Ecological Applications最新文献

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.

While it is widely recognized that reduced river-floodplain connectivity has contributed to the decline of biodiversity in floodplain rivers, surprisingly few studies have quantified the relationship between connectivity, pool persistence, and fish assemblage structure to the level required to generate measurable targets for management. The task is further complicated by the inherent complexity of accurately describing fish assemblages. We maximized our capacity to describe unbiased hydrology–fish relationships by sampling fish assemblages in floodplain pools with a variety of connection histories (60 sampling events), and by using a hierarchical multispecies occupancy model that accounts for changes in sampling design and species detection. Our study was conducted in a tropical wet-dry river threatened by water resource development and elevated temperatures associated with climate change, the Fitzroy River (Western Australia). Our results revealed that wet season (river-floodplain connectivity) and dry season (pool persistence) components of the hydrological cycle influenced fish occurrence in floodplain pools. Pools that were connected to the river by short distances were substantially more species rich than distal pools. This effect was strong at distances <2000 m but negligible at distances greater than 3000 m. Species richness in floodplain pools increased when wet season connection to the river lasted more than 25 days, and when river stage height exceeded 6 m. Prolonged connection to the river (up to 90 days) during overbank flooding (river stage height >11 m) maximized fish species richness in floodplain pools. Dry season components of the hydrological cycle also influenced fish assemblage structure, with pools that persisted during the preceding dry season twice as species rich as those that dried. Our model revealed that sampling gear influenced species detectability, indicating that accounting for variable detection is critical when assessing fish assemblage structure. Given that large flood events are less likely to be impacted by water take, we recommend that managers seeking to maintain floodplain fish diversity ensure that water resource development does not negatively impact pool persistence during the dry season.

Seamounts are unique habitats in the deep sea facing anthropogenic stressors, including future deep-sea mining. To conserve patchy marine habitats such as seamounts, it is critical to design conservation area networks that maintain connectivity by larval dispersal. This study conducted biophysical modeling to quantify larval dispersal among 18 seamounts in the Northwest Pacific, within the scope of a regional environmental management plan for mining under development by the International Seabed Authority. Seamounts formed a single dispersal network, but excluding seamounts with mining potential showed the network could become fragmented. Two seamounts whose mining potential was relinquished in 2024 were identified as key stepping stones, suggesting that environmental conservation at these two seamounts can contribute to maintaining a single dispersal network. Predominant eastward or westward currents, likely related to the North Equatorial Intermediate Current, made the upstream, distant seamounts vital larval sources. Trajectories of Argo floats and gene flows of amphipods provided physical and biological support for the modeled dispersal. This study highlights the potential for effective conservation area placement based on a seamount network connected by upstream-based larval dispersal.

River-floodplain ecosystems near urban centers are heavily engineered for flood protection and water delivery, which has led to a loss of lateral hydrologic connectivity between rivers and their floodplains. This study has two objectives: (1) Does increased lateral connectivity resulting from floodplain inundation increase chlorophyll a biomass? (2) Does that bump in chlorophyll a get transported downstream? The San Francisco Estuary in California, USA, has a robust and long-term monitoring network for water quality. We integrated water temperature, chlorophyll a, flow, and floodplain inundation data from multiple sources creating a continuous dataset with fine temporal resolution spanning two decades. We used a consistent generalized additive mixed model structure across three regions: the floodplain, the mainstem of the river adjacent to the floodplain, and the section of the river downstream from both the floodplain and mainstem. We found that when the floodplain is not inundated, chlorophyll a biomass is mainly influenced by water temperature. However, when the floodplain is laterally connected during periods of inundation, water spreads over a larger surface area in the floodplain, flows decrease and water temperatures increase creating favorable conditions for chlorophyll a production. High flows during the flood pulse quickly transport chlorophyll a downstream, flushing the estuary with food. Under optimal conditions, tidal mixing in the downstream portion of the estuary can continue to boost chlorophyll a biomass in the system even after the flood waters have retreated. This study can guide the design, enhancement, and management of water conveyance structures to meet environmental flow regulations and to benefit the estuarine food web.

Quantifying the impact of lower trophic level species abundance on higher trophic level predators (and vice versa) is critical for understanding marine ecosystem dynamics and for implementing ecosystem-based management. Trophic ecosystem models generally predict a tight coupling between prey and fish predators, such that higher abundance of lower trophic species increases the abundance of higher trophic level predators. This assumes that predator feeding rates are limited by prey availability to some degree. Despite being a key component of predator–prey interactions and multispecies fisheries management, relatively few studies have assessed the impacts of prey availability on predation patterns of mobile, generalist fish predators using spatiotemporal models and local-scale stomach content, predator, and prey data. In this study, we explore the association between local density of key prey and predator stomach contents, and predator–prey spatiotemporal overlap and predation indices, using the Baltic Sea as a case study. We use three decades of spatially resolved biomass and stomach content data on Atlantic cod (Gadus morhua), and biomass data on three of its key prey: herring (Clupea harengus), the isopod Saduria entomon, and sprat (Sprattus sprattus). Using geostatistical generalized linear mixed-effects models fitted to relative biomass density and prey-mass-per-predator-mass, we estimate spatiotemporal trends and annual indices of biomass- weighted and area-expanded per-capita and population-level predation, predator–prey overlap, and the correlation between these indices. Range shifts have resulted in reduced predator–prey overlap over time, which is now the lowest in three decades. For Saduria, we find an association between prey availability and stomach contents, but not for herring or sprat. Similarly, only in Saduria do we find a positive correlation between population-level predation indices and the spatiotemporal overlap. Although behavioral interactions with pelagic prey are challenging to infer from stomach content and acoustic data due to high mobility leading to fine-scale spatiotemporal mismatch, the weak connection with local-scale availability, and low correlation between population-level predation and spatial overlap, could imply weaker coupling between pelagic prey and cod than previously thought. These findings provide key information on the strength of species interactions, which is crucial for the continued development of multispecies models and ecosystem-based fisheries management.