Black-tailed prairie dog (Cynomys ludovicianus) reintroduction can limit woody plant proliferation in grasslands

mmerrick — Fri, 17 Jul 2020 20:43:34 +0000

Authors

Sarah L. Hale

John L. Koprowski

Steven R. Archer

Tree and shrub proliferation has been widespread in grasslands worldwide, and has altered ecosystem function and wildlife habitat. Several causes have been proposed for the woody plant encroachment phenomenon. The widespread eradication of a native keystone herbivore in North American grasslands, the prairie dog (Cynomys spp.), is one potential contributing factor that has received relatively little attention. We hypothesized prairie dogs would have historically suppressed woody plants by creating “browse traps” through their systematic clipping of vegetation. We tested this hypothesis by conducting surveys and experimentally manipulating shrub accessibility via exclosures and artificial saplings on and around recently reestablished black-tailed prairie dog (Cynomys ludovicianus) colonies in southeastern Arizona, United States. Shrubs were common on the nascent colonies (mean ± SE = 132 ± 32.7 plants ha–1), but at substantially reduced densities compared to off colonies (305 ± 94.9 plants ha–1). Among branches placed on colonies to simulate “saplings” 89% were damaged within 3 days of “planting,” whereas those placed off colonies were virtually untouched. This was true for both a deciduous, N2-fixing shrub (velvet mesquite, Prosopis velutina) and an evergreen non-N2-fixing shrub (creosote bush, Larrea tridentata). Prairie dogs on newly established colonies did not extirpate woody plants over the time-frame of our study, but reduced their abundance and suppressed their growth, which would ostensibly prevent them from achieving dominance. Implications for extending the longevity of widely practiced “brush management” grassland restoration treatments are discussed in the context of perceptions of prairie dogs as rangeland pests. Prairie dogs represent an enigma in keystone conservation. Whereas the reintroduction of large or charismatic keystone species [e.g., sea otters (Enhydra lutris)] are conducted to restore critical ecological function, reintroductions of other keystone species, such as gray wolves (Canis lupus) and in our case, prairie dogs, are highly controversial. Our findings suggest reintroductions of this negatively perceived small herbivore could function as a tool to locally suppress woody plant proliferation that is widely regarded as an impediment to livestock production. Accordingly, prairie dogs could promote restoration efforts to re-establish and maintain habitat for grassland endemics while promoting biological diversity and other ecosystem services.

Additional Information

Frontiers in Ecology and Evolution

Date of publication:

2020

Topics

keystone species

browse trap

grasslands

restoration ecology

Research Categories

Behavioral Ecology Human Wildlife Conflict Natural History Threatened and Endangered Species

Native lagomorphs suppress grass establishment in a shrub-encroached, semiarid grassland

mmerrick — Wed, 05 Jun 2019 18:23:28 +0000

Authors

Abercrombie, S. T.

Koprowski, J. L.

Nichols, M. H.

Femhi, J. S.

Shrub encroachment into arid grasslands has been associated with reduced grass abundance, increased soil erosion, and local declines in biodiversity. Livestock over‐ grazing and the associated reduction of fine fuels has been a primary driver of shrub encroachment in the southwestern United States, but shrublands continue to persist despite livestock removal and grassland restoration efforts. We hypothesized that an herbivory feedback from native mammals may contribute to continued suppression of grasses after the removal of livestock. Our herbivore exclusion experiment in southeastern Arizona included five treatment levels and allowed access to native mammals based on their relative body size, separating the effects of rodents, lago‐morphs, and mule deer. We included two control treatments and replicated each treatment 10 times (n = 50). We introduced uniform divisions of lawn sod (Cynodon dactylon) into each exclosure for 24‐hr periods prior to (n = 2) and following (n = 2) the monsoon rains and used motion‐activated cameras to document herbivore visita‐ tions. In the pre‐monsoon trials, treatments that allowed lagomorph access had less sod biomass relative to other treatments (p < 0.001), averaging 44% (SD 36%) and 29% (SD 45%) remaining biomass after the 24‐hr trial periods. Following the onset of monsoons, differences in remaining biomass among treatments disappeared. Desert cottontails (Sylvilagus audubonii) were detected more frequently than any of the other 11 herbivore species present at the site, accounting for 83% of detections dur‐ ing the pre‐monsoon trials. Significantly more (p < 0.001) desert cottontails were de‐ tected during the pre‐monsoon trials (2,077) compared to the post‐monsoon trials (174), which coincided with biomass removal from lagomorph accessible treatments. We conclude that desert cottontails are significant consumers of herbaceous vegeta‐ tion in shrub‐encroached arid grasslands and they, along with other native herbi‐ vores, may act as a biotic feedback contributing to the competitive advantage and persistence of shrubs.