Research Article |
Corresponding author: Santiago José Elías Velazco ( svelazco@sdsu.edu ) Academic editor: Marcus Vinicius Cianciaruso
© 2025 Anderson Igomar Antonio, Admir Cesar de Oliveira Junior, Fabricio Villalobos, Santiago José Elías Velazco.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Antonio AI, Oliveira Junior ACde, Villalobos F, Velazco SJE (2025) Environmental heterogeneity as a determinant of bee diversity patterns in the Atlantic Forest. Frontiers of Biogeography 18: e142410. https://doi.org/10.21425/fob.18.142410
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The Atlantic Forest encompasses a wide range of environmental and geographical gradients with high endemism and species diversity among several taxonomic groups, including bees. Environmental heterogeneity is a determining factor for species diversity, as environments with greater heterogeneity tend to offer a greater variety of conditions, thus supporting higher species richness. However, bee richness patterns and their relationship with environmental heterogeneity in the Atlantic Forest remain underexplored. In this study, we aimed to describe the bee diversity patterns and investigate how different components of environmental heterogeneity—specifically temperature seasonality, topographic and geomorphic heterogeneity, and stream density—influence species richness, both for the entire biome and within each ecoregion. To do so, we modeled and estimated the distribution of 466 bee species. Relationships between bee species richness and environmental heterogeneity variables were analyzed using Generalized Linear Models, variable importance, and partial dependence curves. We found that the highest richness was in the southwestern regions of the Atlantic Forest, particularly in the Serra do Mar Coastal Forests and Araucaria Moist Forests. The most important variables positively related to species richness were temperature seasonality, followed by topographic and geomorphic heterogeneity, whereas stream density showed the lowest importance. At the ecoregion level, temperature seasonality was the most important variable for 9 of the 11 ecoregions, followed by topographic and geomorphic heterogeneity. In ecoregions with the highest bee richness, environmental heterogeneity showed a low explanatory power. Notably, the relationships between the environmental heterogeneity variables and species richness varied across ecoregions. Our findings highlight the significant role of environmental factors in shaping bee species richness in the Atlantic Forest at multiple scales. Furthermore, the distinct relationship observed between environmental heterogeneity and species richness across ecoregions reinforces the necessity of multi-scale diversity studies to elucidate the unique characteristics of each ecoregion.
Bee species richness in the Atlantic Forest is greatest in the south-west and southern regions.
Seasonal temperature was the most important variable for predicting species richness, showing a positive effect in nine of the 11 ecoregions.
Topographic and geomorphic heterogeneity contributed significantly to species richness in certain ecoregions.
Relationship between species richness and environmental heterogeneity variables varied among ecoregions.
Ecoregions with higher richness were poorly explained by environmental heterogeneity, suggesting other influencing factors.
Multiscale analysis reveals that different regions may have unique species richness drivers, crucial to understanding species diversity in this biodiversity hotspot.
