Rucete ✏ AP Environmental Science In a Nutshell
2. The Living World: Biodiversity
This unit explores the forms, functions, and importance of biodiversity in ecosystems, from genetic diversity to ecosystem services. It also addresses factors affecting species richness, extinction risk, adaptation, and ecological succession.
2.1 Introduction to Biodiversity
Levels of Biodiversity
• Genetic Diversity: the variety of genes within a species, influencing adaptability.
• Species Diversity: the number of different species in an area (e.g., rainforests > deserts).
• Ecosystem Diversity: the range of ecosystems within a region.
Factors That Increase Biodiversity
• Diverse habitats
• Moderate environmental disturbances
• High habitat heterogeneity
• Evolutionary processes
• Intermediate succession stages
• High trophic-level diversity
Factors That Decrease Biodiversity
• Environmental stress and extreme conditions
• Habitat destruction and fragmentation
• Invasive species
• Pollution and overexploitation
• Geographic isolation
Importance of Biodiversity
• Stabilizes ecosystems and increases resilience to disturbances.
• Maintains food webs and nutrient cycles.
• Allows ecosystems to recover through alternate functional pathways.
Anthropogenic Threats to Biodiversity
• Burning fossil fuels → acid rain harms aquatic species.
• Deforestation → habitat loss and fragmentation.
• Industrial agriculture → monocultures reduce variety.
• Overfishing → disrupts food webs, threatens keystone species.
• Pesticides → kill non-target beneficial species.
• GMOs → reduce genetic variation.
• Water pollution → oxygen depletion, nutrient imbalance.
Population Bottleneck
• Occurs when a catastrophic event drastically reduces population size.
• Decreases genetic diversity and resilience in future generations.
• Example: Northern elephant seals were reduced to ~30 individuals in the 1890s; today, low genetic diversity remains despite population growth.
Generalist vs. Specialist Species
• Generalists (e.g., raccoons): broad diet and habitat tolerance → more resilient.
• Specialists (e.g., pandas): narrow diet and habitat requirements → more vulnerable.
Species Richness
• Refers to the number of different species in an ecosystem.
• Generally increases toward the equator and contributes to resilience.
2.2 Ecosystem Services
Definition
• Ecosystem services are the benefits humans receive from nature and ecosystem functions.
• These services are essential for human survival and economic well-being.
Four Main Types of Ecosystem Services
1. Cultural Services
• Non-material benefits that ecosystems provide.
• Examples: recreational fishing, spiritual enrichment, aesthetic value, cultural heritage.
2. Provisioning Services
• Products obtained directly from ecosystems.
• Examples: food, water, timber, fiber, genetic resources, medicinal plants.
3. Regulating Services
• Benefits obtained from regulation of ecosystem processes.
• Examples: climate regulation, pest control, pollination, air and water purification.
4. Supporting Services
• Services necessary for the production of all other ecosystem services.
• Examples: nutrient cycling, soil formation, primary productivity, biodiversity support.
Examples of Benefits
• Healthy aquatic ecosystems → recreational fishing (cultural)
• Livestock → milk, meat, and fiber (provisioning)
• Predatory birds and bats → natural pest control (regulating)
• Soil formation and fertility → higher crop yields (supporting)
2.3 Island Biogeography
Definition and Concept
• Island biogeography is the study of species richness and diversification on isolated natural “islands.”
• An “island” can be a literal island or any habitat isolated by human development (e.g., mountaintops, fragmented forests).
The Theory of Island Biogeography
• Species richness on islands is determined by immigration and extinction rates.
• Larger islands and those closer to the mainland have more species due to higher immigration and lower extinction rates.
Influencing Factors
• Distance from Mainland: closer islands receive more immigrant species and thus have greater biodiversity.
• Island Size: larger islands offer more diverse habitats and support larger populations, reducing extinction risk.
• Habitat Suitability: influenced by climate, existing flora/fauna, and historical conditions.
• Human Impact: habitat fragmentation and edge effects reduce diversity.
• Ocean Currents: affect species dispersal and nutrient flow.
Edge Effect
• Occurs when habitat edges alter species interactions and reduce biodiversity in those areas.
• Interior species may face higher predation or limited reproduction near edges.
Case Study: Darwin’s Finches
• Discovered in the Galápagos Islands by Charles Darwin in 1835.
• Finches on separate islands evolved into distinct species due to geographic and reproductive isolation.
• Demonstrates how isolation and time lead to speciation.
Key Points
• Larger and closer islands have higher biodiversity.
• Habitat fragmentation on continents mimics island isolation effects.
• Island biogeography helps predict extinction risk and conservation needs.
2.4 Ecological Tolerance
Definition
• Ecological tolerance is the range of abiotic and biotic conditions an organism can endure before injury or death occurs.
• It explains species distribution and abundance within ecosystems.
Law of Tolerance
• States that organisms can survive only within a certain range of environmental conditions (minimum, maximum, optimum).
• Outside of these tolerance ranges, species experience stress, reduced fitness, or population decline.
Abiotic Factors
• Include temperature, pH, salinity, sunlight, water availability, and soil nutrients.
• Species with narrow tolerances (specialists) are more vulnerable to environmental changes.
• Species with broad tolerances (generalists) can survive in varied environments.
