Fig 1.
Location of the Desert Tortoise Research Natural Area (DTRNA) in eastern Kern County, California.
The DTRNA is located at the western edges of the Mojave Desert and the geographical range of the desert tortoise.
Fig 2.
Topographical and vegetational map of the study area at the Desert Tortoise Research Natural Area.
Defined habitat strata within this area include: “alluvial fans” (white), “hills” (gray stipple), and “stream channels” (black). Note, “small stream channels” (1–2 m wide), which occur sparsely throughout the study site, are not shown. The black dashed line delineates the study area where plant diversity and abundance was estimated.
Table 1.
Estimates of perennial plant abundance, relative abundance, cover, and relative cover in the hill stratum sampled with 42 10 m2 quadrats at the Desert Tortoise Research Natural Area, eastern Kern County, California.
Table 2.
Estimates of perennial plant abundance, relative abundance, cover, and relative cover in the alluvial fan stratum sampled with 48 10 m2 quadrats at the Desert Tortoise Research Natural Area, eastern Kern County, California.
Table 3.
Estimates of perennial plant abundance, relative abundance, cover, and relative cover in the stream channel stratum sampled with 10 10 m2 quadrats at the Desert Tortoise Research Natural Area, eastern Kern County, California.
Table 4.
Estimates of perennial plant abundance, relative abundance, cover, and relative cover in the hill, alluvial fan, and stream channel strata combined sampled with 100 10 m2 quadrats at the Desert Tortoise Research Natural Area, eastern Kern County, California.
Table 5.
Estimates of abundance and relative abundance of annual plants during the first phenological period (1 March–30 April) at the Desert Tortoise Research Natural Area, eastern Kern County, California.
Table 6.
Foods eaten by desert tortoises during the first phenological period (1 March–30 April) at the Desert Tortoise Research Natural Area, eastern Kern County, California.
Fig 3.
Tortoise diet in relation to annual plant abundance during early spring.
Solid black bars show the relative abundance of each species found in the study area, whereas white bars indicate the relative abundance of each species in tortoise diet during the same period. Star symbols above bars denote plants in tortoise diet that were not detected in the plant survey.
Fig 4.
Tortoise diet in relation to perennial plant abundance during early spring.
Solid black bars show the relative abundance of each species found in the study area, whereas white bars indicate the relative abundance of each species in tortoise diet during the same period. Star symbols above bars denote plants in tortoise diet that were not detected in the plant survey.
Table 7.
Estimates of abundance and relative abundance of annual plants during the second phenological period (1 May–31 May) at the Desert Tortoise Research Natural Area, eastern Kern County, California.
Table 8.
Foods eaten by desert tortoises during the second phenological period (1 May–31 May) at the Desert Tortoise Research Natural Area, eastern Kern County, California.
Fig 5.
Tortoise diet in relation to annual plant abundance during mid-spring.
Solid black bars show the relative abundance of each species found in the study area, whereas white bars indicate the relative abundance of each species in tortoise diet during the same period. Star symbols above bars denote plants in tortoise diet that were not detected in the plant survey.
Fig 6.
Tortoise diet in relation to perennial plant abundance during mid-spring.
Solid black bars show the relative abundance of each species found in the study area, whereas white bars indicate the relative abundance of each species in tortoise diet during the same period. Star symbols above bars denote plants in tortoise diet that were not detected in the plant survey.
Table 9.
Estimates of abundance and relative abundance of annual plants during the third phenological period (1 June–30 June) at the Desert Tortoise Research Natural Area, eastern Kern County, California.
Table 10.
Foods eaten by tortoises during the third phenological period (1 June–30 June) at the Desert Tortoise Research Natural Area, eastern Kern County, California.
Fig 7.
Tortoise diet in relation to annual plant abundance during late-spring.
Solid black bars show the relative abundance of each species found in the study area, whereas white bars indicate the relative abundance of each species in tortoise diet during the same period. Star symbols above bars denote plants in tortoise diet that were not detected in the plant survey. (D) indicates that the plants were in a dried phenological state.
Fig 8.
Tortoise diet in relation to perennial plant abundance during late-spring.
Solid black bars show the relative abundance of each species found in the study area, whereas white bars indicate the relative abundance of each species in tortoise diet during the same period.
Star symbols above bars denote plants in tortoise diet that were not detected in the plant survey.
Table 11.
Foods eaten by adult desert tortoises during during spring 1992 (24 March–21 June) at the Desert Tortoise Research Natural Area, eastern Kern County, California.
Fig 9.
A snapshot of food plant availability and desert tortoise dietary selections throughout the spring foraging season.
All summary statistics were derived from Tables 4–10 and plants in the “Unknown plant spp.” category were not included in the estimates. Also, because tortoises largely favored plants in a succulent state, the numbers under the 3rd Phenological Period only represent annual plants that were in a succulent state. The photo shows an adult male desert tortoise eating from an individual Astragalus layneae. This plant species, which is a legume and herbaceous perennial, was one of the most preferred food plants during this study. As shown in the photo, these plants often grow in clusters of several individuals. The gray object on the posterior end of the tortoise’s shell is a radio telemetry transmitter (photo credit: W.B. Jennings).