Combining paleo-data and modern exclosure experiments to assess the impact of megafauna extinctions on woody vegetation

Molecular Interaction Mechanisms Between Lubricant-Infused Slippery Surfaces and Mussel-Inspired Polydopamine Adhesive and DOPA Moiety

Lubricant-infused slippery surfaces have recently emerged as promising antifouling coatings, showing potential against proteins, cells, and marine mussels. However, a comprehensive understanding of the molecular binding behaviors and interaction strength of foulants to these surfaces is lacking. In this work, mussel-inspired chemistry based on catechol-containing chemicals including 3,4-dihydroxyphenylalanine (DOPA) and polydopamine (PDA) is employed to investigate the antifouling performance and repellence mechanisms of fluorinated-based slippery surface, and the correlated interaction mechanisms are probed using atomic force microscopy (AFM). Intermolecular force measurements and deposition experiments between PDA and the surface reveal the ability of lubricant film to inhibit the contact of PDA particles with the substrate. Moreover, the binding mechanisms and bond dissociation energy between a single DOPA moiety and the lubricant-infused slippery surface are quantitatively investigated employing single-molecule force spectroscopy based on AFM (SM-AFM), which reveal that the infused lubricant layer can remarkably influence the dissociation forces and weaken the binding strength between DOPA and underneath per-fluorinated monolayer surface. This work provides new nanomechanical insights into the fundamental antifouling mechanisms of the lubricant-infused slippery surfaces against mussel-derived adhesive chemicals, with important implications for the design of lubricant-infused materials and other novel antifouling platforms for various bioengineering and engineering applications.

Biomolecular condensates and disease pathogenesis

Biomolecular condensates or membraneless organelles (MLOs) formed by liquid-liquid phase separation (LLPS) divide intracellular spaces into discrete compartments for specific functions. Dysregulation of LLPS or aberrant phase transition that disturbs the formation or material states of MLOs is closely correlated with neurodegeneration, tumorigenesis, and many other pathological processes. Herein, we summarize the recent progress in development of methods to monitor phase separation and we discuss the biogenesis and function of MLOs formed through phase separation. We then present emerging proof-of-concept examples regarding the disruption of phase separation homeostasis in a diverse array of clinical conditions including neurodegenerative disorders, hearing loss, cancers, and immunological diseases. Finally, we describe the emerging discovery of chemical modulators of phase separation.

Nature-inspired adhesive systems

Many organisms in nature thrive in intricate habitats through their unique bio-adhesive surfaces, facilitating tasks such as capturing prey and reproduction. It's important to note that the remarkable adhesion properties found in these natural biological surfaces primarily arise from their distinct micro- and nanostructures and/or chemical compositions. To create artificial surfaces with superior adhesion capabilities, researchers delve deeper into the underlying mechanisms of these captivating adhesion phenomena to draw inspiration. This article provides a systematic overview of various biological surfaces with different adhesion mechanisms, focusing on surface micro- and nanostructures and/or chemistry, offering design principles for their artificial counterparts. Here, the basic interactions and adhesion models of natural biological surfaces are introduced first. This will be followed by an exploration of research advancements in natural and artificial adhesive surfaces including both dry adhesive surfaces and wet/underwater adhesive surfaces, along with relevant adhesion characterization techniques. Special attention is paid to stimulus-responsive smart artificial adhesive surfaces with tunable adhesive properties. The goal is to spotlight recent advancements, identify common themes, and explore fundamental distinctions to pinpoint the present challenges and prospects in this field.

Expanding the molecular language of protein liquid-liquid phase separation

Understanding the relationship between a polypeptide sequence and its phase separation has important implications for analysing cellular function, treating disease and designing novel biomaterials. Several sequence features have been identified as drivers for protein liquid-liquid phase separation (LLPS), schematized as a 'molecular grammar' for LLPS. Here we further probe how sequence modulates phase separation and the material properties of the resulting condensates, targeting sequence features previously overlooked in the literature. We generate sequence variants of a repeat polypeptide with either no charged residues, high net charge, no glycine residues or devoid of aromatic or arginine residues. All but one of 12 variants exhibited LLPS, albeit to different extents, despite substantial differences in composition. Furthermore, we find that all the condensates formed behaved like viscous fluids, despite large differences in their viscosities. Our results support the model of multiple interactions between diverse residue pairs-not just a handful of residues-working in tandem to drive the phase separation and dynamics of condensates.

Trophic rewilding as a restoration approach under emerging novel biosphere conditions

Rewilding is a restoration approach that aims to promote self-regulating complex ecosystems by restoring non-human ecological processes while reducing human control and pressures. Rewilding is forward-looking in that it aims to enhance functionality for biodiversity, accepting and indeed promoting the dynamic nature of ecosystems, rather than fixating on static composition or structure. Rewilding is thus especially relevant in our epoch of increasingly novel biosphere conditions, driven by strong human-induced global change. Here, we explore this hypothesis in the context of trophic rewilding - the restoration of trophic complexity mediated by wild, large-bodied animals, known as 'megafauna'. This focus reflects the strong ecological impacts of large-bodied animals, their widespread loss during the last 50,000 years and their high diversity and ubiquity in the preceding 50 million years. Restoring abundant, diverse, wild-living megafauna is expected to promote vegetation heterogeneity, seed dispersal, nutrient cycling and biotic microhabitats. These are fundamental drivers of biodiversity and ecosystem function and are likely to gain importance for maintaining a biodiverse biosphere under increasingly novel ecological conditions. Non-native megafauna species may contribute to these effects as ecological surrogates of extinct species or by promoting ecological functionality within novel assemblages. Trophic rewilding has strong upscaling potential via population growth and expansion of wild fauna. It is likely to facilitate biotic adaptation to changing climatic conditions and resilience to ecosystem collapse, and to curb some negative impacts of globalization, notably the dominance of invasive alien plants. Finally, we discuss the complexities of realizing the biodiversity benefits that trophic rewilding offers under novel biosphere conditions in a heavily populated world.

Natural Polymer-Polyphenol Bioadhesive Coacervate with Stable Wet Adhesion, Antibacterial Activity, and On-Demand Detachment

Medical adhesives are emerging as an important clinical tool as adjuvants for sutures and staples in wound closure and healing and in the achievement of hemostasis. However, clinical adhesives combining cytocompatibility, as well as strong and stable adhesion in physiological conditions, are still in demand. Herein, a mussel-inspired strategy is explored to produce adhesive coacervates using tannic acid (TA) and methacrylate pullulan (PUL-MA). TA|PUL-MA coacervates mainly comprise van der Waals forces and hydrophobic interactions. The methacrylic groups in the PUL backbone increase the number of interactions in the adhesives matrix, resulting in enhanced cohesion and adhesion strength (72.7 Jm-2), compared to the non-methacrylated coacervate. The adhesive properties are kept in physiologic-mimetic solutions (72.8 Jm-2) for 72 h. The photopolymerization of TA|PUL-MA enables the on-demand detachment of the adhesive. The poor cytocompatibility associated with the use of phenolic groups is here circumvented by mixing reactive oxygen species-degrading enzyme in the adhesive coacervate. This addition does not hamper the adhesive character of the materials, nor their anti-microbial or hemostatic properties. This affordable and straightforward methodology, together with the tailorable adhesivity even in wet environments, high cytocompatibility, and anti-bacterial activity, enables foresee TA|PUL-MA as a promising ready-to-use bioadhesive for biomedical applications.

