Revista de Biología Tropical, ISSN electrónico: 2215-2075, Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)
The geographic bias of mammal studies: a comparison
of a half a century of research on Palearctic and Neotropical mammals
José Guerrero-Casado
1, 2
*; https://orcid.org/0000-0002-2537-3116
Julián Monge-Nájera
1. Department of Zoology, University of Córdoba. Campus de Rabanales, 14071 Córdoba, Spain;
2. Departamento de Medicina Veterinaria. Facultad de Ciencias Veterinarias, Universidad Técnica de Manabí. Portoviejo,
Manabí, Ecuador; guerrero.casado@gmail.com; *Correspondence.
3. Laboratorio de Ecología Urbana UNED, 2050 San José, Costa Rica; julianmonge@gmail.com
Received 24-IX-2020. Corrected 23-I-2021. Accepted 29-I-2021.
Introduction: There are no studies that specifically compare research output of Palearctic and Neotropical
mammalogy; such comparison would be useful for informed decisions in conservation and management.
Objective: To compare the scientific documents and citations about Palearctic and Neotropical mammals over
half a century. Methods: We compared 50 years (1970-2019) of documents on 60 medium and large-sized
(heavier than 1 kg) mammal species, in Scopus and the Web of Science (WoS) Core Collection, considering
number of documents and four citation indicators at the species level (h-index, citation rate, total citations,
and citations per year). Results: We retrieved 13 274 documents in Scopus and 12 913 in WoS. We found that
Palearctic mammals have 3.77 times more documents than Neotropical species in Scopus (3.91 times in WoS),
and that the documents recorded 5.95 more total citations in Scopus (6.93 times more in WoS). Palearctic docu-
ments also record more yearly citations and a higher h-index in both Scopus and WoS. Scopus retrieved more
articles for Neotropical species (2 782 vs. 2 631 in WoS) and had more citations (28 120 vs. 24 977 in WoS);
differences for the citation indicators between regions were marker in WoS. The h-index and total citations are
greatly affected by how many studies are published, i.e. the region with more production is the one with higher
values. The Neotropical articles showed a greater growth rate in the last decade, decreasing the gap between
both regions. Conclusion: There is a regional bias in WoS and Scopus, which retrieve more articles and cita-
tions about Palearctic mammals than about Neotropical mammals; this bias is worse in WoS and means that an
urgent increase in indexed research about Neotropical species is needed to be on par with Palearctic research.
Key words: citation; geographical bias; Mammalia; research impact; scientometrics; wildlife conservation.
Previous studies have shown that, in the
field of natural resources, some regions of
the world are much more studied than others.
Forest biomes of North America and Europe
are generally more studied, whereas many
tropical ecosystems are severely understudied
(Lawler et al., 2016; Christie et al., 2020); and
therefore, the most biodiverse countries (often
located in tropical regions) are underrepre-
sented in the biodiversity conservation litera-
ture (Wilson et al., 2016; Reboredo, Romano,
& Armsworth, 2020). Reducing publication
biases could help to mitigate biodiversity loss
in tropical regions, often more threatened,
yet less studied (Sitas, Baillie, & Isaac, 2009;
Christie et al., 2020), because peer-reviewed
Guerrero-Casado, J., & Monge-Nájera, J. (2021). The geographic
bias of mammal studies: a comparison of a half a century of
research on Palearctic and Neotropical mammals. Revista
de Biología Tropical, 69(2), 391-402. DOI 10.15517/rbt.
DOI 10.15517/rbt.v69i2.43961
Revista de Biología Tropical, ISSN electrónico: 2215-2075 Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)
publications are an important component of
evidence-based policy to ensure the effective-
ness of conservation actions (Pullin, Knight,
Stone, & Charman, 2004; Wilson et al. 2016;
Christie et al., 2020).
