Ecology Letters

O_LISeasonal migration in birds involves a substantial spatial redistribution of avian biodiversity each year and drives seasonal changes in community composition. Migrants experience different combinations of species interactions over space and time, generating regular disassembly and reassembly of bird communities throughout their annual cycles. However, the effects of seasonal migration on phylogenetic community structure remain poorly understood. C_LIO_LIWe assess spatiotemporal variation in phylogenetic community structure of North American passerines to test how seasonal migration restructures the evolutionary relatedness and dominant assembly mechanisms in bird communities throughout the annual cycle. Using distributional projections, we calculated metrics describing the phylogenetic dispersion of passerine communities each week of the year. We then tested the relationship between seasonal turnover in community phylogenetic dispersion and seasonal variation in species richness and proportion of migratory species. C_LIO_LISeasonal migration, by changing spatial patterns of avian diversity, simultaneously drives a complex continental redistribution of phylogenetic community structure. We find evidence of taxonomic scale dependency to our results, wherein throughout North America, the seasonal influx of migrant passerines yields communities that are overall more phylogenetically clustered, yet also exhibit greater phylogenetic overdispersion at smaller taxonomic scales. C_LIO_LISeasonal shifts in phylogenetic dispersion, though complex, track changes in diversity, manifesting as fluctuations in phylogenetic dispersion between northern and southern regions as seasonal migrants move between these regions. Our findings reveal a dynamic continental landscape of phylogenetic community structure directed by the movements of seasonal migrants. C_LI

Investigating the factors that stabilize biological communities is a central topic in ecology. Response diversity, defined as variation in species responses to environmental change, has been proposed as a key mechanism underlying the biodiversity-ecosystem functional stability (BEFS) relationship, whereby greater species diversity enhances ecological stability. Previous studies have shown that response diversity promotes ecological stability by generating asynchronous population fluctuations and the resulting compensatory dynamics. Although several metrics have been proposed to quantify response diversity, they do not explicitly consider the presence of insensitive species whose performance is unaffected by current environmental conditions. To examine how insensitive species influence response diversity, species persistence, and ecological stability, we conducted numerical simulations of a generalized Lotka-Volterra model under environmental forcing. We first confirmed that increasing variation among sensitive species increased the response diversity index and stabilized community dynamics. We then examined a scenario in which response diversity depended solely on the proportion of sensitive and insensitive species, assuming that all sensitive species responded identically to environmental change. Under this assumption, the response diversity index was maximized when sensitive and insensitive species occurred in equal proportions, whereas increasing the number of sensitive species monotonically destabilized community dynamics. Consequently, the relationship between response diversity and community stability depended on how response diversity was generated, such that higher response diversity could even be associated with lower community stability. These findings demonstrate that overlooking environmentally insensitive species can obscure the mechanisms linking response diversity and ecological stability. More broadly, our results reveal that response diversity comprises at least two distinct biological components--species sensitivity and response variation among sensitive species--that can have contrasting consequences for community stability. We therefore highlight the need to quantify sensitive species empirically and to develop response diversity metrics that distinguish these components. Author SummaryUnderstanding why some communities remain stable despite environmental change is a longstanding goal in ecology. Response diversity, which refers to differences in how species respond to environmental change, has been proposed as a key mechanism explaining why greater biodiversity (species richness) can promote ecological stability. Because species respond differently to changing environments, declines in some species can be compensated by increases in others, helping to stabilize community dynamics. However, previous studies have rarely considered species that are insensitive to current environmental changes. Using a mathematical model, we show that response diversity can arise from two distinct biological components--the number of sensitive species and variation in their responses--and that these components can have contrasting effects on ecological stability. When response diversity reflects variation among sensitive species, greater response diversity stabilizes community dynamics, as expected. In contrast, when response diversity changes only because of the proportions of sensitive and insensitive species, higher response diversity can be associated with lower community stability. Our findings highlight the importance of quantifying the number of sensitive species and developing response diversity metrics that distinguish species sensitivity from variation in responses among sensitive species.

