The first detailed study of an ecosystem's evolution over thousands of years has found that the small mammal population of western North America coped well with the end of the last Ice Age. Unfortunately, human-induced disturbances mean the same environments are now much worse placed to preserve biodiversity in the face of Global Warming.
Owls vomit up pellets of undigested hair, teeth and bones. Disgusting though we might find this, it is also extremely useful, providing a record of their diet through time.
Oregon State University’s Dr Rebecca Terry used pellets from Homestead Cave, Utah to build a record of mammals living in the Great Basin over 12,800 years. “These owl pellets provide a really spectacular fossil record that allow us to track biologic changes continuously through thousands of years,” said Terry, who reported her findings in the Proceedings of the National Academy of Sciences.
The end of the last Ice Age 13,000 years ago changed the local vegetation dramatically, as lakes and forests were replaced with desert shrubs. This changed the animal mix. However, Terry says that the energy flow, measured by the total kilojoules of food energy local animals consumed each day, remained stable as new species replaced those that couldn’t handle the heat.
More recent changes are very different. Not only is the region warming, but it has been invaded by cheatgrass, which is replacing native shrubs and grasses. Cheatgrass burns easily and is contributing to more frequent fires. Small animal populations are crashing from the dual impact of the cheatgrass and higher temperatures.
“Species distributions change over time, and that's not necessarily bad in itself,” Terry said. “But this research shows that ecosystem level properties, which are often assumed to stay relatively stable even when perturbations happen, are now changing as well. The ecosystems are losing their natural resilience, the ability of one group of species to compensate for the loss of another.”
The end of the ice age saw a drastic drop in the number of animals weighing 250–500 grams (9–18 ounces), but this was compensated with a rise in even smaller animals. Each of the smaller animals would have consumed less food, and were adapted to a drier environment, but total food consumption remained remarkably stable until very recently.
The paper notes, “Research on the ecological impacts of environmental change has primarily focused at the species level, leaving the responses of ecosystem-level properties like energy flow poorly understood.”
In part this focus on species is a reflection of the difficulty of accessing information about long gone environments, but the authors add, “Emphasis on species-level responses to environmental change is rooted in the paradigm that populations are highly dynamic while the aggregate properties of a community remain relatively stable and are thus more robust to perturbation.”
For 13,000 years Homestead Cave owls have had a nice view. Oregon State University/Flickr.
Top image, Oregon State University/Flickr.
1
