Discussion Paper |
Corresponding author: Tina Heger ( t.heger@wzw.tum.de ) Academic editor: David Richardson
© 2021 Tina Heger, Jonathan M. Jeschke, Johannes Kollmann.
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:
Heger T, Jeschke JM, Kollmann J (2021) Some reflections on current invasion science and perspectives for an exciting future. NeoBiota 68: 79-100. https://doi.org/10.3897/neobiota.68.68997
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Species spreading beyond their native ranges are important study objects in ecology and environmental sciences and research on biological invasions is thriving. Along with an increase in the number of publications, the research field is experiencing an increase in the diversity of methods applied and questions asked. This development has facilitated an upsurge in information on invasions, but it also creates conceptual and practical challenges. To provide more transparency on which kind of research is actually done in the field, the distinction between invasion science, encompassing the full spectrum of studies on biological invasions and the sub-field of invasion biology, studying patterns and mechanisms of species invasions with a focus on biological research questions, can be useful. Although covering a smaller range of topics, invasion biology today still is the driving force in invasion science and we discuss challenges stemming from its embeddedness in the social context. Invasion biology consists of the building blocks ‘theory’, ‘case studies’ and ‘application’, where theory takes the form of conceptual frameworks, major hypotheses and statistical generalisations. Referencing recent work in philosophy of science, we argue that invasion biology, like other biological or ecological disciplines, does not rely on the development of an all-encompassing theory in order to be efficient. We suggest, however, that theory development is nonetheless necessary and propose improvements. Recent advances in data visualisation, machine learning and semantic modelling are providing opportunities for enhancing knowledge management and presentation and we suggest that invasion science should use these to transform its ways of publishing, archiving and visualising research. Along with a stronger focus on studies going beyond purely biological questions, this would facilitate the efficient prevention and management of biological invasions.
biological invasions, evidence-based management, grand unified theory, invasion science, open science, philosophy of science, social-ecological systems, theory development
During biological invasions, organisms spread and establish outside their native range. These processes are investigated in a vibrant and still-growing research field, with the number of papers published in specific outlets, as well as in general ecological journals having increased exponentially during the past decades (
Several times, it has been questioned whether ‘invasion biology’ should be addressed as a discipline at all, the main argument being that the process of invasion does not fundamentally differ from other ecological processes as, for example, colonisation (e.g.
Due to the diversity of reasons for studying the phenomenon, as well as the high complexity of influencing factors, biological invasions are investigated in a multitude of different ways. This has substantially increased our knowledge about invasive species and their impacts, while the expansion of the field increasingly creates conceptual and practical challenges. For example, it is nearly impossible to keep track of all case studies that are published on the patterns and processes of biological invasions and improved efforts are needed to ensure that individual results become integrated into the body of theory (
In light of these challenges, we suggest three topics that, from our point of view, need further consideration. First, we discuss the delineation of the field, recalling the previously-proposed distinction between ‘invasion science’ and ‘invasion biology’. Second, we will discuss the structure of invasion biology and ask whether, given the increasing breadth and diversity of the field, there is a need for a unified theoretical framework. We will draw from recent publications in philosophy of science and argue that invasion biology may be a well-functioning discipline without one grand unifying theory, but that more integration, nevertheless, is desirable. Third, we will suggest future steps that could be taken to reach such integration, given the ongoing rapid technological advances and the current changes in the processes involved in scientific publication.
As one of many problem-orientated disciplines, invasion biology, just like ecology in general, is located at the intersection between nature and society (Fig.
Research on biological invasions is located at the intersection between natural sciences (biological and physical context) and the social sciences and humanities (social, political and economic context). The concept of ‘social-ecological systems’ (outer light blue box) emphasises that both realms are closely connected, with human activities affecting organisms, communities, ecosystems and landscapes and vice versa. Invasion biology addresses biological questions about patterns and mechanisms of invasions and, thus, has a focal interest in the biological and physical context. The broader field of invasion science contains research analysing patterns and mechanisms of invasions from a social-economic point of view, effects of invaders on people’s values and perspectives and many other, non-biological aspects of species invasions.
