Hostile Takeover

Birds, lizards, and tortoises are aiding the invasion of alien plants in the Galápagos Islands by eating the fruit and spreading their seeds, scientists report in Proceedings of the Royal Society B.

The invasive plant problem in the Galápagos is so severe that the islands now house more alien plant species than native species. Some of the worst offenders are guava, blackberry, and lantana. Animals happily munch on the fruit of these plants and can disperse the seeds through their feces.

The researchers decided to find out how thoroughly the alien plants had exploited this system of seed distribution. They collected 2,879 droppings from 18 bird and reptile species, then studied seeds found in the droppings under a microscope to identify the plants.

Only about 5 percent of the seeds came from alien plants, the study authors found. But 24 percent of the plant species identified were alien, and 15 of the bird and reptile species carried alien plant seeds. Lava lizards, ground finches, mockingbirds, and giant tortoises were among the most prolific seed distributors.

The alien plants might be boosting their chances of dispersal by bearing fruit outside the peak fruit season, the study authors speculate. Most of the islands’ native fruit growth peaks in May, but blackberries peak in February and guava in late summer. By offering tasty snacks when native fruit is scarce, the alien plants may entice more animals to assist their invasion. Roberta Kwok | 22 November 2012

Source: Heleno, R.H. et al. 2012. Seed dispersal networks in the Galápagos and the consequences of alien plant invasions. Proceedings of the Royal Society B doi: 10.1098/rspb.2012.2112.

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