Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

CABI Book Chapter

Invasion biology: hypotheses and evidence.

Book cover for Invasion biology: hypotheses and evidence.


This book, containing 18 chapters, combines the hierarchy-of-hypotheses (HoH) approach with hypothesis networks for invasion biology. This book aims to further develop the HoH approach by inviting critical comments (Part I), apply it to 12 major invasion hypotheses (Part II) and explore how it can be expanded to a hierarchically structured hypothesis network (Chapter 7 and Part III). It is importa...

Chapter 11 (Page no: 92)

Enemy release hypothesis.

The enemy release hypothesis is a prominent explanation for invasion success. It is, however, a complex multi-faceted hypothesis and has multiple sub-hypotheses. Empirical tests of the enemy release hypothesis therefore often address very different questions. For this reason, we previously applied the hierarchy-of-hypotheses (HoH) approach to analyse the level of evidence for the enemy release hypothesis and its sub-hypotheses, taking into account this variety of formulations and research questions. This chapter provides an update and extension of that analysis by including recently published evidence and implementing some of the suggestions made in Chapters 3 to 6, this volume, concerning the HoH approach. In detail, we: (i) re-organized the HoH, now separating research approaches from working hypotheses; (ii) displayed results including bar charts in order to avoid a classification of the level of evidence for the different hypotheses; and (iii) tested the robustness of our results based on the precision of the tests (estimated as number of replicates), their generality (using number of focal species as a proxy), realism (i.e. whether they were conducted in the lab, an enclosure or in the field) and their general approach (observation or experiment). We found relatively strong support for the enemy release hypothesis in studies looking at release in the sense of reduced enemy pressure. However, this is not paralleled by strong evidence for enhanced performance. Support for the enemy release hypothesis differs according to which question is asked. It is highest if species in their native vs introduced range are compared and lowest if invasive aliens are compared to non-invasive aliens. There is a comparatively high level of supporting evidence if specialist enemies are considered. From these findings, we conclude that future studies should focus on testing whether invaders show enhanced performance if released from specialist enemies - an underexplored research question so far. Our robustness analysis indicates that empirical results are influenced by the generality (estimated by the number of focal species) and realism (estimated by the number of replicates) of studies addressing the enemy release hypothesis. We suggest that future studies in the context of enemy release should preferentially be done in the field rather than in the lab and use more than ten focal alien species.

Other chapters from this book

Chapter: 1 (Page no: 3) Invasion biology: searching for predictions and prevention, and avoiding lost causes. Author(s): Cassey, P., García-Díaz, P., Lockwood, J. L., Blackburn, T. M.
Chapter: 2 (Page no: 14) The hierarchy-of-hypotheses approach. Author(s): Heger, T., Jeschke, J. M.
Chapter: 3 (Page no: 19) Hierarchy of hypotheses or hierarchy of predictions? Clarifying key concepts in ecological research. Author(s): Farji-Brener, A. G., Amador-Vargas, S.
Chapter: 4 (Page no: 23) Mapping theoretical and evidential landscapes in ecological science: Levins' virtue trade-off and the hierarchy-of-hypotheses approach. Author(s): Griesemer, J.
Chapter: 5 (Page no: 30) A hierarchy of hypotheses or a network of models. Author(s): Scheiner, S. M., Fox, G. A.
Chapter: 6 (Page no: 38) The hierarchy-of-hypotheses approach updated - a toolbox for structuring and analysing theory, research and evidence. Author(s): Heger, T., Jeschke, J. M.
Chapter: 7 (Page no: 49) A network of invasion hypotheses. Author(s): Enders, M., Jeschke, J. M.
Chapter: 8 (Page no: 60) Biotic resistance and island susceptibility hypotheses. Author(s): Jeschke, J. M., Debille, S., Lortie, C. J.
Chapter: 9 (Page no: 71) Disturbance hypothesis. Author(s): Nordheimer, R., Jeschke, J. M.
Chapter: 10 (Page no: 79) Invasional meltdown hypothesis. Author(s): Braga, R. R., Gómez Aparicio, L., Heger, T., Vitule, J. R. S., Jeschke, J. M.
Chapter: 12 (Page no: 103) Evolution of increased competitive ability and shifting defence hypotheses. Author(s): Müller, C.
Chapter: 13 (Page no: 124) Tens rule. Author(s): Jeschke, J. M., Pyšek, P.
Chapter: 14 (Page no: 133) Phenotypic plasticity hypothesis. Author(s): Torchyk, O., Jeschke, J. M.
Chapter: 15 (Page no: 140) Darwin's naturalization and limiting similarity hypotheses. Author(s): Jeschke, J. M., Erhard, F.
Chapter: 16 (Page no: 147) Propagule pressure hypothesis. Author(s): Jeschke, J. M., Starzer, J.
Chapter: 17 (Page no: 157) Synthesis. Author(s): Jeschke, J. M., Heger, T.
Chapter: 18 (Page no: 167) Conclusions and outlook. Author(s): Heger, T., Jeschke, J. M.