Ecosphere

Journal: Ecosphere

Publisher

Ecological Society of America

ISSN

2150-8925

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Publications 1 - 10 of 16

Positive association between the diversity of symbionts and parasitoids of aphids in field populations
Hafer-Hahmann, Nina; Vorburger, Christoph (2021)
Ecosphere
Parasites and pathogens are crucial in shaping immune systems. Many animals and especially insects have outsourced part of their immune function to protective symbionts. There is good evidence that, akin to immune systems, parasites shape the occurrence and diversity of protective symbionts and that likewise, protective symbionts can shape the occurrence and diversity of parasites. Such a relationship should result in a correlation between symbiont and parasite diversity in nature. Aphids are well known for possessing symbionts that provide specific and effective protection against parasitoid wasps. We compared symbiont and parasitoid diversity across multiple populations of different aphid species of the genus Aphis and their parasitoid wasps. The diversity of protective symbionts and parasitoids was indeed positively associated. Even though this association was very noisy, it is in line with the hypothesis that parasitoids and symbionts promote each other’s diversity. © 2021 The Authors.
Disentangling the factors driving tree reproduction
Davi, Hendrik; Cailleret, Maxime; Restoux, Gwendal; et al. (2016)
Ecosphere
Seed production is a strong indicator of plant fitness and plays a major role in population dynamics. However, the environmental and endogenous factors driving seed production are still poorly described and are often hard to disentangle. Consequently, we combined principal components analysis and mixed‐effects linear models that can consider the multicollinearity of the explanatory variables and quantify their respective influence on the spatio‐temporal variability in reproduction. We applied this method to analyze the relationships between cone production in Abies alba Mill. trees (6829 individual reports of cone production). We estimated the relationships between cone production and climate, elevation, tree size (diameter and height), age, crown defoliation rate, and past radial growth. We found that the distribution of annual cone production was highly skewed; 21% of the trees did not produce any cones, whereas 3.7% produced more than 100 cones in a single year. Among the endogenous factors, tree size explained 57% of the variation in cone production with large trees being the most productive. Low radial growth rates in previous years were mostly associated with higher cone production (14% of the variation), while elevation and crown defoliation had non‐monotonic effects on reproduction. Finally, years of high cone production were strongly correlated with the difference between the April temperatures of the two previous years and were also associated with a dry spring 2 yr prior to cone production followed by a humid spring the previous year. These results highlight the complexity of the abiotic and biotic factors involved in reproduction and their respective and interactive influence on the interannual and interindividual variability in cone production.
Comparison of two detailed models of Aedes aegypti population dynamics
Legros, Mathieu; Otero, Marcelo; Aznar, Victoria Romeo; et al. (2016)
Ecosphere
The success of control programs for mosquito‐borne diseases can be enhanced by crucial information provided by models of the mosquito populations. Models, however, can differ in their structure, complexity, and biological assumptions, and these differences impact their predictions. Unfortunately, it is typically difficult to determine why two complex models make different predictions because we lack structured side‐by‐side comparisons of models using comparable parameterization. Here, we present a detailed comparison of two complex, spatially explicit, stochastic models of the population dynamics of Aedes aegypti, the main vector of dengue, yellow fever, chikungunya, and Zika viruses. Both models describe the mosquito's biological and ecological characteristics, but differ in complexity and specific assumptions. We compare the predictions of these models in two selected climatic settings: a tropical and weakly seasonal climate in Iquitos, Peru, and a temperate and strongly seasonal climate in Buenos Aires, Argentina. Both models were calibrated to operate at identical average densities in unperturbed conditions in both settings, by adjusting parameters regulating densities in each model (number of larval development sites and amount of nutritional resources). We show that the models differ in their sensitivity to environmental conditions (temperature and rainfall) and trace differences to specific model assumptions. Temporal dynamics of the Ae. aegypti populations predicted by the two models differ more markedly under strongly seasonal Buenos Aires conditions. We use both models to simulate killing of larvae and/or adults with insecticides in selected areas. We show that predictions of population recovery by the models differ substantially, an effect likely related to model assumptions regarding larval development and (direct or delayed) density dependence. Our methodical comparison provides important guidance for model improvement by identifying key areas of Ae. aegypti ecology that substantially affect model predictions, and revealing the impact of model assumptions on population dynamics predictions in unperturbed and perturbed conditions.
