Evolving Spring: Plant and Animal Vulnerabilities to Climate Change

Why do many of us believe that there is a serious problem heading our way called climate change? It's not a matter of blind faith. Like evolutionary theory it is an increasingly supported hypothesis based on a commensurate body of evidence. "Plants earlier bloom times hurting some creatures" reads the title of a recent Washington Post article by Brigid Schulte. See http://www.washingtonpost.com/local/plants-earlier-bloom-times-hurting-some-creatures/2011/04/08/AF42He4C_story.html. It goes on to describe field botanists' surprise that some flowers like “Dutchman’s breeches” and cut-leaved toothwort are blooming 2 weeks early. The culprit is global warming:

"Bloom hunters like Fleming, who for 40 years have been tramping through the woods, roaming along riverbanks and scrambling over rocky outcrops to document the first blooms of spring in the Washington area, worry that what they have been seeing is nothing less than the slow, inexorable shift of global warming.

They even have a name for it: season creep. And it’s happening all over the world."

Some causal evidence is experimental and comes from labs. A recent Science Friday show (http://www.sciencefriday.com/newsbriefs/read/200) made this point citing data from the University of Melbourne on the Australian common brown butterflies (heteronympha merope). They are emerging from their cocoons an average of ten days earlier than they did 65 years ago. The researchers attribute the butterflies’ early appearance to warming temperatures in the region. To test this they raised caterpillars of the common brown butterfly in a lab and then measured how quickly they emerged when exposed to different temperatures. The warmer the temperature, the earlier the butterflies took flight. They then used these measurements along with historic records of air temperatures around Melbourne, which rose about .25°F per decade, to predict when the butterflies emerged each year. Their predictions closely matched recorded observations. They concluded that:
"warming temperatures are coaxing the butterflies around Melbourne from their cocoons earlier each year, at a rate of about 1.6 days per decade."
(Photo by Flickr user Ibsut.)

The researchers believe the change in temperature is the result of human greenhouse gas emissions, not climate variability. A steady trend supported by 40 consecutive years of research at the Rocky Mountain Biological Laboratory also shows a warming trend. Flowers are blooming a month earlier than just 10 years ago. This is not all good for them, since some bloom early enough to be killed off by a late frost. That's another part of the problem, a trend towards greater weather variability. That's something easy to intuit since things are changing to a new normal. See http://www.sciencefriday.com/blog/2011/04/2031/ for a long list of evidence for climate change.

Biological warning signs of change are numerous and easily documented since many cultures have finely tuned agriculture to depend on spring for a release from winter famine. Cultures like the Korean have long records of when the first cherry blossoms of spring arrive and there is a 300 year European record on when grapevines bloom since planting time is critical to a good harvest.

A summary graphic in the Post shows how many plant species in the DC area are"creeping earlier" into spring. Bad for us, and it also has worrisome consequences for the naturally evolved plant and animal world. Evolution has fine tuned seasonal timing for many species. Our local squirrel population is dependent on the nut harvest to get them through winter. They have a frantic winter breeding seasons where females are in estrus for just 8 hours, but it results in spring-born squirrel babies (March to May) when there is again a natural supply of food. But some species in the complex chain of interdependence have been unable to keep up when seasonal timing is off.

In Europe, the leaves of the English oak are coming out earlier and this is OK for some animals. The winter moth caterpillars that feeds on them are also coming out earlier. But the pied flycatcher birds that eat those caterpillars aren't year around residents. They are migrating north at that time. Now when they arrive, many of the the caterpillars have already turned into moths and have flown off. It's a delicate ecological balance and changed timing has resulted in a severe decline of flycatcher population in recent years.

In San Francisco, some butterfly populations like Edith’s Checkerspot butterfly are simply gone. With the gradual warming of Earth and ocean temperatures that has also shifted rainfall patterns, the leaves of the plantago plant come out earlier. The leaves, which the checkerspot caterpillar depends on for food, are already dried and withered by the time the larvae emerge.

It's a deadly problem for migrating and seasonally dependent animal species. Even the largest creatures alive on the planet are affected - giant trees like our redwoods. A recent study finds that declining fog cover on the California's coast could leave the state's famous redwoods "high and dry." Among the tallest and longest-lived trees on Earth, redwoods grow where the summer fog provides water. But the fog is diminishing and climate change seems to be contributing to this decline in a high-pressure climatic system that lingers on the coast. See http://news.nationalgeographic.com/news/2010/02/100215-redwoods-california-global-warming/+.

Plant evolution has produced wonders, but unlike animals, they can’t just get up and relocate. The speed of change is something that vast numbers of species may fall to. Something to think about amidst this year's blossoms.