The Latitudinal Diversity Gradient: Novel Understanding through Mechanistic Eco-evolutionary Models

Dispersal-diversity feedbacks and their consequences for macroecological patterns

Dispersal is a key process in ecology and evolution. While the effects of dispersal on diversity are broadly acknowledged, our understanding of the influence of diversity on dispersal remains limited. This arises from the dynamic, context-dependent, nonlinear and ubiquitous nature of dispersal. Diversity outcomes, such as competition, mutualism, parasitism and trophic interactions can feed back on dispersal, thereby influencing biodiversity patterns at several spatio-temporal scales. Here, we shed light on the dispersal-diversity causal links by discussing how dispersal-diversity ecological and evolutionary feedbacks can impact macroecological patterns. We highlight the importance of dispersal-diversity feedbacks for advancing our understanding of macro-eco-evolutionary patterns and their challenges, such as establishing a unified framework for dispersal terminology and methodologies across various disciplines and scales. This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

The macro-eco-evolutionary interplay between dispersal, competition and landscape structure in generating biodiversity

Theory links dispersal and diversity, predicting the highest diversity at intermediate dispersal levels. However, the modulation of this relationship by macro-eco-evolutionary mechanisms and competition within a landscape is still elusive. We examine the interplay between dispersal, competition and landscape structure in shaping biodiversity over 5 million years in a dynamic archipelago landscape. We model allopatric speciation, temperature niche, dispersal, competition, trait evolution and trade-offs between competitive and dispersal traits. Depending on dispersal abilities and their interaction with landscape structure, our archipelago exhibits two 'connectivity regimes', that foster speciation events among the same group of islands. Peaks of diversity (i.e. alpha, gamma and phylogenetic), occurred at intermediate dispersal; while competition shifted diversity peaks towards higher dispersal values for each connectivity regime. This shift demonstrates how competition can boost allopatric speciation events through the evolution of thermal specialists, ultimately limiting geographical ranges. Even in a simple landscape, multiple intermediate dispersal diversity relationships emerged, all shaped similarly and according to dispersal and competition strength. Our findings remain valid as dispersal- and competitive-related traits evolve and trade-off; potentially leaving identifiable biodiversity signatures, particularly when trade-offs are imposed. Overall, we scrutinize the convoluted relationships between dispersal, species interactions and landscape structure on macro-eco-evolutionary processes, with lasting imprints on biodiversity.This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

Eco-evolutionary evidence for the global diversity pattern of Cycas (Cycadaceae)

The evolution of the latitudinal diversity gradient (LDG), characterized by a peak in diversity toward the tropics, has captured significant attention in evolutionary biology and ecology. However, the inverse LDG (i-LDG) mechanism, wherein species richness increases toward the poles, remains inadequately explored. Cycads are among one of the oldest lineages of extant seed plants and have undergone extensive diversification in the tropics. Intriguingly, the extant cycad abundance exhibits an i-LDG pattern, and the underlying causes for this phenomenon remain largely elusive. Here, using 1,843 nuclear genes from a nearly complete sampling, we conducted comprehensive phylogenomic analyses to establish a robust species-level phylogeny for Cycas, the largest genus within cycads. We then reconstructed the spatial-temporal dynamics and integrated global environmental data to evaluate the roles of species ages, diversification rates, contemporary environment, and conservatism to ancestral niches in shaping the i-LDG pattern. We found Cycas experienced decreased diversification rates, coupled with the cooling temperature since its origin in the Eocene from continental Asia. Different regions have distinctively contributed to the formation of i-LDG for Cycas, with the northern hemisphere acting as evolutionary museums and the southern hemisphere serving as cradles. Moreover, water-related climate variables, specifically precipitation seasonality and potential evapotranspiration, were identified as paramount factors constraining Cycas species richness in the rainforest biome near the equator. Notably, the adherence to ancestral monsoonal climates emerges as a critical factor in sustaining the diversity pattern. This study underscores the imperative of integrating both evolutionary and ecological approaches to comprehensively unravel the mechanisms underpinning global biodiversity patterns.

Radiating diversification and niche conservatism jointly shape the inverse latitudinal diversity gradient of Potentilla L. (Rosaceae)

BACKGROUND

The latitudinal diversity gradient (LDG), characterized by an increase in species richness from the poles to the equator, is one of the most pervasive biological patterns. However, inverse LDGs, in which species richness peaks in extratropical regions, are also found in some lineages and their causes remain unclear. Here, we test the roles of evolutionary time, diversification rates, and niche conservatism in explaining the inverse LDG of Potentilla (ca. 500 species). We compiled the global distributions of ~ 90% of Potentilla species, and reconstructed a robust phylogenetic framework based on whole-plastome sequences. Next, we analyzed the divergence time, ancestral area, diversification rate, and ancestral niche to investigate the macroevolutionary history of Potentilla.

RESULTS

The genus originated in the Qinghai-Tibet Plateau during the late Eocene and gradually spread to other regions of the Northern Hemisphere posterior to the late Miocene. Rapid cooling after the late Pliocene promoted the radiating diversification of Potentilla. The polyploidization, as well as some cold-adaptive morphological innovations, enhanced the adaptation of Potentilla species to the cold environment. Ancestral niche reconstruction suggests that Potentilla likely originated in a relatively cool environment. The species richness peaks at approximately 45 °N, a region characterized by high diversification rates, and the environmental conditions are similar to the ancestral climate niche. Evolutionary time was not significantly correlated with species richness in the latitudinal gradient.

CONCLUSIONS

Our results suggest that the elevated diversification rates in middle latitude regions and the conservatism in thermal niches jointly determined the inverse LDG in Potentilla. This study highlights the importance of integrating evolutionary and ecological approaches to explain the diversity pattern of biological groups on a global scale.

Global arthropod beta-diversity is spatially and temporally structured by latitude

Global biodiversity gradients are generally expected to reflect greater species replacement closer to the equator. However, empirical validation of global biodiversity gradients largely relies on vertebrates, plants, and other less diverse taxa. Here we assess the temporal and spatial dynamics of global arthropod biodiversity dynamics using a beta-diversity framework. Sampling includes 129 sampling sites whereby malaise traps are deployed to monitor temporal changes in arthropod communities. Overall, we encountered more than 150,000 unique barcode index numbers (BINs) (i.e. species proxies). We assess between site differences in community diversity using beta-diversity and the partitioned components of species replacement and richness difference. Global total beta-diversity (dissimilarity) increases with decreasing latitude, greater spatial distance and greater temporal distance. Species replacement and richness difference patterns vary across biogeographic regions. Our findings support long-standing, general expectations of global biodiversity patterns. However, we also show that the underlying processes driving patterns may be regionally linked.

