Byers, 2002

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Impact of Non-Indigenous Species on Native Species

Introduction

  • Author: James E. Byers, Dept of Zoology, University of New Hampshire.

  • Anthropogenic disturbances shift environmental conditions, possibly reversing competitive advantages of native species over non-native species.

  • Rapid habitat alterations may result in well-adapted native species becoming disadvantaged in competition with non-native species.

Key Concepts and Definitions

  1. Anthropogenic Habitat Alteration: Changes in habitat caused by human activities that impose new environmental pressures on species.

  2. Competitive Advantage: The idea that native species usually have superiority over newly arrived species due to long-term adaptation and evolutionary history.

  3. Selection Regime Modification (SRM): Significant anthropogenic disturbances that introduce new selective forces unfamiliar to resident species.

Mechanisms by which Non-Indigenous Species Displace Natives

  1. Disturbance Creation:

    • New microhabitats and niches emerge that facilitate invasion (Parker et al. 1993; Carlton 1996).

  2. Reduction of Native Species:

    • Disturbance can reduce or eliminate native predators and competitors, hindering their capacity to control invasions (D'Antonio 1993; Moyle and Light 1996).

  3. Introduction of Propagules:

    • Disturbance events can facilitate the introduction of non-indigenous species' propagules to previously inaccessible areas (Usher 1988; Lonsdale 1999).

Evidence and Discussion on SRM Mechanism

  • The manuscript emphasizes that rapid environmental changes can disadvantage native species by shifting the selection pressures they face.

  • Evidence supporting SRM is limited but studies provide insights into how anthropogenic influences lead to invasive species success:

    • Example Study: Byers (2002) found that non-indigenous species have varying impacts based on disturbance levels.

Hypothesis and Testable Predictions

  1. Experimental Framework:

    • Two approaches exist to test SRM:
      a) Identify changes in environmental variables that favored the invader over the native.
      b) Directly show disturbance alterations led to competitive advantages for the invader.

  2. Predictions of SRM:

    • The impact of invader species on native species should be greater in disturbed environments compared to undisturbed ones.

Case Studies

  1. Eutrophication Effects:

    • Eutrophication increases nutrients leading to low O2 conditions that may disproportionately benefit non-native species (Officer et al. 1984; Elmgren 1989).

    • Example: In Lake Balaton, the biomass of non-indigenous species rose significantly post-eutrophication (Biro 1997).

  2. Altered Apex Predation Abundance:

    • Removal of top predators reduces pressure on lower trophic levels, altering selection dynamics (Chapin et al. 1997; Barshares et al. 2001).

    • Changes in predation dynamics often create competitive advantages for non-native species.

Conclusion

  • Anthropogenic alterations may favor the establishment of non-indigenous species, compromising native species’ survival chances.

  • The paper advocates for further investigation of SRM mechanisms in ecological contexts as threats to biodiversity increase due to human impacts.