The scale of the blind spot is striking. Research on resource subsidies has historically focused on native species, particularly a handful of conspicuous actors such as spawning salmon, storm-driven seaweed, and emerging swarms of aquatic insects. Meanwhile, thousands of studies have catalogued the impacts of non-native species on biodiversity, yet almost none have asked a deceptively simple question: what happens to the flow of energy between ecosystems when an invader arrives? The answer, the new review shows, is that invaders can do everything from delivering pulses of marine nutrients into Patagonian forests to severing the supply of insects that feed spiders along stream banks. Because these effects are often indirect and rarely the original focus of ecological research, the true footprint of biological invasions may be substantially underestimated.

To build the synthesis, the researchers systematically searched the Scopus database for studies combining the concepts of trophic, spatial, or resource subsidies with non-native, invasive, alien, or introduced species, screening every article published up to the end of 2024. From an initial pool of 307 papers, supplemented by backward reference searches, 143 met the criteria and yielded 212 individual case studies. For each case, the team recorded the continents involved, the donor and recipient ecosystems, the taxonomic identity of the invading species, the affected native biota, the methods used, and the biological and chemical variables measured. The result is a global map of invasion-mediated resource flows that reveals both what science knows and, more revealingly, what it has ignored.

The geographic and taxonomic biases are stark. North America dominates the literature, followed by Europe, where only a handful of countries, including the United Kingdom, Germany, France, Spain, and Portugal, account for most of the output. Africa is severely understudied, contributing just 2.8 percent of all publications, with Asia at 7.7 percent. Oceania presents a particular paradox: despite hosting some of the world’s most threatened endemic biodiversity and suffering some of the worst invasion impacts, only 12 studies from the region examined invasion-mediated connectivity. The tropics, which harbor the greatest biodiversity and face accelerating invasions, remain largely absent from the record. Taxonomically, the picture is equally lopsided. Non-native plants account for 28.8 percent of case studies, fish for 25.5 percent, and mammals for 21.7 percent, while fungi represent a mere 0.9 percent and bacteria 2.4 percent, despite their fundamental roles in decomposition and nutrient cycling.

What the existing cases do show is remarkable in its variety. Non-native species can add entirely new subsidies to ecosystems. Introduced Pacific salmon in Patagonia transport marine-derived nutrients into otherwise nutrient-poor streams and forests when they spawn and die, enriching food webs from invertebrates to birds and mammals. Mass die-offs of the invasive Asian clam Corbicula fluminea generate carrion pulses that feed decomposer communities in both aquatic and terrestrial systems. The nitrogen-fixing albizia tree injects nitrogen into invaded Hawaiian ecosystems, fueling bottom-up changes that cascade through the food web. In some cases, invaders even create spatial connections that never existed before, such as the non-native melaleuca tree in Florida, which forces panthers to travel farther for resources, linking habitats that were previously unconnected.

Just as often, invaders cut existing subsidies off. On tropical islands, non-native rats prey on seabird chicks and eggs, collapsing colonies and halting the flow of marine-derived guano that fertilizes soils and coastal waters. Where rats strip islands of seabirds, the surrounding coral reefs lose nutrients, and reef fish biomass declines. In riparian zones, non-native fish such as brook trout consume terrestrial invertebrates that fall into streams, reducing food available to native species, while also preying on aquatic insect larvae before they can emerge as adults to feed spiders, birds, and bats on land. The green alder sawfly and European bird cherry strip or replace native riparian vegetation, cutting the supply of terrestrial insects to streams. Even behavioral disruption plays a role: freshwater crocodiles in Australia, poisoned by invasive cane toads, abandon terrestrial foraging altogether, severing an aquatic-terrestrial energy pathway.

