Open Population Spatial Capture-Recapture (OPSCR) models provide a unifying framework to simultaneously model demography and movement while accounting for imperfect detection of individuals. In OPSCR models, movements of individual home ranges between primary occasions usually follow a random walk process that neglects the role of the landscape. Here, we developed a non-Euclidean OPSCR model to explicitly estimate the extent to which home range shifts are shaped by spatial descriptors of the landscape, also referred to as landscape connectivity. We used simulations to validate the robustness of the model and then applied it to a 5-year, noninvasive genetic monitoring dataset of brown bears (Ursus arctos) in the Pyrenees mountain range (France, Spain, and Andorra). We found that male bears' home range movements were smaller close to main roads. The estimated resistance of the distance to roads was negative (-1.49 95% CrI [-2.86, -0.33]), meaning that the cost of moving their home ranges was higher close to roads. Our new OPSCR model provides a data-driven tool to assess the impact of landscape fragmentation on population connectivity at the scale of home range movement using noninvasive spatial capture-recapture data.
Periodic outbreaks of forest insect pests shape northern forest dynamics, yet interactions between multiple insect-host systems-and their role in ecosystem metastability and resilience-remain poorly understood. To elucidate these spatiotemporal interactions, we investigated the coupled dynamics of two dominant insect-host systems-spruce budworm (SBW) associated with late-successional fir and spruce, and forest tent caterpillar (FTC) associated with early-successional aspen. We assess whether asynchronous outbreak patterns shift over time and whether those shifts are consistent with forest compositional change. Using tree-ring data from mixedwood sites across a 20,000-km2 hemiboreal landscape at the United States-Canada border, we reconstructed outbreak histories (1928-2005) and applied multi-scaled analyses guided by resilience theory. We analyzed outbreak dynamics across a continuous range of temporal resolutions, summarizing patterns into short (years), intermediate (decade), and long (multi-decade) windows to evaluate spatial persistence and cross-species correlations, and examined whether patterns over the longest windows align with contemporary forest composition. SBW and FTC cycled independently over short windows, but cross-correlations became increasingly negative as windows lengthened to multi-decadal scales, consistent with compositional feedbacks. Spatial persistence within species shifted from positive over short windows to strongly negative over long windows, where outbreak centers reciprocally inverted between early and contemporary periods-a "trading spaces" dynamic indicative of metastability. These patterns show that insect outbreaks are not passive responses but feedback-driven agents interacting with anthropogenic legacies that accelerate compositional change. Our findings highlight how cross-scale feedbacks involving slow and fast regulatory processes shape disturbance regimes, thus supporting resilience theory and the concept of dynamic stability. Forest homogenization through fire suppression and past logging may collapse the stability landscape into a biphasic regime dominated by SBW and FTC, whereas increasing compositional and structural diversity can expand it into multiphasic regimes that attenuate disturbance amplitudes and promote asynchronous dynamics-underscoring the role of diversity-stability and resilience principles in guiding forest management.
Human-modified tropical landscapes are mosaics of farmland, young regrowing forests, and old-growth forests. These fragmented landscapes are hotter and drier than forested landscapes and, combined with climate change, may lead to shifts in forest community composition. We asked how macroclimate and surrounding landscape shape community-level drought strategies of young regrowing secondary forests. We assessed community composition of 37 young secondary dry and wet forests in Ghana during the first 3 years of succession, collected drought-related leaf and stem traits of their pioneer species, and quantified surrounding landscape cover within an 800-m radius around each plot. Macroclimate had the strongest influence on community drought strategies. Dry forest communities avoided drought through leaf shedding, delayed drought through small compound leaves that reduce heat load, and tolerated drought through dense wood and slow-wilting leaves that both help maintain function during drought stress. Wet forest communities showed the opposite suite of traits, reflecting prioritization of fast growth under high water availability. Landscape context reinforced different forest recovery trajectories by further shaping community traits. Agricultural cover reduced community wood density in the dry forest, whereas it increased wood density in the wet forest and tended to increase drought traits such as small, compound, and deciduous leaves. Surrounding secondary forest cover promoted fast-growing species with acquisitive leaves and low leaf mass per area in the dry forest, likely due to increased propagule pressure of pioneer species. Greater surrounding old-growth cover increased leaf dry matter content in the wet forest, supporting the recruitment of conservative, shade-tolerant late-successional species. Macroclimate, landscape context, and their interaction thus jointly shape community functional composition and drought strategies of regrowing forests.
