Ecosphere最新文献

Models of the future of coral reefs are potentially sensitive to theoretical assumptions, variable selectivity, interactions, and scales. A number of these aspects were evaluated using boosted regression tree models of numbers of coral taxa trained on ~1000 field surveys and 35 spatially complete influential environmental proxies at moderate scales (~6.25 km²). Models explored influences of climate change, water quality, direct human-resource extraction, and variable selection processes. We examined the predictions for numbers of coral taxa using all variables and compared them to models based on variables commonly used to predict climate change and human influences (eight and nine variables). Results indicated individual temperature variables alone had lower predictive ability (R² < 2%–7%) compared to human influence variables (6%–18%) but overall climate had a higher training–testing fit (70%) than the human influence (63%) model. The full variable model had the highest fit to the full data (27 variables; R² = 85%) and indicated the strongly interactive and complex role of environmental and human influence variables when making moderate-scale biodiversity predictions. Projecting changes using Coupled Model Intercomparison Project (CMIP) 2050 Representative Concentration Pathways (RCP2.6 and 8.5) water temperature predictions indicated high local variability and fewer negative effects than predictions made by coarse scale threshold and niche models. The persistence of coral reefs over periods of rapid climate change is likely to be caused by smaller scale variability that is poorly simulated with coarse scale modeled predictions.

Reed canarygrass (Phalaris arundinacea L.) is one of the most common invaders of floodplains and wetlands in North America. In the Upper Mississippi River floodplain, invasion by reed canarygrass in forest understories can inhibit forest regeneration when gaps form in the overstory. Understanding the distribution of reed canarygrass in forest understories is essential for effective management and control. We used an ensemble of species distribution models including Bayesian additive regression trees, boosted trees, and random forest algorithms to predict habitat suitability for reed canarygrass in forest understories across the Upper Mississippi River floodplain (~41,000 ha). Data from forest inventory study plots with reed canarygrass presence and absence were combined with 10 hypothesized environmental predictors of reed canarygrass invasion. We applied three approaches to better understand and incorporate the influence of spatial autocorrelation among our predictor variables, including random cross-validation, spatial cross-validation, and spatial cross-validation with Euclidean distance fields. Flood frequency, distance to contiguous floodplain, distance to forest edge, and distance to invaded wet meadow were among the most important environmental predictors across the three algorithms. Generally, the mean probability of reed canarygrass presence decreased with increasing flood depth, distance to contiguous floodplain, distance to invaded wet meadow, forest cover, and forest height, while relationships with other predictors were more variable. The ensemble of the three models (i.e., the average prediction) was used to map and summarize potential reed canary grass habitat suitability across the landscape. The maps generated quantified the habitat suitability for reed canarygrass and areas of agreement among the models in forest understories across the floodplain. This information can be used to better understand the extent of invasion, prioritize restoration efforts, and develop further research.

Parrot feather (Myriophyllum aquaticum) is an introduced, noninvasive amphibious plant found in coastal provinces, but it has the potential to become an invasive species in China. The plant is heterophyllous, with both emergent (aerial) and submerged (aquatic) leaves, and has two distinct root types: aquatic (adventitious) and edaphic (sediment) root systems. This morphological plasticity allows M. aquaticum to effectively absorb nutrients from different layers of the environment, making it a suitable model plant for exploring nutrient dynamics in both water and soil systems and investigating how wetland plants respond to cultural eutrophication. We designed an outdoor mesocosm experiment to assess plant growth traits and root topological indices in response to different nitrogen (N) and phosphorus (P) concentrations. The results indicated that the plant has a high tolerance to N loading. In contrast, the P content had greater impacts than the N content on plant growth and root topological indices, indicating that the P content was the main influencing factor affecting and suppressing the development of M. aquaticum. The aquatic or edaphic root branching did not change, but the aquatic root topology of M. aquaticum exhibited similar stable trends with increasing P concentration, indicating typical herringbone branching; additionally, its edaphic roots exhibited decreasing topological indices, indicating more typical dichotomous branching with increasing P concentration. The plant has a high tolerance to N, and it may become invasive following the current trend of increasing cultural eutrophication.

