🌿Biology for Non-STEM Majors Unit 19 – Population and Community Ecology

Key Concepts and Definitions

• Populations consist of individuals of the same species living in a specific area at a given time
• Communities include multiple populations of different species interacting in a shared environment
• Ecosystems encompass both biotic (living) and abiotic (non-living) components interacting with each other
• Carrying capacity represents the maximum population size an environment can sustain given available resources
• Density-dependent factors (competition, predation) have a greater impact on population growth as density increases
• Density-independent factors (natural disasters, climate) affect populations regardless of their density
• Niches describe an organism's role and position within its environment and community
  • Fundamental niche includes all resources an organism could potentially use
  • Realized niche represents the actual resources used due to competition and other constraints

Population Dynamics

• Population growth depends on birth rates, death rates, immigration, and emigration
• Exponential growth occurs when populations increase rapidly without limitations (bacteria in a petri dish)
• Logistic growth involves an initial exponential phase followed by a leveling off as the population approaches carrying capacity
• r-selected species have high reproductive rates, short lifespans, and invest less in offspring (mice, weeds)
  • Adapted to unstable environments with abundant resources
• K-selected species have lower reproductive rates, longer lifespans, and invest more in offspring (elephants, humans)
  • Adapted to stable environments with limited resources
• Survivorship curves depict the proportion of individuals surviving at each age
  • Type I curves show high survival until old age (humans)
  • Type II curves show a constant mortality rate throughout life (birds)
  • Type III curves show high mortality in early life stages (fish)

Community Interactions

• Competition occurs when organisms vie for limited resources
  • Intraspecific competition happens within the same species
  • Interspecific competition happens between different species
• Predation involves one organism (predator) consuming another (prey)
  • Predators can control prey populations and influence their evolution (camouflage, warning coloration)
• Symbiosis describes close, long-term interactions between different species
  • Mutualism benefits both species (flowers and pollinators)
  • Commensalism benefits one species without affecting the other (remora fish and sharks)
  • Parasitism benefits one species (parasite) while harming the other (host)
• Keystone species have a disproportionately large impact on their communities (sea otters in kelp forests)
• Trophic cascades occur when changes at one trophic level affect multiple levels of the food chain (wolf reintroduction in Yellowstone)

Ecosystem Roles and Niches

• Producers (plants) convert solar energy into chemical energy through photosynthesis
• Consumers obtain energy by eating other organisms
  • Primary consumers (herbivores) eat producers
  • Secondary consumers (carnivores) eat primary consumers
  • Tertiary consumers (top predators) eat secondary consumers
• Decomposers (bacteria, fungi) break down dead organisms and recycle nutrients back into the ecosystem
• Food chains depict linear energy transfer from producers to consumers
• Food webs illustrate complex, interconnected feeding relationships within a community
• Ecological pyramids represent the flow of energy, biomass, or numbers at each trophic level
  • Energy pyramids show a 90% energy loss between trophic levels due to heat, movement, and waste
• Resource partitioning allows similar species to coexist by utilizing different resources (finches in the Galapagos)

Environmental Factors and Adaptation

• Abiotic factors include temperature, light, water, and soil nutrients
• Biotic factors include interactions with other organisms (competition, predation, symbiosis)
• Adaptations are traits that enhance an organism's survival and reproduction in a specific environment
  • Structural adaptations involve physical features (bird beaks, leaf shapes)
  • Physiological adaptations involve internal processes (enzymes, hormones)
  • Behavioral adaptations involve actions and responses (migration, courtship rituals)
• Natural selection favors adaptations that increase fitness in a given environment
• Convergent evolution occurs when unrelated species develop similar adaptations to similar environments (cacti and euphorbs)
• Divergent evolution occurs when related species develop different adaptations to different environments (Darwin's finches)

Human Impact on Ecosystems

• Habitat destruction reduces available space and resources for organisms
  • Deforestation removes trees and disrupts forest ecosystems
  • Urbanization converts natural habitats into cities and towns
• Pollution introduces harmful substances into the environment
  • Air pollution (smog, acid rain) affects respiratory health and damages plants
  • Water pollution (oil spills, agricultural runoff) harms aquatic life and contaminates drinking water
  • Plastic pollution (microplastics) accumulates in food chains and harms wildlife
• Overexploitation involves unsustainable harvesting of resources
  • Overfishing depletes fish populations and disrupts marine ecosystems
  • Poaching threatens endangered species (elephants for ivory, rhinos for horns)
• Invasive species outcompete native species and alter ecosystem dynamics
  • Kudzu vine grows rapidly and smothers native vegetation in the southeastern United States
  • Burmese pythons disrupt food webs in the Florida Everglades
• Climate change affects temperature, precipitation patterns, and sea levels
  • Coral bleaching occurs when warmer water temperatures stress coral reefs
  • Shifting ranges force species to adapt, migrate, or face extinction

Real-World Applications

• Conservation biology aims to protect and restore biodiversity
  • Protected areas (national parks, wildlife reserves) safeguard habitats and species
  • Captive breeding programs help recover endangered species populations (California condors)
  • Habitat restoration projects revitalize degraded ecosystems (wetland restoration)
• Sustainable resource management balances human needs with ecological health
  • Sustainable forestry practices (selective logging, reforestation) maintain forest ecosystems
  • Sustainable fisheries (catch limits, no-take zones) allow fish populations to recover
  • Renewable energy sources (solar, wind) reduce reliance on fossil fuels and mitigate climate change
• Bioremediation uses organisms to clean up pollutants
  • Bacteria can break down oil spills and industrial waste
  • Plants can absorb heavy metals from contaminated soil (phytoremediation)
• Ecological indicators provide insights into ecosystem health
  • Lichens are sensitive to air pollution and serve as early warning signs
  • Amphibian declines indicate environmental stressors (habitat loss, disease)

Study Tips and Review Questions

• Create concept maps to visualize connections between key terms and ideas
• Use mnemonic devices to remember important concepts (King Penguins Originate From Antarctic Glaciers = Kingdoms, Phyla, Orders, Families, Genera, Species)
• Practice applying concepts to real-world scenarios and case studies
• Collaborate with classmates to discuss and clarify challenging topics
• Review questions:
  • How do density-dependent and density-independent factors affect population growth?
  • Compare and contrast r-selected and K-selected species.
  • Explain the different types of symbiotic relationships and provide examples of each.
  • How do adaptations arise through natural selection?
  • Discuss the major ways in which humans impact ecosystems and the consequences of these impacts.
  • What are some strategies for conserving biodiversity and promoting sustainable resource management?