How human activities have influenced "energy flow" in the environment

A collection of fossilized owl pellets in Utah suggests that when the Earth went through a period of rapid warming about 13,000 years ago, the small mammal community was stable and resilient, even as individual species changed along with the habitat and landscape.
By contrast, human-caused changes to the environment since the late 1800s have caused an enormous drop in biomass and “energy flow” in this same community, researchers reported today in Proceedings of the National Academy of Sciences.
The dramatic decline in this energy flow - a measurement of the energy needed to sustain the biomass of this group of animals for a given amount of time - shows that modern ecosystems are not adapting as well today as they once did in the past.

While climate change is one part of this problem, researchers at Oregon State University and the University of New Hampshire have found that changes in land cover have been far more important in the last century. A particular concern is the introduction and expansion of invasive, non-native annual grasses at the expense of native shrublands. The end result, they say, is the transformation of the Great Basin into an ecosystem that is distinct from its 13,000-year history.
The study is the first of its type to track an ecosystem-level property, energy flow, over many thousands of years, and is ultimately based on the study of owl vomit – little pellets of undigested bones, hair, and teeth that owls regurgitated over millennia into Homestead Cave near the Great Salt Lake. These pellets contain the remains of owls’ prey, mostly mammals that are smaller than a house cat.
“These owl pellets provide a really spectacular fossil record that allows us to track biologic changes continuously through thousands of years,” said Rebecca Terry, an assistant professor in the College of Science at Oregon State University.
“They show a dramatic breakdown in ecosystem behavior since the late 1800s, in a way that doesn’t parallel what happened when major climatic warming took place at the end of the last Ice Age,” she said. “The current state is driven by human impacts to habitat, and these impacts have been a stronger force in shaping the mammal community over the last century than just climate change.”