Global Ecology and Biogeography

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.

Evidence is accumulating that global change is altering species distributions. Yet, detailed knowledge is missing about the relative and joint contribution of different drivers to observed species responses. Here, we implemented an impact attribution framework based on counterfactual simulations to assess the impact of climate and land use change on occupancy dynamics of North American breeding birds. We used a Bayesian framework to fit process-explicit dynamic occupancy models to long-term survey data for 159 species from 1995 to 2019, and quantified predictive performance using spatial and temporal cross-validation. We then assessed the relative importance and effect direction of climate and land use change while accounting for model predictive accuracy. Results indicate that climate change negatively affected 90 % of the species and land use change negatively impacted 96 %. Climate change emerged as more important than land use change for driving changes in occupancy across species. Remarkably, the effects of both drivers were mostly antagonistic rather than acting additively or synergistically. Climate was the most important driver for bird communities in the western USA, while land use change dominated in the southeast, and combined climate and land use change in the northeast. Our analysis demonstrates that recent changes in North American bird distributions are shaped by multiple global change drivers acting in concert. The effect of recent climate and land use change were mostly antagonistic, and thus trends in bird occupancy dynamics could not be understood by studying the impact of those drivers in isolation. By disentangling the effects of climate and land use change on biodiversity trends, impact attribution approaches can improve our understanding of global change impacts and can support conservation planning and more accurate and realistic projections of biodiversity response to global change.

Biodiversity loss is driven by unsustainable human activities, yet the contextual conditions and underlying drivers of threats remain poorly understood. We assessed how protected areas, socioeconomic conditions, and biophysical factors explain global patterns of threat probabilities across six major threat types and four vertebrate taxa. We identified key explanatory variables and their associations with threats using Extreme Gradient Boosting (XGBoost) and SHapley Additive exPlanations (SHAP). Socioeconomic conditions, specifically human development and income inequality, were the strongest predictors. Their associations were complex and non-linear: notably, high human development index (HDI) was associated with both higher and lower threat probabilities, depending on inequality and regional context. Second, land cover and biophysical variables, such as shrubland cover, tree cover, and elevation range, explained additional, but taxon-specific variation. Finally, protected areas showed limited ability to explain threat patterns. By linking threat probabilities to their contextual and socioecological conditions, we aim to build a better understanding of the systemic drivers of biodiversity loss.

Biodiversity aggregators such as GBIF provide unprecedented access to global biodiversity data, yet their representativeness remains uneven across space and taxa. This study examined the spatial and taxonomic structure of global vascular plant data available on GBIF. Six filters were applied to the GBIF vascular plant dataset, resulting in the removal of 54% of all records. Together, the filters explained more than 90% of the identified spatial issues, with duplicate and missing coordinates accounting for most of the variation. A higher number of occurrence records was associated with a greater number of spatial issues. Record distributions became progressively more even at finer taxonomic levels, from orders to species. The time series of occurrences for species, genera, and families increased sharply after 1800 and continued to rise, with no apparent stabilisation. Of the 824 ecoregions covered, 73 accounted for 72% of all occurrence records. These ecoregions spanned all continents but were strongly concentrated in Europe, followed by North America and Oceania. The analyses reveal four key patterns: (1) data volume is positively associated with spatial issues; (2) a small number of taxa account for a large proportion of records, whereas many are represented by relatively few; (3) occurrence data aggregated by GBIF have increased continuously since 1800; and (4) record coverage remains highly uneven across the world's ecoregions. These results highlight the substantial contribution of biodiversity data aggregators to expanding access to biological information while demonstrating the persistent spatial and taxonomic biases that shape their contents. Such biases should be explicitly considered when assessing data completeness and quality and when using aggregated occurrence records to infer global biodiversity patterns.

