Ecosphere最新文献

Animals perceive their ecosystems at multiple spatial scales such that the pattern–process relationships that determine their ecological and evolutionary opportunities are also spatially variable. Understanding how spatial scale impacts our observations of ecological and evolutionary patterns and processes is therefore crucial for effective biodiversity management. In this study, using a comprehensive dataset of small mammals from primary field surveys supplemented with literature data across Kenya, we investigated the effects of spatial scale on the distribution patterns of taxonomic, phylogenetic, and functional diversity indices. We also tested how relationships between taxonomic, phylogenetic, and functional diversity and various environmental and anthropogenic variables change across spatial scales. The results showed that with increasing spatial scale, species richness and phylogenetic and functional richness consistently increased. Community-wide mean pairwise distance indices for phylogenetic and functional dimensions also increased, while fine-scale mean nearest taxon distance indices decreased. Notably, community structure indices exhibited nonmonotonic patterns across spatial scales. The associations between diversity patterns and environmental and human covariates increased with scale but were more variable and complex across regions. These findings highlight a negative correlation between spatial scale and phylogenetic and functional divergence while reinforcing the species-area hypotheses for richness-dependent diversity indices. Identifying the optimal scales of field studies and conservational actions must factor in the species group of interest and the geographical context.

Wildfire is a natural disturbance in landscapes of the Western United States, but the effects and extents of fire are changing. Differences between historical and contemporary fire regimes can help identify reasons for observed changes in landscape composition. People living and working in the Great Basin, USA, are observing altered fire conditions, but spatial information about the degree and direction of change and departure from historical fire regimes is lacking. This study estimates how fire regimes have changed in the major Great Basin vegetation types over the past 60 years with comparisons to historical (pre-1900) fire regimes. We explore potential drivers of fire regime changes using existing spatial data and analysis. Across vegetation types, wildfires were larger and more frequent in the contemporary period (1991–2020) than in the recent past (1961–1990). Contemporary fires were more frequent than historical in two of three ecoregions for the most widespread vegetation type, basin and Wyoming big sagebrush. Increases in fire frequency also occurred in saltbush, greasewood, and blackbrush shrublands, although current fire return intervals remain on the order of centuries. Persistent juniper and pinyon pine woodlands burned more frequently in contemporary times than in historical times. Fire frequency was relatively unchanged in mixed dwarf sagebrush shrublands, suggesting they remain fuel-limited. Results suggest that quaking aspen woodlands may be burning less frequently now than historically, but more frequently in the contemporary period than in the recent past. We found that increased fire occurrence in the Great Basin is associated with increased abundance and extent of nonnative annual grasses and areas with high concentrations of anthropogenic ignitions. Findings support the need for continuing efforts to reduce fire occurrences in Great Basin plant communities experiencing excess fire and to implement treatments in communities experiencing fire deficits. Results underscore the importance of anthropogenic ignitions and discuss more targeted education and prevention efforts. Knowledge about signals of fire regime changes across the region can support effective deployment of resources to protect or restore plant communities and human values.

Forest patches in urban landscapes make outsized contributions to biodiversity, ecosystem function, and human health and well-being. However, urbanization can alter environmental conditions that underpin forest health. Most studies of forest health in urban landscapes have focused on few forest patches across a single metropolitan region, and synthesis is needed to understand broader patterns. We assessed variation among measures of forest health across land cover gradients and ecoregions by determining (1) whether the degree of urban, agricultural, and forested land surrounding a forest patch was reflected in differences in tree community composition, diversity, and structure and (2) whether these differences were consistent across ecoregions. We synthesized data from 17 observational studies (3334 plots) and remotely sensed land cover (1-km buffer) across four metropolitan regions (Baltimore–Washington DC, Chicago, New York City, and Philadelphia) spanning five ecoregions of the eastern deciduous forest of North America. Land cover surrounding forest patches differed among ecoregions, and forests were surrounded by heterogeneous land cover even in the most urbanized areas. Patterns of tree species composition and forest structure reflected landscape context. Forest patches surrounded by high canopy cover had greater or equal tree species diversity, density, basal area, and diversity of tree sizes relative to patches surrounded by highly agricultural or highly impervious landscapes. In contrast, there was little difference in structure and diversity between forests in highly agricultural and impervious settings. Tree species composition varied among ecoregions, yet tree community assemblages of forests in intensively urbanized areas were consistently distinct from those of forests in other contexts. Forest patches in the most urban and most agricultural landscapes shared predominantly native species communities and were characterized by low tree species diversity, basal area, and size class diversity, as well as high non-native tree abundance, highlighting commonalities among these intensive anthropogenic landscapes. These results point to both common challenges to forest health and common opportunities for forest stewardship in urban and agricultural landscapes.