Linking ecosystem multifunctionality to microbial community features in rivers along a latitudinal gradient

Microorganisms regulate numerous ecosystem functions and show considerable differences along a latitudinal gradient. Although studies have revealed the latitudinal patterns of microbial community structure and single ecosystem function, the latitudinal patterns of ecosystem multifunctionality (EMF) and how microbial communities affect EMF along a latitudinal gradient remain unclear. Here, we collected channel sediments, riparian rhizosphere soils, and riparian bulk soils from 30 rivers across China and calculated EMF using 18 variables related to nitrogen cycling, nutrient pool, plant productivity, and water quality. We also determined microbial diversity (taxonomic and functional) and microbial network complexity using metagenomic sequencing. The results showed that EMF significantly decreased with increasing latitude in riparian rhizosphere and bulk soils but not in channel sediments. Microbial taxonomic and functional richness (observed species) in channel sediments were significantly higher in the low-latitude group than in the high-latitude group. However, microbial co-occurrence networks were more complex in the high-latitude group compared with the low-latitude group. Abiotic factors, primarily geographic and climatic factors, contributed more to EMF than microbial diversity and network complexity parameters in which only betweenness centralization had a significant relationship with EMF. Together, this study provides insight into the latitudinal pattern of EMF in rivers and highlights the importance of large-scale factors in explaining such latitudinal patterns.IMPORTANCEEcosystem multifunctionality (EMF) is the capacity of an ecosystem to provide multiple functions simultaneously. Microorganisms, as dominant drivers of belowground processes, have a profound effect on ecosystem functions. Although studies have revealed the latitudinal patterns of microbial community structure and single ecosystem function, the latitudinal patterns of EMF and how microbial communities affect EMF along a latitudinal gradient remain unclear. We collected channel sediments, riparian rhizosphere soils, and riparian bulk soils from 30 rivers along a latitudinal gradient across China and calculated EMF using 18 variables related to nitrogen cycling, nutrient pool, plant productivity, and water quality. This study fills a critical knowledge gap regarding the latitudinal patterns and drivers of EMF in river ecosystems and gives new insights into how microbial diversity and network complexity affect EMF from a metagenomic perspective.

Global multifaceted biodiversity patterns, centers, and conservation needs in angiosperms

The Convention on Biological Diversity seeks to conserve at least 30% of global land and water areas by 2030, which is a challenge but also an opportunity to better preserve biodiversity, including flowering plants (angiosperms). Herein, we compiled a large database on distributions of over 300,000 angiosperm species and the key functional traits of 67,024 species. Using this database, we constructed biodiversity-environment models to predict global patterns of taxonomic, phylogenetic, and functional diversity in terrestrial angiosperms and provide a comprehensive mapping of the three diversity facets. We further evaluated the current protection status of the biodiversity centers of these diversity facets. Our results showed that geographical patterns of the three facets of plant diversity exhibited substantial spatial mismatches and nonoverlapping conservation priorities. Idiosyncratic centers of functional diversity, particularly of herbaceous species, were primarily distributed in temperate regions and under weaker protection compared with other biodiversity centers of taxonomic and phylogenetic facets. Our global assessment of multifaceted biodiversity patterns and centers highlights the insufficiency and unbalanced conservation among the three diversity facets and the two growth forms (woody vs. herbaceous), thus providing directions for guiding the future conservation of global plant diversity.

Limited ecological opportunity influences the tempo of morphological evolution in birds

According to classic models of lineage diversification and adaptive radiation, phenotypic evolution should accelerate in the context of ecological opportunity and slow down when niches become saturated.1,2 However, only weak support for these ideas has been found in nature, perhaps because most analyses make the biologically unrealistic assumption that clade members contribute equally to reducing ecological opportunity, even when they occur in different continents or specialize on different habitats and diets. To view this problem through a different lens, we adapted a new phylogenetic modeling approach that accounts for the fact that competition for ecological opportunity only occurs between species that coexist and share similar habitats and diets. Applying this method to trait data for nearly all extant species of landbirds,3 we find a widespread signature of decelerating trait evolution in lineages adapted to similar habitats or diets. The strength of this pattern was consistent across latitudes when comparing tropical and temperate assemblages. Our results provide little support for the idea that increased diversity and tighter packing of niches accentuates evolutionary slowdowns in the tropics and instead suggest that limited ecological opportunity can be an important factor determining the rate of morphological diversification at a global scale.

Rapid in situ diversification rates in Rhamnaceae explain the parallel evolution of high diversity in temperate biomes from global to local scales

The macroevolutionary processes that have shaped biodiversity across the temperate realm remain poorly understood and may have resulted from evolutionary dynamics related to diversification rates, dispersal rates, and colonization times, closely coupled with Cenozoic climate change. We integrated phylogenomic, environmental ordination, and macroevolutionary analyses for the cosmopolitan angiosperm family Rhamnaceae to disentangle the evolutionary processes that have contributed to high species diversity within and across temperate biomes. Our results show independent colonization of environmentally similar but geographically separated temperate regions mainly during the Oligocene, consistent with the global expansion of temperate biomes. High global, regional, and local temperate diversity was the result of high in situ diversification rates, rather than high immigration rates or accumulation time, except for Southern China, which was colonized much earlier than the other regions. The relatively common lineage dispersals out of temperate hotspots highlight strong source-sink dynamics across the cosmopolitan distribution of Rhamnaceae. The proliferation of temperate environments since the Oligocene may have provided the ecological opportunity for rapid in situ diversification of Rhamnaceae across the temperate realm. Our study illustrates the importance of high in situ diversification rates for the establishment of modern temperate biomes and biodiversity hotspots across spatial scales.

Marine latitudinal diversity gradients are generally absent in intertidal ecosystems

Current latitudinal diversity gradient (LDG) meta-analyses have failed to distinguish one of the most widespread marine habitats, the intertidal zone, as a separate system despite it having unique abiotic challenges and spatially compressed stress gradients that affect the distribution and abundance of resident species. We address this issue by revisiting published literature and datasets on LDGs since 1911 to explore LDG patterns and their strengths in intertidal benthic, subtidal benthic, and pelagic realms and discuss the importance of recognizing intertidal ecosystems as distinct. Rocky shorelines were the most studied intertidal ecosystem encompassing 64.2% of intertidal LDG studies, and 62.9% of studies focused on assemblage composition, while the remaining 37.1% of studies were taxa specific. While our analyses confirmed LDGs in subtidal benthic and pelagic realms, with a decrease in richness toward the poles, we found no consistent intertidal LDGs in any ocean or coastline across hemispheres or biodiversity unit. Analyzing intertidal and subtidal zones as separate systems increased the strength of subtidal benthic LDGs relative to analyses combining these systems. We demonstrate that in intertidal ecosystems across oceans in both hemispheres, a latitudinal decrease in species richness is not readily apparent, which stands in contrast with significant LDG patterns found in the subtidal realm. Intertidal habitat heterogeneity, regional environmental variability and biological interactions can create species-rich hot spots independent of latitude, which may functionally outweigh a typical latitudinal decline in species richness. Although previous work has shown weaker LDGs in benthic than pelagic systems, we demonstrate that this is caused by combining subtidal and intertidal benthic ecosystems into a single benthic category. Thus, we propose that subtidal and intertidal ecosystems cannot be combined into one entity as the physical and biological parameters controlling ecosystem processes are vastly different, even among intertidal ecosystems. Thus, the intertidal zone offers a unique model system in which hypotheses can be further tested to better understand the complex processes underlying LDGs.

