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Chapter 7 Community Interactions Let’s get ready to ruuuuumble! Community • Community: populations of all species living and interacting in an area at a particular time Four Characteristics of Community Structure • Physical Appearance: size and distribution of its population and species Four Characteristics of Community Structure • Species Diversity/Richness: number of different species Four Characteristics of Community Structure • Species Abundance: number of individuals of each species Four Characteristics of Community Structure • Niche Structure: number of niches, how they compare, and how they interact Differing Physical Appearances • Patch Effects: most large communities usually consist of a mosaic of vegetation “patches” Differing Physical Appearances • Edge Effects: differences in physical appearance at boundaries between ecosystems Edge Effects Edge Effects Ecological Niche Niche: role an organism plays in an ecosystem • niche is like an "occupation“ – a species’ interactions with habitat and other organisms (their role in food web) © Brooks/Cole Publishing Company / ITP Ecological Niche vs. Habitat Habitat: actual location where an organism lives • habitat is like an "address" © Brooks/Cole Publishing Company / ITP Generalists vs. Specialists • Generalist Species have broad niches, can live many places, use a variety of resources e.g., dandelions, cockroaches, coyotes, humans • Specialist Species have narrow niches, live only in specific places e.g., spotted owls, giant pandas © Brooks/Cole Publishing Company / ITP Native Species Native Species: species that normally live & thrive in a particular ecosystem Nonnative Species: (also called exotic, invasive, or alien species) originate in other ecosystems; deliberate or accidental introduction by humans causes problems •e.g., "killer bees”, imported from Africa to Brazil to increase honey production; displace native bees © Brooks/Cole Publishing Company / ITP Indicator Species Indicator Species: species that serve as early warnings that a community or ecosystem is being damaged • e.g., northern spotted owls are indicators of healthy old–growth forest © Brooks/Cole Publishing Company / ITP Keystone Species Keystone Species: species that play a critical role in an ecosystem • Ex: sea otters are keystone species because they prevent sea urchins from depleting kelp beds • Ex: flying foxes are keystone species because they pollinate & disperse tropical trees such as durian “The loss of a keystone species is like a drill accidentally striking a power line. It causes lights to go out all over.” – E.O. Wilson © Brooks/Cole Publishing Company / ITP Species Interactions • the effects of one species on another may be negative, positive, or neutral • five kinds of interactions: POPULATION A COMPETITION PREDATION PARASITISM COMMENSALISM MUTUALISM POPULATION B Interspecific Competition When two or more species use the same limited resource (food, space, etc.) and adversely affect each other •–/– • niche overlap • Ex: fire ants & native ants in North America © Brooks/Cole Publishing Company / ITP No Competition High Relative population density Paramecium aurelia Paramecium caudatum Low 0 2 4 6 8 10 12 Days Each species grown alone 14 16 18 Interspecific Competition High Relative population density Paramecium aurelia Paramecium caudatum Low 0 2 4 6 8 10 12 Days Both species grown together 14 16 18 Resource Partitioning Species with similar resource requirements can coexist because they use limited resources: • at different times • in different ways • in different places © Brooks/Cole Publishing Company / ITP Resource Partitioning Where are the 2 species competing? Why is there no competition here? Resource Partitioning © Brooks/Cole Publishing Company / ITP Resource Partitioning Five species of insect–eating warblers coexist in spruce forests of Maine: • feed in different portions of trees • consume somewhat different insects © Brooks/Cole Publishing Company / ITP Warblers Predation Members of one species (predator) feed on another species (prey); •+/– • Ex: lion feeding on zebra © Brooks/Cole Publishing Company / ITP Parasitism One organism (parasite) lives on part of another organism (host) •+/– • Ex: flea living on a dog © Brooks/Cole Publishing Company / ITP Mutualism Two species interact in a way that benefits both •+/+ • Ex: lichens (algae & fungi) • Ex: clownfish & anemones • Ex: ants & acacias © Brooks/Cole Publishing Company / ITP Commensalism One organism benefits from another, but neither helps nor harms the other organism •+/0 • Ex: epiphyte growing on a tree © Brooks/Cole Publishing Company / ITP Predator-Prey Relationship • What do predators do to increase their chances of getting a meal? • What do prey do to avoid being eaten? Predator-Prey Relationship • Predators get better at catching prey • Prey get better at avoiding capture • Similar to an “arms race” – Ex: During the Cold War, the US and the USSR tried to intimidate the other with bigger and better weapons Predators • Pursuit – Faster (cheetahs) – Better eyesight (eagles) – Hunting in packs (wolves) • Ambush – Camouflage (praying mantis) – Mimicry (alligator snapping turtles) Prey • Camouflage • Ex: walking stick Prey • Chemical warfare • Ex: skunk Prey • Warning colors • Ex: poison dart frog Prey • Mimicry • Ex: king snake Prey • Behavior • Ex: blowfish Ecological Succession Succession: gradual & fairly predictable change in species composition over time © Brooks/Cole Publishing Company / ITP Primary Succession © Brooks/Cole Publishing Company / ITP Primary Succession Primary Succession: gradual establishment of biotic communities in an area where no life existed before • Ex: succession on newly formed islands & after the retreat of a glacier • Early Communities: lichens & mosses colonize bare rock • Mid Communities: small herbs & shrubs colonize • Late Communities: tree species colonize © Brooks/Cole Publishing Company / ITP Primary Succession • Type of succession that occurs where there was no ecosystem before • Occurs on rocks, cliffs, and sand dunes • Pioneer species: the first organism to colonize any newly available area and begin the process of ecological succession Lichens Mosses Parking Lot Secondary Succession © Brooks/Cole Publishing Company / ITP Secondary Succession Secondary Succession: gradual reestablishment of biotic communities in an area where a biotic community was previously present • Ex: "old field succession" © Brooks/Cole Publishing Company / ITP Secondary Succession: Mount St. Helens • Erupted in 1980 • 44,460 acres were burned and flattened • After the eruption, plants began to colonize the debris Disturbance Disturbance: a distinct event that disrupts an ecosystem or community • examples of natural disturbances: fires, hurricanes, tornadoes, droughts, & floods • examples of human-caused disturbances: deforestation, overgrazing, plowing • disturbance initiates secondary succession © Brooks/Cole Publishing Company / ITP The Circle of Life in Secondary Succession Intermediate Disturbance Hypothesis Ecosystem Stability • Inertia: the ability of an ecosystem to resist being disturbed • Resilience: the ability of an ecosystem to “bounce back” after it has been disturbed Precautionary Principle • We should try to prevent potential harm to an ecosystem even though we don’t understand all of the cause-and-effects • “better safe than sorry”