Ch 6 Ecology Complete Study Notes
Ch 6 Ecology – Biology with Mr. Nalaboff
6.1 Ecosystems
Definition of Ecology: Ecology is the study of how living things interact with each other and with their environment. While it is a major branch of biology, it overlaps with geography, geology, climatology, and other scientific fields.
Fundamental Concepts: The study of ecology centers on two concepts: the ecosystem and its organisms.
Organisms: These are individual living things. Despite tremendous diversity, all organisms share basic needs for energy and matter, which must be obtained from the environment.
Environmental Factors:
Abiotic Factors: The nonliving aspects of the environment, including sunlight, soil, temperature, and water.
Biotic Factors: The living aspects of the environment, consisting of other organisms, including members of the same and different species.
The Ecosystem: A unit of nature and the focus of ecological study. It includes all biotic and abiotic factors in an area and their interactions.
Size Variance: Ecosystems can range in size from a large lake to a dead log on a forest floor. Both contain a variety of species interacting with each other and abiotic factors.
Energy and Matter in Ecosystems:
Most ecosystems receive energy from sunlight via photosynthesis.
Energy flows from producers to consumers (e.g., plants to herbivores, then to carnivores).
The flow of energy and the recycling of nutrients and water exemplify the interactions between organisms and their environment.
The Niche: Refers to the role of a species within its ecosystem. It encompasses all ways a species interacts with biotic and abiotic factors. Key aspects include the food a species eats and how that food is obtained.
The Habitat: The physical environment where a species lives and to which it is adapted. Features are determined primarily by abiotic factors like temperature and rainfall, which influence organism traits.
Competitive Exclusion Principle: Two different species cannot occupy the same niche in the same place for very long. If they did, they would compete for the same resources until one species outcompetes and replaces the other.
Character Displacement: To coexist in the same area, species may develop different specializations. An example is two species of lizard sharing the same tree, with one living in the top and the other at the bottom to avoid competition.
6.2 Energy Flow
Energy Influx: Ecosystems require constant energy, entering as sunlight or chemical compounds. Some organisms use this to make food, while others eat the food makers.
Producers (Autotrophs): Organisms that produce food for themselves and others by using energy and simple inorganic molecules to create organic compounds. They are vital for ecosystem stability.
Photoautotrophs: Use sunlight to make food via photosynthesis. Examples: plants, algae, and certain bacteria.
Chemoautotrophs: Use energy from chemical compounds to make food via chemosynthesis. Examples: some bacteria and archaea.
Archaea: Single-celled prokaryotes lacking a nucleus and membrane-bound organelles; often found in extreme environments.
Consumers (Heterotrophs): Organisms that depend on others for food by "eating" or absorbing organic molecules. They include all animals, fungi, many bacteria, and some plants.
Herbivores: Consume producers (e.g., deer, rabbits, mice).
Carnivores: Consume animals (e.g., lions, hawks, salmon). Obligate carnivores are unable to digest plants and must eat only animals.
Omnivores: Consume both plants and animals (e.g., humans, brown bears, crows).
Decomposers: Break down dead remains and wastes, releasing simple inorganic molecules back into the environment for producers to reuse.
Scavengers: Consume soft tissues of dead animals (e.g., vultures, raccoons, blowflies).
Detritivores: Consume detritus (dead leaves, feces, organic debris). Land examples: earthworms, millipedes. Water examples: sea cucumbers, catfish.
Saprotrophs: The final step in decomposition; they feed on remaining organic matter. Includes fungi, bacteria, and protozoa. Fungi are the only organisms capable of decomposing wood.
6.3 Food Chain and 6.4 Trophic Level
Diagrams of Relationships:
Food Chain: A single pathway through which energy and matter flow. These are generally simpler than natural reality.
Food Web: Multiple intersecting pathways; demonstrates that most organisms eat and are eaten by more than one species.
Trophic Levels: The feeding positions in a chain or web. Most have a maximum of four levels.
1st Level: Producer (e.g., plants).
2nd Level: Primary Consumer (e.g., cow, grasshopper).
3rd Level: Secondary Consumer (e.g., bird eating a grasshopper).
