General Biology: Ecology, Biomes, and Population Dynamics Study Notes

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Ecology and Biomes

Ecological Research and Key Concepts

Ecology is the study of interactions between organisms and their environment, encompassing various levels from individuals to ecosystems. Understanding these interactions helps explain the distribution and abundance of life on Earth.

Organism: An individual living entity.
Population: A group of individuals of the same species living in a specific area.
Community: Different populations of species living together in a defined area.
Ecosystem: The community plus the physical environment (energy flow, nutrient cycling).
Landscape: A mosaic of connected ecosystems.
Global: Examines ecological processes at the planetary scale (e.g., global climate patterns).

Climate and Biomes

Biomes are large ecological areas on the Earth's surface, with flora and fauna adapting to their environment. Climate, determined by latitude, season, and other factors, is a primary driver of biome distribution.

Climate Physical Factors: Temperature, precipitation, sunlight, wind.
Seasonality: Caused by Earth's tilt and orbit, leading to wet/dry seasons and temperature changes.
Bodies of Water: Influence local climates by moderating temperatures and increasing humidity.
Mountains: Affect climate through elevation and rain shadow effects.
Disturbance: Events like fires or storms that change communities by removing organisms or altering resource availability.

Major Terrestrial Biomes

Tropical Forest (TF): High rainfall, high biodiversity, layered vegetation.
Desert (D): Low rainfall, extreme temperatures, sparse vegetation.
Savanna (S): Seasonal rainfall, grasses, scattered trees, large herbivores.
Temperate Grassland (TG): Seasonal drought, cold winters, hot summers, grasses dominate.
Northern Coniferous Forest (NCF): Largest terrestrial biome, cold winters, conifer trees.
Temperate Broadleaf Forest (TBF): Warm summers, cold winters, deciduous trees.
Tundra (T): Cold, permafrost, low vegetation, short growing season.

Major Aquatic Biomes

Oceans: Cover 75% of Earth's surface, major influence on climate and oxygen production.
Lakes: Classified by nutrient content (oligotrophic = low nutrients, eutrophic = high nutrients).
Rivers and Streams: Characterized by current, oxygen content, and nutrient levels.
Estuaries: Where freshwater meets saltwater, high productivity.
Intertidal Zones: Area between high and low tide, variable conditions.
Coral Reefs: High biodiversity, sensitive to temperature and water quality.
Marine Benthic Zone: Ocean floor, low temperatures, high pressure.

Population Ecology

Population Characteristics

Population ecology studies the factors that affect population size, structure, and dynamics.

Population (Pop): Group of individuals of the same species in a given area.
Density: Number of individuals per unit area.
Dispersion: Pattern of spacing among individuals (clumped, uniform, random).
Demographics: Statistical study of populations, including birth and death rates.

Estimating Population Size

Mark-Recapture Method: Used to estimate population size by capturing, marking, and recapturing individuals.

Formula:

Where = number marked in first sample, = total in second sample, = recaptured marked individuals.

Survivorship Curves

Type I: High survival early, decline with age (e.g., humans).
Type II: Constant death rate (e.g., squirrels).
Type III: High death rate early, survivors live long (e.g., oysters).

Population Growth Models

Exponential Growth: Population increases under ideal, unlimited resources.

Equation:

Where = population size, = intrinsic rate of increase.

Logistic Growth: Population growth slows as it approaches carrying capacity ().

Equation:

Where = carrying capacity.

Life History Strategies

Semelparity: Single, large reproductive event (e.g., salmon).
Iteroparity: Multiple reproductive cycles over a lifetime (e.g., mammals).
r-selection: High reproductive rate, low survival (e.g., weeds).
K-selection: Low reproductive rate, high survival (e.g., elephants).

Density-Dependent and Density-Independent Factors

Density-Dependent: Factors whose effects increase as population density increases (e.g., competition, disease).
Density-Independent: Factors that affect populations regardless of density (e.g., weather, natural disasters).

Community Ecology

Community Interactions

Communities are shaped by interactions among species, which can be classified by their effects on the participants.

Competition (-/-): Both species are harmed by the interaction.
Predation (+/-): One species benefits, the other is harmed.
Herbivory (+/-): Animals eat plants; plants may evolve chemical defenses.
Parasitism (+/-): Parasite benefits, host is harmed.
Mutualism (+/+): Both species benefit.
Commensalism (+/0): One species benefits, the other is unaffected.

Ecological Niches and Resource Partitioning

Niche: The role and position a species has in its environment.
Resource Partitioning: Differentiation of niches that enables similar species to coexist.
Character Displacement: Tendency for characteristics to be more divergent in sympatric populations than in allopatric populations.

Community Structure and Diversity

Species Richness: Number of different species in a community.
Relative Abundance: Proportion of each species in a community.
Shannon Diversity Index: Measures species diversity in a community.

Equation:

Where = proportion of individuals in the th species.

Trophic Structure

Food Chain: Linear sequence of organisms through which nutrients and energy pass.
Food Web: Complex network of interconnected food chains.
Keystone Species: Species with a disproportionately large effect on community structure.
Ecosystem Engineers: Species that create or modify habitats (e.g., beavers).

Disturbance and Succession

Disturbance: An event that changes a community by removing organisms or altering resource availability.
Intermediate Disturbance Hypothesis: Moderate levels of disturbance foster greater species diversity than low or high levels.
Primary Succession: Occurs in lifeless areas (e.g., after a volcanic eruption).
Secondary Succession: Occurs in areas where a disturbance has destroyed a community but left the soil intact.

Biogeography and Biodiversity

Latitudinal Gradients and Area Effects

Species diversity is generally higher in the tropics and decreases toward the poles.
Larger areas tend to have more species (species-area relationship).

Island Biogeography

Species richness on islands depends on island size and distance from the mainland.
Equilibrium model: Balance between immigration and extinction rates.

Tables

Summary Table: Major Terrestrial Biomes

Biome	Climate	Dominant Vegetation	Key Features
Tropical Forest	High rainfall, warm	Broadleaf evergreen trees	High biodiversity, layered structure
Desert	Low rainfall, hot/cold	Sparse shrubs, cacti	Extreme temperatures, water conservation
Savanna	Seasonal rainfall	Grasses, scattered trees	Large herbivores, fire-adapted
Temperate Grassland	Cold winters, hot summers	Grasses	Fertile soils, periodic fires
Northern Coniferous Forest	Cold, moderate rainfall	Conifer trees	Largest terrestrial biome, migratory animals
Temperate Broadleaf Forest	Warm summers, cold winters	Deciduous trees	Seasonal leaf drop, diverse fauna
Tundra	Cold, low precipitation	Mosses, grasses	Permafrost, short growing season

Summary Table: Types of Species Interactions

Interaction	Effect on Species 1	Effect on Species 2	Example
Competition	-	-	Plants competing for sunlight
Predation	+	-	Lion and zebra
Herbivory	+	-	Caterpillar eating leaves
Parasitism	+	-	Tapeworm in human
Mutualism	+	+	Bees and flowers
Commensalism	+	0	Barnacles on whales

Summary Table: Survivorship Curves

Type	Description	Example
I	High survival early, decline with age	Humans
II	Constant death rate	Squirrels
III	High death rate early, survivors live long	Oysters

Additional info: Some explanations and examples were expanded for clarity and completeness based on standard General Biology curriculum.