Research Article |
Corresponding author: Miha Dominko ( dominkom@ier.si ) Academic editor: Stefano Taiti
© 2022 Miloš Vittori, Miha Dominko.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Vittori M, Dominko M (2022) A bibliometric analysis of research on terrestrial isopods. In: De Smedt P, Taiti S, Sfenthourakis S, Campos-Filho IS (Eds) Facets of terrestrial isopod biology. ZooKeys 1101: 13-34. https://doi.org/10.3897/zookeys.1101.81016
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Terrestrial isopods (Oniscidea) are crustaceans that thrive in terrestrial environments. This study provides an overview of the major topics in terrestrial isopod research during the last 70 years in order to provide an example of publication practices in invertebrate zoology and to examine how basic research in this area is transferred to its applications. Co-citation analysis and bibliographic coupling based on citation data from the Web of Science Core Collection was used. Findings show that while research on terrestrial isopods expanded in applicative research prioritised by research policies, basic research continues to flourish. The most productive countries in the field include the major developed economies and several smaller nations. In the smaller countries, as well as in France and Italy, the bulk of woodlouse research is performed at a few institutions with traditions in this field. Some of the most influential works have been published in periodicals or monographs that are not indexed in Web of Science or Scopus and lack impact factors. Conference proceedings represent some of the most influential publications in the field. Our findings indicate that smaller and developing economies make significant contributions in invertebrate zoology if their research organisations can achieve continuity of research on a topic. Another conclusion is that journal metrics may be a misleading descriptor of the impact of studies and researchers in this field. Ultimately, these results identify several examples of how basic research in invertebrate zoology leads to applications with considerable socio-economic impact.
Citation analysis, crustacean, invertebrate zoology, Oniscidea, scientometrics
Invertebrate zoology, as a scientific field, studies the greater part of all living animals, as invertebrates represent the majority of animal biodiversity. Basic research in this field forms the foundation for applicative studies that may extend to other scientific fields and is essential to conservation efforts. Nevertheless, basic research of invertebrates other than model organisms receives relatively little funding and little attention in educational curricula (
Terrestrial isopods or woodlice (Oniscidea) are a group of crustaceans that has successfully adapted to the terrestrial environment (Fig.
A comprehensive list of literature on terrestrial isopods published prior to 2000 was assembled by
In the present contribution, we use bibliometric methods to obtain an overview of the main topics and trends in research dealing with terrestrial isopods, including fields of research that use woodlice as experimental organisms and do not necessarily focus on the biology of this taxonomic group as such. Our aim is to use terrestrial isopod research as a case study of how invertebrate zoology functions in the modern scientific environment and to outline how basic research on invertebrates is linked to its applications. We quantitatively describe the development of this field during the second half of the 20th century and the first two decades of the new millennium and identify the studies that influenced the development of various research directions in the field, including an account of what types of publications they were published in.
Bibliometrics are becoming an integral part of research evaluation due to the greater availability of article and citation data, as well as the development of new analysis software (
Our bibliometric analysis relies on citations, which provide an objective measure of a paper’s impact in a field of knowledge (
To obtain a relevant dataset of publications on terrestrial isopods, we used the Web of Science Core Collection, which contains publication and citation data. We obtained our dataset by searching for the scientific and trivial names of the taxon Oniscidea, as well as several of the most studied genera of terrestrial isopods that we were able to identify in the World catalogue of terrestrial isopods (
To obtain our dataset we applied the following search using the appropriate Boolean operators (AND, OR, and NOT):
To visualise bibliometric networks, we used VOSviewer (van Eck and Waltman 2010) and CitNetExplorer (
To interpret the obtained bibliometric networks, items displayed on the maps were looked up in the database, allowing us to identify the topics of the items in question and the journals or proceedings in which they were published.
Our search returned 2946 items related to terrestrial isopods in Web of Science (WoS) and a total of 52631 citations (34880 excluding self-citations). At the beginning of the time period covered by our study in the 1950s, the annual numbers of publications on terrestrial isopods indexed in WoS were fewer than ten and the annual numbers of citations were below 5 (Fig.
The annual numbers of citations of these works followed a similar trend, but citation numbers increased at greater rates than publication numbers. While the annual numbers of citations remained below 30 until the end of the 1960s, the frequency of citation grew steadily to ca. 200 citations per year during the 1970s. At this point, the citation rate reached a plateau and remained unchanged until the mid-1990s. After this point, the annual numbers of citations began to increase rapidly, growing by ca. 1000 annual citations every ten years (Fig.
The great majority of indexed publications, more than 88%, are journal articles (Table
If we take into account publications indexed in WoS, the largest output in the study period comes from the United States with 372 publications. France is not far behind with 357 publications, followed by Germany and the United Kingdom with more than 200 publications each. Other countries with research outputs exceeding 100 publications are Italy, Japan, the Netherlands, Brazil, Slovenia and Canada (Table
Numbers of publications on terrestrial isopods in WoS according to publication type.
