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closeThis is not a good theoretical framework
Posted by WardTesta on 01 May 2012 at 20:40 GMT
Horning and Mellish document predation as the leading, almost exclusive proximate cause of mortality among juvenile Steller sea lions in Prince William Sound, Alaska, based on implanted satellite transmitters. That is a useful and important conclusion about the current state of pressures on this portion of the western stock of Steller sea lions. However, the reported precision of their survival estimate is overstated, and the theoretical framework offered by those authors to model the dynamics of the Steller sea lion population decline is questionable. The theoretical framework, in particular, does little to clarify the role of predation in the decline of Steller sea lions, as these authors seem to contend (3 pages of their results and discussion deal with the retrospective record and the range of densities encompassed by the sea lion decline). In my view, this is largely the result of confused theoretical concepts and terminology, and assumptions about density-dependence and predator dynamics that are unlikely to be true in the time frame applied. As a result, it is a poor theoretical foundation for understanding the Steller sea lion decline. Comments to support my contentions are embedded in the article.
RE: This is not a good theoretical framework
TheTechnologist replied to WardTesta on 01 May 2012 at 23:28 GMT
This is an initial response to one of several comments made by Ward Testa on this publication.
First, we have addressed the question of the precision of the cumulative survival rate estimates separately under that comment by Testa, please view the details of calculations and rationale as to why our estimate is correct under that comment.
Second, we very clearly point out in our manuscript that the conceptual framework we present is not a time variant model, and as such cannot be applied to derive inferences on the past decline. Contrary to Testa’s claim, we do not model the dynamics of the decline. Our use of retrospective demographics to consider the merit of different response models is simply by way of the fact that over the course of the historic decline sea lion density must have changed. This imparts a density perspective on historic data, without applying any specific time frame as Testa claims we do. As a result, we do not contest Testa’s statement that the proposed framework is a poor theoretical underpinning for understanding the decline, because it is in fact simply not appropriate for that purpose, and no one makes such a claim.
We will post more detailed replies to individual comments in the near future, and will shortly also post updated survival rate estimates as well as confidence intervals incorporating recent data returns.