Yep, more invasives is not good - relationships between invader abundance and impact
Bradley, B.A., B.B. Laginhas, R. Whitlock, J.M. Allen, A.E. Bates, G. Bernatchez, J.M. Diez, R. Early, J. Lenoir, M. Vila, and C.J.B. Sorte, “Disentangling the abundance-impact relationship for invasive species”, 2019, Proceedings of the National Academy of Sciences
Summary
Invasive species undoubtedly cause negative ecological impacts, but we don’t yet understand how this impact changes as an invasion progresses. Bradley et al. (2019) performed a meta-analysis (synthesis of previous studies) of 1258 studies from 201 papers measuring ecological impacts as invaders increased in abundance. Invasive animals at higher trophic levels (i.e., consumers) caused nearly a 50% decline in the population size and community diversity of native prey, with the most rapid declines in native populations occurring early in the invasion process. This suggests that early detection and rapid response to range shifting insects, fish, and other animals is extremely critical to prevent rapid and significant losses in the native community. Invasive plants and animals at the same trophic levels (i.e., competitors) caused a 20-25% loss of native population abundance and diversity, with a predominantly linear decline, suggesting that managing these invasions at at any level of abundance will still benefit native communities.
Take home points
Even a small infestation of invasive predators or herbivores can cause a rapid decline in native species and communities, with native losses averaging 50%
Invasive consumers cause the greatest negative impact, and the strength of the impact decreases as the invader moves to lower trophic levels (i.e., competitors, producers)
The negative impacts caused by invasive plants within the native community can be seen negatively affecting higher trophic levels, such as native insects and birds.
Management implications
Early detection and rapid response to range-shifting insects, fish, and other animals is critical for preventing ecological impacts because invasive consumers cause the greatest negative impact early in the invasion process
The abundance vs. impact relationship for invasive plants is linear, so managing both emerging and existing populations could be equally beneficial for native communities
Knowing the trophic position and abundance of an invader can now be used to estimate ecological impacts, informing where management will be most effective
Related papers: Allen & Bradley, 2016; Evans et al. 2024
Keywords Range shift, Abundance, ecological impact