Polar lake microbiomes have distinct evolutionary histories

Toward the poles, life on land is increasingly dominated by microorganisms, yet the evolutionary origin of polar microbiomes remains poorly understood. Here, we use metabarcoding of Arctic, sub-Antarctic, and Antarctic lacustrine benthic microbial communities to test the hypothesis that high-latitude microbiomes are recruited from a globally dispersing species pool through environmental selection. We demonstrate that taxonomic overlap between the regions is limited within most phyla, even at higher-order taxonomic levels, with unique deep-branching phylogenetic clades being present in each region. We show that local and regional taxon richness and net diversification rate of regionally restricted taxa differ substantially between polar regions in both microeukaryotic and bacterial biota. This suggests that long-term evolutionary divergence resulting from low interhemispheric dispersal and diversification in isolation has been a prominent process shaping present-day polar lake microbiomes. Our findings illuminate the distinctive biogeography of polar lake ecosystems and underscore that conservation efforts should include their unique microbiota.

Numbers of fish species, higher taxa, and phylogenetic similarity decrease with latitude and depth, and deep-sea assemblages are unique

Species richness has been found to increase from the poles to the tropics but with a small dip near the equator over all marine fishes. Phylogenetic diversity measures offer an alternative perspective on biodiversity linked to evolutionary history. If phylogenetic diversity is standardized for species richness, then it may indicate places with relatively high genetic diversity. Latitudes and depths with both high species and phylogenetic diversity would be a priority for conservation. We compared latitudinal and depth gradients of species richness, and three measures of phylogenetic diversity, namely average phylogenetic diversity (AvPD), the sum of the higher taxonomic levels (STL) and the sum of the higher taxonomic levels divided by the number of species (STL/spp) for modelled ranges of 5,619 marine fish species. We distinguished all, bony and cartilaginous fish groups and four depth zones namely: whole water column; 0 -200 m; 201-1,000 m; and 1,001-6,000 m; at 5°  latitudinal intervals from 75°S to 75°N, and at 100 m depth intervals from 0 m to 3,500 m. Species richness and higher taxonomic richness (STL) were higher in the tropics and subtropics with a small dip at the equator, and were significantly correlated among fish groups and depth zones. Species assemblages had closer phylogenetic relationships (lower AvPD and STL/spp) in warmer (low latitudes and shallow water) than colder environments (high latitudes and deep sea). This supports the hypothesis that warmer shallow latitudes and depths have had higher rates of evolution across a range of higher taxa. We also found distinct assemblages of species in different depth zones such that deeper sea species are not simply a subset of shallow assemblages. Thus, conservation needs to be representative of all latitudes and depth zones to encompass global biodiversity.

Body size and trophic level increase with latitude, and decrease in the deep-sea and Antarctica, for marine fish species

The functional traits of species depend both on species' evolutionary characteristics and their local environmental conditions and opportunities. The temperature-size rule (TSR), gill-oxygen limitation theory (GOLT), and temperature constraint hypothesis (TCH) have been proposed to explain the gradients of body size and trophic level of marine species. However, how functional traits vary both with latitude and depth have not been quantified at a global scale for any marine taxon. We compared the latitudinal gradients of trophic level and maximum body size of 5,619 marine fish from modelled species ranges, based on (1) three body size ranges, <30, 30-100, and >100 cm, and (2) four trophic levels, <2.20, 2.20-2.80, 2.81-3.70, >3.70. These were parsed into 5° latitudinal intervals in four depth zones: whole water column, 0-200, 201-1,000, and 1,001-6,000 m. We described the relationship between latitudinal gradients of functional traits and salinity, sea surface and near seabed temperatures, and dissolved oxygen. We found mean body sizes and mean trophic levels of marine fish were smaller and lower in the warmer latitudes, and larger and higher respectively in the high latitudes except for the Southern Ocean (Antarctica). Fish species with trophic levels ≤2.80 were dominant in warmer and absent in colder environments. We attribute these differences in body size and trophic level between polar regions to the greater environmental heterogeneity of the Arctic compared to Antarctica. We suggest that fish species' mean maximum body size declined with depth because of decreased dissolved oxygen. These results support the TSR, GOLT and TCH hypotheses respectively. Thus, at the global scale, temperature and oxygen are primary factors affecting marine fishes' biogeography and biological traits.

Origination of the modern-style diversity gradient 15 million years ago

The latitudinal diversity gradient (LDG) is a prevalent feature of modern ecosystems across diverse clades^1-4. Recognized for well over a century, the causal mechanisms for LDGs remain disputed, in part because numerous putative drivers simultaneously covary with latitude^1,3,5. The past provides the opportunity to disentangle LDG mechanisms because the relationships among biodiversity, latitude and possible causal factors have varied over time^6-9. Here we quantify the emergence of the LDG in planktonic foraminifera at high spatiotemporal resolution over the past 40 million years, finding that a modern-style gradient arose only 15 million years ago. Spatial and temporal models suggest that LDGs for planktonic foraminifera may be controlled by the physical structure of the water column. Steepening of the latitudinal temperature gradient over 15 million years ago, associated with an increased vertical temperature gradient at low latitudes, may have enhanced niche partitioning and provided more opportunities for speciation at low latitudes. Supporting this hypothesis, we find that higher rates of low-latitude speciation steepened the diversity gradient, consistent with spatiotemporal patterns of depth partitioning by planktonic foraminifera. Extirpation of species from high latitudes also strengthened the LDG, but this effect tended to be weaker than speciation. Our results provide a step change in understanding the evolution of marine LDGs over long timescales.

Molecular ecology meets systematic conservation planning

Integrative and proactive conservation approaches are critical to the long-term persistence of biodiversity. Molecular data can provide important information on evolutionary processes necessary for conserving multiple levels of biodiversity (genes, populations, species, and ecosystems). However, molecular data are rarely used to guide spatial conservation decision-making. Here, we bridge the fields of molecular ecology (ME) and systematic conservation planning (SCP) (the 'why') to build a foundation for the inclusion of molecular data into spatial conservation planning tools (the 'how'), and provide a practical guide for implementing this integrative approach for both conservation planners and molecular ecologists. The proposed framework enhances interdisciplinary capacity, which is crucial to achieving the ambitious global conservation goals envisioned for the next decade.

Late Cenozoic cooling restructured global marine plankton communities

The geographic ranges of marine organisms, including planktonic foraminifera¹, diatoms, dinoflagellates², copepods³ and fish⁴, are shifting polewards owing to anthropogenic climate change⁵. However, the extent to which species will move and whether these poleward range shifts represent precursor signals that lead to extinction is unclear⁶. Understanding the development of marine biodiversity patterns over geological time and the factors that influence them are key to contextualizing these current trends. The fossil record of the macroperforate planktonic foraminifera provides a rich and phylogenetically resolved dataset that provides unique opportunities for understanding marine biogeography dynamics and how species distributions have responded to ancient climate changes. Here we apply a bipartite network approach to quantify group diversity, latitudinal specialization and latitudinal equitability for planktonic foraminifera over the past eight million years using Triton, a recently developed high-resolution global dataset of planktonic foraminiferal occurrences⁷. The results depict a global, clade-wide shift towards the Equator in ecological and morphological community equitability over the past eight million years in response to temperature changes during the late Cenozoic bipolar ice sheet formation. Collectively, the Triton data indicate the presence of a latitudinal equitability gradient among planktonic foraminiferal functional groups which is coupled to the latitudinal biodiversity gradient only through the geologically recent past (the past two million years). Before this time, latitudinal equitability gradients indicate that higher latitudes promoted community equitability across ecological and morphological groups. Observed range shifts among marine planktonic microorganisms^1,2,8 in the recent and geological past suggest substantial poleward expansion of marine communities even under the most conservative future global warming scenarios.

