Figure 1.
Projected Range Transformations
Frequency distribution of projected range transformations for 8,750 bird species by 2100 across the four MA socioeconomic scenarios (histograms, left axis). Within each bar, the height of the shading refers to proportion of projected transformation due to habitat conversion (dark gray) or climate change (light gray). The count of species with exactly zero range transformations is represented as open bars and separated by a gap from the bars representing >0 to ≤100% range transformation. Points with error bars give the average (± SE) current geographic range size (in km2) for species in each range transformation category. Although none of the scenarios is likely to predict the actual pattern of land-cover change, they provide “broad confidence limits” that are likely to span the range of possible futures. The four scenarios are briefly described in Materials and Methods.
Table 1.
The Exposure of Birds to Projected Environmental Change
Figure 2.
Geographic Patterns and Projected Impact of Environmental Change
(A, B) Patterns of change in land cover due to land-use and climate change by 2100.
(C, D) The resulting potential impact for birds: the pattern of richness of species with projected range declines ≥50%. This represents the summed, current-day occurrence of qualifying species across a 0.5° grid. Patterns are given for the environmentally proactive “Adapting Mosaic” scenario (A, C), and the environmentally reactive “Order from Strength” scenario (B, D). Maps are in equal-area cylindrical projection. Colors in C and D vary from dark blue to dark red, and the legends provide labels for select colors along this continuous scale (minimum, ~1/3, ~2/3, maximum of data).
Figure 3.
Environmental Change, Avian Biogeography, and Loss in Range Size
Projected latitudinal pattern in type of global environmental change, geographic range size, species richness, and the resulting loss in geographic range size (8,750 bird species, 1° bands of latitude). Climate (cyan, on top and semitransparent) and land-use (red) changes between now and 2100 are evaluated for two scenarios: on the left, “Adapting Mosaic” (A, C, E), and on the right, “Order from Strength” (B, D, F). Top (A, B): Total area transformed (area plot, lighter color indicates overlap) and average (± SE) current geographic range size of species per latitudinal band (point and line plot); Middle (C, D): Average proportional loss of range size (area plot, lighter color indicating overlap) and total number of bird species whose range currently overlaps at each latitudinal band (point and line plot). Bottom (E, F): Count of species with ≥50% of range transformed jointly by climate change or land-use change (stacked area plot, coloration indicates the proportion of range area that is transformed by each land change type). Whereas climate change leads to a significant net change of habitat in the polar and temperate regions, the small numbers of bird species that live there on average have very large geographic ranges. Thus, proportional contractions in range size there are much smaller than for the vast majority of bird species that live in the tropics and experience significant reductions in their smaller range sizes due to land-use change. The outcome are many species with significant range reduction in the tropics and subtropics, because of the coincidence of habitat conversion with areas of high species richness. This is particularly the case in the environmentally reactive “Order from Strength” scenario, where large areas of land are converted to agriculture.