🌍 AP Environmental Science – Unit 2
Biodiversity
Definition: The variety of life at different levels — genes, species, and ecosystems.
Types:
Genetic diversity: Variety of genes within a population.
More genetic diversity = better survival and adaptation to stressors.
Example: Disease resistance in crops is stronger when genetic diversity is high.
Species diversity: Variety of species in an ecosystem.
Measured by species richness (number of species) and species evenness (how equally individuals are distributed among species).
Habitat (ecosystem) diversity: Variety of ecosystems/habitats in a region.
Example: Forests, wetlands, grasslands, deserts in one region → high habitat diversity.
Genetic Diversity & Population Effects
Bottleneck Effect: Sharp reduction in population size → many genes lost → reduced variation.
Example: Cheetahs went through a bottleneck; very low genetic diversity today.
Founder Effect: A few individuals start a new population → reduced genetic variation.
Example: Small island populations often lack the diversity of mainland populations.
Niche
Definition: The role an organism plays in an ecosystem (its job).
Types:
Fundamental niche: Full range of conditions an organism could occupy without competition.
Realized niche: The actual conditions/resources used due to competition or predation.
Specialist species
Narrow niche, specific food or habitat needs.
Thrive only under stable conditions.
Example: Panda (depends on bamboo).
Generalist species
Broad niche, flexible diet/habitat use.
Can survive in many environments.
Example: Raccoon, cockroach.
Ecosystem Services
Definition: Benefits humans get from ecosystems.
Types:
Supporting services: Nutrient cycling, soil formation, photosynthesis.
Provisioning services: Food, water, timber, medicine.
Cultural services: Recreation, aesthetic, spiritual, educational value.
Regulating services: Climate regulation, water purification, flood control, pollination.
Disruptions (Anthropogenic = human-caused):
Land-use change (deforestation, urbanization).
Pollution (air, water, soil).
Introduced/invasive species.
Overexploitation (overfishing, mining, logging).
Overuse of nonrenewable resources.
Consequences:
Economic: Loss of tourism, crop failures, cost of ecosystem restoration.
Ecological: Habitat loss, species extinctions, disrupted food webs.
Island Biogeography
Theory: Biodiversity on islands depends on island size and distance from the mainland.
Larger islands → more species (more resources, lower extinction risk).
Islands closer to mainland → higher immigration rates.
Applies beyond islands: Any fragmented habitat acts like an island.
Invasive Species
Definition: Non-native species that spread and harm ecosystems.
Effects: Outcompete native species, reduce biodiversity, alter habitats.
Examples: Zebra mussels in Great Lakes, kudzu vine in U.S. Southeast.
Habitat Fragmentation & Corridors
Habitat fragmentation: Large habitats broken into smaller patches (roads, cities, farms).
Leads to smaller populations, more vulnerable to extinction.
Habitat corridors: Strips of habitat that connect patches, allowing species movement and gene flow.
Ecological Tolerance
Definition: The range of conditions (temperature, pH, salinity, etc.) an organism can survive.
Specialists have narrow tolerance; generalists have wide tolerance.
Example: Salmon need specific temperature ranges, while cockroaches tolerate wide ranges.
Indicator Species
Definition: Species that signal ecosystem health or stress.
Examples:
Amphibians (sensitive to water pollution and habitat changes).
Lichens (sensitive to air pollution).
Mass Extinction
Definition: A large-scale event in which many species go extinct in a short time.
Earth has had 5 previous mass extinctions; many scientists argue human activity is causing a 6th.
Survival of the Fittest (Natural Selection)
Definition: Organisms best adapted to their environment are more likely to survive and reproduce.
Example: Peppered moths during the Industrial Revolution changed from light-colored to dark-colored due to soot on trees.
Ecological Succession
Definition: Gradual change in species composition of an ecosystem over time.
Primary succession:
Occurs on bare rock (no soil).
Pioneer species (lichens, mosses) → soil formation → shrubs/trees → climax community.
Example: After volcanic lava flow.
Secondary succession:
Occurs where soil remains after disturbance.
Faster than primary succession.
Example: After fire, flood, farming.
Keystone & Foundational Species
Keystone species:
Disproportionate effect on ecosystem stability.
Example: Sea otters → control sea urchins → protect kelp forests. Wolves → regulate deer → allow forest regeneration.
Foundational species:
Physically create or shape habitats.
Example: Corals build reefs, beavers build dams, kelp forms forests.
Island Biogeography = The study of ecological relationships and distribution of organisms on islands, as well as community structures and evolutionary processes.
Helps explain species richness (biodiversity) in isolated habitats (islands, mountaintops, lakes, and fragmented forests).
🏝 Things to Know About Islands
Islands are colonized by species arriving from elsewhere (mainland or other islands).
Specialists vs. Generalists:
Many island species evolve into specialists due to limited resources.
Generalist species (broad niche) can outcompete and threaten island specialists if introduced.
Invasive Species = Non-native organisms that cause environmental or economic harm. Islands are highly vulnerable because native species lack defenses.
⚖ Immigration vs. Extinction
Species richness on an island depends on the balance between:
Immigration (colonization) of new species.
Extinction of established species.
Equilibrium Point: where immigration rate = extinction rate. This determines the number of species the island supports.
📏 Factors Influencing Biodiversity
Island Size
Larger islands = more resources, habitat diversity → support more species.