There are multiple causes explaining dif-
ferential research effort among regions or
countries, including geographical and environ-
mental variables such as the remoteness and
accessibility of the study area, the presence of
protected areas, and biodiversity indexes (such
as the number of vertebrates species) of the
area (Martin, Blossey, & Ellis, 2012; Hickisch
et al., 2019), or socio-economic variables of
the countries such as the per capita income,
the research and development (R&D) invest-
ment, funding availability, and the number of
researchers itself (King, 2004; Guerrero-Casa-
do, 2017; Vinkler, 2018; Allik, Lauk, & Realo,
2020). Concerning wild animal species, there
are also important biases: birds and mammals,
threatened species, more abundant species,
organisms with larger distribution ranges, char-
ismatic or emblematic species, and large-bod-
ied species are overrepresented in the scientific
literature when compared with other animal
groups (Brooke, Bielby, Nambiar, & Carbone,
2014; Donaldson et al., 2016; dos Santos et al.,
2020). In addition to the total number of publi-
cations, the region also influences the citation
in conservation research papers: the countries
with a high gross domestic product (GDP) and
governance quality are more cited (Meijaard,
Cardillo, Meijaard, & Possingham, 2015). The
previously cited authors argued that countries
with these features invest more money in sci-
ence and usually have better scientific infra-
structure, facilitating the science production
with a visible high impact.
Currently, the most widespread indica-
tors used to measure the scientific impact of
research, universities, or journals, are based on
the number of citations and its derived indi-
ces, such as the journal impact factor and the
h-index, defined as the number of papers with
citation number h (Hirsch, 2005). However,
these indicators are debated by a part of the sci-
entific community owing to some weaknesses
and limitations (Alberts, 2013; Wouters et al.,
2019). One of these weaknesses is that there
are many variables not directly related to the
impact of articles (e.g., the article’s length, the
number of the authors, authors academic rank,
gender, race, and age) which affect the number
of citations (Borsuk, Budden, Leimu, Aars-
sen, & Lortie, 2009; Padial, Nabout, Siqueira,
Bini, & Diniz-Filho, 2010; Tahamtan, Afshar,
& Ahamdzadeh, 2016). Several studies have
also identified that the authors’ country of
affiliation is an important predictor of the
number of citations, meaning that citations are
positively related with high-income countries
(Pasterkamp, Rotmans, De Kleijn, & Borst,
2007; Tahamtan et al., 2016). This could be
explained by the better scientific infrastructure
and greater financial support of more devel-
oped nations (Padial et al., 2010; Tahamtan et
al., 2016). For instance, papers from the United
States of America usually attain higher citation
rates simply by the force of numbers, because
that country has a large research output, a
phenomenon known as ‘national citation’ (Pas-
terkamp et al., 2007; Abramo, D’Angelo, & Di
Costa, 2020).
But there are other reasons why research-
ers in richer countries appear to have a
higher impact. When impact indicators are
calculated only from databases such as Scopus
or Web of Science (WoS), many citations are
missed because they are in scientific papers
not included in these “first world” databases
(Monge-Nájera, & Ho, 2018). For example,
even though most Latin American journals are
indexed in regional databases such as Latin-
dex, Scielo or Redalyc, they are missing from
Scopus and WoS (Crespo-Gascón, Tortosa,
Guerrero-Casado, 2019), and, therefore, the
citations in Scopus and Wos are only a fraction
of the real impact of Latin American research
(Monge-Nájera, 2014).
Nearctic and Palearctic mammals are more
studied than mammals from other zoogeo-
graphic regions (Amori & Gippoliti, 2000),
and even though Neotropical mammals repre-
sent 29 % of all mammal species, only 12 %
of mammal conservation articles are focused
Revista de Biología Tropical, ISSN electrónico: 2215-2075, Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)
on them (Di Marco et al., 2017). These differ-
ences could be partly attributed to the different
scientific output between Palearctic (European)
and Neotropical (Latin American) countries.
