Ecosphere最新文献

We created the first annually resolved records of historical fire occurrence coupled with precise estimates of tree establishment for the northern half of the west slope of the Oregon Cascades, a region that is home to some of the most productive forests on earth. Our reconstructions at 36 randomly located sites document exceptional diversity in historical fire disturbance and successional dynamics. Most stands where we collected data appear to have initiated following stand-replacing fire between 200 and 750 years ago, although many sites exhibited evidence of moderate-severity fire that created multi-aged stands. More than two-thirds of sites experienced multiple non-stand-replacing fires following stand initiation. A spatial generalized linear mixed model demonstrated that historical fire occurrence was negatively associated with average snow disappearance day and time since last fire and positively associated with drought. Significant variability in the number of fires, length of fire return intervals, and sample depth across sites made calculation of informative mean fire return intervals (MFRIs) difficult. Site-level annual probability of fire from our mixed model ranged from 0.039 to 0.003, equivalent to MFRIs of 26–389 years. We used fire and tree establishment records to infer the general location of several large historical fire events that likely burned as much or more area as the >50,000 ha fires that burned across our study region in 2020. We also identified periods of extensive burning and subsequent tree establishment that occurred across seven centuries within six large river drainages that made up our study region. Although tree establishment occurred for up to a century following stand-replacing fire at some sites, we show that these apparent long periods of establishment were relatively short pulses of regeneration separated by reburns. This study demonstrates that many highly productive Douglas-fir-dominated stands in western Oregon are significantly departed from historical fire disturbance regimes. Management that emphasizes rapid re-establishment of closed canopy forest conditions following fire and development of old-growth forest conditions in the absence of fire may fail to provide for the unique and highly valued ecosystem services associated with these forests.

Studies of biodiversity loss commonly imply that species extinctions occurred as a direct result of initial human arrival and thus are attributable to stewardship failures of Indigenous Peoples. However, recent studies have suggested this assumption is not supported by the evidence, prompting a global reevaluation of existing assumptions. To assess the relationship between human arrival in the Hawaiian Islands and documented declines in waterbird biodiversity, we reviewed empirical evidence from paleoecological studies. We first identified the time period that extinct Hawaiian waterbird species were last observed within the fossil record. We then evaluated four hypotheses proposed to explain drivers of Holocene waterbird extinctions: (1) the overkill hypothesis; (2) the deforestation hypothesis; (3) the climate change hypothesis; and (4) the species introductions hypothesis. Of the 18 extinct waterbird species evaluated in this study, 10 were last observed in the fossil record prior to Polynesian arrival, 6 were last observed in the fossil record during the Polynesian era, and 2 were last visually observed after European arrival. Extinctions that possibly occurred during the Polynesian era were likely caused by a suite of factors, some anthropogenic and some non-anthropogenic. Our findings contradict previous studies that attributed Holocene waterbird extinctions to hunting and deforestation by Native Hawaiians and suggest a future line of inquiry regarding a proposed “regime shift extinctions” in hypothesis to explain complex impacts of human-mediated and climatic drivers of extinction in the Anthropocene.

The miombo woodlands, which span about 10% of the African continent, are essential for the ecosystem services they provide. These woodlands are mainly dominated by the genera Julbernardia, Isoberlinia, and Brachystegia. However, there is limited understanding of how species dominance and richness change in relict sites, which are far removed from the core miombo woodlands. In this study, we anticipated that relict sites would show reduced species diversity due to their isolation from the core miombo woodlands and their exposure to different species compositions. We sampled vegetation using modified Whittaker plots (50 m × 20 m) across four sites: core miombo woodland (n = 14), miombo edge (n = 19), Mozambique relict (n = 18), and South Africa relict (n = 21). Within each plot, we measured tree height, basal diameter, and canopy dimensions for mature trees; root collar diameter for saplings (20 m × 5 m subplots); and recorded seedling species and counts (in 5 m × 2 m subplots). Temperature and rainfall gradients were also assessed across the sites. Species richness, Shannon–Wiener diversity, and species evenness were compared between sites using one-way analysis of variance (ANOVA). Species composition differences between sites were evaluated using analysis of similarity (ANOSIM). Our results revealed a pattern where species richness, the Shannon–Wiener index, and evenness increased with decreasing relict size. Interestingly, evenness declined from juvenile to adult stages within sites, suggesting changes in species composition over time. Significant differences in species composition were observed between sites, with the most pronounced dissimilarities between the core miombo woodland and Mozambique relict. Our findings highlight that while key miombo species remained dominant and important, the relict sites demonstrated increased species richness. This suggests that these isolated sites might harbor high biodiversity, potentially due to their high perimeter-to-area ratio, which makes them more susceptible to species invasions. Additionally, the warmer temperatures recorded at the relict sites could be driving thermophilization, further contributing to the richness and diversity observed. These insights are crucial for informing conservation strategies for miombo woodlands and their relicts in the face of ongoing climate change.