Migratory animals can serve as ecological links between geographically distant ecosystems. Moreover, when seasonally linked ecosystems differ in carrying capacity of migrant species, those with high capacity may support population growth with consequences to shared ecosystems with lower capacity through trophic cascades. Agricultural production has increased carrying capacity of lesser snow (Anser caerulescens caerulescens) and Ross's geese (Anser rossii, collectively, “light geese”) in southern agricultural landscapes where these species winter and stage during migration to and from northern breeding areas, resulting in population increase. In subarctic and arctic ecosystems where carrying capacity for geese is lower, high abundance and densities of light geese have caused trophic cascades during summer breeding. This has raised concern for resilience of northern ecosystems to withstand cumulative and intense pressures of above- and belowground herbivory and nest construction. We investigated the empirical relationship between intensity of vegetation disturbance by multidecadal foraging and nest construction by up to ~1.3 million geese and shifts in (1) plant community composition and (2) taxon richness of freshwater plant communities near Karrak Lake, in Canada's central arctic. Intense use by nesting light geese caused shifts from lowland communities dominated by grasses and sedges (collectively, graminoids), Sphagnum spp., and willows (Salix spp.) to those comprised of exposed peat, non-Sphagnum mosses, marsh ragwort (Tephroseris palustris), mare's tail (Hippuris vulgaris), and particularly birch (Betula glandulosa). Community change was less apparent in upland regions that were naturally less vegetated even in the absence of avian herbivores, but fruticose lichens, crowberry (Empetrum nigrum), and white heather (Cassiope tetragona) dominated undisturbed plant communities, whereas crustose lichens and bearberry (Arctostaphylos spp.) comprised disturbed communities. We did not find evidence for dominance by a limited number of species with long-term occupancy by light geese, as taxon richness was equivocal between disturbed and undisturbed plant communities. Cessation of foraging and nesting pressure increased taxon richness and reestablishment of locally eradicated plant species. Overall, herbivory and nesting effects were not uniform across this widespread nesting colony and, together with underlying influence from abiotic gradients, increased heterogeneity in the mosaic of vegetation communities.

The frequency and severity of extreme weather events such as heat waves are increasing globally, revealing ecological responses that provide valuable insights toward the conservation of species in a changing climate. In this study, we utilized data from two populations of GPS-collared female wood bison (Bison bison athabascae) in the boreal forest of northwestern Canada to investigate their movement behaviors in response to the 2021 Western North American Heat Wave. Using generalized additive mixed-effect models and a model selection framework, we identified a behavioral temperature threshold for wood bison at 21°C. Above this threshold, movement rates decreased from ~100 m/h at 21°C to a low of ~25 m/h at 39°C (150% decrease; −9%/°C). Extreme heat also contributed to changes in diurnal movement patterns, reducing wood bison movement rates and shifting the timing of peak activity from midday to early morning. These findings highlight the behavioral adaptations of female wood bison and underscore the need to understand the behavioral and physiological responses of cold-adapted mammals to extreme weather events. Subsequent effects of thermoregulatory behavior may impact individual fitness and population viability, particularly at high latitudes where cold-adapted species are increasingly exposed to severe weather resulting from anthropogenic climate change.

