Table 2. Description of spatial variables, data sources, method of calculation, and predicted influence on great ape density.
|
Variable type |
Variable name | Description | Data source |
Method of calculating variable value and variable summary statistics |
Predicted influence on great ape density |
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| Survey site–specific |
Great ape sign |
Number of gorilla or chimpanzee nests per sampling unit (transect or recce segment) |
Survey data sets | Counts per sampling unit | Response variable (note that effectively nest density was the response variable, as effort (kilometers walked) and detectability (effective strip half-width) associated with each count were included as an offset term in each model) |
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| Gorilla | Chimpanzee | |||||||||
| Min. | 0 | 0 | ||||||||
| 1st Qu. | 0 | 0 | ||||||||
| Median | 0 | 0 | ||||||||
| Mean | 2.254 | 1.219 | ||||||||
| 3rd Qu. | 1 | 1 | ||||||||
| Max. | 114 | 58 | ||||||||
|
Time (year of survey) |
Calendar year | Survey data sets and reports |
Calendar year survey was conducted | Gorilla or chimpanzee density negatively associated with surveys completed in recent years |
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| Min. | 1st Qu. | Median | Mean | 3rd Qu. | Max. | |||||
| 2003 | 2005 | 2006 | 2007 | 2010 | 2013 | |||||
| Guards | Whether or not a site has guards |
Knowledge of sites | Yes or no | Gorilla or chimpanzee density positively associated with sites that have guards |
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| N: | 2407 | |||||||||
| Y: | 3412 | |||||||||
|
Canopy height |
Forest canopy height |
M. Simard, N. Pinto, J. B. Fisher, A. Baccini, Mapping forest canopy height globally with spaceborne lidar. J. Geophys. Res. 116, G04021 (2011) |
0–62 m high across the region, 1-km spatial resolution; from 2005 satellite data |
Gorilla or chimpanzee density positively associated with areas with taller tree cover (intact forest) |
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| Min. | 1st Qu. | Median | Mean | 3rd Qu. | Max. | |||||
| 0 | 27 | 34 | 30.25 | 37 | 46 | |||||
| Slope | Slope of the terrain | Derived from Elevation (see below) |
0–25°, 90-m spatial resolution | Gorilla or chimpanzee density negatively associated with increasing slope |
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| Min. | 1st Qu. | Median | Mean | 3rd Qu. | Max. | |||||
| 0 | 1.066 | 2.203 | 3.287 | 4.043 | 25.309 | |||||
| Elevation | Elevation above sea level |
http://srtm.csi.cgiar.org/index.asp, version 4 |
0–1,126 m, 90-m spatial resolution | Gorilla or chimpanzee density negatively associated with increasing elevation |
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| Min. | 1st Qu. | Median | Mean | 3rd Qu. | Max. | |||||
| 0 | 333 | 493 | 451.9 | 607 | 1,126 | |||||
| HII | Aggregate score for a suite of variables (see data source) |
Last of the Wild data version 2 (http://sedac.ciesin.columbia.edu/wildareas/downloads.jsp#infl) |
HII value corresponding to sample unit location, 1-km spatial resolution |
Density negatively associated with increasing HII (corresponding to higher levels of human influence) |
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| Min. | 1st Qu. | Median | Mean | 3rd Qu. | Max. | |||||
| 1 | 3 | 5 | 6.485 | 9 | 25 | |||||
|
Distance to road |
Proximity to roads |
World Conservation Monitoring Centre data sets (Interactive Atlases for Central Africa) and local adjustments for errors, per year 2003–2013 |
Distance to the nearest road (km) in year of survey |
Gorilla or chimpanzee density positively associated with increasing distance from roads |
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| Min. | 1st Qu. | Median | Mean | 3rd Qu. | Max. | |||||
| 0 | 4.355 | 11.820 | 14.588 | 22.505 | 80.290 | |||||
| HPD | Number of people per km2 |
Gridded Population of the World version 4 (http://sedac.ciesin.columbia.edu/data/collection/gpw-v4) |
Population value (/km2) corresponding to sample unit location, 1-km spatial resolution |
Gorilla or chimpanzee density negatively associated with sites with a higher overall human population density |
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| Min. | 1st Qu. | Median | Mean | 3rd Qu. | Max. | |||||
| 0.598 | 1.470 | 3.427 | 3.951 | 5.230 | 30.543 | |||||
|
Eat gorilla/Eat chimpanzee |
Whether or not gorilla or chimpanzee meat is consumed |
Knowledge of areas | Yes or no | Gorilla or chimpanzee density positively associated with areas where they are not eaten (species-specific analysis) |
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| Gorilla | Chimpanzee | |||||||||
| N: | 396 | 811 | ||||||||
| Y: | 5423 | 5008 | ||||||||
| Ebola | Suspected EVD outbreak occurred in previous 20 years |
Locations of known and suspected EVD outbreaks in Gabon and Congo |
Yes or no | Gorilla or chimpanzee density positively associated with sites where EVD outbreaks did not occur |
||||||
| N: | 5439 | |||||||||
| Y: | 380 | |||||||||
| Country- specific |
Country | Name of country | Not available | Unique value assigned per country | Gorilla or chimpanzee density positively associated with more developed, less corrupt countries where conservation is higher on the agenda |
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| Sampling units per country: | ||||||||||
| Cameroon | 1961 | |||||||||
| CAR | 146 | |||||||||
| Congo | 1476 | |||||||||
| E. Guinea | 83 | |||||||||
| Gabon | 2153 | |||||||||
| Transparency | Degree of corruption |
Transparency International’s Corruption Perceptions Index (CPI) 2003–2013 (year-specific for survey site) (www.transparency.org/policy_research/surveys_indices/cpi) |
Ranges from 0 to 10. Smaller values indicate higher levels of corruption |
Gorilla or chimpanzee density negatively associated with a lower CPI (corresponding to higher levels of corruption) |
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| Min. | 1st Qu. | Median | Mean | 3rd Qu. | Max. | |||||
| 1.80 | 2.20 | 2.45 | 2.52 | 3.00 | 3.50 | |||||
| Regional proxies |
Latitude | Latitude coordinate | Calculated in GIS | Approx. centroid of each transect or recce segment |
Not applicable | |||||
| Min. | 1st Qu. | Median | Mean | 3rd Qu. | Max | |||||
| −4.582 | −1.974 | 0.991 | 0.748 | 2.594 | 6.151 | |||||
| Longitude | Longitude coordinate | Calculated in GIS | Approx. centroid of each transect | Not applicable | ||||||
| Min. | 1st Qu. | Median | Mean | 3rd Qu. | Max | |||||
| 9.248 | 11.464 | 13.706 | 13.422 | 14.999 | 17.788 | |||||