Diets, Parasites, and Predators

for quiz 5

Diets

-most amphibians and reptiles are carnivores: they eat other animals (some are omnivores. A very strict few are herbivores)

-Carnivorous reptiles assimilate ~90% of the energy in vertebrate prey, but herbivores have lower assimilation efficiencies because vertebrates can’t digest cellulose, which makes up the cell walls of plants, so they only get 30-60% of the energy in plant material.
-Carnivores have shorter digestive tracts than herbivores.

Carnivory

-Typically restricted to particular kinds of prey: insects and other invertebrates, fishes and frogs, squamates, or mammals and birds.
-Within each type of prey, carnivores can be categorized by the size of their prey relative to the size of the predator and by specialization on particular types of prey.
-In general, small amphibians and reptiles eat insects and other invertebrates; larger species eat vertebrates.

-Lizards that evolved snakelike shapes could get through dense vegetation, litter, sand, and even soil and get prey that was safe from limbed squamates.

Prey

• Within a species, body size affects prey size.
→Males and females can have different body sizes and hunt different prey.
• Most species eat a wide range of prey taxa within a particular prey type, especially if their prey is insects and other invertebrates.

Specialization

-Dietary specialization is not common but occurs within
both amphibians and reptiles

-Some amphibians and reptiles eat shelled molluscs but
have to deal with the indigestible shell.

-The hawksbill sea turtle (Eretmochelys imbricata) feeds almost exclusively on sponges, whose skeletons are made of silica spicules.

Carrion

• The extent to which amphibians and reptiles feed on carrion is difficult to
assess.
• Not commonly observed, but scavenging by snakes could be greatly underestimated.
• Komodo dragons and aquatic
turtles is common.

Cannabalism

• Technically, cannibals are carnivores.
• Cannibalism is wide-spread among amphibians, especially in the larval stage;
often associated with limited resources, such as ephemeral breeding ponds.
• Benefits: the cannibal gets nutrition and removes a competitor for food or mates.
• Costs:
• If the victim was a relative, that reduces the fitness of the cannibal.
• Some species might avoid eating siblings.
• Increased probability of contracting a disease of acquiring a parasite

Omnivory

• Among amphibians, only the larvae of anurans feed on plants.

• Among reptiles, only some lizards and some turtles eat plants.

• Omnivorous reptiles might eat the most digestible parts of plants, like fruit and flowers

Herbivory

-Unlike mammals, herbivorous reptiles do not exhibit any
parental care, and the gut symbionts needed to digest food
are not passed directly from parents to their offspring.

→Sometimes hatchlings swallow soil from the nest chamber and
nesting area during the first week after hatching; soil bacteria
form a simple fermentation system in the gut that facilitates
digestion of plant material.
→Hatchlings then seek out adults and eat their feces to get gut
symbionts

• Herbivory might be incompatible with small body size.

Ontogenetic Variation in Diet

• Changes in the diets of carnivores during ontogeny reflect an increasing ability to
capture, subdue, and swallow large prey.

• A few species shift from a largely carnivorous diet as juveniles to a largely omnivorous diet as adults, like slider turtles.

Temporal and Spatial Variation in Diet

• Diets vary from season to season, year to year, and place to place.
• Natural communities change and physical and biotic conditions change,
so diets change.

Active Foraging

• Move frequently and rapidly; search large areas; may dig or probe actively for concealed prey.
• Rely on chemosensory cues to find prey.
• Eat a broad range of smallish prey.
• Since they move a lot, cryptic coloration would be pointless.
• Might be eaten by active predators or sit-and-wait predators.

Sit-and-Wait Foraging

• Search from a fixed site until a potential prey item comes within range.
• Capture may follow a brief pursuit, or the predator may wait until the prey can be ambushed.
• Rely on vision more than chemosensory cues to identify prey.
• Eat fewer but larger prey items.
• Some species use parts of their bodies as lures.
• Tongues, tails, toes might resemble worms.
• Can have cryptic coloration to hide from prey.
• Might be eaten by active predators.

Parasite-Host Interactions

• The interaction between parasite and host is prolonged, with the host
providing nutrition (and often a home) for the parasite.
• A predator interacts with prey only very briefly.
• Parasites might kill the host or not.
• Parasites need the host alive at least until the parasite or its offspring can reach a new host.

Internal Parasites

-some internal parasites are very small

-often transmitted directly from one host to another

-multicellular animals can also be internal parasites

→ parasitic flatworms, tapeworms, flukes, roundworms

→typically do no multiply within the host

→they release eggs or larvae that need to find a new host

Predators

• Predators of amphibians and reptiles include invertebrates, fish, other amphibians and reptiles, birds, and mammals.
• Eggs are the most vulnerable stage.

Defensive Mechanisms

• Most herps have to deal with a broad range of predators of many sizes.
• Defenses usually vary ontogenetically.
• A defense used by a young and small individual might not be used later in life.
• Often there is a hierarchy of defenses.

Signaling Inedibility

Prey may be deemed inedible because it is dangerous, noxious, too big or too fast to capture.
• Animals that are unpalatable (taste bad), poisonous (contain a toxic substance that harms a predator when the prey is bitten or eaten), or venomous (can inject a toxin into a predator) are frequently brightly colored.
• This is aposematic coloration.
• Morphological warning devices: e.g., the hoods of cobras, perhaps the spines of some lizards.
• Auditory warning devices: e.g., rattle of rattlesnakes, ‘hissing’ of Echis and Cerastes vipers in Africa, produced by rubbing specially modified scales on adjacent coils against each other.

Signaling Inedibility Cont.

• Some species exhibit warning coloration but lack
the noxious qualities that back up the warning:
Batesian mimicry.
• Prey mimic the appearance of an inedible or noxious
model.
• Müllerian mimicry is when several different species
all have noxious properties and have the same
warning color

Preventing Consumption

• E.g., the armor and large adult size of
most species of turtles and crocodilians;
skinks have a plate of dermal bone within
each scale; spiny lizards.
• Immobility or death-feigning behavior
• Toxins
• Skin secretions of some lizards and many
amphibians
• After ingestion, hatchling red-eared sliders
promote immediate ejection by scratching
and biting inside the predator (predators
such as largemouth bass happily eat dead
ones but spit out live ones).