1. Outline 4-2: What Shapes an Ecosystem?
Photo Credit: ©Michael Fogden/DRK PHOTO
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2. Biotic and Abiotic Factors
Ecosystems are influenced by a combination of biological and physical factors.
The biological influences on organisms within an ecosystem are called biotic factors.
Biotic factors include all the living things with which an organism might interact.
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3. Biotic and Abiotic Factors
Physical, or nonliving, factors that shape ecosystems are called abiotic factors.
Abiotic factors include:
temperature
precipitation
humidity
wind
nutrient availability
soil type
sunlight
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4. Biotic and Abiotic Factors
How do biotic and abiotic factors influence an ecosystem?
Biotic and abiotic factors determine the survival and growth of an organism and the productivity of the ecosystem in which the organism lives.
Biotic and Abiotic Factors
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5. Biotic and Abiotic Factors
The physical area where an organism lives is called its habitat. A habitat includes both biotic and abiotic factors. It might include different areas (forest, prairie, lakes, etc.)
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The Niche
The Niche
A niche is the full range of physical and biological conditions in which an organism lives and the way in which the organism uses those conditions.
Includes:
How it uses space
Feeding habits (herbivore, carnivore, etc.)
Reproductive behavior
Moisture requirements
Temperature requirements
Competition with other organisms
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The Niche
Crested auklet occupies the same niche in the Arctic that penguins do in the Antarctic.
The aye-aye occupies the same niche as typical woodpeckers.
They chew into tree stems and then use long middle finger to get insects out of wood
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The Niche
Aspects of Niches
The entire range of conditions an organism is potentially able to occupy within an ecosystem is called its fundamental niche.
The part of its fundamental niche that a species actually occupies is called its realized niche. This might be only a small portion of its fundamental niche.
Different species can coexist in the same habitat if they occupy very similar, but slightly different, niches.
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9. Community Interactions
When organisms live together in ecological communities, they interact constantly.
Various types of such interactions are: competition
predation
various forms of symbiosis.
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10. Community Interactions
Competition
Competition occurs when organisms of the same or different species attempt to use an ecological resource in the same place at the same time.
A resource is any necessity of life, such as water, nutrients, light, food, or space.
Two types of competition:
Intraspecific competition
Between members of the same species
2. Interspecific competition
Between members of different species
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11. Community Interactions
Direct competition in nature often results in a winner and a loser—with the losing organism failing to survive.
The competitive exclusion principle states that no two species can occupy the exact same niche in the same habitat at the same time.
If you force two very similar species to live in the same exact habitat one of them might go extinct.
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The Niche
Experiment on Paramecium Competition
When P. aurelia and P. caudatum had to live in the same lab environment and eat the same food, one species always went extinct:
P. aurelia always won the competition
P. caudatum always went extinct.
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13. Community Interactions
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The Niche
How is a small realized niche helpful to species?
Robert MacArthur (1950s) suggested that this can reduce competition between species:
The organisms essentially “carve up” the available resources. This is called resource partitioning.
Examples:
Warblers in forest
Barnacles on rocky coastlines
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15. Community Interactions
The distribution of these warblers avoids direct competition, because each species feeds in a different part of the tree. 18 12
Feeding height (m)
Cape May Warbler
Each of these warbler species has a different niche in its spruce tree habitat. By feeding in different areas of the tree, the birds avoid competing with one another for food.
Bay-Breasted Warbler 6
Yellow-Rumped Warbler
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The Niche
Barnacle Competition
Two species of barnacles live on rocks off the coast of Scotland:
1. Chthamalus stellatus
Live in shallow water; exposed to air when the tide goes out
2. Semibalanus balanoides
Live in deeper waters; usually covered with water & rarely exposed to air
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The Niche
Chthamalus
Semibalanus
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The Niche
Joseph Connell’s Experiment on Barnacles
He removed Semibalanus from deeper water
Chthamalus then was able to move down to deeper water and live covered by water
He later reintroduced Semibalanus to deep water
The Chthamalus then got crowded back up
When he placed Semibalanus in shallow water they could NOT survive
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The Niche
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Predation
Predation
An interaction in which one organism captures and feeds on another organism is called predation.
The organism that does the killing and eating is called the predator, and the food organism is the prey.
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Predation
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Predation
Predators can lessen competition
Robert Paine studied sea star & its prey species (clams, mussels)
Originally there were 15 prey species
If he kept the starfish out of experimental plots he found only 8 prey species
7 clam species crowded out by the mussels
Thus, predators can help to promote biodiversity, variety of species present in a community
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Plants & Herbivores
Plants protect themselves with:
Thorns, spines
Defensive chemicals called secondary compounds (mustard oil)
Many herbivores can feed on plants that are protected by chemicals:
Larvae of cabbage butterfly eat mustard
Larvae of Monarch butterflies eat milkweed & become poisonous
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25. Milkweed plant & Monarch butterflies

