Lara A. Ferry-Graham

Using functional morphology to examine the ecology and evolution of specialization.

Abstract Researchers strive to understand what makes species different, and what allows them to survive in the time and space that they do. Many models have been advanced which encompass an array of ecological, evolutionary, mathematical, and logical principles. The goal has been to develop ecological theories that can, among other things, make specific and robust predictions about how and where organisms should live and what organisms should utilize. The role of functional morphology is often an under-appreciated parameter of these models. A more complete understanding of how anatomical features work to allow the organism to accomplish certain tasks has allowed us to revisit some of these ideas with a new perspective. We illustrate our view of this role for functional morphology in ecology by considering the issue of specialization: we attempt to align several definitions of specialization based upon shared ecological and evolutionary principles, and we summarize theoretical predictions regarding why an organism might specialize. Kinematic studies of prey capture in several types of fishes are explored with regard to the potential ecological and evolutionary consequences of specialization, most notably in the area of trade-offs. We suggest that a functional morphological perspective can increase our understanding of the ecological concepts of specialization and it consequences. The kinds of data that functional morphologists collect can help us to quantify organismal performance associated with specialization and the union of functional morphology with ecology can help us to better understand not just how but why organisms interact in the manner that they do.

Linking Cranial Kinematics, Buccal Pressure, and Suction Feeding Performance in Largemouth Bass

The rate and magnitude of buccal expansion are thought to determine the pattern of water flow and the change in buccal pressure during suction feeding. Feeding events that generate higher flow rates should induce stronger suction pressure and allow predators to draw prey from further away. We tested these expectations by measuring the effects of prey capture kinematics on suction pressure and the effects of the latter on the distance from which prey were drawn—termed suction distance. We simultaneously, but not synchronously, recorded 500‐Hz video and buccal pressure from 199 sequences of four largemouth bass, Micropterus salmoides, feeding on goldfish. From the video, we quantified several kinematic variables associated with the head and jaws of the feeding bass that were hypothesized to affect pressure. In a multiple regression, kinematic data accounted for 79.7% of the variation among strikes in minimum pressure. Faster mouth opening and hyoid depression were correlated with lower pressures, a larger area under the pressure curve, and a faster rate of pressure reduction. In contrast, buccal pressure variables explained only 16.5% of the variation in suction distance, and no single pressure variable had a significant relationship with suction distance. Thus, although expected relationships between head kinematics and buccal pressure were confirmed, suction distance was only weakly related to buccal pressure. Three explanations are considered. First, bass may not attempt to maximize the distance from which prey are drawn. Second, the response of prey items to suction‐induced flow depends on prey behavior and orientation and is, therefore, subject to considerable variation. Third, previous theoretical work indicates that water velocity decays exponentially with distance from the predator’s mouth, indicating that variation among strikes in flow at the mouth opening is compressed away from the mouth. These findings are consistent with other recent data and suggest that suction distance is a poor metric of suction feeding performance.

Quantification of flow during suction feeding in bluegill sunfish.

Nearly all aquatic-feeding vertebrates use some amount of suction to capture prey items. Suction prey capture occurs by accelerating a volume of water into the mouth and taking a prey item along with it. Yet, until recently, we lacked the necessary techniques and analytical tools to quantify the flow regime generated by feeding fish. We used a new approach; Digital Particle Image Velocimetery (DPIV) to measure several attributes of the flow generated by feeding bluegill sunfish. We found that the temporal pattern of flow was notably compressed during prey capture. Flow velocity increased rapidly to its peak within 20 ms of the onset of the strike, and this peak corresponded to the time that the prey entered the mouth during capture. The rapid acceleration and deceleration of water suggests that timing is critical for the predator in positioning itself relative to the prey so that it can be drawn into the mouth along with the water. We also found that the volume of water affected by suction was spatially limited. Only rarely did we measure significant flow beyond 1.75 cm of the mouth aperture (in 20 cm fish), further emphasizing the importance of mechanisms, like locomotion, that place the fish mouth in close proximity to the prey. We found that the highest flows towards the mouth along the fish midline were generated not immediately in front of the open mouth, but approximately 0.5 cm anterior to the mouth opening. Away from the midline the peak in flow was closer to the mouth. We propose that this pattern indicates the presence of a bow wave created by the locomotor efforts of the fish. In this scheme, the bow wave acts antagonistically to the flow of water generated by suction, the net effect being to push the region of peak flow away from the open mouth. The peak was located farther from the mouth opening in strikes accompanied by faster locomotion, suggesting faster fish created larger bow waves.

Comparison of fasting and postfeeding metabolic rates in a sedentary shark, Cephaloscyllium ventriosum

Abstract We measured the standard and postfeeding metabolic rates of a sedentary shark, the swellshark, Cephaloscyllium ventriosum (Scyliorhinidae). The average standard metabolic rate (SMR) of juvenile swellsharks (0.14–0.23 kg) was 44.3 ± 6.4 mg O2 kg−1 h−1. Metabolic rate increased and reached a maximum approximately 9 h postfeeding. The maximum postfeeding metabolic rate averaged 2.3 times SMR, and the entire duration of the response was approximately 12 h. The overall pattern and magnitude of the postfeeding response is similar to those previously reported for the small-spotted catshark (Scyliorhinus canicula; Scyliorhinidae) and for many teleosts. The return to a prefeeding metabolic rate appears to be much more rapid in the swellshark than in the small-spotted catshark. Section editor: R. E. Gatten Jr