APES Biodiversity and Ecosystem Services: Comprehensive Study Notes

Biodiversity Basics

  • Biodiversity refers to the diversity of life forms in an ecosystem and is measured on three levels:
    • Genetic diversity: how different the genes are among individuals within a population (same species).
    • Species diversity: the number of different species present and the evenness of their population sizes.
    • Ecosystem diversity: the number of different habitats or ecosystems within a given area.
  • Higher biodiversity generally leads to higher resilience of ecosystems and populations to disturbances.
  • Key definitions from the Essential Knowledge:
    • ERT-2.A.1: Biodiversity includes genetic, species, and habitat diversity.
    • ERT-2.A.2: Greater genetic diversity helps populations respond to environmental stressors; bottlenecks reduce diversity.
    • ERT-2.A.3: Ecosystems with more species are likelier to recover from disruptions.
    • ERT-2.A.4: Loss of habitat leads to loss of specialist species, then generalist species, and reduces species with large territorial needs.
    • ERT-2.A.5: Species richness is the number of different species in an ecosystem.
  • Levels of biodiversity in brief:
    • Genetic diversity: variation in genes within a population; important for adaptation and resilience.
    • Species diversity: variety and relative abundance of species; affects food webs and ecosystem functions.
    • Habitat (ecosystem) diversity: variety of habitats; supports different communities and processes.
  • Relationship to ecosystem resilience:
    • Higher biodiversity increases the likelihood that some species can survive disturbances and maintain ecosystem functions (food, habitat, soil stability, energy cycling).

Levels of Biodiversity (detailed)

  • Genetic diversity
    • Within-population variation arises from mutations and recombination during sexual reproduction.
    • Higher genetic diversity improves population responses to drought, disease, and other stressors.
    • Bottlenecks reduce genetic diversity and increase vulnerability to future stressors.
    • Inbreeding depression arises when small populations mate among relatives, increasing harmful homozygous mutations.
    • Example note: Florida panther population declined to ~30 individuals in the early 1900s due to hunting and habitat loss, leading to inbreeding concerns (historical example referenced).
  • Species diversity
    • The number of species (species richness) and their relative abundances (evenness) shape ecosystem structure and function.
    • Evenness indicates whether one or a few species dominate or whether populations are balanced.
  • Habitat/ecosystem diversity
    • The variety of habitats in a landscape influences community composition and ecosystem processes.
    • More habitats typically support more species and functional roles.

Species Richness and Evenness

  • Definitions:
    • Richness (S): the total number of different species in an ecosystem.
    • Evenness: how evenly individuals are distributed among the species present.
  • Indicators of ecosystem health:
    • High species richness generally signals good resource availability (water, soil quality).
    • Evenness shows whether community structure is balanced or dominated by a few species.
  • Implications:
    • Ecosystems with higher richness and balanced evenness tend to be more resilient to disturbances and capable of faster recovery.

Genetic Diversity and Bottlenecks

  • Random mutations and recombination create genetic diversity within populations.
  • Greater genetic diversity improves adaptability to environmental stressors (e.g., drought, disease).
  • Bottleneck events reduce population size drastically and shrink genetic diversity, making populations more vulnerable to future disturbances.
  • Inbreeding depression occurs when closely related individuals mate, increasing the chance of harmful mutations in offspring.
  • Example: Florida panther and other population bottlenecks illustrate long-term concerns for genetic health.

Inbreeding Depression

  • Definition: adverse genetic consequences when related individuals mate, increasing homozygosity of deleterious alleles.
  • Consequences include reduced fertility, higher incidence of defects, and other fitness costs.
  • Management implications: maintaining genetic diversity is crucial for population viability.

Ecosystem Resilience and Biodiversity

  • Resilience: the ability of an ecosystem to return to its original state after a disturbance (e.g., windstorm, fire, flood, clear-cutting).
  • Relationship: Higher biodiversity generally increases resilience by providing a broader range of responses to disturbances, stabilizing food webs, and maintaining functions like pollination, decomposition, and nutrient cycling.
  • Mechanisms:
    • Redundant species roles can buffer function if some species are lost.
    • Diverse plant communities support diverse herbivores and predators, stabilizing populations.
    • Varied habitats support broader ecological processes that help recover structure after disruption.