Phylogenetic diversity of eastern Asia-eastern North America disjunct plants is mainly associated with divergence time

The underlying causes of biodiversity disparities among geographic regions have long been a fundamental theme in ecology and evolution. However, the patterns of phylogenetic diversity (PD) and phylogenetic beta diversity (PBD) of congeners that are disjunctly distributed between eastern Asia-eastern North America (EA-ENA disjuncts) and their associated factors remain unknown. Here we investigated the standardized effect size of PD (SES-PD), PBD, and potentially associated factors in 11 natural mixed forest sites (five in EA and six in ENA) where abundant EA-ENA disjuncts occur. We found that the disjuncts in ENA possessed higher SES-PD than those in EA at the continental scale (1.96 vs -1.12), even though the number of disjunct species in ENA is much lower than in EA (128 vs 263). SES-PD of the EA-ENA disjuncts tended to decrease with increasing latitude in 11 sites. The latitudinal diversity gradient of SES-PD was stronger in EA sites than in ENA sites. Based on the unweighted unique fraction metric (UniFrac) distance and the phylogenetic community dissimilarity, PBD showed that the two northern sites in EA were more similar to the six-site ENA group than to the remaining southern EA sites. Based on the standardized effect size of mean pairwise distances (SES-MPD), nine of eleven studied sites showed a neutral community structure (-1.96 ≤ SES-MPD ≤ 1.96). Both Pearson's r and structural equation modeling suggested that SES-PD of the EA-ENA disjuncts was mostly associated with mean divergence time. Moreover, SES-PD of the EA-ENA disjuncts was positively correlated with temperature-related climatic factors, although negatively correlated with mean diversification rate and community structure. By applying approaches from phylogenetics and community ecology, our work sheds light on historical patterns of the EA-ENA disjunction and paves the way for further research.

The hierarchy of factors predicting the latitudinal diversity gradient

The numerous explanations for why Earth's biodiversity is concentrated at low latitudes fail to explain variation in the strength and even direction of the gradient through deep time. Consequently, we do not know if today's gradient is representative of what might be expected on other planets or is merely an idiosyncrasy of Earth's history. We propose a hierarchy of factors driving the latitudinal distribution of diversity: (i) over geologically long time spans, diversity is largely predicted by climate; (ii) when climatic gradients are shallow, diversity tracks habitat area; and (iii) historical contingencies linked to niche conservatism have geologically short-term, transient influence at most. Thus, latitudinal diversity gradients, although variable in strength and direction, are largely predictable on our planet and possibly others.

The interactive effects of environmental gradient and dispersal shape spatial phylogenetic patterns

Introduction

The emergence and maintenance of biodiversity include interacting environmental conditions, organismal adaptation to such conditions, and dispersal. To understand and quantify such ecological, evolutionary, and spatial processes, observation and interpretation of phylogenetic relatedness across space (e.g., phylogenetic beta diversity) is arguably a way forward as such patterns contain signals from all the processes listed above. However, it remains challenging to extract information about complex eco-evolutionary and spatial processes from phylogenetic patterns.

Methods

We link environmental gradients and organismal dispersal with phylogenetic beta diversity using a trait-based and eco-evolutionary model of diversification along environmental gradients. The combined effect of the environment and dispersal leads to distinct phylogenetic patterns between subsets of species and across geographical distances.

Results and discussion

Steep environmental gradients combined with low dispersal lead to asymmetric phylogenies, a high phylogenetic beta diversity, and the phylogenetic diversity between communities increases linearly along the environmental gradient. High dispersal combined with a less steep environmental gradient leads to symmetric phylogenies, low phylogenetic beta diversity, and the phylogenetic diversity between communities along the gradient increases in a sigmoidal form. By disentangling the eco-evolutionary mechanisms that link such interacting environment and dispersal effects and community phylogenetic patterns, our results improve understanding of biodiversity in general and help interpretation of observed phylogenetic beta diversity.

Mito-nuclear selection induces a trade-off between species ecological dominance and evolutionary lifespan

Mitochondrial and nuclear genomes must be co-adapted to ensure proper cellular respiration and energy production. Mito-nuclear incompatibility reduces individual fitness and induces hybrid infertility, which can drive reproductive barriers and speciation. Here, we develop a birth-death model for evolution in spatially extended populations under selection for mito-nuclear co-adaptation. Mating is constrained by physical and genetic proximity, and offspring inherit nuclear genomes from both parents, with recombination. The model predicts macroscopic patterns including a community's species diversity, species abundance distribution, speciation and extinction rates, as well as intraspecific and interspecific genetic variation. We explore how these long-term outcomes depend upon the parameters of reproduction: individual fitness governed by mito-nuclear compatibility, constraints on mating compatibility and ecological carrying capacity. We find that strong selection for mito-nuclear compatibility reduces the equilibrium number of species after a radiation, increasing species' abundances and simultaneously increasing both speciation and extinction rates. The negative correlation between species diversity and diversification rates in our model agrees with the broad empirical pattern of lower diversity and higher speciation/extinction rates in temperate regions, compared to the tropics. We conclude that these empirical patterns may be caused in part by latitudinal variation in metabolic demands and corresponding variation in selection for mito-nuclear function.

Evolutionary time and species diversity in aquatic ecosystems worldwide

The latitudinal diversity gradient (LDG) is frequently described as the most dramatic biodiversity pattern on Earth, yet ecologists and biogeographers have failed to reach consensus on its primary cause. A key problem in explaining the LDG involves collinearity between multiple factors that are predicted to affect species richness in the same direction. In terrestrial systems, energy input, geographic area, and evolutionary time for species accumulation tend to covary positively with species richness at the largest spatial scales, such that their individual contributions to the LDG are confounded in global analyses. I review three diversity patterns from marine and freshwater systems that break this collinearity and which may thus provide stronger tests of the influence of time on global richness gradients. Specifically, I contrast biodiversity patterns along oceanic depth gradients, in geologically young versus ancient lakes, and in the north versus south polar marine biomes. I focus primarily on fishes due to greater data availability but synthesize patterns for invertebrates where possible. I find that regional-to-global species richness generally declines with depth in the oceans, despite the great age and stability of the deep-sea biome. Geologically ancient lakes generally do not contain more species than young lakes, and the Antarctic marine biome is not appreciably more species rich than the much younger Arctic marine biome. However, endemism is consistently higher in older systems. Patterns for invertebrate groups are less clear than for fishes and reflect a critical need for primary biodiversity data. In summary, the available data suggest that species richness is either decoupled from or only weakly related to the amount of time for diversification. These results suggest that energy, productivity, or geographic area are the primary drivers of large-scale diversity gradients. To the extent that marine and terrestrial diversity gradients result from similar processes, these examples provide evidence against a primary role for evolutionary time as the cause of the LDG.

