Spatial point pattern analysis of traces (SPPAT): An approach for visualizing and quantifying site-selectivity patterns of drilling predators

Abstract

Site-selectivity analysis of drilling predation traces may provide useful behavioral information concerning a predator interacting with its prey. However, traditional approaches exclude some spatial information (i.e., oversimplified trace position) and are dependent on the scale of analysis (e.g., arbitrary grid system used to divide the prey skeleton into sectors). Here we introduce the spatial point pattern analysis of traces (SPPAT), an approach for visualizing and quantifying the distribution of traces on shelled invertebrate prey, which includes improved collection of spatial information inherent to drillhole location (morphometric-based estimation), improved visualization of spatial trends (kernel density and hotspot mapping), and distance-based statistics for hypothesis testing (K-, L-, and pair correlation functions). We illustrate the SPPAT approach through case studies of fossil samples, modern beach-collected samples, and laboratory feeding trials of naticid gastropod predation on bivalve prey. Overall results show that kernel density and hotspot maps enable visualization of subtle variations in regions of the shell with higher density of predation traces, which can be combined with the maximum clustering distance metric to generate hypotheses on predatory behavior and anti-predatory responses of prey across time and geographic space. Distance-based statistics also capture the major features in the distribution of traces across the prey skeleton, including aggregated and segregated clusters, likely associated with different combinations of two modes of drilling predation, edge and wall drilling. The SPPAT approach is transferable to other paleoecologic and taphonomic data such as encrustation and bioerosion, allowing for standardized investigation of a wide range of biotic interactions.

Drilling predation on Early Jurassic bivalves and behavioral patterns of the presumed gastropod predator—evidence from Pliensbachian soft-bottom deposits of northern Germany

“…Concerning the infaunal species Gresslya intermedia from the upper Pliensbachian (Amaltheus margaritatus Zone and Pleuroceras spinatum Zone), SPPAT shows a concentration of drill holes on the central shell region. In contrast with a previous study of predation by naticid gastropods on bivalve prey (Rojas et al 2015(Rojas et al , 2020, distance-based statistics do not support segregated patterns. The central shell region in Gresslya represents the region with more inflation and also the region where most soft tissues (gonads, stomach) were probably located, while the posterior region was mostly filled with the siphon.…”

“…To evaluate the spatial distribution of drill holes on G. intermedia shells (a total of 38 drill holes on 33 specimens), we used SPPAT (Rojas et al 2020). Point pattern analyses have been used previously to evaluate univariate and bivariate spatial distributions of body fossils preserved in situ (Mitchell et al 2019).…”

“…Spatial distribution of traces on shells are classified as random (complete spatial randomness [CSR]), aggregated (individual traces are placed together into clusters), segregated (individual traces are placed farther apart than they would be under CSR), or some combination of these patterns. In this approach, the K-function is transformed to a straight line using the L-function to facilitate visual assessment of the graphical output (Baddeley et al 2016;Rojas et al 2020). Because the SPPAT approach used herein was originally described through a case study of drilling predation on bivalve prey (Rojas et al 2020), its protocol for morphometricbased estimation of drill-hole location, as well as the interpretation of kernel density maps, hotspot maps, and graphical outputs from distance-based statistics for hypothesis testing (i.e., L-function and PCF) are transferred directly to our study of G. intermedia.…”

Facilitating corals in an early Silurian deep‐water assemblage

“…Recently, SPPA has also been applied to investigate drilling predation distribution in bivalves (Rojas et al . 2020).…”

A new approach for investigating spatial relationships of ichnofossils: a case study of Ediacaran–Cambrian animal traces

“…SPPA of the spatial positions of the Ediacaran body fossil Kimberella and its trace scratch marks Kimberichnus are suggestive of avoidance of pre-grazed patches (Mitchell et al 2020). SPPA have also been used to visualize and quantify the distribution of predatory traces on shelled invertebrates, enabling the resolution of different modes of drilling predation (Rojas et al 2020). In principle, this approach can be extended to trails, trackways, and burrows, whereby the trace fossils are described by line segments (Fig.…”