Ecology

Environmental changes, such as climate warming and higher herbivory pressure, are altering the carbon balance of Arctic ecosystems; yet, how these drivers modify the carbon balance among different habitats remains uncertain. This hampers our ability to predict changes in the carbon sink strength of tundra ecosystems. We investigated how spring goose grubbing and summer warming—two key environmental‐change drivers in the Arctic—alter CO2 fluxes in three tundra habitats varying in soil moisture and plant‐community composition. In a full‐factorial experiment in high‐Arctic Svalbard, we simulated grubbing and warming over two years and determined summer net ecosystem exchange (NEE) alongside its components: gross ecosystem productivity (GEP) and ecosystem respiration (ER). After two years, we found net CO2 uptake to be suppressed by both drivers depending on habitat. CO2 uptake was reduced by warming in mesic habitats, by warming and grubbing in moist habitats, and by grubbing in wet habitats. In mesic habitats, warming stimulated ER (+75%) more than GEP (+30%), leading to a 7.5‐fold increase in their CO2 source strength. In moist habitats, grubbing decreased GEP and ER by ~55%, while warming increased them by ~35%, with no changes in summer‐long NEE. Nevertheless, grubbing offset peak summer CO2 uptake and warming led to a twofold increase in late summer CO2 source strength. In wet habitats, grubbing reduced GEP (−40%) more than ER (−30%), weakening their CO2 sink strength by 70%. One‐year CO2‐flux responses were similar to two‐year responses, and the effect of simulated grubbing was consistent with that of natural grubbing. CO2‐flux rates were positively related to aboveground net primary productivity and temperature. Net ecosystem CO2 uptake started occurring above ~70% soil moisture content, primarily due to a decline in ER. Herein, we reveal that key environmental‐change drivers—goose grubbing by decreasing GEP more than ER and warming by enhancing ER more than GEP—consistently suppress net tundra CO2 uptake, although their relative strength differs among habitats. By identifying how and where grubbing and higher temperatures alter CO2 fluxes across the heterogeneous Arctic landscape, our results have implications for predicting the tundra carbon balance under increasing numbers of geese in a warmer Arctic.

Identifying the factors that affect host–parasite interactions is essential for understanding the ecology and dynamics of vector‐borne diseases and may be an important component of predicting human disease risk. Characteristics of hosts themselves (e.g., body condition, host behavior, immune defenses) may affect the likelihood of parasitism. However, despite highly variable rates of parasitism and infection in wild populations, identifying widespread links between individual characteristics and heterogeneity in parasite acquisition has proven challenging because many zoonoses exist over wide geographic extents and exhibit both spatial and temporal heterogeneity in prevalence and individual and population‐level effects. Using seven years of data collected by the National Ecological Observatory Network (NEON), we examined relationships among individual host condition, behavior, and parasitism by Ixodid ticks in a keystone host species, the white‐footed mouse, Peromyscus leucopus. We found that individual condition, specifically sex, body mass, and reproductive condition, had both direct and indirect effects on parasitism by ticks, but the nature of these effects differed for parasitism by larval versus nymphal ticks. We also found that condition differences influenced rodent behavior, and behavior directly affected the rates of parasitism, with individual mice that moved farther being more likely to carry ticks. This study illustrates how individual‐level data can be examined using large‐scale datasets to draw inference and uncover broad patterns in host–parasite encounters at unprecedented spatial scales. Our results suggest that intraspecific variation in the movement ecology of hosts may affect host–parasite encounter rates and, ultimately, alter zoonotic disease risk through anthropogenic modifications and natural environmental conditions that alter host space use.