Studies creating target knowledge and transformation knowledge are clearly outside the realm of ecology as a natural science. Consequently,
In the following, we will argue that the distinction between invasion biology and invasion science can still be helpful today, as it stresses the difference between studies focusing on biological research questions and other fields of enquiry. It can, thus, contribute to more transparency concerning which kind of research is actually done in the field and thus has the potential to enhance the diversity of research approaches.
For a long time in ecology and biological conservation, humans have been treated as apart from natural processes (
Biological invasions are providing prime examples for the multiple ways in which ecological processes and human activities are influencing each other (
Connections to social sciences are, for example, sought with the aim to enhance the process of evaluating invasive species (e.g.
Moreover, several authors meanwhile made concrete suggestions for addressing biological invasions as processes happening within social-ecological systems. Drawing from methods developed in complexity science,
To give a more concrete example,
Approaches like these, leaving the realm of pure ecological or biological research, are promising and might be the best choice, especially for finding ways to prevent and manage invasions. However, with their literature review,
The usefulness and necessity of interdisciplinary studies does not preclude the need for studies focusing on biological research questions (
Invasion biology in this sense is studying organisms, communities, ecosystems, landscapes and biomes, typically with a focus on ecological and evolutionary questions. It aims, for example, at explaining how invaders change species interaction networks or at predicting which species compositions increase the probability for invasion. Human activities are important here because their effects on the biophysical context are nearly ubiquitous and, thus, are inseparable parts of the study objects. For answering a biological question (for example, about the interaction of two species), however, it is not necessary to study human activities themselves nor their causes (see also
Nevertheless, invasion biology still is embedded in a social context (Fig.
Invasion biology, with its building blocks theory, cases studies and application, is embedded in a societal context. The red arrows show how theory, case studies and application affect each other; the blue arrows depict effects of society on invasion biology and vice versa. The lighter colour of the block ‘application’ indicates that also non-biological questions beyond invasion biology, as defined above, are addressed here – these are part of invasion science (see Fig.
This embeddedness of invasion biology in a societal context leads to complex relationships between facts and values (
The influence of implicit values on research in invasion biology has been discussed within the discipline (e.g.
The relationship of invasion science and invasion biology as sketched in Fig.
A major building block of invasion biology is theory, consisting of conceptual frameworks, statistical generalisations and major hypotheses (Fig.
According to a classic idea of scientific progress, the main purpose of cases studies is to test specific elements of theory. Indeed, many studies in invasion biology do so, i.e. they test ideas that are grounded in theory (Fig.
The knowledge gained in case studies and through theory development can be applied in various ways. With respect to invasion biology, application can mean to use the knowledge for preventing and managing species invasion. In addition to such practical application, new knowledge can be used for prediction and explanation. Explanation is often an implicit part of case studies. An empirical project typically starts with a question or hypothesis, conducts an experiment or survey, analyses the data and then uses the results to explain the observed patterns in the light of theory. If multiple case studies are synthesised, the aim usually is to find explanations that are more broadly applicable; and ideally, these can be used to derive predictions by extrapolating or transferring the insight to other situations.
The abovementioned building blocks (theory, case studies, application) can be linked in various ways (red arrows in Fig.
Theory in invasion biology can take the form of conceptual frameworks, statistical generalisations and major hypotheses (Fig.
In the late 20th century, ecology picked up physics as a role model (
Invasion biology seems to be such a discipline. It does not have one concise unified theoretical framework, but is still based on a substantial body of theory (see, for example,
Even if we conclude that the search for a unified general theory is not a useful aim for invasion biology, this does not mean that integration and synthesis is useless. We suggest the opposite: invasion biology needs more integration and synthesis. The aim, however, should not be to strive for a single general framework or (mathematical) theory that explains everything, but to explore novel ways for integration that allow for plurality and consider the context-dependency of invasions.