Top predators strongly influence food webs, often because they reach large body sizes. Amphibians are typically regarded as prey in such systems, but giant salamanders are a rare exception. Because gigantism entails extreme ontogenetic body size variation, it is expected to drive strong trophic niche shifts and reshape interactions within and among species as individuals grow. However, such trophic shifts in giant amphibians and relationships with other consumers remain largely unexplored, limiting our understanding of the contribution of this flagship species to river food web structure. Here, we used stable isotope analysis (δ13C-δ15N) to investigate the trophic structure of a freshwater community dominated by the Japanese giant salamander (Andrias japonicus). We assessed how extreme ontogenetic body size variation modifies intra- and interspecific interactions and contributes to overall community structure. We also quantified the dominant carbon sources fueling the community, and modeled trophic positions (TPs), niche metrics, and relationships of all major consumer species. By sampling 161 giant salamanders and approximately 700 other consumers for stable isotope analysis, we provide the first comprehensive characterization of food web structure in a freshwater community dominated by A. japonicus. We found clear trophic shifts: smaller individuals overlapped with mesopredators (fish, prawns, turtles), suggesting potential competition, whereas TP increased with size, placing larger individuals above other predators, at the top of the food web. Large salamanders broadened the community δ15N range, contributing significantly to the trophic evenness and total community niche space. Basal source tracing revealed that both aquatic and terrestrial energy pathways sustained the food web. Overall, these findings show that gigantism in A. japonicus shapes trophic hierarchies, contributing significantly to vertical complexity and trophic diversity of the community, and highlighting how ontogenetic shifts in giant predators can structure riverine food webs. By integrating isotopic niches, TP, and basal source contributions at the whole-community scale, this study provides a generalisable framework for linking predator ontogeny to food web structure, with direct relevance for conserving vulnerable freshwater ecosystems; endangered top predators such as A. japonicus may contribute disproportionately to food web resilience and community structure.
Understanding how habitat structure affects disturbance dynamics among connected patches is a central issue in ecology. Network theory predicts that a modular arrangement of habitat patches can limit the spread of local perturbations, reducing the probability of large-scale impacts. We performed a field experiment to test whether modular networks were more resistant to the spread of algal turfs compared to random networks within meadows of the seagrass Posidonia oceanica (L.) Delile. Networks were created by manipulating the canopy of P. oceanica to promote the vegetative propagation of algal turfs among network nodes from initially disturbed patches. Algal turfs spread more widely among nodes in random networks, whereas they remained confined within the nodes of the perturbed module in modular networks. Our findings support the hypothesis that modularity is a key trait of ecological networks for mitigating the spread of perturbations and emphasize the importance of considering habitat structure for conservation efforts.
Soil microbiota influence seedling survival and abundance in mature forests. However, their role in tree species turnover during secondary forest succession remains unclear, especially in species-rich tropical forests. We conducted a shade house experiment to assess variation in the direction and strength of net soil microbial effects on seedling emergence, biomass growth, and mortality of seven tree species. We tested for effects of soil successional stage (0, 15, 25, and 115 years of forest recovery), tree species' association with successional stages (home stages where species peak in abundance vs. away stages), and light level (5% vs. 40% of daylight). We quantified net microbial effects as the ratio of seedling performance in live soil (including microbiota) versus sterilized and fungicide-treated soil. We found net positive or net negative microbial effects on seedling performance in six of the seven tree species, highlighting the prevalence of microbial effects. Overall, fewer seedlings emerged and more died in live than sterilized soils, and under high than low-light levels, although these effects varied greatly among tree species. We found no effect of soil successional stage on seedling performance. Tree species' association with successional stages, however, strongly affected seedling performance: Soil microbiota from a species' home successional stage increased the likelihood of seedling emergence by approximately 16% and reduced seedling mortality by approximately 36%. Our results suggest that soil microbiota exert tree species-specific effects on seedling performance during secondary succession of tropical forest. Positive microbial effects on seedling emergence and survival in tree species' home successional stages may promote tree species' establishment and persistence at home stages and could thereby slow tree species turnover during forest recovery. While the generality of our results needs to be tested across forest ecosystems, they highlight the relatively unexplored role of soil microbiota in determining the pace and direction of successional plant community assembly and promote the development of microbial inoculation as a tool for restoration of functionality and biodiversity of forests globally.
