Biodiversity in a Changing Climate: Linking Science and Management in Conservation by

Language: eng
Format: azw3
ISBN: 9780520278851
Publisher: University of California Press
Published: 2015-06-15T16:00:00+00:00

FIGURE 8.1: Location of the Deep Canyon Transect. Located at the transition between the South Coast Peninsular Ranges and Colorado Desert, Southern California. Basemap source: ESRI.

FIGURE 8.2: The range of vegetation types surveyed along the Deep Canyon Transect. A. Chaparral and oak-conifer woodland (elevation 1800 m). B. Chaparral and pinyonjuniper woodland (elevation 1200 m). C. Mid-elevation desert scrub (elevation 900 m). D. Sonoran desert scrub and Palo Verde Wash (elevation 200 m).

To provide context for our bird observation data, we analyzed temperature and precipitation data from two local weather stations, one on the desert floor at an elevation of 292 m and one in the mountains at an elevation of 1640 m (WRCC 2007, M. Fisher, pers. comm.). We tested long-term trends for maximum temperature (yearly and spring averages of mean monthly maximum temperatures), minimum temperature (yearly and spring averages of mean monthly minimum temperatures), and precipitation (July–June rain-year). To compare cumulative precipitation between the two survey periods, we summed precipitation over a five-year period (each period containing the three survey years plus two preceding years).

To test for distributional shifts, we used methods that were robust to any differences in absolute abundance between the two time periods that might have arisen, for example, due to observer differences. For each species, we calculated abundance as the average number of birds detected over a 1-km transect for each of the 15 sites, for each three-year period. We calculated a weighted mean elevation for each species for each three-year period as the sum of elevations at which the species was present, each multiplied by the abundance of that species at that site, and divided by the total abundance for that species over all sites. We constructed cumulative frequency distribution curves for each species by summing its proportional abundance from its lowest to highest altitudinal occurrence (Box 8.1). Thus, cumulative frequency at the highest elevation site is always 100%. A Kolmogorov–Smirnov (K-S) test was used to test for any difference in the cumulative elevational distribution of individual species between the two periods (Box 8.1), and a paired-sample t-test was used to test for upward elevational shifts in weighted mean elevations at the community level. Three community groups were considered: All species, desert species alone, and montane species alone.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.