Environmental disturbances that vary in space and intensity are major drivers of ecological community structure and ecosystem functioning. Such spatially heterogeneous disturbances can generate environmental gradients that influence species composition and abundance through mechanisms including species sorting, mass effects, or priority effects. Understanding how these processes interact with biodiversity and ecosystem functions remains challenging, particularly in well-connected meta-communities where dispersal can either buffer or amplify local disturbance effects. Here, we investigated these dynamics in a network of interconnected artificial ponds exposed to a natural gradient of tidal influence, which generates variation in water chemistry and hydrology across the system. We found that tidal exposure was strongly associated with environmental variation among ponds, which peaked at intermediate levels of tidal influence. In contrast, beta diversity among macroinvertebrate communities was highest under strong tidal influence and declined at lower tidal intensity. Overall, our result suggests that high connectivity and stochastic processes, overriding environmental filtering, play a key role in structuring communities in ponds most affected by tides, while species sorting dominates under lower tidal intensity. At the landscape scale, the disturbance gradient generates a mosaic of habitats with contrasting environmental conditions and community dynamics. Finally, decomposition rates increased with increasing tidal influence, reflecting the combined effects of tidal dynamics on environmental conditions and macroinvertebrate community structure. These findings provide a framework for understanding how spatially heterogeneous disturbances influence biodiversity and ecosystem functioning in freshwater networks, with implications for the management and conservation of connected ponds.

The export of emergent aquatic insects is a critical energy subsidy for terrestrial food webs. While urbanization is known to alter stream communities, its effects on the size structure of these insect subsidies and the subsequent consequences for riparian predators remain poorly understood. Yet, body size, a key dimension of subsidy quality, can strongly shape resource use by terrestrial predators, given their size-dependent foraging. Here, we investigated how land impervious cover affects the body-size distribution of emergent insects and riparian spider communities along the entire length of two urban streams. We sampled and analyzed emergent insect community composition, three size-structure metrics (i.e., size-spectrum slopes, mean body size and size range) and used stable isotopes to assess spider reliance on aquatic prey. Impervious cover was the strongest driver of the emergent community structure, overriding effects of longitudinal position. Increasing impervious surface cover was associated with community homogenization, a pronounced shift toward smaller individuals, steeper size-spectrum slopes and a contraction of body-size range. Notably, total exported biomass did not change significantly, indicating that the influence of surface imperviousness manifests primarily in qualitative rather than quantitative terms. Those changes led to higher reliance on aquatic prey from riparian spiders. Our work highlights that the homogenization of aquatic prey size distribution is a powerful driver of change within riparian food webs and underscore the importance of integrating body-size composition into assessments of land

jabbrv-ltwa-all.ldf jabbrv-ltwa-en.ldf Many ecosystems worldwide are interconnected by spatial pulses of energy and material capable of structuring and defining their main processes. With global anthropogenic change, the dynamics of such fluxes (i.e., resource type, magnitude and duration) will be modified. Yet, it is still unclear how simultaneous alterations in flux dynamics might interact to influence ecosystem functioning. Here, we provide experimental evidence for interactive effects of resource pulse quality and abruptness level (i.e., magnitude/duration) on aquatic ecosystem functions using experimental mesocosms. Mesocosms were exposed to three resource types (insects, leaves and a mix of both) based on three abruptness levels (high, medium, low) in a 3 x 3 factorial design. With an equal overall amount of resource added, nutrient inputs from insect decomposition spread quickly through ecosystem compartments, supporting the development of diverse autotrophic primary producers and increasing ecosystem stocks. In contrast, leaf decomposition confined nutrient flows within the benthic food web compartment, probably favoring more heterotrophic organisms linked to the decomposition of the vegetal matrix. Finally, our study also revealed that ecological responses arising from insect pulse are more sensitive to changes in abruptness variation – pulsed event of great magnitude over a short period of time leading to higher nutrient flow between ecosystem compartments, increasing the ecosystem impact of nutrient enrichment. Thus, considering both quality and abruptness level of allochtonous resource pulse is important in the understanding of ecological processes changes under such biomass-altering disturbance events.

A document by Cornelia Twining. Click on the document to view its contents.

Parasite occurrence and infection estimates vary through time and space, making understanding the underlying drivers highly complex. Comparative studies based on empirical data must consider the factors of variation involved in estimating infection metrics in natural populations to make appropriate and reliable comparisons. Using a multi-scale approach, we explored the sources of variation in the estimation of infection prevalence, focusing on black spot disease in littoral freshwater fish communities sampled across 15 lakes in Québec, Canada. Our results show that infection prevalence is spatially heterogeneous across the landscape with evidence of infection hotspots and coldspots. Method-related sampling biases led to significant variations in prevalence estimates and spatial patterns of disease occurrence. Our results also indicated that low sampling efforts tend to overestimate the prevalence of infection in the landscape, and that the sampling effort required to estimate an accurate infection prevalence depends on the sampling method employed. Physico-chemical characteristics of the sites and local fish community structure were found to be the best drivers of infection at smaller spatial scales. Furthermore, our results suggest dilution effects due to obstruction and compatibility barriers limit the survival of the free-living cercaria parasite lifestage. Several relationships between infection prevalence and environmental drivers revealed non-linearity, suggesting complex interactions. Examining infection prevalence data at various spatial scales revealed method-induced biases, sampling effort effect and environment driven relationships underscoring the importance of context-dependencies and scale-dependencies in studies on host-parasite interactions.

Approximatively 25 chemical elements are essential for the maintenance, growth and reproduction of all living organisms. Hence, the movement, distribution, and relative proportions of those elements on the landscape should influence the structure and functioning of biological communities. Yet our basic understanding for the spatial distribution of elements across landscapes is limited. Here, we propose to apply tools from community and landscape ecology to study spatial patterns in elements. We illustrate this framework using tree leaves elemental composition and demonstrate how spatial grain and spatial dissimilarity of elements interact leading to predictable patterns in elemental distributions at various spatial scales. Meanwhile, further analysis revealed that potassium and calcium are the most important elemental contributors to spatial dissimilarity in leaf elements, raising new questions about their role in, or response to, distributions of biodiversity and ecosystem functions. Our framework provides a way to integrate abiotic and biotic processes, demonstrating how we can use community metrics to investigate variability of individual elements across landscapes. We conclude by hypothesizing that changes in the evenness or beta-diversity of elements should reflect the structure of biotic communities, providing a long-sought mechanistic link between community and ecosystem processes that can be measured directly in the field.

The integration of ecosystem processes over large spatial extents is critical to predicting whether and how global changes may impact biodiversity and ecosystem functions. Yet, there remains an important gap in meta-ecosystem models to predict multiple functions (e.g., carbon sequestration, elemental cycling, trophic efficiency) across ecosystem types (e.g., terrestrial-aquatic, benthic-pelagic). We derive a flexible meta-ecosystem model to predict ecosystem functions at landscape extents by integrating the spatial dimension of natural systems as spatial networks of different habitat types connected by cross-ecosystem flows of materials and organisms. We partition the physical connectedness of ecosystems from the spatial flow rates of materials and organisms, allowing the representation of all types of connectivity across ecosystem boundaries as well as the interaction(s) between them. Through simulating a forest-lake-stream meta-ecosystem, our model illustrated that even if spatial flows induced significant local losses of nutrients, differences in local ecosystem efficiencies could lead to increased secondary production at regional scale. This emergent result, which we dub the ‘cross-ecosystem efficiency hypothesis’, emphasizes the importance of integrating ecosystem diversity and complementarity in meta-ecosystem models to generate empirically testable hypotheses for ecosystem functions.