Comparing categorical and continuous ecological analyses: Effects of "wave exposure" on rocky shores

  • Lindegarth M
  • Gamfeldt L
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Abstract. Development of general theories and subsequent empirical testing are fun- damental ingredients in ecological science. The progress of such efforts is determined by the logical coherence among central concepts, theories, and predictions on one hand, and ultimately to differences in conclusions about the relative importance of ecological pro- cesses. experimental design, statistical analyses, and interpretation of results on the other. Here, we specifically explore an example of how differences in the way ecological concepts are defined lead to differences in the formulation and statistical testing of hypotheses and role is widely agreed upon. Nevertheless, generalizations about its effects and use for accurate prediction of assemblages are often limited. This may partly be explained by the frequent use of categorical rather than quantitative definitions of wave exposure. We com- pared the conclusions about the importance of wave exposure from (1) analyses of variance based on relative classification of wave exposure and geographic location to those of (2) regression analyses based on continuous measures from 16 locations on the Swedish west coast. Variability in richness was substantially better explained by the regression analyses, while for the cover of individual taxa there was no consistent difference between the two geographic location indicated that interactive effects and differences between geographic areas were predominant. Regression analyses of absolute, continuous measures suggested that mean significant wave height was a better predictor than geographic location and interactive terms. Thus, the choice of definition of wave exposure has important conse- quences for how causes of spatial patterns of intertidal assemblages are perceived. Cate- consequences of these findings are discussed in the context of rocky shore ecology as well as in a general perspective of ecological models, hypotheses, experimentation, and analysis.

Author-supplied keywords

  • Environmental factors
  • Experimental design
  • Spatial patterns
  • Statistical analysis
  • Wave exposure

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  • Mats Lindegarth

  • Lars Gamfeldt

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