Disentangling the abundance-impact relationship for invasive species
Bethany A Bradley1,2, Brittany B Laginhas2, Raj Whitlock3
1Department of Environmental Conservation, University of Massachusetts, Amherst, MA 01003; bbradley@eco.umass.edu.
Summary
Understanding invasive alien species (IAS) impacts is key. Higher trophic level invaders cause rapid native declines, while same-level invaders cause linear declines, informing management strategies.
Area of Science:
- Ecology
- Conservation Biology
- Invasive Species Research
Background:
- Predicting biological invasion threats requires understanding invasive alien species (IAS) impacts on native species.
- The relationship between IAS abundance and native species response is poorly understood across ecosystems and taxa.
- Trophic position of IAS is hypothesized to strongly influence native species and community responses.
Purpose of the Study:
- To assess the shape, direction, and strength of native population and community responses to increasing IAS abundance.
- To investigate how native responses vary with the relative trophic position of IAS.
- To differentiate impacts at population versus community levels.
Main Methods:
- Global meta-analysis of 1,258 empirical studies from 201 scientific publications.
- Quantified native population declines and community metric changes in response to IAS abundance.
- Tested the influence of IAS trophic position on native species responses.
Main Results:
- Native populations declined nonlinearly by 20% on average as IAS abundance increased.
- Community metrics showed a linear decline of 25% with increasing IAS abundance.
- Higher trophic level invaders caused strong, nonlinear native declines, especially at low abundance; same-trophic-level invaders caused linear declines; lower-trophic-level invaders had inconsistent impacts.
- IAS abundance significantly impacted species evenness and diversity more than species richness at the community level.
Conclusions:
- Native species responses to IAS are critically dependent on invader abundance and trophic position.
- Abundance-impact relationships reveal invasion dynamics and inform IAS management timing.
- Understanding these relationships is crucial for predicting and mitigating biological invasion threats.
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