Long‐term population dynamics of a migrant bird suggests interaction of climate change and competition with resident species

The separation of abiotic and biotic factors affecting populations and communities is an important step in understanding how climate change can influence ecological processes, but quantifying their relative contribution to community changes is a challenge. We assessed the effect of temperature and species interactions on the population dynamics of a forest bird community with a hierarchical dynamic population model in a Bayesian framework. We used a long‐term time‐series (1956–2012) of four secondary cavity‐nesting birds with similar food and nesting requirements but different migration habits, to analyse the effects of the four species population size and the local weather fluctuations on each species’ population dynamics. We found clear evidence of a negative effect of two resident species (blue tit and great tit) on a long‐distance migrant (pied flycatcher). Among the residents we only found a competition effect of the great tit on the marsh tit. The birds showed opposite responses to weather: the pied flycatcher favoured colder springs whereas the blue tit and great tit favoured warmer springs. Although alternative mechanisms cannot be ruled out, our results suggest that the resident species (blue tit and great tit) could adjust to increasing spring temperature while the migrant species (pied flycatcher) could not, leading progressively to the exclusion of the pied flycatcher from the area. These results point out the potential role of competitive interactions by providing insightful clues, call for refined research, and support recent efforts to include population dynamics in species distribution models.     

Self-optimization, community stability, and fluctuations in two individual-based models of biological coevolution

We compare and contrast the long-time dynamical properties of two individual-based models of biological coevolution. Selection occurs via multispecies, stochastic population dynamics with reproduction probabilities that depend nonlinearly on the population densities of all species resident in the community. New species are introduced through mutation. Both models are amenable to exact linear stability analysis, and we compare the analytic results with large-scale kinetic Monte Carlo simulations, obtaining the population size as a function of an average interspecies interaction strength. Over time, the models self-optimize through mutation and selection to approximately maximize a community potential function, subject only to constraints internal to the particular model. If the interspecies interactions are randomly distributed on an interval including positive values, the system evolves toward self-sustaining, mutualistic communities. In contrast, for the predator–prey case the matrix of interactions is antisymmetric, and a nonzero population size must be sustained by an external resource. Time series of the diversity and population size for both models show approximate 1/f noise and power-law distributions for the lifetimes of communities and species. For the mutualistic model, these two lifetime distributions have the same exponent, while their exponents are different for the predator–prey model. The difference is probably due to greater resilience toward mass extinctions in the food-web like communities produced by the predator–prey model.      

Long-term population genetic structure of an invasive urochordate: the ascidian Botryllus schlosseri

The accelerated pace of marine biological invasions raises questions pertaining to genetic traits and dynamics underlying the successful establishment of invasive species. Current research stresses the importance of multiple introductions and prolonged gene flow as the main sources for genetic diversity, which, along with genetic drift, affect invasive species success. We here attempt to determine the relative contribution of gene flow and mutation rates as sources of genetic variability using the invasive tunicate Botryllus schlosseri as a model. The study was performed over a 13-year period in the Santa Cruz Harbor, California. With a characteristic life history of five generations/year, the Santa Cruz Botryllus population has already experienced approximately 155 generations since the onset of its invasion. The results (278 specimens, 127 scored alleles, five microsatellite loci) support limited gene flow rate (2.89?×?10^?3) and relative genetic isolation. Furthermore, the study population was found to be influenced by both, genetic drift and a high mutation rate (2.47?×?10^?2). These findings were supported by high fluctuations in the frequencies of microsatellite alleles, the appearance of new alleles and the loss of others. The balance between genetic drift and a high mutation rate is further elucidated by the high, stable level of genetic variation. We suggest that rapid mutation rates at the microsatellite loci reflect genome-wide phenomena, helping to maintain high genetic variability in relatively isolated populations. The potential adaptability to new environments is discussed.     

