Predation Lecture Overview: Importance, Responses, and Dynamics

1. PredationLecture 15

2. Overview • Chapter in Text: 15, 17 • Predation and Herbivory • Responses of individuals to predation • Responses of populations to predation – refuges • Importance of Predators • Maintenance of ecosystem diversity • as a Keystone species

3. What is a predator? • Narrow sense • Broad sense • Ecological definition of predator: • Herbivores: • Grazers and browsers – consume part of plant/plant not killed • Seed eaters + planktinovores: consume entire plant • Parasite: generally do not kill host • Parasitoid: lay eggs in host – feeding by larvae eventually kill host

4. Under simple laboratory conditions, the predator often exterminates its prey • It then becomes extinct itself having run out of food!

5. Lotka-Volterra Models and Predator-Prey cycling: • Developed during 1920s • Assume mutual interaction of predator and prey numbers • Predict persistence of both predator and prey populations • The Lotka–Volterra equations for predator and prey populations link the two populations • Each population functions as a density-dependent regulator on the other • Predator as a source of density-dependent regulation on the mortality of the prey population • Prey as a source of density-dependent regulation on the birthrate of the predator population

6. The paired equations, when solved, show that the two populations rise and fall in oscillations • The cycle can continue indefinitely — the prey is never quite destroyed; the predator never completely dies out

7. “Now, here you see, it takes all the running you can do, to keep in the same place” – the Red Queen • Coevolution: as prey species evolve ways to avoid being caught, predators evolve more effective means to capture them • Natural selection (think in terms of fitness)  • “smarter,” more evasive prey • “smarter,” more skilled predators

8. Prey defenses to avoid being detected, selected, and captured by predators: • Chemical defense • Alarm pheromones • Repellants • Toxins • Cryptic coloration • Warning coloration • Protective armor • Behavioral defense

9. Blue jay Chemical Defenses • Some animals receive an added benefit from eating plants rich in secondary chemical compounds • Caterpillars of monarch butterflies concentrate and store these compounds • They then pass them to the adult and even to eggs of next generation • Birds that eat the butterflies regurgitate them I’m not eating this again!

10. Plant Responses to Herbivores • Physical • Thorns • Height • Heavy seed coat • Chemical • Toxins • Digestion inhibitors • Nutritional • Low levels of N in older foliage • Tough, difficult to masticate foliage

11. Adult Green caterpillar Chemical Responses of Plants to Herbivory • Mustard oils protected plants from herbivores at first • At some point, however, certain insects evolved the ability to break down mustard oil • These insects were able to use a new resource without competing with other herbivores for it • Cabbage butterfly caterpillars

12. Monarch butterfly Viceroy butterfly Animal Defenses against Predation • Physical • Behavioral • Chemical • Toxins • Coloration • Cryptic • Warning coloration – aposmatic • Batesian mimicry – harmless mimics • After Henry Bates, a 19th century British naturalist • Müllerian mimicry – common coloration of toxin bearing spp • After Fritz Müller, a 19th century German biologist

13. Self Mimicry • Involves adaptations where one animal body part comes to resemble another • This type of mimicry is used by both predator and prey • Example • “Eye-spots” found in many butterflies, moths and fish

14. Yellow jacket Masaridwasp Sand wasp Anthidiine bee Müllerian Mimicry • Two or more unrelated but protected (toxic) species come to resemble one another • Thus a group defense is achieved

15. Yellow jacket

16. Predation and Behavior Modification - Refuges • Schooling of prey fish – response to predator attack – some survive • Alarm calls – Prairie dogs, ground squirrels • Song birds mob and harass predator bird species • Avoidance – temporal, spatial • Refuges

17. Refuges • A mechanism that allows exploited population to escape predation/parasitism – many forms: • Place/form of cover, schooling, synchronized reproduction (large numbers at one time), size • May not provide absolute sanctuary, enough for species to survive • Important for survival of predator too!

18. Protection in Numbers • Living in a large group provides a “refuge.” • Predator’s response to increased prey density: Prey consumed x Predators = Prey Consumed Predator Area Area • Wide variety of organisms employ predator satiation defense. • Prey can reduce individual probability of being eaten by living in dense populations.

19. Examples of Predator Satiation • Synchronous widespread seed and fruit production by plants - masting. • Synchronized emergence of Cicadas – 16-17 year cycle • Williams estimated 1,063,000 cicadas emerged from 16 ha study site. • 50% emerged during four consecutive nights. • Losses to birds was only 15% of production

20. Size As A Refuge • If large individuals are ignored by predators, then large size may offer a form of refuge. • Peckarsky observed mayflies (Family Ephenerellidae) making themselves look larger in the face of foraging stoneflies. • In terms of optimal foraging theory, large size equates to lower profitability.

21. Is regulation top-down or bottom-up? • ie. primary productivity versus limits imposed by predator populations

22. Ch 18 p 344

23. Diffuse predator–prey interactions • The lynx, coyote, and horned owl are responsible for the periodic cycles in the snowshoe hare population • Diffuse mutualism • A single plant species may depend on a variety of animal species for successful reproduction

24. Hare popul crashes as: 1. Reduced forage  weakened hares, high lynx prdation 2. Forage produced after heavy browsing accumulates plant defense chemicals less palatable Lynx predates weakened hares – eventually crashes

25. Is regulation top-down or bottom-up? • ie. primary productivity vs. limits imposed by predator populations

26. Predators and Diversity – see pages 340-344 • Alter competitive balance amongst prey spp. • Robert Paine studies: sea star exclusion in intertidal plots  decreased prey diversity (15  8 spp) • Selective alteration of competitive relationships • Peter Morin studies – altered competitive relationships amongst immature frog spp by predatory newt

28. Keystone Predator (or Keystone Consumer –) • Species essential to maintenance of ecosystem structure/diversity • Example (there are many): CA sea otter – kelp forest community

30. THINGS TO WORRY ABOUT • Your Pores — Portals for Invasion? • Musty Dankness • Fleas & Ticks — Tiny TerroristsWhat's Embedded in Your Bed? • What Your Mother Never Told You About Those Hidden Corners and Cracks • Pink Mold — Slime or Scourge?Mildew — Mold's Evil Twin