Publication type | Number | % of all publications |
---|---|---|
Article | 2597 | 88.1% |
Proceedings paper | 111 | 3.8% |
Review | 104 | 3.5% |
Meeting abstract | 102 | 3.5% |
Note | 50 | 1.7% |
Letter | 43 | 1.5% |
Other | 62 | 2.1% |
Numbers of publications on terrestrial isopods by country. The table lists the top ten countries according to the numbers of publications in WoS. These are also the countries with more than 100 publications in the dataset.
Country | Number of publications | % of all publications |
---|---|---|
United States of America | 372 | 12.63% |
France | 357 | 12.12% |
Germany | 280 | 9.50% |
United Kingdom | 270 | 9.17% |
Italy | 197 | 6.69% |
Japan | 173 | 5.87% |
Netherlands | 135 | 4.58% |
Brazil | 126 | 4.28% |
Slovenia | 122 | 4.14% |
Canada | 103 | 3.50% |
Almost all among the ten most productive organisations in the field of terrestrial isopod biology (Table
Considering the contributions of individual organisations, we can deduce that in small countries, such as the Netherlands, Slovenia, Portugal and Tunisia, almost all publications on terrestrial isopods were produced at a single institution. In Italy and France, a few dominant organisations contributed the bulk of the total research output. The same conclusion can be made for most countries outside Europe, such as Brazil, where a handful of institutions contributed the majority of publications (Suppl. material
Top ten organisations that contributed the most publications in WoS in the field of terrestrial isopod biology.
Organisation | Country | Number of publications | % of all publications |
---|---|---|---|
University of Poitiers (Université de Poitiers) | France | 196 | 6.6% |
University of Ljubljana (Univerza v Ljubljani) | Slovenia | 116 | 3.9% |
Free University of Amsterdam (Vrije Universiteit Amsterdam) | The Netherlands | 107 | 3.6% |
National Research Council (Consiglio Nazionale delle Ricerche) | Italy | 83 | 2.8% |
University of Tunis El Manar (Université de Tunis El Manar) | Tunisia | 73 | 2.5% |
University of Aveiro (Universidade de Aveiro) | Portugal | 57 | 1.9% |
Ulm University (Universität Ulm) | Germany | 53 | 1.8% |
Federal University of Rio Grande do Sul (Universidade Federal do Rio Grande do Sul) | Brazil | 53 | 1.8% |
National Centre for Scientific Research (Centre national de la recherche scientifique) | France | 40 | 1.4% |
University of Catania (Università degli Studi di Catania) | Italy | 36 | 1.2% |
In order to determine the impact of individual publications and which research topics relating to terrestrial isopods were continuously prominent, we conducted a co-citation analysis, identifying the publications most often cited by the publications in our database, regardless of whether or not the cited works were included in our WoS-derived dataset. This allowed us to identify relevant works published before 1950 and those published in non-indexed publications. As a result, the period in which these works were published is considerably longer, including most of the 20th century and the first two decades of the 21st century. While many more works on terrestrial isopods were published during this period (see
The visualisation of the co-citation network of the 200 most frequently cited works allows us to discern six major clusters, corresponding to major topics in terrestrial isopod research (Fig.
By considering a subset of the 100 most influential publications along a timeline, we can identify publications that are predecessors and successors in continuous topics in the field using CitNetExplorer (Fig.
The systematics cluster is relatively scattered and works within it do not interconnect very frequently with each other, suggesting that they are not often cited together. Furthermore, relatively long time intervals elapsed between these works (Fig.
Numerous links are obvious between systematics and ecophysiology and particularly between this cluster and ecotoxicological publications. By contrast, the clusters dealing with microbe-host interactions and biomineralisation are again more distant from other clusters, which is consistent with the results of the broader co-citation analysis (Fig.
The topics of journals with the most publications relevant to the field of terrestrial isopod biology fall into five major clusters on the basis of bibliographic coupling (Fig.
Considering the average year of publication of the articles, journals in the ecotoxicological cluster stand out: most cited publications in this area have been published recently (Fig.
Bibliographic coupling network of journals that have been cited by publications in the database at least 50 times A clustering of journals, revealing several major topics that they cover B heat-map of the network presented in A showing the average year of publication of articles published in these journals and cited in the database.
Ten journals that published the most publications on terrestrial isopods during the study period. The entry for the French periodical ‘Comptes rendus hebdomadaires des séances de l’Académie des sciences’ includes articles published in its ‘Serie D’.
Journal title | Published items | % of all items |
---|---|---|
Comptes rendus hebdomadaires des séances de l’Académie des sciences | 120 | 4.1% |
Crustaceana | 89 | 3% |
ZooKeys | 66 | 2.2% |
Journal of Experimental Biology | 49 | 1.7% |
Pedobiologia | 48 | 1.6% |
European Journal of Soil Biology | 47 | 1.6% |
Applied Soil Ecology | 37 | 1.3% |
Environmental Toxicology and Chemistry | 37 | 1.3% |
Zootaxa | 35 | 1.2% |
Zoological Science | 34 | 1.1% |
Apart from ecological and ecotoxicological journals, journals covering systematics, such as ‘Zootaxa’ and ‘ZooKeys’, have been very active in the new millennium (Fig.