The development and harmonisation of conceptual frameworks seems to be a useful way forward. Frameworks have the aim to organise knowledge and can function as guidelines for research and communication. Notably, most of the established frameworks in invasion biology have a focus on classification and description, often in a management context. For example, of the 24 papers included in the already-mentioned special issue (
In addition, we believe that invasion biology could profit from a more explicit consideration of how knowledge is generated and from systematically analysing its conceptual basis (see suggestions in
A multitude of different methods, ranging from field surveys and experiments to molecular studies and mathematical models are used to address various basic and applied questions in invasion biology. The majority of studies in invasion biology focus on terrestrial plants (
In ecology, there have been several initiatives to synthesise evidence from empirical studies to allow for efficient, evidence-based conservation (www.conservationevidence.com) and environmental management (www.environmentalevidence.org; see also www.eklipse-mechanism.eu and
Evidence-based invasion management would become an even more promising approach if human-environment interactions were a regular research topic in invasion science. Modelling invasion syndromes as adaptive cycles or as complex networks including humans as actors has a strong potential to enhance predictability in invasion science (
A significant increase in interdisciplinary research is needed, as invasion biological studies with a focus on biological questions will not suffice for facing the diverse challenges posed by biological invasions.
A more philosophical, general problem is how to utilise empirical results for theory development. As indicated above, case studies are not necessarily linked to a specific element of theory, but even if they are, their interpretation is not always straightforward. Is a single negative test result sufficient to discard an entire major hypothesis? According to an interpretation of the ‘hypothetico-deductive method’ based on
In addition to methodological heterogeneity, a challenge for synthesising the results of single cases studies is the high complexity of potentially relevant factors driving observed patterns. In the past, a general strategy to deal with the high complexity of interacting factors has been to focus on single factors. Explanation, prediction and management, however, will certainly profit from including more complexity. Respective suggestions have been repeatedly made in invasion biology (e.g.
It could be highly rewarding to additionally develop methods that allow for the identification of recurring causal patterns, thus fostering improved possibilities for mechanistic explanations.
Theory development could also be enhanced by fostering closer connection amongst fragmented elements of theory. For example, it has been suggested to demonstrate links and overlaps of established invasion frameworks by arranging them in a hierarchical way, thus creating a ‘hierarchy of invasion frameworks’ (
Technological advances in computer science in addition provide innovative tools for visualising knowledge (
An openly-accessible, searchable knowledge base for invasion biology that provides search outputs in an intuitively structured way would, therefore, be a major achievement (
In addition to the recent technological advances providing the respective technical possibilities, the ongoing shift in scientific publication practices could also turn out to be facilitative for developing such tools. Calls for openly-accessible data and publications are gaining momentum (
In conclusion, we believe that exciting developments are under way and we hope that our contribution stimulates efforts to seize these upcoming opportunities. Respective projects would require teaming up with experts from other disciplines, but the results would certainly make up for the effort such a crossing of disciplinary boundaries demands.
This manuscript is based on the Habilitation Thesis of T.H. at Technical University of Munich and she thanks Hanno Schäfer for co-mentoring the thesis. Additionally, we are grateful to William Bausman, Steve Elliot, Alkistis Elliot-Graves, James Griesemer, Marie Kaiser, Elijah Milgram and Gerhard Schurz for patient introductions to and inspiring discussions on recent approaches and developments in philosophy of science. We thank Guillaume Latombe, David Richardson, Ana Vaz and two anonymous reviewers for their insightful comments on a previous version of this manuscript.
T.H. and J.M.J. received funding from German Federal Ministry of Education and Research (BMBF) within the Collaborative Project “Bridging in Biodiversity Science (BIBS)” (funding number 01LC1501).