However, there are no studies that specifically
compare research effort and citation among
Neotropical and Palearctic mammals. Our goal
in this paper is, therefore, to compare the
number of Palearctic and Neotropical papers,
and their citation rates, for large mammals’
research, and to do it over a long period of time
Palearctic and Neotropical species selec-
tion: Considering that latitude affects the bio-
diversity conservation literature (Di Marco et
al., 2017), we compared mammals from the
Western Palearctic region, which ranges from
Ireland to Western Russia (Baquero & Tell-
ería, 2001; Holt et al., 2013), with Neotropi-
cal mammals, from central Mexico to central
Argentina (Holt et al., 2013; Noguera-Urbano
& Escalante, 2017). For a valid comparison, we
only used medium and large-sized native mam-
mal species (i.e. with an adult body mass over 1
kg; Weng et al., 2020), because larger animals
are the most studied (Brooke et al., 2014), and
therefore better candidates for a valid compari-
son. Twenty-eight Palearctic species met these
selection criteria (Baquero & Tellería, 2001),
excluding exotic species whose native distribu-
tion range is located outside of this region (e.g.
Procyon lotor), and species native to Palearctic
Region but also located in other biogeographi-
cal regions (e.g. Alces Alces or Rangifer taran-
dus, also found in the Nearctic region).
Considering that the number of mammal
species is much higher in the Neotropical
Region, a similar number of mammal species
(32 species) was randomly selected to avoid
an unbalanced design. This selection was made
using the mammals of the Neotropical realm
including in the IUCN red list as a baseline
database, in which the 30 species were random-
ly selected. Similarly, exotic species located
in the Neotropical region were excluded, and
Neotropical native species that also occur in
others regions were also not considered (e.g.
Pecari tajacu and Puma concolor also occur
in the Nearctic). The 60 selected species were
listed in Digital Appendix 1.
Scientific literature search & citation
indicators: Using the scientific and common
names for each of the 60 species in the article
title, we retrieved all journal articles, confer-
ences and proceedings papers, books, and book
chapters published from 1970 to 2019, and
included in Scopus and the Web of Science
(WoS) Core Collection (the search was carried
out on April 2020), thus only primary scientific
literature was considered in the study. In both
databases and for each species separately, the
search used the scientific name and the most
used common names in the article title, which
ensured that the article topic is focused on the
species. Previous scientific works whose aims
were to identify patterns in wildlife research
efforts also used the scientific and common
names in the search criteria (e.g. Fleming &
Batemandos, 2016; Jarić, Roberts, Gessner,
Solow, & Courchamp, 2017; dos Santos et al.,
2020). The search criteria for every species
were detailed in Digital Appendix 1.
The first step was to obtain, from Scopus
and WoS separately, and for each document,
the publication year and the number of times it
has been cited according to the particular data-
base. From these data we calculated the aver-
age document citations per year (Cai, Chang, &
Yip, 2020) with this formula (Formula 1):
Formula 1
Then, for each species and for the whole
study period, in Scopus and WoS separately,
we obtained the total number of documents per
species (“documents”), how many times the
documents were cited (“total citations”), the
h-index (defined as the number of documents
with a citation number h, Hirsch, 2005), the
citation rate (Formula 2), and the average cita-
tions per year (citations/year).
Revista de Biología Tropical, ISSN electrónico: 2215-2075 Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)
Formula 2.
For each indicator, we also calculated a
regional ratio by dividing the mean values
of each indicator (documents, total citations,
citations per paper, h-index and citations/year)
for all the Palearctic mammal species, by the
mean values for all the Neotropical mammals.
This ratio can be considered as a measure
of the difference between both regions for
each indicator.
Statistical analysis: To compare the
growth in document production between both
regions, the study period was divided in five
decades (1970-1980; 1981-1990; 1991-2000;
2001-2010; 2011-2019), and we calculated the
growth rate using the slope of the regression (b)
between years and the number of documents.
The greater slope, the greater growth rate: this
allowed us to check the trend in each decade.
These calculations were done separately for
Scopus and WoS.
