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1Fish as Predators• Predator-prey relations:• Predators have to eat (if they don’t eat, fitness = 0)• Prey die if they are eaten (if they are eaten, fitness = 0) • Predator-prey “arms race” can drive evolution of form and function• In other words, as predators get better at finding/consuming prey, prey must get better at avoiding predators Predation Cycle-5 parts• Searching•Pursuing• Attacking• Capturing• Handling2Predation Cycle-5 parts• Searching•Pursuing• Attacking• Capturing• HandlingSearching-Active or Passive• Active Searching (fish swims around, actively searching for food!)– Make use of all senses• Vision (lots of fish), olfaction (sharks), gustation (sharks), hearing (sharks), touch (sturgeon and cod), electroreception (eels, catfish, and knife fish)– Speculation searching (e.g. chicken scratch)• Probe into potential hiding places (e.g. goatfish - pictured)• Actively flush prey out via some disturbance (e.g. turning over rocks, etc.)3Searching-Active or Passive• Passive Searching (sit & wait predators!)– Buried by sediment (e.g. Synodontids)– Projections and color have frequently evolved to match substrates for “camouflage.”– Passive water column predators just hang in water column. • Allow prey to habituate and/or make use of counter shading– Most passive predators use vision to detect prey (elasmobranchsalso use electroreception).• Active vs. Passive Strategies– Passive strategy saves energy, but relies on prey coming to you (hence, a tradeoff!).• May be risky to wait for prey, but don’t spend energy looking• Tradeoff between certainty of prey capture and energy spent catching prey• Two different strategies (that are both successful) to solve the same problem (i.e. eating) Searching-Active or Passive4Searching• Reaction distance = Maximum distance at which a prey item can be detected by the predator– Affected by water clarity, illumination, size of prey, prey coloration– Potential “arms race” b/n predator and prey• Predators want to increase their reaction distance– Better vision• Prey want to decrease a predator’s reaction distance– Become smaller (Adaptively or Plastically) and/or become clear (e.g. midge larvae)Searching• Advantages of group foraging:– predators foraging in groups may locate and capture prey more quickly; group foragers tend to have higher growth rates than dosolitary searchers– Increase in effective search area• Rely on others in a shoal (= unorganized school) to find prey and react to their feeding behavior– It is easier to see a 10cm fish feeding 5 meters away than it is to see 2mm long Daphnia from 5 meters away.– Less time on the lookout for predators• Tradeoff: feeding with others increases likelihood of competition.– Hence, group foraging only works when prey are abundant and thusnot very limiting. – Competition increases with group size!Group Foraging5Predation Cycle-5 parts• Searching•Pursuing• Attacking• Capturing• HandlingPursuit-Chasers or Deceivers• Chasers– Sustained chasing• Very streamlined, tail with high aspect ratio, fins fit in grooves (e.g. tunas)– Maneuvering (esp. near shore)• Big fins and broad tails allow quick braking, sharp turns• “fine-tuned” swimming to catch prey in complex habitats– Fast Start• Lie-in-wait predators; elongate bodies, fins far back on body• Tradeoff: Very fast for short distances, but can’t maintain speed for long stretches(e.g. gar, pike, barracuda)6• Fast start swimmers are a good example of convergent evolution• Figure shows similar body plan for a diverse group of fish• Lepisosteiformes• Ostariophysi• Atherinomorpha• PercomorphaPursuit-Chasers or Deceivers• Deceivers– Lure prey within striking distance– Make part of their bodies look like food for prey• First dorsal spine modified into a lure (esca)• Predator’s body camouflaged• Predator sucks prey in and holds them with backward facing teeth7Pursuit-Slow Stalking• Many of these fish approach prey head on and make use of disruptive coloration (disrupts outline)– Split-head color pattern = a form of disruptive coloration that splits up the outline of the fish’s head to fool prey– Convergent trait– Visually breaks up shape of whole head– Prey have delayed recognition of predator Predation Cycle-5 parts• Searching•Pursuing• Attacking• Capturing• Handling8Attack and Capture• Refers to the moment a predator makes its move to engulf prey• Predator attacks by overtaking prey with simultaneous mouth extension and suction (if they can, i.e. these are derived traits and capabilities)Attack and Capture• Fast-start predators overtake prey– Target the prey’s center of mass= part of prey that moves the least• Benthic, lie-in-wait predators - great suction capacity• Some fish swim and passively sieve prey from water (e.g. manta rays).• Some incapacitate prey during attack and then “capture”(e.g. electric eels)9Attack and Capture• Predators often separate out individual prey from the prey’s shoal or school.– Greatly increases success rate of predation– Attacks on “stragglers” more likely to be successful• Some predators mimic shoal members or non-threatening species (e.g. Indo-pacific grouper, one cichlid)Attack and CapturePredators often attack those prey that are different within the shoal (i.e. don’t be different, you will be eaten!)– Produces strong selection for morphological and behavioral uniformity within schooling prey species10Predation Cycle-5 parts• Searching•Pursuing• Attacking• Capturing• HandlingHandling• Handling = Post-capture manipulation– Aids in ingestion and digestion– Removal of spines, toxic skins, etc.– Reducing size of prey (i.e. tearing it apart)– Very important: maneuver prey to go in head first!• allows prey fins to depress, also less chance of escape– Use jaw and head movements to maneuver prey– Some use the term ‘handling’ to include digestion11HandlingPrepare prey to swallow--use your teeth!• Different types of predators have different types of teeth– Piscivores = sharp teeth for holding or shredding prey– Insectivores = teeth stout and recurved– Mollusk feeders = molar like teeth– Coral feeders = beak like teeth (e.g. parrotfish) Handling• Gill rakers keep prey from escaping through opercular openings– Gill raker spacing related to size of prey (i.e.


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UA ECOL 482 - Fish as Predators

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