Abundance correlations cannot reveal ecological interactions without an assumption about the covariance of environmental noise. A natural biological expectation is that similar species respond similarly to environmental fluctuations, generating positive correlations. Yet the same species also tend to overlap more strongly in resource use and therefore compete more intensely, generating negative correlations. The simplest plausible benchmark is thus to take environmental-response correlations proportional to niche overlap. We show that, under this assumption and across a broad class of stochastic community models, the two effects cancel exactly: equal-time abundance correlations vanish, independently of interaction strength, heterogeneity, and system size. Away from this matched point, the observed correlations measure primarily the mismatch between shared environmental response and competition, rather than the interaction matrix itself. Correlations can recover information about niche overlap when competitive feedback is delayed relative to environmental forcing, but the inference then depends on a resource-response timescale that is generally not determined by the abundance time series alone. When stochasticity enters through the mechanism that generates similarity itself--for example, through fluctuating shared resources--nonzero correlations may persist, but they reflect yield-depletion mismatch rather than niche overlap. Abundance correlations therefore report how environmental variability reaches the community at least as much as they report who competes with whom.

Equivalent numbers represent biodiversity as the effective number of equally distinct units, typically species, and can be partitioned across scales. In practice, they summarize each unit of biodiversity by a single value and compare units pairwise, misrepresenting units that are better described as distributions and the relationships between several units that share the same space. We introduce an equivalent-number index for assemblages of units represented as probability density functions (PDFs) over a continuous space, estimated as the integral of the pointwise maximum across abundance-weighted PDFs. Resulting equivalent PDF numbers fulfil elementary properties of classical equivalent numbers, and support additive partitioning across any number of nested scales. We illustrate the framework with case studies across three domains: (1) measuring trait diversity considering intraspecific variability in grasslands, (2) partitioning realized bioclimatic niches among clades of Carnivora, and (3) understanding seasonal changes in the partitioning of fish home ranges in geographic space.

The shape of density-dependence governs species persistence, and ecosystem stability. Yet, whether per-capita growth declines sublinearily, or superlinearily with density remains hotly debated. Growth rates across the tree of life have been shown to decline sublinearly with density, whereas theory founded on resource competition predicts the opposite. Here, we resolve this discrepancy and show that sublinearity can readily emerge from geometric constraints on consumer interactions. By linking inter individual spacing, movement and interference rates, we derive two limiting-interference regimes, one of which the well-mixed limit recovers the form of classic Beddington DeAngelis interference response. We then developed an individual-based model from first principles which reproduces the derived sublinearity response, and further use empirical data from published consumer-resource experiments that also bears the signature of sublinear density-dependence. Further, embedding the interference mechanisms underlying the emergence of sublinear density-dependence in coexistence theory opens a new regime for species coexistence where classical theory fails to predict. Our framework indicates that non-consumptive interactions are not merely a correction to resource competition but might be a distinct axis along which diverse communities may potentially coexist.

Although cities are increasingly recognized as ecological islands, a unified framework explaining their susceptibility to alien plant invasion remains lacking. Using the most recent and comprehensive global dataset of urban alien plants, we modelled alien richness, mimicking island biogeography theory (IBT). Across all models, neither city size nor geographic isolation independently explained alien richness. Instead, richness was consistently associated with their interaction, supporting the central IBT prediction. However, the strength of this interaction depends on how city size was quantified, with socio-economic dimensions exhibiting stronger positive interactions with geographic isolation than physical measures of city size. Introduction-hub identity further modified these relationships. North America was the only hub for which the interaction between city size and isolation was consistently weakened, indicating that donor regions of alien plants are not ecologically equivalent. Simulations of simultaneous increases in city size and isolation showed that larger, more connected cities generally accumulated more alien plants despite increasing geographic distance, but the magnitude and direction of these responses are hub dependent. Our findings inspire an extension of classical IBT to a mechanistic explanation for global variation in urban alien plant richness in this increasingly urbanized and globally connected world.

