AP Environmental Science: Ecosystem Services, Biodiversity, and Population Ecology

Ecosystem Services and Forest Management

Definition of Ecosystem Services:
- Ecosystem services are the natural processes by which the environment produces resources for human benefit, which humans frequently take for granted.
Categories of Ecosystem Services:
- Provisioning Services:
- Definition: Specific material goods provided by ecosystems that usually have direct monetary value.
- Examples: Food, timber/lumber, textiles, plants used for medicine, raw water, and air.
- Key Distinction: Water and air themselves are provisioning services.
- Regulating Services:
- Definition: Services that maintain environmental parameters necessary for provisioning services to exist, specifically focusing on the regulation and maintenance of clean air, clean water, and climate.
- Examples: Carbon sinks, as well as plants that actively filter and remove pollutants from air and water.
- Key Distinction: While air and water are provisioning services, the plants that remove pollutants from air and water provide a regulating service.
- Supporting Services:
- Definition: Fundamental environmental conditions and processes that allow other ecosystem services to exist and function.
- Examples: Land space required to grow food or maintain a forest, habitat for fisheries, and pollination of both native and agricultural plants.
- Cultural Services:
- Definition: Non-material benefits and recreational opportunities derived from natural environments.
- Examples: Tourism sites and outdoor recreational areas.
Forest Management and Logging Practices:
- Clear Cutting:
- Identified as the least sustainable logging practice.
- Identified as the most economically advantageous method in the short term.
- Sustainable Harvesting Methods:
- Includes selective logging, seed tree harvesting, shelterwood harvesting, and strip cutting.
- Mechanism: All of these methods leave a portion of trees standing behind to continue providing ecosystem services and to allow the forest to regrow and regenerate naturally.

Biological Diversity: Metrics and Genetic Mechanisms

Core Concepts of Biological Diversity:
- Species Diversity: Defined as the number (richness) and distribution/relative abundance (evenness) of different species within a given community.
- Genetic Diversity: Defined as the genetic variability (differences in DNA) among individual organisms within each species.
- Mechanisms that generate genetic diversity:
  - DNA mutations.
  - Random mating.
  - Meiosis.
- Ecological Diversity (Ecosystem Diversity): Defined as the variety of different ecosystems present across a region.
Species Richness vs. Species Evenness:
- Definition of Richness: The total number of distinct species present in an ecosystem.
- Definition of Evenness: The relative abundance and balance among the individuals of each species present.
- Comparative Forest Example:
- Forest A: Contains $4$ tree species, each making up $25\%$ of the forest ( $25\%$ , $25\%$ , $25\%$ , $25\%$ ).
- Forest B: Contains $6$ tree species with a distribution of $20\%$ , $75\%$ , $1\%$ , $1\%$ , $1\%$ , and $2\%$ .
- Ecosystem Evaluation:
- Forest B has higher species richness ( $6$ species compared to $4$ species in Forest A).
- Forest A has higher species evenness ( $25\%$ for all species versus Forest B's dominant species at $75\%$ ).
- Forest A is ecologically preferred because it maintains both species richness and species evenness.
- Vulnerability: Even though Forest B has higher species richness, it lacks species evenness. If a pathogen or disease affects the species comprising $75\%$ of the forest, the system suffers a catastrophic loss of total organisms.

Ecological Strategies: Generalists, Specialists, and Reproductive Selection

Generalist vs. Specialist Species:
- Generalist Species:
- Possess wider ecological tolerances.
- Utilize a wide variety of food sources.
- Can inhabit a broad range of habitats, temperatures, and pH ranges.
- Specialist Species:
- Possess narrow ecological tolerances and specific environmental requirements.
- Inhabit a smaller geographic range and require a highly specific diet.
- Highly susceptible to population collapse or extinction if their primary food source or habitat is compromised.
K-Selected vs. r-Selected Species:
- K-Selected Species ("K" represents carrying capacity, the maximum population size an environment naturally sustains):
- Physical Traits: Larger body size, slower movement, mature later in life.
- Parental Care: Provide significant amounts of parental care.
- Offspring Quantity: Produce only $1$ to $2$ offspring at a time.
- Endangerment Vulnerability:
  - Because they produce only $1$ to $2$ offspring per reproductive cycle, population replenishment after a loss takes a long time.
  - Because they mature slowly, individuals require significant time to reach reproductive age.
- r-Selected Species ("r" represents reproduction rate, characterized by producing high volumes of offspring):
- Physical Traits: Small body size, faster movement, mature early in life.
- Parental Care: Provide little to no parental care.
- Offspring Quantity: Produce a very large number of offspring at once.
- Survivorship Dynamics: Experience a massive die-off (high mortality rate) in early life stages because parents provide no care, relying on sheer offspring quantity so that a small fraction survives to adulthood.

Island Biogeography and Ecological Succession

Principles of Island Biogeography:
- Distance from Mainland:
- Islands located farther from the mainland are harder for species to migrate to, resulting in lower colonization rates and lower overall biodiversity.
- Island Size:
- Smaller islands have fewer resources and less space, resulting in higher extinction rates and lower overall biodiversity compared to larger islands.
- Comparative Distinctions:
- A large island far from the mainland has less biodiversity than a large island close to the mainland due to migration difficulty.
- A small island far from the mainland has less biodiversity than a large island far from the mainland due to limited space and resources.
Ecological Succession:
- Primary vs. Secondary Succession:
- Primary succession is uniquely defined by the total absence of soil (e.g., bare rock substrate).
- Secondary succession occurs in environments where an ecosystem was disturbed but soil remains intact.
- Ecosystem Resilience:
- A mature climax community is significantly more resilient to disturbances than pioneer species colonizing bare rock.
- Reason: Climax communities feature a wide variety of species, providing ecological redundancy and stability to withstand diseases and environmental disruptions.

Keystone and Indicator Species

Indicator Species:
- Purpose and Function: Serve as environmental indicators that reflect the overall health and quality of an ecosystem.
- Population Signals: A decline in indicator species population signals poor ecosystem health and indicates changes in environmental parameters such as temperature, pH, food availability, or space.
Keystone Species:
- Purpose and Function: Species that play a pivotal, critical role in maintaining the structure and operational integrity of an ecosystem. They exhibit strong interactions with other organisms that directly dictate community health and survival.
- Examples:
1. Top Predators: Function as keystone species by maintaining prey populations and prey geographical ranges in check, preventing overpopulation and habitat degradation.
2. Pollinators: Function as keystone species by enabling the reproductive success of flowering plants, which subsequently provide critical habitat and resources for numerous other species.

Practice Free-Response Questions (FRQ) Review

Key FRQ Discussion Topics:
- Impacts of Logging on Forest Characteristics: Changes in canopy structure, microclimate conditions, soil integrity, and overall species habitat upon logging.
- Economic Services Provided by Forests: Production of timber/lumber, job creation, and commercial resource extraction.
- Ecological Services and Illegal Logging: Essential services including carbon sequestration, water filtration, and habitat provision, and how unregulated illegal logging severely degrades these functions.
- Sustainable Logging Solutions: Implementation of selective cutting, strip cutting, shelterwood, or seed tree harvesting to maintain standing trees, preserve ecosystem services, and foster forest regeneration.