Dataset: Legacy of predators: morphometrics

We conducted laboratory experiments to test whether previous predator exposure had a sustained effect on prey foraging and in turn on a basal resource, even after the predator was removed. We tested for both behavioral and morphological legacies of prior predation. The study system consisted of a tri-trophic food chain, using the red rock crab, Cancer productus, as the predator, the carnivorous whelk, Nucella ostrina, as the prey species, and the California mussel, Mytilus californianus, as the basal resource.

The first step of the experiment consisted of conditioning the intermediate consumer (Nucella ostrina) in the tri-trophic food web to the presence of predators or not. The above conditioning period lasted 75 days, a duration that has been documented in previous studies to cause a morphological change in Nucella. Then we tested for proportional changes in the length and weight of our snails that may have occurred during the conditioning phase and the weight:length ratio by repeating the measurements we had made at the outset of our experiments. Using a subset of the conditioned and naïve snails (n=80 each), we next tested how predator conditioning affected their behavior and foraging when they were subsequently exposed to predator cue or not (Ng & Gaylord (2020), Fig. 2). If predator conditioning altered Nucella morphology and their foraging, we also wanted to examine whether a snail's size might alter its response to predator cue and its foraging on mussels. We therefore first grouped the Nucella into five size classes of 16 Nucella each, from smallest to largest, creating a size gradient. We created this array of multiple size classes for both predator-conditioned and naïve snails. We then divided each set of 16 snails into two containers (33 mm × 20 mm × 11.5 mm) with eight Nucella individuals per container; half of the containers received outflow from sumps containing crabs and half received seawater free of predator cue (this overall protocol thus yielded 2 conditioning exposures x 5 size classes x 2 cue treatments = 20 containers total). All 20 containers were then supplied with 20 juvenile mussel individuals each, as a basal food source for the carnivorous snails. This configuration created a 2 × 2 design stratified by size with conditioning history as one treatment and predator cue as the second treatment. We then measured the number of mussels consumed by the snails daily over the course of the next 15 days, without replacement of consumed mussels, along with the number of snails above or below the water line within each container as a metric of anti-predatory escape behavior.

Further methods are detailed in Ng and Gaylord (2020). This dataset has the raw morphometrics of the whelks (Nucella) used in the experiment and includes wet weight and length of shell. The dataset includes morphometrics at the start of the experiment and repeated measures over time. In addition, the type of treatment the Nucella experienced is also included; in the control treatment, snails were exposed to just running seawater over the course of the experiment, and in the crab treatment, snails were exposed to Cancer productus cues. Snails were housed in multiple containers, which were used as random factors in the analysis. At the start of the experiment, snails were transferred from small containers (denoted as ‘Container’ in the dataset) into larger containers labeled as New.containers.