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers.

Mapping species diversification metrics in macroecology: Prospects and challenges

The intersection of macroecology and macroevolution is one of today’s most active research in biology. In the last decade, we have witnessed a steady increment of macroecological studies that use metrics attempting to capture macroevolutionary processes to explain present-day biodiversity patterns. Evolutionary explanations of current species richness gradients are fundamental for understanding how diversity accumulates in a region. Although multiple hypotheses have been proposed to explain the patterns we observe in nature, it is well-known that the present-day diversity patterns result from speciation, extinction, colonization from nearby areas, or a combination of these macroevolutionary processes. Whether these metrics capture macroevolutionary processes across space is unknown. Some tip-rate metrics calculated directly from a phylogenetic tree (e.g., mean root distance -MRD-; mean diversification rate -mDR-) seem to return very similar geographical patterns regardless of how they are estimated (e.g., using branch lengths explicitly or not). Model-based tip-rate metrics —those estimated using macroevolutionary mixtures, e.g., the BAMM approach— seem to provide better net diversification estimates than only speciation rates. We argue that the lack of appropriate estimates of extinction and dispersal rates in phylogenetic trees may strongly limit our inferences about how species richness gradients have emerged at spatial and temporal scales. Here, we present a literature review about this topic and empirical comparisons between select taxa with several of these metrics. We implemented a simple null model approach to evaluate whether mapping of these metrics deviates from a random sampling process. We show that phylogenetic metrics by themselves are relatively poor at capturing speciation, extinction, and dispersal processes across geographical gradients. Furthermore, we provide evidence of how parametric biogeographic methods can improve our inference of past events and, therefore, our conclusions about the evolutionary processes driving biodiversity patterns. We recommend that further studies include several approaches simultaneously (e.g., spatial diversification modeling, parametric biogeographic methods, simulations) to disentangle the relative role of speciation, extinction, and dispersal in the generation and maintenance of species richness gradients at regional and global scales.

Estimating ancient biogeographic patterns with statistical model discrimination

The geographic ranges in which species live is a function of many factors underlying ecological and evolutionary contingencies. Observing the geographic range of an individual species provides valuable information about these historical contingencies for a lineage, determining the distribution of many distantly related species in tandem provides information about large-scale constraints on evolutionary and ecological processes generally. We present a linear regression method that allows for the discrimination of various hypothetical biogeographical models for determining which landscape distributional pattern best matches data from the fossil record. The linear regression models used in the discrimination rely on geodesic distances between sampling sites (typically geologic formations) as the independent variable and three possible dependent variables: Dice/Sorensen similarity; Euclidean distance; and phylogenetic community dissimilarity. Both the similarity and distance measures are useful for full-community analyses without evolutionary information, whereas the phylogenetic community dissimilarity requires phylogenetic data. Importantly, the discrimination method uses linear regression residual error to provide relative measures of support for each biogeographical model tested, not absolute answers or p-values. When applied to a recently published dataset of Campanian pollen, we find evidence that supports two plant communities separated by a transitional zone of unknown size. A similar case study of ceratopsid dinosaurs using phylogenetic community dissimilarity provided no evidence of a biogeographical pattern, but this case study suffers from a lack of data to accurately discriminate and/or too much temporal mixing. Future research aiming to reconstruct the distribution of organisms across a landscape has a statistical-based method for determining what biogeographic distributional model best matches the available data.

Tropical–temperate comparisons in insect seed predation vary between study levels and years

The biotic interaction hypothesis, which states the species interaction becomes stronger in the tropics, is deeply rooted in classic ecological literature and widely accepted to contribute to the latitudinal gradients of biodiversity. Tests in latitudinal insect–plant interaction have emphasized leaf‐eating insects on a single or a few plant species rather than within an entire community and mixed accumulating evidence, leaving the biotic interaction hypothesis disputed. We aimed to test the hypothesis by quantifying insect seed predation in a pair of tropical and temperate forest communities with similar elevations. We applied a consistent study design to sample predispersal seeds with systematically set seed traps in 2019–2020 and examined internally feeding insects. The intensity of seed predation was measured and further applied to tropical versus temperate comparison at two levels (cross‐species and community‐wide). Our results showed every latitudinal pattern associated with different study levels and years, that is, negative (greater granivory in the tropics in community‐wide comparison in 2020), positive (less granivory in the tropics in community‐wide and cross‐species comparison in 2019), and missing (similar level of granivory in the tropics in cross‐species comparisons in 2020). The cross‐species level analyses ignore differences among species in seed production and weaken or even lose the latitudinal trend detected by community‐wide comparisons. The between‐year discrepancy in tropical–temperate comparisons relates to the highly variable annual seed composition in the temperate forest due to mast seeding of dominant species. Our study highlights that long‐term community‐level researches across biomes are essential to assess the latitudinal biotic interaction hypothesis.

Diversity of cave Phlebotomines (Diptera: Psychodidae) from a Colombian cave

Sandflies are vector species of Leishmania, among many other pathogens, with a global distribution and a variety of ecological niches. Previous samplings have found that karstic formations (i.e., caves, grottos, and folds formed by the erosion of limestone) serve as a natural habitat to sandfly species. The majority of samplings of cave sandfly diversity have occurred in Brazil and to date none have studied the species composition in a cave in the Northern Andes. We collected sandflies in the Cave "Los Guácharos", in the state of Antioquia, Colombia. The sampling was carried out during two consecutive nights in September 2019. CDC-type light traps were installed inside the cavern and in other surrounding karst systems (caves, rock-breaks, and folds). In total, we identified 17 species of sandfly from the cave and surrounding karst systems, including a new record for Colombia (Bichromomyia olmeca), and provide the first karstic reports for four other species (Lutzomyia gomezi, Lutzomyia hartmanni, Pintomyia ovallesi, and Psychodopygus panamensis). We then used the results of our survey and published literature to test two hypotheses. First, that sandfly diversity in Neotropical caves is richest nearer to the equator, and second that there is a phylogenetic signal of karstic habitat use in sandflies. Counter to our predictions, we found no evidence that diversity follows a latitudinal gradient. Further, we find no evidence of a phylogenetic signal of karstic habitat use, instead finding that the use of caves likely evolved multiple times across several genera. Our results highlight the importance of a wide sampling to understand the natural habitat of sandflies and other disease vectors.