4th Level: Tertiary Consumer (e.g., human or wolf eating the bird).
Quaternary Consumer: Examples like an owl or eagle at the top of certain chains.
Energy Transfer (The Rule): Generally, only about of energy at one level is available to the next. The other is used for metabolic processes or lost as heat. This explains why chains rarely exceed four levels.
Ecological Pyramids: Model the decrease in energy, biomass, or numbers.
Biomass: The total mass of organisms at a trophic level. While organisms at higher levels are often larger, their smaller numbers result in less total biomass.
6.5 Water Cycle
Biogeochemical Cycles: The continuous recycling of chemical elements and water through biotic (bio) and abiotic (geo) components of the biosphere.
Cycle Components:
Exchange Pool: Part of a cycle holding an element for a short time (e.g., the atmosphere holds water vapor for a few days).
Reservoir: Part of a cycle holding an element for a long time (e.g., the deep ocean holds water for thousands of years).
Water Cycle Processes:
Evaporation: Water on the surface changes to water vapor due to sun heat.
Sublimation: Ice and snow change directly into water vapor.
Transpiration: Plants release water vapor through leaf pores called stomata.
Evapotranspiration: Combined evaporation from land and transpiration from plants.
Condensation: Water vapor cools and changes into liquid droplets, forming clouds.
Precipitation: Rain, snow, sleet, or hail. Most falls into the ocean.
Runoff: Water flowing over the ground surface into bodies of water.
Infiltration: Water soaking into the ground to become groundwater.
Aquifer: An underground layer of rock that stores water for potentially thousands of years.
6.6 Carbon Cycle
Significance: Carbon is the primary ingredient of organic compounds necessary for life. Organisms cannot create carbon; it must be recycled.
Storage and Reservoirs: Major reservoirs include sedimentary rock and the ocean. Carbon is also stored in the atmosphere, living organisms, and fossil fuel deposits.
Cycle Speed: Carbon cycles quickly between organisms and the atmosphere. In the atmosphere, it exists mostly as carbon dioxide ().
Key Processes:
Cellular Respiration: Releases as a byproduct.
Photosynthesis: Removes from the atmosphere to make organic compounds.
Human Impact: Burning fossil fuels and clearing forests (reducing autotrophs) has increased atmospheric to levels higher than in hundreds of thousands of years, contributing to the greenhouse effect.
6.7 Nitrogen Cycle
Importance: Nitrogen makes up of the atmosphere and is found in proteins, nucleic acids, and chlorophyll.
Nitrogen Gas (): Plants cannot use atmospheric nitrogen because of a very stable triple bond between atoms.
Processes:
Nitrogen Fixation: Nitrogen-fixing bacteria (often in the roots of the pea family) transform into ammonium via ammonification.
Nitrification: Nitrifying bacteria change ammonium ions into nitrites and nitrates.
Assimilation: Plants use nitrates to build organic compounds, which are then passed to animals.
Denitrification: Denitrifying bacteria convert nitrates in the soil back into nitrogen gas.
6.8 Biomes and Climate
Biome: A group of similar ecosystems with the same general abiotic factors and primary producers.
Climate: The average weather in an area over a long period. Weather is day-to-day. Climate is defined by temperature and moisture.
Temperature Factors:
Latitude: Temperature falls from the equator to the poles (Tropical, Temperate, and Arctic zones).
Proximity to Ocean: Water gains/loses heat slowly, leading to cooler summers and warmer winters on the coast.
Altitude: Temperature falls at higher altitudes.
Moisture Factors: Classified as arid, semi-arid, humid, or semi-humid. Depends on precipitation (increases moisture) and evaporation (decreases moisture).
Plant Growth and Soil:
Growing Season: Period warm and wet enough for plant growth.
Soil Quality: Best in temperate climates. Decomposition is too slow in cold climates and too fast in hot, wet climates for organic matter to accumulate.
Biodiversity: Usually increases from the poles toward the equator and is higher in humid climates.
Adaptations: Plants in arid biomes may store water; animals in cold biomes use insulation like fur and fat or enter dormancy (slowing cellular activities).
