Community EcologyCommunity Ecology

Community: a group of populations living and inter-acting with each other in the same area

Everglades community

Coral Reef community

The ecological niche is … the sum total of an organism's use of abiotic

& biotic resources in the environment: its habitat (the place where it is found); its interaction with organisms within the

community; its position in the movement of energy in a

particular ecosystem.

Lion: heterotroph, carnivore, consumer of large herbivores, at the top of the food chain on the savannah in C. Africa.

The ecological niche is … an organism’s address

and occupation.

Bamboo: autotroph, primary producer, food for the Giant

Pandas in the Wolong Nature Reserve of

southwestern China.

The competitive exclusion principle says that two species cannot coexist in a community if their niches are identical. Competition forces one species to move or

die. Domestic cattle and sheep out-compete

native herbivores, such as deer, for food.

Introduced weeds out-compete native plants.Ex: melaluca trees

from Australia in S. Florida take space needed byother organisms.

When species interact one usually benefits while the other suffers, but not always.

There are several types of interactions: competition, herbivory, predation, parasitism, mutualism, commensalism.

Remora on a shark

Competition - an attempt to use the same scarce resources. The interaction is detrimental to both

species. Competitors must adapt, or one loses its

niche. Usually one surrenders a part of the habitat. Ex. barnacles on rocks at the seashore.

Rarely, one species drives the other away:

Ex: humans compete for space.

Video (populations)

Herbivory - animals eating plants. Animal benefits; plant does not.

Animals often develop specialized teeth for grinding

Plant defenses against herbivores include spines and chemical

compounds that are toxic.

Ex: oleander & Digitalis are deadly, but humans develop medicines from these plants.

Herbivory - animals eating plants. Sheep and horses graze on plants; they are

herbivores. Many insects, such as aphids and caterpillars,

eat plants.

Predation – one species (the predator) eats another species (the prey). The interaction is beneficial to one

species. Predator adaptations: claws, teeth, fangs,

poison, heat-sensing organs, speed, and agility.

Prey adaptations: claws, horns,

camouflage, speed, agility, group behaviors

(herding), etc.Lions hunting zebras

Predation – one species (the predator) eats another species (the prey). Owls are predators of small animals. A preying mantis eats other insects.

Adaptations of teeth to a particular niche Note

differences:

Symbiosis - two different species living together intimately. Does not include eating relationships. Includes parasitism, mutualism, & Includes parasitism, mutualism, &

commensalism.commensalism.

Parasitism – One organism (the parasite) lives on or in a host & depends on the host for nutrition. Don’t usually kill the host, unlike a

predator; also usually much smaller. (If parasites killed the host quickly they wouldn’t reproduce.) Malarial blood parasite

and intestinal worms weaken humans.

Parasitism - predators live on or in a host. Pathogens are disease-causing organisms

that can be considered predators.Bacteria Streptococcus pyogenes Staphylococcus aureus Neisseria gonorrhea

Viruses weaken plants & animals Influenza virus Polio virus Tobacco

mosaic virus

Mutualism – both species benefit from their interaction. Humans protect their domesticated

animals, which provide food and clothing. Dogs return protection

and comfort.Humans on horsesherding sheep withthe help of dogs.

Mutualism – both species benefit from their interaction. Plants provide food for pollinators, which

help plants reproduce. Animals disseminate fruits.

Mutualism – both species benefit from their interaction. Lichen: an association of a fungus &

cyanobacteria or a fungus & green algae.

The fungus absorbs nutrients(like N & P), and algae or

bacteria photosynthesize making food.

Mutualism – both species benefit from their interaction. Escherichia coli bacteria in human

intestines help us digest food and produce Vitamin K that we can’t make.

Protists in the gut of termites help them digest wood.

Commensalism – one species benefits; the other is neither helped or hurt. Boxing crab pushes stinging sea

anemones at predators. Anemone is unaffected; crab benefits.

Anemone may get bits of left-over food.

Commensalism – one species benefits; the other is neither helped or hurt. Barnacles ride on whale’s body to new

food sources. Whale is unaffected.

Amensalism – one species suffers; the other is neither helped or hurt. Humans dump garbage or waste

materials into the river, which hurts the fish, but people are not affected.

Antibiosis – one species makes a chemical that inhibits another species living nearby. Soil bacteria produce toxins that inhibit

the growth of other bacteria or fungi – the source of antibiotics.

Ecological Ecological

SuccessionSuccession

Definition: A sequence of community changes after a disturbance - a transition in species compo-sition over ecological time. Primary succession begins in a lifeless

area with no soil. Ex: after a glacier

retreats, mosses and lichens colonize first

and produce soil by breaking down rock.

Primary succession begins in a lifeless area - no soil. Ex: glacial retreats

1) Lichens and mosses produce soil.2) First colonists are small, fast-growing

plants, like “weeds”. They improve soil, but compete poorly.

3) Next trees and shrubs move in carried by wind and animals.

Primary succession begins in a lifeless area - no soil. Ex: glacial retreats

4) Eventually a climax community is reached that resists invasion from new plants and is stable over long periods of time. These are the biomes: the coniferous forest, savannah, etc.

Primary succession begins in a lifeless area - no soil.

Ex: volcanic eruption The island of Surtsey off

southern Iceland rose from the sea in 1963.

2005

Living organisms change the abiotic environment during succession, making it friendlier. Soil concentrations of nutrients change over

time. Nitrogen rises from biological fixation by

bacteria. Organic compounds increase as dead plants

decay. Transpiration raises humidity. Levels of CO2 and O2 change slightly. Reflectance of the ground changes, affecting

local temperatures. The land becomes more hospitable to life.

In the case of Mt. St. Helens in Washington, USA, the eruption produced ash, not lava, so there was a type of soil afterward. Plants & animals arrived quickly.

Secondary succession occurs after an existing community has been cleared but soil remains. Ex: after a forest fire, or when pasture or

farmland is abandoned and returns to forest.

Fire in Yellowstone National Park, 1988

Secondary succession – disaster leaves soil intact. Ex: after a forest fire, or when pasture or

farmland is abandoned and returns to forest. Grasses grow first, then trees and other

organisms.

Seeds are often in place already – some conifer trees need fire to open cones and release the seeds.

Yellowstone Park, 2005

Biodiversity declines after a catastrophe, whether natural or

man-made. We always assume Earth can recover.

Gaia’s breath – the planet lives