Tags

, , , , , ,

species_level_link_distro

Fig. 1 - Species-level trophic link distribution for entire coral reef.

We’ve examined records of fish occurrences on Jamaican reefs for the past 10 years, and compared it to our “master” food web. Of the 196 species in our food web, 136 have records in Jamaica. Many of these species are present in very low numbers, and some reefs are noticeably depauperate, recording less than 60 species. Nevertheless, to be conservative, we assume that we can integrate over all the reefs, thereby counting all 136 species as being present. We next expanded our metanetwork, or guild-level food web (in this case almost exactly the same as a trophic species-based web) to the species level, therefore accounting for all expected links in the food web. For the master or pristine web, this yields an overall connectance of 0.059. The trophic link distribution is shown in Fig. 1. Interestingly, this is clearly not a decay distribution (e.g. power law), but has a definite modality of about 25 links. One needs to question the extent to which under-sampling of natural food webs, and aggregation into trophic species, affects interpretation of link distributions.

The next step of course is to assess the state of the Jamaican reef system. Our initial analysis has been to simply remove the “missing” species (extirpated) from the web, and to re-calculate the statistics. Connectance declines to 0.055. Is this significant? Probably impossible to answer that question for network connectance. Also, it should be noted that hundreds of invertebrate species are included here, and they will dampen the impact of any fish removals or additions. Perhaps the next question regards the link properties of the extirpated species.

Advertisements