Three different statistical analyses were
applied: a) for each region, we compared WoS
and Scopus (independent variable) with Wil-
coxon paired tests (paired by species) for the
number of documents, citation rate, citations/
year, h-index, and total citations, which were
the dependent variables; b) Mann-Whitney U
tests were applied to compare the same five
indicators (dependent variables) between Pale-
arctic and Neotropical species (independent
variable) separately for Scopus and WoS; c)
four linear models (four for Scopus and four
for WoS) were applied to assess the influence
of number of documents on the other four indi-
cators (h-index, citation rate, total citations and
citations/year), which were used as response
variables. Bonferroni correction for multiple
comparisons were applied by multiplying the
original p-value by the number of simultane-
ously tested hypotheses (response variables)
(Chen, Feng, & Yi, 2017).
We used general linear models (GLM)
for the h-index, citation rate, and citations/
year, because the normality of the residuals
was confirmed, and generalized linear models
(GLM) for total citations as response variable,
using a negative binomial distribution with
log-link function, in which the homocedasticity
and the lack of overdispersion of the residu-
als were confirmed. In all these models, the
independent variables were the documents,
the region (Neotropical & Palearctic), and the
interaction (Region*Documents). Scatterplots
were generated to illustrate the effect of the
Region*Documents interaction on the response
variables. In all the statistical analysis, the spe-
cies was the experimental unit (N = 60) and the
statistical software was InfoStat (Di Rienzo et
al., 2020).
Overall results: The selected species
accounted for 13 274 and 12 913 documents in
Scopus and WoS respectively, of which 5 413
belong to Neotropical species (2 782 in Scopus
and 2 631 in WoS) and 20 774 to Palearctic
species (10 492 in Scopus and 10 282 in WoS).
Palearctic mammals have 3.77 and 3.91 times
more documents than Neotropical species in
Scopus and WoS, respectively. Palearctic arti-
cles accumulated a total of 228 069 and 167 546
citations in WoS and Scopus, respectively,
whereas Neotropical articles have 24 977 and
28 120 citations, which means 9.13 and 5.95
times more total citations for Palearctic species.
Temporal trends: In the 1970’s and
1980’s, the number of documents in the Neo-
tropical region was exceptionally low (75 and
112 documents in Scopus in 1970’s and 1980’s
respectively) with a poor increase (b 1970’s =
0.2; b 1980’s = -0.157 ), but in the last decade
the Neotropical growth rate was higher than
the rate for Palearctic articles (Table 1; Fig. 1).
The P/N Ratio was much greater in the first
three decades than in the last two, and it was
greater for WoS than Scopus, suggesting that
the differences between both regions are get-
ting smaller (Table 1). In the last decade, the
growth rate of Palearctic articles is near zero
Revista de Biología Tropical, ISSN electrónico: 2215-2075, Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)
(b = 0.333) in Scopus and negative in WoS (b
= -9.45), whereas for Neotropical articles the
growth rate was positive and more evident in
Scopus (b = 6.83) (Table 1; Fig. 1).
Comparison between Wos and Scopus:
For Neotropical species, Scopus had a great-
er number of documents, total citations, and
h-index than WoS, whereas no significant dif-
ferences were obtained in the citation rate and
citations/year (Table 2). For Palearctic species,
the number of documents was similar in both
databases, citations were greater in Scopus,
and after Bonferroni correction, citation rate,
h-index, and citations/year, marginally sig-
nificant differences between both databases
were obtained (Table 2). In both databases,
Palearctic mammals had more documents and
total citations, and higher citation rates, h-index
values and citations/year than Neotropical spe-
cies (Table 3). The Palearctic/Neotropical ratio
showed that the Palearctic mammals had 4.47
and 4.31 more articles and 7.95 and 6.79 more
citations in WoS and Scopus respectively, but
differences are less marked for citation rate,
h-index and citations/years (Table 3).
Effect of the number of documents and
region on the citation indicators: In all the
models, the variable Region was significant,
with greater values obtained for the Palearctic
mammals (Table 4). The variable Documents
influenced positively the h-index values and
total citations in both databases (Table 4).
However, the interaction between the variables
Region and Documents was also significant
in some models, which means that documents
affected the response variables in a differ-
ent way depending on the region (Table 4;
Fig. 2). According to these interactions, the
number of documents was more correlated
with the h-index in the Neotropical Region,
and with the total number of citations in the
Palearctic (Fig. 2).
