It’s all connected: birds, introduced trout, and talking trees

We all know about food webs—or we think we do. Herbivores eat plants, then predators eat herbivores, and if one part of the web is affected, other parts are impacted too. Seems pretty simple—except that the threads in those webs sometimes connect things you would never expect.

For example: trout and a songbird, the Gray-crowned Rosy-Finch, in an alpine habitat. The fish are in the water and the birds are on land—how connected can they be? If the birds were Bald Eagles or Ospreys or Great Blue Herons, sure, they would be connected because the birds eat the fish. If the birds were ducks, maybe the trout would be an occasional threat to the ducklings. But this is a Gray-crowned Rosy-Finch:


Photo by Blake Matheson*

They’re not going to be eating fish, and their babies definitely don’t float about on the water.

The reason that we need to worry about what threads on the food web those trout might be tugging at is that the trout are introduced, nonnative species. Alpine lakes often don’t have any fish in them naturally. In the Sierra Nevada and many other mountain habitats, however, people have stocked these lakes with fish so that people can come and fish them for fun. This has been a problem for aquatic species such as frogs, which get gobbled up quite happily by the new fish, but nobody was particularly worried about the effects on songbirds.

It turns out that we should have been.

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Think like a scientist: human-driven selection

A salmonella outbreak on chicken has hospitalized over a hundred people so far. Salmonella is on a lot of chicken; if you cook chicken at all regularly, you have definitely purchased and handled salmonella-tainted chicken. But that’s okay, because you cook it, and the bacteria die from the heat, and then the chicken does not kill you. No worries!

This chicken might want to kill you... Photo by Ido Mor

This chicken might want to kill you…
Photo by Ido Mor

Except that those 100+ sick people probably weren’t eating chicken sushi. Even if they did all manage to undercook their chicken, there’s this: a Costco found salmonella on its rotisserie chicken after they were cooked at 180 Fahrenheit. Chicken is “safe” when it’s cooked at 165 Fahrenheit, so 180 should be extra safe. Now, I’m not a salmonella investigator; maybe Costco lied about its cooking temperature, or maybe someone handled raw chicken and then the rotisserie chicken and that’s how they got contaminated. But there is a third option: maybe a strain of salmonella has evolved, under selection driven by you and me and everyone else who cooks their chicken, to survive cooking.

We all know what natural selection can do, how the pressure of competing with other individuals and evading predators and finding food and staying the right temperature so that you can make the most babies can drive the evolution of “forms most beautiful and most wonderful” (Darwin).

A form beautiful and wonderful: male greater kudu in Kenya.

A form beautiful and wonderful: male greater kudu in Kenya.

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