. Biology of the Heteromyidae. Heteromyidae. HETEROMYID FORAGING 561. 15,000 10 Fig. 3.—Average seed densities per m- in seventeen microhabitats in the Sonoran Desert. The values are extrapolated from numerous smaller soil samples or small seed traps as though they were for an entire square meter, but do not imply that such densities actually occur over an entire square meter (from Reichman, 1984). The microhabitats are 1 — NW of Larea bush, 2 —SE of Larrea bush, 3 —NW of Ambrosia bush, 4 —SE of Ambrosia bush, 5—area between bushes, 6 —normally dry wash, 7 —NW of small obstruction, 8 —SE of ob
. Biology of the Heteromyidae. Heteromyidae. HETEROMYID FORAGING 561. 15,000 10 Fig. 3.—Average seed densities per m- in seventeen microhabitats in the Sonoran Desert. The values are extrapolated from numerous smaller soil samples or small seed traps as though they were for an entire square meter, but do not imply that such densities actually occur over an entire square meter (from Reichman, 1984). The microhabitats are 1 — NW of Larea bush, 2 —SE of Larrea bush, 3 —NW of Ambrosia bush, 4 —SE of Ambrosia bush, 5—area between bushes, 6 —normally dry wash, 7 —NW of small obstruction, 8 —SE of obstruction, 9 —natural depression, 10—area of extensive rodent digging, 11—upper 2 mm of soil, 12 —upper 2 cm of soil, 13 —seed trap in open area, 14 — trap NW of Larrea bush, 15—trap NE of Larrea bush, 16—trap SE of Larrea bush, 17—trap SW of Larrea bush. vores by evolving physical traits that pro- mote their distribution into microhabitats which are unacceptable to rodents. Extrinsic seed characteristics such as clumping and microhabitat distribution ap- pear to be very important for heteromyid foraging. As noted in an earlier section, larg- er bipedal species preferentially harvest seeds from high density patches while qua- drupedal pocket mice include low density patches. Applying economic principles to foraging, Price's (1983^) model of patch choice predicts that body size should gen- erally affect the optimal degree of special- ization on dense, profitable seed patches. One attempt to detect specializations on patch densities in the field (Frye and Ro- senzweig, 1980) failed, perhaps because a single millet seed on the soil surface may be perceived as a profitable "patch" relative to what is normally available (cf. Bowers et al., 1987). Movement patterns of free-ranging animals (Table 2, Bowers, 1982; Thomp- son, 1982a, 1985) suggest that larger species are utilizing fewer of the available seed patches than are smaller species.
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