Ecological Applications最新文献

Anthropogenic land use change due to farming and livestock grazing has altered biodiversity composition greatly in ecosystems around the world. This is especially true in grasslands and rangelands; however, these ecosystems in high-altitude regions remain understudied. Moreover, anthropogenic effects in these habitats in the long term remain poorly understood. We studied bird densities and composition across four different habitats along a gradient of intensity of land use (crop fields, grazed meadows, grazed steppe, and ungrazed steppe), in the Trans-Himalayan region of Spiti Valley in Himachal Pradesh, India. Started in 2002, this continuing study is one of the longest running bird monitoring programs in India. We found that bird community composition differed significantly along the land use intensity gradient. Although crop fields had the highest bird densities, the bird community here was homogenized, comprising mainly habitat generalist species. Ungrazed steppe harbored more habitat specialist species and high bird densities. Grazed habitats were generally unfavorable for birds, with lower densities and possibly lower species richness. Decadal changes in densities revealed declines in the least used ungrazed steppe habitat, highlighting a possible role of climate change. Our study underscores the importance of land use type in affecting avifauna in the Trans-Himalaya. Holistic land management practices, including continuing traditional (organic) farming and maintaining ungrazed patches in grazed rangelands, could help maintain coexistence between biodiversity and people in these multiuse landscapes.

Anthropogenic activities such as livestock grazing and deforestation are primary causes of land degradation in drylands such as the Sahel Zone of Africa, threatening the livelihoods of rural communities and biodiversity. To restore degraded habitats, measures such as farmer-managed livestock grazing exclusion, where the native vegetation is protected and can naturally regenerate, have been implemented. Yet the benefits of such measures for biodiversity remain poorly understood, especially in regions that experience strong seasonality. Here, we used passive acoustic monitoring to study how livestock grazing exclusion affects the avifauna at the community and species level across the dry and wet seasons. Focusing on an NGO-driven initiative that has implemented a large network of small-scale farmer-managed grazing exclusions in Burkina Faso, we show that species richness and occurrence probability of most bird species were higher in grazing exclusions compared to control sites. These positive effects were more pronounced during the dry season, suggesting an ecological refuge effect when resources are limited. Despite overall positive effects on birds, we found species- and guild-specific responses to grazing exclusion with species positively or negatively affected. While grazing exclusions typically had negative effects on open-habitat specialists, frugivores, insectivores, species associated with woodlands, and Afro-Palearctic migratory species were winners. Grazing exclusions, even at small scale, show a great potential to combat desertification, reverse land degradation and halt biodiversity loss thereby being in line with the UN Decade on Ecosystem Restoration. Yet, we emphasize the need for further studies including a socioeconomic perspective to ensure durable benefits for rural communities.

Integration of agroecosystems and other working landscapes with protected lands and waters is critical to the conservation of Earth's biodiversity. Rice agroecosystems support many species by providing aquatic habitat where natural wetlands have been altered or drained. In regions with long dry seasons, rice fields and associated irrigation canals provide essential habitat for wetland-dependent species. We quantified the spatial scale and magnitude of the effect of rice growing on the growth and survival of the giant gartersnake (Thamnophis gigas), a threatened species that persists primarily in areas of rice agriculture in the Central Valley of California, USA. We used structural causal models to identify drought condition as a key confounder to adjust for when estimating the total effect of rice growing on demographic rates. We analyzed capture-mark-recapture data from 19 populations of giant gartersnakes with an integrated growth–survival model and used distance-weighted covariates to account for the decline in influence of rice with increasing distance from our study sites. We found strong support for a positive effect of rice grown within 1.9 km of a canal on giant gartersnake growth. There was also support for a positive effect of rice on giant gartersnake survival, although the spatial scale extended out to 5 km or more. Our results demonstrate how active rice growing benefits giant gartersnakes inhabiting irrigation canals and demonstrate an approach for studying landscape effects on wildlife in agroecosystems.

Exploring solutions to expanding industrial activities and climate change requires assessments of the combined effects of multiple stressors on wildlife populations. We present a spatially explicit state-space model for the health, survival, reproduction, and somatic growth of individuals in a long-lived, wide-ranging species. The model is applied to critically endangered North Atlantic right whales (Eubalaena glacialis) to investigate the combined effects of three primary stressors affecting the species' viability: entanglements in fishing gear, vessel strikes, and prey availability. We estimate exposure to these stressors in space and time and assess how their effects may combine in the pathway from exposure to vital rates. Results suggest that changes in whale distribution after 2010 led to increased entanglement risk. Poorer prey conditions were associated with an increased effect of carrying fishing gear, but, overall, results on combined effects were not conclusive and depended on model formulation. We also incorporated the estimated effects of stressors into a population viability analysis to explore alternative scenarios of stressor reduction. This integrated analysis highlighted the importance of the declining trend in maximum body length and its effect on reproduction, in addition to the documented impact of entanglements on survival. Model development and application elucidated critical data needs and the influence of underlying mechanistic assumptions. Specifically, models for the combined effects of stressors hinge on the availability of extended longitudinal measurements of individual health and life history outcomes, extensive datasets on the spatiotemporal distribution of stressors, and information on individual space use affecting rates of exposure to stressors. Lessons from this data-rich case study will support the generalization of the modeling approach to other long-lived species where measuring the population-level consequences of multiple stressors directly is unfeasible.