Mycoplasma ovipneumoniae is a primary causative agent responsible for initiating polymicrobial pneumonia in bighorn sheep (Ovis canadensis). Infections of bighorn sheep populations are typically characterized by initial all-age epizootics followed by long-term periods of repressed juvenile (lamb) survival. Populations of bighorn sheep in New Mexico, USA, were thought to be free of this pathogen prior to 2017 but recent infection of multiple herds raised concerns regarding impacts on population size and juvenile:female ratios. Using aerial survey, survival, and disease sampling data in an exploratory framework, we (1) characterize age-related differences in M. ovipneumoniae prevalence and seroprevalence, (2) quantify differences in lamb:ewe ratios pre- and post-M. ovipneumoniae detection, and (3) investigate differences in survival between previously exposed and naïve individuals. From 2007 to 2022, we sampled 466 bighorn sheep across 19 populations in New Mexico for M. ovipneumoniae exposure. While the timing of initial herd infections varied across populations, one population sustained active infections for over 15 years. We found reduced juvenile:female ratios post M. ovipneumoniae exposure for both desert (O. c. mexicana) and Rocky Mountain (O. c. canadensis) bighorn sheep populations. Post-exposure ratio declines ranged from 20% to 69%. Evaluation of population size and environmental condition effects on juvenile:female ratios indicated varying impacts for each subspecies. Notably, population size was negatively related to Rocky Mountain juvenile:female ratios only after populations were exposed to M. ovipneumoniae. Additionally, climatic conditions in the previous lambing season and pre-parturition time frame were associated with juvenile:female ratios for Rocky Mountain populations, while juvenile:female ratios of desert bighorn appeared to only be affected by pre-parturition climatic conditions. Kaplan–Meier survival estimation of previously exposed, but putatively recovered, individuals (n = 31) and naïve individuals (n = 70) revealed lower (75%; 95% CI: 62%–93%) but not statistically significant (p = 0.2) 1-year survival rates for individuals that were seropositive but not actively infected, when compared to seronegative individuals (88%; 95% CI: 81%–97%). These results collectively suggest that following M. ovipneumoniae introduction, bighorn sheep populations in New Mexico could be limited by lamb survival.

Invertebrates have a central role in food webs and ecosystem functioning. By boosting productivity, allochthonous nutrient inputs influence the food webs of recipient communities. Understanding how allochthonous nutrient subsidies affect invertebrates is crucial, particularly in highly productive coastal areas. Here, we examine how mangrove macroinvertebrates are impacted by nutrient-rich guano delivered by nesting seabird populations at Aldabra Atoll in the Indian Ocean. We compare nitrogen and carbon stable isotope ratios and nitrogen composition of basal resources and macroinvertebrate consumers in mangroves with and without nesting seabirds. Seabird-derived nutrient enrichment increased the nitrogen content of basal food sources and herbivorous littorinid gastropods and sesarmid crabs. In mangroves with breeding seabirds, mean carapace widths of sesarmid and omnivorous portunid crabs were 6% and 11% larger, respectively. Isotopic niches of littorinid gastropods and sesarmid crabs were larger and had higher overlap at seabird compared to non-seabird sites. Epiphytic macroalgae and guano comprised >50% of resource contributions to littorinid gastropods and sesarmid crabs at seabird sites. This differed markedly from non-seabird sites where the main resource contributions were 77% mangrove leaves for littorinid gastropods, 36% sediment organic matter, and 41% mangrove leaves for sesarmid crabs. The increased sizes of mangrove crabs suggest that seabird nutrient enrichment can promote mangrove crab fisheries productivity and benefit the provisioning of mangrove ecosystem services. By shifting resource use of functionally important macroinvertebrates, we discuss how seabirds modify trophic interactions, with potential consequences for mangrove ecosystem processes and resilience.

The Belowground Ecosystem Resiliency Model (BERM) is a geoinformatics tool that was developed to predict belowground biomass (BGB) of Spartina alterniflora in salt marshes based on remote sensing of aboveground characteristics and other readily available hydrologic, climatic, and physical data. We sought to characterize variation in S. alterniflora BGB over both temporal and spatial gradients through extensive marsh field observations in coastal Georgia, USA, to quantify their relationship with a suite of predictor variables, and to use these results to improve performance and expand the parameter space of BERM. We conducted pairwise comparisons of S. alterniflora growth metrics measured at nine sites over 3–8 years and found that BGB grouped by site differed in 69% of comparisons, while only in 21% when grouped by year. This suggests that BGB varies more spatially than temporally. We used the BERM machine learning algorithms to evaluate how variables relating to biological, climatic, hydrologic, and physical attributes covaried with these BGB observations. Flooding frequency and intensity were most influential in predicting BGB, with predictor variables related to hydrology composing 61% of the total feature importance in the BERM framework. When we used this expanded calibration dataset and associated predictors to advance BERM, model error was reduced from a normalized root-mean-square error of 13.0%–9.4% in comparison with the original BERM formulation. This reflects both an improvement in predictive performance and an expansion in conditions for potential model application. Finally, we used regression commonality analysis to show that model estimates reflected the spatiotemporal structure of BGB variation observed in field measurements. These results can help guide future data collection efforts to describe landscape-scale BGB trends. The advanced BERM is a robust tool that can characterize S. alterniflora productivity and resilience over broad spatial and temporal scales.

Understanding the causes of mortality for a declining species is essential for developing effective conservation and management strategies, particularly when anthropogenic activities are the primary threat. Using a competing hazards framework allows for robust estimation of the cause-specific variation in risk that may exist across multiple dimensions, such as time and individual. Here, we estimated cause-specific rates of severe injury and mortality for North Atlantic right whales (Eubalaena glacialis), a critically endangered species that is currently in peril due to human-caused interactions. We developed a multistate capture–recapture model that leveraged 30 years of intensive survey effort yielding sightings of individuals with injury assessments and necropsies of carcass recoveries. We examined variation in the hazard rates of severe injury and mortality due to entanglements in fishing gear and vessel strikes as explained by temporal patterns and the age and reproductive status of the individual. We found strong evidence for increased rates of severe entanglement injuries after 2013 and for females with calves, with consequently higher marginal mortality. The model results also suggested that despite vessel strikes causing a lower average rate of severe injuries, the higher mortality rate conditional on injury results in significant total mortality risk, particularly for females resting from a recent calving event. Large uncertainty in the estimation of carcass recovery rate for vessel strike deaths permeated into the apportionment of mortality causes. The increased rates of North Atlantic right whale mortality in the last decade, particularly for reproducing females, has been responsible for the severe decline in the species. By apportioning the human-caused threats using a quantitative approach with estimation of relevant uncertainty, this work can guide development of conservation and management strategies to facilitate species recovery. Our approach is relevant to other monitored populations where cause-specific injuries from multiple threats can be observed in live and dead individuals.

