Figure 44.5: Species Composition Changes as the Climate Changes (A) Fossilized plant remains extracted from ancient packrat middens indicate that 14,000 years ago, when the climate was moist, valleys in the U.S.–Mexico Borderlands held lakes whose shores were clothed in piñon–juniper woodland. (B) In today’s more arid climate, the lakes have dried up and the woodland has given way to desert grassland—and more recently to shrubland, following human disturbance (see the opening story of Chapter 41).