Unit 2 AP Environmental Science Study Guide
Biodiversity and Its Three Nested Levels
Definition of Biodiversity: Biodiversity is the diversity of different life forms found in an ecosystem. While seemingly simple, it is categorized into three distinct, nested levels that are essential for ecosystem health and stability.
Genetic Biodiversity: - Definition: The variance of genes or traits found within individuals of a population. - Benefit: A high wide range of different traits increases the probability that a population can adapt to environmental disturbances or changes. If a population has high genetic diversity, some members are more likely to possess genes that allow them to survive new stressors. - The Sparrow Example: In a sparrow population experiencing a drought, the seeds they consume may become dry and harder to crack. If high genetic diversity exists, some individuals may have bigger, stronger beaks allowing them to crack these seeds, ensuring the survival of the species.
Species Biodiversity: - Definition: The diversity of different types of organisms found in an ecosystem. There are two primary metrics used to measure this level: - Species Richness: A simple count of the total number of different species found in a given ecosystem. - Species Evenness: The distribution or balance of the population sizes of all the different populations present. - Comparison of Ecosystem Resilience: Consider two forests with the same species richness. Forest #1 has high species evenness, while Forest #2 is dominated () by one deciduous tree species. If a disease strikes that specific species, Forest #2 could lose of its tree cover, whereas Forest #1 would remain relatively stable because it has plenty of other species (conifers and different deciduous trees) to repopulate the area.
Ecosystem Biodiversity: - Definition: The variance in the different ecosystems found in a given area or biome. - Benefit: Just as genetic diversity benefits populations and species diversity benefits ecosystems, ecosystem diversity benefits entire biomes. - Examples: A tropical rainforest has high ecosystem diversity, containing rivers, different tree stands, and edge habitats (where forest meets open area). In contrast, a desert biome has lower ecosystem diversity, which in turn supports lower species richness.
Ecosystem Services: Financial Benefits of Nature
Definition: Ecosystem services are the financial or life-sustaining benefits humans receive from the natural function of ecosystems. These are categorized into four key areas:
Provisioning Services: - Definition: Goods provided directly to humans by natural ecosystems. - Example: Wood from forests used for furniture or houses, which can be harvested and sold for a profit.
Supporting Services: - Definition: Ecosystem processes that support valuable human actions, specifically agriculture. - Example: Insects like bees and moths pollinating a farmer's crops. While food could be produced without them, pollinators significantly increase yields and profits.
Regulating Services: - Definition: The stabilization of climate or environmental factors by ecosystems, which saves humans money on cleanup or mitigation of unstable conditions. - Example: Trees sequestering carbon dioxide (). This reduction in greenhouse gas reduces expensive climate consequences like crop-damaging droughts or storm damage to infrastructure.
Cultural Services: - Definition: Recreational, intellectual, or aesthetic benefits derived from nature. - Example: Tourists visiting the Grand Canyon pay park fees and stay in local hotels, generating revenue. Additionally, scientists who research ecosystems may write books or reports leading to the creation of valuable products.
Disruption of Services: Human activities can severely impact these benefits. - Case Study: The Deepwater Horizon oil spill in the Gulf Coast of Mexico. - Impacts: Fishermen lost profits due to inability to catch fish; mangrove swamps and salt grasses died, leading to coastline destabilization and increased storm damage costs; the tourism industry suffered as beaches were covered in oil.
Theory of Island Biogeography
General Principles: Island biogeography boils down to two simple rules regarding species richness: - Rule 1: Distance from the Mainland: If two islands are of equal size, the island closer to the mainland will have higher species richness. More species are capable of migrating (flying or swimming) a shorter distance. This is an inverse relationship: as distance from the mainland increases, species richness decreases. - Rule 2: Island Size: If two islands are at the same distance from the mainland, the larger island will have higher species richness. Larger islands offer higher habitat/ecosystem diversity (forests, grasslands, ponds), supporting a wider variety of species. This is a direct relationship: as island area increases, the number of supported species also increases.
Specialist Species and Invasives: - Island ecosystems offer narrow food and habitat choices, leading to highly specific adaptations. Species on islands are often "Specialists." - The Dodo Bird: Evolved from the pigeon family roughly million years ago on the island of Mauritius. Due to a lack of predators and herbivore competition, it evolved a larger body size and lost the ability to fly. - Vulnerability: Because specialists are uniquely adapted to narrow island conditions, they are often unable to compete with or adapt to invasive species. The Dodo went extinct because it was not afraid of humans (Dutch sailors) and was hunted at a rate faster than it could repopulate.