AimHere we aim to disentangle species-specific bioclimatic drivers of forest site productivity and project their future dynamics, providing a spatially explicit basis for anticipating climate-driven shifts in productivity and their implications for forest carbon sequestration. LocationIberian Peninsula. Time period1985-2014 (calibration); 2071-2100 (projected under CMIP6 scenarios). Major taxa studied21 Iberian tree species. MethodsWe used Site Form (SF) maps derived from the Third Spanish National Forest Inventory, spatially interpolating plot-level SF estimates as a continuous productivity index and relating them to 25 bioclimatic variables. Multiple linear regression models were selected via complementary stepwise and subset regression and validated on independent hold-out data (80%/20% split). ResultsValidated [Formula] ranged from 0.46 (Quercus faginea) to 0.97 (Pinus pinaster); 17 of 21 species reached [Formula]. BI013 precipitation of the wettest month), not BI014, was the most frequently retained predictor (15/17); BI014 was retained in only (11/17 models with a near-even sign split. Combining projected changes in mean productivity and habitat extent under SSP5-8.5, fifteen of sixteen applicable species lose total productivity by 2071-2100, six -- including Fagus sylvatica and Betula alba -- collapsing to below 1% of their reference-period value; only Pinus pinaster gains, and only under the lowest-emission pathway (up to 175%) -- under SSP5-8.5 it too loses productivity, albeit less than any other species (35% of its reference-period value retained). Limiting warming to SSP1-2.6 spares Mediterranean pine and oak species but not Euro-Siberian and montane ones. Main conclusionsThese validated, extrapolation-aware models reveal a near-universal, climate-driven collapse in Iberian forest site productivity, with direct implications for the carbon-sink potential currently attributed to these forest types, and provide a route to dynamic, climate-aware carbon-uptake estimates for the region.

Land-use change, such as the transformation of woody ecosystems into open pastures, acts as a strong ecological filter, favouring some species while excluding others according to differences in ecological niche breadth. Understanding how differences in niche breadth influence species responses under anthropogenic filters is crucial to anticipate their persistence or displacement. In this study, we quantified realized niche breadth in two sympatric ecosystem engineers, the Neotropical leaf-cutter ants Atta cephalotes and Atta laevigata, to test whether breadth differences are consistent with specialist and generalist ecological strategies. We characterized realized niche breadth across fine-scale environmental gradients by integrating hemispherical photography, microclimatic data, mound architecture, and edaphic profiles from 114 colonies across a regional transect in the Colombian Andes, alongside macroclimatic data from Copernicus. Principal Component Analysis (PCA) and PERMANOVA identified canopy openness and bushes- and tree-type vegetation density as the principal axes of interspecific niche partitioning. The observed differences in realized niche breadth were consistent with specialist and generalist ecological strategies. A. laevigata was predominantly associated with open-canopy areas, warmer micro- and macroclimatic conditions, and narrower edaphic dispersion. In contrast, A. cephalotes occupied a wider range of microhabitat conditions. This broader realized niche breadth is compatible with previous reports of A. cephalotes occurring in urban areas. Together, these findings suggest that niche breadth may influence how Neotropical leaf-cutter ants respond to habitat transformation, helping to understand the ecological consequences of land-use change.

Biological invasions are a major driver of global change, reshaping ecosystems and threatening biodiversity worldwide. Anticipating where invaders will establish and where they will exert the strongest ecological impacts are key challenges for early detection and targeted management. Although Species Distribution Models (SDMs) are widely used to forecast biological invasions, they often provide uncertain estimates of establishment ranges and limited insight into invader performance, making it difficult to anticipate ecological impacts. Here, we address these limitations by integrating physiological information on invader performance with SDMs to identify regions of high invasion risk. Using the brown alga Rugulopteryx okamurae, one of the most prominent marine invaders in Europe, we first test alternative hypotheses of northern establishment limits: (i) a cold-survival constraint driven by winter temperatures and (ii) a growth constraint derived from the species' thermal performance. To identify the more likely scenario, we combine cold-tolerance experiments with seasonal growth comparisons between the invader and a native macroalga Dictyota dichotoma, whose established distribution allows physiological performance to be directly related to realised presence. Finally, we project seasonal growth of the invader across the predicted establishment range as a proxy for biomass accumulation and potential ecological impacts. Our results indicate that northern limit in Europe will be more likely constrained by winter survival rather than growth, extending the potential establishment range of Rugulopteryx to mid-Norway. In contrast, the highest impacts are likely to remain concentrated in southern Europe, where thermal conditions sustain high year-round growth. Overall, our approach illustrates how understanding the physiological response of invaders to their environment can improve the interpretation of SDM outputs and help identify areas at greatest risk of impact within their potential establishment range.

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

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.

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.

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.