Moth Diversity Increases along a Continent-Wide Gradient of Environmental Productivity in South African Savannahs

Environmental productivity, i.e., the amount of biomass produced by primary producers, belongs among the key factors for the biodiversity patterns. Although the relationship of diversity to environmental productivity differs among studied taxa, detailed data are largely missing for most groups, including insects. Here, we present a study of moth diversity patterns at local and regional scales along a continent-wide gradient of environmental productivity in southern African savannah ecosystems. We sampled diversity of moths (Lepidoptera: Heterocera) at 120 local plots along a gradient of normalized difference vegetation index (NDVI) from the Namib Desert to woodland savannahs along the Zambezi River. By standardized light trapping, we collected 12,372 specimens belonging to 487 moth species. The relationship between species richness for most analyzed moth groups and environmental productivity was significantly positively linear at the local and regional scales. The absence of a significant relationship of most moth groups' abundance to environmental productivity did not support the role of the number of individuals in the diversity-productivity relationship for south African moths. We hypothesize the effects of water availability, habitat complexity, and plant diversity drive the observed moth diversity patterns.

Temperature-dependent evolutionary speed shapes the evolution of biodiversity patterns across tetrapod radiations

Biodiversity varies predictably with environmental energy around the globe, but the underlaying mechanisms remain incompletely understood. The evolutionary speed hypothesis predicts that environmental kinetic energy shapes variation in speciation rates through temperature- or life history-dependent rates of evolution. To test whether variation in evolutionary speed can explain the relationship between energy and biodiversity in birds, mammals, amphibians, and reptiles, we simulated diversification over 65 million years of geological and climatic change with a spatially explicit eco-evolutionary simulation model. We modelled four distinct evolutionary scenarios in which speciation-completion rates were dependent on temperature (M1), life history (M2), temperature and life history (M3), or were independent of temperature and life-history (M0). To assess the agreement between simulated and empirical data, we performed model selection by fitting supervised machine learning models to multidimensional biodiversity patterns. We show that a model with temperature-dependent rates of speciation (M1) consistently had the strongest support. In contrast to statistical inferences, which showed no general relationships between temperature and speciation rates in tetrapods, we demonstrate how process-based modelling can disentangle the causes behind empirical biodiversity patterns. Our study highlights how environmental energy has played a fundamental role in the evolution of biodiversity over deep time.

Factors related to species richness, endemism, and conservation status of the herpetofauna (Amphibia and Reptilia) of Mexican states

Mexico is a megadiverse country with high endemicity in its herpetofauna. We examine how species richness, proportion of state and country endemic species, and proportion of species in a category of conservation concern using listings in the International Union for Conservation of Nature (IUCN) Red List and the Secretaría del Medio Ambiente y Recursos Naturales (SEMARNAT) in 27 of 32 Mexican states are related to environmental and human demographic and socioeconomic variables. Amphibian and reptile species richness were positively related to latitude range and number of physiographic regions and negatively related to latitude. The proportion of state endemic amphibian species in a state was negatively related to latitude whereas no variables influenced the proportion in reptiles. The proportion of country endemics in a state was positively related to human population density and the number of physiographic regions and negatively related to per capita gross domestic product (GDP) and latitude range for amphibians; it was positively related to human population density and elevation range and negatively related to latitude range for reptiles. The proportion of amphibian species in an IUCN category of concern in a state was positively related to human population density and negatively related to latitude; for reptiles, it was negatively related to human population density. The proportion of SEMARNAT-listed species in a state was positively related to human population density for both amphibians and reptiles and negatively related to latitude range for amphibians. Our analyses found that larger macroecological patterns (e.g., latitudinal species gradient, heterogeneity-richness relationships) and human population density play important roles in determining the richness and conservation status of Mexican amphibians and reptiles.

Leveraging remote learning during the Covid‐19 pandemic to enhance student understanding of biodiversity

We evaluated whether individual nature‐based ecological (NBE) study used in tandem with group collaboration enhanced undergraduate student understanding of ecological concepts and pro‐environmental perceptions. In response to the Covid‐19 pandemic, we developed a multiweek unit on the latitude diversity gradient (LDG) for fully online instruction that leveraged the unique situation of students learning in disparate geographic locations. Student understanding of the LDG and pro‐environmental perceptions were assessed with surveys administered both pre‐ and post‐activity in an introductory‐level biology laboratory course. Student understanding of the geographic location where biodiversity is the highest was high prior to the start of the laboratory unit and exhibited only a small improvement after the unit. In contrast, students’ higher order thinking around the LDG was enhanced by the lab activity. Student environmental perceptions shifted toward ecocentric views and away from anthropocentric views after the laboratory unit. The greatest gains in ecological understanding and shifts toward ecocentric viewpoints occurred in the group of students who visited their field sites most often. Our results provide further evidence as to the value of NBE for the introductory biology laboratory, even in an online learning setting. The lab unit described in this study provides a potential approach to teaching ecology in an online format that could easily be adapted to fit the needs of a particular curriculum.

Phylogenetic analysis of adaptation in comparative physiology and biomechanics: overview and a case study of thermal physiology in treefrogs

Comparative phylogenetic studies of adaptation are uncommon in biomechanics and physiology. Such studies require data collection from many species, a challenge when this is experimentally intensive. Moreover, researchers struggle to employ the most biologically appropriate phylogenetic tools for identifying adaptive evolution. Here, we detail an established but greatly underutilized phylogenetic comparative framework - the Ornstein-Uhlenbeck process - that explicitly models long-term adaptation. We discuss challenges in implementing and interpreting the model, and we outline potential solutions. We demonstrate use of the model through studying the evolution of thermal physiology in treefrogs. Frogs of the family Hylidae have twice colonized the temperate zone from the tropics, and such colonization likely involved a fundamental change in physiology due to colder and more seasonal temperatures. However, which traits changed to allow colonization is unclear. We measured cold tolerance and characterized thermal performance curves in jumping for 12 species of treefrogs distributed from the Neotropics to temperate North America. We then conducted phylogenetic comparative analyses to examine how tolerances and performance curves evolved and to test whether that evolution was adaptive. We found that tolerance to low temperatures increased with the transition to the temperate zone. In contrast, jumping well at colder temperatures was unrelated to biogeography and thus did not adapt during dispersal. Overall, our study shows how comparative phylogenetic methods can be leveraged in biomechanics and physiology to test the evolutionary drivers of variation among species.

A comprehensive phylogeography of the widespread pond snail genus Radix revealed restricted colonization due to niche conservatism

To clarify the effect of niche conservatism on evolutionary history, we focused on freshwater snails, which have different ecological and phylogenetic properties from previously tested taxa. We conducted a phylogenetic analysis using 750 lymnaeid individuals from 357 sites of eleven Radix species. Then, we estimated the ancestral distribution using the geographic coordinates and colonization routes. In addition, a statistical test of the colonization distances in the latitudinal and longitudinal directions was performed. We also conducted ecological niche modeling for two widely distributed species using climatic data. Ancestral geographic reconstruction estimated the origin of the genus to be around the Indian subcontinental region and showed that latitudinal immigration distances were shorter than longitudinal immigration distances in the diversification process. Ecological niche models suggested that the current distribution was restricted by climate, with annual mean temperature and precipitation of the driest month as particularly strong factors. Niche conservatism to the climate can affect the diversification of freshwater snails.