Assessing contemporary Arctic habitat availability for a woolly mammoth proxy

Interest continues to grow in Arctic megafaunal ecological engineering, but, since the mass extinction of megafauna ~ 12-15 ka, key physiographic variables and available forage continue to change. Here we sought to assess the extent to which contemporary Arctic ecosystems are conducive to the rewilding of megaherbivores, using a woolly mammoth (M. primigenius) proxy as a model species. We first perform a literature review on woolly mammoth dietary habits. We then leverage Oak Ridge National Laboratories Distributive Active Archive Center Global Aboveground and Belowground Biomass Carbon Density Maps to generate aboveground biomass carbon density estimates in plant functional types consumed by the woolly mammoth at 300 m resolution on Alaska's North Slope. We supplement these analyses with a NASA Arctic Boreal Vulnerability Experiment dataset to downgrade overall biomass estimates to digestible levels. We further downgrade available forage by using a conversion factor representing the relationship between total biomass and net primary productivity (NPP) for arctic vegetation types. Integrating these estimates with the forage needs of woolly mammoths, we conservatively estimate Alaska's North Slope could support densities of 0.0-0.38 woolly mammoth km-2 (mean 0.13) across a variety of habitats. These results may inform innovative rewilding strategies.

Meta-analysis shows that wild large herbivores shape ecosystem properties and promote spatial heterogeneity

Megafauna (animals ≥45 kg) have probably shaped the Earth's terrestrial ecosystems for millions of years with pronounced impacts on biogeochemistry, vegetation, ecological communities and evolutionary processes. However, a quantitative global synthesis on the generality of megafauna effects on ecosystems is lacking. Here we conducted a meta-analysis of 297 studies and 5,990 individual observations across six continents to determine how wild herbivorous megafauna influence ecosystem structure, ecological processes and spatial heterogeneity, and whether these impacts depend on body size and environmental factors. Despite large variability in megafauna effects, we show that megafauna significantly alter soil nutrient availability, promote open vegetation structure and reduce the abundance of smaller animals. Other responses (14 out of 26), including, for example, soil carbon, were not significantly affected. Further, megafauna significantly increase ecosystem heterogeneity by affecting spatial heterogeneity in vegetation structure and the abundance and diversity of smaller animals. Given that spatial heterogeneity is considered an important driver of biodiversity across taxonomic groups and scales, these results support the hypothesis that megafauna may promote biodiversity at large scales. Megafauna declined precipitously in diversity and abundance since the late Pleistocene, and our results indicate that their restoration would substantially influence Earth's terrestrial ecosystems.

Functional traits-not nativeness-shape the effects of large mammalian herbivores on plant communities

Large mammalian herbivores (megafauna) have experienced extinctions and declines since prehistory. Introduced megafauna have partly counteracted these losses yet are thought to have unusually negative effects on plants compared with native megafauna. Using a meta-analysis of 3995 plot-scale plant abundance and diversity responses from 221 studies, we found no evidence that megafauna impacts were shaped by nativeness, "invasiveness," "feralness," coevolutionary history, or functional and phylogenetic novelty. Nor was there evidence that introduced megafauna facilitate introduced plants more than native megafauna. Instead, we found strong evidence that functional traits shaped megafauna impacts, with larger-bodied and bulk-feeding megafauna promoting plant diversity. Our work suggests that trait-based ecology provides better insight into interactions between megafauna and plants than do concepts of nativeness.

Nature-Inspired Wet Drug Delivery Platforms

Nature has created various organisms with unique chemical components and multi-scale structures (e.g., foot proteins, toe pads, suckers, setose gill lamellae) to achieve wet adhesion functions to adapt to their complex living environments. These organisms can provide inspirations for designing wet adhesives with mediated drug release behaviors in target locations of biological surfaces. They exhibit conformal and enhanced wet adhesion, addressing the bottleneck of weaker tissue interface adhesion in the presence of body fluids. Herein, it is focused on the research progress of different wet adhesion and bioinspired fabrications, including adhesive protein-based adhesion and inspired adhesives (e.g., mussel adhesion); capillarity and Stefan adhesion and inspired adhesive surfaces (e.g., tree frog adhesion); suction-based adhesion and inspired suckers (e.g., octopus' adhesion); interlocking and friction-based adhesion and potential inspirations (e.g., mayfly larva and teleost adhesion). Other secreted protein-induced wet adhesion is also reviewed and various suckers for other organisms and their inspirations. Notably, one representative application scenario of these bioinspired wet adhesives is highlighted, where they function as efficient drug delivery platforms on target tissues and/or organs with requirements of both controllable wet adhesion and optimized drug release. Finally, the challenges of these bioinspired wet drug delivery platforms in the future is presented.

Worldwide Late Pleistocene and Early Holocene population declines in extant megafauna are associated with Homo sapiens expansion rather than climate change

The worldwide extinction of megafauna during the Late Pleistocene and Early Holocene is evident from the fossil record, with dominant theories suggesting a climate, human or combined impact cause. Consequently, two disparate scenarios are possible for the surviving megafauna during this time period - they could have declined due to similar pressures, or increased in population size due to reductions in competition or other biotic pressures. We therefore infer population histories of 139 extant megafauna species using genomic data which reveal population declines in 91% of species throughout the Quaternary period, with larger species experiencing the strongest decreases. Declines become ubiquitous 32-76 kya across all landmasses, a pattern better explained by worldwide Homo sapiens expansion than by changes in climate. We estimate that, in consequence, total megafauna abundance, biomass, and energy turnover decreased by 92-95% over the past 50,000 years, implying major human-driven ecosystem restructuring at a global scale.

Substantial light woodland and open vegetation characterized the temperate forest biome before Homo sapiens

The extent of vegetation openness in past European landscapes is widely debated. In particular, the temperate forest biome has traditionally been defined as dense, closed-canopy forest; however, some argue that large herbivores maintained greater openness or even wood-pasture conditions. Here, we address this question for the Last Interglacial period (129,000-116,000 years ago), before Homo sapiens-linked megafauna declines and anthropogenic landscape transformation. We applied the vegetation reconstruction method REVEALS to 96 Last Interglacial pollen records. We found that light woodland and open vegetation represented, on average, more than 50% cover during this period. The degree of openness was highly variable and only partially linked to climatic factors, indicating the importance of natural disturbance regimes. Our results show that the temperate forest biome was historically heterogeneous rather than uniformly dense, which is consistent with the dependency of much of contemporary European biodiversity on open vegetation and light woodland.

