Ecosphere最新文献

Ants are one of the most widespread groups of insects, but the mechanisms allowing them to coexist despite having similar nutritional needs remain unclear. In this study, we investigated the structure and competitive dynamics of ant assemblages in pineapple agrosystems of La Réunion Island. Using an imagery approach that combined in-field image captures and a computer vision algorithm based on convolutional neural networks, we analyzed ant dominance hierarchies, foraging and recruitment behaviors, niche partitioning between day and night, as well as the impact of environmental variables. This approach provided highly detailed data on the strategies of individual species. Additionally, to better understand the resource exploitation strategies employed by ant species, we then tested the discovery-dominance trade-off. Our results revealed that Pheidole megacephala and Solenopsis geminata were the two dominant species, displaying high recruitment investment and frequent bait monopolization, particularly at night. In contrast, Brachymyrmex cordemoyi used a scout-based foraging strategy that allowed it to rapidly locate baits and maintain moderate dominance levels, during both day and night periods. With lower abilities to discover and control baits, subordinate species had to rely on alternative foraging strategies to persist. We found a significant positive correlation between the discovery and dominance abilities supporting a discovery–defense strategy rather than a discovery-dominance trade-off. This finding implies that resource monopolization in simplified ecosystems may benefit species optimizing both rapid resource location and competitive defense. Environmental factors, including plant species richness, plant cover, and mulch cover, influenced species abundance and occurrence, even though dominant species appeared to remain unaffected by habitat variations. The impacts of environmental factors highlight the role of habitat complexity in mediating competitive interactions shaping ant coexistence.

Landscapes encompass both aquatic and terrestrial ecosystems that experience the same climate but may respond to climate in divergent ways. For example, the time lag between seasonal dry-down of terrestrial soil moisture and decline in streamflow has important implications for species and ecosystem processes across the aquatic–terrestrial interface. How these lags between aquatic and terrestrial hydrology vary with climate and spatial location within watersheds remains largely unexplored. Here, we examine seasonal patterns of aquatic–terrestrial dry-down across seven watersheds in the northwestern USA, spanning a wide range of aridity. We compared daily streamflow data from USGS gages at watershed outlets with simulated daily soil moisture (1979–2020) from multiple locations within each watershed. In all watersheds, annual dry cycles progressed sequentially through the following features: evapotranspiration, precipitation, shallow soil moisture, deep soil moisture, and finally streamflow. Seasonal streamflow minima lagged behind soil moisture minima for shorter durations in more arid watersheds and drier years. Within watersheds, lag times varied spatially due to interactions between elevation and aridity, with short lags in low-elevation soils near streams in arid watersheds and longer lags in less arid watersheds. Collectively, these results indicate shorter lags between seasonal aquatic and terrestrial dry periods in drier watersheds and years, and show that these tighter linkages are spatially aggregated in drier watersheds. The co-occurrence of seasonally dry conditions in both aquatic and terrestrial systems under increasing aridification is likely to intensify stressors on ecosystems and services. Recognizing these patterns may be critical for predicting ecosystem vulnerabilities and informing adaptation strategies to mitigate the impacts of seasonally dry conditions.

Phenology, the timing of biological life cycles, is a key indicator of global climatic change, with numerous studies showing that species' phenologies are shifting in response to climate change. Despite general trends (e.g., warming causing earlier arrival of spring events such as leaf-out and flowering onset), studies repeatedly reveal that phenological changes tend to be species-specific and thus may alter species interactions. Less-studied is the potential feedback between biotic interactions and phenology and the impacts on species' fitness. To understand the consequences of shifting phenology for species and communities, we need to quantify how phenology and competition interact to affect species' fitness. Here, we studied the potentially interacting effects of species' phenology and competition on plant fecundity (as a proxy for fitness). We sowed seeds of various species combinations to test how variation in competitor species richness, identities, and densities affect the phenology and fecundity of an annual wildflower, Clarkia purpurea. We found that C. purpurea's flowering phenology varied with competitor identity and competitor species richness, that fecundity was negatively correlated with competitor density but not species richness, and that the strength of competition tended to vary by competitor identity, but appeared unrelated to the relative phenology of the competitor. These findings offer unique evidence that competitive interactions may impact plant phenology and fecundity in complex ways and could influence species' persistence and coexistence conditions in our changing global environment.

