Abstract:

Patterns of sclerobiont encrustation constitute important data in studies of paleosynecology and autecology, yet methods used to collect this information are not standardized. The variation among different methods may be attributed to the need for uniquely designed methods applied to address a specific question. As a result, comparisons between sclerobiont studies are cumbersome, results are sometimes contradictory, and the interpretive value among published results is low. A comparison of techniques commonly used for computing sclerobiont abundance and distribution upon host substrates revealed that the simplest measure of abundance, numerical abundance, under-reported large colonial organisms and over-reported small colonial and solitary organisms when compared to calculated baseline values obtained from digitized photos in ArcGIS. Spatial abundance methods, also examined, show areal percent coverage estimation over-reports total encrustation, but not substantially.

Methods commonly used to determine sclerobiont abundance, including spatial, numerical, and frequency of encrustation techniques, were applied to a sample set of the relatively flat, concavo-convex Ordovician brachiopod Rafinesquina. Spatial estimation was the only method to preserve rank abundance calculated by ArcGIS. Frequency of encrustation ranked nearly half the sclerobionts differently than the calculated values in terms of abundance. Most spatially based grid overlay methods produced different abundance rankings; grid overlays with fewer grid sections better reflected baseline values. Different methods employed in reporting sclerobiont encrustation patterns introduce biases unique to each method. Understanding the biases inherent to each method allows more highly resolved interpretations, and promotes more consistent approaches to sclerobiont analysis.

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