Ecological Applications最新文献

There is substantial interest in restoring tidal wetlands because of their high rates of long-term soil carbon sequestration and other valued ecosystem services. However, these wetlands are sometimes net sources of greenhouse gases (GHG) that may offset their climate cooling potential. GHG fluxes vary widely within and across tidal wetlands, so it is essential to better understand how key environmental drivers, and importantly, land management, affect GHG dynamics. We measured methane (CH₄) and nitrous oxide (N₂O) fluxes at 26 reference and restored tidal wetland sites and eight nontidal pastures (mostly diked former tidal wetlands) in five estuaries in the Pacific Northwest (PNW), USA. We measured fluxes 7–8 times over one year to assess the effects of environmental drivers, wetland type, and land management on CH₄ and N₂O fluxes. Linear relationships between CH₄ fluxes and environmental drivers were poor, but a machine-learning approach with boosted regression trees provided strong predictability for fluxes based upon wetland surface elevation, water-table level, and salinity. Less important variables were groundwater pH, wetland type, and temperature. Under oligohaline conditions, CH₄ fluxes were variable and sometimes very high, but fluxes at salinities above 2 ppt were relatively low on an annual basis. Fluxes of CH₄ were higher in restored tidal marshes and wet pastures than in reference tidal marshes, tidal swamps, and dry pastures. The N₂O model had lower predictive power than the CH₄ model, with wetland type as the most important factor, although N₂O fluxes across all wetland types were low (median of zero). Our results indicate that estuarine hydrologic gradients are a key driver of CH₄ fluxes and that wetland land use impacts on CH₄ fluxes are largely mediated by their varying environmental conditions. In the PNW, estuarine wetlands that have low salinity, lower elevation, and have high water tables are more likely to have increased CH₄ emissions that may offset their carbon sequestration benefits until they gain enough elevation through accretion. This study also provides a transferrable modeling approach to predict the consequences of coastal wetland management on GHG fluxes using monitoring data from a limited set of key environmental drivers.

Globalization has led to a significant increase in the establishment of forest plantations with exotic species and to the accidental introduction of forest insects worldwide. Cumulatively, these factors contribute to the increased occurrence of novel associations between phytophagous insects and trees, leading to new interactions between species that have not historically co-occurred. Here, we reviewed the patterns of novel associations between herbivorous insects and pines and eucalypts at a global scale and identified factors that could favor the occurrence of novel associations and their impacts on forestry. We recorded 766 novel associations of insects with pines and 356 with eucalypts, involving 852 species of herbivorous insects. Most of the novel associations occurred in the Neotropic, Austro-Pacific, and Palearctic regions. In all biogeographic regions, novel associations involved mostly native insects on exotic trees, except for the Nearctic, where exotic insects were dominant. Generalist insects were more frequently involved in novel associations, but specialist ones caused higher damage levels. Foliage feeders and wood and phloem feeders were the most frequent feeding guilds involved in new associations, while sap feeders, shoot feeders, and fruit and seed feeders were rare. For pines, non-native insects were more frequently associated with trees phylogenetically related to hosts in their native range, and native insects were more frequently associated with unrelated hosts. However, for both exotic and native insects, novel associations with eucalypts primarily involved hosts that are unrelated to hosts in their native range. The significance of extensive forest plantations with non-native species and the biogeographic context are emphasized as factors associated with the occurrence of novel associations between insects and trees. This study highlights the importance of international collaboration in forest insect monitoring and surveillance programs to facilitate the early detection of novel associations as an important first step toward minimizing their impact.

