| Popis: |
Variation in terrestrial mammalian craniodental morphology and skull shape is known to constrain feeding performance, which in turn influences dietary habits and ultimately fitness. Otters have evolved two feeding specializations: underwater raptorial capture of prey (mouth-oriented) and capture of prey by hand (hand-oriented), which likely correspond to craniodental morphology and bite performance. However, feeding biomechanics and performance data for otters, aquatic mustelids that consume prey above water, are sparse. The first goal of the study was to investigate the relationship between feeding morphology and bite performance between two mouth-oriented piscivores (giant river otters and North American river otters) and two hand-oriented invertebrate specialists (sea otters and Asian small-clawed otters) using morphometric approaches. The second goal was to investigate fluctuating asymmetry in the cranium of otters. The third goal was to characterize feeding mechanisms (kinematics and jaw musculature) and role of bite performance in the trophic ecology of sea otters. Mouth-oriented piscivores possessed longer skulls and mandibles, with jaws designed for increased velocity at the expense of bite capability. Hand-oriented possessed more blunt skulls and mandibles designed for increased bite capability. Sea otters displayed a greater degree of fluctuating asymmetry of the skull, which is likely linked to environmental stresses. Bite performance and durophagous feeding behavior in sea otters was characterized in detail in the feeding kinematics. Estimated bite forces of sea otters were large enough to crush all size classes of butter and littleneck clams tested in the lab. However, sea otters are size selective predators and generally choose bivalves of small to medium size. Medium sized butter and littleneck clams required an intermediate breaking force, and are buried at a shallower depth than larger clams. Clams requiring an intermediate breaking force could decrease consumption time, thus overall handling time. |