A third category of impact is subtler: modification. Invaders rarely just add or subtract; they change the character of what flows. The river red gum, an Australian tree introduced elsewhere, sheds leaf litter that leaches more dissolved compounds and breaks down differently than native vegetation, altering the detrital base of streams. Non-native bivalves such as Corbicula fluminea release nitrogen through their biodeposits at rates that reshape nutrient cycling in stream sediments. Armored catfish in nutrient-limited streams create biogeochemical hotspots through their dense daytime aggregations and excretion, changing the quality and availability of nutrients for other organisms. Even marine wrack washing ashore differs in nutritional value depending on whether it comes from native or non-native algae, shifting the composition of the invertebrate communities that depend on it.

The review frames these effects through four critical dimensions: the quantity, quality, timing, and duration of subsidies. Quantity matters because ecosystems have thresholds. Low levels of an invader’s subsidy may boost productivity, but excessive inputs can trigger eutrophication, oxygen depletion, and abrupt ecological collapse, a pattern documented after mass mortalities of invasive bivalves. Quality determines whether a subsidy is assimilated or toxic: some non-native plants leach allelochemicals that harm water fleas and amphibian larvae, while others, like the high-nitrogen Himalayan balsam, support denser and more diverse invertebrate communities than native plants. Timing can desynchronize resource availability from the life cycles of dependent organisms, and duration determines whether effects are transient pulses or chronic pressures that permanently restructure ecosystems. The review notes that these thresholds have never been formally assessed in invaded systems, representing a critical gap.

The methodological landscape reflects the field’s youth. Field-based studies dominate at 43 percent of case studies, followed by stable isotope analysis at 17 percent and diet content analysis. Controlled experiments, which allow manipulation of environmental variables while retaining ecological realism, account for 10 percent. Emerging tools remain rare: DNA analysis appears in just 1.2 percent of cases, remote sensing in 0.4 percent, and field-monitoring techniques such as telemetry and camera trapping in 3.6 percent. The authors argue that this is precisely where the field must go next. Environmental DNA and metabarcoding are revolutionizing the detection of non-native species across ecosystems, while combining molecular tools with fatty acid and stable isotope tracers could reveal the fine-scale mechanisms by which invaders redirect energy flows. Machine learning and artificial intelligence offer the capacity to process large datasets, model invasion pathways, and predict which ecosystems are most vulnerable before invasions occur.

Ultimately, the review’s central message is that biological invasions cannot be understood, managed, or costed without accounting for their cross-ecosystem reach. An invader established in one habitat can extend its ecological footprint well beyond the boundaries of that habitat, affecting stakeholders and ecosystems that may appear entirely disconnected from the site of introduction. As global change drivers such as climate warming, land-use transformation, and pollution continue to alter both the quality and quantity of natural resource flows, the added layer of invasion-mediated disruption becomes increasingly consequential. The authors call for long-term monitoring, multilingual and multi-database literature searches to correct geographic biases, explicit study of overlooked groups such as fungi, bacteria, and amphibians, and the integration of local ecological knowledge in data-poor regions. Without these steps, the global network of invasion-altered resource flows will remain only partially mapped, and conservation strategies will continue to underestimate the true reach of the species humans have moved across the planet.

Subject of Research: How non-native species mediate resource subsidies across ecosystem boundaries

Article Title: Resource subsidies mediated by non-native species: a review

Article References: Alves, L., Padilha, J., Haubrock, P. J., Subalusky, A., & Sousa, R. (2026). Resource subsidies mediated by non-native species: a review. NeoBiota, 109, 315-343. https://doi.org/10.3897/neobiota.109.193175

Image Credits: AI Generated

DOI: 10.3897/neobiota.109.193175

Keywords: invasive species, resource subsidies, ecosystem connectivity, biological invasions, cross-ecosystem flows, nutrient cycling, food webs, NeoBiota, trophic ecology, seabirds, riparian ecosystems, eDNA

The research team, led by Weina Zhen and Donghui Shi, focused on the BTH urban agglomeration, a sprawling region of roughly 218,000 square kilometers that encompasses the megacities of Beijing and Tianjin along with eleven prefecture-level cities in Hebei Province. The region is an ideal natural laboratory for studying urban water dynamics. It holds only about 0.84 percent of China’s total water resources despite its enormous population, with per-capita water availability of roughly 243 cubic meters per year. Annual precipitation ranges from about 370 to 730 millimeters, nearly 70 percent of which falls in summer, and drought ranks among the region’s most damaging natural hazards. At the same time, decades of intensive urbanization, massive inter-basin water transfers and ambitious ecological restoration programs have reshaped the hydrological landscape in ways that vary dramatically from city to city.

