A rancher dies, and butterflies lose the farm

Research in the journal Nature reveals that changing patterns of land use can tempt organisms into cruel and deadly evolutionary traps.

Much human activity is detrimental to the habitats of plants and animals across the globe. Occasionally, however, our pursuits lead to unexpected benefits: military training areas, or abandoned weapons factories have been shown to provide accidental sanctuary for wildlife and biodiversity.

More rarely, our labours hold out deadly promise to animals: a tempting novel resource that seems like a bounty but is actually toxic or otherwise unsuitable. An example of this is the decline in Australian monitor lizards (from the genus Varanus) after the introduction of the tasty-looking, but poisonous, cane toad (Rhinella marina). Situations like this are known as “ecological traps”.

Now research has identified a never-before reported variant of these: eco-evolutionary traps.

Twenty-five years ago, three ecologists visited a spring-fed meadow in Carson City, Nevada, in the US. The meadow was part of a cattle ranch owned by a fellow named Harry Schneider, and the ecologists saw in it a looming disaster. An isolated population of Edith’s checkerspot butterfly (Euphydryas editha) was beginning to develop a taste for an introduced plant species, Plantago lanceolate, over its traditional food source, Collinsia parviflora.

Plantago, introduced to the area by cattle ranchers, is a perennial plant, while Collinsia is a very short-lived native annual, thus the new arrival provided food for much longer, luring the butterflies to it to lay eggs.

By 2005 all the butterflies in Schneider’s meadow had evolved to eat and lay eggs on Plantago exclusively. The researchers had seen this coming, writing in 1993, “By adapting genetically to human-induced changes, the insects risk becoming dependent on continuation of the same practices. This is a serious risk, because human cultural evolution can be even faster than the rapid genetic adaptation that the insects can evidently achieve.”

The eco-evolutionary trap was set.

Now two of those ecologists, Michael Singer and Camille Parmesan, both from the University of Plymouth in the UK, report that the trap has finally been sprung. With the death of Harry Schneider, the meadow is no longer used for cattle grazing.

The fertilisers and land management left the meadow with an abundance of nutrients which fuelled a burst of growth for many taller grass species. This lush flora overshadowed the smaller Plantago, leaving the heat-loving butterfly larvae in the shade and surrounded by new-found predators that accompanied the grasses.

Searches beween 2008 and 2012 revealed that the Edith’s checkerspot butterfly population was extinct. Lured by the eco-evolutionary trap to evolve to a specific form of land use, the butterflies were fatally vulnerable to further changes – yet another thing for beleaguered conservation biologists to worry about.

These traps are not always obvious, say the authors, “but understanding them may become increasingly important to species conservation in the Anthropocene.”

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