturbance was minor. Gopher disturbance increased with soil depth in our system (Figure 3; see also Marcy et al 2013). Pocket gophers tend to occupy the upper soil layer where plant roots are most dense, approximately 6-20 cm (Reichman and Seabloom 2002), and although the lowest average soil depth across our sites was approximately 80 cm, sites with deeper soil profiles had more gopher disturbance.…”

Molecular data and ecological niche modelling reveal the evolutionary history of the common and Iberian moles (Talpidae) in Europe

“…In other subterranean mammals, like pocket gopher, interspecific differences in body size and digging strategy have been shown to confer competitive dominance of one species over another depending on soil characteristics (Marcy et al . ). In regions where divergent soil types co‐occur, the ranges of different pocket gopher species can overlap (Thaeler ).…”