Oecologia最新文献

Beech leaf disease (BLD) poses a serious threat to the health of beech forests throughout the northeastern USA and Canada. Caused by invasive nematodes, BLD first appeared in 2012 in Ohio and has rapidly spread eastward. We investigated the effects of BLD on leaf and litter chemistry and leaf litter decomposition rate from four infected beech stands in Falmouth, Massachusetts. Attached leaves exhibiting differential infection intensity were collected from trees in October 2023 and analyzed for metrics of carbon (C) and nitrogen (N) content including %C, δ¹³C, %N, and δ¹⁵N. Severely infected and asymptomatic newly fallen leaf litter was gathered in November 2023 and analyzed for %C and %N only. We tested the effect of BLD-altered litter chemistry (separate from BLD-altered leaf structure) on litter decomposition rates by incubating ground litter in soil. Despite notably lower C:N in severely infected (C:N ~ 25) vs. asymptomatic (C:N ~ 43) litter, the difference in CO₂ evolution was negligible in short-term incubations. Percent N was significantly higher in severely infected (cupped) vs. asymptomatic litter (P = 0.00076), but significantly lower in severely infected leaves compared to asymptomatic green leaves (P = 0.021). δ¹³C tended to increase with infection intensity, possibly reflecting increased water use efficiency with infection stress; δ¹⁵N showed no clear pattern. The severely symptomatic cupped leaves (gathered in October) and litter (gathered in November) had indistinguishable %N, suggesting trees retranslocated far less N out of infected leaves than out of asymptomatic leaves prior to leaf fall.

Under the scenario of global warming, the response of carbon (C) fluxes of arid and semi-arid ecosystems, is still not well understood. A field warming experiment using open top chambers (OTCs) was conducted in a shrub-grass patagonian steppe to evaluate the effects on bare soil respiration (R_soil), and ecosystem respiration (R_eco), gross primary productivity (GPP) and net C exchange (NEE) during the growing season. Air (T_air) and soil (T_soil) temperature, and soil available phosphorus changed significantly while there were no changes in soil moisture, soil organic carbon, total soil nitrogen and root biomass, after one-year of treatment. Inside OTCs R_soil increased by 61%, with larger changes found during the daytime than during nighttime and tended to increase the temperature sensitivity (Q₁₀) from 1.49 to 1.58. Enhanced daytime NEE was observed inside OTCs mainly in the shrub Senecio filaginoides patches where C sequestration increased by 37% and GPP by 35% without effects on R_eco. In the grass Poa ligularis patches changes in C fluxes were not significant, but lower decrease in GPP than in R_eco tended to increase C uptake inside OTCs. This study reveals that future climate scenarios will lead to an enhanced C sequestration of vegetated patches but also to a higher bare soil CO₂ emission which may turn this ecosystem in a substantial C source if bare soil fraction increases due to global changes.

Understanding the relative importance of biotic interactions, multiple environmental drivers, and neutral processes in shaping community diversity and composition is a central question for both theoretical and applied ecology. We analysed a dataset describing 125 earthworm communities sampled in 10 localities in French Guiana. DNA barcodes were used to delimit operational taxonomic units (OTUs) that we considered as species surrogates to avoid the taxonomic deficit and calculate community-scale species richness and pair-wise Sørensen beta-diversity. We used log-ratio and generalised linear models to highlight the effects of biotic interactions and environment as drivers of alpha diversity, and generalised dissimilarity models to figure out the relative contribution of space and environment to beta-diversity at different spatial extents. Community-scale alpha diversity was mainly explained by habitat filtering (soil texture) and interspecific competition that limit the number of locally co-existing species. Beta diversity between pairs of communities was mainly explained by distance when comparing communities in similar habitats, by topography and available soil phosphorus when comparing communities in different habitats, and by distance, elevation and climate when comparing all possible pairs of communities. While community composition is determined locally by neutral processes and environmental filtering, biogeographic processes linked to dispersal limitation and adaptation to local environment are the most influential on a regional scale. This highlights the complex interplay of dispersal limitation, biotic interactions and environmental filtering during the process of community assembly.

