Ecology and Evolution: Study Guide for BIO 106 Unit 4

Population Ecology

Population Concepts

A population is a group of individuals of the same species living in the same geographic area. Understanding populations involves studying their size, density, distribution, and the factors that influence their growth and decline.

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

• Population Distribution (Dispersion): The spatial arrangement of individuals within a population. Three main patterns:

  • Clumped: Individuals occur in groups, often due to uneven resource distribution (most common).

  • Uniform: Individuals are evenly spaced, often due to territorial behavior or competition.

  • Random: Individuals are distributed unpredictably, typically when resources are consistently available.

Population Dynamics

• Birth Rate (Natality): Number of individuals produced per unit time.

• Death Rate (Mortality): Number of individuals dying per unit time.

• Immigration: Movement of individuals into a population.

• Emigration: Movement of individuals out of a population.

Population Growth Models

• Exponential Growth: Population increases under ideal conditions, producing a J-shaped curve. The equation is: $G = rN$ Where:

  • G = number of individuals added

  • r = per capita growth rate

  • N = population size

• Carrying Capacity (K): The maximum population size that an environment can support. Logistic growth produces an S-shaped curve as the population approaches K.

Regulation of Population Size

• Density-Dependent Factors: Effects increase as population density increases (e.g., disease, predation, competition, parasitism).

• Density-Independent Factors: Affect populations regardless of size (e.g., frost, fires, floods, hurricanes, droughts).

Survivorship Curves

• Type I: Low juvenile mortality, high mortality late in life (e.g., humans, elephants).

• Type II: Constant mortality rate at all ages (e.g., songbirds).

• Type III: High juvenile mortality, few survive to adulthood (e.g., insects, many plants).

Life History Strategies

• r-Selected Species: Many offspring, little parental care, early reproduction, short lifespan (e.g., insects, weeds).

• K-Selected Species: Few offspring, extensive parental care, longer lifespan (e.g., humans, elephants).

Community Ecology

Community Structure

A community consists of all populations of different species living together in a particular area.

• Habitat: The physical place where an organism lives.

• Niche: The role of a species in its environment, including resource use, habitat, food sources, and reproductive strategies.

Species Interactions

• Competition: Occurs when organisms depend on the same limited resources.

• Symbiosis: Close interactions between species:

  • Mutualism (+/+): Both benefit (e.g., bees and flowers).

  • Commensalism (+/0): One benefits, other unaffected (e.g., barnacles on whales).

  • Parasitism (+/-): One benefits, host is harmed (e.g., ticks, tapeworms).

• Predation (+/-): One organism kills and consumes another (e.g., wolves and deer).

Adaptations in Communities

• Camouflage: Allows organisms to blend into surroundings (e.g., leaf insects).

• Mimicry: One organism resembles another for protection or advantage.

• Keystone Species: Species whose impact on its community or ecosystem is disproportionately large relative to its abundance (e.g., sea otters).

Ecosystems and Energy Flow

Ecosystem Structure

An ecosystem includes all living (biotic) and nonliving (abiotic) components in a particular area.

• Biotic Components: Plants, animals, fungi, archaea, bacteria.

• Abiotic Components: Water, temperature, soil, sunlight, salinity.

Trophic Levels

• Producers (Autotrophs): Make their own organic molecules (e.g., plants, algae).

• Consumers (Heterotrophs): Obtain energy by eating other organisms.

• Decomposers: Break down dead organisms and return nutrients to the ecosystem (e.g., bacteria, fungi).

Biogeochemical Cycles

• Carbon Cycle: Carbon enters the atmosphere via cellular respiration, burning fossil fuels, and release of carbon dioxide.

Aquatic Ecosystems: Lakes

• Littoral Zone: Near shore, shallow, well-lit.

• Limnetic Zone: Open water, well-lit.

• Profundal Zone: Deep water, low light.

• Benthic Zone: Bottom sediment.

Eutrophication

• Caused by excess nitrogen and phosphorus.

• Leads to algal blooms, oxygen depletion, fish kills, and dead zones (e.g., Gulf of Mexico).

Biomes

Major Terrestrial Biomes

Biomes are large ecological areas defined primarily by temperature and precipitation.

