391

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

;

https://orcid.org/0000-0001-7764-2966

1. Department of Zoology, University of Córdoba. Campus de Rabanales, 14071 Córdoba, Spain;

guerrero.casado@gmail.com

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.

ABSTRACT

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.

v69i2.43961

DOI 10.15517/rbt.v69i2.43961

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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, author’s 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

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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

(1970-2019).

MATERIALS AND METHODS

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).

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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).

RESULTS

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

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(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.

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DISCUSSION

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

TABLE 1

Growth rate and regression slope value (b) for articles about Neotropical and Palearctic mammals

in Scopus and Web of Science (1970-2019)

Decade

Neotropical Palearctic

Ratio P/N

Nº Documents

Scopus

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

WoS

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.

TABLE 2

Wilcoxon paired tests comparing indicators for Scopus and WoS separately. Corrected p-value

was calculated multiplying the p-value by 5

Indicator

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

h-index

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.

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TABLE 3

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

Corrected

p-value

Ratio

(P/N)

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

h-index

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

Corrected

p-value

Ratio

(P/N)

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

h-index

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).

TABLE 4

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

Corrected

p-value

Estimate SE t-value

Corrected

p-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.

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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.

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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

400

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.

ACKNOWLEDGMENTS

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.

RESUMEN

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.

REFERENCES

Abramo, G., D’Angelo, C.A., & Di Costa, F. (2020). The

role of geographical proximity in knowledge diffu-

sion, measured by citations to scientific literature.

Journal of Informetrics, 14, 101010. DOI: 10.1016/j.

joi.2020.101010

Alberts, B. (2013). Impact factor distortions. Science, 340,

787. DOI: 10.1126/science.1240319

Allik, J., Lauk, K., & Realo, A. (2020). Factors Pre-

dicting the Scientific Wealth of Nations. Cross-

Cultural Research, 54(4), 364-397. DOI:

10.1177/1069397120910982

Amori, G., & Gippoliti, S. (2000). What do mammalogists

want to save? Ten years of mammalian conservation

biology. Biodiversity and Conservation, 9, 785-793.

DOI: 10.1023/A:1008971823774

Baquero, R.A., & Tellería, J.L. (2001). Species richness,

rarity and endemicity of European mammals: A

biogeographical approach. Biodiversity and Conser-

vation, 10, 29-44. DOI: 10.1023/A:1016698921404

Borsuk, R.M., Budden, A.E., Leimu, R., Aarssen, L.W., &

Lortie, C.J. (2009). The Influence of Author Gender,

National Language and Number of Authors on Cita-

tion Rate in Ecology. The Open Ecology Journal, 2,

25-28. DOI: 10.2174/1874213000902010025

401

Revista de Biología Tropical, ISSN electrónico: 2215-2075, Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)

Brooke, Z.M., Bielby, J., Nambiar, K., & Carbone, C.

(2014). Correlates of Research Effort in Carnivores:

Body Size, Range Size and Diet Matter. PLoS ONE,

9, e93195. DOI: 10.1371/journal.pone.0093195

Cai, Z., Chang, Q., & Yip, P.S.F. (2020). A scientometric

analysis of suicide research: 1990-2018. Journal of

Affective Disorders, 266, 356-365. DOI: 10.1016/j.

jad.2020.01.121

Chen, S.Y., Feng, Z., & Yi, X. (2017). A general introduc-

tion to adjustment for multiple comparisons. Journal

of Thoracic Disease, 9, 1725-1729. DOI: 10.21037/

jtd.2017.05.34

Chinchilla-Rodríguez, Z., Sugimoto, C.R., & Larivière,

V. (2019). Follow the leader: On the relationship

between leadership and scholarly impact in interna-

tional collaborations. PLoS One, 14, e0218309. DOI:

10.1371/journal.pone.0218309

Christie, A.P., Amano, T., Martin, P.A., Petrovan, S.O.,

Shackelford, G.E., Simmons, B.I., Smith, R.K.,

Williams, D.R., Wordley, C.F.R., & Sutherland, W.J.