Mixed-species groups (MSGs) pose a particular challenge for our understanding of sociality in animals. Though MSGs are widespread social assemblages that form to enhance foraging success and reduce predation risk of participants, the role of traits in mediating grouping has received less attention. In particular, the role of body colour has not been tested quantitatively, despite the fact that visual similarity can reduce individual predation risk. Here, we examine whether plumage colour structures mixed-species bird flocks (MSFs) at a global scale. Using data spanning four continents, we developed a new metric that quantifies colour similarity among flock participants and compared observed flocks to null assemblages constructed from all flocking species at each site. We further examined whether MSF participants represented a colour subset of the available colours in the regional species pool. We found striking evidence that birds in MSFs were more similar in colour than expected by chance across all sites, indicating that plumage colour is a non-random structuring trait that shapes assembly of flocks globally. The strength and prevalence of colour structuring varied across geographies, but not flock size. Within communities, MSF participants differed systematically in colour composition from the regional species pool, occupying a restricted region of colour space dominated by yellow and brown plumage. Thus, plumage colour affects MSFs influencing both overall flock participation as well as species co-occurrence within flocks. Our findings illustrate the importance of visual traits in structuring interspecific social systems, by highlighting that birds of a feather do indeed flock together.

The shared trade-off in microbial resource-utilization strategies has been proposed to resolve the paradox of the plankton, which states that the diversity observed in nature greatly exceeds the theoretically predicted upper bound that limits the number of coexisting species to the number of available resources. However, three important aspects remain unaddressed in this line of work. First, trade-offs have been quantified not only for phenotypes associated with alternative resource utilization, but also for other modes of microbial interaction. Second, in natural systems, not all taxa are subjected to the same trade-offs. Third, existing trade-off-based models do not explain the empirically observed clustering of taxa according to functional similarity. Here, we extend the trade-off-based framework to incorporate multiple types of resources. We assume that different subsets of taxa are constrained by distinct sets of trade-offs. Under this framework, our model predicts the emergence of clusters: while taxa with similar strategies can belong to the same cluster, each cluster is sustained by taxa with substantially different strategies. The resulting system supports high diversity with an effectively unlimited number of coexisting taxa, yet can still be described as a low-diversity community in which the number of coexisting functional clusters does not exceed the theoretical upper bound.

1. Migration is a widespread phenomenon across taxa, yet the ecological mechanisms underlying its evolution and maintenance, particularly whether migratory behaviors are primarily driven by access to spatially restricted breeding sites or by seasonal tracking of trophic resources, remain poorly documented outside birds and large mammals. Despite increasing evidence that reptiles perform seasonal migrations, the ecological mechanisms underlying these movements have rarely been formally tested. 2. The critically endangered Galapagos pink land iguana (Conolophus marthae), endemic to Wolf Volcano, Isabela Island, exhibits partial migration along a steep altitudinal gradient, providing an opportunity to disentangle the relative roles of breeding-site availability, trophic resource dynamics, and thermoregulatory conditions as drivers of migration. 3. We used GPS tracking data from 22 individuals (7 males, 15 females) monitored between 2019 and 2023, combined with high-resolution spatio-temporal models of vegetation productivity and air temperature across the species' altitudinal range, to characterize population-level movement patterns and evaluate competing hypotheses explaining the evolution of this migratory behavior. 4. Movement models revealed a clear pattern of partial migration: 16 out of 22 tracked individuals performed seasonal altitudinal movements between a restricted high-elevation mating area and a larger dispersal area at lower elevation, with males reaching the mating area approximately 48 days earlier than females. The dispersal area remained consistently more productive than the mating area throughout the year, rejecting the prediction that individuals should track the shifting trophic resource peaks. Instead, the mating season coincided with the local productivity peak within the mating area, whereas temperature differences between areas were small (ca. 2{degrees}C) and did not explain migration timing. 5. These results support a site-dependent hypothesis of partial migration over a resource-tracking hypothesis, indicating that access to spatially restricted breeding sites is the primary driver of migration in this species, with local trophic resource dynamics fine-tuning reproductive timing. Providing empirical evidence for the ecological mechanisms underlying migration in a large terrestrial reptile, our results extend site-dependent theories of migration beyond birds and mammals and identify breeding-site availability as a key ecological driver of migratory behaviors across taxa.