Ecometabolomics of plant–herbivore and plant–fungi interactions: a synthesis study
Sardans, Jordi; Gargallo-Garriga, Albert; Urban, Otmar; et al. (2021)
Ecosphere
The functional adaptive responses of higher plants to biotic interactions with herbivores and fungi have long been topics of research. One constraint to obtaining a comprehensive understanding of the most general plant responses, however, has been the difficulty of studying all plant functional shifts simultaneously due to analytical limitations. Now this is possible with the advent of metabolomics. Using 151 records from the WEB of SCIENCE database, we have analyzed the development and application of metabolomic profiles to ecological studies in the last two decades. We have used meta-analysis and pathway enrichment analyses to assess the whole set of constitutive and inducible defenses. Constitutive defenses against herbivores were mainly based on a significant high level of the metabolism of several amino acids with parallel increases in the concentrations of flavones (phenolics) and saponins (glycosides). Inducible defenses, though, were mainly based on the increases in concentration of methyl-ketone, pantothenate, and Coenzyme A. Butyrate metabolism and the mitochondrial electron-transport chain were upregulated, in agreement with previous reports that herbivory-activated plant chemical defenses were mainly based on jasmonic acid, salicylic acid, and ethylene-associated pathways. The metabolic responses/acclimations to pathogenic fungi were mainly linked with increases in aspartate and pyruvate metabolism, the transfer of acetyl groups within mitochondria, and the upregulation of branched-chain amino acids degradation pathways. These responses/acclimations were accompanied by higher concentrations of the most important groups of secondary metabolites such as phenolics (anthocyanins, flavonoids), quinones, alkaloids, terpenoids, and polyamines and other compounds related to antistress mechanisms such as proline. The leaves of mycorrhized plants accumulated nucleotide sugars, sphingolipids, and methylhistidine. These responses were associated with maintaining the integrity of plant cell membranes under fungal hypha penetration. The responses were accompanied by increases in the concentrations of phenolics, blumenols, and alkaloids and decreases in the concentrations of polyamines, consistent with the mycorrhizal inhibition of polyamines. This summary provides a clear synthesis of the most successful plant strategies selected after millions of years of evolution and will be a very promising tool for the management of crops and ecosystems and for selecting the main lines in breeding studies for future research.
A dryland re‐vegetation in northern China: Success or failure? Quick transitions or long lags?
Chen, Ning; Ratajczak, Zak; Yu, Kailiang (2019)
Ecosphere
Intensified anthropogenic activities have drastically altered many ecosystems, motivating the use of restoration to regain key ecosystem functions and services and to stem biodiversity losses. Restoration is particularly difficult when human activities have pushed an area into a new state with self‐reinforcing feedbacks. This study investigated a long‐term restoration project in a dryland ecosystem of the Tengger Desert in northwestern China, initiated in 1956. We analyzed shrub and grass cover for 49 yr after the installation of restoration infrastructure that altered external conditions (i.e., using packed straw to reduce wind erosion) and system state (by planting shrubs). After 37–40 yr, the re‐vegetation project was successful in restoring the system to a state similar to native vegetation, with high grass cover (30–50%), low shrub cover (8–10%), and a thick biological soil crust (biocrust). However, the shift to high grass cover did not begin until year 37, before which shrub cover was high (15–20%) and grasses were subdominant (usually <10%). The shift from shrub to grass dominance was abrupt, registering significant nonlinear changes over time and relative to a key driver of vegetation dynamics, estimated biocrust thickness. Biocrust thickness increased gradually over time, which reduced rainfall infiltration into deep soil and thus increased soil moisture available for the shallow‐rooted grasses. The shift from the bare soil state to the steppe state exhibited a long time lag, suggesting that it can take decades to determine whether dryland restoration efforts succeed. The results indicate that persistence might be critical to forcing desired state transitions and that dryland restoration can proceed as a series of time lags, punctuated by abrupt changes in ecosystem state
