The Human Release Hypothesis for biological invasions: human activity as a determinant of the abundance of invasive plant species

Heike Zimmermann,Henrik Von Wehrden,Patric Brandt,Erik Welk,Joern Fischer

doi:10.12688/f1000research.4008

Heike Zimmermann, Henrik Von Wehrden + Show 3 more

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https://doi.org/10.12688/f1000research.4008

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Abstract

Research on biological invasions has increased rapidly over the past 30 years, generating numerous explanations of how species become invasive. While the mechanisms of invasive species establishment are well studied, the mechanisms driving abundance patterns (i.e. patterns of population density) remain poorly understood. Invasive species typically have higher abundances in their new environments than in their native ranges, and patterns of invasive species abundance differ between invaded regions. To explain differences in invasive species abundance, we propose the Human Release Hypothesis. In parallel to the established Enemy Release Hypothesis, this hypothesis states that the abundance of invasive species may be partly explained by the level of human activity or landscape maintenance, with intermediate levels of human activity providing optimal conditions for high abundance. The Human Release Hypothesis does not negate other important drivers of species invasions, but rather should be considered as a potentially important additional or complementary mechanism. We illustrate the hypothesis via a case study on an invasive rose species, and hypothesize which locations globally may be most likely to support high abundances of invasive species. We propose that more extensive empirical work on the Human Release Hypothesis could be useful to test its general applicability.

Highlights

Biological invasions can threaten ecosystems[1], economies[2], and human health[3]
Several journals are partly (e.g. Diversity and Distributions, Natural Areas Journal) or fully (e.g. Biological Invasions, Invasive Plant Science and Management, NeoBiota) devoted to research, management and policy issues related to invasive species
We propose that the abundance of an alien species in a given landscape can be explained by the level of active landscape maintenance by humans

Summary

Introduction

Biological invasions can threaten ecosystems[1], economies[2], and human health[3]. The Scientific Committee on Problems of the Environment (SCOPE) put biological invasions on top of its research agenda in 19834. While existing hypotheses explain the establishment and naturalization process of invasions, little work has attempted to explain the (potential) abundance of invasive species in their new environments Part of this gap may be effectively addressed by the Human Release Hypothesis (Figure 1). Having considered a wide range of existing hypotheses (Table 1), we found that additional insights into the invasion patterns of R. rubiginosa may be gained by the Human Release Hypothesis This is because a key difference between native and introduced environments appears to be the level of active landscape maintenance. Native R. rubiginosa populations occur in areas with higher proportions of cropland, residential areas and human population densities than invasive populations (Figure 2c) These conditions very likely correspond to a high degree of landscape maintenance, and little available habitat for R. rubiginosa in its native range.

Crooks JA

Di Castri F

14. Wilkinson D

28. Hobbs R

Findings

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