As natural populations continue to decline globally, direct forms of intervention are increasingly necessary to prevent extinction. One type of intervention, known as demographic rescue, occurs when individuals are added directly to a population to increase abundance and ultimately prevent population extinction. However, the role of infectious disease in demographic rescue remains unknown. To examine the effects of pathogens on demographic rescue, we used a host–pathogen system with the aquatic crustacean Daphnia dentifera as the host and the fungus Metschnikowia bicuspidata as the pathogen. We constructed a randomized 3 × 2 factorial experiment with three rescue treatments (none, low, high) and two pathogen treatments (unexposed, exposed), where the pathogen was introduced via infected individuals during rescue events. We found that adding more individuals to demographically depressed populations increased abundance over the short term; highly supplemented populations initially had 62% more individuals than populations that had no introduced individuals. However, by the end of the experiment, populations that did not have any individuals introduced averaged 640% higher abundance than populations where infected individuals had been added. Thus, the introduction of infected individuals can result in worse demographic outcomes for populations than if no rescue is attempted.

Species interactions shape biodiversity patterns, community assemblage, and the dynamics of wildlife populations. Ecological theory posits that the strength of interspecific interactions is fundamentally underpinned by the population sizes of the involved species. Nonetheless, prevalent approaches for modeling species interactions predominantly center around occupancy states. Here, we use simulations to illuminate the inadequacies of modeling species interactions solely as a function of occupancy, as is common practice in ecology. We demonstrate erroneous inference into species interactions due to error in parameter estimates when considering species occupancy alone. To address this critical issue, we propose, develop, and demonstrate an abundance‐mediated interaction framework designed explicitly for modeling species interactions involving two or more species from detection/non‐detection data. We present Markov chain Monte Carlo (MCMC) samplers tailored for diverse ecological scenarios, including intraguild predation, disease‐ or predator‐mediated competition, and trophic cascades. Illustrating the practical implications of our approach, we compare inference from modeling the interactions in a three‐species network involving coyotes (Canis latrans), fishers (Pekania pennanti), and American marten (Martes americana) in North America as a function of occupancy states and as a function of abundance. When modeling interactions as a function of abundance rather than occupancy, we uncover previously unidentified interactions. Our study emphasizes that accounting for abundance‐mediated interactions rather than simple co‐occurrence patterns can fundamentally alter our comprehension of system dynamics. Through an empirical case study and comprehensive simulations, we demonstrate the importance of accounting for abundance when modeling species interactions, and we present a statistical framework equipped with MCMC samplers to achieve this paradigm shift in ecological research.

Young tropical secondary forests play an important role in the local and global carbon cycles because of their large area and rapid biomass accumulation rates. This study examines how environmental conditions and forest attributes shape biomass compartments and the productivity of young tropical secondary forests. We compared 36 young secondary forest stands that differed in the time since agricultural land abandonment (2.3–3.6 years) from dry and wet regions in Ghana. We quantified biomass stocks in living and dead stems, roots, and soil, and aboveground biomass and litter productivity. We used structural equation models to evaluate how macroclimate, soil nutrients (N, P), and forest attributes (structure, diversity, and functional composition) affect ecosystem functioning. After three years of succession, tropical wet forests stored on average 115 t biomass ha⁻¹ (the sum of aboveground living and dead biomass, belowground fine root biomass, and soil organic matter), and dry forests stored 99 t ha⁻¹. These values represent 31% (in the wet forest) and 39% (in the dry forest) of the biomass compared with neighboring old‐growth forests. The majority of forest ecosystem biomass was stored in the soil (70%) and aboveground living vegetation (25%). Macroclimate strongly shaped forest attributes, which in turn determined biomass stocks and productivity. Soil phosphorus strongly increased litter production and soil organic matter, confirming that it is a limiting element in tropical ecosystems. Tree density and species diversity increased forest biomass stocks, suggesting crown packing and complementary resource use enhance forest functioning. A more conservative trait composition (high wood density) increased biomass stocks but reduced productivity, indicating that quantity, identity, and quality of species affect ecosystem functioning.