Fig. 1. Temporal variation in the number of documents in Scopus and WoS for Palearctic (grey) and Neotropical (black)
mammal species selected in our study. The dashed lines indicate the tendency in each decade.
Revista de Biología Tropical, ISSN electrónico: 2215-2075 Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)
When comparing Neotropical and Pale-
arctic mammals, our results indicate that both
databases reported more articles about Pale-
arctic mammals. This result matches previous
findings from the last two decades: biodiversity
and the financial resources to study it are con-
centrated in opposite latitudes, and, as a result,
the lower biodiversity of Northern biomes is far
more studied than the higher biodiversity of the
less industrialized Tropical countries (Amori
& Gippoliti, 2000; King, 2004; Hickisch et
al., 2019; Christie et al., 2020). The Palearctic
realm is mainly formed by countries with high
per capita incomes, leading to a higher invest-
ment in research and development, and more
researchers, which in turn produce a higher
number of papers and citations (Prathap, 2017;
Allik et al., 2020). Therefore, the greater num-
ber of papers and citations of Palearctic species
could be to a good extent be explained by the
highest R&D investment of the countries of
this realm. Our results also showed that articles
Growth rate and regression slope value (b) for articles about Neotropical and Palearctic mammals
in Scopus and Web of Science (1970-2019)
Neotropical Palearctic
Ratio P/N
Nº Documents
Nº Documents
1970-1980 75 0.2 618 4.24 8.24
1981-1990 112 -0.157 1 093 5.15 9.76
1991-2000 227 2.56 2 098 17.55 9.24
2001-2010 726 9.68 3 016 12.54 4.15
2010-2019 1 583 6.83 3 533 0.333 2.23
1970-1980 162 1.22 613 9.77 3.78
1981-1990 313 0.103 1 429 4.67 4.57
1991-2000 494 4.15 2 185 10.95 4.42
2001-2010 622 8.33 3 290 15.07 5.29
2010-2019 1 216 3.38 3 564 -9.45 2.93
P/N Ratio = Palearctic articles / Neotropical articles.
Wilcoxon paired tests comparing indicators for Scopus and WoS separately. Corrected p-value
was calculated multiplying the p-value by 5
Neotropical Palearctic
Mean-dif SD Z Corrected p-value Mean-dif SD Z Corrected p-value
Documents 4.72 23.12 2.76 0.022 7.5 36.12 1.05 0.2974
Total citations 161.78 381.89 3.46 0.001 289.5 596.11 3.14 0.004
0.88 1.48 2.74 0.025 1 3.64 2.5 0.062
Citation rate -0.05 3.5 1.8 0.34 0.52 1.14 2.41 0.076
Citation/year -0.17 1.56 2.19 0.143 0.07 0.18 2.44 0.055
Mean-dif indicates the mean difference between Scopus and WoS calculated as Scopus - WoS (e.g. Scopus documents - WoS
documents). SD = standard deviation.
Revista de Biología Tropical, ISSN electrónico: 2215-2075, Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)
Mann-Whitney U tests comparing scientific impact indicators for Neotropical and Palearctic articles in WoS and Scopus.
Corrected p-value was calculated multiplying the p-value by 5
Web of Science
Neotropical Palearctic
Mean SD Median Mean SD Median
Documents 82.22 160.08 28 367.21 585.47 171.5 172.5 0.0005 4.47
Total citations 718.78 1501 254.5 5694 10462 2608 130 0.0005 7.92
Citation rate 8.23 4.09 8.34 13.96 4.6 14.01 149 0.0005 1.70
10.91 9.11 8.5 29.64 17.96 26 120.5 0.0005 2.72
Citations/year 0.72 0.32 0.74 1.13 0.32 0.98 150 0.0005 1.57
Scopus Mean SD Median Mean SD Median
Documents 86.94 150.17 34 374.71 574.89 173 171 0.0005 4.31
Total citations 880.56 1872 306.5 5983 10498 2990 139 0.0005 6.79
Citation rate 8.18 3.77 8.58 14.48 4.94 14.72 138 0.0005 1.77
11.78 9.85 9.5 30.64 17.87 28 132 0.0005 2.60
Citations/year 0.83 0.36 0.86 1.2 0.38 1.06 213 0.0025 1.45
SD = standard deviation. Ratio (P/N) is the result of dividing the mean values of Palearctic Region (P) by the mean values
of Neotropical Region (N).