Human Impacts on Ecosystem Services (Overview)

  • Ecosystem services are typically categorized into four types:
    • Provisioning: tangible goods obtained from ecosystems (e.g., food, water, wood).
    • Regulating: regulation of ecosystem processes (e.g., climate regulation, pollination, water purification).
    • Cultural: non-material benefits (recreation, aesthetics, inspiration).
    • Supporting: basic ecological processes that enable all other services (habitat, soil formation, nutrient cycling).
  • Four categories with examples:
    • Provisioning services: timber, food, medicine, water, fibers.
    • Regulating services: climate regulation, air and water purification, flood control, disease regulation, pollination.
    • Cultural services: recreation, aesthetics, tourism, education, research.
    • Supporting services: photosynthesis, soil formation, nutrient cycling, habitat provision; foundational for all other services.
  • Economic framing:
    • Some benefits are monetizable (e.g., tourism revenue, fuel, wood products) but many have intrinsic or societal value beyond market price.
  • Disturbances to ecosystem services:
    • Anthropogenic activities can disrupt provisioning, regulating, cultural, and supporting services, with ecological and economic consequences.
    • Examples from slides: deforestation reduces CO2 sequestration and climate regulation; overfishing leads to population declines and future economic losses.

Ecosystem Services in Depth

  • Provisioning services: direct goods obtained from ecosystems (e.g., fish, lumber, berries, honey).
  • Regulating services: earth system processes moderated by ecosystems (e.g., wetlands filter water, trees sequester CO2, pollinators support crop yields).
  • Cultural services: non-material benefits (recreation, aesthetic value, research, inspiration).
  • Supporting services: underpin all other services (primary production, soil formation, nutrient cycling, habitat creation).
  • Distinctions and overlaps:
    • Some classifications vary (AP Classroom/UN vs. other sources) on whether pollination and water purification are categorized as regulating or supporting, but the core idea remains: these services underpin human well-being and ecosystem health.
  • Impacts of disturbance on services:
    • Deforestation reduces carbon storage and climate regulation capacity; wetland loss reduces water purification; habitat loss reduces biodiversity, which can feed back to reduce ecosystem resilience and service provision.

FRQ Practice (Key Takeaways from 2.1 and 2.2)

  • FRQ 2.1: Describe one of the three levels of biodiversity and explain how high biodiversity at that level benefits ecosystems.
    • Possible level choices and benefits:
    • Ecosystem diversity: provides a wide variety of habitats and resources, supporting resilience and stability of ecosystems.
    • Species diversity: a diverse food web supports multiple pathways for energy flow and resource use, increasing stability.
    • Genetic diversity: enhances adaptation and reduces risk of population collapse under stress; higher genetic variation increases the likelihood that some individuals endure changing conditions.
  • FRQ 2.2: Describe an ecosystem service that intact forest ecosystems provide for humans, and identify one human activity that could degrade this service and explain how the activity decreases its value.
    • Example service: Oxygen production, carbon sequestration, habitat provision, water filtration, biodiversity maintenance, climate regulation, cultural/recreational value.
    • Example activities that degrade services: deforestation or clear-cutting reduces oxygen production via photosynthesis, lowers carbon storage, reduces habitat for wildlife, and decreases water regulation and soil stabilization; pollution or intensive land-use changes can impair water quality and pollination.
  • FRQ 2.3 (Island Biogeography): Describe the processes of colonizing an island habitat and explain how the island’s distance from the mainland influences the number of species that colonize.
    • Colonization processes: movement and migration of individuals from the mainland or other populations to an island habitat.
    • Distance effect: as the distance from the mainland increases, the number of colonizing species decreases (inverse relationship); closer islands experience more colonization and higher species richness.
    • Island size effect: larger islands support more species due to more habitats and larger population sizes; there is a positive correlation between island size and species richness.