To determine the impacts of global warming on pollinator-plant interactions, we recorded phenological variations in alpine flowers and bumble bees during 10-12 years in northern Japan, and analyzed the effects of weather conditions and phenological shift on worker population dynamics of four Bombus species. Flowering patterns of alpine plants were formed by the combination of early-flowering fellfield and late-flowering snowbed communities, where snowbed flowers were important resources for worker bees. The flowering phenology of the fellfield communities was correlated with early season air temperature, whereas that of the snowbed communities was clearly predicted by snowmelt time. It was predicted that 1 °C warming with 10 days earlier snowmelt would advance the peak flowering time of the fellfield and snowbed communities by 3.6 and 9.5 days, respectively, resulting in a 9.2 day shorter flowering period. In contrast, the peak time of worker abundance was consistent between years, independent of temperature and snowmelt time. As a result, the time lag between the peak flowering of snowbed plants and the peak abundance of worker bees, i.e., the phenological mismatch, increased with earlier snowmelt. Mid-summer temperature was negatively correlated with worker abundance for three Bombus species, and the effect of phenological mismatch varied between Bombus species. The abundance of B. hypocrita decreased with increasing phenological mismatch in the previous year, the abundance of B. beaticola and B. yezoensis increased, and B. hypnorum showed no clear response. Therefore, changes in the phenology of alpine plants due to global warming affect pollinators in highly species-specific ways.

Despite the water-limited nature of dryland ecosystems, interannual variability in precipitation (PPT) fails to explain a significant fraction of interannual variability in net primary productivity (NPP). One hypothesis states that these weak temporal NPP-PPT associations arise from the lagged effects of previous-year conditions, denoted as "legacy effects," which may amplify or constrain NPP in subsequent years. Although evidence suggests the existence of legacy effects in many ecosystem types, their generality in drylands remains unclear. We used long-term (35-year) remotely sensed estimates of NPP, climate, and a vegetation structure across the western United States to quantify the sign, magnitude, and drivers of legacy effects, defined as the lagged effects of previous-year weather and NPP anomalies on current-year NPP. Legacy effects exert a widespread effect on interannual variability in NPP across drylands spanning annual and perennial grasslands to hot and cold deserts. Previous-year NPP anomalies were the strongest predictor of current-year NPP anomalies, both across the entire time series and during specific extreme-to-average year transitions. The association between previous- and current-year NPP anomalies was consistently positive, indicating that a productive previous year will tend to result in a productive current year, and vice versa, even after accounting for the effect of current-year PPT. The strength of legacy effects increased slightly with increasing mean annual PPT and decreased slightly with an increase in the average fraction of herbaceous NPP. We conclude that legacy effects consistently effect current-year NPP in drylands and that consideration of these effects can improve predictions of temporal variation in dryland NPP.

Functional traits allow ecologists to infer processes that structure ecological communities and quantify interactions between trophic levels. Insects are a ubiquitous group that exhibits a variety of functional traits, and studying these traits could prove useful for understanding insect community assembly. We use insect trait measurements, community sampling along a disturbance gradient, and a cafeteria-style feeding assay to elucidate the mechanisms that govern insect herbivore community assembly processes. Using a trait principal component analysis, we first identified life history trade-offs between herbivore feeding and nutrition based on 3 traits measured on 14 grasshopper species collected across 30 pine savanna field sites. In the field, we tested hypotheses regarding how competition or environmental filtering might structure communities by examining dispersion patterns of functional traits. We found that grasshopper incisor strength and C:N ratio were consistently under-dispersed, patterns that indicate trait-clustering resulting from environmental filtering. Using mesocosms, we tested the hypothesis that grasshopper species should exhibit differentiation in their feeding niches based on the traits of the plants they consume and that feeding traits should correlate with traits of consumed plants. We demonstrated that grasshopper species strongly differentiated their feeding niche based on the traits of plants incorporated into their diets. We also found linkages between herbivore incisor strength and plant leaf dry matter content, and between grasshopper C:N ratio or body size and plant C:N ratio. This study revealed likely mechanisms that govern the interactions between insect herbivores, the plants they feed on, and how they partition resources to coexist.

Microscopic soil invertebrates are known to play an important role in forest ecosystems through their interactions with the rhizosphere and belowground food webs. However, little is known about the abundance, diversity, distribution, and ecological roles of micro-invertebrates above the forest floor, particularly within tree-related microhabitats (TreMs). In this study, we sampled 18 distinct types of TreMs in the UNESCO World Heritage old-growth beech forest of La Massane, located in the southeastern Pyrenees. We extracted and counted various groups of micro-invertebrates (nematodes, tardigrades, rotifers, and mites) associated with these TreMs, and identified nematodes to the species level. Additionally, we measured the stable isotopic signatures of carbon and nitrogen in various resources and invertebrate groups to reveal the structure of TreM-associated food webs in unprecedented detail. TreMs emerged as hotspots of both abundance (averaging 195 individuals per gram of dry TreM substrate) and diversity (98 nematode morphospecies across 20 families). We found significant differences among TreM types in terms of community composition and food web structure, revealing distinct species assemblages and trophic pathways. These differences could be linked to factors such as the stage of wood decomposition, occupation by larger animals (e.g., insects, birds), and the position of TreMs within trees. Our findings suggest that micro-invertebrates serve as valuable ecological indicators, adding a new layer of biodiversity and functional understanding to TreM typology. This, in turn, supports more comprehensive strategies for nature conservation and forest management.