Global change is driving rapid ocean warming, exposing organisms to both chronic temperature increases and acute marine heatwaves. Understanding how species cope with thermal stress is critical for predicting ecosystem resilience. Echinoderms are globally distributed and often function as foundational species, yet comparative assessments of upper thermal tolerance among species occupying contrasting thermal environments remain limited. Here, we address this gap by comparing upper thermal tolerance across three sea urchins with distinct biogeographic distributions: the latitudinally broad purple sea urchin (Strongylocentrotus purpuratus), the circumpolar green sea urchin (S. droebachiensis), and the tropical variegated sea urchin (Lytechinus variegatus). We quantified thermal limits after two acclimation treatments: ambient temperatures approximating native habitat conditions for each species and an elevated temperature (+6 C). We developed a novel assay to measure critical thermal maximum (CTmax), comparing variability and inconsistencies associated among multiple assays. Upper thermal tolerance increased with acclimation to elevated temperatures in all three species, but acclimatory capacity differed markedly, with S. droebachiensis showing the strongest response and S. purpuratus the weakest. Conversely, S. purpuratus had the highest thermal safety margin and thus the lowest proximity to its thermal ceiling. Our adhesion based CTmax method was more reproducible and the most precise compared to other metrics tested, providing an improved framework for quantifying physiological thermal limits of sea urchins. Together, these findings reveal substantial but unevenly distributed thermal resilience in ecologically diverse sea urchins, advancing our understanding of how foundational marine species may respond to future global change.

1. Species loss can erode food-web functioning not only through secondary extinctions, but also through biomass redistribution, weakened energy pathways, and threshold-like functional collapse. Common topology-, connectivity-, and extinction-based robustness metrics provide valuable summaries of structural disassembly and cascade risk, but they are not designed to quantify continuous biomass retention, collapse-associated species sets, and non-additive group-level effects within a single dynamic framework. 2. We develop a dynamic biomass-based framework for assessing food-web robustness under progressive species removal. The framework introduces Dynamic Area-based Robustness (DAR), which quantifies the weighted area between slow- and fast-collapse reference trajectories of total ecosystem biomass retention. Building on these trajectories, we operationally define the Minimal Vital Species Set (MVSS) as the smallest fast-collapse-prefix species set whose removal first drives biomass below a predefined functional-collapse threshold. We further propose Cluster Influence (CI), which compares the biomass effect of simultaneous group removal with the mean effect of removing the same species individually. 3. We evaluated the framework using 120 niche-model virtual food webs spanning controlled gradients of species richness and connectance, and further demonstrated its applicability on 16 empirical stream food webs. We compared DAR with AUC- and secondary-extinction-based robustness metrics and assessed the sensitivity of DAR, MVSS, and CI to key bioenergetic parameters and parameter uncertainty. 4. DAR captured biomass-based robustness patterns that were only partly aligned with structural and extinction-based metrics, indicating that dynamic functional degradation provides complementary information. In virtual food webs, MVSS subsets were strongly enriched in basal species or basal resource nodes, and smaller MVSS proportions were associated with stronger positive CI under fast-collapse trajectories. Together, DAR, MVSS, and CI provide a reproducible framework for linking food-web structure, biomass dynamics, collapse thresholds, and non-additive species-set effects, offering a practical tool for dynamic robustness assessment in theoretical and empirical food webs.

The number of species introduced outside of their historical ranges by human activity continues to rise. A subset of these species establishes, form self-sustaining populations, and some (invasive alien species) go on to cause substantial harm to biodiversity and ecosystems. Preventing new invasive alien species from establishing is the key focus of interventions, because post-establishment management is costly and often fails. However, it remains unclear how effective multilateral efforts have been in curbing the rise. Here we show that the emergence of new invasive alien species across countries is slowing, and trends are similarly negative across geographically diverse countries. Using data and modelling advances, we find a 35% reduction in the establishment of new invasive alien species over a policy-relevant 50-year time frame. The findings directly inform the assessment of progress for the invasive alien species target of the Kunming-Montreal Global Biodiversity Framework, and provide a global baseline for monitoring rates of invasive alien species establishment. Furthermore, the slowdown suggests that policy and investment over recent decades to prevent invasive alien species from entering and establishing in countries have had a positive effect.

Urbanization is reshaping freshwater ecosystems, with well-documented effects across gradients of land-use change, hydrologic alteration, and habitat degradation. However, how biodiversity is organized among neighboring urban aquatic habitats that differ in hydrologic connectivity, disturbance transmission, residence time, management history, and opportunities for species movement is often less clear. This creates a challenge for interpreting urban fish communities at local scales as species occurrence may reflect both contemporary habitat filtering and historical contingencies including native persistence, interbasin transfer, stocking, and nonindigenous introductions. Here we use eDNA detections, historical records, phylogenetic information, and species trait data to investigate the fish assemblages of the Charlotte metropolitan region. We detect a highly mixed fauna that also depicts a strong signature of structured biodiversity profiles across taxonomic, phylogenetic, functional, and life-history dimensions between habitat types. In particular, bounded habitats contained assemblages with larger-bodied species that are fecund and faster to reproduce relative to free-flowing habitats. Species-level occurrence models did not support a simple trait-by-habitat rule. Instead our results demonstrate that urban aquatic habitats can sort historically mixed regional species pools into predictable assemblage-level life-history profiles while simultaneously retaining signatures of evolutionary and historical biogeographic contingency.

