Journal of Biogeography
SUPPORTING INFORMATION
Importance of biotic interactions in species distribution models: a test of the Eltonian
noise hypothesis using parrots
Carlos B. de Araújo, Luiz Octavio Marcondes-Machado and Gabriel C. Costa
Appendix S1 Methods for selection of parrot species for this study, the plant species of their
diet, and estimation of diet richness.
We have chosen a subsample of the species reported by da Silva (1995), based on two datasets: (1) presence of the species over a wide range of cerrado habitats (Braz & Cavalcanti,
2001; Lopes & Braz, 2007; Olmos & Brito, 2007; Lopes et al., 2008; Pacheco & Olmos,
2010; Telles & Dias, 2010); and (2) availability of data on the species’ diet. In order to select
plant species to add to each parrot model, we considered an extensive review of parrot diet
studies (Roth, 1984; Galetti, 1993, 1997; Barros, 1995; Santos, 2001; Ragusa-Netto, 2004,
2006, 2008; Ragusa-Netto & Fecchio, 2006; Paranhos et al., 2007, 2009; Bianchi, 2009;
Seixas, 2009; da Silva, 2009; Antas et al., 2010; de Araújo & Marcondes-Machado, 2011; de
Araújo, 2011). We examined a total of 2756 feeding bouts published in these 17 papers,
which registered the consumption of 275 different plant species by the 11 parrot species
analyzed. We used the number of feeding bouts in order to measure the quality of the paper,
and we chose papers that had at least 30 feeding bouts, as we felt that papers that presented a
sample size smaller than 30 would not have enough sampling effort in order to minimally
describe a species’ diet. Also, all of these papers have a sampling duration of at least one year
(with the exception of da Silva, 2011, which did not sample in November and December
during the four years of data acquisition), even though not all of them presented feeding
records for every sampled month.
Not every plant in the diet of a species may have an effect on its distribution. A food
resource used in large quantities should be of greater importance for the species’ maintenance
in an area, as higher consumption indicates higher dependence on that resource. On the other
hand, a rarely used resource should not reflect dependence, and therefore may not improve a
distribution model. In order to select proper plant species to add to each parrot model, we had
to take this into account, as only key plant species could potentially explain the distribution of
a parrot species, even in generalist species. We therefore created an index based on both the
proportion of feeding records as well as the number of different localities in which a parrot
species used a specific plant. The most important plant species in the parrot’s diet were the
ones with high consumption over a large number of studies and localities (when more than
one study was available). To do this, we first calculated the proportion of feeding bouts (pi)
of each plant species, for each study:
pi = number of feeding bouts / total bouts
(1)
We then standardized this value by multiplying each pi by a factor F; this varied between
studies, and was the reciprocal of the maximum pi found in the study (eq. 2). That way, the
importance of each plant in each study (I′i) varied between 0 and 1.
F = 1 / pi-max
(2)
I′i = pi × F
(3)
We summed the values of I′i (eq. 3) for each plant species, so that we considered the consumption of a plant in multiple studies. By so doing, we allowed that a key plant in multiple localities could be chosen, even when it did not represent the most-used item in any of the individual studies/localities. Next, we selected for use as biotic variables for each parrot species in
our modelling exercise, plants with a value of I higher than 0.7. This value was select to
ensure that each parrot species would have at least one plant species selected. All plant
species used in the modelling and their corresponding parrot species are listed in Table S1.
In order to allow comparable estimations of diet breadth among parrot species across
studies, we performed a rarefaction analysis. Rarefaction has proven to be an effective approach to make diversity comparisons between data of different sample sizes (Legendre &
Legendre, 1998; Krebs, 1999). We rarefied all diet richness data from the original sample
size to a sample size of 30, using ECOLOGICAL METHODOLOGY 5.2 (Kenney & Krebs, 2000).
We obtained a standardized estimation of diet richness for a sample size of 30 samples. In
other words, we obtained an estimative of how many different plant species we would have if
we had a sample size of 30. For this analysis, we were not able to obtain the number of feeding bouts for Forpus xanthopterygius, as the data found only presented the months in which
the resources were used, so this species was not used in the regression analysis. Also, data
from Diopsittaca nobilis were obtained from an ongoing study (P.A. Silva, Universidade do
Oeste Paulista, unpubl. data), and the data contained only the two most-used plant species.
We therefore did not use this species in the analysis.
Table S1 Total unique localities gathered for each key plant species, the AUC value for the
plant model, parrot species the plant model was used as biotic variable, and the importance
index of that plant species in the parrot’s diet, for 24 species of parrot in the Brazilian
cerrado.
Plant species
Total
AUC
Parrot species
Index (I)
Astronium fraxinifolium
Tabebuia heptaphylla
Tabebuia impetiginosa
Vitex cymosa
Psidium guajava
Orbignya speciosa
Vatairea macrocarpa
Buchenavia capitata
Scheelea phalerata
Caryocar brasiliense
Mimosa claussenii
Chorisia speciosa
Inga vera
Ochroma pyramidale
Protium heptaphyllum
Syagrus romanzoffiana
Melia azedarach
Syzigium cumini
Cecropia pachystachya
Ficus guaranítica
Mauritia flexuosa
Croton floribundus
Dicella bracteosa
Pachystroma longifolium
79
24
94
48
78
19
53
41
15
109
75
30
292
58
422
58
37
25
169
37
33
125
38
46
0.950
0.931
0.935
0.913
0.887
0.833
0.900
0.925
0.795
0.972
0.987
0.920
0.855
0.926
0.886
0.964
0.924
0.925
0.942
0.953
0.886
0.976
0.955
0.972
Amazona aestiva
Amazona aestiva
Amazona aestiva
Amazona aestiva
Ara ararauna
Aratinga aurea
Aratinga aurea
Ara chloropterus
Anodorhynchus hyacinthinus
Alipiopsitta xanthops
Alipiopsitta xanthops
Brotogeris chiriri
Brotogeris chiriri
Brotogeris chiriri
Brotogeris chiriri
Brotogeris chiriri
Diopsittaca nobilis
Diopsittaca nobilis
Forpus xanthopterygius
Forpus xanthopterygius
Orthopsittaca manilata
Pionus maximiliani
Pionus maximiliani
Pionus maximiliani
1.00
0.93
0.96
1.07
0.84
1.00
1.00
0.83
0.76
1.09
0.88
1.10
1.00
1.00
1.00
1.33
n/a
n/a
1.00
0.71
1.00
0.89
1.00
0.72
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