Global transport of organisms by humans provides novel resources to wild species, which often respond maladaptively. Native herbivorous insects have been killed feeding on toxic exotic plants, which acted as ‘ecological traps’1,2,3,4. We document a novel ‘eco-evolutionary trap’ stemming from the opposite effect; that is, high fitness on an exotic resource despite lack of adaptation to it. Plantago lanceolata was introduced to western North America by cattle-ranching. Feeding on this exotic plant released a large, isolated population of the native butterfly Euphydryas editha from a longstanding trade-off between maternal fecundity and offspring mortality. Because of this release—and despite a reduced insect developmental rate when feeding on this exotic—Plantago immediately supported higher larval survival than did the insects’ traditional host, Collinsia parviflora5. Previous work from the 1980s documented an evolving preference for Plantago by ovipositing adults6. We predicted that if this trend continued the insects could endanger themselves, because the availability of Plantago to butterflies is controlled by humans, who change land management practices faster than butterflies evolve6. Here we report the fulfilment of this prediction. The butterflies abandoned Collinsia and evolved total dependence on Plantago. The trap was set. In 2005, humans withdrew their cattle, springing the trap. Grasses grew around the Plantago, cooling the thermophilic insects, which then went extinct. This local extinction could have been prevented if the population had retained partial use of Collinsia, which occupied drier microhabitats unaffected by cattle removal. The flush of grasses abated quickly, rendering the meadow once again suitable for Euphydryas feeding on either host, but no butterflies were observed from 2008 to 2012. In 2013–2014, the site was naturally recolonized by Euphydryas feeding exclusively on Collinsia, returning the system to its starting point and setting the stage for a repeat of the anthropogenic evolutionary cycle.
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P. R. Ehrlich introduced M.C.S. to E. editha in 1967; C. D. Thomas, H. L. Billington, D. Ng, L. E. Gilbert and J. L. B. Mallet helped to initiate the project. D. D. Murphy performed the 2010 census. C.L. Boggs, R. A. Steward, J. L. B. Mallet and C. S. McBride critiqued the manuscript. The 2013 Integrative Biology Faculty Merit Review Committee, University of Texas at Austin, provided incentive to complete the study. J. Schneider and B. Schneider, the Drudge family, Clear Creek Tahoe and The Nature Conservancy allowed access to the site.
Nature thanks T. Oliver, M. Friberg and the other anonymous reviewer(s) for their contribution to the peer review of this work.
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