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The spatial patterns of disruption of plant -animal interactions within a population dynamic approach

Final Report Summary - DISLOOP (The spatial patterns of disruption of plant -animal interactions within a population dynamic approach)

The decline or extinction of native species involved in biotic interactions (i.e. the disruption of interactions) can cause significant changes in ecosystem processes (Bronstein, 1994). Ecosystem structure and functioning is most likely to be affected in habitats that already have lost functional redundancy, and or those which limited functionality at the regional species pool level (e.g. islands where few species can interact there naturally; Rejmánek 1996). The case of the Mediterranean basin is quite paradoxical: despite being one of the global biodiversity hotspots (Myers et al 2000), human activities have extensively impacted its ecosystems for more than 8,000 years which is significantly longer than any other hotspot (Delanoë et al. 1996). For such reason, Mediterranean islands are extremely vulnerable as their small size increases the effects of loss of biodiversity and ecosystem functioning. The project DISLOOP was proposed to improve our understanding of the direct and indirect consequences of the disruption of plant-disperser interactions within the context of the spatial-explicit population dynamics. This project is focussed on a well-know plant-disperser interaction between the endangered shrub Daphne rodriguezii Teixidor (Thymelaeaceae) and its only seed disperser, the frugivorous lizard Podarcis lilfordi Gunter (Lacertidae), both endemic to the Balearic Islands (Western Mediterranean).

Plant populations are under two extreme ecological conditions (in which the disperser is present and absent), which is a rare and essential requisite in the study of the disruption of plant-animal interactions and especially useful for model validation (see below).

The main approach of this project requires a combination of advanced modeling techniques and profound knowledge of the natural history of the species of interest. The model is rooted in a valuable and interdisciplinary dataset, comprising the data analysis of plant and animal demography, animal movement and spatial distribution of plants. In consequence, the main challenge of this project is to integrate heterogeneous field information into the general framework of spatially-explicit and individual-based models (IBM).

A first major achievement of the project was the description and analysis of observed patterns which were based on two methodologies. First, we developed habitat quality models to define the landscapes from the perspective of the plant and the lizard, both in the plant populations with and without seed disperser. We hypothesize that the activity patterns of the frugivorous lizard directly influence the spatial distribution of the plant species. To evaluate this hypothesis, we first analysed lizard activity and identified its main determinants at several spatial scales of habitat aggregation. In a second step, the most important determinants of lizard activity plus those describing habitat structure were used to predict the presence of adult and juvenile plants. The main result was that the interplay between lizard activity and local habitat features determines the spatial patterns of juvenile-plant presence and leaves a lasting signature on adult-plant distribution (Rodríguez-Pérez et al. in press).

The complete Summary is attached.