Ecosphere最新文献

Aquatic invasive species (AIS) threaten biodiversity and ecosystem services around the world, but their management has been hampered by the lack of quantifiable control targets. The introduction of Silver Carp (Hypophthalmichthys molitrix) throughout the mid-western United States epitomizes both the impacts of AIS and the need for quantitative control targets. Silver Carp are large-bodied planktivores that compete with native planktivores, which can cause cascading effects throughout the food web. Our study tested the threshold of abundance beyond which Silver Carp alter fish assemblage structure. We used a community size spectra (CSS) approach to evaluate fish community size structure across temporal and spatial gradients of Silver Carp abundances. We hypothesized that Silver Carp would flatten the size spectra slope because they are large-bodied and feed at a low trophic position. Electrofishing data were obtained for the La Grange Pool of the Illinois River (1994–2021) and for six pools of the Ohio River (2015–2020). Results supported our hypothesis, showing a 98% probability that the relative biomass of Silver Carp is positively related to the CSS slope (resulting in “flattening”). This pattern was strongest in the Illinois River, where Silver Carp made up >30% of fish assemblage biomass in recent years. The pattern was weakest in the Ohio River (78% probability of a positive relationship) where Silver Carp rarely exceeded 20% of total fish biomass. Subsequent changepoint models indicated that a Silver Carp relative biomass of ~24% represents a threshold below which negative food web impacts should be minimized. Our study demonstrates a clear shift in fish community size structure following invasion by Silver Carp and suggests that pre-invasion CSS slopes may serve as a restoration target. It also illustrates the benefits of CSS to guide Silver Carp and other AIS management.

Urban growth is occurring rapidly, and the land use changes associated with urbanization may have consequences for pollinators and the plants that rely on them. Despite its importance in the face of pollinator declines and expanding urban ecosystems, our understanding of the effects of urbanization on pollination mutualisms is scant. There is both evidence that urban areas support diverse pollinator communities and evidence that they degrade them. The influence of urbanization on the pollination of urban plants is even less understood. Urban agriculture relies on plant–pollinator interactions for crop production, providing a relevant framework to study pollination in an urban context. We therefore grew 240 plants across six sites at varying levels of urbanization in Chicago, Illinois, to investigate how urbanization relates to pollination of Cucurbita pepo (squash) and the buzz-pollinated Solanum lycopersicum (tomato). We used a pollen limitation experiment to test whether the reproduction of plants at urban farms is pollen-limited and whether the magnitude of pollen limitation varies with the extent of urbanization (quantified as the percent of surrounding impervious surface around each site). We also examined how pollinator visitation rates vary with urbanization. In S. lycopersicum but not C. pepo, the pollen addition treatment had a consistent and significant positive effect on reproductive success, indicating that plants of S. lycopersicum are pollen-limited in our study area. The magnitude of pollen limitation increased with greater impervious surface, illustrating that S. lycopersicum plants at more urban sites are more pollen-limited. For C. pepo, there was only evidence of pollen limitation at the most urban site, and a weak trend of pollen limitation of fruit set (but not seed set) increasing with impervious surface. Our results demonstrate that urban plants are likely experiencing deficits in pollination services but in ways that vary with both the type of pollination system and the level of urbanization in the surrounding area.