Genetic and species-level biodiversity patterns are linked by demography and ecological opportunity

The processes that give rise to species richness gradients are not well understood, but may be linked to resource-based limits on the number of species a region can support. Ecological limits placed on regional species richness should also affect population demography, suggesting that these processes could also generate genetic diversity gradients. If true, we might better understand how broad-scale biodiversity patterns are formed by identifying the common causes of genetic diversity and species richness. We develop a hypothetical framework based on the consequences of regional variation in ecological limits set by resource availability and heterogeneity to simultaneously explain spatial patterns of species richness and neutral genetic diversity. Repurposing raw genotypic data spanning 38 mammal species sampled across 801 sites in North America, we show that estimates of genome-wide genetic diversity and species richness share spatial structure. Notably, species richness hotspots tend to harbor lower levels of within-species genetic variation. A structural equation model encompassing eco-evolutionary processes related to resource availability, habitat heterogeneity, and contemporary human disturbance supports the spatial patterns we detect. These results suggest broad-scale patterns of species richness and genetic diversity could both partly be caused by intraspecific demographic and evolutionary processes acting simultaneously across species.

Evolutionary drivers of the hump-shaped latitudinal gradient of benthic polychaete species richness along the Southeastern Pacific coast

Latitudinal diversity gradients (LDG) and their explanatory factors are among the most challenging topics in macroecology and biogeography. Despite of its apparent generality, a growing body of evidence shows that 'anomalous' LDG (i.e., inverse or hump-shaped trends) are common among marine organisms along the Southeastern Pacific (SEP) coast. Here, we evaluate the shape of the LDG of marine benthic polychaetes and its underlying causes using a dataset of 643 species inhabiting the continental shelf (<200 m depth), using latitudinal bands with a spatial resolution of 0.5°, along the SEP (3-56° S). The explanatory value of six oceanographic (Sea Surface Temperature (SST), SST range, salinity, salinity range, primary productivity and shelf area), and one macroecological proxy (median latitudinal range of species) were assessed using a random forest model. The taxonomic structure was used to estimate the degree of niche conservatism of predictor variables and to estimate latitudinal trends in phylogenetic diversity, based on three indices (phylogenetic richness (PD_SES), mean pairwise distance (MPD_SES), and variation of pairwise distances (VPD)). The LDG exhibits a hump-shaped trend, with a maximum peak of species richness at ca. 42° S, declining towards northern and southern areas of SEP. The latitudinal pattern was also evident in local samples controlled by sampling effort. The random forest model had a high accuracy (pseudo-r² = 0.95) and showed that the LDG could be explained by four variables (median latitudinal range, SST, salinity, and SST range), yet the functional relationship between species richness and these predictors was variable. A significant degree of phylogenetic conservatism was detected for the median latitudinal range and SST. PD_SES increased toward the southern region, whereas VPD showed the opposite trend, both statistically significant. MPD_SES has the same trend as PD_SES, but it is not significant. Our results reinforce the idea that the south Chile fjord area, particularly the Chiloé region, was likely the evolutionary source of new species of marine polychaetes along SEP, creating a hotspot of diversity. Therefore, in the same way as the canonical LDG shows a decline in diversity while moving away from the tropics; on this case the decline occurs while moving away from Chiloé Island. These results, coupled with a strong phylogenetic signal of the main predictor variables suggest that processes operating mainly at evolutionary timescales govern the LDG.

Influence of historical changes in tropical reef habitat on the diversification of coral reef fishes

Past environmental changes are expected to have profoundly impacted diversity dynamics through time. While some previous studies showed an association between past climate changes or tectonic events and important shifts in lineage diversification, it is only recently that past environmental changes have been explicitly integrated in diversification models to test their influence on diversification rates. Here, we used a global reconstruction of tropical reef habitat dynamics during the Cenozoic and phylogenetic diversification models to test the influence of (i) major geological events, (ii) reef habitat fragmentation and (iii) reef area on the diversification of 9 major clades of tropical reef fish (Acanthuridae, Balistoidea, Carangoidea, Chaetodontidae, Haemulinae, Holocentridae, Labridae, Pomacentridae and Sparidae). The diversification models revealed a weak association between paleo-habitat changes and diversification dynamics. Specifically, the fragmentation of tropical reef habitats over the Cenozoic was found to be a driver of tropical reef fish diversification for 2 clades. However, overall, our approach did not allow the identification of striking associations between diversification dynamics and paleo-habitat fragmentation in contrast with theoretical model's predictions.

National-scale changes in crop diversity through the Anthropocene

Expansion of crops beyond their centres of domestication is a defining feature of the Anthropocene Epoch. This process has fundamentally altered the diversity of croplands, with likely consequences for the ecological functioning and socio-economic stability of agriculture under environmental change. While changes in crop diversity through the Anthropocene have been quantified at large spatial scales, the patterns, drivers, and consequences of change in crop diversity and biogeography at national-scales remains less explored. We use production data on 339 crops, grown in over 150 countries from 1961 to 2017, to quantify changes in country-level crop richness and evenness. Virtually all countries globally have experienced significant increases in crop richness since 1961, with the early 1980s marking a clear onset of a ~ 9-year period of increase in crop richness in countries worldwide. While these changes have increased the similarity of diversity of croplands among countries, only half of countries experienced increases in crop evenness through time. Ubiquitous increases in crop richness within nearly all countries between 1980 and 2000 are a unique biogeographical feature of the Anthropocene. At the same time, we detected opposing changes in crop evenness, and only modest signatures of increased homogenization of croplands among countries. Therefore context-dependent and, at least, national-scale assessments are needed to understand and predict how changes in crop diversity influence agricultural resistance and resilience to environmental change.

Earth history events shaped the evolution of uneven biodiversity across tropical moist forests

Tropical moist forests harbor much of the world’s biodiversity, but this diversity is not evenly distributed globally, with tropical moist forests in the Neotropics and Indomalaya generally exhibiting much greater diversity than in the Afrotropics. Here, we assess the ubiquity of this “pantropical diversity disparity” (PDD) using the present-day distributions of over 150,000 species of plants and animals, and we compare these distributions with a spatial model of diversification combined with reconstructions of plate tectonics, temperature, and aridity. Our study demonstrates that differences in paleoenvironmental dynamics between continents, including mountain building, aridification, and global temperature fluxes, can explain the PDD by shaping spatial and temporal patterns of species origination and extinction, providing a close match to observed distributions of plants and animals.

Far from a uniform band, the biodiversity found across Earth’s tropical moist forests varies widely between the high diversity of the Neotropics and Indomalaya and the relatively lower diversity of the Afrotropics. Explanations for this variation across different regions, the “pantropical diversity disparity” (PDD), remain contentious, due to difficulty teasing apart the effects of contemporary climate and paleoenvironmental history. Here, we assess the ubiquity of the PDD in over 150,000 species of terrestrial plants and vertebrates and investigate the relationship between the present-day climate and patterns of species richness. We then investigate the consequences of paleoenvironmental dynamics on the emergence of biodiversity gradients using a spatially explicit model of diversification coupled with paleoenvironmental and plate tectonic reconstructions. Contemporary climate is insufficient in explaining the PDD; instead, a simple model of diversification and temperature niche evolution coupled with paleoaridity constraints is successful in reproducing the variation in species richness and phylogenetic diversity seen repeatedly among plant and animal taxa, suggesting a prevalent role of paleoenvironmental dynamics in combination with niche conservatism. The model indicates that high biodiversity in Neotropical and Indomalayan moist forests is driven by complex macroevolutionary dynamics associated with mountain uplift. In contrast, lower diversity in Afrotropical forests is associated with lower speciation rates and higher extinction rates driven by sustained aridification over the Cenozoic. Our analyses provide a mechanistic understanding of the emergence of uneven diversity in tropical moist forests across 110 Ma of Earth’s history, highlighting the importance of deep-time paleoenvironmental legacies in determining biodiversity patterns.