Two hypotheses have been used to explain the loss of plant diversity with nutrient addition. The nutrient identity hypothesis posits that biodiversity loss is due to a specific limiting nutrient, such as nitrogen (N) or phosphorus (P), while the niche dimension hypothesis posits that adding a larger number of limiting nutrients, regardless of their identity, results in biodiversity loss. These two hypotheses have not previously been tested together simultaneously. Here, we conduct that analysis to enable their relative effect sizes to be compared. We manipulated the supply of eight nutrients in the same experimental meadow grassland site to isolate the effects of the identity of added nutrients versus the number of added nutrients on biodiversity loss. We found support for both hypotheses, with the largest negative effects on biodiversity measures being due to N, or N and P treatment, with additional more minor effects of the number of added nutrients. Structural equation models (SEMs) suggested both identity and number of added nutrients had direct negative effects on biodiversity, likely caused by species' innate ability to competitively respond to nutrients, especially in response to disease, herbivory, and stress. SEMs also suggested indirect effects arising from nutrient‐driven increases in aboveground biomass, which resulted in intensified competition for light and the competitive exclusion of short‐statured species. These effects were exacerbated by the nutrients N and P which caused a shift in biomass accumulation from belowground to aboveground. The results highlight that a multi‐nutrient perspective will improve our ability to effectively manage, monitor, and restore ecosystems.

Although invertebrate herbivores commonly impact terrestrial plant diseases by facilitating transmission of plant pathogens and increasing host susceptibility to infection via wounding, less is known about the role of herbivores in marine plant disease dynamics. Importantly, transmission via herbivores may not be required in the ocean since saline ocean waters support pathogen survival and transmission. Through laboratory experiments with eelgrass (Zostera marina), we showed that isopods (Pentidotea wosnesenskii) and snails (Lacuna spp.) created grazing scars that increased disease severity and thus indirectly facilitated transmission of Labyrinthula zosterae (Lz), a protist that causes seagrass wasting disease. Experiments also quantified different feeding preferences among herbivores: Amphipods (Ampithoe lacertosa) selectively consumed diseased eelgrass, while isopods and snails selectively grazed asymptomatic leaves, suggesting different herbivore taxa may have contrasting impacts on disease dynamics. Our experiments show no sign that herbivores directly vector Lz from diseased to asymptomatic eelgrass. However, we isolated live Lz from isopod, amphipod, and snail feces and detected Lz with quantitative polymerase chain reaction in amphipods and snails, suggesting that herbivores eating diseased eelgrass could pass the live pathogen. Finally, field surveys demonstrated a close association between seagrass wasting disease and invertebrate grazing scars; disease prevalence was 29 ± 4.7% (95% CI) higher on eelgrass leaves with herbivore scars. Collectively, these findings show that some herbivores can increase eelgrass disease risk by facilitating the spread of an important pathogen via wounding, but not via direct transmission. Thus, herbivores may play different roles in plant disease dynamics in terrestrial versus marine ecosystems depending on the pathogen's ability to survive and transmit without a vector.

Diel partitioning of animals within ecological communities is widely acknowledged, yet rarely quantified. Investigation of most ecological patterns and processes involves convenient daylight sampling, with little consideration of the contributions of nocturnal taxa, particularly in marine environments. Here we assess diel partitioning of reef faunal assemblages at a continental scale utilizing paired day and night visual census across 54 shallow tropical and temperate reefs around Australia. Day–night differences were most pronounced in the tropics, with fishes and invertebrates displaying distinct and opposing diel occupancy on coral reefs. Tropical reefs in daytime were occupied primarily by fishes not observed at night (64% of all species sighted across day and night, and 71% of all individuals). By night, substantial emergence of invertebrates not otherwise detected during sunlit hours occurred (56% of all species, and 45% of individuals). Nocturnal emergence of tropical invertebrates corresponded with significant declines in the richness and biomass of predatory and herbivorous diurnal fishes. In contrast, relatively small diel changes in fishes active on temperate reefs corresponded to limited nocturnal emergence of temperate invertebrates. This reduced partitioning may, at least in part, be a result of strong top‐down pressures from fishes on invertebrate communities, either by predation or competitive interference. For shallow reefs, the diel cycle triggers distinct emergence and retreat of faunal assemblages and associated trophic patterns and processes, which otherwise go unnoticed during hours of regular scientific monitoring. Improved understanding of reef ecology, and management of reef ecosystems, requires greater consideration of nocturnal interactions. Without explicit sampling of nocturnal patterns and processes, we may be missing up to half of the story when assessing ecological interactions.