Eight linear models using the different scientific impact indicators, separately obtained in Scopus and WoS,
as response variables. Corrected p-value was calculated multiplying the p-value by 4
Scopus WoS
Estimate SE t-value
Estimate SE t-value
Response variable: Citation rate
Intercept 7.51 0.88 8.54 0.004 8.081 0.867 9.321 <0.001
Region 6.32 1.31 4.82 0.004 5.249 1.305 4.024 0.0002
Documents 0.01 0.01 1.51 0.136 0.002 0.005 0.371 0.7118
Region* Documents -0.01 0.01 -1.13 0.265 -0.0001 0.005 -0.018 0.9855
Response variable: h-index
Intercept 6.51 1.31 4.99 0.004 6.6 1.22 5.39 <0.001
Region 13.79 1.95 7.08 0.004 12.96 1.84 7.03 <0.001
Documents 0.06 0.01 7.95 0.004 0.05 0.01 7.61 <0.001
Region* Documents -0.03 0.01 -4.17 0.004 -0.02 0.01 -3.48 0.004
Response variable: Citations/year
Intercept 0.751 0.074 10.186 0.004 0.69 0.06 10.85 <0.001
Region 0.449 0.11 4.081 0.004 0.39 0.1 4.04 <0.001
Documents -0.001 0.0001 2.111 0.156 0.001 0.001 0.99 0.3268
Region* Documents -0.001 0.0001 -2.038 0.184 -0.001 0.001 -0.62 0.5369
Response variable: Total citations
Intercept 5.31 0.181 642.6 0.004 5.23 0.179 29.28 0.004
Region 2.10 0.269 204.2 0.004 2.11 0.268 7.861 0.004
Documents 0.008 0.001 256.1 0.004 0.008 0.001 8.122 0.004
Region* Documents -0.006 0.001 -192.8 0.004 -0.006 0.001 -5.968 0.004
Estimates of the categorical variable Region were calculated using Palearctic as a reference value. SE = standard error.
Revista de Biología Tropical, ISSN electrónico: 2215-2075 Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)
about Palearctic mammals received more total
citations, more citations/year, and had a higher
h-index than articles about Neotropical mam-
mals. Taken at face value, this seems to reflect
the fact that researchers in Northern countries
are better financed and more cited thanks
partly to their access to journals included in
Scopus and the WoS (Borsuk et al., 2009;
Pasterkamp et al., 2007; Padial et al., 2010;
Tahamtan et al., 2016). However, it is impor-
tant to highlight that a proportion of articles
about tropical regions are written in collabora-
tion with authors affiliated with foreign institu-
tions, mainly from North America and Europe
(Tydecks, Jeschke, Wolf, Singer, & Tockner,
2018; Reboredo et al., 2020). Indeed, the scien-
tific output of some Neotropical countries (e.g.
Panama, Ecuador and Peru) is highly depen-
dent on international collaboration (Chinchilla-
Rodríguez, Sugimoto, & Larivière, 2019), and
a great proportion of the articles are led by
researchers from temperate countries (Dangles
et al., 2016; Chinchilla-Rodríguez et al., 2019).
Therefore, the biases concerning the number of
articles and citations are only partly explained
by the scientific wealth of the Neotropical
and Palearctic countries, and therefore, other
factors must be causing these differences and
need study.
