2.1 ENDURING UNDERSTANDING: Ecosystems have structure and diversity that change over time.

LEARNING OBJECTIVE ERT-2.A Explain levels of biodiversity and their importance to ecosystems.

ESSENTIAL KNOWLEDGE:

• Biodiversity in an ecosystem includes genetic, species, and habitat diversity.

• The more genetically diverse a population is, the better it can respond to environmental stressors. Additionally, a population bottleneck can lead to a loss of genetic diversity.

• Ecosystems that have a larger number of species are more likely to recover from disruptions.

• Loss of habitat leads to a loss of specialist species, followed by a loss of generalist species. It also leads to reduced numbers of species that have large territorial requirements.

• Species richness refers to the number of different species found in an ecosystem.

2.2 ENDURING UNDERSTANDING: Ecosystems have structure and diversity that change over time.

LEARNING OBJECTIVE ERT-2.B Describe ecosystem services. ERT-2.C Describe the results of human disruptions to ecosystem services.

ESSENTIAL KNOWLEDGE:

• There are four categories of ecosystem services: provisioning, regulating, cultural, and supporting.

• Anthropogenic activities can disrupt ecosystem services, potentially resulting in economic and ecological consequences.

2.3 ENDURING UNDERSTANDING: Ecosystems have structure and diversity that change over time.

LEARNING OBJECTIVE ERT-2.D Describe island biogeography. ERT-2.E Describe the role of island biogeography in evolution.

ESSENTIAL KNOWLEDGE:

• Island biogeography is the study of the ecological relationships and distribution of organisms on islands, and of these organisms’ community structures.

• Islands have been colonized in the past by new species arriving from elsewhere.

• Many island species have evolved to be specialists versus generalists because of the limited resources, such as food and territory, on most islands. The long-term survival of specialists may be jeopardized if and when invasive species, typically generalists, are introduced and outcompete the specialists.

2.4 ENDURING UNDERSTANDING: Ecosystems have structure and diversity that change over time.

LEARNING OBJECTIVE ERT-2.F Describe ecological tolerance.

ESSENTIAL KNOWLEDGE:

• Ecological tolerance refers to the range of conditions, such as temperature, salinity, flow rate, and sunlight that an organism can endure before injury or death results.

• Ecological tolerance can apply to individuals and to species.

2.5 ENDURING UNDERSTANDING: Ecosystems have structure and diversity that change over time.

LEARNING OBJECTIVE ERT-2.G Explain how natural disruptions, both short and long-term, impact an ecosystem.

ESSENTIAL KNOWLEDGE:

• Natural disruptions to ecosystems have environmental consequences that may, for a given occurrence, be as great as, or greater than, many human-made disruptions.

• Earth system processes operate on a range of scales in terms of time. Processes can be periodic, episodic, or random.

• Earth’s climate has changed over geological time for many reasons.

• Sea level has varied significantly as a result of changes in the amount of glacial ice on Earth over geological time.

• Major environmental change or upheaval commonly results in large swathes of habitat changes.

• Wildlife engages in both short- and long-term migration for a variety of reasons, including natural disruptions.

2.6 ENDURING UNDERSTANDING: Ecosystems have structure and diversity that change over time.

LEARNING OBJECTIVE ERT-2.H Describe how organisms adapt to their environment.

• Organisms adapt to their environment over time, both in short- and long-term scales, via incremental changes at the genetic level.

• Environmental changes, either sudden or gradual, may threaten a species’ survival, requiring individuals to alter behaviors, move, or perish.

2.7 ENDURING UNDERSTANDING: Ecosystems have structure and diversity that change over time.

LEARNING OBJECTIVE ERT-2.I Describe ecological succession. ERT-2.J Describe the effect of ecological succession on ecosystems.

• There are two main types of ecological succession: primary and secondary succession.

• A keystone species in an ecosystem is a species whose activities have a particularly significant role in determining community structure.

• An indicator species is a plant or animal that, by its presence, abundance, scarcity, or chemical composition, demonstrates that some distinctive aspect of the character or quality of an ecosystem is present.

• Pioneer members of an early successional species commonly move into unoccupied habitat and over time adapt to its particular conditions, which may result in the origin of new species.

• Succession in a disturbed ecosystem will affect the total biomass, species richness, and net productivity over time.