Dr. BSCI106 Sara Via
Outline 7
Species interactions II Consumption (predation and herbivory)
Fall 2008, p. 1
Does predation affect prey population size? Could predation regulate prey population size ? Predation is usually density-dependent- good start Predation CAN keep prey pop. well below carrying capacity.
Pesticide is counterproductive - predators
killed!
Predators can drive prey locally extinct Mite alone- cycles
Efficient predator
quickly kills all the prey.
Could these two species ever coexist?
Predators and prey can coexist if there are places for prey to hide (refugia) Huffakers orange experiment complex environment -trays of oranges and orange rubber balls. some predator time is wasted looking for prey
Do prey always go extinct? Predators and prey can coexist if there are places for prey to hide (refugia) Huffakers orange experiment Hide and seek Predator efficiency reduced in complex habitats, Useful in biological control!
BSCI106 Dr. Sara Via
Outline 7
Fall 2008, p. 2
Competition and predation can interact Predation releases populations from competition (why) But if prey population gets too big to be controlled by predator i.e., outbreak and overshoot of K Competition kicks in and reduces population size to a point where predation can again be effective. (how) Top Down or Bottom Up Control?
TOP DOWN: predator controls the population size of the prey BOTTOM UP: preys food controls its population size
Does predation cause population cycles?
Hares show a regular cycle of population size - period about 11 years Are the lynx responsible? Traditional view Lynx have a cycle that is correlated with the hares, but lagged But, next observation: Hares cycle even in the absence of lynx! Hmmm we dont get it yet
Turns out that plants contribute to hare population regulation (bottom up) Hare: resource availability (competition) AND predation Lynx: prey availability Species interactions cause natural selection! Adaptations in prey evolve Structural defenses Chemical defenses Camouflage, mimicry Evasive behavior - moths and bats
Structural defense Spines, fibers, stings, etc. Chemical defense in plants Tannins- indigestible Nicotine, caffeine, opium, strychnine, digitalis -
Bugs call them poison,we call them drugs!
Counter-evolution in herbivores
BSCI106 Dr. Sara Via
Outline 7
Fall 2008, p. 3
Insects can evolve tolerance to the plant defense and then specialize on plant
Cabbage white are butterflies attracted to smell of mustard oil in broccoli, cabbage
etc. Evolve to tolerate toxin and specialize: Heliconius butterflies and Passiflora Sequester the poison - use it for own defense Monarch butterflies Counter-evolution in herbivores
OR, Avoid the poison! More adaptations of prey
Camouflage- Blend into background It usually works to look like something gross
Camoflauge also works for predators! Scare your attacker
Many prey suddenly flash bright colors or eye spots Mislead your attacker deceptive patterns and/or coloration Confuse your attacker background coloration can break up the body outline (and often conceal eyes) Appearance can be confusing background coloration can break up the body outline (and often conceal eyes) Appearance can advertise! Aposematic Coloration - a warning about defense to potential predators Im poisonous - E.g. Arrow frogs
E.g. Monarch butterflies
(note:only works if predator learns- what if it dies?)
BSCI106 Dr. Sara Via
Outline 7
Fall 2008, p. 4
Mimicry Similarity in appearance between two (or more) species arising by natural selection Implies a benefit to at least one species Batesian Mimicry
A harmless, tasty species (the mimic) evolves similarity to a harmful or unpalatable species (the model) Coral snakes and their mimics
Batesian Mimicry: does it really work? Experiment: - put out artificial * king snakes * brown snakes - who gets attacked? be sure you get why this shows an advantage to mimics! Batesian Mimicry
Batesian mimicry is a response in prey species to natural selection by predators.
Who benefits - model or mimic? Who (if anyone) gets hurt? What would happen if mimics became very abundant relative to models?
Mullerian Mimicry
Distasteful or harmful species evolve to resemble each other E.g. Monarch and Viceroy butterflies E.g. Heliconius butterflies How does natural selection here differ from Batesian mimicry? Batesian + Mullerian Mimicry Both types of mimicry may be acting at once within a group of species Costa Rican Butterflies and moths
BSCI106 Dr. Sara Via
Outline 7
Fall 2008, p. 5
Coevolution Species interactions can produce reciprocal forces of natural selection * Predation favors prey that can escape * Prey populations evolve defense * Predators evolve counter-defenses coevolutionary arms race
What do you think?? Is the diversity of interactions among organisms responsible for much of Earths biodiversity?