Invasive species can have significant effects on resource
availability and can suppress or enhance the relative
abundance of native species, without necessarily being the
driving force behind community change (Didham, et al. 2005).
It is now accepted that invasive species are one of the leading causes in world biodiversity loss, it has been assumed that the reasoning behind this domination is there ability to move into a degraded area or system and take advantage of the already imposed decline of the natural species within the affected area. But another plausible hypothesis has come to light; can exotic species dominance be the indirect consequence of habitat modification, driving natural species loss (Didham, et al. 2005).
In a paper by MacDougall and Turkington, they have created the first direct test of whether invasive species are drivers of community change or just passengers along for the ride. The 'driver' model predicts that invaded communities are highly interactive, with subordinate native species being limited or excluded by competition from exotic dominants.
The 'passenger' model predicts that invaded communities are primarily structured by non-interactive factors (environmental changes, dispersal limitation) that are less containing on the exotics, thus they dominate (MacDougall and Turkington, 2004).
In order to prove this theory an area of oak savanna with different species of grass cover was located and the scientists then manipulated the weather conditions, soil condition and soil depth, grass species removal to see if the invasive species had an easier time adapting to these changes compared with the native species. The results of this testing showed that 36 of the 79 of native species did not respond to the treatments and declined. Seed numbers revealed that some of the species were dispersal limited and competition alone could not explain their rarity (MacDougall and Turkington, 2004). The results of MacDougall and Turkington's work show a lean towards the passenger model as the major cause of invasive species dominance, although the effects of the driver model on the ecological community was still quite substantial.
References:
It is now accepted that invasive species are one of the leading causes in world biodiversity loss, it has been assumed that the reasoning behind this domination is there ability to move into a degraded area or system and take advantage of the already imposed decline of the natural species within the affected area. But another plausible hypothesis has come to light; can exotic species dominance be the indirect consequence of habitat modification, driving natural species loss (Didham, et al. 2005).
In a paper by MacDougall and Turkington, they have created the first direct test of whether invasive species are drivers of community change or just passengers along for the ride. The 'driver' model predicts that invaded communities are highly interactive, with subordinate native species being limited or excluded by competition from exotic dominants.
The 'passenger' model predicts that invaded communities are primarily structured by non-interactive factors (environmental changes, dispersal limitation) that are less containing on the exotics, thus they dominate (MacDougall and Turkington, 2004).
Species threatened by invasive species with New South Wales. Source: spa.nsw.gov.au. Assessed on the 13th of April 2014.
In order to prove this theory an area of oak savanna with different species of grass cover was located and the scientists then manipulated the weather conditions, soil condition and soil depth, grass species removal to see if the invasive species had an easier time adapting to these changes compared with the native species. The results of this testing showed that 36 of the 79 of native species did not respond to the treatments and declined. Seed numbers revealed that some of the species were dispersal limited and competition alone could not explain their rarity (MacDougall and Turkington, 2004). The results of MacDougall and Turkington's work show a lean towards the passenger model as the major cause of invasive species dominance, although the effects of the driver model on the ecological community was still quite substantial.
References:
- MacDougall, A.S. and Turkington, R. (2005) Are invasive species the drivers or passengers of change in degraded ecosystems? Ecology 86, 42–55.
- Didham, R.K., Ewers, R.M., Gemmell, N.J., Hutchison, M.A., Tylianakis, J.M. (2005) Are Invasive Species the drivers of ecological change? Trends in Ecology and Evolution. Vol.20 No.9. 470 - 475.
This is an interesting post. It is nice to see that there are some proponents of alternative theories.
ReplyDeleteSo if it is driven by the passenger model is correct, how do you think we should tackle the problem of invasive species? As well how do should one then approach restoration.
ReplyDeleteIf the passenger model is indeed the correct, in order to limit and possibly control the influx of invasive species into declining areas. There needs to be more emphasis placed on rehabilitation. An example of this would be a species management plan where species are ID and counted within a degraded area, then soil and environmental work ups are done to look into what is exactly causing this habitat decline. Once these factors are taken into consideration it is then possible to form an action plan that should theoretically improve the wellbeing of the degraded area. Making it impossible to the invasive species to get a foot hold in the area.
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