Human disturbance is the major driver of vegetation changes in the Caatinga dry forest region

Drastic changes in vegetation structure caused by exceeding ecological thresholds have fueled the interest in tropical forest responses to climate and land-use changes. Here, we examine the potential successional trajectories experienced by the largest dry tropical forest region in South America, driven by climate conditions and human disturbance. We built potential distribution models for vertebrate taxa associated with forest or shrub habitats to estimate natural vegetation cover. Distribution patterns were compared to current vegetation across the entire region to identify distinct forest degradation levels. Our results indicate the region has climatic and soil conditions suitable for more forest cover than is currently found, even in some areas with limited precipitation. However, 11.04% of natural cover persists across such an immense region, with only 4.34% consisting of forest cover. Forest degradation is characterized by the dramatic expansion of shrubland (390%), farming, and non-vegetation cover due to changes in land-use, rather than climatic conditions. Although different climate conditions have been the principal drivers for natural forest distribution in the region, the forest seems unable to resist the consequences of land-use changes, particularly in lower precipitation areas. Therefore, land-use change has exceeded the ecological thresholds for the persistence of forests, while climate change may exacerbate vegetation-type transitions.

North American pollen records provide evidence for macroscale ecological changes in the Anthropocene

Recent global changes associated with anthropogenic activities are impacting ecological systems globally, giving rise to the Anthropocene. Critical reorganization of biological communities and biodiversity loss are expected to accelerate as anthropogenic global change continues. Long-term records offer context for understanding baseline conditions and those trajectories that are beyond the range of normal fluctuation seen over recent millennia: Are we causing changes that are fundamentally different from changes in the past? Using a rich dataset of late Quaternary pollen records, stored in the open-access and community-curated Neotoma database, we analyzed changes in biodiversity and community composition since the end Pleistocene in North America. We measured taxonomic richness, short-term taxonomic loss and gain, first/last appearances (FAD/LAD), and abrupt community change. For all analyses, we incorporated age-model uncertainty and accounted for differences in sample size to generate conservative estimates. The most prominent signals of elevated vegetation change were seen during the Pleistocene-Holocene transition and since 200 calendar years before present (cal YBP). During the Pleistocene-Holocene transition, abrupt changes and FADs were elevated, and from 200 to -50 cal YBP, we found increases in short-term taxonomic loss, FADs, LADs, and abrupt changes. Taxonomic richness declined from ~13,000 cal YBP until about 6,000 cal YBP and then increased until the present, reaching levels seen during the end Pleistocene. Regionally, patterns were highly variable. These results show that recent changes associated with anthropogenic impacts are comparable to the landscape changes that took place as we moved from a glacial to interglacial world.

4D Bioprinting via Molecular Network Contraction for Membranous Tissue Fabrication

Generation of thin membranous tissues (TMT), such as the cornea, epidermis, and periosteum, presents a difficult fabrication challenge in tissue engineering (TE). TMTs consist of several cell layers that are less than 100 µm in thickness per layer. While traditional methods provide the necessary resolution for TMT fabrication, they require significant handling and incorporation of several layers is limited. Extrusion bioprinting offers precise control over deposition of different biomaterials and cell populations within the same construct but lacks the resolution to generate biomimetic TMTs. For the first time, a 4D bioprinting strategy that allows for the generation of cell-laden TMTs is developed. Anionic gelatin methacrylate (GelMA) hydrogels are treated with cationic poly-l-lysine (PLL), which induces charge attraction, microscale network collapse, and macroscale hydrogel shrinking. The impact of shrinking on hydrogel properties, print resolution, and cell viability is presented. Additionally, this work suggests that a novel mechanism is occurring, where PLL exhibits a contractile force on GelMA and PLL molecular weight drives GelMA shrinking capabilities. Finally, it is shown that this phenomenon can occur while maintaining an encapsulated cell population. These findings address a critical barrier by generating macroscale tissue structures with their microscale TMT counterparts in the same print.

Megafaunal extinctions, not climate change, may explain Holocene genetic diversity declines in Numenius shorebirds

Understanding the relative contributions of historical and anthropogenic factors to declines in genetic diversity is important for informing conservation action. Using genome-wide DNA of fresh and historic specimens, including that of two species widely thought to be extinct, we investigated fluctuations in genetic diversity and present the first complete phylogenomic tree for all nine species of the threatened shorebird genus Numenius, known as whimbrels and curlews. Most species faced sharp declines in effective population size, a proxy for genetic diversity, soon after the Last Glacial Maximum (around 20,000 years ago). These declines occurred prior to the Anthropocene and in spite of an increase in the breeding area predicted by environmental niche modeling, suggesting that they were not caused by climatic or recent anthropogenic factors. Crucially, these genetic diversity declines coincide with mass extinctions of mammalian megafauna in the Northern Hemisphere. Among other factors, the demise of ecosystem-engineering megafauna which maintained open habitats may have been detrimental for grassland and tundra-breeding Numenius shorebirds. Our work suggests that the impact of historical factors such as megafaunal extinction may have had wider repercussions on present-day population dynamics of open habitat biota than previously appreciated.

Impacts of large herbivores on terrestrial ecosystems

Large herbivores play unique ecological roles and are disproportionately imperiled by human activity. As many wild populations dwindle towards extinction, and as interest grows in restoring lost biodiversity, research on large herbivores and their ecological impacts has intensified. Yet, results are often conflicting or contingent on local conditions, and new findings have challenged conventional wisdom, making it hard to discern general principles. Here, we review what is known about the ecosystem impacts of large herbivores globally, identify key uncertainties, and suggest priorities to guide research. Many findings are generalizable across ecosystems: large herbivores consistently exert top-down control of plant demography, species composition, and biomass, thereby suppressing fires and the abundance of smaller animals. Other general patterns do not have clearly defined impacts: large herbivores respond to predation risk but the strength of trophic cascades is variable; large herbivores move vast quantities of seeds and nutrients but with poorly understood effects on vegetation and biogeochemistry. Questions of the greatest relevance for conservation and management are among the least certain, including effects on carbon storage and other ecosystem functions and the ability to predict outcomes of extinctions and reintroductions. A unifying theme is the role of body size in regulating ecological impact. Small herbivores cannot fully substitute for large ones, and large-herbivore species are not functionally redundant - losing any, especially the largest, will alter net impact, helping to explain why livestock are poor surrogates for wild species. We advocate leveraging a broad spectrum of techniques to mechanistically explain how large-herbivore traits and environmental context interactively govern the ecological impacts of these animals.

