Vegetation zonation with elevation has shifted over the last 40,000 years in the Grand Canyon. Evidence from 89 middens (the elevation and radiocarbon ages of which are shown as data points)
depicts a clear pattern of individualistic species response to climate change. These findings from packrat midden research challenge the ecological theory that biological communities retain their integrity during times of change- in other words, they
migrate or are displaced en masse. Rather, the fossil record shows that biological communities are loose amalgamations of species with similar physiological tolerances; these amalgamations reorganize into both similar and different combinations during
times of change.
Graphic adapted from Cole .
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