2Communities Habitat is the environment in which an organism lives. A population's niche is its role in the communityHow it uses the biotic and abiotic resources of its habitat
3Community interactions There are five main types of relationships among species within communitiesCompetitionPredationParasitismCommensalismMutualism
4Community interactions Interspecific competition occurs betweentwo populations if they both require the same limited resourceIntraspecific competition occurs between organisms of the same species.Resources include food, water, nesting sitesPlants compete for sunlight, water, soil nutrients, space
5The competitive exclusion principle Populations of two species cannot coexist in a community if their niches are nearly identicalHigh tideChthamalusBarnacle expt shows two outcomes possible:Remove blue barnacles, brown ones grow down and cover entire rock.Ther4, blues outcompeting brown for low space on rock.Remove brown ones, blue ones do NOT grow up. Ther4, resource (space on rock) has been divided and only brown are adapted to drier upper zones of rock.BalanusOceanLow tideFigure 36.2
6Competition between species with identical niches has two possible outcomes One population will eventually eliminate the otherNatural selection may lead to resource partitioning (division)
7Predation Predation is an interaction where one species eats another consumer = predatorfood species = preyPredation is severe form of natural selection. Leads to many diverse adaptations designed to escape predation and to make more successful predators.Explains why the most successful parasite is not a fast killer.Examples: mistletoe on oaks, dodder on phosyn plants, fungal hyphae on nematodes
8Adaptations are driven by these relationships…COEVOLUTION! Prey gain protection against predators through a variety of defense mechanisms1. Mechanical defenses, such as the quills of a porcupine
92. Chemical defensesAnimals are often brightly colored to warn predatorsExample: the poison-arrow frogMany interesting chemicals from amphibs. Antibiotic megainan, anithestic.
16How does predation affect the community? Eliminates weaker individualskeystone predator maintains diversity by reducing numbers of the strongest competitors in a community- Ex. sea star is a keystone predatorFigure 36.4A
17Predation by killer whales on sea otters, allowing sea urchins to overgraze on kelp Sea otters represent the keystone species
18Parasitism Parasitism is a form of predation Parasite, host Not immediately lethalExample: mistletoe on oaks, tapeworm in human intestine
19Commensalism - one partner benefits and the other is unaffected Examples- Algae that grow on the shells of sea turtlesBarnacles that attach to whalesBirds that feed on insects flushed out of the grass by grazing cattle
20Mutualism: both partners benefit Examples: - Nitrogen-fixing bacteria and legumesAcacia trees and the ants of the genus PseudomyrmexFigure 36.5B
21SymbiosisAny long term biological interaction is known as symbiosis or a symbiotic relationshipSome biologists only characterize mutualism and commensalism as symbiosisOthers include parasitism as wellEndosymbiosis is the theory that several eukaryotic organelles are the result of a symbiotic relationship between specialized prokaryotic cells.
22Your task… Community Interaction comic Pick one of the types of interactions we discussed. (competition, predation, parasitism, mutualism, commensalism)Draw a comic showing the interaction.Comic must have at least three panelsNo words are necessary, but it must clearly show the type of interactionDo not write the type of interaction on your comic or your nameWhen it is finished, bring it to me for a number and further directions.