Ecological Applications
• Helps predict species responses to climate change, pollution, or habitat changes.
• Explains zonation patterns (e.g., plant bands on mountains, intertidal species distribution).
• Useful in conservation biology and species reintroduction planning.
2.5 Natural Disruptions to Ecosystems
Definition
• Natural disruptions are non-anthropogenic events that alter ecosystems, species interactions, and biodiversity.
• These can cause temporary or permanent shifts in community structure and ecosystem function.
Types of Natural Disruptions
Flooding
• Kills organisms, removes vegetation, and destroys nests or burrows.
• Causes erosion and nutrient runoff.
• Deposits nutrient-rich sediments in floodplains.
• Some species are adapted to survive seasonal floods.
Volcanic Eruptions
• Destroys habitat but eventually creates fertile soil for new colonization.
• Adds water vapor and gases (e.g., sulfur) to the atmosphere, cooling global temperatures.
• Contributes to atmospheric formation and land creation over geological time.
Wildfires
• Destroys vegetation but can release nutrients (e.g., ash and charcoal) back into the soil.
• Promotes seed dispersal in fire-dependent species (e.g., pine trees with resin-covered cones).
• Increases sunlight exposure for surviving plants.
Scales of Natural Events
• Episodic: occurs irregularly (e.g., El Niño, La Niña every 2–7 years).
• Periodic: occurs regularly (e.g., tides, seasonal floods).
• Random: occurs without predictable pattern (e.g., meteorite strikes).
Sea-Level Change
• Caused by glacial melting, thermal expansion of oceans, and land subsidence.
• Past ice ages and interglacial periods caused fluctuations of hundreds of feet in sea level.
• Current changes are largely driven by global warming and ice loss.
Wildlife Migration
• Organisms may migrate to escape extreme weather, natural disasters, or to follow food and breeding patterns.
• Can be seasonal, short-term, or long-term.
2.6 Adaptations
Definition
• Adaptation is a biological process where organisms adjust to new or changing environments to increase survival and reproduction.
• Occurs through natural selection and can be short-term or long-term.
Types of Adaptations
1. Behavioral Adaptations
• Instinctive actions like migration, mating rituals, or hunting techniques.
• Example: Bird calls or seasonal migration patterns.
2. Physiological Adaptations
• Internal processes like temperature regulation or specialized digestion.
• Example: Sweating, venom production, or digestive enzyme variation.
3. Structural Adaptations
• Physical traits such as fur, feathers, beak shape, or root systems.
• Example: Camouflage, thick fur in cold environments, cactus spines.
Short-Term Adaptations
• Temporary and non-genetic changes in response to environmental variation.
• Not inherited or evolutionary (e.g., eating different food after a resource loss).
Long-Term Adaptations
• Genetic changes passed through generations due to selective pressure.
• Involve changes in the gene pool and contribute to evolution.
Case Study: The American Pika
• Pikas live in high-elevation, cool habitats in western North America.
• As climate warms, their habitat becomes too hot and dry, but there’s no higher elevation for them to migrate to.
• Pikas face extinction risk because the pace of climate change is faster than their ability to adapt or relocate.
2.7 Ecological Succession
Definition
• Ecological succession is the natural, gradual process of change in the composition and structure of a biological community over time.
• It leads to the development of a stable, mature climax community.
Types of Succession
Primary Succession
• Occurs in lifeless areas with no soil (e.g., after volcanic eruption or glacier retreat).
• Pioneer species (e.g., lichens, mosses) colonize first and create conditions for soil development.
• Takes hundreds to thousands of years.
Secondary Succession
• Occurs in areas where life previously existed but was disturbed (e.g., wildfire, flood).
• Soil is already present; succession is faster than primary.
• Pioneer species include grasses and fast-growing plants.
Successional Dynamics
• Early succession: r-strategists dominate (fast growth, low diversity).
• Late succession: K-strategists dominate (slower growth, higher diversity and stability).
• Biodiversity, soil nutrients, and biomass all increase over time.
• Ecosystem becomes more stable and resistant to disturbance as succession progresses.
Facilitation, Inhibition, and Tolerance
• Facilitation: one species modifies the environment to support others.
• Inhibition: one species prevents establishment of others.
• Tolerance: species coexist without directly affecting each other.
Productivity and Nutrient Cycling
• Early stages: high net primary productivity (NPP), low biomass.
• Climax community: high gross productivity, but energy loss to respiration increases, so NPP decreases.
Ecological Disturbances
• Can initiate or reset succession (e.g., fire, flood, volcano).
• The effect depends on disturbance intensity, frequency, season, and topography.
Keystone Species
• Keystone species have a disproportionately large effect on ecosystem function.
• Examples: sea stars, prairie dogs, grizzly bears, and certain bats.
Indicator Species
• Their presence or absence indicates environmental health.
• Examples: lichens (air pollution), stoneflies (water quality), mosses (soil acidity).
In a Nutshell
Biodiversity—including genetic, species, and ecosystem diversity—supports ecosystem stability and resilience. Ecosystems provide vital services to humans and rely on species interactions, adaptations, and successional processes to respond to change. Natural disruptions, island dynamics, and ecological tolerance shape community structure, while succession and keystone species ensure long-term balance. Protecting biodiversity is essential for sustaining life on Earth.