Coastal wetlands are one of the most productive ecosystems on Earth with the capacity to sequester large amounts of carbon dioxide (CO₂). Wetland loss due to anthropogenic and natural causes reduces the carbon (C) storage capacity and potentially releases previously fixed C in biomass and soil to the water column and atmosphere through decomposition. Coastal wetland restoration has the potential to mitigate some of the C losses depending on the balance of C fluxes. However, the role of vegetation and environmental conditions in governing rates of C accumulation in restoration sites is not well resolved. The purpose of this study was to examine seasonal C fluxes, specifically, gross ecosystem productivity (GEP), ecosystem respiration (ER), and net ecosystem exchange (NEE) of CO₂ in unvegetated and vegetated (Spartina alterniflora) areas of a 2-year old created marsh, and S. alterniflora and Spartina patens communities in a “natural” reference brackish marsh. S. alterniflora-dominated areas were sinks for CO₂ in both the newly created and reference marsh with an average CO₂ uptake rate of 7.0 ± 1.0 μmol m⁻² s⁻¹. The unvegetated areas in the newly created marsh and S. patens areas in the reference marsh had approximately net neutral CO₂ fluxes. S. alterniflora areas of the created marsh had similar carbon fluxes to that in the reference marsh, despite a much lower soil organic matter content. Because vegetation develops much faster than soil properties, restored marshes can be a C sink equivalent to natural marshes as soon as the marsh is vegetated. Ecosystem productivity and C assimilation in S. alterniflora areas of the reference marsh were enhanced by lower elevations (up to 6 cm) and higher soil bulk density (up to 0.28 g cm⁻³). At similar elevations, S. alterniflora in both the created and reference marshes was a greater C sink than S. patens areas of the reference marsh. Our findings illustrate that establishment of vegetation is critical to promoting C sink functions in created marshes and, notably, species do matter.

Eradicating feral pigs from island ecosystems can assist in restoring damaged biodiversity values and protect commercial industries such as agriculture. Although many feral pig eradications have been attempted, management decisions are often led by practitioner experience rather than empirical evidence. Few interventions have been guided by population models to identify harvest intensity necessary to achieve eradication within a specified time frame, nor have they applied data on control effort and costs to evaluate the relative cost-effectiveness of proposed control strategies. We used effort and cost data from a feral pig-control program on Kangaroo Island, South Australia, over 17 months to derive functional-response relationships between control effort (in hours per pig) and pig abundance for four control methods: (1) ground-based shooting, (2) trapping with remote triggers, (3) poison baiting, and (4) thermal-assisted aerial culling. We developed a stochastic Leslie matrix with compensatory density feedback on survival to project population trajectories from an initial population (N₀) of 250 female pigs with an estimated island-wide carrying capacity (K) of 2500 over 3 and 10 years for populations subjected to an annual harvest of 35%–95%. We built functional-response models to calculate annual effort and cost for six cull scenarios across all harvest rates. We derived total cost and effort over 3- and 10-year projections from the sum of annual cost and effort within the projection intervals. Pig populations were reduced to <10% N₀ based on harvest rates >80% and 60% for culls of 3- and 10-year durations, respectively. In all scenarios above, the minimum required harvest rate and the total cost to reduce population to ≤10% of N₀ decreased with increasing harvest proportion, with lower total costs incurred over 3 years compared to 10 years. The simulations suggest that the most cost-effective approach for most scenarios is to maximize annual harvest and complete eradication effort over the shortest periods.

Sea otters (Enhydra lutris) were extirpated from much of their range in the North Pacific by the early 1900s but have made a remarkable recovery in Southeast Alaska. Sea otter populations have been particularly successful in Glacier Bay, Alaska, a protected tidewater glacier fjord with a diverse and productive nearshore habitat. Collection of sea otter foraging observations in Glacier Bay began in 1993, along with high-resolution aerial surveys that provide estimates of sea otter abundance and distribution. We integrated these two data sources to investigate how sea otter diet changed in space and time as sea otters established and spread across Glacier Bay. Specifically, we developed a multilevel Bayesian model to capture how sea otter diet at a location (the number, type, and size of prey collected) changed as a function of local cumulative otter abundance and the year in which the location was first occupied. This framework enabled us to estimate the sequence of sea otter prey selection and switching as prey populations responded to sea otter foraging pressure. We found that local sea otter diet changed substantially as the population established, shifting away from large urchins, crabs, and clams to Modiolus mussels and small urchins, and lastly to small clams and Mytilus mussels. We also found that sea otter diet at newly occupied sites changed as otters spread over the main channel and into the arms of Glacier Bay. Further, by 2019, sea otters across the bay were primarily foraging on small prey, regardless of the local occupancy history. The absence of a spatial gradient in the size of prey captured late in the study suggests that feedbacks between the top-down effects of sea otter foraging, sea otter dispersal processes, and local variation in habitat productivity may have homogenized the size structure of available prey across Glacier Bay.

