Biology 1 Notes: Ecology

Ecology: Levels of Organization

• Ecology is the study of organisms interacting with each other and their nonliving environment.
• Ecological levels of organization:
  • Organism → Population → Community → Ecosystem → Biome → Biosphere

Abiotic & Biotic Factors

• Abiotic factors: Nonliving or physical factors.
  • Examples: light, temperature, rocks, water, pH, humidity, wind, sand, water current, soil type.
  • Included in Ecosystem, Biome, and Biosphere levels.
• Biotic factors: Living factors.
  • Examples: mammals, insects, fish, birds, bacteria, protozoans, plants, trees, fungi.
  • Included in all ecological levels.

Ecological Levels of Organization

• Organism: A single living thing (e.g., a lion).
• Population: A group of organisms of the same species in a certain area (e.g., a pride of lions).
• Community: All the populations of different species in an area (biotic factors only).
  • Example: pride of lions, herd of zebra, grove of acacia trees, flock of storks, group of dung beetles.
• Ecosystem: The biotic community and its abiotic surroundings.
  • Example: Community or organisms, sunlight, warm temps, rainfall, rocks
• Biome: A group of ecosystems that share similar climates and typical organisms.
  • Defined by climate and vegetation.
  • Can change with latitude and elevation.
  • Example: Savanna Grasslands
• Biosphere: The entire planet, with all its organisms and physical environments.
  • All of the biomes combined

Community Interactions

• Habitat: The actual place where an organism lives, containing specific biotic and abiotic factors (Organism’s “address”).
• Niche: An organism’s role or function within its habitat, including interactions and resource acquisition (Organism’s “job”). Helps reduce competition

Types of Ecological Relationships

• Competition
• Predation & Herbivory
• Symbiosis
  • Mutualism
  • Commensalism
  • Parasitism

Competition

• Competition: When two organisms attempt to use the same resources.
  • Example: Plants competing for sunlight and water.
• Competitive exclusion principle: No two species can occupy the same niche in the same habitat at the same time.

Predation & Herbivory

• Predation: When a consumer preys on another consumer.
  • Predators can impact where prey species spend their time
    • Ex: If wolves catch elk more easily in open meadows, elk may spend more time in woodlands
• Herbivory: When an herbivore preys on a producer.
  • Grazing behaviors can influence the diversity and distribution of a plant community.

Symbiosis

• Symbiosis: A close, interdependent relationship between two species.
• Mutualism: Both species benefit.
  • Example: Clownfish and Sea Anemones
    • Clownfish are immune to anemone stings and hide in sea anemones from predators
    • Clownfish chase away anemone-eating fish, protecting the anemone
    • Clownfish swimming through anemones improves water circulation which makes the anemone healthier also
• Commensalism: One species benefits, and the other is unaffected.
  • Example: Barnacles attaching to whales.
    • Barnacles are filter feeders and benefit from their swimming host but the whale seems to be unaffected
• Parasitism: One organism harms another.
  • Parasite obtains nutritional needs from host
  • Weakens but doesn’t usually kill the host
  • Example: Ticks on a deer.

Keystone Species

• Keystone Species: A species that greatly impacts the entire ecosystem.
  • Play vital and unique roles in maintain structure, stability, and diversity in an ecosystem
  • Example: Sea otters in Pacific Northwest of US eating sea urchins, which protects kelp and allows kelp forests to grow, providing habitats for many species. Without kelp forest habitats, many fish species, seabirds, and other disappeared

Energy Flow in Ecosystems

• Producers: Capture energy from nonliving sources and convert it into a usable form.
  • Most producers capture light energy through photosynthesis.
  • Some producers capture chemical energy through chemosynthesis.
  • All producers are at the bottom of global food chains.
    • They introduce usable energy to ecosystems
• Consumers: Acquire energy from other organisms.
  • Consumers are classified by how they usually acquire energy
  • Categories of Consumers: Carnivores, Herbivores, Omnivores, Decomposer, Scavengers, and Detritivores
• Food Chain: A single, linear feeding relationship.
• Food Web: Interconnected network of feeding relationships.
  • Decomposers help recycle nutrients & create detritus

Ecological & Energy Pyramids

• Trophic level: Each step in a food chain/web, with producers at the first level.
• Ecological pyramids visually represent trophic levels.
• Only 10\% of the available energy at one trophic level is transferred to the next trophic level.