Neutral processes and species sorting in benthic microalgal community assembly: effects of tidal resuspension

Benthic microalgae (BMA) provide vital food resources for heterotrophs and stabilize sediments with their extracellular secretions. A central goal in ecology is to understand how processes such as species interactions and dispersal, contribute to observed patterns of species abundance and distribution. Our objectives were to assess the effects of sediment resuspension on microalgal community structure. We tested whether taxa‐abundance distributions could be predicted using neutral community models (NCMs) and also specific hypotheses about passive migration: (i) As migration decreases in sediment patches, BMA α‐diversity will decrease, and (ii) As migration decreases, BMA community dissimilarity (β‐diversity) will increase. Co‐occurrence indices (checkerboard score and variance ratio) were also computed to test for deterministic factors, such as competition and niche differentiation, in shaping communities. Two intertidal sites (mudflat and sand bar) differing in resuspension regime were sampled throughout the tidal cycle. Fluorometry and denaturing gradient gel electrophoresis were utilized to investigate diatom community structure. Observed taxa‐abundances fit those predicted from NCMs reasonably well (R² of 0.68–0.93), although comparisons of observed local communities to artificial randomly assembled communities rejected the null hypothesis that diatom communities were assembled solely by stochastic processes. No co‐occurrence tests indicated a significant role for competitive exclusion or niche partitioning in microalgal community assembly. In general, predictions about relationships between migration and species diversity were supported for local community dynamics. BMA at low tide (lowest migration) exhibited reduced α‐diversity as compared to periods of immersion at both mudflat and sand bar sites. β‐diversity was higher during low tide emersion on the mudflat, but did not differ temporally at the sand bar site. In between‐site metacommunity comparisons, low‐ and high‐resuspension sites exhibited distinct community compositions while the low‐energy mudflats contained higher microalgal biomass and greater α‐diversity. To our knowledge this is the first study to test the relevance of neutral processes in structuring marine microalgal communities. Our results demonstrate a prominent role for stochastic factors in structuring local BMA community assembly, although unidentified nonrandom processes also appear to play some role. High passive migration, in particular, appears to help maintain species diversity and structure communities in both sand and muddy habitats.     

The cell ratchet: Interplay between efficient protrusions and adhesion determines cell motion

Many physiological and pathological processes involve directed cell motion. In general, migrating cells are represented with a polarized morphology with extending and retracting protrusions at the leading edge. However, cell motion is a more complex phenomenon. Cells show heterogeneous morphologies and high protrusive dynamics is not always related to cell shape. This prevents the quantitative prediction of cell motion and the identification of cellular mechanisms setting directionality. Here we discuss the importance of protrusion fluctuations in directed cell motion. We show how their spatiotemporal distribution and dynamics determine the fluctuations and directions of cell motion for NIH3T3 fibroblasts plated on micro-patterned adhesive ratchets.¹ We introduce efficient protrusions and direction index which capture short-term cell motility over hours: these new read-outs allow the prediction of parameters characteristic for the long-term motion of cells over days. The results may have important implications for the study of biological phenomena where directed cell migration is involved, in morphogenesis and in cancer.     

Trophic niches and feeding relationships of shorebirds in southern Brazil

Niche theory predicts that sympatric species should differ in some ecological characteristic, to allow co-existence and reduce competition for key resources. Food is critical on wintering grounds and stopover areas for migratory species that need to accumulate reserves in order to complete their migration. Wetlands of the Rio Grande do Sul coastal plain, in southern Brazil, host several species of shorebirds with similar morphology, foraging methods and diet. When these species are in sympatry, some trophic niche overlap is expected. Diets and trophic niches of migratory and resident shorebirds were investigated during the austral summer on Torotama Island, Lagoa dos Patos Estuary, Brazil. Complementary methods were used to determine the trophic ecology of three shorebird species; diet was determined through analysis of feces and food samples, using stable isotopes of carbon and nitrogen. The local invertebrate community was sampled to determine potential prey and ascertain feeding preferences of birds. Coleoptera was the most abundant taxon in the feces of all shorebirds. Trophic niche overlap in the diets was high, with the widest trophic niche found for the buff-breasted sandpiper Calidris subruficollis. Isotopic mixing models indicated differences in the main food sources of shorebirds. The isotopic niche breadth was widest for the American golden-plover Pluvialis dominica. These species, as well as the resident southern lapwing Vanellus chilensis, consumed some prey in higher proportions over others, although they had generalist diets. Migratory species with generalist habits benefit from heterogeneous environments such as floodplains during the non-breeding season.     