These are the periodicals that published the most articles on the subject of terrestrial isopods, but which periodicals published the most influential studies? When considering the 100 most influential publications (Fig.
Among other articles in the top 100, three journals published four articles each: ‘Canadian Journal of Zoology’, ‘Environmental Pollution’, and ‘Journal of Animal Ecology’, while two journals contributed four articles each: ‘Soil Biology and Biochemistry’ and ‘American Zoologist’.
A network of 100 keywords that appeared in the database most often is presented in Fig.
Keywords relating to ecotoxicology are consistently frequently cited (Fig.
Bibliographic coupling network of keywords in publications cited in the database A clustering of keywords according to bibliographic coupling B heat-map of keywords illustrating the frequency of their citation - the citation score of an individual keyword is divided by the mean citation score of all keywords (citation scores above 1 indicate higher than average citations).
Our study provides a concise overview of the development of terrestrial isopod research during the last 70 years in terms of how the extensive bibliography on this subject is structured according to publication types and the geographical distribution of publication output.
While the top countries in terms of research output include the leading developed economies with large research expenditures, which can be observed in other scientific fields as well (
The language bias of international scientific databases may distort the representation publications in languages other than English (
By analysing bibliometric networks, we were able to identify several major topics in terrestrial isopod research, the past and current development, and the relationships between these topics. Keyword analysis, co-citation analysis, and bibliographic coupling have identified roughly the same set of general research topics in research related to terrestrial isopods. These are: (1) ecotoxicology, (2) systematics, (3) microbe-host interactions, (4) ecology, with a great focus on population ecology and life histories, and (5) physiology. In the last field, the dominating topics are digestive physiology, ecophysiology (particularly in relation to evolutionary transition to land), and biomineralisation. Many of these topics, such as ecotoxicology, microbe-host interactions, and life-history ecology, have been identified as major topics in this field by authors who reviewed work on terrestrial isopod biology (
Ecotoxicology is an obvious topic on the rise. This is attested by the dominance of this field when it comes to citations and the prominent increase in the number of papers on terrestrial isopods that are published in ecotoxicological journals (Figs
A similar success story is the use of terrestrial isopods in studies on biomineralisation. Here, the initial work in the co-citation network (Fig.
As can be deduced from the importance of the publications and keywords relating to this subject, microbe-host interactions in terrestrial isopods have been a very influential topic as well. A large part of the success of the topic likely results from work on the association of terrestrial isopods with the feminising bacterium Wolbachia, which is of great importance to evolutionary biology and the ecology of microbe-host interactions. Although these studies were, to a large extent, conducted on A. vulgare, Wolbachia is of wider interest as it is capable of infecting numerous arthropods and manipulating their sex. As this is also true for many insects, Wolbachia can potentially be used in pest management. This organism is, of course, not the only one studied in woodlice; several commensals and pathogens have been identified in these crustaceans, as well as potential symbionts aiding in the digestion of plant material and other physiological processes (reviewed in
The examples of research on ecotoxicology, biomineralisation and microbe-host interactions in terrestrial isopods show how basic research on the biology of an invertebrate group later led to the establishment of the animals in question as experimental organisms in more general, even applicative, research topics. Naturally, other topics in woodlouse research had a broader impact on human knowledge as well, as we can expect from any well-conducted scientific inquiry, and these two cases were only discussed at length here as the most obvious examples in the bibliographic networks we obtained.
Despite poor funding opportunities in the field of invertebrate systematics (
As demonstrated by the co-citation analysis, the central publications in the field of terrestrial isopod biology during the last 50 years were often conference proceedings and articles published in institutional periodicals, many of which are not indexed in WoS or Scopus and lack impact factors. While the importance of scientific meetings is diminishing and conference proceedings resonate only briefly in most scientific fields (
The findings of this study point out that publishing in invertebrate zoology follows somewhat specific principles, with great importance of in-person meetings and publications not captured by conventional bibliographic metrics. In addition, major contributions in this field are produced in small and developing economies at institutions that can achieve continuity of research on a topic despite changing research trends. Ultimately, the example of terrestrial isopods shows that basic research on the biology of a seemingly marginal group of invertebrates can lead to flourishing applicative research on some of today’s most pressing issues. This is all the more reason not to neglect such research in the future, as the findings of today can help resolve the issues of tomorrow.
This work was financed by the Slovenian Research Agency, Research Programs P1-0184 and P5-0096.
Number publications according to country
Data type: Bibliometric data.
Explanation note: A table listing countries with corresponding numbers of publications on terrestrial isopods in the period between 1950 and 2020.
Number of publications according to institution
Data type: Bibliometric data.
Explanation note: A table listing institutions with corresponding numbers of publications on terrestrial isopods in the period between 1950 and 2020.
Most influential publications on terrestrial isopods
Data type: Bibliometric data.
Explanation note: A table listing 100 publications on the subject of terrestrial isopods with the highest citation scores.