Coacervate-Enhanced Deposition of Sprayed Pesticide on Hydrophobic/Superhydrophobic Abaxial Leaf Surfaces

Deposition of high-speed droplets on inverted surfaces is important to many fundamental scientific principles and technological applications. For example, in pesticide spraying to target pests and diseases emerging on abaxial side of leaves, the downward rebound and gravity of the droplets make the deposition exceedingly difficult on hydrophobic/superhydrophobic leaf underside, causing serious pesticide waste and environmental pollution. Here, a series of bile salt/cationic surfactant coacervates are developed to attain efficient deposition on the inverted surfaces of diverse hydrophobic/superhydrophobic characteristics. The coacervates have abundant nanoscale hydrophilic/hydrophobic domains and intrinsic network-like microstructures, which endow them with efficient encapsulation of various solutes and strong adhesion to surface micro/nanostructures. Thus, the coacervates with low viscosity achieve high-efficient deposition on superhydrophobic abaxial-side of tomato leaves and inverted artificial surfaces with a water contact angle from 170° to 124°, much better than that of commercial agricultural adjuvants. Intriguingly, the compactness of network-like structures dominantly controls adhesion force and deposition efficiency, and the most crowded one leads to the most efficient deposition. The tunable coacervates can help comprehensively understand the complex dynamic deposition, and provide innovative carriers for depositing sprayed pesticides on abaxial and adaxial sides of leaves, thereby potentially reducing pesticide use and promoting sustainable agriculture.

Liquid sculpture and curing of bio-inspired polyelectrolyte aqueous two-phase systems

Aqueous two-phase systems (ATPS) provide imperative interfaces and compartments in biology, but the sculpture and conversion of liquid structures to functional solids is challenging. Here, inspired by phase evolution of mussel foot proteins ATPS, we tackle this problem by designing poly(ionic liquids) capable of responsive condensation and phase-dependent curing. When mixed with poly(dimethyl diallyl ammonium chloride), the poly(ionic liquids) formed liquid condensates and ATPS, which were tuned into bicontinuous liquid phases under stirring. Selective, rapid curing of the poly(ionic liquids)-rich phase was facilitated under basic conditions (pH 11), leading to the liquid-to-gel conversion and structure sculpture, i.e., the evolution from ATPS to macroporous sponges featuring bead-and-string networks. This mechanism enabled the selective embedment of carbon nanotubes in the poly(ionic liquids)-rich phase, which showed exceptional stability in harsh conditions (10 wt% NaCl, 80 ^oC, 3 days) and high (2.5 kg/m²h) solar thermal desalination of concentrated salty water under 1-sun irradiation.

Re-framing deer herbivory as a natural disturbance regime with ecological and socioeconomic outcomes in the eastern United States

Natural disturbances are critical ecosystem processes, with both ecological and socioeconomic benefits and disadvantages. Large herbivores are natural disturbances that have removed plant biomass for millions of years, although herbivore influence likely has declined during the past thousands of years corresponding with extinctions and declines in distributions and abundances of most animal species. Nonetheless, the conventional view, particularly in eastern North America, is that herbivory by large wild herbivores is at unprecedented levels, resulting in unnatural damage to forests. Here, we propose consideration of large herbivores as a natural disturbance that also imparts many crucial ecological advantages, using white-tailed deer (Odocoileus virginianus), the only wild large herbivore remaining throughout the eastern U.S., as our focal species. We examined evidence of detrimental effects of browsing on trees and forbs. We then considered that deer contribute to both fuel reduction and ecological restoration of herbaceous plants and historical open forests of savannas and woodlands by controlling tree and shrub densities, mimicking the consumer role of fire. Similarly to other disturbances, deer disturbance 'regimes' are uneven in severity across different ecosystems and landscapes, resulting in heterogeneity and diversity. In addition to biodiversity support and fuel reduction, socioeconomic benefits include >$20 billion dollars per year by 10 million hunters that support jobs and wildlife agencies, non-consumptive enjoyment of nature by 80 million people, cultural importance, and deer as ecological ambassadors, whereas costs include about $5 billion and up to 450 human deaths per year for motor vehicle accidents, along with crop damage and disease transmission. From a perspective of historical ecology rather than current baselines, deer impart a fundamental disturbance process with many ecological benefits and a range of socioeconomic effects.

Solutions to fire and shade: resprouting, growing tall and the origin of Eurasian temperate broadleaved forest

Tree species of Eurasian broadleaved forest possess two divergent trait syndromes with contrasting patterns of resource allocation adapted to different selection environments: short-stature basal resprouters that divert resources to a bud bank adapted to frequent and severe disturbances such as fire and herbivory, and tall trees that delay reproduction by investing in rapid height growth to escape shading. Drawing on theory developed in savanna ecosystems, we propose a conceptual framework showing that the possession of contrasting trait syndromes is essential for the persistence of broadleaved trees in an open ecosystem that burns. Consistent with this hypothesis, trees of modern Eurasian broadleaved forest bear a suite of traits that are adaptive to surface and crown-fire regimes. We contend that limited opportunities in grassland restricts recruitment to disturbance-free refugia, and en masse establishment creates a wooded environment where shade limits the growth of light-demanding savanna plants. Rapid height growth, which involves investment in structural support and the switch from a multi-stemmed to a monopodial growth form, is adaptive in this shaded environment. Although clustering reduces surface fuel loads, these establishment nuclei are vulnerable to high-intensity crown fires. The lethal effects of canopy fire are avoided by seasonal leaf shedding, and aerial resprouting enhances rapid post-fire recovery of photosynthetic capacity. While these woody formations satisfy the structural definition of forest, their constituents are clearly derived from savanna. Contrasting trait syndromes thus represent the shift from consumer to resource regulation in savanna ecosystems. Consistent with global trends, the diversification of most contemporary broadleaved taxa coincided with the spread of grasslands, a surge in fire activity and a decline in wooded ecosystems in the late Miocene-Pliocene. Recognition that Eurasian broadleaved forest has savanna origins and persists as an alternative state with adjacent grassy ecosystems has far-reaching management implications in accordance with functional rather than structural criteria. Shade is a severe constraint to the regeneration and growth of both woody and herbaceous growth forms in consumer-regulated ecosystems. However, these ecosystems are highly resilient to disturbance, an essential process that maintains diversity especially among the species-rich herbaceous component that is vulnerable to shading when consumer behaviour is altered.