(2020). The challenge of biased evidence in conser-

vation. Conservation Biology, 0, 1-13. DOI: 10.1111/

cobi.13577

Crespo-Gascón, S., Tortosa, F.S., & Guerrero-Casado, J.

(2019). Producción de revistas científicas en Amé-

rica Latina y El Caribe en Scopus, Journal Citation

Reports y Latindex en el área de los recursos natura-

les: su relación con variables económicas, ambienta-

les y de inversión en investigación. Revista Española

de Documentación Científica, 42, 224. DOI: 10.3989/

redc.2019.1.1533

Dangles, O., Loirat, J., Freour, C., Serre, S., Vacher, J., &

Le Roux, X. (2016). Research on Biodiversity and

Climate Change at a Distance: Collaboration Net-

works between Europe and Latin America and the

Caribbean. PLoS One, 11, e0157441. DOI: 10.1371/

journal.pone.0157441

De Groote, S.L., & Raszewski, R. (2012). Coverage of

Google Scholar, Scopus, and Web of Science: A case

study of the h-index in nursing. Nursing Outlook, 60,

391-400. DOI: 10.1016/j.outlook.2012.04.007

Di Marco, M., Chapman, S., Althor, G., Kearney, S.,

Besancon, C., Butt, N., Maina, J., Possingham, H.,

von Bieberstein, K., Venter, O., & Watson, J.E.M.

(2017). Changing trends and persisting biases in

three decades of conservation science. Global Eco-

logy and Conservation, 10, 32-42. DOI: 10.1016/j.

gecco.2017.01.008

Di Rienzo, J.A., Casanoves, F., Balzarini, M.G., Gonzalez,

L., Tablada, M., & Robledo, C.W. (2020). InfoStat

(versión 2020). Universidad Nacional de Córdoba,

Argentina. Recuperado de http://www.infostat.com.ar

Donaldson, M.R., Burnett, N.J., Braun, D.C., Suski, C.D.,

Hinch, S.G., Cooke, S.J., & Kerr, J.T. (2016). Taxo-

nomic bias and international biodiversity conser-

vation research. Facets, 1, 105-113. DOI: 10.1139/

facets-2016-0011

dos Santos, J.W., Correia, R.A., Malhado, A.C.M., Cam-

pos-Silva, J.V., Teles, D., Jepson, P., & Ladle, R.J.

(2020). Drivers of taxonomic bias in conserva-

tion research: a global analysis of terrestrial mam-

mals. Animal Conservation (in press). DOI: 10.1111/

acv.12586

Falagas, M.E., Pitsouni, E.I., Malietzis, G.A., & Pappas,

G. (2008). Comparison of PubMed, Scopus, web of

science, and Google scholar: strengths and weaknes-

ses. The FASEB Journal, 22, 338-342. DOI: 10.1096/

fj.07-9492LSF

Fleming, P.A., & Bateman, P.W. (2016). The good, the

bad, and the ugly: which Australian terrestrial mam-

mal species attract most research? Mammal Review,

46(4), 241-254. DOI: 10.1111/mam.12066

Guerrero-Casado, J. (2017). Producción científica lati-

noamericana indexada en Scopus en el área de las

ciencias agropecuarias: Análisis del período 1996-

2016. Idesia (Arica), 35, 27-33. DOI: 10.4067/

S0718-34292017000400027

Hickisch, R., Hodgetts, T., Johnson, P.J., Sillero-Zubiri,

C., Tockner, K., & Macdonald, D.W. (2019). Effects

of publication bias on conservation planning. Con-

servation Biology, 33, 1151-1163. DOI: 10.1111/

cobi.13326

Hirsch, J. E. (2005). An index to quantify an individual’s

scientific research output. Proceedings of the Natio-

nal Academy of Sciences of the United States of

America, 102(46), 16569-16572. DOI: 10.1073/

pnas.0507655102

Holt, B.G., Lessard, J.P., Borregaard, M.K., Fritz, S.A.,

Araújo, M.B., Dimitrov, D., Fabre, P.H., Graham,

C.H., Graves, G.R., Jønsson, K.A., Nogués-Bravo,

D., Wang, Z., Whittaker, R.J., Fjeldså, J., & Rahbek,

C. (2013). An update of Wallace’s zoogeographic

regions of the world. Science, 339, 74-78. DOI:

10.1126/science.1228282

IUCN (2020). The IUCN Red List of Threatened Species

(Base de datos). Recuperado de https://www.iucn-

redlist.org

Jarić, I., Roberts, D.L., Gessner, J., Solow, A.R., & Cou-

rchamp, F. (2017). Science responses to IUCN Red

Listing. PeerJ, 2017(11), e4025. DOI: 10.7717/

peerj.4025

King, D.A. (2004). The scientific impact of nations. Natu-

re, 430, 311-316. DOI: 10.1038/430311a

Lawler, J.J., Aukema, J.E., Grant, J.B., Halpern, B.S.,

Kareiva, P., Nelson, C.R., Ohleth, K., Olden, J.D.,

Schlaepfer, M.A., Silliman, B.R., & Zaradic, P.

(2006). Conservation science: a 20-year report

card. Frontiers in Ecology and the Environment, 4,

473-480.

Martin, L.J., Blossey, B., & Ellis, E. (2012). Mapping

where ecologists work: biases in the global distribu-

tion of terrestrial ecological observations. Frontiers

in Ecology and the Environment, 10, 195-201. DOI:

10.1890/110154

402

Revista de Biología Tropical, ISSN electrónico: 2215-2075 Vol. 69(2): 391-402, April-june 2021 (Published 11 Feb. 2021)

Martín-Martín, A., Orduna-Malea, E., Thelwall, M., &

López-Cózar, E.D. (2018). Google Scholar, Web

of Science, and Scopus: A systematic comparison

of citations in 252 subject categories. Journal of

Informetrics, 12(4), 1160-1177. DOI: 10.1016/j.

joi.2018.09.002

Meho, L.I., & Sugimoto, C.R. (2009). Assessing the scho-

larly impact of information studies: A tale of two cita-

tion databases—Scopus and Web of Science. Journal

of the American Society for Information Science and

Technology, 60, 2499-2508. DOI: 10.1002/asi.21165

Meijaard, E., Cardillo, M., Meijaard, E.M., & Possingham,

H.P. (2015). Geographic bias in citation rates of

conservation research. Conservation Biology, 29(3),

920-925. DOI: doi.org/10.1111/cobi.12489

Monge-Nájera, J. (2014). La invalidez del Factor de

Impacto como indicador del impacto de las revistas

científicas latinoamericanas. Revista de Biología

Tropical, 62, 407-412.

Monge-Nájera, J. (2017). The power of short lectures to

improve support for biodiversity conservation of

unpopular organisms: an experiment with worms.

Cuadernos de Investigación UNED, 9(1), 145-150.

Monge-Nájera, J., & Ho, Y.S. (2018). Guatemala articles

in the Science Citation Index Expanded: bibliometry

of subjects, collaboration, institutions and authors.

Revista de Biología Tropical, 66, 312-320. DOI:

