Scientists issue warning after making troubling discovery about elusive deer species: 'It had never been demonstrated as robustly'

A study published in the Journal of Applied Ecology revealed a troubling connection between native deer populations across Brazil's Atlantic rainforest and human activity and influence.

What's happening?

As Agência FAPESP reports, a team of Brazilian researchers spent years trying to assess the population density of five deer species in the rainforest.

This is particularly tricky with deer because they are so elusive. After collecting samples at 31 sites across 21 conservation units using detection dogs and then analyzing fecal DNA, they estimated the density of each species.

The results were alarming. In some areas, deer populations were as low as 0.14 individuals per square kilometer. The data showed that human pressures had the greatest impact on the deer populations. These included hunting, domestic dogs, diseases introduced by livestock, and competition with wild boar, which are an invasive species in many regions, including Brazil.

The only exception was the presence of human park rangers. The study found that the more park rangers there were protecting an area, the greater the density of deer.

First author Márcio Leite de Oliveira said the study offers the clearest picture of how human influence is affecting these mammals. "Although the direct relationship between deer population density and threats was expected, it had never been demonstrated as robustly as we have now," he said.

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Why is human impact on deer populations concerning?

Deer are crucial to forest health. They disperse seeds, shape vegetation growth, and provide food for native predators. Their disappearance can throw food chains off balance and threaten ecosystems, which are interconnected.

The findings also raise concerns about the health of the habitat. If human influence is impacting deer populations, it's likely that other elements are being similarly impacted. This can set off a ripple effect that can harm soil health, threaten biodiversity, and reduce water quality — all changes that affect local communities.

What's being done to protect deer populations?

The findings have already been incorporated into Brazil's National Action Plan for the Conservation of Ungulates. The evidence of higher deer densities in areas with more park rangers is also a promising sign that boots-on-the-ground conservation efforts work.

The researchers say repeated assessments every five to 10 years will be key to tracking trends and informing future forest management. Expanding protected areas, managing invasive species, and enforcing antipoaching measures are all equally important.