The increasing societal demands on the seabed due to the expansion of offshore wind energy highlight an urgent need to better understand the relationship between human activities and the structure and function of seabed ecosystems. In this paper, we propose an empirically derived approach to quantify relative ecological risk to benthic invertebrate assemblages from future offshore wind development. Using benthic data from over 22,000 seabed grab samples across the UK shelf and wider North Sea contained in OneBenthic, a freely available online data repository, we produce modeled raster layers for three biological criteria upon which we define ecological risk. These are (1) relative benthic sensitivity based on response traits expression, (2) benthic biodiversity, and (3) assemblage rarity. We create a holistic map based on these three layers and discuss how this information may be used, using a new online tool, to assist decisions regarding future offshore development to minimize potential impacts on benthic assemblages. Given the broad spatial coverage of our maps, our tool could help expedite the expansion of offshore wind in a large area of the northeast Atlantic, whilst the underlying methodology can be applied to other regions with extensive benthic survey data, thereby facilitating international commitments to reduce carbon emissions. We propose how the maps may be improved and discuss the future incorporation of extra criteria into the framework.

The operational sex ratio (OSR), that is, the local ratio of fertilizable females to sexually active males at any given time, is of key importance for the strength of sexual selection and the reproduction of populations. We hypothesize that sex-specific cohort splitting, that is, when one sex mostly metamorphoses while the other mostly enters diapause, may lead to OSR bias in nature. The OSR of an aquatic moth, Acentria ephemerella, has been shown to be strongly male-biased in situ. Here, we use a mesocosm experiment in which we determine the sexes of active, diapausing, and metamorphosing larvae to test whether the male bias in Acentria is due to sex-specific mortality or sex-specific cohort splitting. Fish predation did not result in a strong male bias of the whole population but increased male bias in pupae and female bias in diapausing larvae. The opposite effect of fish on pupal versus diapausing larval sex ratios suggests that fish-induced sex-specific cohort splitting, rather than sex-specific mortality, caused the OSR bias of Acentria observed in situ. Future research needs to study whether the OSR bias is an adaptive response to the presumably higher fish predation pressure on females or a maladaptive byproduct of sex-specific activity and growth responses to fish presence. Overall, shifts in OSR due to sex-specific cohort splitting could be a more common component of arthropod life histories than previously thought.

We report direct measurements of changes in diving and movement behavior for 53 goose-beaked whales (Ziphius cavirostris) in relation to experimentally controlled mid-frequency (3–4 kHz) active sonar (MFAS) signals. These signals simulate powerful Navy sources that have been associated with multiple mortal stranding events for this species. We deployed a multi-scale combination of tags to monitor individual whales, including 50 long-duration (weeks), coarse-resolution satellite-transmitting tags and 3 short-duration (hours), high-resolution archival depth, orientation, and acoustic tags. We evaluated behavioral responses during 13 experimental trials (9 MFAS; 4 no-MFAS controls), resulting in 72 exposure events; some individuals were exposed in multiple trials. Whales were exposed at known and modeled horizontal ranges from ~2 to >200 km and from below ambient noise levels to received levels (RLs) up to ~142 dB re: 1μPa (root-mean-square [RMS]). We investigated changes in diving and movement behavior separately, with a suite of metrics, descriptive evaluations, and statistical tests. We observed similar patterns and probabilities of behavioral changes for control trials and the lowest RL conditions (<100 dB). Above 100 dB RLs, increasingly prevalent and consistent responses occurred, including extended deep dives, prolonged periods between deep dives, directed spatial movement away from the source, and cessation of echolocation. Aspects of these cryptic responses typically persisted for hours following exposure but did not result in broad-scale habitat abandonment. Our study builds upon experimental and observational studies conducted on sonar testing ranges and expands our understanding of the response of this species to MFAS in a region where operational sonar use occurs far less commonly than on Navy testing ranges. These data are directly applicable in the conservation and effective management of this sensitive, protected species.