Cold seeps are chemosynthesis-based ecosystems powered by microbial primary production that support diverse and specialized faunal assemblages in the deep sea. Despite Nankai Trough in Japan being a geologically active margin hosting numerous seeps, much of the faunal diversity remains undocumented. Here, we present results from the first coordinated biological survey across five methane seep sites in the Nankai Trough with different water depths: Daini Tenryu Knoll (600 m), Ryuyo Canyon (1000 m), Oomine Ridge (2000 m), Yukie Ridge (2500 m), and the Off Cape Muroto 4600 m Site. The seep sites were imaged in situ using a combination of high-definition video cameras and still cameras, and biological samples were taken using suction and scoop sampling in addition to grab samples collected directly using the submersible's manipulator. Our results, together with existing records, together reveal a total of 80 seep-associated macro- and megafaunal animal species in these five Nankai Trough seeps (33 molluscs, 23 annelids, 11 arthropods, five nemerteans, four echinoderms, three cnidarians, and a bryozoan), over a fivefold increase compared to the previous number (14). The species diversity at each site also increased from 1–6 to 15–30. These findings include numerous range extensions, new records at seeps, and previously undocumented associations. Our results shed light on the exceptional and underappreciated diversity of seep fauna along the Nankai Trough. In light of growing interest in methane hydrate exploitation in this region, our findings provide essential biodiversity baselines and highlight the need for site-specific conservation measures to protect endemic, depth-segregated communities from anthropogenic disturbance.

Across savanna ecosystems worldwide, the decline of large trees and the rapid expansion of shrubs present major conservation challenges. These trends are especially pronounced in South Africa's Kruger National Park (KNP), the country's largest protected area. To quantify their extent and identify their drivers, we conducted a spatial assessment of tree cover and density across KNP from 2011 until 2022. We then evaluated how these response variables are influenced by abiotic factors, including fire, climate, soil, and geology, and by biotic factors, such as the densities of African elephant adult male bulls and herds, including females and calves. We defined trees as land-cover elements that cast a distinct shadow and stand taller than 5 m. Using Collect Earth, an open-source software for augmented visual interpretation of high-resolution satellite imagery, we assessed tree cover and density on 4258 plots of 0.5 ha each. We recorded 27,918 trees, equivalent to an average density of 13 trees/ha. Counts in each plot were truncated to a maximum of 30 individuals. We validated our estimates of tree cover and height against independent, high-resolution airborne LiDAR measurements, which yielded an RMSE of 8.89% for trees taller than 3 m. The relative influence of selected predictors on tree cover and density was analyzed through logistic and survival regressions. Geology had the greatest influence on tree distribution, where both tree cover and density were higher on nutrient-poor granitic substrates than on nutrient-rich basalts. Tree cover and density were higher in areas with low fire frequency, close to main rivers, and with higher sand content in the soil. The mean annual rainfall showed a positive correlation with tree cover, while it had a negative correlation with the number of trees. Elephant bulls were found to be negatively correlated with both tree cover and density. In contrast, elephant herds exhibited a positive correlation with tree cover and density. This study highlights the importance of understanding the effects of multiple factors on tree distribution and aims to provide a baseline for assessing tree cover and density across KNP to support ongoing tree management strategies and contribute to future conservation priorities.