The reproduction of many long-lived plants is highly variable and synchronized, known as masting. Masting is a key driver of plant regeneration dynamics and has cascading effects on food webs and carbon and nutrient fluxes through ecosystems. Masting patterns can respond to changes in climate, but natural long-term variability in masting behavior (i.e., baseline variability) is poorly understood. Here we use tree-rings to create a four-century reconstruction of annual cone production to uncover centennial-scale evolution in masting of Araucaria araucana, a dioecious masting species in South America. Over the last four decades, direct observations of annual cone production in this species revealed remarkable range-wide synchrony of masting. Our tree-ring-based reconstruction places this in a long-term context, revealing that intense regional masting is not a consistent feature of A. araucana reproduction. For extensive periods over the last four centuries, masting has been a site-specific phenomenon, with variability in cone production that was not regionally synchronized. Comparison with regional climate reconstructions indicates that regional synchrony of masting varies with regional temperature trends, including during recent decades. During warmer periods, synchrony is enhanced, and during cooler periods, regional synchrony breaks down. These dynamics have implications for understanding the reproduction of this iconic and endangered tree species and provide evidence of long-term linkages between climate change and masting behavior. Our study demonstrates the potential for novel tree-ring-based reconstructions of masting to reveal crucial insights into baseline variability and the response of masting to climate change.

Tropical peat swamp forests provide many important ecosystem services, especially their function as global carbon sinks. These carbon-rich wetlands are widespread in South America, yet few studies have examined carbon stocks or losses due to land use change. In the lower Amazon, they are being converted to pastures largely utilized by domestic water buffalo (Bubalus bubalis). We quantified carbon stocks in intact peat forests and recently converted pastures (<10 years) at the Lago Piratuba Biosphere Reserve (LPBR) in the lower Amazon of Brazil. The soils of intact forests were typified by shallow organic (peat) horizons at the soil surface. The mean total ecosystem carbon stock (TECS) in intact forests was 354 ± 28 Mg C ha⁻¹. In contrast, the TECS of disturbed sites was significantly lower (p = 0.02) with a mean of 248 ± 17 Mg C ha⁻¹. We estimated greenhouse gas (GHG) emissions from water buffalo (due to enteric fermentation and manure deposition) to be 7.5 Mg CO₂e ha⁻¹ year⁻¹. Considering GHG emissions from this land use, the social carbon costs (SCCs) arising from the degradation of coastal Amazon peatlands are as high as US$2742 ha⁻¹ year⁻¹. The SCC of meat produced from this land use is as high as US$100/kg of meat produced, which far exceeds the economic returns from livestock. Based on the estimated numbers of water buffalo for the southern portion of the LPBR and the time since initial disturbance, the annual GHG emissions from this land use are estimated to be 602,846 Mg CO₂e year⁻¹ with an SCC as high as US$111,526,524 million year⁻¹. This land use also eliminates opportunity values and services of carbon storage and biodiversity that would be possible from a regenerating biosphere reserve.