Accelerated cropland expansion into high integrity forests and protected areas globally in the 21st century

Intact forests and protected areas (PAs) are central to global biodiversity conservation and nature-based climate change mitigation. However, cropland encroachment threatens the ecological integrity and resilience of their functioning. Using satellite observations, we find that a large proportion of croplands in the remaining forests globally have been gained during 2003-2019, especially for high-integrity forests (62%) and non-forest biomes (60%) and tropical forests (47%). Cropland expansion during 2011-2019 in forests globally has even doubled (130% relative increase) than 2003-2011, with high medium-integrity (190%) and high-integrity (165%) categories and non-forest (182%) and tropical forest biomes (136%) showing higher acceleration. Unexpectedly, a quarter of croplands in PAs globally were gained during 2003-2019, again with a recent accelerated expansion (48%). These results suggest insufficient protection of these irreplaceable landscapes and a major challenge to global conservation. More effective local, national, and international coordination among sustainable development goals 15, 13, and 2 is urgently needed.

Polyelectrolyte-multivalent molecule complexes: physicochemical properties and applications

The complexation of polyelectrolytes with other oppositely charged structures gives rise to a great variety of functional materials with potential applications in a wide spectrum of technological fields. Depending on the assembly conditions, polyelectrolyte complexes can acquire different macroscopic configurations such as dense precipitates, nanosized colloids and liquid coacervates. In the past 50 years, much progress has been achieved to understand the principles behind the phase separation induced by the interaction of two oppositely charged polyelectrolytes in aqueous solutions, especially for symmetric systems (systems in which both polyions have similar molecular weight and concentration). However, in recent years, the complexation of polyelectrolytes with alternative building blocks such as small charged molecules (multivalent inorganic species, oligopeptides, and oligoamines, among others) has gained attention in different areas. In this review, we discuss the physicochemical characteristics of the complexes formed by polyelectrolytes and multivalent small molecules, putting a special emphasis on their similarities with the well-known polycation-polyanion complexes. In addition, we analyze the potential of these complexes to act as versatile functional platforms in various technological fields, such as biomedicine and advanced materials engineering.

Contrasting seasonal patterns in diet and dung-associated invertebrates of feral cattle and horses in a rewilding area

Trophic rewilding is increasingly applied in restoration efforts, with the aim of reintroducing the ecological functions provided by large-bodied mammals and thereby promote self-regulating, biodiverse ecosystems. However, empirical evidence for the effects of megafauna introductions on the abundance and richness of other organisms such as plants and invertebrates, and the mechanisms involved still need strengthening. In this study, we use environmental DNA (eDNA) metabarcoding of dung from co-existing feral cattle and horses to assess the seasonal variation in plant diet and dung-associated arthropods and nematodes. We found consistently high diet richness of horses, with low seasonal variability, while the generally lower dietary diversity of cattle increased substantially during summer. Intriguingly, season-specific diets differed, with a greater proportion of trees in the horses' diet during winter, where cattle relied more on shrubs. Graminoids were predominantly found in the diet of horses, but were generally underrepresented compared to previous studies, possibly due to the high prevalence of forbs in the study area. Dung-associated arthropod richness was higher for cattle, largely due to a high richness of flies during summer. Several species of dung-associated arthropods were found primarily in dung from one of the two herbivores, and our data confirmed known patterns of seasonal activity. Nematode richness was constantly higher for horses, and nematode communities were markedly different between the two species. Our results demonstrate complementary effects of cattle and horses through diet differences and dung-associated invertebrate communities, enhancing our understanding of large herbivore effects on vegetation and associated biodiversity. These results are directly applicable for decision-making in rewilding projects, suggesting biodiversity-benefits by inclusion of functionally different herbivores.

Field-Theoretic Simulation Method to Study the Liquid-Liquid Phase Separation of Polymers

Liquid-liquid phase separation (LLPS) is a process that results in the formation of a polymer-rich liquid phase coexisting with a polymer-depleted liquid phase. LLPS plays a critical role in the cell through the formation of membrane-less organelles, but it also has a number of biotechnical and biomedical applications such as drug confinement and its targeted delivery. In this chapter, we present a computational efficient methodology that uses field-theoretic simulations (FTS) with complex Langevin (CL) sampling to characterize polymer phase behavior and delineate the LLPS phase boundaries. This approach is a powerful complement to analytical and explicit-particle simulations, and it can serve to inform experimental LLPS studies. The strength of the method lies in its ability to properly sample a large ensemble of polymers in a saturated solution while including the effect of composition fluctuations on LLPS. We describe the approaches that can be used to accurately construct phase diagrams of a variety of molecularly designed polymers and illustrate the method by generating an approximation-free phase diagram for a classical symmetric diblock polyampholyte.

Mussel-Inspired Reversible Molecular Adhesion for Fabricating Self-Healing Materials

Nature offers inspiration for the development of high-performance synthetic materials. Extensive studies on the universal adhesion and self-healing behavior of mussel byssus reveal that a series of reversible molecular interactions occurring in byssal plaques and threads play an essential role, and the mussel-inspired chemistry can serve as a versatile platform for the design of self-healing materials. In this Perspective, we provide an overview of the recent progress in the detection, quantification, and utilization of mussel-inspired reversible molecular interactions, which includes the elucidation of their binding mechanisms via force-measuring techniques and the development of self-healing materials based on these dynamic interactions. Both conventional catechol-medicated interactions and newly discovered chemistry beyond the catechol groups are discussed, providing insights into the design strategies of advanced self-healing materials via mussel-inspired chemistry.

When disturbances favour species adapted to stressful soils: grazing may benefit soil specialists in gypsum plant communities

Background

Herbivory and extreme soils are drivers of plant evolution. Adaptation to extreme soils often implies substrate-specific traits, and resistance to herbivory involves tolerance or avoidance mechanisms. However, little research has been done on the effect of grazing on plant communities rich in edaphic endemics growing on extreme soils. A widespread study case is gypsum drylands, where livestock grazing often prevails. Despite their limiting conditions, gypsum soils host a unique and highly specialised flora, identified as a conservation priority.

Methods

We evaluated the effect of different grazing intensities on the assembly of perennial plant communities growing on gypsum soils. We considered the contribution of species gypsum affinity and key functional traits of species such as traits related to gypsum specialisation (leaf S accumulation) or traits related to plant tolerance to herbivory such as leaf C and N concentrations. The effect of grazing intensity on plant community indices (i.e., richness, diversity, community weighted-means (CWM) and functional diversity (FD) indices for each trait) were modelled using Generalised Linear Mixed Models (GLMM). We analysed the relative contribution of interspecific trait variation and intraspecific trait variation (ITV) in shifts of community index values.

Results

Livestock grazing may benefit gypsum plant specialists during community assembly, as species with high gypsum affinity, and high leaf S contents, were more likely to assemble in the most grazed plots. Grazing also promoted species with traits related to herbivory tolerance, as species with a rapid-growth strategy (high leaf N, low leaf C) were promoted under high grazing conditions. Species that ultimately formed gypsum plant communities had sufficient functional variability among individuals to cope with different grazing intensities, as intraspecific variability was the main component of species assembly for CWM values.