Resilient ecosystems maintain similar species diversity and composition despite extreme environmental variation, while ecosystem collapse can be characterized by high mortality rates and decreased species diversity. Submerged aquatic macrophytes often support species diversity by providing habitat, shelter, food, and oxygen for fish and invertebrates. Can submerged macrophytes cause extreme chemical fluctuations, high mortality, and rapid ecosystem collapse in a small floodplain pond in the temperate zone? We measured fish survival from spring to fall and used mesocosms to assess diel fluctuations of dissolved oxygen (DO) and pH during spring, summer, and fall in patches of aquatic macrophytes (metaphyton, Chara, Potamogeton foliosus, and Lemna minor). Submerged macrophytes (metaphyton, Chara, and P. foliosus) dominated in spring and summer before being overgrown by a floating macrophyte in fall (L. minor). Of the four fish species, only western mosquitofish survived from spring to fall. In spring, high rates of photosynthesis in submerged macrophytes led to long periods of supersaturation (12–16 h/day) and basicity (2–10 h/day of pH >9.0). High rates of microbial respiration in summer were driven by elevated temperatures (≈35°C), high nutrient levels (average TN and TP = 4.4 and 0.17 mg/L), and decaying submerged macrophytes, resulting in long durations of hypoxia (4.8–19.6 h/day of DO < 1.0 mg/L). In fall, cooler temperatures (≈10°C) diminished extreme fluctuations in DO and pH beneath a floating mat of L. minor. All macrophytes died back in winter. This seasonal cycle of colonization during spring runoff and ecosystem collapse in summer was not a transition to an alternative stable state dominated by floating macrophytes as in other lentic ecosystems. Warm temperatures and nutrient enrichment can produce extreme diel fluctuation in DO and pH in patches of submerged macrophytes, resulting in high rates of mortality in floodplain ponds, one of the most common types of wetlands in the world.

As cities grow, lakes are often assumed to suffer from increasing non-point pollution. Many waterbodies have become more eutrophic in recent decades, as expected—but many others became less eutrophic, especially in urban/suburban areas. What policies, practices, and ecosystem processes have helped some lakes stay stable or become less eutrophic even in a growing city? Identifying and understanding success stories are important to continue protecting these lakes and improving other urban/suburban lakes. We found one such success story when we examined water-quality trends over the past 25 years (1998–2022) in Lake Washington, a well-studied large lake in the Seattle metro area. The watershed population grew rapidly during that time (34% from 2000 to 2020), yet Lake Washington became substantially less eutrophic and indicators of development impacts stabilized or decreased. Chlorophyll concentrations during the main spring bloom decreased sharply (−25% per decade), and water clarity and near-bottom dissolved oxygen both increased (8.5% and 17% per decade, respectively). Alkalinity and specific conductance had increased during the 1970s–1990s, but in recent decades, they held stable. Peak winter/spring nitrogen and phosphorus concentrations decreased (−4.9% and −5.6% per decade, respectively), indicating decreased watershed inputs. The type of development during this time was likely a key contributor: we found no net loss of forest area and little increase in developed land area (4.7% from 2001 to 2021). Instead of expanding into new areas, redevelopment increased density on already-developed land and likely drove improvements in stormwater treatment and other environmental protections. Future work comparing stream watersheds could help discern which specific aspects of redevelopment helped reduce nutrients and other impacts. However, nutrient reductions were not the only factors controlling the lake's trophic state; chlorophyll decreased much more strongly than phosphorus did. Lake Washington is a complex ecosystem governed not only by water chemistry but also by interactions with physical and biological factors such as stratification, warming, phytoplankton community shifts, or food-web interactions. A better understanding of all these factors is essential to provide sound scientific guidance and ensure that Lake Washington and other lakes can thrive in a growing city.