Low spatial autocorrelation in mountain biodiversity data and model residuals
Chevalier, Mathieu; Mod, Heidi; Broennimann, Olivier; et al. (2021)
Ecosphere
Spatial autocorrelation (SAC) is a common feature of ecological data where observations tend to be more similar at some geographic distance(s) than expected by chance. Despite the implications of SAC for data dependencies, its impact on the performance of species distribution models (SDMs) remains controversial, with reports of both strong and negligible impacts on inference. Yet, no study has comprehensively assessed the prevalence and the strength of SAC in the residuals of SDMs over entire geographic areas. Here, we used a large‐scale spatial inventory in the western Swiss Alps to provide a thorough assessment of the importance of SAC for (1) 850 species belonging to nine taxonomic groups, (2) six predictors commonly used for modeling species distributions, and (3) residuals obtained from SDMs fitted with two algorithms with the six predictors included as covariates. We used various statistical tools to evaluate (1) the global level of SAC, (2) the spatial pattern and spatial extent of SAC, and (3) whether local clusters of SAC can be detected. We further investigated the effect of the sampling design on SAC levels. Overall, while environmental predictors expectedly displayed high SAC levels, SAC in biodiversity data was rather low overall and vanished rapidly at a distance of ~5–10 km. We found low evidence for the existence of local clusters of SAC. Most importantly, model residuals were not spatially autocorrelated, suggesting that inferences derived from SDMs are unlikely to be affected by SAC. Further, our results suggest that the influence of SAC can be reduced by a careful sampling design. Overall, our results suggest that SAC is not a major concern for rugged mountain landscapes.
Positive plant–plant interactions expand the upper distributional limits of some vascular plant species
Raath‐Krüger, Morgan J.; McGeoch, Melodie A.; Schöb, Christian; et al. (2019)
Ecosphere
Biotic interactions can shape species’ distributions through their impact on species’ realized niches, potentially constraining or expanding the range of conditions under which species occur. We examine whether fine‐scale plant–plant interactions scale up to shape broad‐scale species’ distributions, using Azorella selago, a widespread cushion plant that facilitates other species, and the rest of the vascular flora of sub‐Antarctic Marion Island as a model system. We compared the upper elevational distributional limit of each species when growing on vs. away from A. selago to test how the interaction with this cushion plant species affects species’ ranges. Three out of 19 vascular plant species occurred at higher altitudes in the presence of A. selago than in the absence of A. selago: Acaena magellanica (+26 m higher), Colobanthus kerguelensis (+37 m higher), and Lycopodium saururus (+19 m higher). Therefore, A. selago's fine‐scale impacts scaled up to shape the distribution of a subset of the vascular flora of Marion Island. Plant–plant interactions thus have the potential to expand species upper distributional limits by increasing the niche space that a species can occupy, although the influence of these interactions may be strongly species‐specific.
Gap pattern of the largest primeval beech forest of Europe revealed by remote sensing
Hobi, Martina L.; Ginzler, Christian; Commarmot, Brigitte; et al. (2015)
Ecosphere
Little is known about the gap pattern of primeval beech forests, since large‐scale studies with continuous coverage are lacking. Analyses of forest structural patterns have benefitted from advances in remote sensing, especially with the launch of satellites providing data of submetric ground resolution. These developments can strongly advance our knowledge of natural forest dynamics and disturbance regimes. The Uholka‐Shyrokyi Luh forest in the Ukrainian Carpathians, the largest remnant of primeval European beech (Fagus sylvatica L.) covering 102.8 km2, is an outstanding object to analyze the frequency distribution of gap sizes and to infer processes of forest dynamics. A stereo pair of very high‐resolution WorldView‐2 satellite images was used to characterize the forest's gap pattern. Canopy gaps were first digitized stereoscopically based on the image pair. In a second step, spectral properties in the red and yellow frequency bands were used to distinguish the stereoscopically mapped gap areas from non‐gap areas, which enabled gap mapping over the entire study area. To validate the spectral gap mapping 338 randomly distributed