Effective nut dispersal by magpies (Pica pica L.) in a Mediterranean agroecosystem

The ecological and evolutionary significance of effectiveness landscapes in mutualistic interactions

Mutualism effectiveness, the contribution of an interacting organism to its partner's fitness, is defined as the number of immediate outcomes of the interactions (quantity component) multiplied by the probability that an immediate outcome results in a new individual (quality component). These components form a two-dimensional effectiveness landscape with each species' location determined by its values of quantity (x-axis) and quality (y-axis). We propose that the evolutionary history of mutualistic interactions leaves a footprint that can be identified by three properties of the spatial structure of effectiveness values: dispersion of effectiveness values, relative contribution of each component to the effectiveness values and correlation between effectiveness components. We illustrate this approach using a large dataset on synzoochory, seed dispersal by seed-caching animals. The synzoochory landscape was clumped, with effectiveness determined primarily by the quality component, and with quantity and quality positively correlated. We suggest this type of landscape structure is common in generalised coevolved mutualisms, where multiple functionally equivalent, high-quality partners exert similarly strong selection. Presumably, only those organisms located in high-quality regions will impact the evolution of their partner. Exploring properties of effectiveness landscapes in other mutualisms will provide new insight into the evolutionary and ecological consequences of mutualisms.

Winter habitat selection of Corvids in an urban ecosystem

Urban areas attract birds during the winter when cities provide a predictable source of food and relatively stable weather conditions. However, many other factors determine the occurrence of birds in cities. This study analysed the relationship between corvids wintering in the city of Poznań, in western Poland and habitat features. Each of 32 research site was investigated three times. The most abundant species was the rook (mean = 17.4 individuals/site); the most frequent was the Eurasian magpie (88% of all sites). To determine variables that influence the abundance of birds, a set of generalised linear models was created, with model averaging being selected for each species. The abundance of hooded crows was positively influenced by surface of parks, water and by the length of tram tracks. The number of rooks was positively linked with the number of walnut trees, garbage cans and the surface of the water and negatively linked with the length of watercourses. Jackdaw was affected positively by the number of garbage cans, the surface of the water and negatively by the cover of trees. The number of magpies was associated with the number of walnut trees, garbage cans and negatively influenced by the surface of trees. None of the investigated habitat variables significantly affected the abundance of European jay. We also found a positive correlation between the abundances of hooded crow, rook, jackdaw and magpie. The results indicate that corvids wintering in urban ecosystems exhibit selectivity toward specific habitat features and that preferences differ among the studied species.

The endemic Mediterranean dwarf palm boosts the recolonization of old-fields: Implications for restoration

Understanding the mechanisms underlying the recolonization of old-fields is critical to promote the recovery of the ecosystem functioning, particularly in regions where agricultural abandonment has increased in the last 60 years. Given that seed arrival and seedling survival often limit the recolonization process by woody species in many Mediterranean habitats, the 'perching' and 'nursing' effects exerted by some pioneer species could be crucial for the restoration of such abandoned lands. We examined the role of an endemic Mediterranean palm (Chamaerops humilis) on the recolonization of old-fields by woody species in southern Iberian Peninsula. We chose three independent old-fields differing in their shrub encroachment levels. To identify potential facilitation by C. humilis, we used a spatially-explicit approach and analyzed its spatial associations with ten common woody species (e.g. Asparagus spp., Daphne gnidium, Olea europaea var. sylvestris, Pyrus bourgaeana). We detected positive spatial associations between C. humilis and woody species at small-scale (1-5 m) in the three plots. Most of such small-scale associations were linked to the bird-dispersal of woody species. Nonetheless, there were marked differences among plots in spatial associations between C. humilis and woody plants, being Asparagus spp. the only species positively associated with C. humilis within the three studied old-fields. These species-specific differences were likely related to variations among old-fields in encroachment level and the legacy of human management. Such small-scales spatial associations between C. humilis and woody species across Iberian old-fields were linked to the perching and nursing effects exerted by the palm. We emphasize the strong potential of this pioneer Mediterranean palm for the restoration of native ecosystems and the recovery of ecosystems services.