Genetic composition of resident populations influences establishment success of immigrant species

We conducted an outdoor container experiment to test the hypothesis that the genetic composition of resident populations influences the establishment success of immigrant species. We manipulated the genetic compositions (source populations) of populations of the water flea Daphnia magna, a strong competitor in pond and shallow lake zooplankton communities, and monitored the establishment success of immigrant cladoceran species of a regional species pool. We show that establishment success is affected by the source population of the resident D. magna as well as by the presence/absence of macrophytes and the presence/absence of fish in the containers. Our results provide evidence that the genetic composition of resident populations can impact community assembly and metacommunity dynamics, and that community genetics can influence ecosystem functioning.     

The distribution of native and exotic plants in a naturally fragmented sagebrush-steppe landscape

We tested two general hypotheses for the diversity of native and exotic plants in an undisturbed, naturally fragmented sagebrush-steppe landscape in SE Idaho, USA, evaluating whether the MacArthur–Wilson hypothesis of island biogeography or a suite of environmental variables explained the distributions of native and exotic plants. We also tested a third hypothesis, which incorporated assumptions about the origin of exotic plants and their interaction with native plants. Of the three hypotheses we tested, the hypothesis that included exotic species best explained the diversity of the native plant community. The MacArthur–Wilson model of island biogeography did not explain the diversity of native (R ² = 0.13) or exotic plants well (R ² = 0.11), and the model fit the data poorly. A model of environmental variables better explained the diversity of native (R ² = 0.48) and exotic plants (R ² = 0.57), but it also fit the data poorly. Instead, proximity to a railroad explained the cover (R ² = 0.59) and richness of exotic plants (R ² = 0.63), which then explained the species richness of native plants (R ² = 0.34), and the model fit was adequate and had the lowest AIC value. This suggests that the transportation corridor had a significant, though indirect, effect on the native plant community, even in this undisturbed area. Moreover, explained variance, model fit, and the AIC model selection criteria favored the model with the railroad and exotic species over the M–W and environmental models. Since the habitat patches we studied were largely undisturbed by people and their activities, our results further suggest that the transportation corridor influenced the distribution of exotic plants by serving as a vector for colonization, rather than as a source of disturbance. Additionally, the results suggest that exotic plant species have had a negative effect on the diversity of the native plant community and have changed its composition. The results also support the inference that the nascent exotic plant community is influenced by source-sink (Pulliam in Am Nat 132:652–661, 1988) and assembly dynamics. In contrast, the native plant community appears to be more strongly influenced by environmental conditions associated with an elevational gradient, but there is evidence that the native community also has undergone directional change in species composition, associated with the invasion by non-native species.     

Synchrony in small mammal community dynamics across a forested landscape

Long‐term studies at local scales indicate that fluctuations in abundance among trophically similar species are often temporally synchronized. Complementary studies on synchrony across larger spatial extents are less common, as are studies that investigate the subsequent impacts on community dynamics across the landscape. We investigate the impact of species population fluctuations on concordance in community dynamics for the small mammal fauna of the White Mountain National Forest, USA. Hierarchical open population models, which account for imperfect detection, were used to model abundance of the most common species at 108 sites over a three year period. Most species displayed individualistic responses of abundance to forest type and physiographic characteristics. However, among species, we found marked synchrony in population fluctuations across years, regardless of landscape affinities or trophic level. Across the region, this population synchrony led to high within‐year concordance of community composition and aggregate properties (e.g. richness and diversity) independent of forest type and low among‐year similarity in communities, even for years with similar species richness. Results suggest that extrinsic factors primarily drive abundance fluctuations and subsequently community dynamics, although local community assembly may be modified by species dispersal abilities and biotic interactions. Concordant community dynamics across space and over time may impact the stability of regional food webs and ecosystem functions.     

Species assembly in model ecosystems, I: Analysis of the population model and the invasion dynamics

Recently we have introduced a simplified model of ecosystem assembly (Capitán et al., 2009) for which we are able to map out all assembly pathways generated by external invasions in an exact manner. In this paper we provide a deeper analysis of the model, obtaining analytical results and introducing some approximations which allow us to reconstruct the results of our previous work. In particular, we show that the population dynamics equations of a very general class of trophic-level structured food-web have an unique interior equilibrium point which is globally stable. We show analytically that communities found as end states of the assembly process are pyramidal and we find that the equilibrium abundance of any species at any trophic level is approximately inversely proportional to the number of species in that level. We also find that the per capita growth rate of a top predator invading a resident community is key to understand the appearance of complex end states reported in our previous work. The sign of these rates allows us to separate regions in the space of parameters where the end state is either a single community or a complex set containing more than one community. We have also built up analytical approximations to the time evolution of species abundances that allow us to determine, with high accuracy, the sequence of extinctions that an invasion may cause. Finally we apply this analysis to obtain the communities in the end states. To test the accuracy of the transition probability matrix generated by this analytical procedure for the end states, we have compared averages over those sets with those obtained from the graph derived by numerical integration of the Lotka-Volterra equations. The agreement is excellent.     