Droughts are expected to increase in severity and frequency with climate change, and it is important to understand why some ecosystems are more sensitive to drought than others. Currently, there is considerable evidence that ecosystem sensitivity to drought, quantified by reductions in aboveground net primary production (ANPP), is negatively related to mean annual precipitation (MAP). Thus, arid ecosystems are more likely than mesic systems to experience dramatic reductions in productivity during drought. However, evidence for this pattern is primarily from studies that span multiple biomes making it difficult to discern if abiotic (MAP) or biotic factors (differences in plant communities) underlie this relationship. To disentangle these, we assessed patterns of drought sensitivity within a single biome, the semiarid shortgrass steppe of the western U.S., where the dominant vegetation varies minimally compared to cross-biomes studies. We used 23 years of satellite derived ANPP proxies, the Normalized Difference Vegetation Index (NDVI) and the Enhanced Vegetation Index (EVI, 157,929 pixels, 1 km² resolution) with gridded precipitation data to assess relationships between drought sensitivity and MAP within this biome. Consistent with previous multi-biome studies, we found a negative, although relatively weaker, relationship between MAP (250-625 mm) and drought sensitivity within the shortgrass steppe. We conclude that while differences in vegetation types almost certainly contribute to patterns of drought sensitivity, the long-term precipitation history of an ecosystem (e.g. MAP) may also play a role in determining differences in drought sensitivity within ecosystems.

Traditional sampling methods have limited our understanding of the behavioral ecology of leaf litter fauna. Substrate-borne vibrations provide a window that addresses this shortcoming. Under natural conditions, we implemented a passive monitoring system that measures vibrations produced by two miniaturized Puerto Rican geckos: Sphaerodactylus grandisquamis in the mesic karst forest and Sphaerodactylus townsendi in the coastal dry forest. The dichotomy between habitats allowed us to test the hypothesis that microclimate conditions drive divergence in thermoregulatory behavior. For each species in its native habitat, thirty individuals were monitored inside a field enclosure, excluding other vibration sources. We measured vibrations at two strata depths (i.e., surface and bottom) to characterize behavioral responses to diel cycle, microclimate, and predatory bird calls. Vibrational data revealed contrasting activity patterns across strata. Mesic S. grandisquamis showed continuous daytime activity at all strata levels, regardless of microclimate. Dry forest S. townsendi featured a biphasic activity pattern, peaking midday and at dusk, and increased activity in deeper litter strata during hot and dry conditions (i.e., midday). Analysis at fine temporal scales for S. grandisquamis revealed a reduction in surface activity after the onset of bird calls from three species that pose a predation risk. Our results demonstrate interspecific differences in thermoregulatory behavior that likely increase the fitness of each species in their respective habitats. Furthermore, vibrational monitoring strongly suggests Sphaerodactylus exploit their niche in a three-dimensional manner, mirroring habitat use patterns of arboreal fauna and highlighting the importance of incorporating multiple strata levels when studying leaf litter microhabitats.

Many plant species are moving to higher elevations due to global warming, but the effects of these elevational shifts on plant-pollinator interactions are not well understood. This study aimed to examine how flower visitation and seed set of lowland plants change after they shift uphill, and whether they compete for pollinators with plants native to the mountains. We conducted an experiment using two plant groups: lowland species pre-planted in a greenhouse and transplanted to both lowland and mountain sites, and mountain species. Pollinators were recorded at lowland sites for planted species and at mountain sites for both planted and native species. We also used pan traps in white, yellow, and blue colours to collect pollinators at both sites. Afterwards, seed sets of the planted species were counted to compare pollination success between elevations. Flower visitation rates on planted species were not significantly affected by elevation, although pollinator abundance in pan traps was higher in the mountains. The pollinator spectrum varied across elevations and plant species, influenced by flower and pan trap colour. However, planted species produced more seeds at lowland sites, indicating higher pollination success there. Overall, we found no evidence of competitive advantage for range-shifting lowland species in terms of pollination.