Predation Lecture 14

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

Which of these are predators? Hawk Rabbits Mice Coral The basidiocarp on your pizza Earthworms Goats Sheep Bacteria living in your intestine House flies Fungus between your toes Blue whales Green algae Paramecium Chickens Banana slug Vole Chickadee You – a human opossum

Predator-Prey Interactions Predation is the consuming of one organism by another –Under simple laboratory conditions, the predator often exterminates its prey It then becomes extinct itself having run out of food!

Lynx predates weakened hares – eventually crashes

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 Model both predator and prey populations

Lotka-Volterra Equations: Change in prey population: dN prey /dt = rN prey -cN prey N pred Change in predator population dN pred /dt = b(cN prey N pred )-dN pred – Linked by cN prey N pred = mortality of prey due to predation cN prey = per capita prey consumption – Predator and prey populations function as density-dependent regulators of each other

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

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

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

Optimal Foraging Theory (see page 152) Time invested in foraging need to balance against other costs of living – Producing/rearing of young – Escape predation Natural selection favors ‘efficient’ foragers – Various decisions  cost:benefit What to eat* How long to pursue Where to search How to search Research focus: – Understanding of behavior/ecosystem interactions in terms of costs and benefits – usually prey selection

Co-evolution and predator-prey interactions Red-Queen Hypothesis – maintenance of balance between predator and prey Prey defenses – vary plant vs. animal prey – Chemicals Alarm pheromones Repellants Toxins – Coloration patterns – Behavior patterns

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 19 th century British naturalist Müllerian mimicry – common coloration of toxin bearing spp –After Fritz Müller, a 19 th century German biologist Animal Defenses against Predation Monarch butterfly Viceroy butterfly

Some animals receive an added benefit from eating plants rich in secondary chemical compounds – Caterpillars of monarch butterflies concentrate and store these compounds Animal 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!

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 waspAnthidiine 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

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 PredatorAreaArea 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 – 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.

Predators and Diversity – see pages 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 – p ) 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