Within-Site Variation in Feather Stable Hydrogen Isotope (δ2Hf) Values of Boreal Songbirds: Implications for Assignment to Molt Origin

Understanding bird migration and dispersal is important to inform full life-cycle conservation planning. Stable hydrogen isotope ratios from feathers (δ²H_f) can be linked to amount-weighted long-term, growing season precipitation δ²H (δ²H_p) surfaces to create δ²H_f isoscapes for assignment to molt origin. However, transfer functions linking δ²H_p with δ²H_f are influenced by physiological and environmental processes. A better understanding of the causes and consequences of variation in δ²H_f values among individuals and species will improve the predictive ability of geographic assignment tests. We tested for effects of species, land cover, forage substrate, nest substrate, diet composition, body mass, sex, and phylogenetic relatedness on δ²H_f from individuals at least two years old of 21 songbird species captured during the same breeding season at a site in northeastern Alberta, Canada. For four species, we also tested for a year × species interaction effect on δ²H_f. A model including species as single predictor received the most support (AIC weight = 0.74) in explaining variation in δ²H_f. A species-specific variance parameter was part of all best-ranked models, suggesting variation in δ²H_f was not consistent among species. The second best-ranked model included a forage substrate × diet interaction term (AIC weight = 0.16). There was a significant year × species interaction effect on δ²H_f suggesting that interspecific differences in δ²H_f can differ among years. Our results suggest that within- and among-year interspecific variation in δ²H_f is the most important source of variance typically not being explicitly quantified in geographic assignment tests using non-specific transfer functions to convert δ²H_p into δ²H_f. However, this source of variation is consistent with the range of variation from the transfer functions most commonly being propagated in assignment tests of geographic origins for passerines breeding in North America.     

Temporal variability of forest communities: empirical estimates of population change in 4000 tree species

Long‐term surveys of entire communities of species are needed to measure fluctuations in natural populations and elucidate the mechanisms driving population dynamics and community assembly. We analysed changes in abundance of over 4000 tree species in 12 forests across the world over periods of 6–28 years. Abundance fluctuations in all forests are large and consistent with population dynamics models in which temporal environmental variance plays a central role. At some sites we identify clear environmental drivers, such as fire and drought, that could underlie these patterns, but at other sites there is a need for further research to identify drivers. In addition, cross‐site comparisons showed that abundance fluctuations were smaller at species‐rich sites, consistent with the idea that stable environmental conditions promote higher diversity. Much community ecology theory emphasises demographic variance and niche stabilisation; we encourage the development of theory in which temporal environmental variance plays a central role.     

Limiting similarity and functional diversity along environmental gradients

Recent developments in community models emphasize the importance of incorporating stochastic processes (e.g. ecological drift) in models of niche‐structured community assembly. We constructed a finite, spatially explicit, lottery model to simulate the distribution of species in a one‐dimensional landscape with an underlying gradient in environmental conditions. Our framework combines the potential for ecological drift with environmentally‐mediated competition for space in a heterogeneous environment. We examined the influence of niche breadth, dispersal distances, community size (total number of individuals) and the breadth of the environmental gradient on levels of species and functional trait diversity (i.e. differences in niche optima). Three novel results emerge from this model: (1) niche differences between adjacent species (e.g. limiting similarity) increase in smaller communities, because of the interaction of competitive effects and finite population sizes; (2) immigration from a regional species pool, stochasticity and niche‐assembly generate a bimodal distribution of species residence times (‘transient’ and ‘resident’) under a heterogeneous environment; and (3) the magnitude of environmental heterogeneity has a U‐shaped effect on diversity, because of shifts in species richness of resident vs. transient species. These predictions illustrate the potential importance of stochastic (although not necessarily neutral) processes in community assembly.     

