Electronic supplemental material
Title: Abundance-area relationships in bird assemblages along an Afrotropical elevational
gradient: space limitation in montane forest selects for higher population densities
Authors: Michal Ferenc, Jon Fjeldså, Ondřej Sedláček, Francis Njie Motombi, Eric Djomo
Nana, Karolína Mudrová and David Hořák
Corresponding author e-mail: david.horak@natur.cuni.cz
Appendix 1 Analyses utilizing abundance estimates based on a distance sampling protocol.
Fig. A1.1: Comparison between observed and distance sampling based estimates of mean
abundances of passerine species occurring along the elevational gradient of Mt. Cameroon
(Spearman´s rho = 0.42, n = 59, p < 0.001). Estimates were based on detection functions
fitted by the Distance v6.2 software (Thomas et al. 2010) for species with at least 10
detections. The outliers (depicted as stars) represent rarely or quietly vocalizing species
(Cya_ori, Elm_alb, Mus_adu, Nes_she, Plo_ins), or species occurring in small flocks, i.e. with
clustered occurrences (Phy_poe, Phy_pol, And_tep). The first five species have their
elevational midpoint in the montane forest (above 1600 m a.s.l.), while the latter three have
their elevational midpoint at mid-elevations (all have midpoint above 1300 m a.s.l.). Note
the unrealistic mean abundance estimates based on detection functions (x-axis) for these
species. Species abbreviations: And_tep: Andropadus tephrolaemus, Cya_ori: Cyanomitra
oritis, Elm_alb: Elminia albiventris, Mus_adu: Muscicapa adusta, Nes_she: Nesocharis
shelleyi, Phy_poe: Phyllastrephus poensis, Phy_pol: Phyllastrephus poliocephalus, Plo_ins:
30
oPhy_pol
20
o And_tep
oPhy_poe
oPlo_ins
o Elm_alb
10
Observed mean abundance
40
50
Ploceus insignis.
Nes_she
o
0
50
Cya_ori
o Mus_adu
o
100
Estimated mean abundance
150
Fig. A1.2: Abundance-range size relationship of passerine species occurring along the
elevational gradient of Mt. Cameroon (Spearman´s rho = -0.25, n = 108, p < 0.05).
Abundance estimates are derived from a distance sampling protocol for species with at least
10 detections. Note that range sizes (x-axis) are log transformed, estimated abundances (yaxis) are square-root transformed. The depicted trend is a regression line fitted by the
ordinary least squares method. Grey triangles represent endemic species or sub-species.
300
250
Estimated abundance
200
150
100
50
5
1
2
10
Range size (1°x1° cells)
3
10
Fig. A1.3: Mean abundances of passerine species across elevations (Kruskal-Wallis chisquare: 18.00, df = 2, p < 0.001) divided into three groups based on the position of the
midpoint of their elevational distribution on Mt. Cameroon (see Methods). Abundance
estimates are derived from a distance sampling protocol for species with at least 10
200
150
100
50
0
Estimated abundance
250
300
detections.
lowland
middle
Midpoint position
montane
Appendix 2 References to primary resources used to determine the upper and lower
elevational limits of occurrence of passerines on Mt. Cameroon
1. Bannermann, D.A. 1915. Report on the birds collected by the late Mr. Boyd
Alexander (Rifle Brigade) during his last expedition to Africa - Part IV. The birds of
Cameroon Mountain. - Ibis 57: 473-526.
2. Bayly, N. and Motombe, F. N. 2004. Final report of an ornithological survey of Mount
Cameroon. - Wildlife Conservation Society.
3. Boulton, R. and Rand, A. L. 1952. A collection of birds from Mount Cameroon. Fieldiana 34: 35-64.
4. Eisentraut, M. 1973. Die Wirbeltierfauna von Fernando Poo und Westkamerun.
Bonner -Zoologische Monographien, 3.
5. Serle, W. 1950. A contribution to the ornithology of the British Cameroons. - Ibis 92:
602-638.
6. Serle, W. 1964. The lower altitudinal limit of the montane forest birds of the
Cameroon Mountain, Weat Africa. - Bulletin of the British Ornithologists‘ Club 84: 8791.
7. Stuart, S.N. 1986. Conservation of Cameroon montane forests. - International Council
for Bird Preservation, Cambridge, UK.
8. Young, CH.G. 1946. Notes on some birds of the Cameroon Mountain district. - Ibis 88:
348-382.
Appendix 3 Assemblage-level abundance-range size relationships along elevations
Fig. A3: Abundance-range size relationships of individual passerine bird assemblages along the elevational gradient of Mt. Cameroon. a) 350 m
a.s.l.: Spearman´s rho = 0.39, n= 53, p < 0.01; b) 650 m a.s.l.: rho = 0.26, df = 61, p < 0.05; c) 1100 m a.s.l.: rho = -0.20, df = 50, p = 0.15; d) 1500
m a.s.l.: rho = -0.40, n= 34, p < 0.05; e) 1850 m a.s.l.: rho = -0.37, n= 32, p < 0.05; f) 2200 m a.s.l.: rho = -0.14, n= 21, p = 0.54. Trends are
depicted by regression lines fitted by the ordinary least squares method. Note log-scale used on x-axes and square-root transformation on yaxes.
50
45
40
35
30
a) 350 m
b) 650 m
c) 1100 m
d) 1500 m
e) 1850 m
f) 2200 m
25
20
15
10
Abundance
5
1
50
45
40
35
30
25
20
15
10
5
1
1
10
2
3
10
1
10
2
Range size (1°x1° cells)
10
3
1
10
2
10
3