samples were assigned manually to gap and non‐gap areas based on the ortho‐images. We found excellent agreement except for an overestimation of gaps close to clouds due to diffuse image areas. The frequency distribution of gap size revealed the forest to be structured by a small‐scale mosaic of gaps mainly <200 m2 (98% of the gaps). Only a few large, stand‐replacing events were detected, most probably caused by a wind storm in March 2007 and a heavy wet snow fall in October 2009. The small canopy gaps reflect fine‐scale processes shaping forest structure, i.e., the death of single trees or groups of a few trees and is in line with the findings of the terrestrial forest inventory. We conclude that remote sensing approaches based on very high‐resolution satellite images are highly useful to characterize even small‐scale forest disturbance regimes and to study long‐term gap dynamics. Stereo satellite images provide two viewing angles of the study area, thus allowing for a highly accurate mapping of canopy gaps in forests with a complex topography.
Beyond predator and prey: First evidence of an association between ocelot and opossum individuals
Gálvez, Dumas; Ketola, Christopher; Piga, Angelo; et al. (2025)
Ecosphere
Interspecific associations can provide various benefits, including reducing predation risk, sharing information, or acquiring food. Studying these associations is key to understanding the drivers and mechanisms underlying non-kin cooperation. Here, we present the first evidence of single individuals of ocelot (Leopardus pardalis) and common opossum (Didelphis marsupialis) associating and moving together in the rainforest. This association, unknown until now, was captured in four independent events, through camera-trap videos and photographs taken across different times and locations, suggesting a consistent pattern among different individuals. Additionally, we experimentally show that opossums are significantly more attracted to ocelot scent cues, on which they often rub their bodies, compared to control and puma scents. Both the ocelot and the common opossum are nocturnal, solitary species that share territories and can overlap diets; yet, ocelots can also prey on opossums. This puzzling association might emerge because both species could benefit from each other's presence, potentially improving foraging efficiency or safety. Such a newly discovered association offers insight into the complex dynamics of interspecific associations in tropical ecosystems. Future research investigating its prevalence and benefits will deepen our understanding of the ecological and evolutionary conditions driving this behaviour.
Tree regeneration in models of forest dynamics: A key priority for further research
Díaz-Yáñez, Olalla; Käber, Yannek; Anders, Tim; et al. (2024)
Ecosphere
Tree regeneration is a key process in forest dynamics, particularly in the context of forest resilience and climate change. Models are pivotal for assessing long-term forest dynamics, and they have been in use for more than 50 years. However, there is a need to evaluate their capacity to accurately represent tree regeneration. We assess how well current models capture the overall abundance, species composition, and mortality of tree regeneration. Using 15 models built to capture long-term forest dynamics at the stand, landscape, and global levels, we simulate tree regeneration at 200 sites representing large environmental gradients across Central Europe. The results are evaluated against extensive data from unmanaged forests. Most of the models overestimate recruitment levels, which is compensated only in some models by high simulated mortality rates in the early stages of individual-tree dynamics. Simulated species diversity of recruitment generally matches observed ranges. Models simulating higher stand-level species diversity do not feature higher species diversity in the recruitment layer. The effect of light availability on recruitment levels is captured better than the effects of temperature and soil moisture, but patterns are not consistent across models. Increasing complexity in the tree regeneration modules is not related to higher accuracy of simulated tree recruitment. Furthermore, individual model design is more important than scale (stand, landscape, and global) and approach (empirical and process-based) for accurately capturing tree regeneration. Despite the mismatches between simulation results and data, it is remarkable that most models capture the essential features of the highly complex process of tree regeneration, while not having been parameterized with such data. We conclude that much can be gained by evaluating and refining the modeling of tree regeneration processes. This has the potential to render long-term projections of forest dynamics under changing environmental conditions much more robust.

Publications 1 - 10 of 16

Journal: Ecosphere

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