‘Selfish herds’ of guppies follow complex movement rules, but not when information is limited

Abstract

Under the threat of predation, animals can decrease their level of risk by moving towards other individuals to form compact groups. A significant body of theoretical work has proposed multiple movement rules, varying in complexity, which might underlie this process of aggregation. However, if and how animals use these rules to form compact groups is still not well understood, and how environmental factors affect the use of these rules even less so. Here, we evaluate the success of different movement rules, by comparing their predictions with the movement seen when shoals of guppies (Poecilia reticulata) form under the threat of predation. We repeated the experiment in a turbid environment to assess how the use of the movement rules changed when visual information is reduced. During a simulated predator attack, guppies in clear water used complex rules that took multiple neighbours into account, forming compact groups. In turbid water, the difference between all rule predictions and fish movement paths increased, particularly for complex rules, and the resulting shoals were more fragmented than in clear water. We conclude that guppies are able to use complex rules to form dense aggregations, but that environmental factors can limit their ability to do so.

Ontogeny of collective behavior reveals a simple attraction rule

“…Our rule bears some resemblance to rules from the selfish herd hypothesis (15) used to explain tight group formations in the presence of a predator at an unknown location (35)(36)(37)(38)(39)(40). Hamilton considered moving to the center of mass of the two closest neighbors as the ideal rule and moving to the closest neighbor as a simpler rule.…”

Altered visual environment affects a tropical freshwater fish assemblage through impacts on predator–prey interactions

“…Crenicichla are often found under rocks and in roots near or on the benthos, and both Hoplias and Crenicichla deposit eggs in gravel nests making them vulnerable to heavy silt deposition that can interfere with respiration. Both taxa care for their young, and Crenicichla herds them in large schools (Prado, Gomiero & Froehlich 2006), presumably conferring protection from predation; the efficacy of schooling may be lost in murky waters (Borner et al 2015;Kimbell & Morrell 2015). Whereas the abundance of these predators in this tropical stream system tend to be mostly constant over time in relatively undisturbed streams While we documented shifts in predator numbers in streams with and without quarries, we did not see a concomitant shift in the abundance of their shared prey, the guppy.…”

“…Both taxa care for their young, and Crenicichla herds them in large schools (Prado, Gomiero & Froehlich 2006), presumably conferring protection from predation; the efficacy of schooling may be lost in murky waters (Borner et al 2015;Kimbell & Morrell 2015). Crenicichla are often found under rocks and in roots near or on the benthos, and both Hoplias and Crenicichla deposit eggs in gravel nests making them vulnerable to heavy silt deposition that can interfere with respiration.…”

Off-Shore Fly or Die Holograms for Desert Locust Swarms

“…Under the threat of predation, animals can decrease their risk by moving towards other individuals and form compact groups (Kimbell & Morrell, 2015). Individuals watch the decisions of others before making their own decisions.…”