Population dynamics are governed by the so-called four BIDE processes: birth, immigration, death, and emigration. However, most population models fail to explicitly consider all four processes, which may hinder a comprehensive understanding of how and why populations change over time. The advent of Integrated Population Models (IPMs) and recent developments in spatial mark–recapture models have enabled deeper insights into demography and dispersal. In this study, we merged both kinds of models into a spatially explicit IPM. By integrating count, reproduction, mark–recapture, and dispersal data, this framework permitted the separate modeling of all BIDE processes, which subsequently allowed (1) a fine-scale estimation of population dynamics and (2) the estimation of central population parameters and stages that have traditionally been elusive in demographic studies but are key to applied conservation, such as the long-term dynamics of floaters (sexually mature non-breeders), sink–source status, and dispersal processes. Using this approach, we carried out a fine-scale assessment of the long-term dynamics and demographic drivers of one long-lived Bonelli's eagle population from Western Europe (1986–2020). Our results illustrated a considerable population decline and subsequent recovery alongside multiple demographic insights scarcely documented to date in long-lived species. First, we reported a decrease and subsequent increase in floater numbers probably associated with parallel changes in the breeding population, hence contributing to the scarce empirical knowledge available about the role and dynamics of floaters. Second, we detected a change in average population functioning from a sink to a neutral contributor, thus shedding light on the flexibility and drivers of sink-source dynamics. Third, we underscored the central role of non-breeder survival for population recovery, suggesting that long-lived species conservation action should not only focus on adult or breeding populations, as is typically the case. Fourth, we quantified the magnitudes and variations of local and dispersal processes in the long term and discussed their potential implications in terms of management implementation. Overall, our study highlights the potential of spatially explicit IPMs to build more complete assessments of population dynamics, contribute to better-informed conservation action, and help fill knowledge gaps in ecological sciences.

Despite extensive studies revealing differences in the composition of aquatic assemblages between restored streams and natural or pre-restoration states, understanding the ecological consequences and trajectories of stream restoration remains challenging. Food webs are an important way of mapping biodiversity to ecosystem functioning by describing feeding linkages and energy transfer pathways. Describing food webs can provide ecological insights into stream restoration. This study analyzed an unprecedented large quantity of food web data (more than 1700 webs) based on long-term (2008–2018) biomonitoring data in South Korea using a feeding link extrapolation. By doing so, we aimed to describe general patterns for the reassembly of aquatic food webs in restored streams. Specifically, we analyzed 12 indices related to the food web structure and robustness of restored streams and compared them with those of natural streams. First, the species richness, link numbers, link density, and connectance of the restored streams were all lower than those of the natural streams, indicating smaller food webs with less complexity. Second, the scaling relationship analyses between the other food web indices and species richness and connectance showed different mechanisms for structuring food webs in restored streams compared with natural streams. In particular, greater generalist feeding by consumers was identified as a major mechanism that increased the connectance of restored streams, which may increase their robustness against external disturbances. The fractions of the top, intermediate, and basal nodes in the restored streams changed rapidly as species richness increased compared with those of natural streams. Food web connectance and robustness in the restored streams tended to increase over time, reaching a level similar to that of natural streams. This suggests that the long-term ecological recovery of the restored food webs is underway. Overall, our findings indicate that restored stream food webs have ecological features distinct from those of natural streams, suggesting high compositional flexibility, and that consumers with a broad diet are the major driving forces behind these differences. Our food web analyses provide a greater understanding of restored streams and help support sustainable stream management through restoration strategies. These results provide new insights into the ecological potential of stream restoration.

Avian biodiversity in agricultural landscapes is declining globally. In Europe and America, agricultural homogenization and the decline of smallholder farming are key drivers of bird population declines. In South Asia, large expanses of compositionally diverse agricultural landscapes still exist. Yet, how resident and migratory avian populations respond to landscape composition and configuration on wintering grounds is largely unknown. Leveraging recent advances in remote sensing, we mapped landscape composition and configuration to analyze their impacts on resident and migratory birds in agriculture–savanna mosaics of western India. We measured landscape composition as the proportional cover of annual crops, semi-perennial cash crops (primarily sugarcane), savanna and woody vegetation, and compositional heterogeneity as the Shannon diversity of these land cover types. We measured landscape configuration as the mean crop field size. We modeled the abundance and richness of 118 resident and 26 Palearctic migratory bird species as a function of landscape composition and configuration. The richness and abundance of resident birds increased with an increasing land cover diversity and an increasing proportion of semi-perennial crops. The richness and abundance of Palearctic migratory winter visitors were negatively affected by increasing land cover diversity. A higher proportion of annual crops was associated with higher resident bird densities, whereas the richness response to the proportion of annual crops remained inconclusive. Guild-based models suggested that migratory carnivores tended to be more abundant in less diverse landscapes with a low proportion of cropland. Open-ground preferring Palearctic species were positively associated with a higher proportion of semi-perennial crops and negatively associated with woody vegetation, while shrub-breeders were positively associated with a high proportion of annual crops and woody vegetation. The effect of mean field size on resident and Palearctic migratory birds was inconclusive. We conclude that (1) winter bird assemblages of resident and migratory species in agriculture–savanna mosaics of western India are driven more by agricultural composition than configuration; (2) resident birds adapt to the high compositional heterogeneity of smallholder agriculture; and (3) Palearctic species primarily rely on compositionally simpler, grassy savannas. Therefore, the maintenance of heterogeneous smallholder agriculture and sparing the savannas from agricultural expansion and afforestation should be key conservation priorities.

