Loss of large mammals reshapes Brazil’s dry tropical forests

Jim Crocker
25th November, 2025

Loss of large mammals reshapes Brazil’s dry tropical forests

Figure from study shows a dramatic decline in mammal biomass across the Caatinga region, with contemporary assemblages (red) exhibiting significantly lower aggregate and mean body mass compared to those reconstructed from historical species distributions (blue), indicating widespread defaunation.

Image adapted from: Canassa et al. / CC BY (Source)

Key Findings

  • This study in Brazil’s Caatinga region reveals a severe loss of mammal diversity, with 90% of the area experiencing a 20-80% decline in species
  • Mammal communities in the Caatinga have shrunk by roughly 77% of their original biomass, largely due to habitat loss from agriculture and overhunting
  • Protected areas show lower rates of mammal loss, highlighting their importance for conservation, though even these areas haven’t fully prevented declines
The world is experiencing a dramatic loss of biodiversity, often referred to as the sixth mass extinction event. This isn’t simply about species disappearing; it’s about the breakdown of ecosystems and the services they provide to humans, such as clean water, pollination, and climate regulation. A key component of this crisis is ‘defaunation’ – the loss of animal life from ecosystems[2]. While global studies highlight widespread declines, understanding the specific drivers and extent of defaunation in particular regions is crucial for effective conservation. Researchers from the Federal University of Paraíba, Federal University of Piauí, University of East Anglia, Instituto Juruá, State University of Paraiba, and University of Florida[1] investigated the extent of mammal defaunation in the Caatinga, a tropical dry forest region in northeastern Brazil. This area is particularly vulnerable due to a combination of overhunting and habitat loss driven by agricultural expansion and livestock grazing. The study focused on medium- to large-bodied mammals, as these species often play critical roles in maintaining ecosystem health. The research team analyzed data from 73 local mammal assemblages within the 862,818-km2 Caatinga region, comparing historical species distributions with current observations. They assessed changes in both the presence of species and the structure of the mammal communities – essentially, how different species interact with each other. Their findings revealed a severe loss of mammal diversity. Ninety percent of the Caatinga had experienced a decline of between 20% and 80% of its mammal species, and the overall structure of these communities had shrunk by approximately 77%. Furthermore, over half of the 51 species studied (37 in total) had lost more than 50% of their geographic range within the region. This loss of mammal diversity isn’t just an aesthetic concern; it has significant consequences for the ecosystem’s functionality. The study demonstrated a strong link between defaunation and a decline in essential ecosystem processes. This aligns with broader concerns about the cascading effects of animal declines on ecosystem functioning and human well-being[2]. The researchers identified overhunting, conversion of natural habitat into farmland and pasture, and the presence of livestock as the primary drivers of defaunation. Interestingly, the study also highlighted the positive role of protected areas in mitigating these losses. Areas with formal protection experienced lower rates of defaunation, suggesting that establishing and effectively managing protected areas is a vital conservation strategy. This finding reinforces the importance of conservation efforts in regions facing intense human pressure. The scale of mammal loss in the Caatinga is comparable to that observed in other threatened ecosystems globally. Previous research has documented widespread declines in vertebrate populations, with an average 25% decline in abundance among terrestrial vertebrates since 1500[3]. The Caatinga study provides a detailed regional assessment, pinpointing the specific factors driving these declines. It also builds on the understanding that the loss of species on the brink of extinction can trigger further extinctions through disrupted ecological interactions[3]. The Caatinga’s situation exemplifies this ‘extinction breeds extinctions’ phenomenon. The Caatinga region is characterized by a high degree of poverty and reliance on natural resources. This context is important because it highlights the need for conservation strategies that address both ecological and socioeconomic challenges. The research suggests that protecting remaining dry forests and restoring degraded habitats, alongside efforts to manage hunting and livestock grazing, are crucial steps towards reversing defaunation and safeguarding ecosystem services in this vulnerable region.

EnvironmentWildlifeEcology

References

Main Study

1) Reconstructing the degree of mammal defaunation throughout the Caatinga - the largest dry tropical forest region of South America

Published 24th November, 2025

https://doi.org/10.1371/journal.pone.0336562

Related Studies

2) Defaunation in the Anthropocene.

https://doi.org/10.1126/science.1251817

3) Vertebrates on the brink as indicators of biological annihilation and the sixth mass extinction.

https://doi.org/10.1073/pnas.1922686117


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