Chaos and recruitment in the bryozoan, Membranipora membranacea
The term "chaos" implies that variations in recruitment are inherently (or effectively) random and that the underlying mechanisms cannot be examined within the framework of natural selection. The proposition that chaos describes recruitment is examined for the bryozoan Membranipora membranacea. Stock-recruitment relationships were highly variable (r 2 = 16%), supporting the contention of chaos. However, the complementary recruitment-stock relationship displayed even higher variability (r 2 = 0.03%), indicating that benthic processes are even more chaotic. Variability in recruitment was reduced considerably when (1) intervening life stages and (2) environmental factors were examined. In the former instance, stock-larval abundance and larval abundance-recruitment relationships account for 44% and 69% of the observed variability, respectively. In the latter case, nudibranch predation, up-welling, and temperature are responsible for much of variability in recruitment. A multiple regression indicates that these factors (together with stock size) explain 64% of the variability in recruitment. Because the effects of these factors may be of adaptive significance to Membranipora, recruitment is not chaotic in the sense that variability can be (1) explained by a few causal mechanisms and (2) examined within the framework of natural selection. A further examination of recruitment-stock relationships demonstrates that variability is also highly dependent upon the temporal scale of analysis. In conclusion, variability should be defined relative to life history or environmental perspectives appropriate to specific ecological or evolutionary principles. Chaos represents an oversimplification of this process.
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Document Type: Research Article
Publication date: 1986-09-01
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