Climate Change and Species Interactions

A guest blog by Christopher Schwind

Driving through the foothills of the Sierra Nevada Mountains in April delivers a show reminiscent of the paintings of Claude Monet. This April is the peak of the wildflower bloom here, and the variety of colors, shapes, and smells is intoxicating. The Sierra Nevada are at the heart of the California floristic province, one of the most botanically diverse places on the planet, and where we have come today to collect the Woodland Star flowers and their highly specialized pollinators, Greya moths. These moths depend completely on the Woodland Stars for their survival, and Woodland stars depend heavily on the Greya moths for their reproduction. Looking around at the myriad of wildflowers around us, we know that each wildflower species here depends on some pollinator or group of pollinators for its reproduction, and the future of each depends on these interactions. Unfortunately, this web of interactions is under threat right now as the climate changes.

Wildflowers of the Sierra Nevada foothills (photo credit: C. Schwind).

Wildflowers of the Sierra Nevada foothills (photo credit: C. Schwind).

Climate change is causing species to migrate in order to remain in suitable habitat. Since some species may not move as quickly as others, and some depend most heavily on certain aspects of the climate (i.e. temperature vs. precipitation), interacting species may be pushed in different directions, and into places where they no longer interact. In the case of Greya moths and Woodland Stars, these species have slightly different climactic requirements, but because of their dependence on one another, they are limited to habitat that suits them both. Their dependence on one another therefore limits the available future range for both parties, thus reducing their ability to cope with continued climactic changes.  In general, as plants and pollinators get pushed in different directions, who interacts with who will change, likely leading  to reduced numbers and diversity of wildflowers in places like this, and slowly draining the color out of our painting.

Dead Ponderosa Pine trees (left) due to infestation by the Mountain Pine Beetle (right). Photos: C. Schwind.

Dead Ponderosa Pine trees (left) due to infestation by the Mountain Pine Beetle (right). Photos: C. Schwind.

Another way that climate change is affecting species interactions is by changing the context in which they interact. Here in the Sierra Nevada, there is a dramatic example.  The once thriving Ponderosa Pine forests here are quickly dying due in large part to infestation by the Mountain Pine Beetle. John Muir once wrote of Ponderosa Pines, “Of all pines, this one gives off the finest music to the winds”. In all respects, these are some of the most majestic trees of California. The Mountain Pine Beetle is native to the area, and the Pines here have coexisted with it for millennia. However, the current drought in California has weakened these trees.  The primary defense of the trees is to fill the holes drilled by beetles with sap. Drought stricken trees can’t make enough sap to fight them off, and the Mountain Pine Beetle populations have soared. It is estimated that California has lost at least 66 million trees since 2010.  This loss is due to the changed context in which pines and Mountain Pine Beetles interact, as a result of severe drought. Rather than a direct effect of climate change, it is an indirect effect via a change in an interaction between species.  As the climate continues to change, California is expected to see more severe and prolonged droughts, which will continue to change the context in which species interact. This is likely to bring about a cascade of other problems.  In this case, the loss of so many pines will have enormous consequences for the communities of plants and animals that make these forests their homes.

Species interactions are the glue that holds communities and ecosystems together. Our forests, meadows, and streams are not simply collections of species, much like our own communities are not simple collections of people.  They are built on the  relationships amongst those people. The losses we sustain due to climate change are underestimated when we only consider the direct effects on species. While some losses are now inevitable, the magnitude of loss is not set in stone. Much of this loss could be averted if we continue to push for cleaner ways to produce our energy and food. If we want our grandchildren to understand Monet’s inspiration, and the music John Muir so loved, we must protect our species and the interactions that tie them together.

Christopher Schwind is a Masters Student in Ecology and Evolutionary Biology at UCSC.