For the first time, a team of Brazilian scientists has successfully estimated the population densities of five deer species inhabiting the vast Atlantic Rainforest, a biodiversity hotspot stretching along Brazil’s eastern coastline. This groundbreaking research provides critical insights into how human activities adversely affect ungulate populations, exposing a stark correlation between anthropogenic pressures and declining deer densities in this ecologically vital biome. Utilizing advanced fecal DNA analysis facilitated by trained detection dogs, the study represents a novel and highly accurate methodology for wildlife population assessment in dense forest ecosystems where direct observation is notoriously challenging.
The Atlantic Rainforest, known locally as Mata Atlântica, has suffered extensive habitat fragmentation and degradation due to decades of agricultural expansion, urban development, and resource extraction. Within this precarious landscape, deer species face compounded threats, including hunting, competition with invasive wild boars, and predation by domestic dogs. The research team’s comprehensive approach factored in these diverse pressures by performing field surveys across 31 strategically chosen locations within 21 protected conservation units spanning the biome’s entire geographic range, from the Northeast to southern Brazil. This wide spatial sampling ensured robust representation of the forest’s heterogeneous environments.
Central to the study was an innovative method combining environmental DNA (eDNA) sampling of deer feces with statistical models that incorporate species-specific defecation rates for accurate density estimations. Trained dogs located fecal samples in the dense understory, circumventing the difficulties of direct visual identification in the complex rainforest vegetation. The fecal samples then underwent genetic analyses to precisely identify each deer species, a technique that significantly reduces observer bias and enhances species detection even at low population densities. This approach provides a replicable framework for monitoring elusive ungulate populations in tropical forests worldwide.
The findings are sobering. Deer densities were found to be markedly lower in areas exhibiting high levels of human-induced disturbances. Anthropogenic influences such as hunting pressure, disease transmission linked to domestic cattle, and competition with invasive wild boars emerged as predominant factors shaping population distributions. Statistical analyses revealed that these human-associated variables exert a more substantial negative effect on deer density than traditional environmental factors like altitude, slope, or latitude. This insight underscores the profound ecological footprint of human activity on wildlife even within formally protected areas.
Among the species studied, the roe deer (Mazama rufa) exhibited the lowest recorded density of only 0.14 individuals per square kilometer in the Araucárias National Park, Santa Catarina. In contrast, the red deer (Passalites nemorivagus) population density peaked at 18.17 individuals per square kilometer in the Sooretama Biological Reserve, Espírito Santo, although average densities for this species across sampled areas ranged between 1.47 and 3.42 individuals per square kilometer. This exceptional density outlier for red deer is attributed to localized factors and highlights the variability of population dynamics shaped by site-specific environmental and anthropogenic conditions.
Interestingly, the study revealed a counterintuitive positive correlation between deer densities and the presence of park rangers working within these protected areas. The researchers hypothesize that increased ranger presence enhances enforcement against poaching and other illegal activities, indirectly supporting higher deer survival and detection rates. This positive human influence contrasts sharply with other anthropogenic pressures, emphasizing the key role of effective conservation management in mitigating wildlife declines.
The invasive wild boar (Sus scrofa), a prolific and adaptable species introduced to Brazil, competes directly with native deer for resources, including food and habitat space. Moreover, wild boars are potential vectors for diseases transmissible to both livestock and wildlife, compounding the health risks faced by deer populations. The presence of domestic dogs in forested areas poses an additional predation threat, intensifying mortality rates in already vulnerable deer assemblages. Collectively, these factors contribute to a precarious conservation status for Atlantic Rainforest ungulates.
The data amassed not only advances scientific understanding of cervid ecology in tropical rainforests but has already informed public policy. The robust population density indicators developed by the study have been integrated into the Brazilian Ministry of the Environment and Climate Change’s National Action Plan for the Conservation of Ungulates. This inclusion marks a significant step forward in policy-driven conservation efforts, providing quantifiable benchmarks to guide habitat protection, species management, and threat mitigation strategies.
The methodological rigour and extensive temporal scope of the research—spanning over a decade—sets a benchmark for future monitoring efforts. The authors advocate for regular, repeated population assessments every five to ten years to detect temporal trends, informing adaptive management actions responsive to changing environmental and anthropogenic contexts. This monitoring framework is critical for establishing long-term conservation priorities that are grounded in empirical evidence rather than anecdotal observations.
Coordinated by Márcio Leite de Oliveira of the University of Araraquara and supported by researchers including José Maurício Barbanti Duarte of São Paulo State University and Fernando de Camargo Passos of the Federal University of Paraná, the multidisciplinary team leveraged a combination of ecology, genetics, and conservation science. Their integrated approach, underpinned by funding from the São Paulo Research Foundation (FAPESP), demonstrates the power of scientific collaboration in addressing complex biodiversity challenges endemic to tropical forest regions.
This pioneering study enhances our understanding of species competition, population dynamics, and the broader ecological impacts of invasive species within highly endangered rainforest ecosystems. By highlighting the outsized role of human activity in shaping faunal community structure, it serves as a clarion call for intensified conservation measures that balance ecological preservation with sustainable human development. The refined, evidence-based tools developed promise to improve the efficacy of conservation policies and foster resilience in neotropical ungulate populations facing an uncertain future.
Ultimately, the research underscores the imperative for preserving and expanding protected areas within the Atlantic Rainforest to safeguard its unique cervid biodiversity. It also highlights the importance of integrating comprehensive wildlife monitoring techniques that leverage genetic tools alongside classical ecological methods. This multidimensional approach ensures higher accuracy in population assessments, enabling targeted interventions that can mitigate extinction risks while promoting ecosystem stability and integrity in one of the world’s most biologically rich yet vulnerable landscapes.
Subject of Research: Population density estimation and anthropogenic impact assessment of deer species in the Atlantic Rainforest
Article Title: Lower ungulate population density in rainforests under anthropogenic influences
News Publication Date: 27-Jan-2025
Web References:
- https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/1365-2664.14858
- https://bv.fapesp.br/en/pesquisador/692606/marcio-leite-de-oliveira
- https://www.gov.br/icmbio/pt-br/assuntos/biodiversidade/pan/pan-ungulados
Image Credits: Pedro H. F. Peres
Keywords: Species competition, Population density, Invasive species, Wildlife, Environmental monitoring