Recent work has highlighted the importance of complex, multi-threaded, sediment, and wood-retentive channels (“stage 0” channel morphology). Widespread channel evolution from a variety of perturbations threatens these crucial habitat types by shifting river channels to higher energy, more erosive environments. In this paper, we expand our understanding of the effects of loss of these resources with a quantitative, multi-decadal dataset of fish and habitats across National Forest sites in the Gulf Coastal Plains of Mississippi. Channel morphological analysis indicated a gradient from incised, wide, shallow channels with coarse substrates typical of advanced channel evolution processes to relatively unincised, narrower, deeper, more sediment, and wood-retaining channels typical of stage 0 conditions. Multivariate analysis of community-scale resource use suggested a gradient from communities which predominately use resources available in more erosive channels to those found in more stage 0-type channels. Regional constrained ordination, intra-watershed meta-analyses, and inter-watershed aggregate analyses all linked the channel morphology erosion gradient to community-scale resource use gradients. Measures of functional versus taxonomic diversity suggest a loss of functional but not taxonomic diversity. Our results demonstrate links between resource types available in channels and how communities structure themselves based on resource use. Further, our results suggest that this initial stage of channel evolution has a different outcome than later stages, which filter out habitat specialists in favor of generalist species. We integrate existing studies of fish community response to channel evolution with our data to build a broader understanding of the process and its ecological impacts in the Mississippi Embayment. Our results have implications for biodiverse and imperiled fish faunas globally.

The American Plains Bison (Bison bison) is recognized as a grassland keystone species; however, their effect on grassland ecosystem function can vary widely among different plant communities, ranging from degradation to enhancement. Grazing dynamics, environmental conditions, and the capacity for plants to compensate for losses due to herbivory largely govern the degree and magnitude of herbivory-induced ecosystem change, making it challenging to manage grazing ecosystems. Here, we examine how different grazing intensities and environmental conditions affect aboveground herbaceous production and herbaceous nitrogen yield within high-elevation, semi-arid grasslands of the Grand Canyon ecosystem in northern Arizona, United States. We conducted a replicate herbivore exclusion experiment in grassland meadows using both long-term exclosures (0.40 ha) and temporary grazing exclusion cages (1 m²) to quantify herbaceous production and nitrogen yield in sites with high bison density (Grand Canyon National Park) and low bison density (Kaibab National Forest). Our goal was to assess the influence of bison grazing on aboveground herbaceous production, the relationship between herbaceous consumption (offtake) and production, and evaluate potential differences in herbaceous nitrogen yield. We found that bison grazing enhanced herbaceous production 1.32-fold and nitrogen yield 1.61-fold, regardless of grazing intensity, availability of soil nutrients, or spatiotemporal variation in climate during our study. Although we expected herbaceous production to decline at the highest levels of herbaceous offtake, we observed a linear positive relationship between offtake and production in Grand Canyon. Over the 2-year study, bison grazing was the primary influential factor explaining variation in grassland production compared to other environmental variables (i.e., temperature, precipitation, and soil nutrients). Our results show no evidence of degradation in aboveground plant productivity, which is an important metric of ecosystem function, from the current dynamics of bison herbivory in the grasslands of the North Rim of Grand Canyon National Park.

The combined effects of coral and macroalgal propagule dispersal, local bistability dynamics and pressures that span the land-sea interface are not well understood, and consequently, are not well accounted for in coral reef management planning. In particular, fishing and sedimentation from nearby watersheds can tip reefs from coral-dominated stable states to macroalgal-dominated stable states. To address these knowledge gaps, we developed a mathematical model of the benthic cover dynamics of a 75-Reef network in Fiji to compare the effectiveness of three different management intervention types: extending the area of periodic fishery closures to encompass more reefs (modeled by increasing herbivore grazing rates; managing a sea-based pressure), improving water quality across Fiji (modeled by decreasing coral mortality rates; managing a land-based pressure) and the two interventions combined (managing land and sea-based pressures simultaneously). We ran the model with three grazing scenarios (low, medium, high) to account for uncertainty in actual herbivore grazing rates among reefs, as well as to represent regimes of macroalgal-dominated, bistable and coral-dominated dynamics in isolated reefs. Our results indicate that the presence of connectivity in the model stabilized the dynamics, with the final benthic cover and management effects exhibiting almost no sensitivity to initial conditions under the medium grazing scenario. The model predicts that the integrated land-sea management is the most effective management intervention for ensuring high coral cover (>30%). We also find that fishery closure management that improves the grazing rate in less than half of the reef network can lead to increases in coral cover across the entire reef network. This result suggests that, as long as a few reefs in the network have high grazing, reefs across the network may trend to high coral cover as long as environmental conditions do not change. Based on an expected value of perfect information analysis, we find that the effectiveness of the integrated land-sea management intervention is robust to the three grazing scenarios and suggests that this model can inform management decisions even with uncertainty. These findings advance our understanding of how a network of ecosystem patches with local bistability could behave and informs their management.

