Rodent declines track regional climate variability in North American drylands

Regional long-term monitoring can enhance the detection of
biodiversity declines associated with climate change, improving
future projections by reducing reliance on space-for-time
substitution and increasing scalability. Rodents are diverse and
important consumers in drylands, which cover ~45% of Earth’s land
surface and face increasingly drier and more variable climates.
Here, we analyzed abundance data for 22 rodent species across
grassland, shrubland, ecotone, and woodland habitats in the
southwestern USA. We captured two time series: 1995-2006 and
2004-2013 that coincide with phases of the Pacific Decadal
Oscillation (PDO), which influences drought in southwestern North
America. Regionally, rodent species diversity declined 20-35%, with
greater losses during the later time period. Abundance also declined
regionally, but only during 2004-2013, with losses of ~5% of animals
captured. During the first time series (PDO wet phase), plant
productivity outranked climate variables as the best regional
predictor of rodent abundance for 70% of taxa, whereas during the
second period (dry phase), climate best explained rodent abundance
for 60% of taxa. Temporal dynamics in rodent diversity and abundance
differed spatially among habitats and sites, with the largest
declines in woodlands and shrublands of central New Mexico and
Colorado. Both habitat type and phase of the PDO modulated which
species were winners or losers under increasing drought and
amplified interannual variability in drought. Fewer taxa were
significant winners (18%) than losers (30%) under drought, but the
identities of winners and losers differed among habitats for 70% of
taxa. Our results suggest that the sensitivities of rodent species
to climate contributed to regional declines in diversity and
abundance during 1995 - 2013. Whether these changes portend future
declines in drought-sensitive consumers in the southwestern USA will
depend on the climate during the next major phase of the PDO.