The Neotropical montane cloud forests are among the most diverse forest ecosystems in the New World, stretching from Aramberri in Nuevo León, northeastern Mexico, at roughly 24 degrees north, to Catamarca Province in northwestern Argentina, at about 28 degrees south. They occupy mid to upper elevations between 600 and 3,800 meters, with Andean cloud forests typically found between 2,000 and 3,500 meters and northern Neotropical forests between 1,500 and 2,500 meters. Under exceptionally humid coastal conditions they can descend as low as 500 meters. Their frequent and prolonged orographic clouds generate high moisture from rain and fog, promoting an exuberant, dense vegetal cover rich in epiphytes, and supporting exceptionally high levels of endemism that have attracted quantitative biogeographic analysis since the 1990s.

The review team examined published literature from the 1990s through 2025, searching Google Scholar and Web of Science for studies that identified and delimited areas of endemism in these forests using methods such as track analysis, Parsimony Analysis of Endemism (PAE), the optimality-based NDM/VNDM method, and phenetic analyses of similarity (UPGMA). The compiled studies covered fungi, vascular plants, epiphytic bromeliads and orchids, butterflies and other insects, amphibians, birds, rodents, bats, and marsupials, analyzed at local, regional, and continental spatial scales with geographic units ranging from 0.25-degree grids to raw locality records. The authors defined an area of endemism as a region where two or more taxa with different dispersal capacities show a non-random congruence in their distributions, relying on strict and extensive sympatry as the main identification criterion.

Because independently published delimitations vary in scale, grid origin, species score, and endemism index, the team compared the authors’ published maps and descriptions using two operational categories of spatial congruence: nested endemism, when one area is fully contained within another, and partial spatial congruence, when areas overlap but differ in extent and boundaries. An area was considered well-supported if at least two independently proposed maps showed total or partial spatial congruence along the same mountain chains. This procedure allowed the researchers to address nested endemism directly, recognizing, for example, that a broad continental area of endemism for birds extending from eastern Mexico to north-central Nicaragua contains the much smaller amphibian area of endemism in the northern Altos de Chiapas.

The seven well-supported areas of endemism correspond to the main mountain chains of the Neotropics: (1) Northeastern Mexico, encompassing the northern Sierra Madre Oriental, supported by vascular plants, fungi, and amphibians; (2) Western and Central Mexico, spanning the Sierra Madre Occidental, the Transmexican Volcanic Belt, and the Sierra Madre del Sur, with three nested areas for bromeliads, orchids, and fungi and partial overlap with butterflies and birds; (3) Southern Mexico in the Sierra Madre del Sur, where twelve nested areas were recognized for birds, butterflies, orchids, bromeliads, and amphibians; (4) Eastern Mexico to north-central Nicaragua, the largest area of endemism, running from the Sierra Madre Oriental to the Chiapas Highlands, congruent with three areas for vascular plants, butterflies, and fungi and containing sixteen nested areas for birds, plants, fungi, orchids, bromeliads, and amphibians; (5) Northwestern South America, including the Sierra Nevada de Santa Marta and Serranía de Perijá, supported by rodents and birds; (6) Western South America, defined by vascular plants and birds; and (7) the Southern Andean Yungas, supported by insects, bats, and marsupials. Each region encompasses different levels of species richness and composition.

The review also compiled a diagnostic list of the endemic taxa supporting each natural biotic unit, validating scientific names against standard online classification systems. Northeastern Mexico is diagnosed by fungi such as Xylaria juniperus and X. subcoccophora and by amphibians including Chiropterotriton multidentatus and Craugastor decoratus. Western and Central Mexico is supported by dozens of vascular plants, by birds such as the endemic Arremon virenticeps, Cyanocorax dickeyi, Eupherusa ridgwayi, Rhynchopsitta pachyrhyncha, and Streptoprocne semicollaris, and by butterflies and fungi. Southern Mexico is diagnosed by birds including Cyanolyca mirabilis, Eupherusa cyanophrys, and E. poliocerca, by orchids such as Prosthechea obpiribulbon and Rhynchostele candidula, and by a striking radiation of amphibians, including multiple species of the salamander genus Thorius and Sarcohyla hazelae. The Mesoamerican area is supported by orchids such as Stanhopea tigrina, birds including Oreophasis derbianus and Rhynchopsitta terrisi, and numerous fungi and amphibians. Northwestern South America is diagnosed by birds such as Heliangelus mavors, Myioborus albifrons, and Poospiza goeringi and by rodents including Nephelomys childi and N. meridensis. Western South America is defined by plants such as Bomarea distichifolia, Fuchsia ayavacensis, and Monactis flaverioides and by the birds Heliangelus regalis and Scytalopus parkeri. The Southern Andean Yungas is supported by insects including Adejeania andina and Bassania schreiteri and by bats and marsupials such as Thylamys cinderella and T. sponsorius.

