Multi-scale patterns in co-occurrence of rocky inter-tidal gastropods along the west coast of India

Over the last five decades, inter-tidal ecology has evolved from being a purely descriptive science to using quantitative and experimental approaches to understand community structure. However, this has sometimes come at the cost of understanding generality since many studies have focused on local spatial scales and patch dynamics. This study aimed to assess the generality of co-occurrence patterns at a large spatial scale, covering over 1000 km, by comparing empirical association patterns with random patterns generated by simulations. Species co-occurrence patterns are useful to examine the role of abiotic and biotic factors in community assembly. Our results show non-random patterns of species association at large spatial scales, mainly reflecting increasing community similarity with decreasing geographical distance, although random patterns of species association were found at the smallest spatial scales. Negative associations between species dominated the association pattern when all species pairs were considered, but most of the significant associations were positive. There was low congruence of association strengths of the same species-pairs in different clusters, indicating that associations are likely to be contingent on local conditions. Finally, association strength of con-familial species pairs was found to be higher than species belonging to different families, probably reflecting habitat filtering. This study emphasizes the role and importance of examining general patterns and of using a combination of experimental and observational studies to gain insights at multiple scales.