Predation by shell-breaking crabs on a marine gastropod along a latitudinal gradient in the SW Atlantic: Influence of extrinsic and intrinsic factors

Biotic interactions—and predation in particular—are thought to follow a
latitudinal gradient, increasing towards the tropics; yet empirical
evidence remains contradictory and largely based on studies from the
Northern Hemisphere. Moreover, the role of environmental variables shaping
latitudinal gradients of predation intensity has seldom been tested. Here,
we quantify predation by shell-breaking crabs on modern shells of the
marine gastropod Trophon geversianus along a latitudinal gradient
(40°–54°S) on the SW Atlantic coast. We further evaluate how intrinsic
factors (four shell morphometric traits) and extrinsic factors (seven
environmental variables and the biogeographic region) jointly influence
predation patterns. Fragmentation from crushing predation affected 37% of
the shells (544 out of 1,480), with the most frequent damage types being
major body whorl damage (28%), deep aperture chips (11%), and extensive
aperture chips (6%). When analysed by biogeographic province,
fragmentation increased significantly towards the south in the Magellan
province. Notably, random forest modelling revealed that intrinsic
factors—particularly shell size and thickness—were stronger predictors
than extrinsic factors in driving latitudinal variability of
shell-breaking crab predation. By highlighting the dominant influence of
intrinsic factors over extrinsic ones, this study emphasises the crucial
role of species-specific traits in shaping predator-prey interactions
across biogeographic regions.