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Summary Spatial and temporal heterogeneity in flowering occur in many plant species with abiotic pollination and may confer fitness advantages through mechanisms such as predator satiation or pollination efficiency. Environmental factors such as light quality or quantity and temperature play an important role in inducing synchronization on wide geographic scales. On a smaller geographic scale, external factors such as resource availability and herbivory are theorized to trigger flowering, while genetic factors may also play an important role. In this study, we assessed the importance of ecological and genetic factors in shaping seascape‐level spatial heterogeneity in flowering of the seagrass Posidonia oceanica. By investigating spatially close sites (<20 km) with similar seascape configurations and depth, we assume that major environmental drivers (temperature and light) were equivalent. We assessed four ecological factors (productivity, leaf nitrogen and carbon content and herbivory) and three genetic factors (heterozygosity, relatedness and clonality) to assess three hypotheses for synchronized flowering in P. oceanica: (i) clone synchronization (internal clock hypothesis), (ii) variation in nutrient availability, potentially caused by spatial heterogeneity in herbivory rates or nutrient translocation via clonal integration (resource budget hypothesis) or (iii) kin selection and sibling synchronization. Internal relatedness and heterozygosity had a significant positive effect on the abundance of flowers. Moreover, productivity and genotypic richness (clonality) were negatively associated with flower density, although at a lower level of significance. In addition, we found that clones were almost exclusively shared among mass‐flowering patches and patches without mass‐flowering, respectively. Synthesis. The results shed new light on seagrass flowering patterns and on the mechanisms of flower synchronization at the patch level within a wider spatial scale. We found support for the kin selection hypothesis and indirect evidence for the resource budget hypothesis. Thus, a combination of mainly genetic but also ecological factors causes the observed heterogeneous flowering patterns in Posidonia oceanica seascapes. In addition, we found a strong positive relationship between the number of flowers and heterozygosity, adding evidence to the controversial association between heterozygosity and fitness when a limited number of loci are used. To our knowledge, this study is the first to link both ecological and genetic factors with flower abundance in a species with a presumed masting strategy.

Predicting where state-changing thresholds lie can be inherently complex in ecosystems characterized by nonlinear dynamics. Unpacking the mechanisms underlying these transitions can help considerably reduce this unpredictability. We used empirical observations, field and laboratory experiments, and mathematical models to examine how differences in nutrient regimes mediate the capacity of macrophyte communities to sustain sea urchin grazing. In relatively nutrient-rich conditions, macrophyte systems were more resilient to grazing, shifting to barrens beyond 1 800 g m −2 (urchin biomass), more than twice the threshold of nutrient-poor conditions. The mechanisms driving these differences are linked to how nutrients mediate urchin foraging and algal growth: controlled experiments showed that low-nutrient regimes trigger compensatory feeding and reduce plant growth, mechanisms supported by our consumer–resource model. These mechanisms act together to halve macrophyte community resilience. Our study demonstrates that by mediating the underlying drivers, inherent conditions can strongly influence the buffer capacity of nonlinear systems.

Significance Consumption transfers energy and materials through food chains and fundamentally influences ecosystem productivity. Therefore, mapping the distribution of consumer feeding intensity is key to understanding how environmental changes influence biodiversity, with consequent effects on trophic transfer and top–down impacts through food webs. Our global comparison of standardized bait consumption in shallow coastal habitats finds a peak in feeding intensity away from the equator that is better explained by the presence of particular consumer families than by latitude or temperature. This study complements recent demonstrations that changes in biodiversity can have similar or larger impacts on ecological processes than those of climate.

Summary The prevalence of local adaptation and phenotypic plasticity among populations is critical to accurately predicting when and where climate change impacts will occur. Currently, comparisons of thermal performance between populations are untested for most marine species or overlooked by models predicting the thermal sensitivity of species to extirpation. Here we compared the ecological response and recovery of seagrass populations (Posidonia oceanica) to thermal stress throughout a year‐long translocation experiment across a 2800‐km gradient in ocean climate. Transplants in central and warm‐edge locations experienced temperatures > 29°C, representing thermal anomalies > 5°C above long‐term maxima for cool‐edge populations, 1.5°C for central and < 1°C for warm‐edge populations. Cool‐edge, central and warm‐edge populations differed in thermal performance when grown under common conditions, but patterns contrasted with expectations based on thermal geography. Cool‐edge populations did not differ from warm‐edge populations under common conditions and performed significantly better than central populations in growth and survival. Our findings reveal that thermal performance does not necessarily reflect the thermal geography of a species. We demonstrate that warm‐edge populations can be less sensitive to thermal stress than cooler, central populations suggesting that Mediterranean seagrasses have greater resilience to warming than current paradigms suggest.

There is increasing uncertainty of how marine ecosystems will respond to rising temperatures. While studies have focused on the impacts of warming on individual species, knowledge of how species interactions are likely to respond is scant. The strength of even simple two-species interactions is influenced by several interacting mechanisms, each potentially changing with temperature. We used controlled experiments to assess how plant-herbivore interactions respond to temperature for three structural dominant macrophytes in the Mediterranean and their principal sea urchin herbivore. Increasing temperature differentially influenced plant-specific growth, sea urchin growth and metabolism, consumption rates and herbivore preferences, but not movement behaviour. Evaluating these empirical observations against conceptual models of plant-herbivore performance, it appears likely that while the strength of herbivory may increase for the tested macroalga, for the two dominant seagrasses, the interaction strength may remain relatively unchanged or even weaken as temperatures rise. These results show a clear set of winners and losers in the warming Mediterranean as the complex factors driving species interactions change.