Posted by: oikosasa | October 8, 2013

Multi-scale co-ocurrence patterns in India

How species associate with each other and other co-ocurrence patterns have been studied by Mahi Puri and colleagues along the west coast of India. Read the new Early View paper here:  “Multi-scale patterns in co-occurrence of rocky inter-tidal gastropods along the west coast of India

Below is a short summary by Mahi Puri:

The study was carried out as a Master’s thesis, which meant it had to be completed within a period of 6 months. The fieldwork component was only half of that duration! Having previously never worked on marine and inter-tidal fauna, I was eager to learn about this ecosystem. Most of the classical literature on intertidal fauna is based on experimental work to determine relationships between different taxa and species, done at patch level or small spatial scales. Unfortunately there has been little such work on marine ecosystems in India, though it has a really long coastline (8100 km); most of the work is either descriptive in nature or based on physiological condition affecting the distribution of species. I was interested in looking at association patterns among different species at the community level at much broader scales (essentially examine pairs of species that competed or co-occurred with one another), incorporating the expanse of the Indian west coast.

Because of the large scale of the study and the fact that we were dealing with the entire community and not just a few select species, it was not logistically feasible to incorporate experiments in this study. Based on Jared Diamond’s work on assembly rules and Nicholas Gotelli’s analytical approach (i.e. null model analysis) which did not require experiments to assess association patterns among different species, our study was designed to cover 12 sites spread across nearly 1100 km of the Indian west coast. All the study sites were rocky beaches and we looked at gastropod species occupying these rocky intertidal habitats.

We found non-random patterns of species association at large spatial scales indicating that community assembly is not determined by random factors such as tidal drift. Most pairs of species competed with one another, although the pairs with significant associations co-occurred. We also found pairs of some species displaying different association patterns in different locations i.e. they competed in some locations but co-occurred in others. This study highlights the importance of examining general patterns and of using observational studies to gain insights at multiple scales.

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