To map these changes, the researchers drew on the China Land Cover Dataset, a 30-meter-resolution land cover product built from 335,709 Landsat images processed on the Google Earth Engine platform. For every year from 2000 to 2023, they extracted and merged the water and wetland classes to define urban blue space. While the underlying dataset achieves an overall classification accuracy of 79.31 percent nationally, the team conducted their own regional validation for 2000, 2010 and 2020 using stratified random sampling and manual visual interpretation against high-resolution historical imagery from Google Earth. The resulting average overall accuracy of 94.33 percent gave them confidence that the observed trends reflect real landscape change rather than classification noise.

The headline finding is stark. Blue-space area across the BTH region declined at a statistically significant average rate of about 16.82 square kilometers per year, falling from 3,182.61 square kilometers in 2000 to a peak of 3,299.93 square kilometers in 2004 before sliding to 2,909.11 square kilometers by 2010 and then fluctuating between roughly 2,900 and 3,000 square kilometers through 2023. A Pettitt change-point test identified 2009 as a statistically significant structural breakpoint, with mean blue-space area dropping from 3,199.26 square kilometers in the 2000–2009 period to 2,941.21 square kilometers from 2010 onward. The timing coincides with a period of rapid land conversion and severe hydroclimatic stress, including the 2008–2009 drought that gripped northern China, while the subsequent stabilization aligns plausibly with strengthened water-resource management, ecological restoration and large-scale water-transfer programs, though the authors are careful to note these correspondences do not establish causation.

Beneath the regional average, however, lies a patchwork of divergent local stories. Nine of the thirteen cities recorded statistically significant increases in blue-space area, led by Baoding, which gained an average of 3.60 square kilometers per year, expanding from 101.95 square kilometers in 2000 to 156.89 square kilometers in 2023. Shijiazhuang, Qinhuangdao, Handan, Xingtai, Chengde and Langfang also expanded significantly. In sharp contrast, Tianjin lost the most water surface, shrinking from 1,246.01 square kilometers in 2000 to 905.38 square kilometers in 2023, a cumulative loss of 340.62 square kilometers, while Tangshan lost 169.49 square kilometers. Zhangjiakou and Hengshui showed no statistically significant monotonic trend. Any assessment based on regional averages alone would have buried these dramatic intra-regional differences.

The study’s most innovative contribution lies in its treatment of landscape configuration as a distinct dimension of blue-space health. Rather than relying on area alone, the researchers computed ten landscape metrics capturing quantity, patch size distribution, fragmentation, shape complexity and connectivity, including the number of patches, patch density, the largest patch index, the landscape shape index, the perimeter-area fractal dimension, patch cohesion, effective mesh size, the splitting index and the aggregation index. These were synthesized into a single Composite Landscape Index, or CI, using an entropy-weighted TOPSIS method that objectively weights each indicator and ranks observations by their distance from ideal values. Pooling 312 city-year observations ensured the index remained spatially and temporally comparable across the entire study period.