Smaller islands = higher extinction rates.
Distance from Mainland
Islands closer to the mainland = higher immigration rates → greater biodiversity.
Remote islands = fewer colonizers, lower biodiversity.
🌳 Habitat Fragmentation & Corridors
Habitat Fragmentation = Large habitats split into smaller, isolated patches by human activity.
This is an “artificial island” surrounded by an unsuitable habitat (urban areas). Ex. Central Park in New York City
These fragmented habitats can lead to decreased species interactions, reduced gene flow, and ultimately higher extinction rates. To combat these effects, wildlife corridors can be established, allowing species to move between fragmented habitats and maintain genetic diversity.
Habitat Corridors (wildlife/green corridors) = Connect fragmented patches, allowing gene flow and migration → reduce extinction risk.
Corridors serve as vital links that facilitate the movement of wildlife, enabling animals to access food, mates, and other resources essential for survival. This connectivity also promotes ecosystem resilience, as diverse species can adapt to environmental changes more effectively.
Wildlife corridors can also facilitate migration and enhance the resilience of ecosystems by allowing populations to adapt to changing environmental conditions and access new resources.
🔬 Role in Evolution
Isolation + limited resources = adaptive radiation (e.g., Darwin’s finches).
Promotes speciation and unique endemic species.
Makes ecosystems fragile to disturbances and invasive species.
Pioneer Species → First species to colonize a barren or disturbed area (e.g., lichens, mosses). Start soil formation.
Ecological Succession → Natural, gradual change in species composition of an ecosystem.
Primary Succession → Begins on bare rock (no soil). Example: after volcanic eruption.
Secondary Succession → Begins in an area with soil but disturbed (e.g., after fire or farming). Faster than primary.
Climax Community → Relatively stable, long-term community at the end of succession (often forests in many biomes).
Biodiversity (3 levels):
Genetic → Variety of genes within a species (important for adaptation).
Species → Variety of species in an ecosystem.
Habitat/Ecosystem → Variety of habitats within a region.
Niche → The role a species plays in its ecosystem (its job + habitat + interactions).
Fundamental Niche → Where a species could live without competition.
Realized Niche → Where a species actually lives due to competition/predators.
Species Richness → Number of different species in an ecosystem.
Species Evenness → How evenly individuals are distributed among species (higher evenness = healthier ecosystem).
Bottleneck Effect → Sharp reduction in population → reduced genetic diversity.
Founder Effect → Small group of individuals start a new population with limited genetic variation.
Survival of the Fittest → Natural selection; individuals with favorable traits survive and reproduce.
Mass Extinction → Event in which large % of species go extinct in a short time.
Specialist Species → Narrow niche; thrive in specific conditions (e.g., koalas, pandas). Vulnerable to change.
Generalist Species → Broad niche; adapt to many environments (e.g., raccoons, cockroaches).
Indicator Species → Signal environmental health (e.g., amphibians = water quality).
Keystone Species → Species with a critical role in ecosystem balance (e.g., sea otters controlling sea urchins).
Foundational Species → Create/enhance habitats for others (e.g., coral reefs, beavers).
Anthropogenic → Human-caused effects on environment (pollution, climate change, deforestation).
Economic Consequences → Financial impacts (cost of invasive species, disasters, loss of ecosystem services).
Ecological Consequences → Environmental impacts (loss of biodiversity, habitat degradation).
Island Biogeography → Study of species richness on islands (real islands or “habitat islands” like fragmented forests). Biodiversity depends on island size and distance from mainland.
Invasive Species → Non-native organisms that spread rapidly and harm ecosystems (often generalists).
Habitat Fragmentation → Large habitats split into smaller, isolated patches by roads, farms, cities.
Habitat Corridors → Strips of habitat that connect fragments, allowing movement of species and genetic flow.
Ecosystems provide natural benefits grouped into four categories:
Supporting → Basic ecosystem processes (nutrient cycling, soil formation, primary productivity).
Provisioning → Goods/resources (food, water, timber, medicine).
Regulating → Climate regulation, flood control, water purification, pollination.
Cultural → Recreation, tourism, spiritual, aesthetic value.
Ecological Tolerance → Range of conditions (temperature, salinity, sunlight, nutrients) a species can survive.
✅ Summary:
Island biogeography explains how island size and distance from the mainland affect biodiversity. Larger, closer islands support more species. Habitat fragmentation creates “island-like” conditions on land. Invasive species and generalists threaten fragile island specialists, while corridors help reduce biodiversity loss. Furthermore, understanding these dynamics is essential for conservation efforts, as they highlight the importance of maintaining habitat connectivity and minimizing human impact on ecosystems.
✅ Key Definitions Recap
Biodiversity: Variety of life (genes, species, habitats).
Niche: Role of a species in its ecosystem.
Ecosystem services: Benefits to humans (supporting, provisioning, cultural, regulating).
Anthropogenic: Human-caused impacts.
Island biogeography: Species diversity depends on island size and isolation.
Invasive species: Harmful non-native species.
Habitat fragmentation: Splitting ecosystems into smaller patches.
Ecological tolerance: Range of conditions an organism can survive.
Indicator species: Signal ecosystem health.
Succession: Natural changes in ecosystems over time.
Keystone species: Species critical to ecosystem balance.
Foundational species: Species that build or define ecosystems.