Invasive species are an economic and ecological burden, and efforts to limit their impact are greatly improved with reliable maps based on species distribution models (SDMs). However, the potential distribution of new invaders is difficult to anticipate because they are still spreading with few observations in their invaded habitat. Therefore, an accepted practice in predicting the distribution of invasive species has been to incorporate habitat information from its entire geographic distribution (invaded and native ranges) into SDMs. Yet, this approach, due to niche shifts, niche expansions, and data deficiencies, commonly misrepresents where an invasive species is found in its new range. Here, we use time series records (invasion stages) from 13 invasive plant species in North America to explore the tension between modeling invasive species using global range and invaded range data and to determine if there is a “tipping point” at which one SDM strategy performs better than the other in predicting the ultimate distribution. At the earliest invasion stage, models developed using both invaded range and global occurrences on average performed better and had less variability across species than other model strategies at this stage. However, after as few as 100 observations of an invasive plant had been made, US-invaded range models, on average, outperformed global range models and models that combined occurrences. By building models with global and US-scale predictors, we show that higher performance of invaded range models was in part because of greater data quality at the invaded-range scale. Our work demonstrates that after relatively few observations of an invasive species in its invaded range, it is more accurate to model its potential distribution using only information from the invaded range while disregarding information from other regions. This work develops a robust and comprehensive approach to modeling novel distributions of newly observed invasive species.

Atmospheric deposition of nitrogen and sulfur, after land use change, is one of the most impactful stressors to terrestrial biodiversity. Deposition effects on ecosystems are pervasive, impacting species distributions and disrupting natural communities and associated ecosystem services. Decision makers in particular areas have in the past been limited to using critical loads from faraway research sites or from networks of plots that may or may not overlap with or represent their particular management area. That potential mismatch between the management area and available data presents scientific and possibly legal challenges. Here, we develop spatially explicit critical loads using convex hulls to fill this key knowledge gap in the translation of science to decision making. Specifically, we used convex hulls to understand how representative critical loads are to the broader landscape by comparing the environmental conditions from a set of roughly 15,000 sampled locations with critical loads to a broader landscape for which there is no direct sampling. We performed separate analyses for critical loads of forest and grassland biodiversity and of individual herbaceous species. We found that the sampled plots, though unevenly distributed across the landscape, represented forest and grassland canopy communities very well across the contiguous United States aside from areas in the Southeast and the coastal Pacific Northwest. For the 198 species assessed, 161 species (81%) had 50% or more of their historical range inside the convex hull, and 197 species (99%) had 50% or more of their historical range within 1 SD of the convex hull. These results indicate that most critical loads may be used with confidence across species' ranges to support decision making. These results also can guide future sampling efforts in strategic areas. Further, the use of convex hulls as a general tool for other efforts may greatly increase the utility of various existing datasets to support land managers and decision makers charged with protecting ecosystems.