Predators are known to impact prey populations through both consumptive and nonconsumptive effects, and the magnitude of prey responses has long been assumed to depend on the lethality of the predator. Yet, there are few, if any studies, that have empirically tested this assumption. While there are studies that have approximated lethality and provide support for this assumption, difficulties arise given there is a need to estimate encounter rates and subsequent predation events while simultaneously separating prey risk responses from such events to truly determine predator lethality. Without the separation of risk responses from predation events, predator lethality may be erroneously assigned; for example, a highly lethal predator may elicit strong and early antipredator responses from prey, reducing actual capture and consumption, making the predators 'seem' less lethal than they actually are. We used a marine crab-snail system consisting of Carcinus maenas or Hemigrapsus sanguineus (crab predators) with Nucella lapillus (snail prey), pairing large and small crabs with large and small snails in a two-phase mesocosm experiment. We first eliminated prey's behavioral risk responses to determine predator lethality and second estimated prey's risk responses after rendering the predators nonlethal. We found that the specific lethality of a predator for a given prey did not drive prey risk responses. Our most lethal treatments (large crabs paired with small snails) had similar risk responses to our least lethal treatments (small crabs paired with large snails). The greatest risk responses came from treatments with large crabs paired with large snails (only medium lethality). Thus, while our results do not support the assumption that lethality itself drives prey risk responses, we did find that overall snails responded the most to the largest predators. This is likely due to the ability of these predators to consume prey over a wide size range and prey's inability to recognize their own relative size. Furthermore, prey state (body size) is clearly an equal if not greater contributor to prey risk responses than a predator's ability to kill.
Identifying the key drivers of changes in species biomass, abundance, and distribution across trophic levels in terrestrial ecosystems represents a fundamental challenge in ecology. The shape of trophic pyramids-reflecting the relative biomass or abundance of various trophic groups, such as herbivores, omnivores, predators, and parasitoids-is anticipated to vary with both the quantity and nutritional quality of plants. However, a comprehensive understanding of how these factors influence the shape of trophic pyramids in grassland ecosystems remains elusive. In this study, we utilize replicated monocultures of 15 herbaceous species in the Inner Mongolian grassland to investigate the effects of plant biomass, macronutrients (including protein, carbohydrate, and phosphorus), and micronutrients (such as sodium) on the structure of arthropod trophic pyramids and the abundances within different trophic levels. Our results demonstrated that plant biomass, leaf protein-to-carbohydrate ratio, and sodium content collectively contributed to a top-heavy structure in arthropod trophic pyramids, characterized by a relatively higher proportion of predators and parasitoids. Specifically, plant biomass enhanced this top-heaviness both directly, by increasing the abundance of predators and parasitoids, and indirectly, by increasing chewing and sucking herbivores, which in turn bolstered the abundance of predators and parasitoids. Furthermore, leaf sodium and the protein-to-carbohydrate ratio positively influenced parasitoid abundance through increasing the abundance of sucking herbivores and endophytes. Given that climate change and human activities, such as nitrogen fertilization and saline water irrigation, are altering plant biomass, nutrient composition, and sodium availability globally, our findings suggest that these changes will have significant cascading effects on arthropod trophic structures and overall ecosystem functioning.
Dispersal regulates patterns of diversity in metacommunities, but a primary focus on dispersal rates may mischaracterize effects that actually arise from dispersal kernels. Kernels describe probabilistic movements between donor and recipient patches, with steep kernels displaying a rapid decline in dispersal probability with distance, and shallow kernels decaying gradually over longer distances. We used simulations to measure how kernels affect diversity across metacommunity scales and ecological contexts, and developed a novel approach quantifying the effects of environmental filtering, competition, stochasticity, and dispersal on fitness. Metacommunities with shallow kernels followed expectations: emigration increased α-diversity but decreased β-diversity and γ-diversity. Metacommunities with steeper kernels did not follow expectations: steep kernels maintained regional diversity by reducing interspecific competition and stochastic extinctions, while weakening the fitness benefits of low dispersal and costs of high dispersal. Our work suggests dispersal kernels and rates jointly regulate exposure to environmental variation and the balance of assembly mechanisms in metacommunities.
