ap biology unit 8 study guides

Key Concepts and Definitions

• Ecology studies the interactions between organisms and their environment at various levels of organization
• Biotic factors include living components of an ecosystem (plants, animals, microorganisms)
• Abiotic factors encompass non-living components (temperature, light, water, soil)
• Habitat refers to the physical environment where an organism lives and interacts with biotic and abiotic factors
• Niche describes an organism's role within an ecosystem, including its resource use and interactions with other species
• Biodiversity measures the variety of life at all levels, from genes to ecosystems, and plays a crucial role in maintaining ecosystem stability and resilience
• Ecological succession is the gradual process of change in species composition over time, leading to the establishment of a climax community
• Keystone species have a disproportionately large impact on their ecosystem relative to their abundance (sea otters, wolves)

Levels of Ecological Organization

• Organisms are individual living entities that belong to a species and interact with their environment
• Populations consist of individuals of the same species living in a specific area at a given time
• Communities are assemblages of multiple populations of different species that interact within a shared environment
• Ecosystems encompass both biotic and abiotic components, as well as the interactions and energy flow between them
  • Terrestrial ecosystems include forests, grasslands, and deserts
  • Aquatic ecosystems can be freshwater (lakes, rivers) or marine (oceans, coral reefs)
• Biomes are large-scale ecosystems characterized by distinct climate patterns and dominant vegetation (tropical rainforest, tundra)
• The biosphere is the global sum of all ecosystems, encompassing all living organisms and their interactions with the Earth's surface and atmosphere

Ecosystem Components and Interactions

• Producers, also known as autotrophs, convert light energy or chemical energy into organic compounds through photosynthesis or chemosynthesis
  • Primary producers form the foundation of most food webs (plants, algae, cyanobacteria)
• Consumers, or heterotrophs, obtain energy and nutrients by feeding on other organisms
  • Primary consumers are herbivores that feed on producers (rabbits, zooplankton)
  • Secondary consumers are carnivores that feed on primary consumers (snakes, small fish)
  • Tertiary consumers are carnivores that feed on secondary consumers (hawks, sharks)
  • Omnivores consume both plant and animal matter (bears, humans)
• Decomposers, such as bacteria and fungi, break down dead organic matter, releasing nutrients back into the ecosystem
• Symbiotic relationships involve close interactions between two species
  • Mutualism benefits both species (flowers and pollinators)
  • Commensalism benefits one species without significantly affecting the other (barnacles on whales)
  • Parasitism benefits one species at the expense of the other (tapeworms in mammals)
• Competition occurs when two or more species vie for limited resources, such as food, space, or mates
  • Interspecific competition happens between different species (lions and hyenas)
  • Intraspecific competition occurs within a single species (male deer for mates)

Energy Flow and Nutrient Cycles

• Energy flows through ecosystems in a unidirectional manner, typically starting with solar energy captured by primary producers
• Trophic levels represent the position of an organism in a food chain or food web
  • Energy transfer between trophic levels is inefficient, with only about 10% of energy passed on to the next level
• Food chains are linear sequences of energy transfer from producers to consumers
• Food webs are more complex, depicting the interconnected feeding relationships within an ecosystem
• The carbon cycle involves the exchange of carbon between the atmosphere, living organisms, and Earth's crust
  • Photosynthesis and respiration play key roles in the biological carbon cycle
• The nitrogen cycle encompasses the transformation of nitrogen between various forms, including atmospheric nitrogen, ammonia, nitrites, and nitrates
  • Nitrogen fixation converts atmospheric nitrogen into forms usable by living organisms
  • Denitrification returns nitrogen to the atmosphere
• The water cycle, or hydrologic cycle, describes the continuous movement of water through evaporation, transpiration, precipitation, and surface and groundwater flow
• Nutrient cycling is essential for maintaining ecosystem productivity and stability

Population Dynamics

• Population size is the number of individuals of a species in a given area at a specific time
• Population density measures the number of individuals per unit area or volume
• Population distribution can be clumped, uniform, or random, depending on resource availability and species interactions
• Birthrate and death rate influence population growth
  • Exponential growth occurs when resources are abundant, and the population grows rapidly
  • Logistic growth happens when a population approaches its carrying capacity, and growth slows due to limited resources
• Carrying capacity is the maximum population size an environment can sustain given available resources
• Life history strategies describe an organism's allocation of resources towards growth, reproduction, and survival
  • r-selected species have high reproductive rates, short lifespans, and thrive in unstable environments (bacteria, annual plants)
  • K-selected species have lower reproductive rates, longer lifespans, and are adapted to stable environments (elephants, humans)

Community Ecology

• Species richness is the number of different species present in a community
• Species evenness refers to the relative abundance of each species within a community
• Species diversity accounts for both richness and evenness, providing a comprehensive measure of community composition
• Ecological succession is the gradual process of change in species composition over time
  • Primary succession occurs on newly formed or bare substrates (volcanic islands, glacial moraines)
  • Secondary succession happens following a disturbance that removes existing vegetation (forest fires, abandoned agricultural fields)
• Pioneer species are the first to colonize a disturbed or newly formed area, initiating succession (lichens, grasses)
• Climax communities represent the final, relatively stable stage of succession, characterized by long-lived, slow-growing species (old-growth forests)
• Disturbances such as fires, storms, and human activities can disrupt community structure and reset succession

Human Impact on Ecosystems

• Habitat destruction, fragmentation, and degradation are major threats to biodiversity
  • Deforestation, urbanization, and agricultural expansion contribute to habitat loss
• Overexploitation of natural resources, such as overfishing and poaching, can lead to species declines and extinctions
• Invasive species, introduced intentionally or accidentally by humans, can disrupt native ecosystems and outcompete native species
  • Invasive species examples include kudzu in the southeastern United States and the Burmese python in the Florida Everglades
• Pollution, including air, water, and soil contamination, can have detrimental effects on ecosystem health and species survival
  • Eutrophication is the excessive growth of algae and aquatic plants due to nutrient pollution, leading to oxygen depletion and fish kills
• Climate change, driven by human activities such as fossil fuel combustion and deforestation, alters temperature, precipitation patterns, and sea levels, affecting species distributions and ecosystem functioning
• Conservation efforts aim to protect and restore ecosystems and biodiversity
  • Protected areas, such as national parks and wildlife reserves, safeguard habitats and species
  • Habitat restoration and species reintroduction programs help recover degraded ecosystems and threatened populations

Ecological Research Methods

• Field observations involve studying organisms and their interactions in their natural habitats
  • Transect sampling uses a line or belt of a specific length to estimate population density and distribution
  • Mark-recapture methods estimate population size by capturing, marking, releasing, and recapturing individuals
• Controlled experiments manipulate variables to test hypotheses about ecological processes
  • Mesocosm experiments are outdoor enclosures that mimic natural conditions while allowing for variable control
  • Microcosm experiments are small-scale, laboratory-based setups used to study specific ecological interactions
• Mathematical models simulate ecological processes and predict outcomes based on input variables and assumptions
  • Population growth models, such as the exponential and logistic models, describe changes in population size over time
  • Food web models analyze the structure and dynamics of trophic interactions within a community
• Remote sensing techniques, such as satellite imagery and aerial photography, enable large-scale monitoring of ecosystems and land-use changes
• Molecular tools, including DNA barcoding and environmental DNA (eDNA) analysis, aid in species identification and biodiversity assessment
• Long-term ecological research (LTER) sites provide valuable data on ecosystem processes and responses to environmental changes over extended periods