Just like invertebrates are underrepresent-
ed in research when compared with birds and
mammals (Donaldson et al., 2006; Monge-
Nájera, 2017), Neotropical mammals are
understudied when compared with their Pale-
arctic relatives (Di Marco et al., 2017). Fur-
thermore, the growth in the number of articles
was more constant for the Palearctic region
during the whole study period, whereas the
growth in the number of Neotropical articles
was more evident from the year 2000, suggest-
ing a certain geographic delay in the production
pattern for scientific literature. However, it is
also noteworthy that, in the last decade, the
output increase was greater in the Neotropical
region, and that the gap between both regions is
becoming smaller, i.e. the P/N ratio is smaller,
or the difference in number of documents
between regions is falling.
One important consideration to properly
interpret our results is the different number of
species found in both biogeographic realms.
According to the IUCN red list, in the Neotrop-
ical realm there are 1691 species of terrestrial
mammals, whereas in the Palearctic realm there
Fig. 2. Relationship between total number of documents and citation indicators in WoS and Scopus for Neotropical (grey
spots) and Palearctic (dark spots) mammals. Only statistically significant effects are shown.
Revista de Biología Tropical, ISSN electrónico: 2215-2075, Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)
are 870 species (IUCN, 2020). This entails that
the number of papers about Palearctic mam-
mals per species could be greater due to the
lower number of species to study, and for the
same reason, the number of papers per species
of Neotropical mammals could be lower owing
to the higher species richness of this region.
Nevertheless, we deem that our results, based
on total number of documents per species and
their derivate citations indicators, could be use-
ful to quantify by how much the neotropical
mammals are less studied and their publica-
tions less cited than Palearctic mammals.
It is often assumed that quality and
research impact are correlated (e.g. Padial
et al., 2010; Tahamtan et al., 2016), but is it
fair to use the number of citations to compare
the quality of articles about Neotropical and
Palearctic mammals? Our results show that the
probability of being cited is a clear function of
another factor: quantity; in our data, citation
impact is strongly biased towards papers about
Palearctic species because the total citations
and the h-index were positively correlated
with the total number of documents (Table 4;
Fig. 2). Hence, if the Palearctic mammals are
more studied than Neotropical mammals, these
indicators should be therefore interpreted with
caution. This does not mean that the citation is
not among possible objective indicators within
the context of these two databases, but this
bias should be considered when comparing
articles produced by institutions or research-
ers from different regions. Additional criteria
should be tested in the future to compare the
impact of articles from both regions, such as
the social impact measured by Altmetrics or
the citations received in other databases such
as Google Scholar.
Additionally, De Groote, & Raszewski
(2012) previously noticed that Scopus and WoS
produce inconsistent impact factors; both data-
bases fail to cover the majority of the world’s
journals, and this has a strong impact in the
resulting h-index values (Vieira & Gomes,
2009; Martín-Martín, Orduna-Malea, Thelwall,
& López-Cózar, 2018). In the case of Latin
America, an important amount of the scientific
literature is published in journals not included
by Scopus or WoS, missing the large major-
ity of citations (Monge-Nájera, 2014; Monge-
Nájera & Ho, 2018). This bias also exists in
Europe, but it may be less marked there (Mon-
geon & Paul-Hus, 2016).
Our results also provide additional infor-
mation about the use of Scopus and the WoS
for bibliometric research. While the number
of Palearctic articles was similar in both data-
bases, the Palearctic/Neotropical ratio indi-
cated a greater difference between both regions
in WoS. By including more journals, Scopus
produced a less biased result, identifying more
articles and more citations. Particularly, our
results also showed that in the last two decades
the growth rate was greater in Scopus than WoS
for the Neotropical articles, which also sup-
ports the less biased results obtained in Scopus.
This does not mean that Scopus is a satisfactory
database to study Neotropical science, because
it still misses most publications that are pro-
duced in Latin America. For instance, Central
America (excluding Mexico) publishes over
8 000 academic journals according to Latindex,
of which only one, Revista de Biología Tropi-
cal, is included in WoS (Monge-Nájera & Ho,
2018). Other studies have found that Google
Scholar presents a better view of current sci-
ence, followed distantly by Scopus and, even
more distantly, by the WoS (Falagas, Pitsouni,
Malietzis, & Pappas, 2008; Meho, & Sugimoto,
2009; Martín-Martín, et al., 2018).
