Ecology: Study Guide for General Biology (Chapters 52, 53, 54, 55)

Ecology: Study Guide for General Biology

Chapter 52: Introduction to Ecology and the Biosphere

Ecology is the scientific study of the interactions between organisms and their environment. This chapter introduces the major abiotic and biotic factors that influence the distribution and abundance of organisms on Earth.

• Abiotic Factors: Non-living components such as temperature, water, sunlight, wind, and soil that affect living organisms.

• Biotic Factors: Living components, including other organisms, that influence an organism's survival and reproduction.

• Climate: The long-term prevailing weather conditions in a given area. Climate is determined by temperature, precipitation, sunlight, and wind.

• Macroclimate vs. Microclimate: Macroclimate refers to patterns on the global, regional, and landscape level, while microclimate consists of very fine, localized patterns.

• Biomes: Major life zones characterized by vegetation type (terrestrial biomes) or physical environment (aquatic biomes).

• Distribution of Organisms: Influenced by abiotic factors (e.g., temperature, water, sunlight, wind, rocks, and soil) and biotic factors (e.g., predation, competition, mutualism).

Example: The distribution of saguaro cacti is limited by temperature (cannot survive freezing), water availability, and pollinator presence.

Chapter 53: Population Ecology

Population ecology examines the factors that affect population size and how and why it changes over time.

• Population: A group of individuals of the same species living in the same area at the same time.

• Population Density: The number of individuals per unit area or volume.

• Dispersion Patterns: The way individuals are spaced within their area (clumped, uniform, random).

• Demography: The study of the vital statistics of populations and how they change over time (e.g., birth rates, death rates, age structure).

• Population Growth Models:

  • Exponential Growth: Population increases under ideal conditions, represented by the equation: $\frac{dN}{dt} = r_{max}N$ where $N$ is population size, $r_{max}$ is the maximum per capita growth rate.

  • Logistic Growth: Population growth slows as it approaches carrying capacity ($K$): $\frac{dN}{dt} = r_{max}N\left(1-\frac{N}{K}\right)$

• Carrying Capacity ($K$): The maximum population size that a particular environment can sustain.

• Life History Traits: Traits that affect an organism's schedule of reproduction and survival (e.g., age at first reproduction, number of offspring, parental care).

• Density-Dependent Factors: Factors whose effects on population size increase or decrease depending on population density (e.g., competition, predation, disease).

• Density-Independent Factors: Factors that affect population size regardless of density (e.g., weather, natural disasters).

Example: The logistic growth model describes how a population of yeast in a laboratory flask grows rapidly at first, then levels off as nutrients become limited.

Chapter 54: Community Ecology

Community ecology studies the interactions between species in communities and how these interactions shape community structure and dynamics.

• Community: An assemblage of populations of different species living close enough for potential interaction.

• Species Interactions:

  • Competition (-/-): Species compete for a resource in short supply.

  • Predation (+/-): One species, the predator, kills and eats the other, the prey.

  • Herbivory (+/-): An organism eats parts of a plant or alga.

  • Symbiosis: Individuals of two or more species live in direct and intimate contact with one another.

    • Mutualism (+/+): Both species benefit.

    • Commensalism (+/0): One species benefits, the other is not affected.

    • Parasitism (+/-): One organism derives nourishment from another, harming it.

  • Facilitation (+/+ or 0/+): One species has positive effects on another species without direct and intimate contact.

• Ecological Niche: The sum of a species' use of the biotic and abiotic resources in its environment.

• Resource Partitioning: Differentiation of niches that enables similar species to coexist.

• Defensive Adaptations: Cryptic coloration (camouflage), aposematic coloration (warning), mimicry (Batesian and Müllerian), mechanical and chemical defenses.

• Trophic Structure: The feeding relationships between organisms in a community.

• Keystone Species: Species that have a disproportionately large effect on community structure.

• Species Diversity: The variety of different kinds of organisms that make up the community (species richness and relative abundance).

Example: Sea otters are a keystone species in kelp forest communities; their predation on sea urchins helps maintain kelp populations.

Chapter 55: Ecosystems and Restoration Ecology

This chapter explores how energy flows and nutrients cycle through ecosystems, and how ecosystems can be restored after disturbance.

• Ecosystem: All the organisms in a community plus the abiotic factors with which they interact.

• Energy Flow: Energy enters ecosystems as sunlight, is converted to chemical energy by autotrophs, and flows through food webs, eventually being lost as heat.

• Nutrient Cycling: Elements such as carbon, nitrogen, and phosphorus are recycled within ecosystems.

• Primary Production: The amount of light energy converted to chemical energy by autotrophs during a given time period.

• Gross Primary Production (GPP): Total primary production in an ecosystem.

• Net Primary Production (NPP): GPP minus energy used by primary producers for respiration: $NPP = GPP - R_a$

• Trophic Efficiency: The percentage of production transferred from one trophic level to the next, usually about 10%.

• Decomposition: The breakdown of organic matter, returning nutrients to the ecosystem.

• Restoration Ecology: The study and implementation of renewing and restoring degraded, damaged, or destroyed ecosystems.

Example: Wetland restoration projects aim to reestablish the natural water flow and native plant communities to improve ecosystem function.

Key Terms and Concepts Table

Term	Definition
Abiotic Factor	Non-living chemical and physical parts of the environment
Biotic Factor	Living components of the environment
Carrying Capacity (K)	Maximum population size an environment can sustain
Exponential Growth	Population growth under ideal conditions; J-shaped curve
Logistic Growth	Population growth that levels off as carrying capacity is reached; S-shaped curve
Keystone Species	Species with a large impact on community structure
Primary Production	Amount of light energy converted to chemical energy by autotrophs
Restoration Ecology	Study and practice of renewing damaged ecosystems