The foramen ovale is a vital part of fetal circulation, allowing blood to flow directly from the right atrium to the left atrium, bypassing the non-functional fetal lungs. After birth, the foramen ovale closes due to increased pressure in the left atrium, leaving a depression called the fossa ovalis.
In a deer species that lives in groups, some individuals act as sentinels and are vigilant for predators but there is a trade-off between foraging and vigilance. A researcher collects data on the foraging rates of edge (black) and central (grey) members of the group in two similar forests, one with and one without predators. Which one of the following figures best supports the hypothesis that members at the edge are acting as sentinels in this deer species?