Upload
katherine-greer
View
221
Download
0
Tags:
Embed Size (px)
Citation preview
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
• Some animals receive an added benefit from eating plants rich in secondary chemical compounds– Caterpillars of monarch butterflies concentrate and store
these compounds
Chemical Defenses
• 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!
• Physical– Thorns– Height– Heavy seed coat
• Chemical– Toxins– Digestion inhibitors
• Nutritional– Low levels of N in older foliage– Tough, difficult to masticate foliage
Plant Responses to Herbivores
• Mustard oils protected plants from herbivores at first– At some point, however, certain insects evolved the
ability to break down mustard oil
Chemical Responses of Plants to Herbivory
• These insects were able to use a new resource without competing with other herbivores for it
–Cabbage butterfly caterpillars
Adult
Green caterpillar
• 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
Animal Defenses against PredationMonarch butterfly
Viceroy butterfly
• 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
Self Mimicry
• Two or more unrelated but protected (toxic) species come to resemble one another
Müllerian Mimicry
– Thus a group defense is achieved
Yellow jacket
Masarid wasp
Sand wasp Anthidiine bee
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
• 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
Lynx predates weakened
hares – eventually
crashes
Hare popul crashes as:1. Reduced forage weakened hares, high lynx prdation2. Forage produced after heavy browsing accumulates plant defense chemicals less palatable
• Is regulation top-down or bottom-up?
• 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