Humans have totally altered small mammal communities in just a few centuries

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Newswise — Researchers have found that small mammal communities today are fundamentally different from what they were centuries ago in pre-colonial North America. They identified archaeological Anthropocene and Holocene small mammal remains along a geographic area with varying degrees of human impact and examined the diversity between these sites and time periods. Optimistically, the researchers also found that even small protected areas can retain native communities of small mammals, highlighting their important role in urban conservation projects.

Characterized by rapid climate change, pollution, and landscape alteration, the Anthropocene is an unofficial geological unit of time and is defined as the most recent period in Earth’s history (1950s to present). ) where human activity began to have a significant impact on the planet’s ecosystems and climate. This impact is increasingly altering natural ecosystems and threatening biodiversity, for example due to rapid urbanization.

Stanford University researchers have now found that modern communities of small mammals in the Anthropocene are less diverse and are structured differently than they were centuries ago, during the Holocene (about 500 years ago), showing the extent of the impacts of human activities on our ecosystems. The results were published in Frontiers in Ecology and Evolution.

Excellent study subjects

“We wanted to understand the impacts of land modification on small mammals, which are the foundation of terrestrial ecosystems,” said Dr Viteri, from Stanford University.

Small mammals, such as rats and shrews, are ideal subjects for spatiotemporal studies. Due to their population abundance, small geographic range, and habitat specificity, small mammals respond quickly to changes in land use, habitat, and climate, making them good indicators of ecosystem health. They also have a low extinction rate due to their high fertility, abundance, and growth rate. They therefore remained taxonomically stable for thousands of years.

Although fairly resilient to extinctions, small mammal communities may be altered by human impact and environmental change in less obvious ways. Reductions in populations and diversity at the community level can show declines in ecosystem health and could predict future extinctions. Tracking the diversity of small mammals on spatio-temporal gradients can reveal the magnitude of human impacts on all types of species.

Diminished diversity

The researchers studied small mammals along a geographic gradient of human modification: Jasper Ridge Biological Preserve (least human modification), Stanford Student Observatory (medium human modification), and the university campus from Stanford (high human modification).

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

The results showed three major findings: “First, the diversity of small mammals has declined with increased human modification today,” Viteri said. Species richness and evenness have declined at modern sites based on the level of human modification.

“Second, the overall composition of small mammal communities today is fundamentally distinct from communities of the past, even 500 years ago.” This shows that human activities have impacted even the most resilient species in Earth’s ecosystems.

Small conservation areas

The study’s third finding is more optimistic: “Our results demonstrate that even a relatively small protected area can at least partially protect native wildlife communities,” Viteri continued.

Conservation scientists have long debated the size of protected areas to cushion the loss of species in an increasingly human-modified world. Numerous studies have shown that large reserves are more successful in conserving biodiversity. However, this study shows the importance of small protected areas in urban areas, where large conservation areas are lacking.

“The study shows that how we manage land matters and it’s not too late to protect our land to protect biodiversity,” Viteri said. However: “While biological reserves can buffer changes in biodiversity across spatio-temporal gradients of human impact, they cannot completely attenuate the overwhelming signal of the Anthropocene on today’s ecosystems.”

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