Download Lecture 11 Interspecific Interactions

Predation
Lecture 15
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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
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
– Under simple
laboratory conditions,
the predator often
exterminates its prey
• It then becomes
extinct itself having
run out of food!
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
• 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
“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
• 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
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!
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
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
Adult
Green caterpillar
Animal Defenses against Predation
• Physical
• Behavioral
• Chemical
– Toxins
• Coloration
– Cryptic
– Warning coloration – aposmatic
• Batesian mimicry – harmless mimics
Monarch butterfly
Viceroy butterfly
– After Henry Bates, a 19th century British naturalist
• Müllerian mimicry – common coloration of toxin
bearing spp
– After Fritz Müller, a 19th century German biologist
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
Müllerian Mimicry
• Two or more unrelated but protected (toxic) species come
to resemble one another
Yellow jacket
– Thus a group
defense is
achieved
Masarid wasp
Sand wasp
Anthidiine bee
Yellow jacket
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
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!
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.
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
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.
• Is regulation top-down or bottom-up?
• ie. primary productivity versus limits
imposed by predator populations
Ch 18 p 344
• 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
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
• Is regulation topdown or bottomup?
• ie. primary
productivity vs.
limits imposed by
predator
populations
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
Keystone Predator (or Keystone Consumer –)
• Species essential to maintenance of ecosystem
structure/diversity
• Example (there are many): CA sea otter – kelp forest
community
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