Temperate forest understories hold the majority of the plant diversity present in these ecosystems and play an essential role in the recruitment and establishment of native trees. However, the long-term persistence of diverse and functional forest understories is threatened by the impacts of invasive plants. As a result, a common practice is the removal of the agent of invasion. Despite this, we know little about the success of these practices and lack a comprehensive understanding of what intrinsic and extrinsic factors shape the recovery. In a multiyear field experiment, we investigated (Q1) whether native propagule availability drove native community recovery, (Q2) what the characteristics of successfully recovering communities were, and (Q3) under which environmental conditions native community recovery rates were faster. After initial removal of invasives, we seeded native species to manipulate assembly history and mimic restoration practices, we also implemented a repeated, versus once, removal treatment, all in a full-factorial design. We collected data on plant species composition and abundance (i.e., species level percent cover) and on environmental conditions (i.e., light and soil water availability) in the three subsequent summers. Our results show that native community recovery rates were independent of seeding additions or frequency of invasive plant removal. The fastest rates of recovery were associated with high native species richness, native communities with higher values of specific leaf area (SLA), and low drought stress years. Our results suggest that restoration practices post-invasive plant removal should be tailored to enhance natural dispersal, or artificial addition if the resident community is species-poor, of native species with traits compatible with high resource availability, such as species with high SLA. In addition to the importance of the native community characteristics, our results underscore the need for assessing environmental conditions, favoring management practices during years of low drought stress to maximize native community recovery.

Greater diversity of habitats on islands is often correlated with higher species richness (including endemic and threatened taxa), implying the need to understand species-habitat associations. Such habitat associations could also point toward the role of abiotic filtering and competition in structuring species communities, necessitating the examination of the role of species traits and phylogenetic relationships in intra-island community organization, an aspect poorly examined in the literature. We investigated the composition and structuring of forest bird communities in closely co-occurring evergreen and deciduous forests within South Andaman Island (Indian Ocean), wherein the importance of deciduous forests for birds is undervalued. We sampled 27 transects over 2 years and compared bird species composition and diversity across the two habitats. We examined species-specific associations with habitat (forest) type, basal area, and distance from human settlements, and tested whether these associations were explained by species functional traits and tested for phylogenetic signal after factoring in the effects of environmental predictors. Bird species compositions were markedly distinct across the two habitat types, with deciduous forests having greater taxonomic and functional, but not greater phylogenetic, diversity of forest birds. The distribution of forest birds, including several endemic and threatened species within the island, was largely explained by habitat type (with 39% of the bird species analyzed showing higher occurrence probabilities in deciduous forests), followed by distance from human settlements and basal area. We did not find evidence of species traits or phylogenetic relationships mediating these habitat preferences, perhaps due to a relatively impoverished species pool, as is typical on islands. Nevertheless, our results underscore the value of deciduous forests in harboring high islandic species diversity and being the preferred habitat of several endemic and threatened bird species. Given the historic focus on evergreen forests and the increasing anthropogenic pressure on the forests of the Andamans, we highlight the critical need to include rapidly diminishing deciduous forests in existing conservation plans.

Despite decades of progress, much remains unknown about successional trajectories of carbon (C) cycling in north temperate forests. Drivers and mechanisms of these changes, including the role of different types of disturbances, are particularly elusive. To address this gap, we synthesized decades of data from experimental chronosequences and long-term monitoring at a well-studied, regionally representative field site in northern Michigan, USA. Our study provides a comprehensive assessment of changes in above- and belowground ecosystem components over two centuries of succession, links temporal dynamics in C pools and fluxes with underlying drivers, and offers several conceptual insights to the field of forest ecology. Our first advance shows how temporal dynamics in some ecosystem components are consistent across severe disturbances that reset succession and partial disturbances that slightly modify it: both of these disturbance types increase soil N availability, alter fungal community composition, and alter growth and competitive interactions between short-lived pioneer and longer-lived tree taxa. These changes in turn affect soil C stocks, respiratory emissions, and other belowground processes. Second, we show that some other ecosystem components have effects on C cycling that are not consistent over the course of succession. For example, canopy structure does not influence C uptake early in succession but becomes important as stands develop, and the importance of individual structural properties changes over the course of two centuries of stand development. Third, we show that in recent decades, climate change is masking or overriding the influence of community composition on C uptake, while respiratory emissions are sensitive to both climatic and compositional change. In synthesis, we emphasize that time is not a driver of C cycling; it is a dimension within which ecosystem drivers such as canopy structure, tree and microbial community composition change. Changes in those drivers, not in forest age, are what control forest C trajectories, and those changes can happen quickly or slowly, through natural processes or deliberate intervention. Stemming from this view and a whole-ecosystem perspective on forest succession, we offer management applications from this work and assess its broader relevance to understanding long-term change in other north temperate forest ecosystems.