Table 2. Relationships in univariate spatial models between the slope of the power and semi-logarithmic species-area relationships (SARs), and measures of the rate of increase in habitat heterogeneity (from 10 km to 290 km quadrats); temperature; normalized difference vegetation index (NDVI, a measure of plant productivity); human population density, and species richness. Model fit is measured by Akaike Information Criteria (AIC), and we report ΔAIC values, i.e., the difference between the focal model’s AIC and that of the best fitting model, i.e., that with the smallest AIC. These exploratory analyses were conducted to decide which form of each variable should be included in subsequent multiple regression analyses. The selected variables, based on AIC values, were: increase in broad habitat diversity, summer temperature (10 km grain), annual NDVI (10 km grain), log10 human density (10 km grain), and species richness (10 km grain). Parameter estimates for the intercept and predictor variables are provided, with positive and negative effects indicated by + and – respectively. Note that r² values cannot be calculated from these spatial models, but are reported for nonspatial equivalents solely to give an indication of explanatory power.
| |
| |
|
Predictor |
Spatial
grain (km) |
Slope
of power SAR (z) |
Slope
of semi-log SAR (m) |
| Intercept |
Predictor |
ΔAIC |
r² |
Intercept |
Predictor |
ΔAIC |
r² |
| |
| Increase in fine habitat richness
|
10–290 |
0.110 |
+0.002 |
219.3 |
0.39 |
13.558 |
+0.165 |
278.4 |
0.36 |
| Increase in broad habitat richness |
" |
0.119 |
+0.007 |
207.1 |
0.25 |
14.141 |
+0.538 |
258.0 |
0.25 |
| Increase in fine habitat diversity
|
" |
0.109 |
+0.032 |
0.4 |
0.11 |
13.346 |
+2.333 |
10.1 |
0.16 |
| Increase in broad habitat diversity
|
" |
0.113 |
+0.043 |
0.0 |
0.08 |
13.668 |
+3.100 |
0.0 |
0.11 |
| Summer temperature |
10 |
0.356 |
-0.017 |
0.0 |
0.25 |
31.292 |
-1.223 |
0.0 |
0.29 |
| " |
290 |
0.292 |
-0.012 |
221 |
0.20 |
28.058 |
-1.000 |
241.5 |
0.25 |
| Annual temperature |
10 |
0.269 |
-0.017 |
20.2 |
0.16 |
24.921 |
-1.226 |
8.5 |
0.22 |
| " |
290 |
0.201 |
-0.011 |
36.5 |
0.13 |
22.131 |
-1.005 |
250.1 |
0.15 |
| Summer NDVI |
10 |
0.162 |
-0.067 |
20.7 |
0.12 |
16.0 |
-2.695 |
2.9 |
0.08 |
| " |
290 |
0.437 |
-0.509 |
13.8 |
0.20 |
32.983 |
-30.08 |
10.6 |
0.17 |
| Annual NDVI |
10 |
0.166 |
-0.086 |
0.0 |
0.70 |
16.619 |
-4.449 |
0.0 |
0.05 |
| " |
290 |
0.276 |
-0.295 |
24.1 |
0.80 |
23.672 |
-17.802 |
8.4 |
0.08 |
| Log10 human density |
10 |
0.137 |
-0.009 |
0.0 |
0.22 |
15.448 |
-0.628 |
0.0 |
0.25 |
| " |
290 |
0.217 |
-0.043 |
23.3 |
0.32 |
20.617 |
-2.850 |
74.1 |
0.31 |
| Species richness |
10 |
0.257 |
-0.002 |
0.0 |
0.88 |
24.187 |
-0.112 |
0.0 |
0.86 |
| " |
290 |
-2.116 |
+0.013 |
3225.5 |
0.32 |
138.64 |
+0.856 |
5826.2 |
0.43 |
|
| |
|