Under selection, an endangered species runs low on evolutionary “fuel”

Atlapetes pallidiceps

A pale-headed brushfinch, Atlapetes pallidiceps. (Wikimedia Commons:Aves y Conservación/NBII Image Gallery)

The pale-headed brushfinch, Atlapetes pallidiceps, is a conservation success story, or at least the first chapter of one. The birds were thought to be extinct, until a 1998 survey [PDF] of Ecuador’s Yunguilla Valley found four nesting pairs, and observed them foraging for insects and fruit. Following that rediscovery, the Fundacion Jocotoco secured a reserve encompassing the brush finches’ known territory, and took steps to control brood-parasitic cowbirds that were threatening them. Now, the population is five times bigger, with as many as 200 of the birds living in the reserve.

Have the brush finches’ rebounded enough to secure their population for the future? Populations that decline so precipitously can lose genetic variation, and may not regain it even if their numbers increase again. With reduced genetic variation, species that have undergone such a “population bottleneck” event may be unable to respond to natural selection imposed by disease or changing environments.

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