Expression of Actin-interacting Protein 1 Suppresses Impaired Chemotaxis of Dictyostelium Cells Lacking the Na+-H+ Exchanger NHE1

Increased intracellular pH is an evolutionarily conserved signal necessary for directed cell migration. We reported previously that in Dictyostelium cells lacking H⁺ efflux by a Na⁺-H⁺ exchanger (NHE; Ddnhe1⁻), chemotaxis is impaired and the assembly of filamentous actin (F-actin) is attenuated. We now describe a modifier screen that reveals the C-terminal fragment of actin-interacting protein 1 (Aip1) enhances the chemotaxis defect of Ddnhe1⁻ cells but has no effect in wild-type Ax2 cells. However, expression of full-length Aip1 mostly suppresses chemotaxis defects of Ddnhe1⁻ cells and restores F-actin assembly. Aip1 functions to promote cofilin-dependent actin remodeling, and we found that although full-length Aip1 binds cofilin and F-actin, the C-terminal fragment binds cofilin but not F-actin. Because pH-dependent cofilin activity is attenuated in mammalian cells lacking H⁺ efflux by NHE1, our current data suggest that full-length Aip1 facilitates F-actin assembly when cofilin activity is limited. We predict the C-terminus of Aip1 enhances defective chemotaxis of Ddnhe1⁻ cells by sequestering the limited amount of active cofilin without promoting F-actin assembly. Our findings indicate a cooperative role of Aip1 and cofilin in pH-dependent cell migration, and they suggest defective chemotaxis in Ddnhe1⁻ cells is determined primarily by loss of cofilin-dependent actin dynamics.     

Electrical Fluctuations Associated with Active Transport

Measurements were made of the spectrum of the voltage fluctuations developed in the 0.025-10 Hz band during active transport by frog abdominal skin with Ringer's solution on both sides. Decreasing the potential across the skin by an external supply of current diminishes the voltage fluctuations, but they do not disappear, reaching a minimum finite value. Thus, fluctuations in both the resistance of the skin and the electric current attendant to the active transport of sodium contribute to the voltage fluctuations. Ouabain eliminates the current fluctuations but not those of the resistance. At 20°C, the spectral intensities of the resistance and current fluctuations are nearly identical, varying as 1/f^a, where f is frequency and a = 1.6-2.0. At 32°C, the spectrum of the voltage fluctuations is sigmoid shaped, evidencing a relaxation process with a time constant of 0.6 sec. The fluctuations can be accounted for by stochastic variations in the concentration of a complex formed between a carrier molecule, fixed or mobile, and the actively transported species, sodium.     

Priority effects: How the order of arrival of an invasive grass,Bromus tectorum,alters productivity and plant community structure when grown with native grass species

Theories and models attempt to explain how and why particular plant species grow together at particular sites or why invasive exotic species dominate plant communities. As local climates change and human‐use degrades and disturbs ecosystems, a better understanding of how plant communities assemble is pertinent, particularly when restoring grassland ecosystems that are frequently disturbed. One such community assembly theory is priority effects, which suggests that arrival order of species into a community alters plant–plant interactions and community assembly. Theoretically, priority effects can have lasting effects on ecosystems and will likely be altered as the risk of invasion by exotic species increases. It is difficult to predict how and when priority effects occur, as experimental reconstruction of arrival order is often difficult in adequate detail. As a result, limited experimental studies have explored priority effects on plant community assembly and plant invasions. To determine if and how priority effects affect the success of invasive species, we conducted a greenhouse study exploring how the arrival order of an invasive grass, Bromus tectorum, affects productivity and community composition when grown with native grasses. We found evidence for priority effects, as productivity was positively related to dominance of B. tectorum and was greater the earlier B. tectorum arrived. This suggests that priority effects could be important for plant communities as the early arrival of an invasive species drastically impacted the productivity and biodiversity of our system at the early establishment stages of plant community development.     

Assembly-history dynamics of a pitcher-plant protozoan community in experimental microcosms

Background

History drives community assembly through differences both in density (density effects) and in the sequence in which species arrive (sequence effects). Density effects arise from predictable population dynamics, which are free of history, but sequence effects are due to a density-free mechanism, arising solely from the order and timing of immigration events. Few studies have determined how components of immigration history (timing, number of individuals, frequency) alter local dynamics to determine community assembly, beyond addressing when immigration history produces historically contingent assembly.