10.15517/rbt.v66i1.29875

Mongeon, P., & Paul-Hus, A. (2016). The journal coverage

of Web of Science and Scopus: a comparative analy-

sis. Scientometrics, 106, 213-228. DOI: 10.1007/

s11192-015-1765-5

Noguera-Urbano, E.A., & Escalante, T. (2017). The Neo-

tropical region sensu the areas of endemism of terres-

trial mammals. Australian Systematic Botany, 30,

470-484. DOI: 10.1071/SB16053

Padial, A.A., Nabout, J.C., Siqueira, T., Bini, L.M., &

Diniz-Filho, J.A.F. (2010). Weak evidence for

determinants of citation frequency in ecological

articles. Scientometrics, 85, 1-12. DOI: 10.1007/

s11192-010-0231-7

Pasterkamp, G., Rotmans, J.I., De Kleijn, D.V.P., & Borst,

C. (2007). Citation frequency: A biased measure of

research impact significantly influenced by the geo-

graphical origin of research articles. Scientometrics,

70, 153-165. DOI: 10.1007/s11192-007-0109-5

Prathap, G. (2017). Scientific wealth and inequality within

nations. Scientometrics, 13, 923-928. DOI: 10.1007/

s11192-017-2511-y

Pullin, A.S., Knight, T.M., Stone, D.A., & Charman, K.

(2004). Do conservation managers use scientific

evidence to support their decision-making? Biologi-

cal Conservation, 119(2), 245-252. DOI: 10.1016/j.

biocon.2003.11.007

Sitas, N., Baillie, J.E.M., & Isaac, N.J.B. (2009). What

are we saving? Developing a standardized approach

for conservation action. Animal Conservation, 12(3),

231-237. DOI: 10.1111/j.1469-1795.2009.00244.x

Sutherland, W.J., Taylor, N.G., MacFarlane, D., Amano,

T., Christie, A.P., Dicks, L.V., Lemasson, A.J., Litt-

lewood, N.A., Martin, P.A., Ockendon, N., Petro-

van, S.O., Robertson, R.J., Rocha, R., Shackelford,

G.E., Smith, R.K., Tyler, E.H.M., & Wordley, C.F.R.

(2019). Building a tool to overcome barriers in

research-implementation spaces: The conservation

evidence database. Biological Conservation, 238,

108199. DOI: 10.1016/j.biocon.2019.108199

Reboredo, A.L., Romano, D., & Armsworth, P.R. (2020).

Who studies where? Boosting tropical conservation

research where it is most needed. Frontiers in Eco-

logy and the Environment, fee.2146. DOI: 10.1002/

fee.2146

Tahamtan, I., Afshar, A.S., & Ahamdzadeh, K. (2016). Fac-

tors affecting number of citations: a comprehensive

review of the literature. Scientometrics, 107, 1195-

1225. DOI: 10.1007/s11192-016-1889-2

Tydecks, L., Jeschke, J.M., Wolf, M., Singer, G., & Toc-

kner, K. (2018). Spatial and topical imbalances in

biodiversity research. PLOS ONE, 13(7), e0199327.

DOI: 10.1371/journal.pone.0199327

Vieira, E.S., & Gomes, J.A. (2009). A comparison of Sco-

pus and Web of Science for a typical university. Scien-

tometrics, 81, 587. DOI: 10.1007/s11192-009-2178-0

Vinkler, P. (2018). Structure of the scientific research and

science policy. Scientometrics, 114(2), 737-756. DOI:

10.1007/s11192-017-2568-7

Wen, Z., Cai, T., Feijó, A., Xia, L., Cheng, J., Ge, D., &

Yang, Q. (2020). Using completeness and defau-

nation indices to understand nature reserve’s key

attributes in preserving medium- and large-bodied

mammals. Biological Conservation, 241, 108273.

DOI: 10.1016/j.biocon.2019.108273

Wilson, K.A., Auerbach, N.A., Sam, K., Magini, A.G.,

Moss, A.S.L., Langhans, S.D., Budiharta, S., Terza-

no, D., & Meijaard, E. (2016). Conservation research

is not happening where it is most needed. PLOS

Biology, 14(3), e1002413. DOI: 10.1371/journal.

pbio.1002413

Wouters, P., Sugimoto, C.R., Larivière, V., McVeigh,

M.E., Pulverer, B., de Rijcke, S., & Waltman, L.

(2019). Rethinking impact factors: better ways to

judge a journal. Nature, 569, 621-623. DOI: 10.1038/

d41586-019-01643-3

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