As long‐lived tropical trees grow into the multi‐layered canopy and face different environmental conditions, the relationships between leaf traits and whole‐plant survival can vary over ontogeny. We tested the strength and direction of the relationships between leaf traits and long‐term survival data across life stages for woody species from a subtropical forest in Puerto Rico. Trait–survival relationships were largely consistent across ontogeny with conservative traits leading to higher survival rates. The stage‐specific relationship R² increased by up to one order of magnitude compared to studies not considering ontogenetic trait variations. Stage‐specific traits were significant predictors of their corresponding stage‐specific survival: Seedlings traits were better predictors of seedling survival than adult traits, and adult traits were better predictors of maximum adult survival than seedling traits. Our results suggest that stage‐specific leaf traits reflect different strategies over ontogeny and can substantially improve predictability of survival models in tropical forests.

Urbanization in temperate climates often advances the beginning and peak of biological events due to multiple factors, especially urban heat islands. However, the effect of urbanization on insect phenology remains understudied in more tropical areas, where temperature may be a weaker phenological cue. We surveyed moths across an urban gradient in a subtropical city weekly for a year to test how impervious surface and canopy cover impact phenology at the caterpillar and adult life stages. For macro‐moths, we also examine how these effects vary with life history traits. When pooling all individuals, we found no effect of urbanization proxy variables on timing of caterpillar or adult phenology. At the species‐specific level, we found timing of peak adult macro‐moths is influenced by canopy cover, which also interacts with two traits: temperature niche and body size. Cold‐adapted species delay timing of peak abundance in more shaded sites, while warm‐adapted species were not affected. Smaller species, associated with lower dispersal ability, were more phenologically sensitive to canopy cover than larger bodied species. These results highlight the importance of canopy cover within cities and its interaction with species' traits in mediating impact of urbanization on moth phenology in subtropical systems.

Substantial evidence suggests that biodiversity can stabilize ecosystem function, but how it does this is less clear. In very general terms, the hypothesis is that biodiversity stabilizes function because having more species increases the role of compensatory dynamics, which occur when species in a community show different responses to the environment. Here, we focus on two forms of compensatory dynamics, cross‐scale redundancy (CSR) and response diversity (RD). CSR occurs when species respond to a disturbance at different scales such that scale‐specific disturbances do not negatively affect all species. RD occurs when species contributing to the same function show different responses to an environmental change. We developed a new analytical approach that can compare the strength of CSR and RD in the same dataset and used it to study native bee pollination of blueberry at 16 farms that varied in surrounding agricultural land use. We then asked whether CSR and RD among bee species are associated with the stability of blueberry pollination. Although CSR and RD were both present, only RD was associated with higher stability of pollination. Furthermore, the effects of RD on stability were due to a single widespread species, Andrena bradleyi, that is a specialist on blueberry and, unlike other bee species, was highly abundant at farms surrounded by intensive blueberry agriculture. Thus, the stabilizing effect we observed was attributable to an “identity effect” more than to species richness per se. Our results demonstrate how CSR and RD can be empirically measured and compared and highlight how the theoretical expectations of the biodiversity–ecosystem functioning field are not always upheld when confronted with real‐world data.

Smaller grazers consistently show greater preference for recently burned patches than larger species. Energy optimization theory posits that this pattern is driven by small‐ versus large‐bodied herbivores seeking to maximize energy intake by choosing high‐quality recently burned grasses, or high‐quantity unburned grasses, respectively. We propose that if burn preference is driven by an energy‐maximization mechanism, then preference should change over time as grass regrows and progresses across the optimal feeding heights of herbivores of increasing body size. To test this, we used a camera trap array in the Serengeti National Park to quantify changes in the relative preference for burned patches of seven ruminant herbivore species. We compared observed patterns to simulation results from a grass production‐herbivore patch selection model. Burn preference and herbivore body size scaled negatively for 6 months after fire, but this relationship disappeared after 7 months when smaller species stopped selecting burns, and larger herbivores selected burns after 10 months, in a reversal of classic grazer succession. Simulations recreated the former but not the latter relationship, suggesting that an energy‐maximization mechanism can drive allometric scaling of burn preference immediately after fire, but over longer periods, grazer‐driven feedbacks are required to explain large herbivore burn preferences.