Ecological Tolerance
Definition: The range of conditions (temperature, pH, salinity) an organism or species can tolerate before death or serious injury occurs.
Human Temperature Example: - Optimal Range: Roughly to . In this range, bodies function optimally for survival, growth, and development. - Zone of Physiological Stress: If temperature goes above or below , the organism enters stress. Thinking and movement slow down, and it cannot remain in this state long without consequences. - Zone of Intolerance: Temperatures above or below lead quickly to death.
Role of Genetic Diversity: Within a species' general tolerance range, individual variation exists due to genetic diversity. Some individuals have wider optimal ranges, acting as a buffer against environmental change. If conditions change, these tolerant individuals survive and pass on their genes, allowing the population to evolve.
Natural Disruptions to Ecosystems
Frequency Categories: - Periodic Events: Occur with regular frequency (e.g., rainy and dry seasons). - Episodic Events: Occur somewhat regularly when conditions are right, but not on a fixed schedule (e.g., hurricanes and forest fires). - Random Events: Occur with no rhyme or reason (e.g., asteroid strikes or volcanic eruptions).
Natural Climate Change and Milankovitch Cycles: Earth's climate changes naturally over tens of thousands of years due to changes in its orbit around the sun: 1. Eccentricity: Changes in the shape of the orbital path. 2. Axial Precession: The wobble of the Earth on its axis. 3. Obliquity: Changes in the tilt of the Earth.
Consequences of Natural Cycles: - These cycles change Earth's temperature by altering its distance from or orientation to the sun. - Sea Level Rise: There is a clear link over the last years between global temperature and sea level. Warming periods cause sea level rise through the melting of glacial/polar ice sheets and the thermal expansion of water molecules. - Ecosystem Impacts: Rising sea levels can flood and destroy estuaries or deepen shallow ocean waters, preventing light from reaching coral reefs.
Natural Adaptations
Definition: An adaptation is a genetic mutation that gives an organism a higher likelihood of surviving and reproducing in its environment.
Case Study: Homo habilis and Opposable Thumbs: - Roughly years ago, a random genetic mutation in thumb muscle arrangement occurred. This allowed for a tighter, more nuanced grip. - This enabled the creation of stone tools used to crack open animal bones for energy-rich marrow. - Individuals with this adaptation had a massive energetic advantage, survived longer, and passed the trait to offspring.
Environmental Pressures: Early hominids adapted to moving from dense forests to grasslands. This made standing upright (Homo erectus) advantageous for surveying the environment and wielding tools.
The Rule of Change: Organisms either adapt to environmental disturbances or they go extinct.
Ecological Succession
Primary Succession: - Starts in a bare rock ecosystem (no soil). - Pioneer Species: Moss and lichen, transported as seeds/spores by wind. - Process: These species secrete acids to release minerals from rock through chemical weathering. The cycle of growth and death, combined with weathering, creates shallow rocky soil. - Progression: Shallow soil allows for grasses, wildflowers, and shrubs. Continued organic matter accumulation leads to intermediate species (shade-intolerant, fast-growing trees). Finally, slow-growing, shade-tolerant trees like Oak and Maple take over. - Climax Community: The final stage with large amounts of biomass and high species richness.
Secondary Succession: - Occurs where soil is already present after a disturbance (forest fire, glacial retreat, abandoned agriculture). - Pioneer Species: Grasses and wildflowers with seeds dispersed by wind or animals. - This process is much faster than primary succession because the soil-building phase is skipped.
Keystone Species and Ecosystem Engineers
Keystone Species: A species vital to ecosystem function; its removal can cause the entire ecosystem to collapse. - Example: Wolves: If removed, deer populations overpopulate and overgraze. This removes vegetation, leading to the loss of food and habitat for other species and eroding river banks as roots no longer stabilize the soil.
Ecosystem Engineers: A type of keystone species that shapes the landscape so dramatically that they create habitats that would not otherwise exist. - Beavers: Create Beaver Ponds through dams. - Mangrove Trees: Create mangrove swamps with stilt-like roots that stabilize the coastline and provide habitat.