Natives On The Move Could Become The Enemies Within

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June 18th, 2010

	Fucus serratus. Image source

Concern for biodiversity under climate change should extend to the potentially harmful effects of native species shifting range.

According to a review by Cascade Sorte and co-researchers, the spread of introduced species and the climate change-induced shift of native species are both “fundamentally biological invasions” and the impacts of shifting native species can be just as great as those of introduced species, with the “potential to seriously affect biological systems”.

This potential for disruption has been largely overlooked in range shift studies, they say, and much can be learnt from invasion biology about what to expect from climate change-driven shifts.

Marine environments are likely to change more quickly than terrestrial ones, because the rates of range shifts are faster in marine than terrestrial environments.

From a review of 55 separate studies, Sorte and colleagues identified 129 marine species, mostly coastal species, that have shifted their ranges. Climate change was considered to be the cause of more than 70% of the range shifts, and 75% of the shifts were in the poleward direction.

Marine range shifts occurred at an average rate of 19 km a year, 30 times faster than the average on land of 0.61 km a year. However, introduced marine species moved more than twice as fast as shifting marine species at an average of 44.3 km a year. 

Community and ecosystem-level effects were documented for less than than 10% of the shifting species (8 of 129 shifting species), and they were always negative.

They included nutrient inputs, competition, herbivory, predation and disease. For example, the urchin Centrostephanus rodgersii (an Australian shift, see East Australian Current bolsters Tasmania's invading sea urchin numbers) has caused a 40-fold decrease in total algal biomass.

The impacts of shifting native species were of similar magnitude to those of introduced species for competition, predation and herbivory, higher for nutrient impacts and lower for disease.

The crucial difference between shifting native species and introduced species is that the initial donor communities and colonised communities are adjacent in range shifts but separated in introductions. The degree of separation influences the success of range-shifters and introduced species.

Reasons proposed for the success of introduced species include enemy release (they have left behind co-evolved natural enemies), competitive release (they have less competition in their new range) and naïve prey.

They would have advantages over shifting species, which are likely to share more evolutionary history with predators, prey and competitors in an adjacent range.

Introductions might also be successful and have greater impacts if humans selectively move robust species as occurs with the introduction of aquarium and aquaculture species.

However, shifting species may have advantages with already-developed defences to, or competitive advantages over, native enemies (in contrast to introduced species), physical and chemical conditions matching those in their original range, and adjacent locations with well-established populations providing a ready source of propagules (new recruits for establishment).

The researchers found that successful shifting species share traits attributed to successful introduced species, such as competitive and predatory superiority, short generation times and broad environmental tolerances.

For example, the shifting alga Fucus serratus is more fecund and grows faster than a native competitor Fucus vesiculosus it suppresses, and shifting fish species tend to be smaller and to mature faster than fish with stable ranges.

It has been suggested that generalists are more prone to expand than specialists, which are more prone to contract.

References

Sorte CJB, Williams SL and Carlton JT. 2010. Marine range shifts and species introductions: comparative spread rates and community impacts. Global Ecology and Biogeography 19(3): 303-316.
 

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