Invasive shrubs dramatically reduce the biodiversity of native plants, making invaded areas important targets of conservation and restoration. Adding seeds of native plant species, in addition to the removal of invasive plants, is a potentially promising means for restoration of native plant communities. However, because seed survival may vary among seasons, it is essential to understand temporal patterns of seed survival. For example, dense habitats created by invasive shrubs exhibit seasonal changes in structure and food resources that could create seasonal variation in seed survival by altering the activity and abundance of native seed-eating rodents. Despite the potential for invasive shrubs to generate seasonal changes in granivory, we lack experimental studies to evaluate changes in granivory caused by invasive plants over a full year. We mechanically removed the widespread invasive species common buckthorn (Rhamnus cathartica) from half of 14 sites (20 × 20 m) in a deciduous oak-maple forest to track rodent and arthropod granivory of three native tree species, basswood (Tilia americana), black cherry (Prunus serotina), and sugar maple (Acer saccharum), and the invasive shrub R. cathartica over a year. Our results reveal that the effect of invasive shrubs on granivory changed across seasons. Seeds in invaded habitats experienced, on average, 25.9% higher seed removal than seeds in areas with R. cathartica removed, with the largest difference in removal occurring in winter. Seed removal was almost entirely due to rodent granivores that removed seeds at similar rates among species. These results indicate that, following removal of invasive shrubs, sowing seeds in winter may optimize seedling establishment by minimizing granivory. Our findings further reinforce the importance of removing invasive shrubs as an important restoration tool because invasions may amplify granivory throughout the year. Understanding the mechanisms that could be affecting seasonal granivory within invaded systems, the important role of rodent granivores, and the similarities in seed consumption between native and nonnative seeds is critical for continual conservation and restoration efforts aimed at promoting forest regeneration.

Fire is crucial for maintaining species diversity and resilience in fire-adapted shrublands of the world's Mediterranean climate zones (MCZs), which include the chaparral shrublands of the North American MCZ. Chaparral is adapted to high-intensity burning, with relatively long intervals between fires (30–100 years) typifying undegraded conditions. Modern fire frequencies are much higher in chaparral, driven largely by high densities of human ignitions and coincidence between ignitions and severe weather conditions. This change in the fire regime has major implications for biodiversity, leading to exotic invasion, decreased ecosystem services, and potential type conversion of shrubland to grassland dominated by exotic species. We studied the impact of increased fire frequencies on the composition and abundance of herbaceous and woody species in the Interior Coast Range of northern California. Our study area is one of the most frequently burned areas in California, which allowed us to investigate higher fire frequencies than previously published in the scientific literature for California. We surveyed fifty-four 250-m² plots to assess changes in plant community composition and postfire regeneration of chaparral shrubs across a wide range of fire frequencies, including plots that have burned up to six times in the past 30 years. Our findings reveal that short-interval fires significantly reduced postfire native woody regeneration, with obligate seeding species experiencing a 99% reduction and facultative species showing an 83% reduction in regeneration in the most frequently burned plots. Moreover, the overall marginal effect of one additional fire since 1985 decreased the proportion of native species cover by 12% and both richness and Shannon diversity by 4%. Consequently, areas with higher fire recurrence supported a more structurally and botanically homogeneous landscape dominated by a homogeneous group of non-native species.

The soil microbiome provides essential services in agroecosystems that can increase plant health and productivity, such as disease suppression and growth promotion. A small number of microbial groups have been proposed as main players behind disease suppression, but the complete picture of the underlying mechanisms remains unclear for both functions in many soil systems. Here, we investigated broad and fine-scale microbial community features for their contributions to disease suppression and growth promotion for potato plants. In a greenhouse study, we grew potato plants in pots sharing a common background soil and inoculated with living soil microbial communities with or without a separate inoculation with Streptomyces scabiei, the causal agent of potato common scab disease. The suppression of common scab and growth promotion abilities of a variety of soil microbial communities were estimated and related to quantitative patterns in microbial community structure. We found that suppression of common scab was mostly driven by fine-scale microbial community features, especially the diversity within the Actinomycetota phylum. Even though opposing components of microbial community structure might be related to the two functions, disease suppression did not cause a negative trade-off in growth promotion. This suggests high functional redundancy in growth promotion. It may be possible to improve the multi-functionality of soil microbial communities by engineering the communities toward optimized disease suppression and growth promotion ability.