The environment to the rescue: can physics help predict predator-prey interactions?

Understanding the factors that determine the occurrence and strength of ecological interactions under specific abiotic and biotic conditions is fundamental since many aspects of ecological community stability and ecosystem functioning depend on patterns of interactions among species. Current approaches to mapping food webs are mostly based on traits, expert knowledge, experiments, and/or statistical inference. However, they do not offer clear mechanisms explaining how trophic interactions are affected by the interplay between organism characteristics and aspects of the physical environment, such as temperature, light intensity or viscosity. Hence, they cannot yet predict accurately how local food webs will respond to anthropogenic pressures, notably to climate change and species invasions. Herein, we propose a framework that synthesises recent developments in food-web theory, integrating body size and metabolism with the physical properties of ecosystems. We advocate for combination of the movement paradigm with a modular definition of the predation sequence, because movement is central to predator-prey interactions, and a generic, modular model is needed to describe all the possible variation in predator-prey interactions. Pending sufficient empirical and theoretical knowledge, our framework will help predict the food-web impacts of well-studied physical factors, such as temperature and oxygen availability, as well as less commonly considered variables such as wind, turbidity or electrical conductivity. An improved predictive capability will facilitate a better understanding of ecosystem responses to a changing world.

Late-line treatment with bevacizumab alone or in combination with chemotherapy in recurrent high-grade gliomas.

PURPOSE: Bevacizumab's use in recurrent high-grade glioma is controversial. This study evaluates outcomes in recurrent high-grade glioma patients receiving bevacizumab alone or combined with chemotherapy as a late-line treatment. METHODS: We retrospectively analyzed patients treated with bevacizumab alone or combined with chemotherapy for high-grade gliomas who showed tumor progression after multiple treatment attempts. Overall survival (OS) and progression-free survival (PFS) were analyzed with Kaplan-Meier curves. Predictors of PFS according to prognostic variables were assessed with regression analysis. RESULTS: Between 2010 and 2022, 31 consecutive patients received bevacizumab alone or combined with chemotherapy as a late-line treatment for recurrent high-grade gliomas. Of these patients, 14 (45.2%) were responders according to RANO criteria, and 17 (54.8%) showed progressive or stable disease. OS at 3, 6, and 12 months was 80.3%, 62.1%, and 43.5. PFS was 48.4%, 34.3%, and 21.8%, respectively. In the multivariate survival analysis, the only factor independently associated with PFS was smaller 2D tumor size in post-contrast T1-weighted MRI at bevacizumab initiation (p = 0.02). Median time-to-progression was 3 months (95%CI: 1-4) in the unmethylated MGMT promoter group and 6 (95%CI: 1-11) in the methylated MGMT promoter group. This difference was not statistically significant (p = 0.37). CONCLUSIONS: Bevacizumab alone or in combination with chemotherapy could be beneficial as a late-line therapy in a subset of patients with recurrent high-grade glioma. Small 2D tumor size in post-contrast T1 weighted MRI at bevacizumab initiation was independently associated with prolonged time to progression.

Embolization before Gamma Knife radiosurgery for cerebral arteriovenous malformations does not negatively impact its obliteration rate: a series of 190 patients.

PURPOSE: Embolization of arteriovenous malformations (AVMs) before radiosurgery has been reported to negatively impact the obliteration rate. This study aims to assess treatment outcomes in a series of 190 patients treated by Gamma Knife radiosurgery (GKRS) for previously embolized AVMs. METHODS: The institutional database of AVMs was retrospectively reviewed between January 2004 and March 2018. The clinical and radiological data of patients treated with GKRS for previously embolized AVMs were analyzed. Predicting factors of obliteration and hemorrhage following GKRS were assessed with univariate and multivariate regression analyses. RESULTS: The mean AVM size was significantly reduced after embolization (p < 0.001). The obliteration rate was 78.4%. Multivariate analyses showed that a lower Spetzler-Martin grade (p = 0.035) and a higher marginal dose (p = 0.007) were associated with obliteration. Post-GKRS hemorrhages occurred in 14 patients (7.4%). A longer time between diagnosis and GKRS was the only factor associated with post-GKRS hemorrhages in multivariate analysis (p = 0.022). Complications related to the combined treatment were responsible for a new permanent neurological disability in 20 patients (10.5%), and a case of death (0.5%). CONCLUSIONS: This study shows that the embolization of AVMs does not have a negative impact on the obliteration rate after radiosurgery. Embolization reduces the AVM size to a treatable volume by GKRS. However, the combined treatment results in an increased complication rate related to the addition of the risks of each treatment modality.

