1. Chapter 15 – How Ecosystems Change
Section 1 - Interactions within Ecosystems
Section 2 – Ecosystem Development and Change

2. Section 1 – Interactions Within Ecosystems
Species change in response to the challenges posed by their environments.
As a result many animals and plants have special characteristics suited to the ecosystem.
Coevolution occurs when two or more species change in response to each other.
Examples: Coevolution of flowering plants and insects
Bright flowers attract insects that can see color
Fragrant flowers attract insects that can sense odors

3. Plant defenses against herbivores includes:
Thorns on rose bushes
Prickles
Sticky hairs
Tough leaves
The most crucial plant defenses are chemical: some are poison and some just taste bad
Many herbivores overcome plant defenses
Certain herbivores specialize in eating only one kind of plant.
Cabbage butterflies exclusively eat plants from the mustard family while all other insects avoid the mustard plants. The caterpillars have the ability to break down the mustard oils into harmless chemicals.

4. Three types of close species interactions: Symbiosis a close, long-term association between two or more species
Parasitism-the relationship between the parasite and its host; parasites obtain nutrition by feeding on the host; the parasite usually does not kill its host and is usually smaller than the organism on which it feeds
Mutualism-a symbiotic relationship in which all participating species benefit. Examples are lichen (a fungus and a green algae), nitrogen-fixing bacteria and plant root, and intestinal bacteria and humans.
Commensalism-a symbiotic relationship where one species benefits and the other is not obviously affected. Examples are barnacles on whales and sea anemones on boxing crabs.

5. Section 2-Ecosystem Development and Change
Every organism in an ecosystem plays a role in the ecosystem.
Any organism may be a predator to one species and a prey to another.
The sum of the organism’s interactions with its physical environment and with other organisms is its niche. The niche describes how an organism lives and its role in the ecosystem. Each species in an ecosystem has a unique niche. The total niche that an organism could potentially use within an ecosystem is that organism’s fundamental niche.
Competition – Situations in which two or more organisms attempt to use the same scarce resources.

6. Sometimes organisms are unable to occupy their entire fundamental niche because another species already occupies part of it. Situations in which two or more organisms attempt to use the same scarce resource are called competition. That part of a fundamental niche that an organism actually occupies as a direct result of competition is called its realized niche.
Competition plays an important role in how ecosystems develop. After serious disruption of an ecosystem, an new habitat is formed in a predictable succession.

7. Stages of Habitat Succession
Stage 1-An empty habitat is quickly occupied. The first organisms to move in are small, fast-growing plants (weeds). The early “settlers” are mosses and lichens which are able to live under harsh conditions.
Stage 2-The habitat becomes more hospitable due to early plant settlers. The next wave of succession is shrubs and trees. The diversity of the ecosystem usually increases as the ecosystem matures.
Stage 3- The habitat has a forest of deciduous trees established. Even though no two episodes of succession is exactly alike, the progression of succession tends to result in similar communities.

8. Ecosystem stability
The ability of an ecosystem to resist change in the face of disturbance is known as stability. Early stages of succession have a low stability, later stages are more stable, and the final community is the most stable.
Most ecologists now agree that more diverse ecosystems tend to be more stable than less diverse ecosystems.
A keystone species is a species whose niche affects many others in the ecosystem and that cannot be readily replaced if lost. Example: starfish in Washington coast – 15 species down to 8 after the removal of the starfish.

9. Two key factors that determine the diversity of an ecosystem are:
The size of the ecosystem- ecosystems that are not subdivided into isolated patches will usually contain a wider variety of physical habitats and therefore usually support more species than small ecosystems.
The latitude of the ecosystem-latitude has a great influence on the diversity because moisture and temperature vary with distance from the equator. There are almost 30 times more bird species in Central America than there are in Alaska.

10. Human Disruption of Ecosystems
Humans alter ecosystems in three principle ways:
By disrupting the physical habitat
By decreasing species diversity
By destroying interactions among species