Chapter 17: Predation and Herbivory

Consumer-Resource Interactions

• All life are both: – consumers (C) of victims Predators

– victims (V) of consumers Prey

• Interactions organize communities into consumer chains (food chains):– consumers benefit at the expense of their resources

– populations are controlled from below by resources and from above by consumers

Opuntia(Prickly pear) Cactoblastis

(cactus moth)

Queensland Australia ~1950’s

Before Cactoblastis introduction After Cactoblastis introduction

Some Definitions

• Predator – catches and consumes individual prey items

– thereby removing them from the prey population (V).

• Parasites – consume parts of a living prey organism, or host

– parasites may be external or internal

– may negatively affect the host but does not directly remove it from the population

Predator

More Definitions…

• Parasitoids – consumes living tissues of their hosts, eventually

killing them– combination parasite and predator

• Herbivores – eat whole plants or parts of plants– may act as predators (eating whole plants) or as

parasites (eating parts of plants):• grazers eat grasses and herbaceous vegetation• browsers eat woody vegetation

Parasitoid Wasp

A detritivore’s niche…

• Detritivores – consume dead organic material. – consume wastes of other species.

– have no direct affect on populations that produce these resources:

• do not directly affect prey abundance• do not directly influence their evolution

– are important in the recycling of nutrients within ecosystems

Predator adaptations.

• Predators vary in size relative to their prey:– predators may be much larger than their prey (whales are

far larger than krill and small fish)

– prey are rarely much larger than their predators:• beyond a certain prey size, a predator cannot successfully subdue

and consume the prey• cooperative hunters are an exception, taking prey substantially

larger than themselves

– form usually tied to specific diet (vertebrate teeth example)

Carnivore consuming small prey items to satisfy requirements(cost increases exponentially as predator size inc.)

General adaptations?

Predator adaptations (cont.)• The variety of predator adaptations is

remarkable:– consider grasping and tearing functions:

• forelegs for many vertebrates

• feet and hooked bills in birds

• distensible jaws in snakes

– digestive systems also reflect diet:• plant eaters feature elongated digestive tracts with

fermentation chambers to digest long, fibrous molecules comprising plant structural elements

Osprey feet

Prey adaptations.

• Prey escape mechanisms:– in animals:

– in plants:

• Bombardier beetle

Crypsis and Warning Coloration

• Crypsis - blending with background:– are typically palatable or edible– match color, texture of bark, twigs, or leaves– not concealed mistaken for inedible objects– behaviors corresponds to appearances.

Crypsis

Peruvian katydid

• Costa Rican

mantid

Lonomia moth in Costa Rica

Scorpion fish in Philippines

• Sage thrasher

• American Dipper

Jack-snipe

Warning Coloration

• Unpalatable animals – Noxious chemicals

• From food• Manufacture

– Often warning is involved• predators learn to avoid such animals after unpleasant

experiences

• certain aposematic colorations occur so widely that predators may have evolved innate aversions

Why aren’t all prey unpalatable?

Mimics

• Henry Bates – palatable species mimic unpalatable (models)

• Fritz Müller –unpalatable species that come to resemble one another (all mimics and models)

Batesian mimics

Müllerian mimics

Parasites adaptation = dispersal

• Parasites usually smaller than host

• Externally (ectoparasite) or internally

– internal parasites exist in a benign environment:• food

• stable conditions

Internal parasite

Tapeworm of US soldier in Hawaii.Left: after barium infusion. Right: after vermifuge treatment

Ectoparasites

Purple finch

Cost of being a parasite…

– parasites must deal with a number of challenges:

• host organisms have mechanisms to detect and destroy parasites

• parasites must disperse through hostile environments,

• often via complicated life cycles with multiple hosts,

Plasmodium life cycle Fusion of gametesZygote forms cyst in gut wall of mosquito

Zygote divides into sporozoites

Salivary glands

Injection of sporozoites into human host’s bloodLiver cells

Merozoites can:1) Reinfect liver cells2) Infect rbc’s

48-hr cycle of invasion, lysing, reinvasion

Some merozoites form into male and female gametes

Feeding mosquito ingests gametes

One strategy…

• Circumventing the host’s immune system:

– suppress it (AIDS virus)

– coat themselves with proteins mimicing host’s proteins (Schistosoma)

– continually coat their surfaces with novel proteins (trypanosomes)

Plants vs. herbivory

• Usually biochemical warfare.

• Plant defenses include:– low nutritional content– toxic compounds– structural defenses

• spines and hairs

• tough seed coats

• sticky gums and resins

constitutive

induced

“Secondary” Compounds

Can herbivores overcome plant’s defenses?

Can herbivores control plant populations?

– prickly pear cactus in Australia• controlled by introduction of a moth, Cactoblastis

– Klamath weed in western US• Controlled by Chrysolina beetles

Other examples…

• Mauna Loa, Hawaii

grazed

Spruce budworm – Algonquin PP in Ontario, Canada