Bellwork: What is a Trophic Cascade? Answer: Powerful indirect interactions that can control entire ecosystems, occurring when predators in a food web suppress the abundance or alter the behavior of their prey, thereby releasing the next lower trophic level from predation (or herbivory if the intermediate trophic level is a herbivore).

Predation – one species feeds on another  enhances fitness of predator but reduces fitness of prey (+/– interaction)

Types of predators Carnivores – kill the prey during attack Herbivores – remove parts of many prey, rarely lethal. Parasites – consume parts of one or few prey, Parasitoids – kill one prey during prolonged attack. Start with definition. Unlike competition, here we have clear winners and losers in the fitness arena. Classification: Based on effects of predators on prey. Clearly, prey can compensate for some forms of predation (grazing) but not others (true predation). Take home message. different kinds of predation, in this classification elicit different coping responses on the part of the prey. by the way, which kind of predator would you try to choose to control populations of a pest? go for specificity and lethality, parasitoids. Let’s look at some examples of these different interactions.

Carrying Capacity https://www.youtube.com/watch?v=QI2ixJeIxEU&t=12s

Why are ecological interactions important? Interactions can affect distribution and abundance. Interactions can influence evolution.

How has predation influenced evolution? Adaptations to avoid being eaten: spines (cactii, porcupines) hard shells (clams, turtles) toxins (milkweeds, some newts) bad taste (monarch butterflies) camouflage aposematic colors mimicry

Camouflage – blending in

Aposematic colors – warning

Is he crazy??? Red on yellow, kill that fellow; red on black, venom lack

Mimicry – look like something that is dangerous or tastes bad

Mimicry – look like something that is dangerous or tastes bad Mullerian mimicry – convergence of several unpalatable species

Predator-prey population dynamics are connected  affects prey death rate  affects predator birth rate Predators kill and eat prey dNprey/dt = rNprey – pNpredatorNprey dNpredator/dt = cpNpreyNpredator – dNpredator with few predators, prey population grows with many prey, predator population grows with many predators, prey population shrinks with few prey, predator population shrinks N time

Lotka-Volterra models describe predator and prey population cycling. Real world predator and prey populations can cycle in size.

Predator/Prey Lab Two Owls and 100 mice to start 3 mice = 1 new owl (drop an extra time for each 3 mice caught) 1 mouse survivor = 1 new offspring (survivors x 2)