Geoscience Reference
In-Depth Information
120
North America
25
Australia
100
20
80
15
60
40
10
20
5
0
0
200
100
180
160
140
Africa
South America
80
120
60
100
80
40
60
40
20
20
0
0
10
-3
10
-2
1 0 0
2
10
3
10
4
10
-3
10
-2
1 0 0
2
10
3
10
4
Body Mass (kg)
Body Mass (kg)
Figure 3.1
Body mass distributions of herbivorous mammals for four continents, showing dispropor-
tionate extinctions of species in the larger size classes (black shading) in the Americas and Australia,
but not in Africa (adapted from Johnson 2009).
Australia, Eurasia, North America, and South America. It is likely that massive ecosystem
reorganisation took place in response to the warming temperatures of the early Holocene
and the loss of large predators, megaherbivores, and other 'ecosystem engineers' (Table 3.1).
For example, without large herbivores, many forests in Europe may have changed from open,
park-like mosaics, to dense, closed-canopy forests with little habitat for light-loving species
(Vera 2000). In North America and Australia, the accumulating, uncropped plant biomass
may have led to massive wildfires, while the productive, grassy mammoth steppe of Eurasia
became a mossy, waterlogged tundra where few plants could thrive (Robinson et al. 2005,
Rule et al. 2012, Zimov et al. 2012). The loss of predators would have cascaded through ecosys-
tem structure and function (Ripple and Van Valkenburgh 2010). Further ecosystem changes
began from the mid-Holocene when crop cultivation and the domestication of animals
began, and the management of forests and rangelands for human benefit transformed many
landscapes (see Chapters 6 and 7). Despite these dramatic changes, there is little evidence of
plant extinction in the late quaternary until recent centuries (Jackson and Weng 1999).
The co-occurrence of dramatic environmental change, human expansion and megafaunal
extinction has led to ongoing debate over the causes of megafaunal loss. On balance, it seems
unlikely that climate alone drove the extinctions, and multiple lines of evidence suggest that
human hunters played a significant role (Barnosky et al. 2004, Koch and Barnosky 2006,
Prescott et al. 2012). Perhaps the most compelling piece of evidence for this is that the climate
of the current interglacial is neither more extreme, nor was the warming more rapid, than
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