BUSCADOR RECOLECTA

Usage Notes: dataset of Generation and maintenance of predation hotspots of a functionally important herbivore in a patchy habitat mosaic Data file contains values for each patch of the accumulated predation rate after 5 days and 10 days of the experiment (response variable) and of the attributes at patch and landscape levels (z-score of HSA) used as predictor in the Multi-model averaging selection. Bold numbers evidence patches where high aggregations of predation risk occurred (predation hotspots). dataset.xlsx, 1. By modifying how critical ecosystem functions are distributed across the landscape, the spatial configuration and characteristics of patches can play a strong role in structuring communities. In strongly predator-controlled ecosystems, this patchy distribution of function can have complex downstream consequences, subjecting some areas to disproportionately high rates of predation, leaving other areas susceptible to herbivore outbreaks. 2. In this study we assess how spatial attributes at patch and landscape scales potentially influence the spatial and temporal distribution of predation on a functionally important herbivore in a patchy Mediterranean marine macrophyte community characterized by strong top-down control. 3. We experimentally tracked how predation risk of tethered sea urchins varied across space over a 10-day period in a patchy seagrass meadow. We related these patterns with patch and landscape-level attributes across the habitat mosaic. 4. At the level of the patch, predation risk was highest in seagrass patches with low canopies, without access to sheltering rocks. Scaling up to the landscape mosaic however, predation risk increased in dense aggregations of patches with high perimeter-to-area ratios close to rocky habitats. Predation aggregated in spatially-explicit hotspots and coldspots that were maintained through time. Interestingly, this pattern of predation risk correlated well with the natural abundance of sea urchins. 5. Our results show that spatial patch configuration can be a strong mediator of top trophic functions in marine ecosystems, causing significant clumping in the way predation – and therefore herbivory – are distributed across space. Given the importance of top-down control for these shallow marine ecosystems, it is crucial to incorporate landscape attributes in understanding the impact of functionally important herbivores on highly fragmented habitats., Peer reviewed

Densities OIKOS Sea urchin densities per size class in two different habitats (macroalgal communities on rocky substrates and Posidonia oceanica seagrass meadows). Data were collected by SCUBA in the NW Mediterranean (Catalan Coast, NE Spain) in 8 different sites and 2 periods., Herbivore outbreaks often trigger catastrophic overgrazing events in marine macrophyte ecosystems. The sea urchin Paracentrotus lividus, the dominant herbivore of shallow Mediterranean seascapes, is capable of precipitating shifts to barrens when its populations explode. P. lividus is found ubiquitously in rocky macroalgal communities and in sandy seagrass meadows of Posidonia oceanica, two of the most important subtidal habitats in the Mediterranean. We explored if habitat-specific regulation across the principal stages of the urchin life cycle could help explain the persistence of these populations in connected mosaics. We measured each of three relevant ecological process (i.e. settlement, post-settlement survival and predation) across a wide stretch of the Mediterranean coast (ca. 600km). Our results show that habitat-specific regulation is critical in determining urchin populations: each habitat limited urchin sub-populations at different life stages. Settlement was never limiting; urchins settled at similar rates in both habitats across the coast. Post-settlement survival was a clear bottleneck, particularly in seagrass meadows where no juvenile urchins were recorded. Despite this bottleneck in seagrasses, adult urchin populations were very similar in both seagrass and macroalgal habitats indicating that other processes (potentially migration) could be key in determining adult distributions across the mosaic. The fact that population regulation is clearly habitat-specific suggests that sea urchin populations may be significantly buffered from bottlenecks in mixed seascapes where both habitats co-occur. Sea urchin populations can therefore persist across the seascape despite strong habitat-specific regulation either by maintaining reproductive output in one habitat or by migrating between them. By affording these regulatory escapes to habitat-modifying species, patchy mosaics may be much more prone to herbivore outbreaks and a host of cascading effects that come in their wake., Peer reviewed