Chapter 10

know that herptiles figure prominently in the trophic dynamics of many ecological communities

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know that foraging behavior is constrained by evolutionary history and foraging behaviors are not easily altered

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be able to describe differences between sit and wait and actively foraging predators

sit and wait: sit and wait: usually camouflage themselves and wait for prey to move within striking range

• when mapped on phylogenies, the sit and wait mode is usually present in basal clades

Actively foraging predators: move through their environment looking for prey

multiple factors influence the diet of herptiles. Be able to summarize and describe these influences

• external

  • prey availability

  • predation risk

  • social interactions (competitions)

  • habitat structure

  • thermal environment

• internal

  • hunger

  • learned behavior

  • age

  • sex and reproductive condition

• phylogenetic (=historical) factors

  • sensory limitation

  • morphological constraints

  • physiological constraints

  • behavioral constraints

be able to explain optimal foraging theory with respect to the diet breadth and giving-up time in a patch of prey

• basic assumption is that natural selection will favor efficient foraging behavior

• individuals will choose the most energetically favorable item when considering prey

• highest energy gain vs lowest energy loss

• P-curve: adding more prey types means more time is spent handling and processing less optimal prey

• S-curve: this curve increases as more prey types are included in the diet

  • major foci are diet breadth and use of a patchy environment

know the primary sensory systems used by each group of herptiles to detect prey and be able to describe them

• five systems: visual (sit and wait predators), olfactory, tactile, temperature, auditory

  • caecilians: olfaction

  • salamanders: vision and olfaction (auditory)

  • anurans: vision (auditory)

  • turtles: vision and olfaction (tactile)

  • squamates: olfaction, vision, temperature, auditory (tactile)

  • crocodillians: vision (auditory, tactile)

be able to describe the composition of snake venoms and different fang types used for delivery of venom

• venomous reptiles possess: venom glands, muscles to move venom to glands, ducts, fangs

• enzymes (proteolytic, thrombin-like, hyaluronidase, phospholipase, acetylcholinase), polypeptides, others (inorganic ions, glycoproteins)

• opisthoglyph (rear-fanged), proteroglyph (front-fanged and fixed), solenoglyph (front-fanged, hinged)

  • small prey, simply biting and swallowing is sufficient

  • larger prey: constriction

  • venom is found in the helodermatidae (bearded lizards), elapidae, viperidae, some colubrids

know how researchers typically describe diet composition (percent prey number, percent prey volume)

• prey percent number: % of total number of prey items that aa specific prey type represents

• percent prey volume: % of total volume or mass of food made up by a specific prey type

know that quantifying prey availability is extremely difficult and how this influences our ability to quantify diet preferences of herptiles

key issue for the biologist studying diets is availability of prey

be able to explain what is meant by the term ontogenetic diet shifts

• changes in an organism’s diet that occur as it grows and develops through different life stages

• if most taxa in a clade exhibit similar foraging behaviors and diet, this is usually indication that the feeding mode evolved early in the history of the group

foraging mode and phylogeny

• foraging behavior is plastic: it can change dependent on the variables of the respective environment

• organisms are integrated suites of characters, and a change in one attribute will affect others

factors influencing foraging behavior

many factors influence foraging mode

• because of these multiple influences, modeling the evolution of foraging is difficult

  • ancestral traits

    sensory capabilities, foraging mode, physiological constraints, thermoregulation, resource availability, time of activity, biomechanics (jaw, tongue), body size

visual prey detection

• primary detection method for sit and wait

• overlapping fields of vision (=binocular vision) enhance success rate

• images are focused on the retina in amphibians by moving a spherical lens relative to the retina; most reptiles focus by changing the shape of the lens, but snakes move the lens relative to the retina

• most vertebrates, including herptiles, have pupils that are horizontal or vertical slits. This allows use of the entire diameter of the lens and detection of multiple wavelengths

Chemosensory prey detections (olfaction)

• there are three locations where chemicals are detected

  • nasal passages - small MW moleculers

  • vomeronasal organ - high MW compounds

  • tongue/buccal cavity - high MW compounds

auditory prey detection

• sound travels as particle displacements and waves

• in amphibians there are two auditory pathways for sound transmission: the tympanum-stages path and the forelimb-opercular path

• aquatic amphibians have neuromast organs that can detect particle displacements

• in squamates, sound waves produce vibrations that can be transmitted via skull bones

thermal prey detection

• heat sensing (IR radiation) neurons associated with the trigeminal nerve are found in many boas and pythons,, and in all viperid snakes

• temperature differences as small as 0.003*C can be detected

tactile prey detection

a few species like the alligator snapp9ing turtle use touch to detect prey