Shrub encroachment, productivity pulses, and core‐transient dynamics of Chihuahuan Desert rodents

Abstract

Drylands worldwide are experiencing shrub encroachment into grasslands with potential consequences for biodiversity and ecosystem services. Climate change could increase the rate of shrub encroachment, amplify precipitation variability, and thus alter bottom‐up processes for animal communities. Desert rodents are important biodiversity elements of arid grasslands and shrublands that exert strong effects on soil, vegetation, and other animal species. We used long‐term data from the Jornada Basin Long Term Ecological Research site in the Chihuahuan Desert of southern New Mexico to ask whether bottom‐up control of desert rodents changes across shrub encroachment gradients. Our design included spatial blocks with replicated ecological states representing transitions from black grama (Bouteloua eriopoda) to honey mesquite (Prosopis glandulosa). Grassland‐to‐shrubland transitions did not produce degraded ecosystems, on average, with reduced net primary production or decreased rodent biomass. However, more rodent biomass was supported on unencroached grasslands following droughts whose frequency and severity may increase in southwestern United States. Hence, the observed evenness in rodent biomass across ecological states should be sensitive to climate change. The best predictors of rodent biomass also differed markedly for two trophic groups. This outcome was explained by considering core‐transient dynamics. Granivores were mostly core species that regularly occurred on sites and responded to lagged net primary production at local scales, whereas folivores included transient species (especially Sigmodon hispidus) that responded to lagged precipitation at broader scales via spillover dynamics. Bottom‐up processes for desert rodents across shrub invasion gradients were understood by integrating lagged responses to productivity pulses with core‐transient structuring of communities.

Harmony on the prairie? Grassland plant and animal community responses to variation in climate across land‐use gradients

“…Land use and climate can interact to drive changes in biodiversity (Oliver and Morecroft ), resulting in context‐dependent community responses to climate variability (de Vries et al , Schooley et al ). For example, land‐use changes can influence dispersal, disturbance regimes, and local climate, all of which can interact to produce complex shifts in biodiversity (Hansen et al ).…”

Constraints on shrub cover and shrub–shrub competition in a U.S. southwest desert

“…), and small mammal and insect herbivory and granivory (Whitford and Bestelmeyer , Schooley et al. ) may be needed to explain what is preventing potential shrub cover from being realized at the Jornada Basin.…”

Shrub encroachment creates a dynamic landscape of fear for desert lagomorphs via multiple pathways

“…The dominant shrubs included honey mesquite, creosote bush, and tarbush ( Flourensia cernua ). Our study sites were on similar soils consisting of sandy to sandy loam surface soils with a petrocalcic horizon layer at depths of 30–100 cm (Schooley et al 2018). Long‐term mean annual precipitation is 245 mm and >50% falls in July–September during the seasonal monsoon.…”

“…Therefore, shrub encroachment into grasslands should shape perceived predation risk by prey. However, most research examining how animals respond to shrub encroachment does so through the lens of species diversity and population abundances or biomass (Bestelmeyer 2005, Blaum et al 2007, Cosentino et al 2013, Schooley et al 2018, Stanton et al 2018). Although shrubs can affect risk perception at the microhabitat scale (Longland and Price 1991, Bouskila 1995, Brown and Kotler 2004), mechanistic pathways for how shrub encroachment alters prey perception of risk at larger scales (Laundré et al 2014, Wheeler and Hik 2014) remain poorly understood.…”