The turnover of plant-frugivore interactions along plant range expansion: consequences for natural colonization processes.

Plant-animal mutualisms such as seed dispersal are key interactions for sustaining plant range shifts. It remains elusive whether the organization of interactions with seed dispersers is reconfigured along the expansion landscape template and, if so, whether its effects accelerate or slow colonization. Here we analyse plant-frugivore interactions in a scenario of rapid population expansion of a Mediterranean juniper. We combined network analyses with field surveys, sampling interactions between individual plants and frugivores by DNA-barcoding and phototrapping over two seasons. We assess the role of intrinsic and extrinsic intraspecific variability in shaping interactions and we estimate the individual plant contributions to the seed rain. The whole interaction network was highly structured, with a distinct set of modules including individual plants and frugivore species arranged concordantly along the expansion gradient. The modular configuration was partially shaped by individual neighbourhood context (density and fecundity) and phenotypic traits (cone size). Interaction reconfiguration resulted in a higher and more uneven propagule contribution, with most effective dispersers having a prominent role at the colonization front stand, where a distinct subset of early arriving plants dominated the seed rain. Our study offers new insights into the key role of mutualistic interactions in colonization scenarios by promoting fast plant expansion processes.

Spatial patterns of an endemic Mediterranean palm recolonizing old fields.

Throughout Europe, increased levels of land abandonment lead to (re)colonization of old lands by forests and shrublands. Very little is known about the spatial pattern of plants recolonizing such old fields. We mapped in two 21-22-ha plots, located in the Doñana National Park (Spain), all adult individuals of the endozoochorous dwarf palm Chamaerops humilisL. and determined their sex and sizes. We used techniques of spatial point pattern analysis (SPPA) to precisely quantify the spatial structure of these C. humilis populations. The objective was to identify potential processes generating the patterns and their likely consequences on palm reproductive success. We used (1) Thomas point process models to describe the clustering of the populations, (2) random labeling to test the sexual spatial segregation, and (3) mark correlation functions to assess spatial structure in plant sizes. Plants in both plots showed two critical scales of clustering, with small clusters of a radius of 2.8-4 m nested within large clusters with 38-44 m radius. Additional to the clustered individuals, 11% and 27% of all C. humilis individuals belonged to a random pattern that was independently superimposed to the clustered pattern. The complex spatial pattern of C. humilis could be explained by the effect of different seed-dispersers and predators' behavior and their relative abundances. Plant sexes had no spatial segregation. Plant sizes showed a spatial aggregation inside the clusters, with a decreasing correlation with distance. Clustering of C. humilis is strongly reliant on its seed dispersers and stressful environmental conditions. However, it seems that the spatial patterns and dispersal strategies of the dwarf palm make it a successful plant for new habitat colonization. Our results provide new information on the colonization ability of C. humilis and can help to develop management strategies to recover plant populations.