Island Biogeography (Key Concepts and Details)

  • Definition: Island biogeography studies ecological relationships and community structures on islands or habitat islands (e.g., Central Park, National Parks).
  • Two basic observations/rules:
    • Easier colonization from the mainland for nearby islands; more colonizing events lead to higher genetic diversity in new populations.
    • Larger islands support more species due to more niches, more food and habitat resources, larger populations, and lower extinction rates.
  • Distance-to-mainland effect:
    • Closer islands tend to have higher species richness because dispersal is more frequent and populations are more likely to persist.
    • Further islands have reduced immigration and potentially higher extinction rates.
  • Evolution on islands:
    • Limited resources lead to specialization; adaptive radiation can occur (single mainland species giving rise to multiple island species with different beaks, diets, or habitats).
    • Example: Galápagos finches show beak variation linked to available food resources.

Ecological Tolerance

  • Ecological tolerance definition: the range of environmental conditions (temperature, salinity, flow rate, sunlight, etc.) that an organism or population can endure before injury or death.
  • Zones of tolerance for individuals and species:
    • Optimal range: conditions where survival, growth, and reproduction are strongest.
    • Zone of physiological stress: survival with stress; reduced growth or reproduction.
    • Zone of intolerance: conditions that cause death.
  • Example:
    • Salmon basic tolerance for temperature: 6^{\, ext{°C}} \, to \, 22^{\circ}\text{C}; some individuals have adaptations extending tolerance beyond the species’ basic range due to genetic diversity.
  • Ecological tolerance as a framing device for FRQs:
    • Connect human activities and climate change to shifts in tolerance ranges; climate warming can push species outside their tolerance, affecting survival and distribution.
  • FRQ writing tips for tolerance questions:
    • Link anthropogenic/climate drivers to shifts in temperature, oxygen availability, drought, etc., and to physiological stresses (e.g., suffocation, thermal shock).
    • Provide a concrete example showing how tolerance limits influence population viability and species distributions.

Natural Disruptions to Ecosystems

  • Definitions:
    • Natural disturbances can be periodic (regular), episodic (occasional), or random (unpredictable).
    • Examples of natural disturbances: tornadoes, hurricanes, fires, droughts, volcanic eruptions, earthquakes.
  • Climate variability over geologic time:
    • Earth's climate has varied due to orbital changes (Milankovitch cycles), leading to mini ice ages and warmer periods.
    • Sea level has varied; glacial cycles cause rises and falls in sea level.
    • CO₂ levels have varied; historical records show fluctuations in atmospheric CO₂ concurrent with climate shifts.
  • Implications for ecosystems:
    • Major disturbances can cause widespread habitat change or loss, altering community structure and species interactions.
    • Wildlife may migrate or shift ranges in response to changing conditions (e.g., wildebeest following rainfall, marine species moving with ocean warming).

Adaptation and Evolution (Adaptation, Natural Selection, Pace of Evolution)

  • Genetic diversity and adaptation:
    • Populations with greater genetic diversity have higher adaptive potential to environmental changes.
    • Random mutations and genetic recombination create new traits; natural selection acts on these traits.
  • Adaptation and natural selection:
    • Individuals with advantageous traits survive and reproduce more, passing traits to offspring.
    • Over time, populations may accrue adaptations, changing the population’s overall trait distribution.
  • Pace of evolution:
    • Rapid evolution is common in organisms with short generation times (e.g., bacteria, viruses).
    • For longer-lived organisms, evolution tends to occur more slowly.
    • If environmental change is too rapid, many species may migrate or go extinct.
  • Pivotal role of genetic diversity:
    • Higher genetic diversity increases the odds that some individuals carry beneficial mutations to survive changing conditions.
  • Example framing for FRQs: be prepared to connect climate change, habitat alteration, and other disturbances to shifts in traits and population viability.

Ecological Succession

  • Definition: A predictable sequence of community development after a disturbance or in newly formed habitat.
  • Two main types:
    • Primary succession: starts on bare rock with no soil; pioneer species (e.g., moss, lichen) contribute to soil formation.
    • Secondary succession: begins in a disturbed area with existing soil; faster progression through stages (grasses, shrubs, young trees) to a climax community.
  • Successional stages and typical players:
    • Pioneer species: fast-growing, wind-dispersed, sun-tolerant (e.g., moss, lichens, annual grasses).
    • Intermediate species: grasses, wildflowers, shrubs, shade-tolerant trees begin to establish.
    • Climax community: large, slow-growing, shade-tolerant trees (e.g., maples, oaks) dominate once soils mature.
  • Timeline examples (illustrative):
    • Primary: bare rock → lichens/moss → grasses → shrubs → shade-tolerant trees over centuries.
    • Secondary: disturbed area → grasses → shrubs → young trees → mature forest over decades to centuries.
  • Keystone and indicator species:
    • Keystone species have a disproportionately large effect on community structure.
    • Indicator species reflect distinctive ecological conditions or changes in ecosystem health.

