1. Predation Lecture 13

2. Predation and Herbivory Responses of individuals to predation
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. Ecological definition of predator:
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. Change in prey population: dNprey/dt = rNprey-cNpreyNpred
Lotka-Volterra Equations: assumes a mutual regulation of predator and prey populations
Change in prey population:
dNprey/dt = rNprey-cNpreyNpred
Change in predator population
dNpred/dt = b(cNpreyNpred)-dNpred
Linked by cNpreyNpred = mortality of prey due to predation (rate at which prey are captured)
d = mortality rate of the predator population
b = birthrate = conversion efficiency of captured prey into new predators
c = efficiency of predation
cNprey = per capita prey consumption

8. Additional factors that influence predator–prey interactions
The Lotka–Volterra model is widely criticized for overemphasizing the mutual regulation of predator and prey populations
Additional factors that influence predator–prey interactions
Coevolution
difficulty in locating prey as it becomes scarcer
Choice among multiple prey species

9. Natural selection (think in terms of fitness) 
“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

10. 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

11. I’m not eating this again!
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
Blue jay
I’m not eating this again!

12. 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

13. 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
Adult
Green caterpillar
These insects were able to use a new resource without competing with other herbivores for it
Cabbage butterfly caterpillars

14. Animal Defenses against Predation
Monarch butterfly
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
Viceroy butterfly

15. 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

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

17. Yellow jacket

18. 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

19. 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!

20. 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.

21. Examples of Predator Satiation
Synchronous widespread seed and fruit production by plants - masting.
Synchronized emergence of Cicadas – 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

22. 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.

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

24. Ch 18 p 344

25. 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

26. Lynx predates weakened hares – eventually crashes
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

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

28. 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

30. Keystone Predator (or Keystone Consumer – p 379 + )
Species essential to maintenance of ecosystem structure/diversity
Example (there are many): CA sea otter – kelp forest community

32. THINGS TO WORRY ABOUT
Your Pores — Portals for Invasion?
Musty Dankness
Fleas & Ticks — Tiny Terrorists What'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