Human-induced climate change, land use changes, and urbanization are predicted to dramatically impact landscape hydrology, which can have devastating impacts on aquatic organisms. For amphibians that rely on aquatic environments to breed and develop, it is essential to understand how the larval environment impacts development, condition, and performance later in life. Two important predicted impacts of climate change, urbanization, and land use changes are reduced hydroperiod and variable larval density. Here, we explored how larval density and hydroperiod affect development, morphology, physiology, and immune defenses at metamorphosis and 35 days post-metamorphosis in the frog Rana pipiens. We found that high-density larval conditions had a large negative impact on development and morphology, which resulted in longer larval periods, reduced likelihood of metamorphosis, smaller size at metamorphosis, shorter femur to body length ratio, and reduced microbiome species evenness compared with animals that developed in low-density conditions. However, animals from the high-density treatment experienced compensatory growth post-metamorphosis, demonstrating accelerated growth in body size and relative femur length compared with animals from the low-density treatments, despite not “catching-up” in size. We also observed an increase in relative gut length and relative liver size in animals that had developed in the high-density treatment than those in the low-density treatment, as well as higher bacterial killing ability, and greater jump distances relative to their leg length across different temperatures. Finally, metabolic rate was higher overall but especially at higher test temperatures for animals that developed under high-density conditions, indicating that these animals may expend more energy in response to acute temperature changes. While the effects of climate change have direct negative effects on larval development and metamorphosis, animals can increase growth rate post-metamorphosis; however, that compensatory growth might come at a cost and reduce their ability to cope with further environmental change such as increased temperatures.

Recent climate warming has resulted in the reduction of lake ice cover and significant changes in phytoplankton communities, but due to the traditional view of low production under lake ice in winter as well as the logistical challenges of winter conditions to field sampling, the influence of under-ice limnological processes on winter diatom dynamics is rarely directly examined and thus remains unclear. Here, lake pelagic diatoms were monitored covering both the open-water season and two ice-covered winter seasons in three alpine lakes on the Chinese Loess Plateau to track diatom succession dynamics and assess the potential influences of under-ice light and nutrient availability on diatom community. The results show clearly that diatom compositional changes during the open-water season in all the lakes were simply linked with lake physical mixing/stratification regimes, while diatom community composition was not consistent between the two winter seasons in each lake under the combined influence of changing under-ice nutrient and light conditions. In deep Lake Gonghai, total phosphorus (TP) explained equally the changes in winter diatom community with temperature, ice cover and associated light availability; in shallow Lake Pipahai, total nitrogen (TN) functioned as the major nutrient factor but was less important than light penetration through the ice; and in Lake Mayinghai, dissolved silica (DSi) outweighed the light effect of winter temperature and ice cover. Despite differing relative importance of nutrient factors between the different morphological types of lakes, winter diatom community changes in each lake were significantly linked with temperature, ice cover and associated changes in under-ice light availability. This study provides a detailed picture that winter temperature and under-ice limnological processes play a substantial role in diatom community dynamics in the alpine lakes of the Chinese Loess Plateau, and improves the understanding of limnological and ecological processes under ice and their driving mechanisms.