Apoidea, Atlantic Forest, geomorphic heterogeneity, nonstationarity, richness pattern, seasonality, species distribution modeling, topographic heterogeneity
The Atlantic Forest biome extends across eastern Brazil, northeastern Argentina, and eastern Paraguay. This region exhibits a wide range of latitudinal, altitudinal, and environmental gradients and comprises multiple ecoregions with distinctive environmental attributes (
The Anthophila clade comprises all bee species and represents a highly diverse group within Apoidea (
Studying diversity patterns is fundamental for understanding the dynamics and structure of ecological communities, as well as for helping manage and conserve biodiversity (
Environmental heterogeneity is defined as the variation in biotic (e.g., vegetation structure) and abiotic (e.g., topography) environmental characteristics within a given area (
Bees are sensitive to environmental changes and have specific requirements for foraging, gathering resources, and maintaining their nests (
The relationship between a response variable (e.g., species richness) and predictor variables (e.g., environmental heterogeneity) can vary significantly at different temporal or spatial scales, a phenomenon known as nonstationarity (
The Atlantic Forest extends along the entire eastern coast of Brazil, from Rio Grande do Norte to Rio Grande do Sul, and through the coastal and continental areas to southern Brazil, eastern Paraguay, and southwestern Argentina (
We used the integrative boundary of the Atlantic Forest (
To construct the species list for the Atlantic Forest, we followed two stages. First, a list of species occurring in the Atlantic Forest was generated from occurrences sourced by
The species list included all bee species with at least one occurrence in the Atlantic Forest. We then removed species without distribution in the Atlantic Forest. We used the Taxonomic Catalog of Brazilian Fauna (https://fauna.jbrj.gov.br/) and the Taxonomic Catalog of Brazilian Fauna and Moure Catalog (https://moure.cria.org.br/) as species origin sources. The scientific names were revised according to the Taxonomic Catalog of Brazilian Fauna and Moure Catalog. The raw occurrence data listed 770 species names, but after scientific name correction and selection of those species native to the study area, 564 native bee species to the Atlantic Forest were listed. Species with only one occurrence (n = 74) were eliminated, leaving 490 species for distribution modeling.
We performed a spatial cleaning that consisted of removing occurrences with invalid coordinates, duplicated coordinates, and georeferenced in centroids of municipalities, provinces/states, and countries. For data integration and cleaning, we used the R packages bdc (
Occurrences compiled from large databases generally have spatial bias, with a higher density of points close to human infrastructure (
Variation in temperature, humidity, and precipitation patterns can directly influence species behavior and resource availability across an environment, thus shaping the geographic distribution of species (
Because the amount of occurrence data affects the performance of Species Distribution Models (SDM), and there are different techniques for dealing with lack of data, we defined three modeling protocols: one for species with ≥ 15 occurrences (n = 183 species), another for species with between 5 and 14 occurrences (n = 156), and another for those with between 2 and 4 occurrences (n = 151). Species with only one occurrence were not included in our analysis. For the first and second protocols, the SDM training area was defined as delimited by ecoregions where a species had at least one presence. We used
No single algorithm can handle all modeling conditions, so we used the following seven algorithms: Artificial Neural Network (NET), Boosted Regression Trees (BRT), Generalized Additive Model (GAM), Generalized Linear Model (GLM), Maximum Entropy (MAXENT, hereafter MAX), Random Forest (RAF), Support Vector Machine (SVM), and Gaussian Process (GAU). The NET, BRT, MAX, RAF, and SVM algorithms have hyperparameters that can affect model performance and predicted suitability patterns (
For species with 5–15 occurrences, the Ensemble of Small Models (ESM) approach was used. This technique is suitable for building models for species with few occurrences and consists of creating bivariate models with a combination of all pairs of predictors and subsequent consensus between the bivariate models weighted by Somers’D metric (D = 2 × (AUC – 0.5)), where AUC is the area under the curve (
For species with 2–4 occurrences, distributions were estimated based on environmental similarity using Gower’s distance for cells within a 50 km radius around the species occurrences (
The SDM and ESM were validated using k-fold and repeated k-fold cross-validation techniques, respectively, with repetitions. Five partitions were used for SDM, and five partitions and five repetitions were used for ESM. We used the Inverse Mean Absolute Error –IMAE– (threshold-independent metric) and Sorensen (
When SDMs are projected over large geographical extents, models tend to predict high suitability areas outside the species’ current range, potentially affecting diversity patterns (
