Fig 1.
Sites surveyed for American pikas in the north Lake Tahoe area, California, USA.
The Pluto triangle is bounded by Lake Tahoe, highway 267, and by the Truckee River, adjacent to highway 89. Current sign of American pika was found both east and west of Pluto triangle; nearly all sites within the Pluto triangle yielded old fecal pellets (see also S1 Table). Map boundaries represent our boundaries for the north Lake Tahoe area.
Fig 2.
Calibrated age ranges for each of the remnant pika scat samples.
The gray curves show the probability distribution of dates corresponding to each sample’s Fm estimate. Samples are stacked for comparison. The blue curve shows the radiocarbon signature of the atmosphere over time. This is the calibration curve used to estimate the ages of the relict pika scat. See text for definition of Fm units.
Fig 3.
Mean annual temperature data from weather station at Tahoe City, California, USA.
Temperatures have increased by 1.9°C during the period of record, 1910–2015 (linear regression, p < 10−12). Tahoe City forms the southwestern vertex of the Pluto triangle (Fig 1).
Fig 4.
Inundation of sky islands surrounding Lake Tahoe by rising tides of warm air.
Panels depict mean summer temperature (MST) for historical conditions, 1910–1955 (current MST -1.45°C), current conditions, 2010 (2001–2010), and future conditions (2030, RCP 8.5, current MST + 1.33°C; 2050, RCP 8.5, current MST + 2.74°C). Fourteen degrees Celsius MST represents an approximate threshold above which pika occupancy becomes tenuous [27]. Projections are the ensemble mean of 17 general circulation models [54]. Temperatures from the mid-20th century and before (upper left panel) appear to have supported spatially continuous pika-habitable temperatures throughout much of the Tahoe region. Current temperatures (upper right) have seen the collapse of the Pluto triangle metapopulation, which occupied the isthmus of habitat connecting the crest of the Sierra with the Carson Range to the east. If pika response is governed by the temperature and dispersal thresholds observed in our study area, climate warming appears poised to cause extensive retraction and fragmentation of pika populations in the greater Lake Tahoe area within decades (bottom panels).