Introduction and spread of non-native plants provide ecologists and evolutionary biologists with abundant scientific opportunities. However, land managers charged with preventing ecological impacts face financial and logistical challenges to reduce threats by introduced species. The available toolbox (chemical, mechanical, or biological) is also rather limited. Failure to permanently suppress introduced species by mechanical and chemical treatments may result in biocontrol programs using host-specific insect herbivores. Regardless of the chosen method, long-term assessment of management outcomes on both the target species and associated biota should be an essential component of management programs. However, data to assess whether management results in desirable outcomes beyond short-term reductions of the target plant are limited. Here, we use implementation of a biocontrol program targeting a widespread wetland invader, Lythrum salicaria (purple loosestrife), in North America to track outcomes on the target plant over more than two decades in New York State. After extensive testing, two leaf-feeding beetles (Galerucella calmariensis and Galerucella pusilla; hereafter “Galerucella”), a root-feeding weevil (Hylobius transversovittatus) and a flower-feeding weevil (Nanophyes marmoratus), were approved for field releases. We used a standardized monitoring protocol to record insect abundance and L. salicaria stem densities and heights in 1-m² permanent quadrats at 33 different wetlands and followed sites for up to 28 years. As part of this long-term monitoring, in 20 of these wetlands, we established a factorial experiment releasing either no insects (control), only root feeders, only leaf beetles, or root and leaf feeders. We documented reduced L. salicaria occupancy and stem densities following insect releases over time, irrespective of site-specific differences in starting plant communities or L. salicaria abundance. We could not complete our factorial experiment because dispersal of leaf beetles to root-feeder-only and control sites within 5 years invalidated our experimental controls. Our data show that it took time for significant changes to occur, and short-term studies may provide misleading results, as L. salicaria stem densities initially increased before significantly decreasing. Several decades after insect releases, prerelease predictions of significant purple loosestrife declines have been confirmed.

Fungi are considered particularly important in regulating the structure and function of dryland ecosystems, yet the response of dryland fungal communities to global change remains notably understudied. Without a clear understanding of how fungi respond to global change drivers, mitigation plans—required for biodiversity and ecosystem service conservation and restoration—are impossible to develop. In this study, we asked the following: (1) How does the fungal community respond to the individual and interactive effects of physical disturbance and drought in a heterogeneous dryland landscape comprised of drought-adapted shrubs separated by adjacent open areas of soil? (2) What are the larger scale impacts of this response? We assessed fungal communities (using fungal-specific DNA metabarcoding analyses) of surface soil samples in an in situ global change experiment that included disturbance and drought in a full factorial design in the northern extent of the Chihuahuan Desert. We found that the fungal community was spatially heterogenous and remarkably resistant to disturbance and drought. We also show that dryland soils harbor high shares of facultative pathogenic and obligately pathogenic fungal taxa, with several concerning taxa reaching high relative abundances under drought. Our results suggest that the fungal community is highly influenced by microclimatic conditions associated with the presence or absence of vegetation. Moreover, our results imply that the fungal community in our experiment was already adapted to the magnitude of stress imposed by two years of experimental disturbance and drought treatments. Overall, our study shows that the fungal community is spatially heterogeneous and resistant to global change drivers and houses many fungal species known for being stress tolerant and pathogenic.

Interruption of frequent burning in dry forests across western North America and the continued impacts of anthropogenic climate change have resulted in increases in fire size and severity compared to historical fire regimes. Recent legislation, funding, and planning have emphasized increased implementation of mechanical thinning and prescribed burning treatments to decrease the risk of undesirable ecological and social outcomes due to fire. As wildfires and treatments continue to interact, managers require consistent approaches to evaluate treatment effectiveness at moderating burn severity. In this study, we present a repeatable, remote sensing–based, analytical framework for conducting fire-scale assessments of treatment effectiveness that informs local management while also supporting cross-fire comparisons. We demonstrate this framework on the 2021 Bootleg Fire in Oregon and the 2021 Schneider Springs Fire in Washington. Our framework used (1) machine learning to identify key bioclimatic, topographic, and fire weather drivers of burn severity in each fire, (2) standardized workflows to statistically sample untreated control units, and (3) spatial regression modeling to evaluate the effects of treatment type and time since treatment on burn severity. The application of our framework showed that, in both fires, recent prescribed burning treatments were the most effective at reducing burn severity relative to untreated controls. In contrast, thinning-only treatments only produced low/moderate-severity effects under the more moderate fire weather conditions in the Schneider Springs Fire. Our framework offers a robust approach for evaluating treatment effects on burn severity at the scale of individual fires, which can be scaled up to assess treatment effectiveness across multiple fires. As climate change brings increased uncertainty to dry forest ecosystems of western North America, our framework can support more strategic management actions to reduce wildfire risk and foster resilience.