Effects of rodent removal on community dynamics in desert grassland and shrubland vegetation.
Baez, Selene*,1, Collins, Scott1, Lightfoot, David1, Koontz, Terri*,1, 1 Department of Biology, Albuquerque, NM, USA
ABSTRACT- Both bottom-up and top-down forces are hypothesized to regulate community structure in many terrestrial and aquatic systems. In grasslands, evidence exists to support either bottom-up or top-down control on plant community structure. In desert grasslands in the southwestern US, however, research suggests that granivory by small mammals can exert strong top-down control on plant community structure. Here, we report results from a long-term (1995-present) small mammal exclosure experiment in desert grassland and shrubland vegetation at the Sevilleta National Wildlife Refuge, central New Mexico, USA. We compared patterns of plant community structure and dynamics from 1995 to 2003 inside replicate small mammal exclosures and in adjacent control areas. Ordination and time-lag analyses showed little directional change in grassland vegetation in either the small mammal exclosures or in open areas; whereas some degree of compositional change is occurring in the exclosures in the creosote-dominated shrublands. There were no statistically significant changes in species richness, diversity or cover of plant functional groups inside and outside exclosures in either the grass- or shrub-dominated site. The only clear change in community structure thus far is a decrease in community heterogeneity in the small mammal exclosures at the shrub-dominated site. On the other hand, there are strong correlations between plant community structure variables and season or annual precipitation for vegetation inside and outside exclosures. Together these results suggest that plant community structure and dynamics at the Sevilleta are strongly driven by bottom-up forces and that plant production probably has a greater impact on small mammal abundances than small mammals have on vegetation.
Key words: plant community, dynamics, rodents, desert
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