Understanding how environmental stress alters the strength of local interactions is key to explaining diversity in current and future plant communities. Along gradients of increasing environmental stress, traditional theory posits that plants experience stronger facilitative interactions and weaker antagonistic interactions. However, it remains unclear whether this pattern extends to the relative host-specificity of plant-microbe interactions along stress gradients. Understanding these dynamics is particularly important for plant interactions with pathogenic and mycorrhizal fungi, which can drive opposing density-dependent processes that shape plant community compositions. We posit that increases in abiotic environmental stress are associated with stronger associations between plants and mutualists as plants increasingly rely on facilitative resource partnerships to cope with abiotic environmental stressors. We tested this prediction along an abiotic stress gradient in the central Cascade Range of Oregon, USA, using overlapping datasets of large high-resolution forest inventory plots, soil chemistry, and amplicon sequencing. Consistent with our predictions, in low-elevation forest stands with benign abiotic conditions and abundant nutrients, tree composition was more correlated with pathogenic fungal composition than ectomycorrhizal fungal composition. However, in forests at high elevations with limited nutrients and harsher climates, tree community composition was more correlated with ectomycorrhizal fungal composition than pathogenic fungal composition. Additionally, we find that spatial aggregation of ectomycorrhizal fungi increases as abiotic stress increases with elevation and opposing patterns of pathogen and ectomycorrhizal relative abundance in different substrate layers. Together, our findings suggest that facilitative interactions in stressful environments extend to mutualist-plant interactions and such interactions play a key role in shaping forest composition along environmental stress gradients.
Dispersal-movement potentially leading to gene flow-is a fundamental ecological process yet notoriously difficult to measure. For solitary bees in particular, determining the spatial scale of dispersal movements and how landscape features influence connectivity is key to achieving conservation goals. Over 2 years, we marked 1698 females of the solitary bee Colletes validus at nesting sites, recaptured marked bees as they dispersed to build nests and as they foraged on flowers, and fit statistical kernels to observed movement distances. In total, we observed 349 dispersal events by 313 individual bees including 13 natal dispersal events (movement from emergence to the first nesting site) and 336 renesting dispersal events (movement among subsequent nesting sites). Solitary bee dispersal kernels were fat-tailed: Most bees made local movements (mean = 143 m), but a small proportion in the distributional tails made substantially longer movements (99% kernel quantile = 1.2 km) and the farthest dispersers were expected to move nearly 3 km. We also recorded 38 foraging movements from nests to flowers by 38 individual bees, allowing us to compare two ecologically distinct movement types. Mean foraging (131 m) and dispersal distances were similar, but upper foraging distances (99% kernel quantile = 554 m) were substantially lower than dispersal. Movement patterns also depended on landscape composition: Both foraging and dispersal movement propensity decreased with increasing inter-patch distance and number of road crossings. Our study highlights fundamental differences in the tails of foraging and dispersal in a central-place forager, demonstrates how landscape features constrain solitary bee movements, and contributes quantitative metrics on the spatial scale of movement for pollinator conservation planning.
Large herbivores are among the most ecologically influential and extinction-prone animals. Megaherbivores, in particular, radically alter vegetation. Yet, few studies have tried to predict the impacts of herbivores-or their extinction-on plant species composition and community structure. First principles suggest that preferred food plants should be most strongly suppressed by herbivores and released by herbivore loss, but this intuition may be misleading if plant responses are strongly contingent on functional traits and/or plant-plant interactions. We sought to predict the responses of plant species to size-selective herbivore-exclusion treatments in an African savanna, using data on herbivore diets and plant functional traits. Our analysis had three stages. First, we identified plant traits that predicted selectivity (use relative to availability) by the dominant herbivore species excluded by each experimental treatment: megaherbivores (elephant, giraffe; ≥1000 kg), mesoherbivores (buffalo, zebra, impala; 40-600 kg), and dik-dik (5 kg). Several plant traits predicted selectivity across multiple herbivore species, but each species' diet was best predicted by a distinctive suite of traits. Second, we tested whether herbivore selectivity alone predicted plant responses. Elephant selectivity uniquely predicted plant responses in exclosures relative to unfenced control plots (R2 = 0.24-0.30); plant taxa strongly favored by elephants were ninefold more abundant inside exclosures. However, herbivore selectivity failed to predict differences in community structure between the different fenced exclusion treatments, suggesting that bottom-up effects of competition may intensify relative to consumptive effects as smaller herbivores are removed. Third, we show that including plant traits as covariates alongside elephant selectivity modestly improved predictability (R2 = 0.27-0.50). Despite various sources of uncertainty and imprecision inherent in our approach, we show that elephant foraging decisions are a major determinant of plant community dynamics. Our findings indicate that models based on readily attainable data can substantially predict plant community responses to the loss or reintroduction of megafauna. Future work can refine our approach by incorporating additional plant traits associated with tolerance and competition, along with mechanistic measurements of herbivore preferences and biomass consumption, to predict even more accurately how large-herbivore population declines and extinctions will impact plant communities.