Biome	Key Characteristics
Tundra	Permafrost, cold temperatures, short growing season
Taiga	Long harsh winters, coniferous trees, nutrient-poor soils
Temperate Grasslands	Nutrient-rich soil, moderate rainfall
Desert	Low rainfall, long taproots, water conservation adaptations
Tropical Rainforest	Warm and wet, extremely high biodiversity, nutrient-poor soils
Savanna	Tropical grassland, seasonal rainfall; decreased rainfall can lead to desertification

Ecological Succession

Types of Succession

• Primary Succession: Occurs where no previous community existed (e.g., new volcanic rock, newly exposed rock). Pioneer species colonize first.

• Secondary Succession: Occurs where a community existed previously (e.g., after forest fire, abandoned farmland).

Human Population Growth and Environmental Issues

Human Population Growth

• Currently resembles exponential growth.

• Population Pyramids:

  • Wide Base: High birth rate, future population growth (e.g., India).

  • Rectangular Shape: Stable population (e.g., United States).

Health and Mortality

Country Type	Leading Causes of Death	Reasons
High-Income	Heart disease, cancer, stroke	Better access to sanitation, vaccines, antibiotics
Low-Income	Infectious diseases	Less access to sanitation, vaccines, antibiotics

Environmental Issues

• Greenhouse Effect: Greenhouse gases trap heat, preventing it from escaping Earth, leading to global warming and climate change.

• Pollution: Any chemical, physical, or biological change that harms living organisms.

• Habitat Destruction: Primary cause of biodiversity loss and modern extinctions.

Evolution and Natural Selection

Basic Concepts

• Evolution: Genetic change in populations over generations.

• Natural Selection (Darwin's Main Idea):

  1. Individuals produce more offspring than can survive.

  2. They compete for limited resources.

  3. Those with advantageous traits survive and reproduce.

• Adaptation: Heritable trait that increases survival and reproduction.

• Artificial Selection: Humans select traits (e.g., broccoli, cabbage, kale, cauliflower all derived from wild mustard).

• Sexual Selection: Traits increase mating success (e.g., female cardinals prefer males with bright red plumage).

Modes of Natural Selection

• Directional Selection: One extreme phenotype favored.

• Stabilizing Selection: Intermediate phenotype favored (e.g., human birth weight).

• Disruptive Selection: Both extremes favored (e.g., Galápagos finch beak sizes).

Population Genetics

Genetic Drift

• Founder Effect: Small group establishes a new population, resulting in reduced genetic diversity.

• Bottleneck Effect: Large portion of population dies, reducing genetic variation.

Hardy-Weinberg Principle

• The Hardy-Weinberg equation describes genetic equilibrium in a population: $p^2 + 2pq + q^2 = 1$ Where:

  • $p^2$ = frequency of homozygous dominant genotype

  • $2pq$ = frequency of heterozygous genotype

  • $q^2$ = frequency of homozygous recessive genotype

Other Key Concepts

• Heterozygote Advantage: Heterozygotes have higher fitness in certain environments (e.g., sickle-cell trait confers malaria resistance).

• Somatic vs Germ Cell Mutations:

  • Somatic mutations: Occur in body cells, not inherited.

  • Germ cell mutations: Occur in gametes, can be inherited.

Summary Table: Key Terms and Concepts

Term	Definition/Example
Population	Same species in same area
Community	Multiple populations
Ecosystem	Biotic + abiotic components
Habitat	Where an organism lives
Niche	How an organism lives
Autotroph	Producer
Heterotroph	Consumer
Decomposer	Bacteria and fungi
Eutrophication	Excess nitrogen/phosphorus
Carrying capacity	Maximum population supported
Keystone species	Disproportionately important species
Permafrost	Tundra
Conifers	Taiga
Nutrient-rich soil	Grasslands
Desert plants	Long taproots
Human population growth	Exponential
Primary succession	No previous community
Pioneer species	First colonizers
Habitat destruction	Leading cause of biodiversity loss
Greenhouse gases	Trap heat
Type I survivorship	Humans
Type II survivorship	Birds
Type III survivorship	Insects/plants
2pq	Heterozygotes (Hardy-Weinberg)
Founder effect	Small colonizing population
Bottleneck effect	Mass die-off
Heterozygote advantage	Sickle-cell trait and malaria resistance

Additional info:

• Understanding the differences between similar ecological and evolutionary terms is crucial for exams.

• Focus on definitions, examples, and the ability to distinguish between concepts such as population vs. community, and r-selected vs. K-selected species.