Can observations distinguish a bloom supplied from within a study volume from one supplied across its boundary? We develop a theoretical framework for that question at plankton bloom onset, conditional on a predeclared, observed or calibrated onset event and a declared set of environmental paths, biological responses, and model forms. The estimand follows source-event labels through forcing-dependent survival and genotype-specific growth. Its central certificate asks whether the local onset fraction is invariant over every source history that produces the same time-expanded observation record. For polyhedral history fibers, a Charnes-Cooper transformation computes both sharp dynamic-data endpoints as linear programs. When each source instead has a fixed normalized onset signature, the certificate reduces to a row-space test; uncertain signatures require a joint lifted program. For a finite compatible scenario ensemble, admissible fractions are the union across scenarios, and a point is justified only when every nonempty scenario gives the same singleton. A synthetic two-genotype witness gives the same observed total but local fractions of 2/3 and 1/3 under reversed forcing-response gains. The observer, mixture, and optimization ingredients are established; the contribution is their target-specific synthesis around source at onset. The framework is diagnostic rather than predictive. It specifies what a study must measure--local sources, boundary inflow, forcing, response, timing, and carrier signatures on one declared window--and returns an interval when missing components have justified bounds, including [0, 1] when they remain unconstrained.

The performance of any natural population in variable environments depends on contemporaneous changes in its vital rates (e.g., survival, reproduction) as well as legacies carried by its population structure. Yet whether the relative contribution of these two pathways can be predicted from life history remains unknown. Here, we use stochastic simulations of 1,986 matrix population models from 137 species to quantify the contribution of transient dynamics to variation in population growth rate, and test its associations with key life history traits. Longer generation times were associated with reductions in transient contributions, contrary to theoretical expectations. Greater stage-specific survival heterogeneities were associated with increases in transient contributions, whereas greater iteroparity was associated with decreases in plants but increases in animals. These associations were robust to body size, phylogenetic relationships, and vital-rate variability. Life history traits therefore provide a strong predictor for when population structure shapes population responses to environmental variability.

Most evidence of the consequences of climate change in natural systems has focussed on shifts in mean temperature (1,2), but the effects of extreme climatic events (ECEs) remain far less understood. This is particularly true for very severe ECEs that may occur only once every few decades. Understanding the consequences of these severe events for natural populations is nonetheless critical, since their frequency is predicted to rise under current climate change (3). Here we combine a unique long-term dataset spanning almost five decades of breeding (>20,000 events) and morphological data (>120,000 observations) in adult and nestling great tits (Parus major) and blue tits (Cyanistes caeruleus) with fine-scale temperature records to examine the effects of an unprecedented heatwave in May 2026 on breeding success and morphology. Average temperature during the heatwave (22-29 May 2026) was 7.85 C above the historical record, reaching +10.5 C (+4.32 SD) at its peak (25-26 May). These record-breaking temperatures significantly reduced adult breeding success and nestling bmass relative to expectation in the absence of a heat-wave. Given the heatwave was widespread (Fig. 1A), our findings from a single, exceptionally well-studied population are likely to generalise to other species exposed to the same event, providing key evidence that severe ECEs can substantially harm wild populations.

Forecasts of biodiversity responses to climate change often rely on space-for-time substitution, in which spatial biodiversity-climate relationships are used to predict biodiversity change through time. Yet this approach is rarely tested directly because long-term biodiversity time series are scarce. Here, we combine global modern and fossil assemblage data of planktonic foraminifera with site-specific sea-surface temperature reconstructions to compare biodiversity-temperature relationships across space and time. Spatial and temporal compositional turnover models showed similar slopes but consistently different intercepts, with spatial models predicting higher turnover across the full temperature gradient. Restricting the spatial comparison to the environmental domain of individual fossil time series reduced, but did not eliminate, this intercept mismatch. For alpha diversity, spatial models more closely recovered the temporal biodiversity-temperature relationship than for compositional turnover. Thus, for the timescales studied here, space-for-time substitution captures the direction of biodiversity change but not its magnitude through time.

