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Community Ecology Chapter 20 Symbiosis • Organisms of different kinds living together i th in the same ecosystem t • Any of the following relationships are considered id d tto b be symbiotic: bi ti - Predator – prey - Parasite – host - Commensalism - Mutualism - Pathogen g - host Predator – Prey (Predation) • Lions and zebras, for example • One hunts and kills, kills the other gets killed and eaten Parasite – Host (Parasitism) • Fleas and dogs for example • The parasite harms the host and benefits from the relationship The host is relationship. harmed, but not usually killed Pathogen - Host • A pathogen is a disease-causing disease causing agent, like a bacterium or a virus E.coli H.I.V. Mutualism • A symbiotic relationship where two organisms are in a mutually t ll b beneficial fi i l relationship l ti hi • Examples: Lichens are not one organism but two – an algae and a fungus living as one. The algae provides the fungus with glucose in return for moisture from the fungus. Clown Fish are protected from predator fish by the stinging tentacles of the anemone. The anemone receives protection from polyp-eating fish, like Butterfly Fish Fish, which the Clown Fish chases away. The anemone also gets fertilizer from the feces of the Clown Fish. Commensalism • In this relationship, one organism benefits but the other is neither harmed nor benefited • Examples: Shark and remora Predator Adaptations Natural selection favors the evolution of predator p adaptations for finding, capturing, and consuming prey. • Rattlesnakes R ttl k have h an acute t sense off smell ll and d heath t sensitive pits for detecting warm-bodies prey. sq irrel squirrel • • • • Sticky webs of spiders Flesh-cutting Flesh cutting teeth of wolves and coyotes Speed of cheetahs Striped patterns of tiger’s coat; provides camouflage in a grassland habitat. Prey Adaptations • Some organisms flee when a predator approaches h • Hiding or resembling an inedible object • Deceptive markings; fake eyes, false heads • Chemical defenses Mimicry One species closely resembles another species. 2 forms: Batesian mimicry: is a form of mimicry typified by a situation where a harmless species has evolved to imitate the warning signals of a harmful species directed at a common predator. King snake Coral snake Mullerian mimicry: two or more harmful species that are not closely related, and share one or more common predators, have come to mimic each other's warning signals. Plant Prey Adaptations • Physical defenses; sharp thorns, spines, sticky hairs, and tough leaves. leaves • Chemical defenses that are poisonous, irritating, or bad-tasting • Secondary compounds: chemicals that are often byproducts of the plants’ metabolism ex: strychnine (used as a pesticide, pesticide particularly for killing small vertebrates such as rodents. Strychnine causes muscular convulsions and eventually death through asphyxia or sheer exhaustion) nicotine Competition Organisms g may y compete p for things g such as: food,, space, sunlight, nutrients, or water. Patterns In Communities Disturbances: events that change communities, remove or destroy organisms from communities, or alter resource activity. Stability: the tendency Stabilit tendenc of a community comm nit to maintain relatively constant conditions. • Relates to the community’s y resistance to disturbance Succession Ecological succession: the gradual, sequential regrowth g of a community y of species p in an area. 2 types: primary succession: the development of a community in an area that has not supported life previously such as a bare rock previously, rock, sand dune dune, or an island formed by volcanic eruption. Soil is not initially present. Secondary succession: the sequential replacement of species that follows disruption of an existing community. it Occurs O where h soil il is i already l d present. t Pioneer species: species of organisms that predominate early in succession. Climax community: a community that has reached a generall stable point. generally point