Depth diversity gradients of macrophytes: Shape, drivers, and recent shifts

Investigating diversity gradients helps to understand biodiversity drivers and threats. However, one diversity gradient is rarely assessed, namely how plant species distribute along the depth gradient of lakes. Here, we provide the first comprehensive characterization of depth diversity gradient (DDG) of alpha, beta, and gamma species richness of submerged macrophytes across multiple lakes. We characterize the DDG for additive richness components (alpha, beta, gamma), assess environmental drivers, and address temporal change over recent years. We take advantage of yet the largest dataset of macrophyte occurrence along lake depth (274 depth transects across 28 deep lakes) as well as of physiochemical measurements (12 deep lakes from 2006 to 2017 across Bavaria), provided publicly online by the Bavarian State Office for the Environment. We found a high variability in DDG shapes across the study lakes. The DDGs for alpha and gamma richness are predominantly hump-shaped, while beta richness shows a decreasing DDG. Generalized additive mixed-effect models indicate that the depth of the maximum richness (D max) is influenced by light quality, light quantity, and layering depth, whereas the respective maximum alpha richness within the depth gradient (R max) is significantly influenced by lake area only. Most observed DDGs seem generally stable over recent years. However, for single lakes we found significant linear trends for R max and D max going into different directions. The observed hump-shaped DDGs agree with three competing hypotheses: the mid-domain effect, the mean-disturbance hypothesis, and the mean-productivity hypothesis. The DDG amplitude seems driven by lake area (thus following known species-area relationships), whereas skewness depends on physiochemical factors, mainly water transparency and layering depth. Our results provide insights for conservation strategies and for mechanistic frameworks to disentangle competing explanatory hypotheses for the DDG.

Ecological opportunity and adaptive radiations reveal eco-evolutionary perspectives on community structure in competitive communities

It is well known that ecological and evolutionary processes act in concert while shaping biological communities. Diversification can, for example, arise through ecological opportunity and adaptive radiations and competition play an essential role in such diversification. Eco-evolutionary components of competition are thus important for our understanding of community assembly. Such understanding in turn facilitates interpretation of trait- and phylogenetic community patterns in the light of the processes that shape them. Here, I investigate the link between competition, diversification, and trait- and phylogenetic- community patterns using a trait-based model of adaptive radiations. I evaluate the paradigm that competition is an ecological process that drives large trait- and phylogenetic community distances through limiting similarity. Contrary to the common view, I identify low or in some cases counterintuitive relationships between competition and mean phylogenetic distances due to diversification late in evolutionary time and peripheral parts of niche space when competition is weak. Community patterns as a function of competition also change as diversification progresses as the relationship between competition and trait similarity among species can flip from positive to negative with time. The results thus provide novel perspectives on community assembly and emphasize the importance of acknowledging eco-evolutionary processes when interpreting community data.

A unified model of species abundance, genetic diversity, and functional diversity reveals the mechanisms structuring ecological communities

Biodiversity accumulates hierarchically by means of ecological and evolutionary processes and feedbacks. Within ecological communities drift, dispersal, speciation, and selection operate simultaneously to shape patterns of biodiversity. Reconciling the relative importance of these is hindered by current models and inference methods, which tend to focus on a subset of processes and their resulting predictions. Here we introduce massive ecoevolutionary synthesis simulations (MESS), a unified mechanistic model of community assembly, rooted in classic island biogeography theory, which makes temporally explicit joint predictions across three biodiversity data axes: (i) species richness and abundances, (ii) population genetic diversities, and (iii) trait variation in a phylogenetic context. Using simulations we demonstrate that each data axis captures information at different timescales, and that integrating these axes enables discriminating among previously unidentifiable community assembly models. MESS is unique in generating predictions of community‐scale genetic diversity, and in characterizing joint patterns of genetic diversity, abundance, and trait values. MESS unlocks the full potential for investigation of biodiversity processes using multidimensional community data including a genetic component, such as might be produced by contemporary eDNA or metabarcoding studies. We combine MESS with supervised machine learning to fit the parameters of the model to real data and infer processes underlying how biodiversity accumulates, using communities of tropical trees, arthropods, and gastropods as case studies that span a range of data availability scenarios, and spatial and taxonomic scales.

Effect of Productivity on Community Size Explains the Latitudinal Diversity Gradient of South American Small Mammals

AbstractAlthough many studies have shown that species richness increases from high to low latitudes (the latitudinal diversity gradient), the mechanisms responsible for generating and maintaining higher species richness in the tropics remain intensely debated. Here we investigate how the effects of temperature on speciation rates (kinetic effects) and the effects of productivity on community size (chemical effects) explain the latitudinal diversity gradient of South American small mammals. We implemented Bayesian models that integrate processes from the neutral and metabolic theories, comparing model predictions with empirical richness patterns. The neutral-metabolic model predicted the latitudinal richness gradient in South American small mammals. We found evidence that the effects of productivity on community size are more important for explaining differences in species richness than the effects of temperature on speciation rates. These results suggest that differences in species richness along latitudinal gradients are regulated primarily by the chemical effects of productivity on speciation-extinction dynamics.

Modelling the tempo and mode of lineage dispersal

Lineage dispersal is a basic macroevolutionary process shaping the distribution of biodiversity. Probabilistic approaches in biogeography, epidemiology, and macroecology often model dispersal as a background process to explain extant or infer past distributions. We propose framing questions around the mode, timing, rate, and direction of lineage dispersal itself, from a lineage- or geography-centric perspective. We review available methods for modelling lineage dispersal. Likelihood- and simulation-based approaches to modelling dispersal have made progress in accounting for the variation of lineage dispersal over space, time, and branches of a phylogeny and its interaction with diversification. Methodological improvements, guided by a focus on model adequacy, will lead to more realistic models that can answer fundamental questions about the tempo and mode of lineage dispersal.

Opportunities and challenges of macrogenetic studies

The rapidly emerging field of macrogenetics focuses on analysing publicly accessible genetic datasets from thousands of species to explore large-scale patterns and predictors of intraspecific genetic variation. Facilitated by advances in evolutionary biology, technology, data infrastructure, statistics and open science, macrogenetics addresses core evolutionary hypotheses (such as disentangling environmental and life-history effects on genetic variation) with a global focus. Yet, there are important, often overlooked, limitations to this approach and best practices need to be considered and adopted if macrogenetics is to continue its exciting trajectory and reach its full potential in fields such as biodiversity monitoring and conservation. Here, we review the history of this rapidly growing field, highlight knowledge gaps and future directions, and provide guidelines for further research.