Oecologia最新文献

Against the backdrop of continuously increasing global nitrogen (N) deposition, the changes in photosynthetic carbon (C) allocation patterns of desert plants and their underlying mechanisms affecting soil C sequestration remain poorly understood. This study selected two representative species from desert ecosystems: the non-vascular moss Syntrichia caninervis and the vascular ephemeral plant Erodium oxyrhinchum as research subjects. Three N deposition levels were implemented: 0 (N0), 10.0 (N10), and 30.0 kg N ha^-1 a^-1 (N30), combined with ¹³C stable isotope labeling technique, to systematically investigate the effects of N deposition on plant photosynthetic C allocation and soil C sequestration. The experiment demonstrated that: (1) Aboveground ¹³C content in both species decreased significantly with increasing N input (P < 0.05); (2) N deposition significantly promoted photosynthetic C transfer to soil, with soil ¹³C allocation increasing from 0.8% (N0) to 4.0% (N30) for S. caninervis, and from 5.0 to 12.2% for E. oxyrhinchum (P < 0.01). N deposition alters photosynthetic C allocation strategies in desert plants, significantly enhancing belowground C transfer and strengthening soil C sink function. This study provides crucial experimental evidence for evaluating arid region C cycle dynamics under global N deposition scenarios.

Understanding how landscape diversity (i.e., land-cover heterogeneity) influences ecosystem stability across spatial scales is critical for predicting ecosystem responses to environmental change and for designing effective landscape-level conservation strategies. This study aims to quantify the scale dependence (ranging from 0.0625 km² to 2500 km²) of landscape diversity effects on multiple dimensions of ecosystem temporal stability, resistance, and resilience in response to climatic events using satellite-derived Normalized Difference Vegetation Index (NDVI) time series from 2000 to 2020 across four major vegetation types (meadows, shrubs, wetlands, and coniferous forests) on the Qinghai-Xizang Plateau. We also calculated temporal stability of growing season temperature and precipitation at matching spatial scales. We found that both landscape diversity and temporal stability of NDVI increased with spatial scales, whereas resistance and resilience showed no consistent scale dependence. The effects of landscape diversity on temporal stability of NDVI varied significantly across spatial scales in all four vegetation types. In alpine wetlands and shrubs, higher landscape diversity was associated with lower precipitation stability, which in turn was linked to reduced temporal stability of NDVI; however, this indirect relationship was reversed in meadows. Our findings demonstrate that precipitation stability modulates the effect of landscape diversity on NDVI temporal stability across spatial scales. This work not only extends diversity-stability theory by incorporating scale-dependent mechanisms and climatic mediators, but also provides novel guidance for landscape-scale conservation and ecosystem management under changing environmental conditions.

Organisms use diel timing mechanisms to anticipate predictable daily environmental fluctuations, such as the start and end of the day light period. There is often ample intraspecific variation in this diel timing, with individuals being consistently active earlier or later than others in the population and therefore having early or late chronotypes. In tit species, early-active males have higher rates of extrapair paternity, and early-active females might have more offspring, thereby increasing their fitness. However, studies on these fitness consequences of chronotype tend to be inconclusive, based on small sample sizes and confounded with seasonal effects on activity timing. Here, we measured the fitness of standardised chronotype in female great tits (Parus major) across three breeding seasons. We extracted activity onsets, when females first left the nest in the morning, from recordings of nest temperatures during incubation and chick provisioning. To account for seasonal and daily variation in the timing of activity, we expressed these onsets relative to the conspecifics active on the same day. The chronotypes of 164 females were tested for differences in fitness and life-history parameters from brood monitoring data. We show that chronotype was not significantly related to fitness parameters, such as the number of fledglings and hatchlings, nor to offspring and female condition. However, extremely early and late chronotypes started breeding later in our population, but not in the re-analysed datasets from three other populations. Our findings suggest that chronotype is not under strong selection, or perhaps under fluctuating selection, allowing high between-individual variation to persist.