Harmful algal blooms (HABs) rapidly change and threaten aquatic ecosystems. HABs in oligotrophic lakes are becoming more commonly observed, despite the long-held paradigm that algal blooms cannot happen in low-nutrient systems. This raises the question of whether nutrient loading, understood as a major driver of HABs, plays an important role in the potential for HAB development in oligotrophic lakes. Using in-lake mesocosms, we examined the effects of a gradient of nitrogen and phosphorus additions on the pelagic communities of an oligotrophic lake over 4 weeks. We hypothesized that increasing nutrients would result in an increased abundance of phytoplankton and an increased dominance by cyanobacteria. Although our nutrient additions caused an increase in the fluorescence of chlorophyll a (i.e., a proxy for total phytoplankton) and phycocyanin (i.e., a proxy for total cyanobacteria), these increases plateaued at low-nutrient concentrations and the increases were short-lived. The identification and enumeration of phytoplankton species confirmed that the composition of the phytoplankton also did not change with added nutrients, nor did the abundance of the dominant zooplankton group (i.e., cladocerans). Furthermore, our biweekly nutrient additions maintained elevated concentrations of total phosphorus and total nitrogen in the water column, with total dissolved phosphorus and nitrate both readily available throughout the experiment. Given that light is very abundant (Secchi depths of 9–10 m), this suggests that another nutrient, such as iron or carbon, may have limited phytoplankton growth. Our findings suggest that excess nutrients may not always drive HABs in oligotrophic lakes and further studies should examine the effects of other micronutrients using similar controlled seminatural mesocosms.

Structural diversity—the volume and physical arrangement of vegetation within the three-dimensional (3D) space of ecosystems—is a predictor of ecosystem function that can be measured at large scales with remote sensing. However, the landscape composition and configuration of structural diversity across macrosystems have not been well described. Using a relatively recently developed method to quantify landscape composition and configuration of continuous habitat or terrain, we propose the application of gradient surface metrics (GSMs) to quantify landscape patterns of structural diversity and provide insights into how its spatial pattern relates to ecosystem function. We first applied an example set of GSMs that represent landscape heterogeneity, dominance, and edge density to Lidar-derived structural diversity within 28 forested landscapes at National Ecological Observatory Network (NEON) sites. Second, we tested for forest type, geographic location, and climate drivers of macroscale variation in GSMs of structural diversity (GSM-SD). Third, we demonstrated the utility of these metrics for understanding spatial patterns of ecosystem function in a case study with NDVI, a proxy of productivity. We found that GSM-SD varied in landscapes within macrosystems, with forest type, geographic location, and climate being significantly related to some but not all metrics. We also found that dominance of high peaks of height and vertical complexity of canopy vegetation and the heterogeneity of the vertical complexity and coefficient of variation of canopy vegetation height within 120-m patches were negatively correlated with NDVI across the 28 NEON sites. However, forest type always had a significant interaction term between these GSM-SD and NDVI relationships. Our study demonstrates that GSMs are useful to describe the landscape composition and configuration of structural diversity and its relationship with productivity that warrants further consideration for spatially motivated management decisions.

In late successional forests of North America, sugar maple (Acer saccharum Marsh.) and American beech (Fagus grandifolia Ehrh.) form a complex ecosystem with intricate interactions. Over the last few decades, several studies have reported a marked increase in American beech dominance relative to sugar maple. Recent evidence suggests that extreme events such as drought could accelerate sugar maple's maladaptation to climate change and favor American beech in its replacement dynamics. In this study, we conducted a greenhouse experiment to investigate the effects of soil water stress and American beech presence on sugar maple seedling growth, structural physiology, leaf nitrogen, and chlorophyll. The seedlings were subjected to the following treatments independently and in combination for 82 days: soil water stress; soil originating from stands with American beech proliferation; soil sterilization; and presence of American beech litter. The results revealed that soil water stress was the primary factor significantly reducing sugar maple seedling growth, which also resulted in an increased root-to-shoot ratio. The presence of soil from stands with American beech proliferation did not exacerbate this negative effect. Soil sterilization, initially expected to reduce seedling growth by eliminating mycorrhizal associations, actually improved seedling growth. This suggests that adverse biotic processes, such as pathogens, were present in the soils regardless of their origin, and their negative effects outweighed the potential benefits from mycorrhization. The addition of American beech litter mitigated the effects of soil water stress but also introduced allelopathic compounds that hindered seedling growth. Overall, this study highlighted the complex interactions affecting sugar maple seedling growth, emphasizing that drought is a major limiting factor.