Climatic extremes can impact the productivity of aquatic species, affecting ecosystems and fishery-dependent communities. Advances in climate products, such as gridded datasets and downscaled projections, may be useful for quantifying freshwater habitat conditions and predicting climate change effects on fish. However, limited guidance exists for selecting climate products to develop indicators of freshwater habitat conditions that influence fish population dynamics. Here, we develop an approach for identifying streamflow and stream temperature models to address this need. We evaluated skill in predicted versus observed streamflow and stream temperature, with predictions depending on different models and gridded climate data as inputs. The best performing models were used in a case study exploring habitat conditions influencing Chinook salmon in the Yukon and Kuskokwim River basins, two remote high-latitude watersheds with few in situ habitat observations and recent salmon declines. Three modeled streamflow datasets had variable performance (median Nash–Sutcliffe efficiencies from 0.39 to 0.70). Three gridded temperature products differed in their ability to explain variation in weekly stream temperatures (median r² from 0.42 to 0.76). We selected a single gridded air temperature dataset to compare two novel predictive stream temperature models, both of which had good accuracy (root mean squared error [RMSE] of 1.19 and 0.95°C). Stream temperature indicators calculated from modeled daily data, maximum temperatures during adult migration and cumulative temperatures during juvenile rearing, had high spatial correlation across tributaries within the Yukon and Kuskokwim River basins and showed significant warming over the past 40 years. Streamflow indicators calculated from modeled daily data, maximum flow during spawning and median flow during rearing, had few trends and were largely uncorrelated within the Yukon River basin and moderately correlated within the Kuskokwim River basin. Overall, we found that generic measures of model performance varied considerably, and it was important to consider the models best suited to our case study. For both streamflow and stream temperature, multiple high-performing models allowed estimation of ecologically relevant conditions affecting Chinook salmon. The approach we used to estimate local-scale habitat conditions has value to identify synchronous conditions that may influence multiple salmon populations under a changing subarctic climate.

Scleractinian coral evolved under nitrogen (N)-limited conditions. The increase in N flux from anthropogenic activities to these otherwise N-depleted environments is threatening coral health and coral reef ecosystem function. We tested the effect of elevated ammonium (NH₄⁺) loading on Acropora metabolism responses (respiration, gross primary production, and NH₄⁺ uptake) on healthy aquacultured Acropora sp. and compared responses to wild Acropora pulchra from Guam where corals are threatened by eutrophication. We quantified ¹⁵N isotope uptake, metabolism in custom metabolism chambers, and tissue N and carbon (C) content following NH₄⁺ loading. For aquacultured Acropora sp., we found that NH₄⁺ loading stimulated primary production and respiration, but did not significantly alter rates of uptake or tissue C or N content. Conversely, the wild A. pulchra did not respond to NH₄⁺ loading and was generally resistant to short-term exposures of NH₄⁺ loading. The change in rates of primary production within the aquacultured coral experiment suggests that sustained increases in N availability could upset stoichiometric regulation in coral. Few studies have coupled N cycling and metabolism rates, so our results serve as an important resource for understanding the biological activity of scleractinian coral, particularly a common wild coral from Guam, where extended events of increased anthropogenic N are increasing disease prevalence and decreasing coral reef diversity.

Many salamander populations are declining, and methods to determine how best to allocate limited resources to slow or reverse these declines could support land managers in their decision-making processes. Multiple types of uncertainty may delay management decisions, including when (1) knowledge of a species' ecology is incomplete, (2) climate change effects on environmental covariates are uncertain, and (3) the efficacy of management alternatives is unknown. For management decisions, a value-of-information analysis can identify which uncertainties are critical to reduce in order to identify an optimal strategy from a set of possible management actions. If the same management action is optimal across the full range of uncertainties, then resources for research can be redirected toward active management. Using value-of-information analyses, we examine the effect of uncertainty on identifying optimal management to maximize the future expected occupancy of Plethodon shenandoah, a Federally Endangered high-elevation endemic salamander that is threatened by climate change. Out of 11 management actions proposed by National Park Service managers, those that increase environmental moisture are expected to maximize occupancy, and we find that the selection of this action is robust to all the identified uncertainties. We show that, even in systems with multiple sources of large uncertainty, value of information analyses discriminate among investments in species management.

The lek hotspot hypothesis predicts that leks will form in areas where males are more likely to encounter females, providing wildlife managers with a framework supporting the use of leks as the focus for prairie and shrubland grouse conservation and monitoring. The lek hotspot hypothesis also implies that the number of males attending leks (lek size) will be higher in areas where there are more females. We used sharp-tailed grouse (Tympanuchus phasianellus) to evaluate whether lek locations and lek size were more influenced by habitat requirements during different seasons or by landscape features that minimized risks to males attending leks or increased the probability of detection of leks by nearby females. First, we evaluated which landscape features influenced habitat selection and mortality risk during different seasons: nesting (April–June), brood-rearing (June–August), early nonbreeding (September–November), and late nonbreeding (December–March) seasons in south-central Wyoming (n = 213 VHF-marked females; 2017–2020). We found that habitat selection and mortality risk varied by season. Subsequently, we modeled lek locations and lek size relative to seasonal habitat requirements (selection and mortality risk) and landscape features to identify key variables explaining lek site selection and lek size. We found that lek site selection was related to landscape features that promoted the detection of leks by females and to seasonal habitat. Specifically, leks were located in areas surrounded by more herbaceous vegetation and litter, less rugged terrain, and more nesting habitat. We found that lek size was related to seasonal habitat, with larger leks surrounded by more brood-rearing habitat. Our findings suggest that leks were located in areas that increased the probability of detection by females and in areas more likely to be frequented by females, consistent with the lek hotspot hypothesis. Our research supports continuing to use lek locations as focal points for habitat management for lekking grouse.