Pyramids of Biomass & Numbers

• Biomass: Total amount of living tissue in a given trophic level, measured in grams per unit area.
• Biomass pyramid shows how biomass decreases at increasing trophic levels.
• Numbers pyramid: Shows relative population sizes at each trophic level.
  • Population sizes also decrease at increasing trophic levels
  • Ex: There are far more herbivores than carnivores

Population Dynamics

• Population Dynamics: The study of changes in the number of individuals in a population.
  • Affected by birth, death, immigration, and emigration.
• Birth Rate & Death Rate
  • If birth rate > death rate, then population is increasing
  • If birth rate < death rate, then population is decreasing
  • If birth rate = death rate, then population stays the same
• Immigration & Emigration
  • Immigration = individuals moving into an area (Increases population)
  • Emigration = individuals moving out of an area (Decreases population)

Measuring Population Growth

• Exponential growth: Growth in unlimited resources with no predators or disease.
  • Exponential growth can occur at first when organisms move into a new environment
• Logistic growth: Growth slows and stops due to limiting factors and carrying capacity.

Carrying Capacity & Limiting Factors

• Carrying capacity: Maximum number of individuals an environment can support.
• Limiting factors stabilize a population at its carrying capacity.
• Limiting Factors: A factor that controls the growth of a population
  • Can be density-dependent or density-independent

Density-Dependent Limiting Factors

• Density-dependent limiting factors affects populations with higher sizes and densities
• Competition: Individuals compete for resources.
• Parasitism & Disease: Spread faster in dense populations.
• Overcrowding stress: Conflict, neglect of offspring, and emigration.
• Predation: Predator-prey relationships influencing population sizes.
  • Ex: Moose & Wolf Population on Isle Royale, Michigan
• Human Predator Activity: Hunting

Density-Independent Limiting Factors

• Density-independent limiting factors affect all populations, no matter the size or density
• Environmental effects: Hurricanes, droughts, wildfires, floods, extreme heat/cold, etc.
• Weather effects that make finding food difficult (ex: heavy snowfall)
• Human impacts: Pollution, habitat loss

Succession

• Ecological succession: Predictable events in a community over time.
  • Ecosystems change over time, especially after disturbances
    • New species move in
    • Populations change
    • Some species die out
• Two Types:
  • Primary succession
  • Secondary succession

Primary Succession

• Pioneer species: First species to appear in succession
• Primary succession begins on newly formed bare rock where no previous community exists
  • Ex: after a volcanic eruption or after glaciers recede
• In primary succession, the pioneer species is lichen because it can grow on bare rock
  • Lichen & moss can break down rock to help form soil
• As soil is built by lichens and mosses, other plants, such as grasses, can move in, which will lead to animals beginning to inhabit the area
• As more plants and animals move in, the area can eventually reach its climax community

Secondary Succession

• Secondary succession occurs when a disturbance affects an existing community but doesn’t completely destroy it
  • Ex: after a wildfire or a hurricane
  • Can also happen following human disturbances, such as logging or development
• In secondary succession, the pioneer species is grasses because there is still soil present from the previous community
• As grasses grow, more plants and animals can move into the area, eventually returning the community to its climax community

Primary v. Secondary Succession

• Primary succession begins with bare rock (no soil) / Secondary succession begins with soil present
• Primary succession is slower / Secondary succession is faster

Climax Communities

• Climax community: Final stage of succession when stable ecosystem is established
• Climax community will depend on the area’s biome
  • Some climax communities could be forests while others could be grasslands
• Secondary succession can lead to a climax community similar to that before the disturbance
• Given enough time, primary succession would lead to the same climax community that secondary would

Human Activities and the Ecosystem

• Invasive species Lanternfly: Imported shipment of cut stone.
• Deforestation Trees convert CO2 to oxygen. Less trees = more CO2
• Biomagnification Increasing concentration of toxins as they move up the food chain
• Fossil Fuels