AP Biology Semester One Review

Unit 1: Ecology

Interactions

  • Biological Systems are characterized by interactions across domains of space and time, emphasizing the significance of both spatial distribution and temporal dynamics in ecological relationships.

  • Example: The interplay between plant root systems and shoot systems is crucial for nutrient uptake and photosynthesis, respectively, while the circulatory system in animals ensures the efficient transport of materials necessary for survival.

  • Emergent Properties: These properties arise from interactions of components at organizational levels below the observable properties, indicating that individual parts contribute collectively to the overall function of a system.

  • Observable Phenomena: Interactions in biological systems result in various observable outcomes, such as changes in population dynamics, behavior adaptations, and ecological succession.

  • Cascading Effects: Any change made to a component within a biological system can create a ripple effect, impacting other components and leading to broader ecological consequences.

Populations

  • Definition: A population is defined as all individuals of one species residing within a specific geographic area, sharing resources and interacting with one another.

  • Population Increase: The factors contributing to population growth include birth rates and immigration, where new individuals join the population.

  • Population Decrease: Conversely, factors leading to a decrease in population include death rates and emigration, where individuals leave the population.

  • Growth Patterns: While populations generally aim for exponential growth, environmental and resource limitations often lead to logistic growth, where the growth rate slows upon reaching the carrying capacity of the environment.

  • Limiting Factors:

    • Density-dependent Factors: These factors, such as availability of food, water, and shelter, exert greater effects as population density increases, influencing competition and survival.

    • Density-independent Factors: These events, including climate changes and natural disasters, affect populations regardless of their size, potentially leading to sudden increases in mortality.

  • Spatial and Temporal Distribution: Populations are distributed through space and time, influenced by environmental factors and interactions with other species.

Communities

  • Symbiosis: This term refers to close and long-term biological interactions between two different organisms, which can be classified into various types:

    • Predation (+/-): One organism (the predator) benefits by consuming another (the prey), which is harmed in the process.

    • Herbivory (+/-): A form of predation where the predator is an animal that consumes plants.

    • Parasitism (+/-): A relationship where the parasite derives nourishment from the host, often causing harm.

    • Mutualism (+/+): A mutually beneficial interaction where both organisms gain advantages (e.g., bees pollinating flowers).

    • Commensalism (+/0): One organism benefits while the other remains unaffected (e.g., epiphytic plants growing on trees).

    • Amensalism (-/0): One organism is negatively impacted while the other is unaffected (e.g., trampling of grass by large animals).

  • Evolutionary Pressures of Interactions: These interactions serve as significant evolutionary pressures, driving species adaptations and co-evolution.

  • Competitive Exclusion Principle: When two populations compete for the same limited resources, one population will typically outperform the other, leading to its decline.

  • Character Displacement: This evolutionary phenomenon occurs when populations evolve different traits to minimize competition, leading to niche differentiation (e.g., finches adapting to different feeding strategies).

Trophic Interactions in Communities

  • Nutrient Cycling: Matter is continuously cycled from one trophic level to another, illustrating the interconnectedness of ecosystems.

  • Role of Consumers and Decomposers: Consumers rely on producers for energy, while decomposers play a critical role in recycling matter back into the ecosystem, aiding nutrient availability.

  • Food Chain vs. Food Web: A food chain outlines a linear path of energy flow, while a food web provides a more comprehensive view of all feeding relationships in a community.

Bottom-Up Control: Primary Productivity

  • Energy Limitation: The amount of energy available to producers constrains the entire trophic structure, influencing community dynamics and species composition.

  • 10% Rule: As energy transfers between trophic levels, only approximately 10% is passed on to the next level, illustrating the inefficiency of energy transfer in ecosystems.

Top-Down Control: Predation

  • Keystone Species: Certain species, known as keystone species, have a disproportionate impact on their ecosystems, maintaining the structure and balance (e.g., apex predators like wolves and their role in regulating prey populations).

  • Case Studies: Examples include the reintroduction of wolves in Yellowstone National Park, which restored balance to the entire ecosystem, and the removal of sea stars causing sea urchin populations to explode, leading to kelp forest declines.

Trophic Cascades

  • Cascading Effects: Actions within an ecological system can trigger cascading effects, leading to significant changes across different trophic levels and altering community structure.

Ecosystems

  • Definition: An ecosystem is defined as a complex network of interactions between living organisms (communities) and their abiotic environment, including nonliving components like air, water, and soil.

  • Terrestrial Biomes: Biome characteristics are determined by temperature, sunlight, and precipitation patterns, influencing the types of communities that can thrive there.

  • Aquatic Biomes: Features of aquatic biomes are shaped by factors including latitude, sunlight penetration, and water depth, resulting in diverse ecosystems.

Dynamic Interactions

  • Facilitation: Organisms can have positive effects on their ecosystem, altering conditions in ways that benefit other species (e.g., beaver activities in creating wetland habitats).

  • Disturbances: Natural or anthropogenic events can disrupt ecosystem structure, leading to changes in species composition and ecological dynamics.

  • Intermediate Disturbance Hypothesis: Ecosystems that experience moderate levels of disturbance tend to display greater biodiversity and resilience compared to those that are either highly stable or frequently disturbed.

  • Biodiversity Hotspots: Regions characterized by high levels of endemic species richness often found in tropical latitudes, driven by optimal conditions for growth such as sunlight, transpiration, and adequate oxygen levels.

Conservation Biology

Human Impact on Biodiversity

  • Extinction Vortex: This concept describes the phenomena where small populations experience reduced genetic diversity, leading to decreased resilience and heightened vulnerability to extinction.

  • Habitat Destruction: Human activities, including deforestation and pollution, significantly impact biodiversity, often leading to species loss and ecosystem decline.

  • Habitat Fragmentation: The division of natural habitats into smaller, isolated patches, which can lead to decreased species diversity and increased risk of extinction.

Anthropogenic Effects

  • Climate Change: These changes, largely driven by increasing atmospheric CO₂, impact global ecosystems, leading to phenomena such as coral bleaching and habitat loss, shifting species distributions, and altering ecological interactions.

  • Pollution: The introduction of chemicals and toxins can accumulate in food chains, leading to bioaccumulation and adversely affecting organisms at all trophic levels.

Human Stewardship

  • Conservation Efforts: Strategies aimed at preserving biodiversity, including habitat restoration, species reintroduction (e.g., apex predators), and sustainable resource management practices, are crucial for maintaining ecological balance.

Population Calculations

  • Intrinsic Rate of Population Growth: Calculated as the birth rate minus the death rate, providing insight into population dynamics.

  • Exponential Growth: Characterized by a constant growth rate, leading to rapid increases in population size, often observed when resources are abundant.

  • Logistic Growth: A more realistic model where growth rate decreases as the population approaches the carrying capacity of the environment, reflecting resource limitations and environmental resistance.