The introduction of non-native predators to a small Spanish island chain has caused a drop in the local lizard population and a concomitant reduction in a highly endangered flowering shrub. Researchers say the new study documenting this chain of events may be the first to demonstrate that biological invasions can disrupt plant-vertebrate partnerships and ultimately result in the extinction of an entire plant species.
According to fossil records, the fruit-eating lizard (Podarcis lilfordi) of Spain's Balearic Islands has seen its numbers decline since Roman times thanks to human introduction of non-native predators such as weasels and cats. Today, the lizards have gone extinct on all but one of their island homes.
This shakeup of the food web has had profound effects that go beyond the lizards themselves, ecologists Anna Traveset and Nuria Riera of the Institut Mediterrani d'Estudis Avancats in Mallorca, Spain, report in the April Conservation Biology. Suspecting that the fallen lizard population might be at the root of the decline of a perennial shrub (Daphne rodriguezii) that the lizards feast on, the researchers collected Daphne seeds from the feces of various island animals. Only seeds recovered from the lizards were still capable of germination, the researchers found. The team reasons that the lizards are therefore critical for the reproductive success of the plant.
The team's findings may be the first to quantitatively show that when such a delicate, specialized plant-vertebrate relationship is disrupted, the plant partner may ultimately face extinction, says Caroline Christian, a senior ecologist at the Nature Conservancy of California. "From a conservation perspective the results are alarming."
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