7: Ecosystems

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Melissa Ha and Rachel Schleiger
Yuba College & Butte College via ASCCC Open Educational Resources Initiative

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Chapter Hook

In semi-urban areas beavers (Castor canadensis) are considered a nuisance as their dams block drainage pipes and cause flooding. However, in wild areas beavers are one of the most important species. Beaver dams are known for altering the flow of water. However, these dams not only slow down the movement of water, but they spread and store water in a way that is much more efficient than human-made dams. In addition, they slow and spread sediment and nutrients as they move through watersheds. What this does is create a mosaic of habitats across a landscape, both aquatic and terrestrial. More habitats lead to more species, both for plants and animals. In this way, beavers create ecosystems, one stick at a time.

American beaver

Figure \(\PageIndex{a}\) American beaver. Image by NeexPix (Public domain)

Attribution

Rachel Schleiger (CC-BY-NC)

7.1: Ecosystem Types and Dynamics
An ecosystem is a community of organisms and their nonliving environment. Ecosystems may be freshwater, marine, or terrestrial. Some ecosystems are more resistant to disturbances than others. Resilience refers to how quickly an ecosystem returns to equilibrium following a disturbance. Foundation species have great influence on community structure.
7.2: Matter
At its most fundamental level, life is made of matter. Matter is something that occupies space and has mass. All matter is composed of elements, substances that cannot be broken down or transformed chemically into other substances. Each element is made of atoms, which can bind together to form molecules. The four biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids.
7.3: Biogeochemical Cycles
Biogeochemical cycles represent the movement of chemical elements through water, air, soil, rocks, and organisms. Carbon cycles slowly between the ocean and land, but it moves quickly from the atmosphere to organisms (through photosynthesis) and back to the atmosphere (through cellular respiration). The nitrogen cycle and phosphorus cycles are other key biogeochemical cycles. Excess nutrients can disrupt aquatic ecosystems through eutrophication.
7.4: Soils
Soil is the outer loose layer that covers the Earth's surface and is the foundation for agriculture and forestry. Soils consist of organic material, inorganic material, water and air, and they differ in proportions of clay, silt, and sand. A soil profile is characterized by horizontal layers called horizons. Climate, organisms, topography, parent material, and time influence soil composition and formation.
7.5: Soil Degradation
Erosion, compaction, salinization, and desertification are interacting processes that degrade soil (lower its quality).
7.6: Data Dive- Beaver Impacts on Wetlands
7.7: Review

Thumbnail image - This sage thrasher’s diet, like that of almost all organisms, depends on photosynthesis.