Prey Selectivity by Drilling Gastropods: a Bambachian Cube Perspective

War, Mewan Banshan (2022) Prey Selectivity by Drilling Gastropods: a Bambachian Cube Perspective. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Mewan Banshan War (17MS146)) 17MS146_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (613kB)

Abstract

Gastropod drilling predation occurs selectively to maximise their net energy gain. Past studies on prey selectivity among gastropods have focussed on parameters that mainly relate to prey morphologies, i.e. the prey taxa were preferred based on their body sizes (prey-size preference) and accessibility of their soft tissues to the drillers, hence, providing easy manipulation of the targeted prey through drill-holes (prey-site selectivity), which could all be traced back in the geological past. Although such studies have rightly contributed towards understanding the factors that could control prey selectivity among gastropod predators through time, they have not, however, considered the ecological characters of the prey organisms that could altogether affect their being targeted by the predators, despite ecology being a holistic representation of an organism’s morphology, diversity and life habits. This study thus attempts to understand prey selective behaviour of gastropod drilling predators on molluscan (bivalve and gastropod) and brachiopod prey according to prey autecologies (here, tiering, motility, and feeding modes) using the classic “Bambachian cubes” concept. Based on collected drilling and ecological data of the prey taxa ranging from the Cambrian to the Pleistocene, I found that only 32 out of 100 potential life modes (here, cubes) were drilled throughout the Phanerozoic. During the Paleozoic, only the most abundant epifaunal prey items were attacked. Contrastingly, the drillers became increasingly more diverse in selecting their prey in the Meso-Cenozoic interval. Apart from epifaunal prey, other tiering forms like infaunal (semi, shallow and deep) modes were also drilled by the predators from the Mesozoic onwards. Slow-moving and facultatively mobile forms were drilled in the late Paleozoic and have been heavily targeted since. Additionally, in terms of feeding, the suspension feeders constituted the vast majority of drilled prey items, followed by the grazers. Upon evaluating each drilled cube (i.e., life mode), I found that in concurrence with my working hypothesis, the shallow infaunal, slow-moving filter-feeding life mode was the most targeted by the gastropod drillers.

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