Sequential hurricane-heatwave events threaten forest resilience via understudied legacy effects. Using Bayesian Structural Time Series, piecewise Structural Equation Modeling, and a 21-event global synthesis, we quantify how structural degradation non-linearly amplifies productivity loss during subsequent heatwaves. Our Hurricane Michael (2018) case study reveals significant negative GPP legacy effects during the 2019 heatwave. Intact, tall and diverse canopies buffer microclimates and moderate thermal sensitivity. Hurricane-induced structural simplification removes this protection, exposing temperature-sensitive shaded leaves to extreme stress. We identified a context-dependent hydraulic trade-off: structural complexity provides shading but exacerbates forest sensitivity to water deficits during peak heat, the vulnerability of which reverses during the recovery phase. Globally, these legacy effects are triggered by heatwave intensity and modulated by soil type, with loamy-soil forests most vulnerable. These findings highlight the critical role of forest structure in forest responses to compound disturbances. Neglecting structural legacies in Earth System Models likely underestimates risks to global carbon sinks.

Citizen science data are increasingly used to infer biodiversity change, but causal claims based on such data are credible only if sampling effort and its temporal shifts are explicitly modeled. Zhang et al. (1) used citizen science data to conclude that greater photovoltaic policy stringency, measured using the photovoltaic policy stringency index (PSI), reduced county-level bird diversity in China. We reproduced their fixed effects and instrumental variable estimates. However, the observed Shannon diversity derived from pooled citizen science records reflects both bird communities and sampling effort, which the authors' controls do not adequately capture. Accounting for observer count changed the reported statistically significant 2.10% decline in Shannon index to a nonsignificant 0.58% increase (P = 0.288) per one-standard-deviation increase in PSI, and rendered the instrumental variable estimate statistically indistinguishable from zero (P = 0.912). Yet observer count is only one of many sources of sampling bias. PSI was also associated with multiple dimensions of sampling effort, consistent with sampling effort acting as a potential mediator in the PSI-diversity chain. The sampling domain also shifted markedly from 2014 to 2023: recorded county-months increased almost 24-fold, median observer count rose from one to three, and zero-duration records declined from 57.2% to 0.17%. Without adequate adjustment, these shifts confound estimates of temporal change in observed bird diversity. Beyond its inadequate treatment of sampling effort, the original study also misinterpreted its statistical results. Although the reported R{superscript 2} values are high, they are dominated by county and year-month fixed effects, with PSI contributing a partial R{superscript 2} of only 0.048% on observed Shannon index. The PSI-photovoltaic-area correlation is also weak (r = 0.0414) and vanishes after accounting for fixed effects (P = 0.977). Furthermore, the released bird observation data contain many erroneous outliers, raising significant concerns about insufficiently rigorous data preprocessing and quality control. These results show that the released data cannot properly distinguish ecological change from sampling effort change. Robust inference from citizen science data requires checklist-level effort metadata, explicit correction for spatiotemporal sampling shifts, and close collaboration among researchers with complementary methodological and ecological expertise.

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.

Climate driven aridification and intensified human activity are placing increasing pressure on Mediterranean freshwater ecosystems. These impacts propagate from land to water, altering nutrient regimes and reshaping aquatic microbial communities. We analysed Arcellinida diversity across 363 lentic inland saline and freshwater sediment samples spanning broad gradients of land use, water chemistry, soil properties, and climate in southern Spain. Random forest models identified terrestrial land use intensity followed by water chemistry as main predictors of community diversity. Diversity declined sharply in sites with population densities above [~]33 inhabitants/km{superscript 2} and under eutrophic conditions, but peaked in oligotrophic systems with stable, carbon rich soils. These threshold responses demonstrate that aquatic protist assemblages integrate both long term terrestrial pressures and current water conditions. Overall, our findings show that landscape transformation and its cascading effects on water quality dominate community assembly, and that the combination of community level diversity metrics with selected taxon-level indicators capture ecosystem degradation more consistently than relying on a single metric.