We created a species richness map by stacking species semi-binary models. The semi-binary models consist of assigning zero to environmental suitability values that are below the threshold and keeping all values above it continuous (
Four environmental heterogeneity variables were explored: topographic heterogeneity, geomorphic heterogeneity, temperature seasonality, precipitation seasonality, and stream density. Topographic heterogeneity was based on a 30 m resolution digital terrain model from the R atlanticr package (https://github.com/mauriciovancine/atlanticr) and was calculated using the standard deviation of the altitudinal variation of the 30 m cells contained in the 5 km resolution cells (i.e., equal to the resolution of the distribution models). For geomorphic heterogeneity, we calculated the Shannon diversity of the different geomorphological features (plane, peak or summit, ridge, shoulder, spur, slope, hollow, slope, valley, and depression) of the 90 m resolution cells contained in 5 km resolution cells. We used Geomorpho90m as the geomorphological feature source (
The relationships between species richness and different environmental heterogeneity variables were analyzed for 12 regions: the Atlantic Forest as a whole and 11 ecoregions. For the extent of the Atlantic Forest, we also performed an analysis including ecoregions as a predictor variable together with environmental heterogeneity to evaluate the contribution of the ecoregion to explain the bee richness pattern. We used multiple regressions constructed using Generalized Linear Models (GLM) using the Poisson distribution family, which is suitable for discrete response variables (i.e., species richness). Assumptions of normality and homogeneity of the residuals were assessed visually. Moran’s I correlograms were used to assess the spatial autocorrelation of the residuals. To correct it, we used a spatial filter method based on eigenvectors (
Temperature seasonality was used both to construct the SDMs and to analyze the relationship between richness and environmental heterogeneity, raising concerns about potential circularity—using the same variable in both modeling and explanatory analyses may artificially inflate the results. However, using one variable to model individual species distributions through SDMs is not the same as using this same variable to model the community-level pattern that emerges from stacking several individual modeled distributions (e.g., species richness;
Ensemble SDM models performed well, with IMAE and Sorensen values of 0.73 (± 0.05) and 0.74 (± 0.08), respectively. Similarly, the ESMs presented a good performance, with average IMAE and Sorensen values between the algorithms of 0.63 (± 0.06) and 0.74 (± 0.11) (Suppl. material
Regarding the relationship between species richness and environmental heterogeneity, we found that the variable with the greatest importance (i.e., explained variance) for the Atlantic Forest was temperature seasonality (87.44), followed by topographic (25.7) and geomorphic (23.6) heterogeneity, which each demonstrated similar levels of importance. Stream density had low explanatory power (Fig.
When we explored the relationship between environmental heterogeneity and bee richness separately for each ecoregion, we found that the influence of environmental heterogeneity on patterns of bee species richness varied among ecoregions. Thus, temperature seasonality was the most important variable in nine of the 11 ecoregions (Fig.
In addition to varying in relative importance, the direction of the relationship between different aspects of environmental heterogeneity and bee species richness varied among the ecoregions (Fig.
In this study, we sought to describe the patterns of bee diversity in the Atlantic Forest and to investigate the influence of different environmental heterogeneity variables on species richness, both for the entire biome and each of its ecoregions. We found that bee richness was higher in the southern and southwestern regions of the Atlantic Forest and that temperature seasonality and topographic heterogeneity together partly explain these patterns. However, we found that the relationship between species richness and each of the features of environmental heterogeneity that we explored varied among ecoregions. This nonstationarity indicates that the relationship between environmental heterogeneity and bee richness is not spatially homogenous and that some environmental features may be more important for determining species richness in some regions than others (
Patterns of estimated bee species richness were consistent with patterns observed for other taxonomic groups. For example, the regional hotspots of bee richness (i.e., the southwestern region of the Atlantic Forest) coincide with high concentrations of bird, mammal, and amphibian species (
We found that temperature seasonality was the most important feature of environmental heterogeneity for bee species richness across the Atlantic Forest biome and within some of its ecoregions. Surprisingly, for most ecoregions (7 of 11), temperature seasonality had a positive relationship with bee species richness. However, this relationship has not been commonly observed in other organisms. For bats and marsupials in the Atlantic Forest, temperature seasonality is negatively associated with species richness (