Biodiversity frequently peaks in fluctuating micro-oxic environments such as marine oxygen minimum zone interfaces, rhizospheric aggregates, sediments, microbial mats, and gut mucus layers. Yet, classical ecological theories do not adequately explain why intermediate oxygen tensions repeatedly favor coexistence and diversification. Herein, we propose a murburn ecological formalism wherein oxygen acts not merely as a metabolic substrate but as a generator of dynamic redox heterogeneity through partial reduction and diffusible reactive species (DRS) and redox-intermediates formation. Integrating empirical observations from marine, gut, soil, and aquatic-interface ecosystems with a reaction-diffusion framework, we show that intermediate oxygen tensions naturally maximize radical-field heterogeneity and produce dynamically shifting fitness landscapes. Numerical simulations demonstrate spontaneous coexistence, biodiversity maxima within micro-oxic zones, localized diversification, and coexistence stabilization without externally imposed niche partitioning. Additional simulations suggest that aquatic macrofauna indirectly enhance biodiversity by restructuring oxygen gradients and generating ecosystem-scale diffusional redox architectures (ESDRA). The framework proposes that fluctuating redox interfaces function as potential ecological zones of elevated adaptive turnover across biological scales.

Marine plankton are functionally diverse and span over five orders of magnitude in diameter, with important consequences for marine biogeochemical cycles. Marine ecosystem simulations are beginning to resolve this diversity; however, major uncertainties persist regarding the structure and function of planktonic ecosystems. Here we diagnosed plankton Species Abundance Distributions (SADs) in large-scale surveys and in a global, mechanistic plankton community simulation. The fitted slopes of the SADs vary by less than 10% across latitude, season, and biome in both observations and the simulation. Fitting parametric SADs further reveals spatial structure in the shape and functional form of the SAD aligned with established biogeographic provinces. Together, these results demonstrate a largely invariant structure of marine plankton communities that persists despite strong environmental gradients and taxonomic turnover. These findings suggest that the emergent shape and scaling of plankton SADs reflect fundamental constraints on community assembly and provide a compact quantitative diagnostic for planktonic ecosystem structure.

Thermal fluctuations increasingly take the form of recurring heatwaves, yet how the acclimation responses of community members shape collective temporal stability remains untested. Using communities of the marine pico-cyanobacterium Synechococcus sp. assembled in microcosms to span a broad range of mean response and response diversity, we tracked total cell density and per-cell chlorophyll a through a 16-day warming-cooling fluctuation regime. Temporal stability of total density was predicted by community mean response and response diversity, but only when computed from acute acclimation responses, not when computed from chronic responses at sustained conditions. Higher acute response diversity increased stability, while a higher mean acute response reduced it, independently of intraspecific richness. Community growth was sub-additive at warming transitions but matched the additive prediction at cooling, indicating that inter-strain interactions suppress community growth specifically as the community enters the warm state. Acclimation response is thus a determinant of both the predictability and the realized dynamics of microbial communities under recurring thermal stress.

As ecosystems face a growing number of threats, coextinctions (resultant extinctions following a primary extinction) are expected to proliferate. However, less is known about the conditions under which coextinctions could outpace primary extinctions. Because coextinctions often occur through lost species interactions, we posit that aspects of food web structure and complexity can help predict differences in vulnerability to coextinction across ecosystems. To test this, we leverage Bayesian network models to assess the extent to which variation in ecosystem vulnerability to coextinction varies with food web structure. We find that food webs with high maximum trophic level are most vulnerable to coextinction, and that maximum trophic level is a better predictor than other aspects of food web structure, such as species richness or trophic connectance. Extending this approach, we also find that maximum trophic level uncovers the relative vulnerability of ecosystem services to species coextinction across 12 empirical food webs.

