In the 2012 US Presidential election campaign, the Republican candidate, Mitt Romney, said: “President Obama promises to SLOW the rise of the oceans and HEAL the planet” (pause for laughter) “I promise to help YOU and YOUR FAMILIES.” Sadly, he did get the laughs. But, seriously, does the planet need healing? We could argue that biodiversity will eventually recover at its own pace and the planet will be fine. On the other hand, it probably won’t be very hospitable for us and our families. I think that Mitt got his argument backwards.
Although future generations of humans will surely lay the blame at our feet for the impacts on their lives of habitat degradation, I find it puzzling that, when blame is forecast, it is most often for the loss of iconic species or communities… polar bears and coral reefs, rather than for the manifold physical stresses we will have inflicted on future humans.
I seriously doubt that loss of polar bears will cut much ice with our descendants, the “shifting baseline” is too real a phenomenon and we are too plastic in our acceptance of almost any degraded, polluted habitat. Look at this photo, which I took north of Palo Alto, Calif., in 1969:
I felt that if I looked at the sky and the ground in quick succession, it was the ground that was the more dazzling, and the air smelled as though someone had just opened five hundred pots of honey. So, for me this is a wonderful memory and I miss being able to repeat the experience.
But do current residents of the San Francisco Bay region miss this spectacle? And do they blame the previous generation for removing it? I doubt it! I could be wrong, but I believe that this experience is simply gone and hardly anyone has noticed. I haven’t visited the floral displays in the Eastern California deserts that have been famous this year, but from images in the news they seem less intense and less speciose than my photo of the serpentine outcrop at Woodside, where the floral display was a predictable annual event, not a rare desert blooming.
What has happened? A few weeks after my photo was taken, the site went under concrete. Most such sites in the San Francisco Bay region have been paved over, but those that escaped the bulldozer have suffered nitrogen pollution from vehicle exhaust (Weiss 1999), favouring invasive exotic plants (eg Erodium) over the native serpentine flora that my old photo shows.
The reason for my visit to Woodside was to record the diet of the Bay Checkerspot butterfly, Euphydryas editha bayensis, a subspecies restricted to serpentine outcrops in and around the San Francisco Bay region, and a long-term subject of my PhD supervisor’s research (Paul Ehrlich). Thinking about the checkerspot allows me to shift to a happier climate story than Mr Romney’s joke. This species has a tendency to evolve to the outer limits of its climatic tolerances, even in the central parts of its range (Singer and Parmesan 2010; Singer 2017; see Box 1 below). As a result, it’s climate-sensitive, with climate-caused population extinctions recorded in the 1970’s and a geographic range that was already shifting significantly polewards and uphill in the 1990’s (Parmesan 1996). So, we might expect this butterfly to be in trouble, but it isn’t! Although two of its endangered subspecies (Quino and Bay Checkerspots) may bite the dust with changing climate, the species as a whole possesses multi-faceted ecotypic variation that gives its populations the opportunity to respond in situ to warming climate by changing their size, timing, host affiliation or geotaxis (Bennett et al 2015). Even subspecies that disappear should be reconstitutable from existing variation if their habitats were restored (Mikheyev et al 2013). In sum, despite its demonstrated climate-sensitivity, Edith’s checkerspot as a species is likely to prove more resilient than humans to continued warming.
Bennett, NL et al 2015. Geographic mosaics of phenology, host preference, adult size and microhabitat choice predict butterfly resilience to climate warming. Oikos 124, 41-53.
Mikheyev, AS et al (2013). Host-associated genomic differentiation in congeneric butterflies: now you see it now you don’t! Molecular Ecology 22: 4753-4766
Parmesan C (1996) Climate and species range. Nature 382: 765-766
Singer MC (2017) Shifts in time and space interact as climate warms. PNAS 114: 12848-12850.
Singer, MC, Parmesan, C (2010). Phenological asynchrony between herbivorous insects and their hosts: signal of climate change or pre-existing adaptive strategy? Phil Trans Roy Soc B 365, 3161-3176
Weiss SB (1999) Cars, cows and checkerspot butterflies: nitrogen deposition and management of nutrient-poor grasslands for a threatened species. Cons Bio 13:1476-1486