Topographic and geomorphic heterogeneity showed positive relationships with bee species richness for the entire Atlantic Forest biome as well as several ecoregions in which these environmental features demonstrated high explanatory power. Topographic heterogeneity is important for maintaining biodiversity in the Atlantic Forest (
Stream density is a relatively understudied variable compared to other metrics of environmental heterogeneity, such as those related to topography or climate. Although water is a fundamental resource for bees (
Despite the importance of seasonal temperature, topographic, and geomorphic heterogeneity in the Atlantic Forest biome and some ecoregions, these variables demonstrated relatively low explanatory power in ecoregions with the highest species richness, such as the Serra do Mar Coastal Forests and Araucaria Moist Forests. Previous research has shown that the distribution of species richness in areas characterized by especially high diversity cannot be explained by environmental heterogeneity alone (
Environmental heterogeneity is increasingly being recognized as an important component in maintaining biodiversity (
Bee species richness was highest in the Serra do Mar Coastal Forests and Araucaria Moist Forest ecoregions, while the coastal regions of the northeast (e.g., the Pernambuco Coastal Forests) and drier inland areas (e.g., the Caatinga and Bahia Inland Forests) showed the lowest diversity. Temperature seasonality emerged as the most important variable explaining species richness, showing a positive relationship with bee richness in most ecoregions. Topographic and geomorphic heterogeneities also play an important role in determining bee richness patterns in some parts of the Atlantic Forest. Moreover, stream density was poorly correlated with richness patterns. We found that the relationship between environmental heterogeneity variables and bee species richness varied substantially between ecoregions. This finding reinforces the need to study diversity patterns at multiple spatial scales to highlight the nuanced drivers of species diversity within each ecoregion. Interestingly, in ecoregions with the highest bee species richness, aspects of environmental heterogeneity showed low explanatory power, suggesting that other factors are the primary determinants of local biodiversity.
We thank B. Rose for reading and editing the first draft of the manuscript. AIA and ACOJ thank CAPES-DS for their master’s degree scholarship. FV Thanks INECOL and CONAHCyT-Mexico for their support. SJEV thanks i) the Center for Open Geographical Science (COGS), Department of Geography, at San Diego State University for the research support, ii) Atlantic Forest Biodiversity Observatory (Instituto de Biologia Subtropical, UNaM CONICET) for computational resources, and iii) funding from FONCyT, Agencia de Ciencia y Tecnología, Ministerio de Ciencia y Tecnología de Argentina (PICTO-2022-10-00097).
Conceptualization (AIA, SJEV), Methodology (AIA, SJEV), Formal analysis (AIA, ACOJ, SJEV), Data curation (AIA, SJEV), Writing – Original Draft (AIA, SJEV), Writing – Review & Editing (AIA, ACOJ, FV, SJEV).
Species occurrence dataset and predictor variables used to construct species distribution, and raster with environmental heterogeneity variables can be accessed at: https://doi.org/10.6084/m9.figshare.28680413.
Figure S1: Map of Atlantic Forest ecoregions; Figure S2: Correlogram of the original predictor variables based on the Pearson correlation matrix; Figure S3: Geographical pattern of environmental heterogeneity variables used to relate with bee richness of the Atlantic Forest; Figure S4: Performance of ESM (esm_) and consensus models (median) based on Sorensen and IMAE metrics; Figure S5: Relationship between different environmental heterogeneity variables in their original scales and species richness of native bees in the Atlantic Forest; Figure S6: Importance of ecoregion and different environmental heterogeneity variables in explaining species richness of native bees in the Atlantic Forest; Figure S7: Relationship between environmental variables in their original scales and species richness in Atlantic Forest ecoregions; Figure S8: Pearson correlation between species suitability and predictor variables used to explore the relationship between species richness and environmental heterogeneity. Each point represents a species. Red-dashed lines represent correlation > |0.7|. 27 species presented correlation > |0.7|; Table S1: List of ecoregions analyzed and original ecoregion names. Ecoregions with small geographic expressions have been joined to larger and closer ecoregions; Table S2: Justification for the inclusion of predictor variables used in species distribution models; Table S3: Parameters and hyperparameters used in each algorithm, values, and number of hyperparameter combinations, and R codes used to generate the sequence of values (.docx)