26. Community Interactions
Symbiosis
Any relationship in which two species live closely together is called symbiosis.
Symbiotic relationships include:
mutualism
commensalism
parasitism
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Mutualism
A symbiotic relationship in which both organisms benefit
Examples:
Aphids and ants
Lichens (fungus & green algae)
Bacteria in digestive tract of cattle
Cleaner fish
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28. Ants taking care of aphids

29. Lichens

30. Cleaner Fish in mouth of Moray Eel

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Commensalism
A symbiotic relationship in which one organism benefits & the other is neither harmed or helped
Examples:
Barnacles living on skin of whales
Epiphytes = plants that grow on other plants (orchids)
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Barnacles on Whales
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33. Epiphytes & Orchids

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Parasitism
A close, long-term symbiosis in which one organism obtains its nutrition from another living organism (lives on or in it)
Parasite = organism that is receiving the benefit
Host = organism that is being harmed
Parasites don’t usually kill their host
Examples: tapeworms, mistletoe, ticks
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35. Tick
Mistletoe
Tapeworm

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Coevolution
Reciprocal evolutionary adjustments between interacting members of an ecosystem.
Example:
Flowering plants depend on animals to disperse their pollen
The pollinating animals have adaptations that allow them to obtain food or other resources from the flower
Long beaks of hummingbirds
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39. Ecological Succession
Ecosystems are constantly changing in response to natural and human disturbances.
As an ecosystem changes, older inhabitants gradually die out and new organisms move in, causing further changes in the community.
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40. Ecological Succession
This series of predictable changes that occurs in a community over time is called ecological succession.
Sometimes, an ecosystem changes in response to an abrupt disturbance.
At other times, change occurs as a more gradual response to natural fluctuations in the environment.
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41. Ecological Succession
Primary Succession
On land, succession that occurs on surfaces where no soil exists is called primary succession. For example, primary succession occurs on rock surfaces formed after volcanoes erupt.
The first species to populate the area are called pioneer species.
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42. Ecological Succession
In this example, a volcanic eruption has destroyed the previous ecosystem.
Primary succession occurs on newly exposed surfaces, such as this newly deposited volcanic rock and ash.
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43. Ecological Succession
The first organisms to appear are lichens.
Primary succession occurs on newly exposed surfaces, such as this newly deposited volcanic rock and ash.
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44. Ecological Succession
Mosses soon appear, and grasses take root in the thin layer of soil.
Primary succession occurs on newly exposed surfaces, such as this newly deposited volcanic rock and ash.
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45. Ecological Succession
Eventually, tree seedlings and shrubs sprout among the plant community.
Primary succession occurs on newly exposed surfaces, such as this newly deposited volcanic rock and ash.
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46. Ecological Succession
Secondary Succession
Components of an ecosystem can be changed by natural events, such as fires.
When the disturbance is over, community interactions tend to restore the ecosystem to its original condition through secondary succession. 
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48. Ecological Succession
Healthy ecosystems usually recover from natural disturbances, but may not recover from long-term, human-caused disturbances.
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49. Ecological Succession
Succession in a Marine Ecosystem
Succession can occur in any ecosystem, even in the permanently dark, deep ocean.
In 1987, scientists documented an unusual community of organisms living on the remains of a dead whale.
The community illustrates the stages in the succession of a whale-fall community.
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50. Ecological Succession
Succession begins when a whale dies and sinks to the ocean floor.
Ecosystems are constantly changing in response to disturbances. In natural environments, succession occurs in stages. A dead whale that falls to the ocean floor is soon covered with scavengers.
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51. Ecological Succession
Within a year, most of the whale’s tissues have been eaten by scavengers and decomposers.
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52. Ecological Succession
The decomposition of the whale’s body enriches the surrounding sediments with nutrients.
When only the skeleton remains, heterotrophic bacteria decompose oils in the whale bones.
This releases compounds that serve as energy sources for chemosynthetic autotrophs.
The chemosynthetic bacteria support a diverse community of organisms.
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