Apex carnivores are known to regulate ecosystem structure and function, including via interactions with syntopic, competitively inferior carnivores. These effects may be dependent on relative carnivore density and resource availability or productivity. We investigated the functional effect of African lions as an apex carnivore on the presence of co-occurring large carnivore species across two adjoining National Parks that contrast in relative densities of carnivores and prey. We employed two-species occupancy models from track data to test statistical interactions between lions and the other syntopic large carnivore species, while accounting for each species' habitat selection. We further investigated the influence of anthropogenic and natural variables on these co-occurrence dynamics. Our models revealed that the occurrence of each carnivore species was best predicted by access to their own key resources. We also found significant statistical interactions between lions and cheetahs, lions and leopards, and lions and spotted hyenas in resource-rich landscapes. Finally, we found limited support for the competition exclusion hypothesis between most species, with the exception of lion-African wild dog co-occurrence patterns. Species' co-occurrence dynamics were all influenced by resource availability, with lion-leopard and lion-cheetah co-occurrence decreasing strongly with increasing resource availability. Most species co-occurrence declined with increasing occurrence of lions. The patterns revealed by this study improves predictions of how changes in resource availability and carnivore occurrence could impact carnivore community dynamics and the functional role of apex carnivores.

Increasing drought events may impair carbon (C) storage in terrestrial ecosystems, but the impacts of isolated vs. recurrent droughts on soil C and its drivers remain unclear. We studied how isolated drought (66% reduction in growing season precipitation over two years) and recurrent drought (the same reduction applied to plots that had previously experienced a 4-year drought followed by two recovery years) influence shallow soil C and its plant-related drivers in two semi-arid grasslands. Despite a one-third decline in soil moisture under both droughts, the responses of above- and belowground C pools and species richness were limited and inconsistent, and soil C remained stable across years, sites, and treatments. Soil C resistance to these droughts was unrelated to the resistance of above- and belowground C pools in the first year of this study. In the second year, the resistance of aboveground forb C pool and belowground C pool promoted soil C resistance under isolated and recurrent drought, respectively. Relationships were observed only at one site, where soil C resistance increased with greater resistance of aboveground biomass, forb, and belowground C pools under isolated drought but decreased with higher species richness under recurrent drought. Overall, short-term isolated or recurrent drought events may not alter shallow soil C when plant-related C drivers show limited negative responses. However, caution is warranted when extrapolating these results, as soil C changes slowly and its response to drought may differ over time and across grassland types.

Fire is a major driver of ecological change in tropical forests, yet the combined effects of fire history and habitat loss on frugivorous birds and post-fire vegetation recovery remain poorly understood. We evaluated how fire severity, extent, and frequency-together with forest cover-shape frugivore abundance and influence short-term (≤ 10 years) forest resilience in the Cantareira-Mantiqueira Corridor, southeastern Brazil. Using frugivore surveys conducted at fixed points across 15 landscapes, combined with satellite-derived fire metrics and kNDVI-based estimates of engineering resilience, we applied a set of hypothesis-driven Generalized Linear Models and segmented regressions. Fire characteristics alone did not explain frugivore abundance; however, a strong interaction between fire severity and forest cover revealed that forest cover buffered fire impacts under a low severity but failed under high-severity conditions, leading to marked declines in frugivore abundance. Forest recovery was primarily governed by fire characteristics rather than by frugivore abundance. Fire extent showed a linear negative effect on kNDVI trend, while fire frequency displayed nonlinear behavior, with a threshold near three fire events beyond which recovery became highly variable and unpredictable. Together, these findings provide evidence that fire and habitat loss interact to shape frugivore communities, and that repeated burning can push fire-sensitive tropical forests toward resilience thresholds. Effective conservation and restoration strategies must therefore integrate both fire prevention and habitat maintenance to safeguard ecosystem recovery.

Many species experience less pressure from herbivores, predators, or pathogens in their introduced range than in their native range. This phenomenon, known as enemy release, is one explanation for the success of introduced plant species worldwide. However, species experience enemy release to different extents, or not at all. Surprisingly, we have little understanding of what types of species or circumstances are associated with strong enemy release. We aimed to test whether ten defensive leaf traits that contribute to plants' palatability to aboveground herbivores can predict the level of enemy release they experience. Our study expands upon previous work, which found enemy release occurring across 16 plant species studied at 12 sites within their native (5 sites; European) and introduced (7 sites; Australian) ranges. Contrary to all predictions, we found no evidence that enemy release was related to ash content, C:N ratio, hair density, leaf dry matter content, leaf mass per area, cyanogen presence, lipid content, phenolic compounds, oxidative activity, or combined chemical, physical, and total defences. This result demonstrates the need to further assess other traits, or environmental variables that may contribute to enemy release, so that we may more accurately predict when and where it is most likely to occur. Finding that these defensive traits do not predict enemy release in our study system brings us a step closer to understanding the mechanisms underlying successful invasion, which is increasingly important in our rapidly changing world.