Do landscape corridors help invasive species?

Landscape corridors are a popular way to expand wildlife habitat. But since these connectors allow native animals and plants to travel between habitat patches, it stands to reason that they might also help exotic species invade new territory. “[T]he same principles that support corridor establishment for threatened species… suggest that corridors could simultaneously jeopardize entire communities through spread of invasive species,” researchers write in Ecology.

The study authors examined the effects of landscape corridors on fire ants, an invasive species that has pushed out native ants around the world. Fire ant colonies come in two flavors: “monogyne” colonies, which have one reproducing queen that can fly long distances, and “polygyne” colonies, which have several reproducing queens that usually don’t stray far from their original home.

The team studied eight landscape sections in South Carolina, each of which contained five habitat patches. Some patches were connected, while others were isolated. The researchers trapped nearly 11,000 ants in the area, tallied the numbers from various species, and figured out whether the fire ant colonies in each section were primarily monogyne or polygyne.

In sections with monogyne colonies, corridors didn’t seem to affect the number of fire ants. But in sections with polygyne colonies, patches connected by corridors had 36 percent more traps containing fire ants than unconnected patches did. Ant species richness was also 23 percent lower in the connected patches.

In other words, the corridors were supposed to help native ants thrive — but the boost to fire ants “apparently negated any potential benefit of corridors to other ant species,” the authors write. The corridors may not have helped the monogyne colonies much because those ants are already adept at travelling long distances.

The study doesn’t imply that we should shut down landscape corridors. But we should keep in mind that when an invasive species isn’t particularly good at spreading on its own, linking habitat patches could give the pests a leg up on the competition. Roberta Kwok | 7 August 2014

Source: Resasco, J. et al. 2014. Landscape corridors can increase invasion by an exotic species and reduce diversity of native species. Ecology doi: 10.1890/14-0169.1.

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