The CI results reveal a systemic quality decline that mirrors, and in some cases contradicts, the area story. Regionally, the CI fell significantly, sharing the same 2009 breakpoint as the area series. Fragmentation metrics rose: more patches, higher patch density, greater subdivision and increasingly irregular patch shapes, while aggregation, cohesion and effective mesh size all declined, signaling weakened connectivity that hinders the movement of material, energy and organisms between water bodies. At the city level, the picture fractured further. Six cities, including Beijing, Shijiazhuang, Baoding, Cangzhou, Qinhuangdao and Langfang, showed significant CI increases, with Cangzhou improving fastest. Five cities, including Tianjin, Tangshan, Zhangjiakou, Chengde and Hengshui, declined significantly. Beijing achieved a structure-led improvement, with stable area but rising CI, while Chengde showed the opposite pattern, gaining water surface that was evidently more dispersed, artificial or seasonal, producing higher fragmentation and lower connectivity. Tianjin and Tangshan suffered simultaneous declines in both extent and configuration, marking them as priority targets for management intervention.

To identify what drives these changes, the team built separate XGBoost regression models for blue-space area and CI, interpreting them through SHAP (SHapley Additive exPlanations) values, a technique borrowed from cooperative game theory that quantifies each variable’s contribution to individual predictions. Eight candidate drivers passed multicollinearity screening: precipitation, temperature, the normalized difference vegetation index, fractional vegetation coverage, population, GDP, urbanization rate and environmental regulation intensity, the last proxied by the share of environment-related sentences in municipal government work reports. XGBoost outperformed Random Forest and Ridge regression baselines, achieving a test R-squared of 0.8984 for area and 0.8740 for CI, and feature-importance rankings proved robust across model architectures.

The SHAP analysis delivered a striking result: population, fractional vegetation coverage, NDVI and urbanization rate together accounted for 83.8 percent of the explanatory importance in the area model and 86.8 percent in the CI model, dwarfing the contributions of climate and policy variables. Population ranked first for area at 28.0 percent, with higher-population cities generally coinciding with larger blue spaces, while vegetation metrics dominated the CI model, with FVC contributing 27.9 percent. Notably, higher vegetation cover showed predominantly negative associations with both variables, which the authors interpret cautiously as a possible spatial competition between blue and green spaces under constrained land availability, or a reflection of vegetation-dominated landscapes where water patches remain small and fragmented. These are statistical associations conditional on city scale and geographic context, not evidence that urbanization benefits water or that vegetation harms it. Climate variables and environmental regulation each contributed roughly 10 percent or less, suggesting that within this dataset, human activity and surface ecological status, rather than macro-climate or governance signals, carry most of the explanatory weight.

The broader implications reach well beyond northern China. The findings align with documented blue-space losses in Delhi, Kolkata and Khulna, yet also echo evidence from the United States and elsewhere that urban water change is not a universal consequence of urbanization but depends on hydroclimatic background, development pressure, water engineering and management choices. The study’s central methodological message is that area and configuration must be assessed as separate dimensions; a city can gain water while losing connectivity, or hold its area constant while its landscape structure quietly improves or collapses. The authors acknowledge limitations, including mixed-pixel effects at 30-meter resolution, the smoothing inherent in city-level aggregation, and the crude proxy used for environmental regulation, and they call for finer spatial units and richer institutional data in future work. For planners in rapidly urbanizing regions worldwide, however, the lesson is already clear: protecting urban water means protecting not just how much there is, but how it is arranged.

Subject of Research: Long-term remote sensing analysis of urban blue space extent, landscape configuration and their drivers in the Beijing–Tianjin–Hebei region

Article Title: Quantifying the spatiotemporal dynamics and drivers of urban blue spaces in the Beijing–Tianjin–Hebei region using remote sensing

Article References: Zhen, W., & Shi, D. (2026). Quantifying the spatiotemporal dynamics and drivers of urban blue spaces in the Beijing–Tianjin–Hebei region using remote sensing. Environmental and Sustainability Indicators, 32, Article 101525. https://doi.org/10.1016/j.indic.2026.101525

Image Credits: AI Generated

DOI: 10.1016/j.indic.2026.101525

Keywords: urban blue spaces, remote sensing, Beijing–Tianjin–Hebei, landscape fragmentation, XGBoost, SHAP, water resources, urbanization, land cover change, ecosystem connectivity, China, sustainable urban planning