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The northern muriqui (Brachyteles hypoxanthus) and the southern muriqui (B. arachnoides) are the two species of the largest genus of primates in the Americas. A study in the Journal for Nature Conservation estimates that their habitat will be reduced by 44% and 61%, respectively, by 2090. In São Paulo, Brazil, the northern muriqui is expected to lose its entire climatically suitable area by the end of the century.

These figures only account for the effect of climate change on the species by the end of the century. They do not consider other factors that threaten primates and their habitats, such as deforestation, forest fragmentation, and hunting. Both muriquis are endemic to the Atlantic Forest and are classified as "critically endangered" by the International Union for Conservation of Nature (IUCN).

"Climate change alone won't lead to the extinction of muriquis, according to our projections. But about half of the current climatically favorable area for them could disappear, which is quite worrying considering that there are other factors putting pressure on these species," says Tiago Vasconcelos, the author of the study and a researcher in the Graduate Program in Biosciences at the Bauru campus of São Paulo State University (UNESP).

The projections are made using specialized software based on data such as the current distribution of muriquis and climate information that is important for their physiological requirements. Current climate data are thus used to characterize the species' preferences, which are then projected into different future climate change scenarios for the coming decades, such as changes in rainfall, warmer months, and drier days.

Challenge in the interior

Previous studies by other researchers had already indicated that climatically suitable areas for the two species of muriqui would be lost by the end of the century. However, Vasconcelos points to the extent of the damage in the short and medium term, specifically by the years 2030, 2050, 2070, and 2090.

"Other authors had already suggested a reduction in areas suitable for both species by 2050 and 2090, but we were able to point out the gradual loss that will occur throughout the century," explains the researcher, who is currently a substitute professor in the Department of Biology and Zootechnics at the Faculty of Engineering (FEIS) at the Ilha Solteira campus of UNESP.

For example, in 2023, an article pointed out that areas expected to be lost by the southern muriqui would be in semi-deciduous forests (which lose part of their leaves during the dry season) in the interior of the states of Paraná and São Paulo. Vasconcelos reached similar conclusions in his current study, but adds that these areas will shrink even further, continuously, over the coming decades until the end of the century. There will also be a shift in the species' range towards the northeast.

"This shift won't occur with an increase in suitable areas, as is predicted to happen with some animal groups. On the contrary. With the significant loss of areas in the west of their current range, the remaining populations are likely to be restricted to the eastern part," he explains.

Vasconcelos's work indicates that the northern muriqui has experienced similar patterns of loss of climatically suitable areas over the decades, with an accelerated reduction expected between 2070 and 2090. Most of this species' losses are expected to occur inland in the eastern and southern parts of Minas Gerais state, as well as central and western portions of Rio de Janeiro state.

By 2090, São Paulo is expected to lose all climatically suitable areas for the species. By that year, only two large climatically suitable areas will remain for the northern muriqui. One will cover the northern population in the state of Bahia and northeastern Minas Gerais. The other will be in the state of Espírito Santo, with a smaller area in northern Rio de Janeiro.

The large climatically suitable areas that will concentrate most of the population by the end of the century are along the coast and associated with ombrophilous forests, a type of coastal or riparian vegetation that occurs in areas with high rainfall.

"Climate change is likely to pose particularly difficult challenges for populations of both species in inland areas associated with semi-deciduous forests."

Solutions

The researcher emphasizes that the predictions only consider climate change, which could mask an even greater risk when considering synergistic threats, such as continuous habitat loss and forest fragmentation. Combined with the reduction of climatically suitable areas, this trend could lead to the isolation of muriqui populations and disrupt gene flow, which could affect the maintenance of viable populations. This could further reduce the species' range. Local extinctions have already been documented in degraded areas of semi-deciduous forests.

Therefore, the author concludes the study by recommending a focus on conservation efforts for these populations and warning of the need for a better understanding of how they will respond to climate change in the coming decades.

In the medium and long term, the study emphasizes the importance of focusing efforts on protecting the two species of muriqui in coastal rainforests and identifying the best locations for ecological corridors to connect currently isolated populations.

"This would give the species the opportunity to maintain gene flow and persist as healthy populations in this century," he concludes.