Ecological context and the probability of mistakes underlie speed choice

Abstract

Movement is fundamental to the ecology of animals, and an animal's choice of movement speed determines the duration, energetic costs, and probability of success of any given activity. It is often assumed that animals should use maximum speeds when escaping from predators, but an increasing number of studies find animals rarely move as fast as they can in nature because faster speeds come with a greater chance of mistakes. Mathematical modelling suggests that, when escaping predators, prey animals should optimise speeds to simultaneously outrun their pursuer and minimise their probability of slipping. This can be particularly important when running along narrow structures like branches. When foraging, however, animals should avoid moving at high speeds, which are often energetically costly and decrease the ability to detect food or predators. In this study, we examined how trade‐offs between speed and probability of slipping influenced the speed choice of wild antechinus (Antechinus mysticus) during escaping and foraging behaviours. We also examined how this trade‐off affected foraging behaviour. Antechinus ran significantly faster when escaping (1.207 ± 0.033 m/s) than foraging (0.145 ± 0.002 m/s), and slipped 37% more often during escapes. However, foraging antechinus still slipped frequently on narrow branches, despite running an order of magnitude more slowly than they did on wide branches. Furthermore, antechinus slipped at lower speeds when foraging than they did when escaping, suggesting that avoiding mistakes is less highly prioritized when foraging. Antechinus visited the feeding station accessed by a wide branch more frequently (and ate more while there) compared with feeding stations accessed by narrow branches, even when those branches were 33% or 67% shorter. This suggests that foraging decisions may be based on potential limitations to speed and the probability of slipping over distance to cover. Though activities such as running can be fundamental to animals’ fitness, a general framework to understand how animals select speeds in nature is still being developed. We test the assumption that animals choose running speeds to minimise their motor mistakes, and demonstrate the cost of mistakes is likely to be different across ecological and behavioural contexts. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13036/suppinfo is available for this article.

Surface friction alters the agility of a small Australian marsupial

“…Our study supports a growing body of evidence showing that animals select running speed based on biomechanical trade-offs (Amir Abdul Nasir et al, 2017;Losos and Sinervo, 1989;Sinervo and Losos, 1991;Wilson et al, 2013a;Wheatley et al, 2018;Wynn et al, 2015) and the terrain over which they are moving (Amir Abdul Nasir et al, 2017;Losos and Sinervo, 1989;Sinervo and Losos, 1991;Vanhooydonck et al, 2015;Wheatley et al, 2018). It is important that researchers both consider and report on the surface structure and friction in their studies, and because the effects of friction will differ among species with different kinds of feet (Höfling et al, 2012), a metric of friction that pairs species and substrate would be ideal.…”

“…These factors interact with biomechanical trade-offs to further constrain movement. For example, buff-footed antechinus (Antechinus mysticus) and northern quolls (Dasyurus hallucatus) both moderate their escape speeds when they run across narrow branches to minimise their risk of slips or falls (Amir Abdul Nasir et al, 2017;Wheatley et al, 2018). Narrow branches offer a smaller target for foot placement, and slower speeds increase the accuracy of footing because speed and accuracy act in opposition to one another.…”

Rapid recovery of locomotor performance after leg loss in harvestmen

“…To simulate predation attempts, we grabbed individuals by their hind legs and then released them. Hence, we interpreted the animal's subsequent movements as escape behaviors 46 . Trials were video recorded with a GoPro HERO4 camera (GoPro, San Mateo, CA, USA) at 120 frames/s.…”

Variation in movement: multiple locomotor gaits in Neotropical harvestmen

“…Our experimental protocol is likely to have mimicked a predation attempt on Prionostemma harvestmen. We thus interpreted three gaits (running, stotting and bobbing) as escape manoeuvres (Wheatley et al, 2018). Stotting had high performance (velocity and acceleration), similar to running, suggesting fast escape.…”

“…Gaits may also be influenced by body condition (Miller et al, 1987;van Berkum et al, 1989;Jakob et al, 1996), which might reflect an animal's hunger level, ontogenetic and/or reproductive stage, parasite load or disease. Extrinsic factors can also modulate which gait an animal uses, including the medium in which the animal moves (air, water or a solid substrate), the physical and threedimensional (3D) properties of that medium (Spagna et al, 2007;Sponberg & Full, 2008;Spence et al, 2010) and the ecological context or stimulus (FitzGibbon, 1993;Moore et al, 2017;Wheatley et al, 2018). For example, escape from predators and performance of courtship displays often involve different locomotory gaits (Caro, 1986).…”