Trophic cascades are important determinants of food web dynamics and functioning, yet mechanisms accounting for variation in trophic cascade strength remain elusive. Here, we used food chain models and a mesocosm experiment (phytoplankton–zooplankton–shrimp) to disentangle the relative importance of two energetic processes driving trophic cascades: primary productivity and energy transfer efficiency. Food chain models predicted that the strength of trophic cascades was increased as the energy transfer efficiency between herbivore and predator (predator efficiency) increased, while its relationship with primary productivity was relatively weak. These model predictions were confirmed by a mesocosm experiment, which showed that the strength of trophic cascade increased with predator efficiency but remained unaffected by nutrient supply rate or primary productivity. Combined, our results indicate that the efficiency of energy transfer along the food chain, rather than the total amount of energy fixed by primary producers, determines the strength of trophic cascades. Our study provides an integrative perspective to reconcile energetic and population dynamics in food webs, which has implications for both ecological research and ecosystem management.

Environmental cues that predict increased risk of herbivory can prime plant defenses; however, few studies have explored how such cues elicit broader plant responses, including potential effects on plant growth and other resource allocations that may affect tolerance to herbivore damage. We exposed goldenrod plants (Solidago altissima) to varying concentrations of the putative sex pheromone of a gall‐inducing herbivore, which has previously been implicated in defense priming. In experiments with two plant genotypes and three herbivore populations, any level of exposure to the pheromone enhanced tolerance of galling, rescuing flower production to levels observed for ungalled plants. Exposure to low doses of the pheromone elicited greater resistance to galling than exposure to high doses, with unexposed plants exhibiting intermediate resistance, suggesting a nonlinear relationship between exposure and defense priming. These findings suggest plant responses to environmental cues associated with biotic stressors are broader and more complex than previously appreciated.

Understanding how demographic parameters change with density is essential for predicting the resilience of small populations. We use long‐term, individual‐based life history data from an isolated population of the Critically Endangered Northern Muriqui (Brachyteles hypoxanthus) inhabiting a 1000‐ha protected forest to evaluate density‐dependent demographic rates before and after an abrupt population decline. We found no effect of density on fertility or birth sex ratio, but mortality rates increased linearly with log density over the 33 years of population growth (1983–2015) and the subsequent 7 years of population decline (2016–2022). We used an age‐ and sex‐structured logistic growth model to project population sizes to 2060. Under the 1983–2015 demographic profile, the projected size was 500 individuals, but this dropped to 200 when including the abrupt change. Although the abrupt decline coincided with the end of a 2‐year drought and a yellow fever outbreak, we found no statistical effects of climate or disease on the continued population decline after 2016. However, the lower projected carrying capacity for muriquis is consistent with reduced forest productivity and increased predator pressures. These findings demonstrate the value of long‐term monitoring for identifying demographic changes that affect the sustainability of wildlife populations in small protected areas.

Although herbivory and allelopathy play important roles in plant invasions, their roles in mediating the effect of plant diversity on invasion resistance remain unknown. In a 2‐year field experiment, we constructed native plant communities with four levels of species richness (one, two, four, and eight species) and used a factorial combination of insecticide and activated carbon applications to reduce herbivory and allelopathy, respectively. We then invaded the communities with the introduced plant Solidago canadensis L. One year after the start of the experiment, there was no statistically significant net effect of species richness on biomass of the invader. However, a structural equation model showed that species richness had a positive direct effect on invader biomass that was partially balanced out by a negative indirect effect of species richness via increased light interception. In the second year, the relationship between invader biomass and species richness was negative when we analyzed the treatment combination with herbivory and allelopathy separately. Therefore, we conclude that joint effects of herbivory and allelopathy may play major roles in driving the diversity–invasibility relationship and should be considered in future studies.

