Ecology and Ecosystems: Study Guide for General Biology

Chapter 52: An Introduction to Ecology and the Biosphere

Biomes and Environmental Gradients

Ecology examines how organisms interact with their environment, including the distribution of life across the planet. Biomes are large ecological areas with distinct climates and communities of organisms.

• Biomes and Altitude: As altitude increases on a mountain, temperature decreases and precipitation patterns may change, leading to different biomes (e.g., from forest to tundra).

• Aquatic Biomes: Aquatic biomes include freshwater (lakes, rivers) and marine (oceans, coral reefs) environments, each with unique traits such as salinity, depth, and light penetration.

• Biotic and Abiotic Factors: Biotic factors are living components (plants, animals, microbes), while abiotic factors are non-living (temperature, water, sunlight, soil).

• Traits of Biomes: Each biome is characterized by specific climate conditions, dominant vegetation, and adapted animal species. For example, deserts have low rainfall and drought-resistant plants.

Chapter 53: Population Ecology

Population Patterns and Growth

Population ecology studies the dynamics of species populations and how they interact with the environment.

• Dispersion Patterns: Populations may be uniform (evenly spaced), clumped (grouped), or random. These patterns reflect resource distribution and social behavior.

• Population Size Estimation: Methods include direct counts, sampling, and mark-recapture techniques.

• Life Tables and Survivorship Curves: Life tables summarize survival and reproductive rates. Survivorship curves (Type I, II, III) graphically show the proportion of individuals surviving at each age.

• Population Growth Models: Exponential growth occurs when resources are unlimited ($N_t = N_0 e^{rt}$). Logistic growth includes carrying capacity ($K$), limiting growth as resources become scarce ($\frac{dN}{dt} = rN \left(1 - \frac{N}{K}\right)$).

• Carrying Capacity: The maximum population size an environment can sustain.

• Logistic Equation Variables: In the logistic equation, $N$ is population size, $r$ is intrinsic growth rate, and $K$ is carrying capacity.

• Life History Strategies: Semelparity (one-time reproduction) vs. iteroparity (multiple reproductive cycles). r-strategists produce many offspring with low survival; K-strategists produce fewer offspring with higher survival.

• Human Population Growth: Human population has shown exponential growth, but growth rates are declining in some regions due to demographic transitions.

• Demographic Transition: The shift from high birth and death rates to low birth and death rates as a country develops.

• Ecological Footprint: The amount of land and resources required to support an individual's lifestyle. Countries vary greatly in their ecological footprints.

Chapters 55 & 56: Ecosystems and Global Change

Energy Flow and Trophic Structure

Ecosystems consist of all organisms in a community and the abiotic factors with which they interact. Energy flows through ecosystems via food webs and trophic levels.

• Trophic Levels: Producers (autotrophs), primary consumers (herbivores), secondary consumers (carnivores), tertiary consumers, and decomposers (break down dead matter).

• Relative Numbers and Biomass: Typically, there are more producers than consumers, and biomass decreases at higher trophic levels.

• Energy Transfer: Only about 10% of energy is transferred from one trophic level to the next; the rest is lost as heat.

• Food Chain Length: Most food chains have four or five trophic levels due to energy loss at each step.

Biogeochemical Cycles

Elements cycle through ecosystems via biogeochemical cycles, including the water, carbon, nitrogen, and phosphorus cycles.

• Water Cycle: Involves evaporation, condensation, precipitation, and runoff.

• Carbon Cycle: Carbon moves between the atmosphere, organisms, and the earth via photosynthesis, respiration, and decomposition.

• Nitrogen Cycle: Nitrogen fixation, nitrification, assimilation, ammonification, and denitrification move nitrogen through the biosphere.

• Phosphorus Cycle: Phosphorus cycles through rocks, soil, water, and living organisms.

Human Impacts and Global Change

Human activities have significant effects on ecosystems and the global environment.

• Pollution: The introduction of harmful substances into the environment, affecting air, water, and soil quality.

• Biological Amplification: Also called biomagnification, this is the increase in concentration of toxins as they move up the food chain.

• Greenhouse Effect: Greenhouse gases (CO2, methane, etc.) trap heat in the atmosphere, contributing to global climate change.

• CFCs and the Atmosphere: Chlorofluorocarbons (CFCs) break down ozone in the stratosphere, increasing UV radiation reaching Earth's surface.

Summary Table: r-Selected vs. K-Selected Species

This table compares the characteristics of r-selected and K-selected species, which represent two ends of a spectrum of reproductive strategies.

Characteristic	r-Selected Species	K-Selected Species
Reproduction	Many offspring, little parental care	Few offspring, high parental care
Survivorship Curve	Type III (high juvenile mortality)	Type I or II (low juvenile mortality)
Population Growth	Rapid, often exponential	Slow, near carrying capacity
Examples	Insects, weeds	Large mammals, trees