Lagomorphs are selective herbivores that can strongly influence rangeland condition if their population densities increase through predator release. However, the effect size of lagomorph herbivory has not previously been quantified for the semiarid rangelands of the southwestern United States, where their predators are suppressed. We used a differential exclosure experiment replicated across 20 sites in a public rangeland in southern Utah to quantify the effect of lagomorph herbivory (jackrabbits and cottontails) for comparison with ungulate herbivory (cattle and bison). Across our 11-year study, we measured aboveground net primary productivity (ANPP; 3 × 1-year data sets) and long-term standing crop (SC; 1 × 8-year data set). We also measured nutrient concentrations in grass and soil samples in plots with complete exclosure (lagomorphs and ungulates out), partial exclosure (lagomorphs in and ungulates out), and no exclosure (open control plots) for 8 years. From the grass data, we calculated the effect size of lagomorph grazing as a 26.6% reduction in ANPP and an 11.3% reduction in SC, compared to ungulate grazing as a 24.9% reduction in grass ANPP and a 72.2% reduction in SC. We found lagomorphs had no effect on forb ANPP but actually increased forb SC, which is consistent with previous evidence that lagomorphs facilitate noxious weeds on these rangelands. There were no significant effects of either lagomorph or ungulate herbivory on plant and soil nutrient levels. Using the effect sizes of lagomorph herbivory on grass ANPP and SC, applied to the animal unit months (AUMs) prescribed for that rangeland, we calculated that lagomorphs currently impose an annual economic cost of between US$30.16 km⁻² (SC) and US$70.64 km⁻² (ANPP) in the Henry Mountains region of southern Utah, USA. We recommend that managers consider the lagomorph effect on rangeland resources in relation to the costs and benefits of conserving their predators, which are currently suppressed indirectly through various anthropogenic effects (raptors) and directly by agency-funded control programs (coyotes).

Subalpine coniferous forest ecosystems are sensitive to climate change. However, the community formation mechanisms of subalpine coniferous forests in northeastern Asia remain poorly understood. In this study, we assessed the factors controlling the phylogenetic community structure in different strata (whole strata, upperstory, and understory) of Abies nephrolepis and Abies koreana forests in the subalpine zone in South Korea. Piecewise structural equation modeling (pSEM) was performed based on terrain, climate, taxonomic diversity, stand structure characteristics, and disturbance factors. The controlling factors presented different responses for each species depending on the stratum and phylogenetic community structure indices (net relatedness index and nearest taxon index). A. nephrolepis showed a unique community formation mechanism and formed climate refugia through high rock exposure, whereas A. koreana showed niche conservation at high elevations and a community overdispersion trend when forest gaps appeared due to overstory vegetation loss. The Mantel test and partial Mantel test were performed to examine the impact of turnover and nestedness on phylogenetic β-diversity, as well as to establish their correlations with climatic, geographic, and environmental distance. Turnover was a major contributing factor to β-diversity and strongly correlated with environmental distance. Further, geographical and climatic distance presented differential contributions to each species depending on the community characteristics. Integrated analyses of phylogenetic community structure and β-diversity provided detailed insights into the mechanisms underlying community formation and biodiversity patterns. This reveals that biodiversity patterns are driven by interactions between community structure and inter-community characteristics, with internal structure as a key mechanism influencing β-diversity.

Invasive species alter habitats and biological communities. The giant river prawn Macrobrachium rosenbergii (de Man 1879) was introduced to Brazil for aquaculture, and invasive populations have established in the Amazon Delta region where they are believed to pose a risk to the native aquatic fauna. To assess potential impacts, we performed dietary metabarcoding using generalist COI primers on 105 stomach contents collected from prawns from the southern Amazon Delta. Overall, M. rosenbergii presents an opportunistic and generalist diet that reflects the dominant aquatic and terrestrial fauna of the region, including the orders Diptera, Characiformes, and Lepidoptera as dominant dietary items in terms of both frequency of occurrence and richness. One unidentified congeneric species was identified in the diet, indicating the potential for negative effects on the native prawn fauna. Additionally, while there is a general overlap in the diet for all categories of sex and reproductive phase, smaller immature individuals and molted females showed reduced diversity in their diet, suggesting limitations in prey handling or access. We conclude that dietary metabarcoding of opportunistic generalists and/or detritivores appears to be a potentially useful tool for monitoring biodiversity as well as understanding their role in the food web.