Conclusions

The positive effects of grazing on plant communities in gypsum soils indicate that livestock may be a key tool for the conservation of these edaphic endemics.

Late Pleistocene megafauna extinction leads to missing pieces of ecological space in a North American mammal community

The conservation status of large-bodied mammals is dire. Their decline has serious consequences because they have unique ecological roles not replicated by smaller-bodied animals. Here, we use the fossil record of the megafauna extinction at the terminal Pleistocene to explore the consequences of past biodiversity loss. We characterize the isotopic and body-size niche of a mammal community in Texas before and after the event to assess the influence on the ecology and ecological interactions of surviving species (>1 kg). Preextinction, a variety of C₄ grazers, C₃ browsers, and mixed feeders existed, similar to modern African savannas, with likely specialization among the two sabertooth species for juvenile grazers. Postextinction, body size and isotopic niche space were lost, and the δ¹³C and δ¹⁵N values of some survivors shifted. We see mesocarnivore release within the Felidae: the jaguar, now an apex carnivore, moved into the specialized isotopic niche previously occupied by extinct cats. Puma, previously absent, became common and lynx shifted toward consuming more C₄-based resources. Lagomorphs were the only herbivores to shift toward C₄ resources. Body size changes from the Pleistocene to Holocene were species-specific, with some animals (deer, hare) becoming significantly larger and others smaller (bison, rabbits) or exhibiting no change to climate shifts or biodiversity loss. Overall, the Holocene body-size-isotopic niche was drastically reduced and considerable ecological complexity lost. We conclude biodiversity loss led to reorganization of survivors and many "missing pieces" within our community; without intervention, the loss of Earth's remaining ecosystems that support megafauna will likely suffer the same fate.

Wetting behavior of polyelectrolyte complex coacervates on solid surfaces

The wetting behavior of complex coacervates underpins their use in many emerging applications of surface science, particularly wet adhesives and coatings. Many factors dictate if a coacervate phase will condense on a solid surface, including solution conditions, the nature of the polymer-substrate interaction, and the underlying supernatant-coacervate bulk phase behavior. In this work, we use a simple inhomogeneous mean-field theory to study the wetting behavior of complex coacervates on solid surfaces both off-coexistence (wetting transitions) and on-coexistence (contact angles). We focus on the effects of salt concentration, the polycation/polyanion surface affinity, and the applied electrostatic potential on the wettability. We find that the coacervate generally wets the surface via a first order wetting transition with second order transitions possible above a surface critical point. Applying an electrostatic potential to a solid surface always improves the surface wettability when the polycation/polyanion-substrate interaction is symmetric. For asymmetric surface affinity, the wettability has a nonmonotonic dependence with the applied potential. We use simple scaling and thermodynamic arguments to explain our results.

Solution structure of recombinant Pvfp-5β reveals insights into mussel adhesion

Some marine organisms can resist to aqueous tidal environments and adhere tightly on wet surface. This behavior has raised increasing attention for potential applications in medicine, biomaterials, and tissue engineering. In mussels, adhesive forces to the rock are the resultant of proteinic fibrous formations called byssus. We present the solution structure of Pvfp-5β, one of the three byssal plaque proteins secreted by the Asian green mussel Perna viridis, and the component responsible for initiating interactions with the substrate. We demonstrate that Pvfp-5β has a stably folded structure in agreement with the presence in the sequence of two EGF motifs. The structure is highly rigid except for a few residues affected by slow local motions in the µs-ms time scale, and differs from the model calculated by artificial intelligence methods for the relative orientation of the EGF modules, which is something where computational methods still underperform. We also show that Pvfp-5β is able to coacervate even with no DOPA modification, giving thus insights both for understanding the adhesion mechanism of adhesive mussel proteins, and developing of biomaterials.

Don't stop me now: Managed fence gaps could allow migratory ungulates to track dynamic resources and reduce fence related energy loss

In semi-arid environments characterized by erratic rainfall and scattered primary production, migratory movements are a key survival strategy of large herbivores to track resources over vast areas. Veterinary Cordon Fences (VCFs), intended to reduce wildlife-livestock disease transmission, fragment large parts of southern Africa and have limited the movements of large wild mammals for over 60 years. Consequently, wildlife-fence interactions are frequent and often result in perforations of the fence, mainly caused by elephants. Yet, we lack knowledge about at which times fences act as barriers, how fences directly alter the energy expenditure of native herbivores, and what the consequences of impermeability are. We studied 2-year ungulate movements in three common antelopes (springbok, kudu, eland) across a perforated part of Namibia's VCF separating a wildlife reserve and Etosha National Park using GPS telemetry, accelerometer measurements, and satellite imagery. We identified 2905 fence interaction events which we used to evaluate critical times of encounters and direct fence effects on energy expenditure. Using vegetation type-specific greenness dynamics, we quantified what animals gained in terms of high quality food resources from crossing the VCF. Our results show that the perforation of the VCF sustains herbivore-vegetation interactions in the savanna with its scattered resources. Fence permeability led to peaks in crossing numbers during the first flush of woody plants before the rain started. Kudu and eland often showed increased energy expenditure when crossing the fence. Energy expenditure was lowered during the frequent interactions of ungulates standing at the fence. We found no alteration of energy expenditure when springbok immediately found and crossed fence breaches. Our results indicate that constantly open gaps did not affect energy expenditure, while gaps with obstacles increased motion. Closing gaps may have confused ungulates and modified their intended movements. While browsing, sedentary kudu's use of space was less affected by the VCF; migratory, mixed-feeding springbok, and eland benefited from gaps by gaining forage quality and quantity after crossing. This highlights the importance of access to vast areas to allow ungulates to track vital vegetation patches.

Rapid Eocene diversification of spiny plants in subtropical woodlands of central Tibet

Spinescence is an important functional trait possessed by many plant species for physical defence against mammalian herbivores. The development of spinescence must have been closely associated with both biotic and abiotic factors in the geological past, but knowledge of spinescence evolution suffers from a dearth of fossil records, with most studies focusing on spatial patterns and spinescence-herbivore interactions in modern ecosystems. Numerous well-preserved Eocene (~39 Ma) plant fossils exhibiting seven different spine morphologies discovered recently in the central Tibetan Plateau, combined with molecular phylogenetic character reconstruction, point not only to the presence of a diversity of spiny plants in Eocene central Tibet but a rapid diversification of spiny plants in Eurasia around that time. These spiny plants occupied an open woodland landscape, indicated by numerous megafossils and grass phytoliths found in the same deposits, as well as numerical climate and vegetation modelling. Our study shows that regional aridification and expansion of herbivorous mammals may have driven the diversification of functional spinescence in central Tibetan woodlands, ~24 million years earlier than similar transformations in Africa.