Methods/Findings

We varied density and sequence effects independently in a two-way factorial design to follow community assembly in a three-species aquatic protozoan community. A superior competitor, Colpoda steinii, mediated alternative community states; early arrival or high introduction density allowed this species to outcompete or suppress the other competitors (Poterioochromonas malhamensis and Eimeriidae gen. sp.). Multivariate analysis showed that density effects caused greater variation in community states, whereas sequence effects altered the mean community composition.

Conclusions

A significant interaction between density and sequence effects suggests that we should refine our understanding of priority effects. These results highlight a practical need to understand not only the “ingredients” (species) in ecological communities but their “recipes” as well.     

Yeast AEP3p Is an Accessory Factor in Initiation of Mitochondrial Translation

Initiation of protein synthesis in mitochondria and chloroplasts normally uses a formylated initiator methionyl-tRNA (fMet-tRNA_f^Met). However, mitochondrial protein synthesis in Saccharomyces cerevisiae can initiate with nonformylated Met-tRNA_f^Met, as demonstrated in yeast mutants in which the nuclear gene encoding mitochondrial methionyl-tRNA formyltransferase (FMT1) has been deleted. The role of formylation of the initiator tRNA is not known, but in vitro formylation increases binding of Met-tRNA_f^Met to translation initiation factor 2 (IF2). We hypothesize the existence of an accessory factor that assists mitochondrial IF2 (mIF2) in utilizing unformylated Met-tRNA_f^Met. This accessory factor might be unnecessary when formylated Met-tRNA_f^Met is present but becomes essential when only the unformylated species are available. Using a synthetic petite genetic screen in yeast, we identified a mutation in the AEP3 gene that caused a synthetic respiratory-defective phenotype together with Δfmt1. The same aep3 mutation also caused a synthetic respiratory defect in cells lacking formylated Met-tRNA_f^Met due to loss of the MIS1 gene that encodes the mitochondrial C₁-tetrahydrofolate synthase. The AEP3 gene encodes a peripheral mitochondrial inner membrane protein that stabilizes mitochondrially encoded ATP6/8 mRNA. Here we show that the AEP3 protein (Aep3p) physically interacts with yeast mIF2 both in vitro and in vivo and promotes the binding of unformylated initiator tRNA to yeast mIF2. We propose that Aep3p functions as an accessory initiation factor in mitochondrial protein synthesis.     

Effects of phylogeny,leaf traits,and the altitudinal distribution of host plants on herbivore assemblages on congeneric Acer species

Historical, niche-based, and stochastic processes have been proposed as the mechanisms that drive community assembly. In plant–herbivore systems, these processes can correspond to phylogeny, leaf traits, and the distribution of host plants, respectively. Although patterns of herbivore assemblages among plant species have been repeatedly examined, the effects of these factors among co-occurring congeneric host plant species have rarely been studied. Our aim was to reveal the process of community assembly for herbivores by investigating the effects of phylogeny, leaf traits, and the altitudinal distribution of closely related host plants of the genus Acer. We sampled leaf functional traits for 30 Acer species in Japan. Using a newly constructed phylogeny, we determined that three of the six measured leaf traits (leaf thickness, C/N ratio, and condensed tannin content) showed a phylogenetic signal. In a field study, we sampled herbivore communities on 14 Acer species within an elevation gradient and examined relationships between herbivore assemblages and host plants. We found that herbivore assemblages were significantly correlated with phylogeny, leaf traits, phylogenetic signals, and the altitudinal distribution of host plants. Our results indicate that the interaction between historical and current ecological processes shapes herbivore community assemblages.     

Accounting for dispersal and biotic interactions to disentangle the drivers of species distributions and their abundances

Although abiotic factors, together with dispersal and biotic interactions, are often suggested to explain the distribution of species and their abundances, species distribution models usually focus on abiotic factors only. We propose an integrative framework linking ecological theory, empirical data and statistical models to understand the distribution of species and their abundances together with the underlying community assembly dynamics. We illustrate our approach with 21 plant species in the French Alps. We show that a spatially nested modelling framework significantly improves the model's performance and that the spatial variations of species presence-absence and abundances are predominantly explained by different factors. We also show that incorporating abiotic, dispersal and biotic factors into the same model bring new insights to our understanding of community assembly. This approach, at the crossroads between community ecology and biogeography, is a promising avenue for a better understanding of species co-existence and biodiversity distribution.