Information is fundamental to biological survival, but the amount of information and its biological value are not equivalent. Shannon information quantifies uncertainty reduction, whereas Volkenstein's value of information measures how information changes the probability of a biologically relevant outcome. Although originally developed for molecular biology contexts, the latter concept has rarely been applied to environmental sensing and ecological interactions. Here we develop a value-of-information framework for microbial predator-prey interactions based on hydrodynamic sensing, in which prey detect fluid disturbances generated by approaching predators. Using a mechanistic model that incorporates sensory thresholds, memory, false alarms, biological benefits and costs, and predator encounter probability, we characterize mutual information from three hierarchical measures of biological value: encounter-conditional value, ecological value, and lifetime fitness value. The framework reveals how small amounts of sensory information can produce disproportionately large survival benefits during predator encounters, generating encounter-level value amplification in which biological value exceeds Shannon information. However, although global sensitivity analysis shows that such amplification is common, it is not universal and becomes progressively diluted at broader ecological and lifetime scales by encounter rarity, background noise, and sensory costs. Across most parameter combinations, the encounter-conditional value exceeded the ecological value, which in turn exceeded the lifetime fitness value. These results demonstrate that environmental sensing should be evaluated not only by how accurately it represents the external world, but by how strongly it changes biologically relevant outcomes. More broadly, the framework extends Volkenstein's concept of information value to ecological interactions and provides a quantitative framework for predicting when environmental information enhances survival and fitness, thereby providing a platform for explaining the evolution, maintenance, diversification, and loss of sensory systems.

Adaptive phenotypic plasticity is expected to evolve when environmental conditions change predictably over time. This has led to the hypothesis that ectotherms in environments with low temperature seasonality, such as the tropics, should evolve lower thermophysiological plasticity than those from more seasonal environments (the Climate Variability Plasticity Hypothesis, or CVHP). Yet, empirical support for the CVHP is incredibly low, creating a need to identify other factors that can help explain how thermal plasticity evolves. Here, we use numerical models to show that the evolution of constitutive thermal tolerance breadth greatly affects the evolutionary benefits of thermal plasticity. In particular, tolerance breadth interacts with within- and between-season temperature variation in ways that can confound expectations of the CVHP, including conditions in which organisms from less seasonal environments benefit 30 most from expressing plasticity. Our findings indicate that a more holistic view of the relationship between thermophysiology and environmental temperature is needed to explain the evolution of thermal plasticity across climatic gradients.

Climate change is disrupting life's seasonal rhythms, altering the timing of key phenophases and reshaping how communities assemble. Beyond shifting flowering times, climate change can modify the extent of floral overlap and the sequence in which species bloom, generating novel assemblages with uncertain consequences for plant-pollinator interactions. Here, we ask whether flowering order generates priority effects in plant-pollinator communities, much like germination order does in plant communities. We tested how flowering order influences bee foraging behaviour and plant reproductive success in two co-flowering species, Hypochaeris radicata and Campanula rotundifolia, using a greenhouse experiment in which we manipulated the sequence of floral availability while allowing bees to forage repeatedly. We quantified changes in visit frequency, interspecific switches, handling time, and seed production. Our findings reveal priority effects in bee foraging that were strong enough to affect plant fitness: both species received more visits when flowering earlier than their co-occurring counterpart, and seed production declined when species flowered later. Overall, our results show that flowering order is an underappreciated driver of plant-pollinator interactions, suggesting that climate-driven phenological shifts could alter priority-effect dynamics with broader implications for community assembly. Key questions remain: How will climate-driven phenological shifts rearrange flowering sequences, and how will these priority effects emerge in more diverse communities in the wild? Our controlled experiment reveals strong flowering-order effects, underscoring the need to evaluate how widespread and impactful such dynamics are under accelerating climate change.