Global change-driven effects on dissolved organic matter composition: Implications for food webs of northern lakes.

Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial-aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)-the messenger between terrestrial and lake ecosystems-with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change-driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice-out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.

Potential for Local Fertilization: A Benthocosm Test of Long-Term and Short-Term Effects of Mussel Excretion on the Plankton.

Mussel aquaculture has expanded worldwide and it is important to assess its impact on the water column and the planktonic food web to determine the sustainability of farming practices. Mussel farming may affect the planktonic food web indirectly by excreting bioavailable nutrients in the water column (a short-term effect) or by increasing nutrient effluxes from biodeposit-enriched sediments (a long-term effect). We tested both of these indirect effects in a lagoon by using plankton-enclosing benthocosms that were placed on the bottom of a shallow lagoon either inside of a mussel farm or at reference sites with no history of aquaculture. At each site, half of the benthocosms were enriched with seawater that had held mussels (excretion treatment), the other half received non-enriched seawater as a control treatment. We monitored nutrients ([PO43-] and [NH4+]), dissolved oxygen and plankton components (bacteria, the phytoplankton and the zooplankton) over 5 days. We found a significant relationship between long-term accumulation of mussel biodeposits in sediments, water-column nutrient concentrations and plankton growth. Effects of mussel excretion were not detected, too weak to be significant given the spatial and temporal variability observed in the lagoon. Effects of mussels on the water column are thus likely to be coupled to benthic processes in such semi-enclosed water bodies.

Bony Regeneration of the Sella after Transsphenoidal Pituitary Surgery.

OBJECTIVE: The purpose of this study is to demonstrate the possible bony regrowth of the sella after transsphenoidal surgery without any intraoperative sellar reconstruction. METHODS: Radiologic findings of the sella were reviewed in patients with pituitary tumors treated by transsphenoidal surgery. In 17 patients who had postoperative cranial computed tomography scans, bony regeneration of the sellar floor was evaluated by comparing immediate and late postoperative scans. The bony opening reduction was measured in transverse and sagittal planes. RESULTS: The median bony opening diameter in the transverse plane was 8.8 mm (interquartile range [IQR] 5.7-11.4) on the first scan and 4.2 mm (IQR 0.8-6.8) on the second scan. In the sagittal plane, it was 4.8 mm (IQR 1.8-6.8) on the first scan and 2.9 mm (IQR 1.6-3.9) on the second scan. These changes occurred in a median time of 36 months (IQR 22-42). There was a statistically significant decrease of the bony opening diameters in both the transverse and sagittal planes (P < 0.0001 and P = 0.0004, respectively). Bone regeneration was observed in 16 of the 17 patients (approximately 94%). CONCLUSION: There is a natural bony regeneration of the sella after transsphenoidal pituitary surgery.

Age-Related Vitamin D Deficiency Is Associated with Reduced Macular Ganglion Cell Complex: A Cross-Sectional High-Definition Optical Coherence Tomography Study.