The comparative synthesis also exposed the methodological fragility underlying endemism delimitation. The quality and quantity of data available for each biological group condition the results, and incomplete, spatially biased sampling remains a pervasive limitation in montane regions. Species delimitation and taxonomy are intrinsically sensitive, since recent diversification and cryptic speciation may be common in these forests. Different grid cell sizes can produce areas of endemism with varying sizes, shapes, and species compositions, and there is no standard for the parameters used to delimit areas, no shared grid origin, species score, or endemism index, to provide a common starting point of comparison. Regional or nationwide studies that include incomplete distribution areas for widespread species can identify areas that lack evolutionary significance. The team noted, for example, that some taxa supporting the Yungas area, such as the bats Artibeus planirostris, Chrotopterus auritus, Eptesicus diminutus, Myotis albescens, M. keaysi, and M. riparius, are widespread across the Neotropics and occur only in small regions within the Yungas, suggesting that the term area of endemism should be reserved for evolutionarily significant studies and a different term used for conservation-focused research.

Despite these methodological differences, the overlap among previously reported areas of endemism, derived from various methods and spatial scales, suggests that these regions harbor a high degree of endemism across different biological groups, including both restricted and shared taxa, indicating a common biogeographic history. Spatial congruence between areas of endemism implies primary biogeographic homology, a hypothesis of shared history in which different taxa are spatially and temporally integrated within the same biota. The nested structure of the detected areas is itself informative: fine-scale endemic areas are consistently embedded within broader biogeographic provinces, particularly in western, central, and southern Mexico, and nested areas may be interpreted as a robust biogeographic signal involving underlying ecological and evolutionary processes in the assembly of larger-scale patterns. The review’s results also agree with independent biogeographic studies, including an Andean pattern of geographic differentiation in tree ferns corresponding to the two South American areas and an oak area of endemism corresponding to Southern Mexico and the Mesoamerican area.

The identification of areas of endemism has important implications for conservation, particularly where regions of high richness across different biological groups overlap. The Neotropical cloud forests are under increasing threat from deforestation and climate change, and recognizing these natural biotic units contributes to setting priorities for biodiversity conservation. The authors emphasize that future research should include several biological groups in biogeographic analysis and integrate phylogenetic and ecological information to identify distribution patterns and their drivers in one of the most biodiverse regions on Earth. The barriers that have shaped these patterns, the Andes, the Marañón River Valley, the Nicaragua Depression, and the lowlands of the Isthmus of Tehuantepec, have not affected all species equally, and Quaternary climate fluctuations remain the most common historical process invoked to explain genetic differentiation among allopatric populations of Neotropical birds.

Taken together, the findings indicate that studying multiple taxonomic groups allows the identification of well-supported areas of endemism in the Neotropics, and that the current distribution of the montane cloud forests, matching the main mountain systems of the New World from central Mexico to northwestern Argentina, is unlikely to be due to chance. Recognizing these areas permits the generation of hypotheses about the history of geographic units and their biotas, provides a framework for examining patterns of diversification among component clades, and facilitates the identification of regions with unique biotic assemblages. For the humid, epiphyte-laden forests that cling to the mountain chains of tropical America, the new synthesis offers both a map of evolutionary distinctiveness and a blueprint for protecting it.

Subject of Research: On the identification of areas of endemism in the Neotropical montane cloud forests: A comparative review

Article Title: On the identification of areas of endemism in the Neotropical montane cloud forests: A comparative review

Article References: Castro-Torreblanca, M., Sánchez-González, L. A., & Luna-Vega, I. (2026). On the identification of areas of endemism in the Neotropical montane cloud forests: A comparative review. Frontiers of Biogeography, 19, Article e174469. https://doi.org/10.21425/fob.19.174469

Image Credits: AI Generated

DOI: 10.21425/fob.19.174469

Keywords: identification, areas, endemism, Neotropical, montane, cloud, forests, comparative, review, scientific research