Practice FRQs (2.4–2.7) – Key Answer Elements

  • FRQ 2.4 (Ecological tolerance and thermal tolerance in salmon):
    • Claim: There is a genetic basis for variation in thermal tolerance in salmon.
    • Support: Variation in tolerance ranges is linked to genetic differences; some individuals possess alleles that confer higher tolerance.
    • Link to climate change: warmer waters can shift temperature outside the tolerance range, increasing stress and potential mortality unless adaptation occurs.
  • FRQ 2.5 (Latitude and first leaf date):
    • Relationship: As latitude increases, the change in first leaf date becomes earlier (or the leaf-out occurs earlier with warming).
    • Explanation: In higher latitudes, warming reduces late-season frost risk, enabling earlier leaf-out; drought patterns and photoperiod cues also influence timing.
  • FRQ 2.6 (Beak size in Galápagos finches):
    • Description: On different islands, mean beak sizes differ due to resource differences (e.g., seed size).
    • Claim: Population on one island adapted to larger seeds, while another island favored smaller beaks due to different food resources.
  • FRQ 2.7 (Ecological succession graph – spruce species):
    • Classification: Spruce is a mid-successional (middle) species because it appears after pioneer species and increases during intermediate stages, but does not dominate in the climax stage where shade-tolerant species prevail.

Key Numerical References and LaTeX-formatted Details

  • Temperature tolerance example: Basic range for salmon: 6^{\circ}\text{C} \le T \le 22^{\circ}\text{C}
  • Island biogeography relationships:
    • Positive relationship: island size to species richness
    • Inverse relationship: distance from mainland to species richness
  • CO₂ and climate context (illustrative from slides):
    • CO₂ levels referenced around CO_2 \, = \, 400 \text{ ppm} in Keeling Curve context
  • Sea level variability: historical variations shown as -30 \text{ m a.s.l.} \text{ to } +20 \text{ m a.s.l.} (masl)
  • Biodiversity components: S = number of species (species richness) in an area
  • Four ecosystem service categories (abbreviated):
    • Provisioning, Regulating, Cultural, Supporting
  • Common timeframes:
    • Succession stages can span from years to centuries (e.g., 0–150+ years in succession graphs)
  • Example population scales:
    • Florida panther historical bottleneck example (~30 individuals in the early 1900s)

Connections to Foundational Principles

  • Biodiversity and resilience:
    • Diversity across genetic, species, and habitat levels underpins ecosystem resilience and function.
  • Evolution and adaptation:
    • Genetic variation fuels adaptation; natural selection acts on heritable traits; pace depends on generation time and environmental rate of change.
  • Human welfare and ecosystem services:
    • Ecosystem services translate ecological processes into benefits for people; disruptions can cause ecological and economic consequences.
  • Island biogeography and conservation:
    • Island size and isolation influence colonization, extinction, and diversification, informing reserve design and habitat restoration strategies.

Quick Reference Formulas and Concepts

  • Biodiversity levels: ext{Genetic diversity}, ext{Species diversity}, ext{Ecosystem diversity}
  • Species richness: S = ext{number of species in a given area}
  • Temperature tolerance example: 6^{\circ}\text{C} \le T \le 22^{\circ}\text{C} (basic range for salmon)
  • Island biogeography relationships:
    • Larger island → higher species richness (positive correlation)
    • Closer distance to mainland → higher species richness (inverse relationship with distance)
  • Tolerance zones: Optimal zone, Zone of physiological stress, Zone of intolerance
  • Four categories of ecosystem services: Provisioning, Regulating, Cultural, Supporting
  • Succession stages: Pioneer → Intermediate → Climax (for both primary and secondary succession, with different starting conditions)

Note: All sections align with learning objectives and essential knowledge for AP Environmental Science topics 2.1–2.7 as presented in the transcript. Use these notes to study the core concepts, definitions, examples, and FRQ strategies.