Spines are an important physical defense for many plant species. Here, the authors describe seven different spine morphologies from the Eocene of central Tibet associated with regional aridification and expansion of herbivorous mammals.

Gypsum endemics accumulate excess nutrients in leaves as a potential constitutive strategy to grow in grazed extreme soils

Extreme soils often have mineral nutrient imbalances compared to plant nutritional requirements and co-occur in open areas where grazers thrive. Thus, plants must respond to both constraints, which can affect nutrient concentrations in all plant organs. Gypsum soil provides an excellent model system to study adaptations to extreme soils under current grazing practices as it harbours two groups of plant species that differ in their tolerance to gypsum soils and foliar composition. However, nutrient concentrations in organs other than leaves, and their individual responses to simulated herbivory, are still unknown in gypsum plants. We studied plant biomass, root mass ratio and nutrient partitioning among different organs (leaves, stems, coarse roots, fine roots) in five gypsum endemics and five generalists cultivated in gypsum and calcareous soils and subjected to different levels of simulated browsing. Gypsum endemics tended to have higher elemental concentration in leaves, stems and coarse roots than generalist species in both soil types, whereas both groups tended to show similar high concentrations in fine roots. This behaviour was especially clear with sulphur (S), which is found in excess in gypsum soils, and which endemics accumulated in leaves as sulphate (>50% of S). Moreover, plants subjected to clipping, regardless of their affinity to gypsum, were unable to compensate for biomass losses and showed similar elemental composition to unclipped plants. The accumulation of excess mineral nutrients by endemic species in aboveground organs may be a constitutive nutritional strategy in extreme soils and is potentially playing an anti-herbivore role in grazed gypsum outcrops.

Trade of commercial potting substrates: A largely overlooked means of the long-distance dispersal of plants

Although long-distance dispersal (LDD) events are rare and stochastic, they are disproportionately important and drive several large-scale ecological processes; yet, we have a very limited understanding of their frequency, extent and consequences. Humanity intentionally spreads several species, which is associated with the accidental dispersal of other plant species. Although the global trade of potted plants and horticultural substrates may disperse large quantities of propagules, it has hardly been studied from an ecological point of view. We assessed the viable seed content of different types of commercial potting substrates to answer the following questions: (i) In what richness and density do substrates contain viable seeds? (ii) Does the composition of substrates influence their viable seed content? and (iii) Are there common characteristics of the species dispersed this way? We detected 438 seedlings of 66 taxa and found that 1 l of potting substrate contains an average of 13.27 seeds of 6.24 species, so an average 20-liter bag of substrate contains 265 viable seeds. There was a high variability in the seed content of the substrates, as substrates containing manure contained a substantially higher number of species and seeds than substrates without manure. Thus, this pathway of LDD is an interplay between endozoochory by grazing livestock and accidental human-vectored dispersal, implying that the diet preference of grazing animals influences the ability of a plant species to be dispersed this way. According to our results, potting substrates can disperse large quantities of seeds of a wide range of plant species over large distances. We conclude that this kind of human-vectored LDD may have complex effects on plant populations and communities; however, as this dispersal pathway is largely understudied and has hardly been considered as a type of LDD, its consequences are still unknown and further studies of the issue are of great importance.

Controlling synthetic membraneless organelles by a red-light-dependent singlet oxygen-generating protein

Membraneless organelles (MLOs) formed via protein phase separation have great implications for both physiological and pathological processes. However, the inability to precisely control the bioactivities of MLOs has hindered our understanding of their roles in biology, not to mention their translational applications. Here, by combining intrinsically disordered domains such as RGG and mussel-foot proteins, we create an in cellulo protein phase separation system, of which various biological activities can be introduced via metal-mediated protein immobilization and further controlled by the water-soluble chlorophyll protein (WSCP)—a remarkably stable, red-light-responsive singlet oxygen generator. The WSCP-laden protein condensates undergo a liquid-to-solid phase transition on light exposure, due to oxidative crosslinking, providing a means to control catalysis within synthetic MLOs. Moreover, these photoresponsive condensates, which retain the light-induced phase-transition behavior in living cells, exhibit marked membrane localization, reminiscent of the semi-membrane-bound compartments like postsynaptic densities in nervous systems. Together, this engineered system provides an approach toward controllable synthetic MLOs and, alongside its light-induced phase transition, may well serve to emulate and explore the aging process at the subcellular or even molecular level.

Membraneless organelles play vital cellular roles, and control over their formation and state could have varied applications. Here, the authors develop photoresponsive synthetic condensates whose activity can be controlled through the use of light to trigger liquid-to-solid phase transition.

Anthropogenic disruptions to longstanding patterns of trophic-size structure in vertebrates

Diet and body mass are inextricably linked in vertebrates: while herbivores and carnivores have converged on much larger sizes, invertivores and omnivores are, on average, much smaller, leading to a roughly U-shaped relationship between body size and trophic guild. Although this U-shaped trophic-size structure is well documented in extant terrestrial mammals, whether this pattern manifests across diverse vertebrate clades and biomes is unknown. Moreover, emergence of the U-shape over geological time and future persistence are unknown. Here we compiled a comprehensive dataset of diet and body size spanning several vertebrate classes and show that the U-shaped pattern is taxonomically and biogeographically universal in modern vertebrate groups, except for marine mammals and seabirds. We further found that, for terrestrial mammals, this U-shape emerged by the Palaeocene and has thus persisted for at least 66 million years. Yet disruption of this fundamental trophic-size structure in mammals appears likely in the next century, based on projected extinctions. Actions to prevent declines in the largest animals will sustain the functioning of Earth's wild ecosystems and biomass energy distributions that have persisted through deep time.

Assessing the Impact of Wildlife on Vegetation Cover Change, Northeast Namibia, Based on MODIS Satellite Imagery (2002–2021)

Human–wildlife conflict in the Zambezi region of northeast Namibia is well documented, but the impact of wildlife (e.g., elephants) on vegetation cover change has not been adequately addressed. Here, we assessed human–wildlife interaction and impact on vegetation cover change. We analyzed the 250 m MODIS and ERA5 0.25° × 0.25° drone and GPS-collar datasets. We used Time Series Segmented Residual Trends (TSS-RESTREND), Mann–Kendall Test Statistics, Sen’s Slope, ensemble, Kernel Density Estimation (KDE), and Pearson correlation methods. Our results revealed (i) widespread vegetation browning along elephant migration routes and within National Parks, (ii) Pearson correlation (p-value = 5.5 × 10−8) showed that vegetation browning areas do not sustain high population densities of elephants. Currently, the Zambezi has about 12,008 elephants while these numbers were 1468, 7950, and 5242 in 1989, 1994, and 2005, respectively, (iii) settlements and artificial barriers have a negative impact on wildlife movement, driving vegetation browning, and (iv) vegetation greening was found mostly within communal areas where intensive farming and cattle grazing is a common practice. The findings of this study will serve as a reference for policy and decision makers. Future studies should consider integrating higher resolution multi-platform datasets for detailed micro analysis and mapping of vegetation cover change.

