The Hare & The Lynx • The Hudson Bay Company kept fur records from 1850‐1930. • Data revealed relationship between Hare population and Lynx population. • Hare eats grass; Lynx eats Hare. • Changes to the Lynx population size are likely caused by changes to the Hare population size. • Changes to the Hare population size were likely due to limited food supply, cyclical overcrowding, overgrazing and predation. Communities • The interactions between populations within a community are complex, but there are 5 main categories. 1. Competition 2. Predation 3. Parasitism 4. Mutualism 5. Commensalism G. F. Gause’s Experiment 1. Competition • G. F. Gause’s competitive exclusion principle: two species cannot co‐exist in a community if they share a niche (compete for the same resources) • If species share the exact same niche: – The species will compete and one will go extinct or… • They will evolve to use different parts of a resource = Resource Partitioning. • They will evolve to use different resources = Character Displacement – Galapagos Island Finches What does this image represent? Read and Interpret 2. Predation • Predation: an organism eating another organism • Organisms evolve defenses against predation. – Plants: spines, thorns, poisons What is another way organisms can interact… – Animals: hiding, fleeing, fighting (costly) – Animals have also evolved passive defenses (less costly) • Crypsis: Camouflage • Aposematic coloration: Bright coloration warning predators that the individual might be poisonous. • Batesian mimicry: Organisms copy the warning coloration of a poisonous species. –Ex: Monarch Butterflies have poison. Viceroy Butterflies look just like Monarch Butterflies but are no poisonous. • Mullerian Mimicry: Two poisonous organisms evolve to share a common appearance so all predators avoid them. Symbiosis • Let’s break down the word….. Close and often long‐ term interaction between two different biological species. 3. Mutualism (+/+) • Mutualism: Both organisms benefit from one another. – Form of Symbiosis: Close and long‐ term interaction between two organisms. – Ex: gut bacteria that produce vitamins for host. 4. Commensalism (+/0) • Commensalism: One organism benefits and has no effect on the other organism. – Form of Symbiosis – Ex: barnacles hitch a ride on the bottom of a totally unaware whale. 5. Parasitism (+/‐) • Parasitism: One organism benefits (the parasite) while the other is harmed (the host). – Form of symbiosis. – Ex: tapeworms steal nutrients while living inside the intestines. Ted Ed‐ Symbiosis • https://www.youtube.com/watch?v=2AM3AR s9MMg.