BACKGROUND: Vitamin D deficiency is associated with smaller volume of optic chiasm in older adults, indicating a possible loss of the visual axons and their cellular bodies. Our objective was to determine whether vitamin D deficiency in older adults is associated with reduced thickness of the ganglion cell complex (GCC) and of the retinal nerve fibre layer (RNFL), as measured with high-definition optical coherence tomography (HD-OCT). METHODS: Eighty-five French older community-dwellers without open-angle glaucoma and patent age-related macular degeneration (mean, 71.1±4.7 years; 45.9% female) from the GAIT study were separated into 2 groups according to serum 25OHD level (i.e., deficient≤25 nmol/L or sufficient>25 nmol/L). Measurements of GCC and RNFL thickness were performed using HD-OCT. Age, gender, body mass index, number of comorbidities, dementia, functional autonomy, intracranial volume, visual acuity, serum calcium concentration and season of testing were considered as potential confounders. RESULTS: Mean serum 25OHD concentration was 58.4±26.8 nmol/L. Mean logMAR visual acuity was 0.03±0.06. Mean visual field mean deviation was -1.25±2.29 dB. Patients with vitamin D deficiency (n=11) had a reduced mean GCC thickness compared to those without vitamin D deficiency (72.1±7.4 µm versus 77.5±7.5 µm, P=0.028). There was no difference of the mean RNFL thickness in these two groups (P=0.133). After adjustment for potential confounders, vitamin D deficiency was associated with reduced GCC thickness (ß=-5.12, P=0.048) but not RNFL thickness (ß=-9.98, P=0.061). Specifically, vitamin D deficiency correlated with the superior medial GCC area (P=0.017) and superior temporal GCC area (P=0.010). CONCLUSIONS: Vitamin D deficiency in older patients is associated with reduced mean GCC thickness, which can represent an early stage of optic nerve damage, prior to RNFL loss.

Plant-herbivore-decomposer stoichiometric mismatches and nutrient cycling in ecosystems.

Plant stoichiometry is thought to have a major influence on how herbivores affect nutrient availability in ecosystems. Most conceptual models predict that plants with high nutrient contents increase nutrient excretion by herbivores, in turn raising nutrient availability. To test this hypothesis, we built a stoichiometrically explicit model that includes a simple but thorough description of the processes of herbivory and decomposition. Our results challenge traditional views of herbivore impacts on nutrient availability in many ways. They show that the relationship between plant nutrient content and the impact of herbivores predicted by conceptual models holds only at high plant nutrient contents. At low plant nutrient contents, the impact of herbivores is mediated by the mineralization/immobilization of nutrients by decomposers and by the type of resource limiting the growth of decomposers. Both parameters are functions of the mismatch between plant and decomposer stoichiometries. Our work provides new predictions about the impacts of herbivores on ecosystem fertility that depend on critical interactions between plant, herbivore and decomposer stoichiometries in ecosystems.

When microbes and consumers determine the limiting nutrient of autotrophs: a theoretical analysis.

Ecological stoichiometry postulates that differential nutrient recycling of elements such as nitrogen and phosphorus by consumers can shift the element that limits plant growth. However, this hypothesis has so far considered the effect of consumers, mostly herbivores, out of their food-web context. Microbial decomposers are important components of food webs, and might prove as important as consumers in changing the availability of elements for plants. In this theoretical study, we investigate how decomposers determine the nutrient that limits plants, both by feeding on nutrients and organic carbon released by plants and consumers, and by being fed upon by omnivorous consumers. We show that decomposers can greatly alter the relative availability of nutrients for plants. The type of limiting nutrient promoted by decomposers depends on their own elemental composition and, when applicable, on their ingestion by consumers. Our results highlight the limitations of previous stoichiometric theories of plant nutrient limitation control, which often ignored trophic levels other than plants and herbivores. They also suggest that detrital chains play an important role in determining plant nutrient limitation in many ecosystems.

Stoichiometric constraints on resource use, competitive interactions, and elemental cycling in microbial decomposers.

Heterotrophic microbial decomposers, such as bacteria and fungi, immobilize or mineralize inorganic elements, depending on their elemental composition and that of their organic resource. This fact has major implications for their interactions with other consumers of inorganic elements. We combine the stoichiometric and resource-ratio approaches in a model describing the use by decomposers of an organic and an inorganic resource containing the same essential element, to study its consequences on decomposer interactions and their role in elemental cycling. Our model considers the elemental composition of organic matter and the principle of its homeostasis explicitly. New predictions emerge, in particular, (1) stoichiometric constraints generate a trade-off between the R* values of decomposers for the two resources; (2) they create favorable conditions for the coexistence of decomposers limited by different resources and with different elemental demands; (3) however, combined with conditions on species-specific equilibrium limitation, they draw decomposers toward colimitation by the organic and inorganic resources on an evolutionary time scale. Moreover, we derive the conditions under which decomposers switch from consumption to excretion of the inorganic resource. We expect our predictions to be useful in explaining the community structure of decomposers and their interactions with other consumers of inorganic resources, particularly primary producers.