Table 2 Description of spatial variables, data sources, method of calculation, and predicted influence on great ape density.
Variable
type
Variable nameDescriptionData sourceMethod of calculating
variable value and variable
summary statistics
Predicted influence on great
ape density
Survey
site–specific
Great ape
sign
Number of gorilla or
chimpanzee nests
per sampling unit
(transect or recce
segment)
Survey data setsCounts per sampling unitResponse 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)
GorillaChimpanzee
Min.00
1st Qu.00
Median00
Mean2.2541.219
3rd Qu.11
Max.11458
Time (year
of survey)
Calendar yearSurvey data sets and
reports
Calendar year survey was conductedGorilla or chimpanzee density
negatively associated with
surveys completed in recent
years
Min.1st Qu.MedianMean3rd Qu.Max.
200320052006200720102013
GuardsWhether or
not a site
has guards
Knowledge of sitesYes or noGorilla or chimpanzee density
positively associated with
sites that have guards
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)
Min.1st Qu.MedianMean3rd Qu.Max.
0273430.253746
SlopeSlope of the terrainDerived from Elevation
(see below)
0–25°, 90-m spatial resolutionGorilla or chimpanzee density
negatively associated with
increasing slope
Min.1st Qu.MedianMean3rd Qu.Max.
01.0662.2033.2874.04325.309
ElevationElevation above sea
level
http://srtm.csi.cgiar.org/index.asp,
version 4
0–1,126 m, 90-m spatial resolutionGorilla or chimpanzee density
negatively associated with
increasing elevation
Min.1st Qu.MedianMean3rd Qu.Max.
0333493451.96071,126
HIIAggregate 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)
Min.1st Qu.MedianMean3rd Qu.Max.
1356.485925
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
Min.1st Qu.MedianMean3rd Qu.Max.
04.35511.82014.58822.50580.290
HPDNumber
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
Min.1st Qu.MedianMean3rd Qu.Max.
0.5981.4703.4273.9515.23030.543
Eat gorilla/Eat
chimpanzee
Whether or
not gorilla or
chimpanzee
meat is consumed
Knowledge of areasYes or noGorilla or chimpanzee density
positively associated with
areas where they are not
eaten (species-specific
analysis)
GorillaChimpanzee
N:396811
Y:54235008
EbolaSuspected
EVD outbreak
occurred in
previous
20 years
Locations of known
and suspected EVD
outbreaks in Gabon
and Congo
Yes or noGorilla or chimpanzee density
positively associated with
sites where EVD outbreaks
did not occur
N:5439
Y:380
Country-
specific
CountryName of countryNot availableUnique value assigned per countryGorilla or chimpanzee density
positively associated with
more developed, less
corrupt countries where
conservation is higher on
the agenda
Sampling units per country:
Cameroon1961
CAR146
Congo1476
E. Guinea83
Gabon2153
TransparencyDegree 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)
Min.1st Qu.MedianMean3rd Qu.Max.
1.802.202.452.523.003.50
Regional
proxies
LatitudeLatitude coordinateCalculated in GISApprox. centroid of each transect
or recce segment
Not applicable
Min.1st Qu.MedianMean3rd Qu.Max
−4.582−1.9740.9910.7482.5946.151
LongitudeLongitude coordinateCalculated in GISApprox. centroid of each transectNot applicable
Min.1st Qu.MedianMean3rd Qu.Max
9.24811.46413.70613.42214.99917.788