Abstract
ABSTRACT Burrowing mammals can be ecosystem engineers by increasing soil aeration and erosion and altering the structure of plant communities. Studies that characterize the constraints on the distributions of fossorial mammal disturbances to soil can help predict changes in ecosystem engineering under future climates. We quantified the density of soil disturbances caused by Thomomys talpoides (northern pocket gopher) over replicate elevation gradients spanning 2,700–4,000 m a.s.l. in the Upper Gunnison Basin, Colorado, USA. As a conceptual framework for predicting biogeographic variation in soil disturbance, we used the abundant center hypothesis (ACH), which proposes that species abundance declines monotonically away from the most abundant location in its distribution, with the assumption that ecosystem engineering scales with gopher abundance. We also evaluated the relative importance of abiotic and biotic variables as correlates of soil disturbance. Gopher disturbance peaked at mid elevations (~3,150 m), supporting the ACH. The best model for predicting gopher-caused soil disturbance contained both abiotic and biotic variables, with increased soil disturbance where mean annual temperature, forb cover, and plant diversity were greatest. Results suggest that mountain ecosystems may experience increases in gopher-caused soil disturbance as climate warms, possibly accompanied by increases in plant diversity and forb cover.
Highlights
Burrowing mammals can have large effects on ecosystems that cascade to soil physical properties, plant composition, and primary productivity
Gopher disturbance increased with forb:grass ratio, inverse Simpson’s diversity, mean annual temperature (MAT), and soil depth, while it decreased with the sine and cosine of aspect (Figure 3)
It is important to note that Brown (1984, 1995) predicated the abundant center hypothesis (ACH) on three assumptions: (1) species abundance depends on the response of a local population to local conditions, (2) species abundance is determined by how closely local conditions meet the species’ Hutchinsonian (1957) n-dimensional niche requirements, and (3) there is spatial autocorrelation in the multidimensional niche requirements that control species’ abundance and distribution
Summary
Burrowing mammals can have large effects on ecosystems that cascade to soil physical properties, plant composition, and primary productivity. The northern pocket gopher (Thomomys talpoides, Geomyidae; hereafter, pocket gopher or gopher) is an ecosystem engineer that creates physical soil disturbances (e.g., eskers, tunnels, mounds) by burrowing belowground and pushing subsoil to the surface. Pocket gophers dig an elaborate network of tunnels (Knight 2009), and, on average, can excavate 26.1 m3/ha a year of soil (Smallwood and Morrison, 1999). This large soil disturbance creates multiple microenvironments (Huntly and Inouye 1988). In the high elevations of central Utah (3,000–3,400 m), gophers primarily consumed and cut dandelion (Taraxacum officinale), penstemon (Penstemon rydbergii), sweet sage (Artemisia discolor), and yarrow (Achillea lanulosa) (Aldous 1951)
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