Climate change will affect every corner of the globe in some way, from rising average temperatures to ocean acidification to increasingly extreme and unpredictable weather. It may eventually lead to coastal habitat becoming submerged and the desertification of once-green areas. Currently, however, one of the areas in which climate change exhibits its most dramatic effects is on mountains.
On mountains, the variation in elevation causes habitats to change over relatively small areas. Species may be adapted to just a small strip of habitat within a certain elevational range. With changing climatic conditions, those strips of habitat may move on the mountain, and species then have to follow that strip – track their climatic niche – or stay put and adapt rapidly to the new conditions there.
Several of my colleagues at the museum have published on the affects of climate change on species in the Sierra Nevada mountains in California – the same mountains where I study juncos.
They found that over the past century, the majority of small mammals have shifted their ranges. The patterns in those shifts are telling: most of the ranges shifted upward (the only downward-shifting species were two shrews), with either upper range limits expanding, lower range limits contracting, or both. High-elevation species, the upper limit of their ranges trapped by the top of the mountain – you can’t live any higher than the ground goes! – saw their ranges shrink as their lower range limit contracted upward.
Two high-elevation species, the bushy-tailed woodrat and the shadow chipmunk, experienced “range collapse”: their ranges didn’t shift, they squeezed, with both the lower limit and upper limit contracting (Moritz et al. 2008).
Out of 53 bird species, over 90% tracked their climatic niche: that is, they followed the temperature and precipitation values that they were adapted to, as those values shifted over the landscape due to climate change (Tingley et al. 2009). That doesn’t sound so bad, as long as you aren’t one of those high-elevation species trapped by the top of the mountain, right? Unfortunately it isn’t as simple as tracking your niche, because sometimes the niche doesn’t exist anymore. Temperature and precipitation changes actually moved in opposite directions, so that temperature pulled birds upslope while precipitation pulled them downslope, and often that just-right niche didn’t exist anywhere anymore (Tingley et al. 2012).
The more we study these issues, the more it becomes clear that lots of factors affect the response of any given species. Clutch size, territoriality, and migratory status all affected the chances of a bird species shifting its range (Tingley et al. 2012). Within the broad patterns of range shifts in birds and small mammals, there is lots of variation, each species doing things slightly differently. One of the goals of my research is to understand the response to variation in environmental conditions so well in one species that we can begin to move past just seeing broad patterns, and actually understand the mechanisms of why any bird species might respond in such a way to such a change.
Moritz C, Patton JL, Conroy CJ, Parra JL, White GC, Beissinger SR. 2008. Impact of a century of climate change on small-mammal communities in Yosemite National Park, USA. Science 322:261-264.
Tingley MW, Monahan WB, Beissinger SR, Moritz C. 2009. Birds track their Grinnellian niche through a century of climate change. PNAS 106 supp. 2:19637-19643.
Tingley MW, Koo MS, Moritz C, Rush AC, Beissinger SR. 2012. The push and pull of climate change causes heterogeneous shifts in avian elevational ranges. Global Change Biology 18:3279-3290.