Pesticide contamination in freshwater habitats is a major global issue, affecting water quality, biodiversity, and ecosystem services. Uncontaminated habitats embedded in agricultural landscapes might act as keystone communities, with the ability to restore diversity and ecological processes in contaminated sites through dispersal. Despite their potential relevance, the role of keystone communities in mitigating agrochemical contamination remains untested. We asked if pristine habitats embedded in agricultural landscapes can act as keystone communities and drive the recovery of contaminated habitats. To answer this question, we conducted a mesocosm experiment to simulate zooplankton metacommunity dynamics under three treatments: uncontaminated, fully contaminated, and partially contaminated metacommunities. We examined communities over time following dispersal and pesticide contamination to analyze their trajectories, diversity, and recovery capacity. Analyses were conducted for all species, as well as for Cladocera and Copepoda separately, at both local (individual communities) and regional scales (three communities linked by dispersal—i.e., metacommunities). Taxon-specific population trajectories indicated that cladoceran densities increased across treatments irrespective of contamination, whereas copepods exhibited species-level declines or increases under local pesticide exposure. These taxon-specific population responses to contamination altered community trajectories, resulting in a greater loss of species in completely contaminated metacommunities. Metacommunities with uncontaminated habitats partially recovered from contamination and showed compositional and gamma diversity patterns comparable to uncontaminated metacommunities. Recovery patterns differed across Cladocera and Copepoda, with recovery being more evident at the regional scales. Keystone communities had a greater influence on the recovery of Cladocera community composition and on Copepoda gamma diversity. Our results supported the prediction that keystone communities play a fundamental role in local and regional dynamics of aquatic metacommunities inserted in landscapes with a heterogeneous structure of contamination. Positioning preserved habitats well connected to impacted sites could allow a quick colonization after pesticide contamination, recovering the system until the next crop management cycle. However, taxon-specific trajectories underscore the need to consider functional and dispersal traits when designing mitigation strategies. We thus suggest a metacommunity perspective for better predictions of risks associated with pesticide use in nature and ways of mitigating them.

As coastal restoration projects around the world continue to grow in scale and frequency, it is critical to consider how modified landscapes support wildlife species of concern and broader ecosystem function. In the northern Gulf of Mexico, particularly coastal Louisiana, maintenance of barrier islands serves to protect inland human settlements, and provide critical breeding habitat for many waterbird populations. To remain productive, colonies must also be linked to high-quality marine foraging areas, though these relationships are rarely evaluated in active restoration areas. To demonstrate how this linkage can be evaluated in dynamic environments at a regional scale, we coupled remote sensing and stable isotope data to generate maps of energetic importance for Gulf menhaden (Brevoortia patronus), one of the most ecologically and economically important fish species in the northern Gulf. We then overlaid these maps with foraging movement data from brown pelicans (Pelecanus occidentalis) nesting at three of the largest remaining colonies in the state to assess how a novel characterization of their prey distribution matched individual bird movements. We found that the quality of foraging habitat (i.e., menhaden resource quality) had a significant influence on space use decisions of pelicans over space, time, and multiple scales of movement, as well as strong spatial segregation between colonies, highlighting the importance of island placement when considering restoration priorities and wildlife response. Our results show the considerable potential that “E-scapes” hold as a valuable tool for future restoration planning, with utility in assessment of coastal ecosystem function from a spatially explicit, multi-trophic perspective.

Techniques to estimate the density of unmarked animals are widely used by ecologists, but accurate estimates from these methods rely on assumptions about the study system. We conducted thermal-imaging drone surveys to test the validity of three assumptions for conducting distance sampling on white-tailed deer (Odocoileus virginianus) via nocturnal spotlight surveys in Iowa, USA. We found that the proportion of the population that occurred within forests that are unsamplable (i.e., availability bias) was negligible when vegetative green-up was sparse but increased to more than 50% as spring green-up progressed. The proportion of deer that were bedded, which are less detectable than standing or walking deer, depended on the day of year and time of night, suggesting these variables should be modeled on detection probability to reduce bias in parameter estimates. Lastly, we found evidence of road avoidance which influences how we analyze distance sampling data from road-based survey designs. Each of these deviations from the assumptions of conventional distance sampling informs future sampling design and analysis and will improve the accuracy of density estimates in our system. More generally, our study provides an example of how drone surveys can be conducted to improve density estimation techniques for a range of animal systems.