Natural communities are exposed to multiple environmental stressors, which simultaneously impact the population and trait dynamics of the species embedded within these communities. Given that certain traits, such as body size, are known to rapidly respond to environmental change, and given that they can strongly influence the density of populations, this raises the question of whether the strength of the eco‐phenotypic feedback loop depends on the environment, and whether stressful environments would enhance or disrupt this feedback or causal linkage. We use two competing freshwater ciliates—Colpidium striatum and Paramecium aurelia—and expose their populations to a full‐factorial design of increasing salinity and temperature conditions as well as interspecific competition. We found that salinity, temperature, and competition significantly affected the density and cell size dynamics of both species. Cell size dynamics strongly influenced density dynamics; however, the strength of this eco‐phenotypic feedback loop weakened in stressful conditions and with interspecific competition. Our study highlights the importance of studying eco‐phenotypic dynamics in different environments comprising stressful abiotic conditions and species interactions.

Butterflies represent a diverse group of insects, playing key ecosystem roles such as pollination and their larval form engage in herbivory. Despite their importance, comprehensive global distribution data for butterfly species are lacking. This lack of comprehensive global data has hindered many large‐scale questions in ecology, evolutionary biology, and conservation at the regional and global scales. Here, I use an integrative workflow that combines occurrence records, alpha hull polygons, species' dispersal capacity, and natural habitat and environmental variables within a framework of species distribution models to generate species‐level native distributions for butterflies at a global scale in the contemporary period. The database releases native range maps for 10,372 extant species of butterflies at a spatial grain resolution of 5 arcmin (~10 km). This database has the potential to allow unprecedented large‐scale analyses in ecology, biogeography, and conservation of butterflies. The maps are available in the WGS84 coordinate reference system (EPSG:4326 code) and stored as vector polygons in the GEOPACKAGE format for maximum compression, allowing easy data manipulation using a standard computer. I additionally provide each species' spatial raster. All maps and R scripts are open access and available for download in Dryad and Zenodo, respectively, and are guided by FAIR (Findable, Accessible, Interoperable, and Reusable) data principles. By making these data available to the scientific community, I aim to advance the sharing of biological data to stimulate more comprehensive research in ecology, biogeography, and conservation of butterflies.

There remains considerable doubt, debate, and confusion regarding how biodiversity responds to gradients of important environmental drivers, such as habitat size, resource productivity, and disturbance. Here we develop a simple but comprehensive theoretical framework based on competition–colonization multispecies communities to examine the separate and interactive effects of these drivers. Using both numerical simulations and analytical arguments, we demonstrate that the critical trade‐off between competitive and colonization ability can lead to complex nonlinear, zig‐zag responses in both species richness and the inverse Simpson index along gradients of these drivers. Furthermore, we find strong interactions between these drivers that can dramatically shift the response of biodiversity to these gradients. The zig‐zag patterns in biodiversity along ecological gradients, together with the strong interactions between the drivers, can explain the mixed findings of empirical studies and syntheses, thereby providing a new paradigm that can reconcile debates on the relationships between biodiversity and multiple drivers.

Diverse drivers such as climate, soil fertility, neighborhood competition, and functional traits all contribute to variation in tree stem demographic rates. However, these demographic drivers operate at different scales, making it difficult to compare the relative importance of each driver on tree demography. Using c. 20,000 stem records from New Zealand's temperate rain forests, we analyzed the growth, recruitment, and mortality rates of 48 tree species and determined the relative importance of demographic drivers in a multilevel modeling approach. Tree species' maximum height emerged as the one most strongly associated with all demographic rates, with a positive association with growth rate and negative associations with recruitment and mortality rates. Climate, soil properties, neighborhood competition, stem size, and other functional traits also played significant roles in shaping demographic rates. Forest structure and functional composition were linked to climate and soil, with warm, dry climates and fertile soil associated with higher growth and recruitment rates. Neighborhood competition affected demographic rates depending on stem size, with smaller stems experiencing stronger negative effects, suggesting asymmetric competition where larger trees exert greater competitive effects on smaller trees. Our study emphasizes the importance of considering multiple drivers of demographic rates to better understand forest tree dynamics.