Consumer-resource Interactions (Chapter 17)

1. Consumer-resource Interactions (Chapter 17) • Overview of community interactions • Predator-prey relationships • Host-parasite relationships • Herbivore-plant relationships

2. Types of consumer-resource interactions

3. Predator – a heterotroph (usually an animal) that kills and eats living organisms for food

4. Characteristics of predators • Size of prey is proportional to size of predator • large prey can be dangerous • small prey don’t provide enough energy

5. Cooperative hunting • allows larger prey to be taken • Ability to tear skin and flesh • sharp teeth • hooked beaks and claws • jaws that open very widely

6. Tactics to Avoid Being Eaten • Escape • early detection of predators • speed • Hiding • stay near cover • reducing activity • Physical defenses • armor • horns, antlers, claws, teeth, etc. • large body size

8. Crypsis – avoiding detection by matching the color or pattern of the background

9. Chemical defenses • noxious sprays • poisonous chemicals in body tissues • often accompanied by aposematic (bright, contrasting) warning coloration

10. Mimicry • Batesian mimicry – a palatable or harmless organism appears similar to an unpalatable or harmful organism • Associated with aposematic colors

12. Müllerian mimicry – when unpalatable species evolve to resemble one another • creates more opportunities for predators to learn to avoid them

13. Large groups • increased detection of predators • decreased odds that any individual is eaten • Predator satiation • overwhelming predator populations by producing many, many seeds or young at irregular intervals • masting – synchronous, widespread seed production

16. Parasite-host Relationships • Parasite – consumes part of a living prey organism (host) • can be internal or external • do not directly kill the host • Parasitoid – animals that lay eggs on living organisms and whose larvae eat and kill the host • usually flies and wasps

18. Parasites can have complex life cycles

19. Virulence – the ability of a parasite to do harm to its host • For parasites, there is a tradeoff • too little virulence: parasite is unable to survive, reproduce • too much virulence: parasite kills its host and cannot reproduce • Most parasites have low virulence

20. Herbivores – eat whole plants or parts of plants. • Grazing – eating grasses, herbaceous vegetation, or algae • Browsing – eating woody vegetation

21. Herbivore impacts on plant communities: • Herbivores can dramatically reduce plant populations • grasslands: herbivores consume 30-60% of above-ground vegetation • forests: herbivores consume 10% of veg. • Some plants are adapted to be grazed

23. Adaptations of herbivores: • Teeth with large grinding surfaces or cutting surfaces • Long guts • Stomach with fermentation chambers

24. Plant defense against herbivory • Low nutritional value of plant tissues • Toxic compounds • Structural defenses • spines • hairs • hard shells on seeds • sticky gums and resins

26. Chemical Defenses of Plants • Secondary compounds – chemicals made by plants to defend themselves against herbivores • tannins – bitter-tasting chemicals that inhibit digestion of proteins • Can have a variety of toxic effects on herbivores • Herbivores often evolve resistance to secondary compound

27. Chemical defenses can be • constitutive – maintained at all times, or • induced – manufactured in response to herbivore damage