Over the past 2.6 million years there have been ~52 glacial-interglacial cycles, which have had profound implications for species’ distributional changes through time. Despite the ecological importance of bees, the long-term historical distributional shifts of most species have not been studied using ecological niche models (ENM) or analyzed in depth biogeographically. To date, ENM studies have been limited for bees in the genus Andrena. However, Andrena is an extraordinarily diverse group represented by > 1,700 species, offering a unique opportunity to address complex biogeographical questions through ENM. The species restricted to North America in the subgenus Plastandrena represent an ideal system for such study due to their common ancestry, occupancy of diverse environments, and polylectic nature. We utilized Chelsa-bioclim V2.1 1981–2010 and Chelsa-TraCE21k climate data in combination with the maximum entropy method (Maxent) to model the potential suitable area for each species during the modern day and Last Glacial Maximum (LGM). Our findings suggest that each of the five species potential distributions may have experienced significant expansions from the LGM to modern day, even though each species occupies distinct environments. Furthermore, we document the species-level biogeography of each taxon, identify new areas of potential discovery, and address regions where colonization may be limited by barriers such as the Sonoran Desert and species-specific phenologies. Future research should test these interpretations through population genetic studies. Highlights First detailed study of Andrena bees using ecological niche models with hindcasting to the Last Glacial Maximum (LGM). Potential significant post-glacial expansions were identified for all five species from the LGM to the present even though each species occupies distinct environments. New potential localities for species discovery are documented across North America. Barriers to colonization, including the Sonoran Desert and specific phenologies, likely restrict Andrena argemonis and Andrena mellea from coastal regions of the Western United States. Andrena crataegi may have undergone splitting into three or more populations during the LGM, followed by a limited reconnection during the modern interglacial period. Our results demonstrate the unique biogeography of these understudied bee species and illustrate how dramatic glacial-interglacial cycles have driven distributional changes, underscoring the need for future population genetic research.
Trees surrounded by low–stature alpine vegetation may function as habitat islands for canopy fauna. We examined whether diversity patterns of canopy–dwelling specialist spiders in an alpine treeline ecotone in the French Alps aligned with predictions of island biogeography. We focused on the lower canopy of pine (evergreen) and larch (deciduous) trees, collecting data in Spring, Summer and Autumn. We mapped forest patches and single trees and calculated insularity metrics (e.g. distance to neighbouring trees). We modelled variation of spiders within each tree (α–diversity, measured with Hill numbers) and between trees (β–diversity) against insularity metrics (e.g. tree height, distance to neighbouring trees, distance to the ecotone), tree phenology, sampling season and elevation. We explored diversity patterns for the entire spider assemblage and for two distinct functional groups: web–weavers and non–web–weavers. Insularity metrics contributed to explaining species α–diversity patterns of the canopy–dwelling spider assemblages. However, web–weavers were not affected by any of these variables. Seasonal fluctuations were associated with host tree needle phenology: evergreen trees consistently hosted higher spider diversity than deciduous ones, especially in Spring before leaf–out. At the onset of the season, dissimilarity in spider assemblages across trees (β–diversity) was mostly explained by geographic distance and insularity predictors, with the effect of geographic distance becoming negligible towards Autumn. These findings suggest that trees in alpine treeline ecotones can constitute habitat islands for specialised canopy–dwelling spiders and these effects are mediated by both sharp seasonal and phenological phases as well as by specific hunting strategies of spiders. Highlights Trees can be perceived as habitat islands and alpine treeline ecotones as habitat archipelagos, by spiders; The response to insularity differs between spider functional groups as defined by hunting strategies; Host tree leaf phenology (deciduous larch vs. evergreen pine) and seasonality also affect spider diversity; Our findings stress the usefulness of functional island biogeographic studies examining plant–animal interactions.
The Neotropics are Earth’s most species-rich region, so understanding how this diversity has emerged is of great interest. Here we address this question by assessing how species richness, speciation and dispersal are connected to geological and climatic history using the Neotropical fern genus Danaea (Marattiaceae) as a model. We evaluated alternative time calibrations to account for uncertain fossil affinities and integrated a dated phylogenetic tree of 78 Danaea species with 2,289 verified occurrence records, ancestral range and niche reconstructions, and biogeographic stochastic mapping. Our results suggest that Danaea diverged from the rest of the extant Marattiaceae ~128 million years ago (Ma), and the deepest divergence within the genus occurred ~53 Ma, likely separating eastern and western Amazonian lineages. The eastern lineage, corresponding to the subgenus Arthrodanaea , remains more restricted to Amazonia and low elevations than the more species-rich western lineage, which gave rise to the subgenera Danaea and Holodanaea . Speciation occurred mainly within regions rather than between adjacent regions. Amazonia has been the most species-rich region throughout the history of the genus, while the Andes have been the most important source of dispersals to other regions. Most Amazonian diversity arose within the last 6 Ma, coinciding with edaphic and climatic changes that occurred in western Amazonia in connection with Andean orogeny. Elsewhere, much of the diversification coincided with uplift of the Northern Andes and the emergence of terrestrial ecosystems in Southern Central America and the Pacific coast. Overall, all three subgenera seem to show parallel evolutionary responses to similar environmental changes. Although neotropical ferns in general show an Andean-centred diversity pattern, we found diversity in the genus Danaea (Marattiaceae) to be Amazon-centred. This may be related to the lack of epiphytes (which are most speciose in tropical mountain forests) in this genus. Even though Marattiaceae is an ancient family, most of the speciation leading to the extant species of Danaea has taken place in the last 6 million years and can be associated with geological processes such as Andean uplift and the draining of Amazonian megawetlands. Several lineages colonised montane areas before expanding further away from the equator, suggesting that physiological adaptation to high elevations may preadapt tropical plants for dispersal into more seasonal climates. In a comparison of different methods to calibrate a phylogenetic tree, the timing based on a molecular clock approach using well-known fossils and evolutionary rates from sister groups gave results more compatible with external biological and geological evidence than timings using fossils representing the target order but with uncertain phylogenetic placement within it.