6.9 Terrestrial Biomes
Tundra: Arctic, arid; short growing season; poor soil; mosses, grasses, lichens; no trees; rodents, foxes, polar bears.
Boreal Forest (Taiga): Subarctic, semi-arid; short growing season; poor soil; conifers (cedar, spruce, pine); bears, moose, caribou.
Temperate Deciduous Forest: Temperate, semi-humid; medium growing season; good soil; broadleaf trees (beech, maple, oak); deer, wolves, bobcats.
Temperate Grassland (Prairie, Steppe): Temperate, semi-arid; medium growing season; excellent soil; grasses only; bison, antelope, kangaroo (Australia).
Chaparral: Temperate, semi-arid; medium growing season; poor soil; shrubs and scrub oak/pine; rodents, deer.
Desert: Temperate/tropical, arid; varying growing season; very poor soil; cacti, sagebrush; reptiles, coyotes.
Tropical Rainforest: Tropical, humid; year-round growing season; poor soil (nutrients leached/recycled too fast); high biodiversity; monkeys, sloths, jaguars.
Tropical Grassland (Savanna): Tropical, semi-arid; year-round growing season; poor soil; grasses and scattered trees; zebras, lions, giraffes.
6.10, 6.11, and 6.12 Aquatic Biomes and Organisms
Limiting Factors: Sunlight, dissolved oxygen, and nutrients.
Sunlight Zones:
Photic Zone: Surface to . Support photosynthesis.
Aphotic Zone: Deeper than . No photosynthesis; food comes from chemosynthesis or marine snow.
Other Zones:
Neritic Zone: Shallow water above the continental shelf.
Oceanic Zone: Water beyond the continental shelf; very challenging with few dissolved substances.
Benthic Zone: The bottom of the body of water. Benthic decomposers and scavengers cycle nutrients.
Marine Specifics: Organisms often have organs to excrete salt.
Intertidal Zone: Strip along coastline; covered at high tide, exposed at low tide.
Hydrothermal Vents: Support communities in deep ocean using chemoautotrophs.
Freshwater Biomes:
Standing: Ponds and lakes.
Running: Streams and rivers.
Wetlands: Areas saturated with water. They store floodwater, prevent erosion, and filter nutrients. Estuaries (e.g., San Francisco Bay) are where fresh and saltwater meet; they are highly productive.
Aquatic Groups:
Plankton: Tiny, cannot move on their own. Phytoplankton (photosynthetic) and Zooplankton (eat phytoplankton).
Nekton: Can move by swimming (e.g., fish, shrimp).
Benthos: Crawl on the bottom (e.g., sponges, clams, anglerfish).
Scientific Research: The Tagging of Pacific Predators program (TOPP) tracks sharks and turtles to study migration and ocean diversity.
6.13 Predation
Definition: Predator eats prey. This relationship accounts for most energy transfers in food webs.
Balance: Populations oscillate. As prey increases, predator food increases, leading to a predator increase. This eventually causes a prey decrease, which then causes a predator decrease.
Limiting Factor: The prey population acts as a limiting factor on the predator population.
Keystone Species: A species that plays an exceptionally important role; changes in its numbers significantly affect the entire community.
Adaptations: Natural selection favors traits like camouflage to help predators hunt or prey hide.
6.14 and 6.15 Competition and Symbiosis
Competition: Striving for the same resources.
Intraspecific: Between members of the same species (e.g., for mates). Drives natural selection.
Interspecific: Between different species. Can lead to extinction of the less-adapted species or specialization.
Symbiosis: Close relationship where at least one species benefits.
Mutualism: Both benefit (e.g., flowering plants and pollinators). Often leads to coevolution.
Commensalism: One benefits, the other is unaffected (e.g., mites hitching rides on insects).
Parasitism: One benefits (parasite), the other is harmed (host). Most parasites do not kill their hosts immediately.
6.16 Succession
Definition: The change in numbers and types of species in a community over time.
Primary Succession: Occurs on bare rock (lava, glacier retreats). Pioneer species like bacteria, lichens, and mosses break down rock to form soil.
Secondary Succession: Occurs in formerly inhabited areas after disturbance (fire, farming). Faster because soil exists. Pioneer species include grasses and birch trees.