In conclusion, researchers should take into
account a regional bias favoring the study and
citation of Palearctic mammals in WoS and
Scopus, and that this bias is worse in WoS.
Citation rate is less biased than the h-index
and total citations, but still, citation rate and
the h-index are far from acceptable measures
of the importance of research. This bias can
be explained by several factors (e.g. research
investment, species richness or scientific infra-
structure), but whatever the cause, having less
scientific information on Neotropical mammals
can affect their conservation (dos Santos et al.,
2020), because sound research is essential to
ensure that conservation efforts are efficient
Revista de Biología Tropical, ISSN electrónico: 2215-2075 Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)
(Sutherland et al., 2019). Therefore, the world-
wide scientific community should reduce this
bias, for example, by promoting collaboration
between scientists from Palearctic and Neo-
tropical regions, by facilitating the access of
Neotropical journals to WoS and Scopus, or
by helping increase the financial support to
research projects on Neotropical mammals.
These measures could increase the scientific
knowledge on Neotropical mammals, which in
turn could help to ensure its conservation and
foster decisions based on science.
Ethical statement: authors declare that
they all agree with this publication and made
significant contributions; that there is no con-
flict of interest of any kind; and that we fol-
lowed all pertinent ethical and legal procedures
and requirements. All financial sources are
fully and clearly stated in the acknowledge-
ments section. A signed document has been
filed in the journal archives.
José Guerrero-Casado was supported by
the European Regional Development Fund
(ERDF) and the Consejería de Economía, Con-
ocimiento, Empresas y Universidad de la Junta
de Andalucía (project reference: 1264483). We
are very grateful to three anonymous reviewers
who helped improve the manuscript.
El sesgo geográfico en el estudio de los mamíferos:
comparación de medio siglo de investigación sobre
mamíferos paleárticos y neotropicales. Introducción:
No existen estudios que comparen, específicamente, la
investigación de la mastozoología paleártica con la neo-
tropical; pero tales comparaciones serían útiles para tomar
decisiones informadas en conservación y manejo. Objeti-
vo: Comparar los documentos científicos sobre mamíferos
paleárticos y neotropicales, y su impacto en citas, durante
medio siglo. Métodos: Comparamos 50 años (1970-2019)
de documentos sobre 60 especies de mamíferos de tamaño
mediano y grande (más de 1 kg), en Scopus y la colección
principal del Web of Science (WoS), considerando el
número de documentos y cuatro indicadores de citas a nivel
de especie (índice h, tasa de citas, total de citas y citas por
año). Resultados: Recuperamos 13 274 documentos en
Scopus y 12 913 en WoS, y encontramos que los mamífe-
ros paleárticos tienen 3.77 veces más documentos que las
especies neotropicales en Scopus (3.91 veces en WoS), y
que los documentos registran 5.95 más citas totales en Sco-
pus (6.93 veces más en WoS). Los documentos paleárticos
también registran más citas anuales y un índice h más alto,
tanto en Scopus como en WoS. Scopus recuperó más artí-
culos para especies neotropicales (2 782 vs. 2 631 en WoS)
y tuvo más citas (28 120 vs. 24 977 en WoS). Las diferen-
cias para los indicadores de citas entre regiones fueron más
marcadas en WoS. El índice h y el total de citas se ven muy
afectados por la cantidad de estudios publicados, es decir,
la región con más producción será la que tenga indicadores
más altos. Los artículos neotropicales mostraron una mayor
tasa de crecimiento en la última década, disminuyendo la
brecha entre ambas regiones. Conclusión: Existe un sesgo
regional en WoS y Scopus, que recuperan más artículos
y citas sobre mamíferos paleárticos que sobre mamíferos
neotropicales; este sesgo es peor en WoS y significa que se
necesita un aumento urgente en la investigación indexada
sobre especies neotropicales para estar al nivel de la inves-
tigación paleártica.
Palabras clave: cita; sesgo geográfico; Mammalia; impac-
to de la investigación; cienciometría; conservación de la
vida silvestre.
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