Community Concept Community - An assemblage of populations interacting with one another within the same environment Composition - a listing of various species in the community. Diversity - includes list of species as well as abundance of each species.

Composition - a listing of various species in the community. Community Structure Composition - a listing of various species in the community.

Community Structure Diversity - includes list of species as well as abundance of each species. More diversity = more species

Diversity and Composition Models Gleason - Individualistic Model Each population is there because its abiotic requirements are met

Species Richness of Communities Species may occupy an area because their tolerance range overlaps Species range is based on tolerance for certain ABIOTIC factors. There is an optimum range

Diversity and Composition Models Clements - Interactive Model Community is the highest level of organization Dependent on biotic interactions

Model of Island Biogeography MacArthur and Wilson Developed a general model of island biogeography Explains and predicts how the community diversity of an island is affected by Distance from mainland Size of the island

Habitat and Ecological Niche The area an organism lives & reproduces in Ecological niche The role a species plays in its community Includes its habitat Its interactions with other organisms

Feeding niches for Wading Birds

Habitat and Ecological Niche Fundamental niche - All conditions under which the organism can survive. Realized niche - Set of conditions under which it exists in nature.

Habitat and Ecological Niche Organisms can occupy their fundamental niche, if little competition pressure. Competition forces an organism to occupy is realized niche. Realized niche < Fundamental niche

Habitat and Ecological Niche Generalist Species – Have a broad range of niches. Bears, racoons, humans Can tolerate a wide range of environments & has a varied diet. Advantage in changing environment

Habitat and Ecological Niche Specialist Species – Have a narrow range of niches. Pandas, Koalas, freshwater dolphins Lives in specific habitats & on a limited diet. Advantage in stable environment

Community Structure Competition When two species compete, the abundance of both species is negatively impacted

Competition Between Populations Interspecific competition Members of different species require the same resource The supply of the resource is limited

Species Interactions

Competition Between Two Lab Populations of Paramecium Competitive Exclusion Principle No two species can occupy the same niche at the same time

Character Displacement in Finches on the Galápagos Islands Competitive Exclusion Principle Resource Partitioning decreases competition & promote niche specialization. Can lead to character displacement

Niche Specialization Among Five Species of Coexisting Warblers Competition Niche Specialization Among Five Species of Coexisting Warblers

Competition Between Two Species of Barnacles

Community Structure Predation (or parasitism) Expected to increase the abundance of the predator (or parasite) And reduce the abundance of the prey (or host)

Species Interactions

Predator-Prey Interactions Predation One living organism, the predator, feeds on another, the prey Predator is larger Predator has lower reproductive rate Prey usually entirely consumed Presence of predators can decrease prey densities, and vice-versa

Predator-prey Interaction Between Paramecium & Didinium

Predator-prey Interaction Between a Lynx and a Snowshoe Hare

Prey Defenses Mechanisms that thwart the possibility of being eaten by a predator: Spines Tough Epidermis Poisonous Chemicals Camouflage Bright Coloration Flocking Behavior

Camouflage in the Anglerfish Cryptic Coloration

Cryptic Coloration (Camouflage)

Anti-predator Defenses Aposematic (Warning) Coloration

Mimicry Mimicry One species resembles another species that possesses an overt antipredator defense

Mimicry Batesian Mimicry Mimic lacks defense of the organism it resembles

Mimicry Müllerian Mimicry Mimic shares same protective defense

Symbiotic Relationships Symbiosis Interactions in which there is a close relationship between members of two species

Species Interactions

Symbiotic Relationships Parasitism Parasite derives nourishment from a host, and may use host as habitat and mode of transmission Endoparasites Ectoparasites

The Life Cycle of a Deer Tick

Commensalism Commensalism A symbiotic relationship in which one species benefits and the other is indifferent Remoras and Sharks Many supposed examples may turn out to be mutualism or parasitism Inferred amount of harm or benefit two species do to one another is subject to investigator bias

Clownfish Among Sea Anemone’s Tentacles

Mutualism Mutualism A symbiotic relationship in which both members of the association benefit Need not be equally beneficial to both species Cleaning Symbiosis Often help each other obtain food or avoid predation Bacteria in human intestinal tract

Mutualism Between the Bullhorn Acacia Tree and Ants

Cleaning Symbiosis

Coevolution Coevolution When 2 species adapt in response to selective pressures imposed by the other. Some Examples: Pollinators and Flowers Cheetah & Gazelle

Community Development Ecological Succession A predictable pattern of change in species replacements following a disturbance Primary Succession Secondary Succession

Ecological Succession Primary Succession - occurs in areas where there is no soil formation

Large-scale Disturbance: Eruption of Mount St. Helens

Ecological Succession Secondary Succession - begins in areas where soil is present Pioneer Species

Moss, a Characteristic Pioneer Species Sporophytes Gametophytes

These are classic pioneer Lichens Moss These are classic pioneer species.

Secondary Succession

Secondary Succession in a Forest Climax Community - remains essentially the same over long periods of time. It is the final stage of ecological succession.

Community Diversity Community stability can be recognized in 3 ways: Persistence through time Resistance to change Recovery once a disturbance has occurred

Intermediate Disturbance Hypothesis Widespread Disturbances occur frequently - diversity will be limited (low)

Intermediate Disturbance Hypothesis Moderate Disturbances occur with moderate frequency -diversity is high

Effect of a Keystone Species Keystone Species has an unusually large role in maintaining function & diversity of an ecosystem. Pisaster (Sea Star) Sea Otter (in a kelp forest) Beavers (create dams & make wetlands)

Exotic Species (Alien, Introduced, Invasive, Non-native) Also call Alien, Introduced, Invasive, Non-native May lead to unbridled competition Resultant reduction in biodiversity Examples: Kudzu vine Cane toad African bees (killer bees)

Kudzu Vine