Locomotor Randomness and Predator Evasion
Measuring locomotor entropy to compare predator evasion ability in sympatric desert rodents
Moore, TY*; Vasudevan, R; Biewener, AA;
SICB 2014 Austin, TX
Both bipedal and quadrupedal rodents are native to Old World deserts. Despite divergent locomotion, they have overlapping food sources, predators, and activity period. While the quadrupedal rodents use largely 2-dimensional (horizontal) trajectories similar to other quadrupeds, the bipedal rodents (Jerboas of the family Dipodidae) use a diverse set of jumps, hops, and skips to move with erratic trajectories in 3 dimensions. These two "locotypes" have spatially partitioned their resources to limit competition and maintain sympatry, with bipeds foraging in open spaces far from burrows and quadrupeds in shrubs near burrows.
We hypothesize that this spatial partitioning is made possible by the high predator evasion ability of the bipedal animals resulting from their more erratic 3D trajectories. To test this, we collected trajectories of bipedal jerboas (A. elater, D. sagitta) and sympatric quadrupedal jirds (M. meridianus) in the field and quantified the predictability of escape behavior of these species in natural conditions by measuring the entropy of their locomotor motifs. We found that bipedal trajectories had significantly higher entropy than quadrupedal trajectories, making them less predictable. Rather than focusing on the extremes of animal locomotion, understanding how behavior is exhibited in nature can reveal locomotor adaptation to selective pressures, in this case allowing us to explain how these bipedal and quadrupedal desert rodents successfully live in sympatry.
