Figure 1.
Graphical illustration of the method used to compute the multiple-site dissimilarity within regional cells of 250,000 km2.
The original data was the presence/absence of species in 1°×1° cells (the upper map represents species richness in the 1°×1° cells, i.e. alpha diversity). A grid of regional cells of 250,000 km2 was superimposed on the original compositional table, and multiple-site dissimilarity was computed among all 1°×1° cells belonging to each regional cell (central row). A multiple-site dissimilarity value (βSOR, βSIM or βNES) was thus assigned to each regional cell (lower map). Regional cells with a low number of 1°×1° cells (n<15) or species (gamma diversity<5) were discarded in subsequent analyses.
Figure 2.
Geographic variation in the beta diversity of regional cells of 250,000 km2, its components and species richness: (a) beta diversity (βSOR), (b) spatial turnover (βSIM), (c) nestedness-resultant dissimilarity (βNES) and (d) species richness in regional cells (i.e. gamma diversity).
The maps were spatially interpolated from original data points (as specified in Fig. 1) for representation by a mobile mean procedure. Colours are scaled from yellow (low values) to dark blue (high values). Grey areas represent no data.
Figure 3.
Relationship between (a) βSIM and regional species richness and (b) between βNES and regional species richness.
Dot size is proportional to the altitudinal range of considered cells.
Figure 4.
Latitudinal patterns of beta diversity and its potential explanatory variables: (a) total dissimilarity in assemblage composition (βSOR), (b) spatial turnover (βSIM), (c) nestedness-resultant dissimilarity (βNES), (d) temperature difference between LGM and the present conditions (TDIF), (e) current temperature (TPRES) and (f) current potential evapotranspiration (PET).
Fitted functions of piecewise regression are shown (gray lines).
Figure 5.
World latitudinal variation (latitude in absolute values) in the ratio between intra-regional turnover (βSIM) and nestedness (βNES) (logarithmic scale).
The sizes of the circles are proportional to the difference in temperature between the present and LGM scenarios. Note the change in both the sizes of the circles and the preponderance of nestedness patterns between 30 and 40 degrees of latitude.
Figure 6.
Partitioning of the variation in βSIM and βNES that can be explained by the significant predictors (see Table 1).
TPRES = Mean annual temperature for current times; TPAST = Mean annual temperature for the LGM period; TDIF = Temperature difference between the current and LGM conditions; PET = Current mean annual potential evapotranspiration; PREC = Current annual precipitation; and ARANGE = Current altitudinal variability.
Table 1.
Pearson correlation coefficients between each explanatory variable and both beta-diversity measures for the complete set of world data (Total) and the regional cells above (>37th) and below (<37th) the 37th parallel.
Table 2.
Percentage of variability (%var) explained by the variables that are significantly correlated with βSIM or βNES (see Table 1) for the regional cells above (>37th) and below (<37th) the 37th parallel.