Potential distributions of pre-Columbian people in Tropical Andean landscapes

Much has yet to be learned of the spatial patterning of pre-Columbian people across the Tropical Andes. Using compiled archaeological data and a suite of environmental variables, we generate an ensemble species distribution model (SDM) that incorporates general additive models, random forest models and Maxent models to reconstruct spatial patterns of pre-Columbian people that inhabited the Tropical Andes east of the continental divide, within the modern countries of Bolivia, Peru and Ecuador. Within this region, here referred to as the eastern Andean flank, elevation, mean annual cloud frequency, distance to rivers and precipitation of the driest quarter are the environmental variables most closely related to human occupancy. Our model indicates that 11.04% of our study area (65 368 km²) was likely occupied by pre-Columbian people. Our model shows that 30 of 351 forest inventory plots, which are used to generate ecological understanding of Andean ecosystems, were likely occupied in the pre-Columbian period. In previously occupied sites, successional trajectories may still be shaping forest dynamics, and those forests may still be recovering from the ecological legacy of pre-Columbian impacts. Our ensemble SDM links palaeo- and neo-ecology and can also be used to guide both future archaeological and ecological studies. This article is part of the theme issue 'Tropical forests in the deep human past'.

Leveraging palaeoproteomics to address conservation and restoration agendas

Archaeological and paleontological records offer tremendous yet often untapped potential for examining long-term biodiversity trends and the impact of climate change and human activity on ecosystems. Yet, zooarchaeological and fossil remains suffer various limitations, including that they are often highly fragmented and morphologically unidentifiable, preventing them from being optimally leveraged for addressing fundamental research questions in archaeology, paleontology, and conservation paleobiology. Here, we explore the potential of palaeoproteomics—the study of ancient proteins—to serve as a critical tool for creating richer, more informative datasets about biodiversity change that can be leveraged to generate more realistic, constructive, and effective conservation and restoration strategies into the future.

Post-fire pickings: Large herbivores alter understory vegetation communities in a coastal eucalypt forest

Fire and herbivores alter vegetation structure and function. Future fire activity is predicted to increase, and quantifying changes in vegetation communities arising from post‐fire herbivory is needed to better manage natural environments. We investigated the effects of post‐fire herbivory on understory plant communities in a coastal eucalypt forest in southeastern Australia. We quantified herbivore activity, understory plant diversity, and dominant plant morphology following a wildfire in 2017 using two sizes of exclosures. Statistical analysis incorporated the effect of exclusion treatments, time since fire, and the effect of a previous prescribed burn. Exclusion treatments altered herbivore activity, but time since fire did not. Herbivory reduced plant species richness, diversity, and evenness and promoted the dominance of the most abundant plants within the understory. Increasing time since fire reduced community diversity and evenness and influenced morphological changes to the dominant understory plant species, increasing size and dead material while decreasing abundance. We found the legacy effects of a previous prescribed burn had no effect on herbivores or vegetation within our study. Foraging by large herbivores resulted in a depauperate vegetation community. As post‐fire herbivory can alter vegetation communities, we postulate that management burning practices may exacerbate herbivore impacts. Future fire management strategies to minimize herbivore‐mediated alterations to understory vegetation could include aggregating management burns into larger fire sizes or linking fire management with herbivore management. Restricting herbivore access following fire (planned or otherwise) can encourage a more diverse and species‐rich understory plant community. Future research should aim to determine how vegetation change from post‐fire herbivory contributes to future fire risk.

Quantitative determination of cation–π interactions between metal ions and aromatic groups in aqueous media by a hydrogel Donnan potential method

The binding ratios of various metal ions to aromatic groups by cation–π interactions in aqueous media have been quantitatively calculated by using Donnan potential measurements.

Late Pleistocene shrub expansion preceded megafauna turnover and extinctions in eastern Beringia

The collapse of the steppe-tundra biome (mammoth steppe) at the end of the Pleistocene is used as an important example of top-down ecosystem cascades, where human hunting of keystone species led to profound changes in vegetation across high latitudes in the Northern Hemisphere. Alternatively, it is argued that this biome transformation occurred through a bottom-up process, where climate-driven expansion of shrub tundra (Betula, Salix spp.) replaced the steppe-tundra vegetation that grazing megafauna taxa relied on. In eastern Beringia, these differing hypotheses remain largely untested, in part because the precise timing and spatial pattern of Late Pleistocene shrub expansion remains poorly resolved. This uncertainty is caused by chronological ambiguity in many lake sediment records, which typically rely on radiocarbon (¹⁴C) dates from bulk sediment or aquatic macrofossils-materials that are known to overestimate the age of sediment layers. Here, we reexamine Late Pleistocene pollen records for which ¹⁴C dating of terrestrial macrofossils is available and augment these data with ¹⁴C dates from arctic ground-squirrel middens and plant macrofossils. Comparing these paleovegetation data with a database of published ¹⁴C dates from megafauna remains, we find the postglacial expansion of shrub tundra preceded the regional extinctions of horse (Equus spp.) and mammoth (Mammuthus primigenius) and began during a period when the frequency of ¹⁴C dates indicates large grazers were abundant. These results are not consistent with a model of top-down ecosystem cascades and support the hypothesis that climate-driven habitat loss preceded and contributed to turnover in mammal communities.

Collapse of the mammoth-steppe in central Yukon as revealed by ancient environmental DNA

The temporal and spatial coarseness of megafaunal fossil records complicates attempts to to disentangle the relative impacts of climate change, ecosystem restructuring, and human activities associated with the Late Quaternary extinctions. Advances in the extraction and identification of ancient DNA that was shed into the environment and preserved for millennia in sediment now provides a way to augment discontinuous palaeontological assemblages. Here, we present a 30,000-year sedimentary ancient DNA (sedaDNA) record derived from loessal permafrost silts in the Klondike region of Yukon, Canada. We observe a substantial turnover in ecosystem composition between 13,500 and 10,000 calendar years ago with the rise of woody shrubs and the disappearance of the mammoth-steppe (steppe-tundra) ecosystem. We also identify a lingering signal of Equus sp. (North American horse) and Mammuthus primigenius (woolly mammoth) at multiple sites persisting thousands of years after their supposed extinction from the fossil record.

Global response of fire activity to late Quaternary grazer extinctions

[Figure: see text].