March lab discussion (Alice’s pick)

2nd March 2010

Discussion lead by: Alice Yeates

Topic: how we measure the impacts of invasive species.

Background paper:

Parker, I.M., Simberloff, D., Lonsdale, W.M., Goodell, K., Wonham, M., Kareiva, P.M., Williamson, M.H., Von Holle, B., Moyle, P.B, Byers, J.E. & Goldwasser, L. (1999).

Impact: Toward a framework for understanding the ecological effects of invaders.

Biological Invasions 1: 3-19.


Much of my work focuses on invasive plant species and the communities that they invade. I have found that many papers state that a specific weed has a negative impact on the community in which they have invaded, however, many of the attempts at quantifying this impact has problems associated with them. As Parker et. al. (1999) outlined that comparative studies are by far the most dominant in the literature to assess impact (81)  and whilst there are several  experimental studies on their own (47), very few studies use a combination of both comparative and experimental approaches (11).


In addition to Parker et. al. (1999), lab members discussed other papers that used either one of these three approaches to highlight the benefits and problems associated with different methods of assessing the effect of invasive species. Discussion included the following: difference between comparative studies looking at presence/absence of the invader and gradients of invader density or abundance; the importance of examining multiple trophic levels and the mechanisms behind the impact; the benefit of long-term studies; and the need to address impact on an appropriate temporal scale for the invader and the community involved. We concluded that assessing the impact of invasive species is a difficult task, and although many approaches have limitations, these studies are beneficial to furthering our understanding of the effect invasive species has on the communities they invade. Whilst it is important to invest time and money into in-depth studies, we should focus on drawing generalisations from these studies and examine the broad mechanisms behind impacts of invasive species. By doing this we may avoid the necessity of in-depth studies on every introduced species and for each invaded community which is impractical and may result in poor management during the early stages of invasion.


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