Climax Community: An old theory of a final stable stage; modern ecologists believe continued change and disturbance are more normal.
6.17, 6.18, 6.19, and 6.20 Populations
Measures:
Population Size: Total number of individuals.
Population Density: Average number of individuals per unit area or volume.
Population Distribution: How individuals are spread (e.g., clumped).
Structure:
Age-Sex Structure: Represented by a population pyramid. Influences growth because younger individuals reproduce and older have higher death rates.
Survivorship Curves:
Type I: Low offspring, high care, high survival (Humans).
Type II: Moderate offspring/care, uniform death (Birds).
Type III: High offspring, no care, low survival (Plants, Fish).
Growth Rate (): The formula is: (where , , , ).
Dispersal and Migration: Dispersal is offspring moving away from parents; migration is seasonal movement for resources.
Growth Patterns:
Exponential Growth: Occurs under ideal conditions; growth accelerates as population increases.
Logistic Growth: Growth slows and levels off at the Carrying Capacity () due to limiting factors.
Selection Strategies:
K-selected: Stable environments, density-dependent control, population near .
r-selected: Unstable environments, rapid growth, many offspring, population usually below .
6.21, 6.22, and 6.23 Human Population
History: Homo sapiens arose in Africa years ago. Left Africa years ago. Agriculture was invented years ago, increasing food supply and birth rates, though diseases also increased in settled cities.
Demographic Transition:
Stage 1: High birth/death rates (slow growth).
Stage 2: Death rates fall (improved hygiene/food), birth rates stay high (fast growth).
Stage 3: Birth rates fall (slow growth).
Stage 4: Birth/death rates both low (zero growth).
Stage 5: Birth rates lower than death rates (negative growth/shrinking population).
Global Status: No country is currently in Stage 1. Poor countries are often stuck in Stage 2. Developed nations (e.g., Sweden) are in Stage 4.
6.24, 6.25, and 6.26 Biodiversity and Extinction
Three Measures: Species diversity (number of species), Genetic diversity (variation within species), and Ecosystem diversity.
Count: As of 2021, million species identified; estimates range from 3 to 100 million.
Benefits: Economic (timber, fibers), Medical (over half of drugs from wild species), Ecosystem services (atmosphere maintenance, soil protection, nutrient cycling, pollination, pest control).
Mass Extinction: Five have occurred due to geological/climatic events. A Sixth Mass Extinction is happening now due to human actions.
Rate: Between and species per year.
Causes: Habitat loss (biggest), exotic species, over-harvesting, climate change, and pollution.
Impact of Predators: Loss of large predators (lions, sharks) causes deer explosions which alter vegetation, or surges in baboons that transfer parasites to humans.
6.27 and 6.28 Resources, Soil, and Water
Renewable Resources: Sunlight, wind, metals (recyclable). Living things are renewable if used sustainably.
Nonrenewable Resources: Fossil fuels (petroleum, coal, natural gas) and nuclear power (uranium). At current rates, petroleum will last decades, and coal less than 300 years.
Soil: Essential for plant growth; removes toxins and breaks down waste. Although technically renewable, it takes hundreds of millions of years to form. Misuse (e.g., the 1930s Dust Bowl) leads to erosion. Conservation includes contour plowing and terracing.
Water: Only of Earth's water is fresh, liquid water. Runoff carries fertilizers, causing algal blooms and dead zones (low oxygen areas).
6.29 and 6.30 Air Pollution and Global Warming
Pollution Causes: Burning fossil fuels, ranching, chemicals, and indoor fumes.
Acid Rain: Low pH precipitation caused by nitrogen/sulfur oxides. Damages plants and aquatic life.
Ozone:
Bad (Ground-level): Harmful to respiratory systems.
Good (Atmospheric): Protects from UV radiation. Being destroyed by chlorine/bromine gases, leading to an ozone hole over Antarctica.
Global Warming: Increase in surface temperature ( or in the last century) caused by enhanced greenhouse effect from .
Consequences: Melting glaciers, sea-level rise, droughts, crop losses, and decline in cold-adapted species (e.g., polar bears).
Solutions: Switching to solar/wind energy and reforestation to remove .