Accidental epiphytes — terrestrial plants that opportunistically establish in trees — occur across climatic regions, but the conditions that allow them to colonise arboreal habitats remain poorly understood. We combined field surveys along a coastal western European transect, from the Netherlands to northern Spain, with curated community-science records and used Bayesian models to test whether accidental epiphyte occurrence, abundance and richness are associated with habitat setting, host size and macroclimatic positioning within each species’ climatic envelope. In the field, accidental epiphytes were more frequent, abundant and species-rich in non-forest settings than in forests and larger trees were more likely to support accidental epiphytes in both habitat types. Across species’ climatic envelopes, Bayesian estimates indicated that accidental epiphytes tended to occur under cooler summer and milder winter conditions, whereas moisture and wind effects were weaker and less consistent. These results suggest that accidental epiphytism is shaped by hierarchical filtering: the availability and traits of terrestrial species determine the potential pool of accidental epiphytes, host size and associated structural complexity affect local arrival, retention and establishment probability, landscape structure determines broader opportunities for arboreal recruitment and macroclimatic context influences where terrestrial species most often appear in trees. By linking local host-level filters with species-level climatic-envelope positions, our study supports an open-landscape pathway into epiphytism, while leaving room for alternative routes in shaded, humid forests. Accidental epiphytes, therefore, provide a promising model for studying terrestrial-to-arboreal transitions across biogeographical contexts. First landscape-scale assessment of accidental epiphyte encounter probabilities. Proposal of a hierarchical-filtering framework in which species availability and traits, dispersal and diaspore retention, host traits and structure, microhabitat availability and microclimate, landscape setting and macroclimate interact to shape accidental epiphytism. Open-landscape trees may provide repeated canopy colonisation opportunities and potential refugia. Open-adapted and closed-forest species may follow complementary routes into epiphytism. Accidental epiphytes can be considered a tool to study early stages of terrestrial-to-arboreal plant transitions.
Understanding the predictors of plant diversity gradients remains a major challenge in biogeography, particularly in understudied arid ecosystems where water availability is highly constrained. Coastal lomas—isolated, fog-fed vegetation oases distributed across the Peruvian and Chilean coastal deserts of South America–provide a unique system for examining how climate, topography, and geography shape plant diversity under extreme aridity. Here, we evaluated the geographic variation and predictors of the taxonomic and phylogenetic diversity of seed plants in these environments. We compiled the most comprehensive data set to date of 71 coastal lomas and used generalized linear models to assess latitudinal diversity gradients. We also evaluated the relative importance of environmental, topographic, and geographic predictors of plant taxonomic and phylogenetic diversity. We found that mean phylogenetic distance (MPD) exhibited non-linear relationships with latitude, and standardized phylogenetic diversity (PD) showed a weak variation with latitude, with both peaking in the hyper-arid core of the Atacama Desert. In contrast, standardized mean nearest taxon distance (MNTD) and species richness (adjusted by area) showed no significant association with latitude. Our results suggest that current climate, environmental heterogeneity, and geographical factors are the primary predictors of seed plant diversity in these regions. Plant species richness (adjusted by area) increased with aridity and cloud cover, while standardized PD decreased with aridity and distance to the coast while increasing with human footprint and northness. Standardized MNTD also increased with human footprint and northness, and decreased with increasing aridity and temperature. Standardized MPD increased with slope, temperature, northness, and aridity, and decreased with cloud cover, isothermality, and distance to the coast. These results suggest that environmental filtering is not the only macroecological process acting on plant diversity across coastal lomas and is often counterbalanced at different points in evolutionary time by factors associated with environmental heterogeneity, possibly reflecting the presence of climate refugia and habitats that promote species coexistence. Over evolutionary time, these factors may have significantly contributed to shaping the current composition of coastal lomas. Highlights Plant diversity did not follow a simple latitudinal gradient across coastal lomas. Aridity predominantly explains variation in diversity facets, underscoring the importance of water availability in shaping coastal lomas. Evolutionary diversity reached its peak unexpectedly in the hyper-arid Atacama Desert. Plant communities were clustered into distinct assemblages that correspond to geographic barriers along the coastal desert. Coastal lomas reflect multiple ecological and evolutionary processes rather than environmental filtering alone.
