Small Protected Spaces Can Be Vital for Small Mammal Conservation, Study Finds

Rodents make up about 40 percent of all mammal species and most of the non-flying mammals on Earth. They evolved at least 178 million years ago and were the first mammals to scurry around underfoot of the dinosaurs, until all but the birds disappeared 66 million years ago, according to Nature.

In a new study, researchers from Stanford University discovered that current communities of small mammals are inherently different from those that existed just a few hundred years ago in pre-colonial North America, reported Phys.org.

The researchers compared the remains of small mammals from Holocene and Anthropocene bone deposits from areas with various amounts of modification.

Although there is debate, the Anthropocene is thought to be the period from the 1950s to the present when humans began to significantly affect the climate and ecosystems of the planet. It is distinguished by pollution, accelerated climate change and landscape modification.

The researchers discovered that small, protected areas have the ability to conserve communities of small native mammals, demonstrating their vital function for conservation projects in urban areas.

Human activity like urban growth is progressively changing the Earth’s natural ecosystems and putting the planet’s biodiversity in jeopardy.

The study revealed that communities of small mammals from the Anthropocene aren’t as diverse and are structured differently than they were during the late Holocene only a few centuries earlier, which demonstrates the scope of human influence on Earth’s ecosystems.

“While we have not lost many small mammal species in the Anthropocene, we have gained non-native species that were not present in the pre-European past. Additionally, highly modified (urban) spaces are much less diverse today than in the Holocene. Regardless of how modified areas are, though, we detected significant changes in overall small mammal community composition from the Holocene to today,” Maria C. Viteri, a Ph.D. graduate in Ecology and Evolution from Stanford University, told EcoWatch in an email.

The study, “Spatiotemporal impacts of the Anthropocene on small mammal communities, and the role of small biological preserves in maintaining biodiversity,” was written by Viteri and Elizabeth A. Hadly, a professor in the Department of Biology at Stanford University, and published in the journal Frontiers in Ecology and Evolution.

Because of the limited geographic ranges of individual small mammals, their abundant populations and the specificity of their habitat, they are good gauges of ecosystem well-being. For millennia, small mammals like shrews and rats have been taxonomically stable due to their high rate of fertility and growth, low rate of extinction and overall abundance. These factors make them the perfect focus of spatiotemporal studies.

“Small mammals are excellent subjects for studies that examine change over both space and time since they are abundant over both of these gradients. In addition, they are foundational to terrestrial ecosystems, being eaten by many different species, and can therefore indicate overall ecosystem health,” Viteri told EcoWatch.

Humans and changes in the environment can alter small mammal communities in ways that aren’t always apparent, since small mammals have lower extinction rates than their larger counterparts. Reductions in the diversity of communities and population numbers can indicate declines in the health of ecosystems and be a predictor of extinctions. The tracking of spatiotemporal gradients of small mammal diversity can show the effects of humans on all species types.

“We found that small mammal communities in our ‘urban’ site were highly uneven, meaning that one species dominated the community at the cost of others. Other studies have shown that low evenness may precede and predict extinction,” said Viteri. “Since small mammals are foundational to ecosystems, dramatic changes in their composition and diversity may lead to declines in the species that rely on them.”

In the study, the scientists surveyed three sites with different levels of land modification by humans. The first was a site with the least amount of human modification, Jasper Ridge Biological Reserve; the second was one with an average amount of human modification, the Student Observatory at Stanford; and the third was a location that had a high amount of human modification, the Stanford University campus.

“We examined thousands of small mammal bones and teeth from modern (Anthropocene) raptor pellets and three (Holocene) archaeological sites along the gradient, representing different levels of human modification today,” said Viteri, as reported by Phys.org.

Three crucial findings were observed.

“First, small mammal diversity decreased with increasing human modification today,” Viteri said.

The evenness and richness of species were reduced across the three sites depending on the amount of human modification.

“Second, the overall make-up of today’s small mammal communities is fundamentally distinct from past communities, even 500 years ago,” said Viteri, according to Phys.org.

This finding revealed the impact human activities have had on even the hardiest of species.

The third finding was more optimistic.

“Our results demonstrate that even a relatively small, protected space can at least partially protect native faunal communities,” said Viteri, as Phys.org reported.

There has been a long-standing debate regarding how big a protected area has to be to act as a buffer for loss of species on a planet that is becoming more and more altered by humans. Study after study has demonstrated that bigger reserves are more successful at preserving biodiversity.

“Although ideally we would be able to set aside large parcels of land for the protection of biodiversity, in many urban or suburban settings this is untenable. Fortunately, our study shows that even a relatively small preserve is able to buffer the loss of our more sensitive small mammal species,” Viteri told EcoWatch.

The study demonstrated that, in urban settings without large areas available for conservation, the protection of smaller spaces can be vital.

“The study shows that the way that we manage lands matters, and that it is not too late to protect our lands in order to protect biodiversity,” Viteri said, as reported by Phys.org.

However, Viteri added, “While biological preserves can buffer biodiversity change across spatiotemporal gradients of human impact, they cannot completely mitigate the overwhelming signal of the Anthropocene on today’s ecosystems.”

Viteri said the importance of ecosystem protection has been demonstrated by the success of Indigenous people at maintaining biodiversity.

“We must become better stewards of both our natural and human-dominated landscapes. The native Muwekma-Ohlone people [of the San Francisco Bay Area] were able to maintain these systems for thousands of years through active management. It is imperative to prioritize the protection of biodiversity through stewardship,” Viteri told EcoWatch.

Correction: A previous version of this article’s headline was misleading. The headline was updated for accuracy and clarity on September 6, 2022.