Community Interactions Chapter 7 Community Interactions

7-1 COMMUNITY STRUCTURE AND SPECIES DIVERSITY

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 Species Diversity/Richness: number of different species Species Abundance: number of individuals of each species 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” Edge Effects: differences in physical appearance at boundaries between ecosystems

Species Diversity Species Rich Environments Tropical Rain Forests Coral Reefs Deep Sea Large Tropical Lakes Tend to have high species diversity but low species abundance Factors that Affect Diversity Latitude (terrestrial) – distance from equator Depth (aquatic) Pollution (aquatic)

Species Abundance Determined by: Rate at which new species immigrate Rate at which species become extinct

Ecological Niche vs. Habitat 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) Habitat: actual location where an organism lives habitat is like an "address"

7-2 GENERAL TYPES OF SPECIES

GENERAL TYPES OF SPECIES Generalist Species Specialist Species Native Species Nonnative Species Indicator Species Keystone Species

Generalist vs. Specialist 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 vs. Nonnative Species Native Species: species that normally live & thrive in a particular ecosystem Nonnative Species: also called exotic, invasive, or alien species originate in other ecosystem deliberate or accidental introduction by humans causes problems may thrive and crowd out native species

The Case of the Killer Bees 1957 Brazil imported wild African bees to help increase honey production Displaced domestic honeybees Actually reduced honey production Moved north in Central America Established populations in Texas, Arizona, New Mexico, Puerto Rico, and California

Snakehead Fish

CANE TOADS!

The Simpsons! Bart vs. Australia

Indicator Species Indicator Species: species that serve as early warnings that a community or ecosystem is being damaged Birds are good indicator species Found everywhere Respond to environmental change quickly northern spotted owls are indicators of healthy old–growth forest Fish are good indicator species in aquatic ecosystems (i.e. trout)

“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 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 tropical trees and disperse seeds, such as durian fruit trees

7-3 SPECIES INTERACTIONS: COMPETITION AND PREDATION

Species Interactions The effects of one species on another may be negative, positive, or neutral Five kinds of interactions: Interspecific competition Predation Parasitism Mutualism Commensalism

Intra- vs. Inter- specific competition Intraspecific Competition – members of the SAME species compete for resources Interspecific Competition – members from 2 or more DIFFERENT species compete for resources When two or more species use the same limited resource (food, space, etc.) they may adversely affect each other niche overlap Ex: fire ants & native ants in North America

Relative population density Each species grown alone No Competition High Low Relative population density 2 4 6 8 10 12 14 16 18 Days Each species grown alone Paramecium aurelia Paramecium caudatum

Interspecific Competition High Paramecium aurelia Relative population density Paramecium caudatum Low 2 4 6 8 10 12 14 16 18 Days Both species grown together

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 Example 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

Predation Members of one species (predator) feed on another species (prey); + / – Ex: lion feeding on zebra © 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 Warning colors Ex: poison dart frog Chemical warfare Ex: skunk Mimicry Ex: king snake Behavior Ex: blowfish

7-4 SPECIES INTERACTIONS: PARASITISM, MUTUALISM, AND COMMENSALISM

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

Species Interactions - + The effects of one species on another may be negative, positive, or neutral five kinds of interactions: POPULATION A POPULATION B COMPETITION - PREDATION + PARASITISM COMMENSALISM MUTUALISM

7-5 ECOLOGICAL SUCCESSION: COMMUNITIES IN TRANSITION

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 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

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

Lichens Parking Lot Mosses

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"

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 disturbance initiates secondary succession Natural disturbances: fires, hurricanes, tornadoes, droughts, & floods Human-caused disturbances: deforestation, overgrazing, plowing

Intermediate Disturbance Hypothesis: moderate disturbances in communities promote greater species diversity than small or major disturbances

Climax Community Climax community: the final and stable community in an ecosystem Will continue to change in small ways, but will remain primarily the same over time (unless disturbed)

The Circle of Life in Secondary Succession

7-6 ECOLOGICAL STABILITY AND SUSTAINABILITY Stability - complex networks of positive and negative feedbacks loops

Ecosystem Stability Inertia/Persistence: the ability of an ecosystem to resist being disturbed Constancy: the ability of a living sysmte such as a population to keep its numbers within the limits imposed by available resources 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”