Ecology

Ecology Definition

Branch of biology dealing with organization levels: population, community, ecosystem, biome, biosphere.

Population Level Focus

Focuses on dynamics of a single species' population (growth/decline, environmental interactions, interactions with other populations).

Birth Rate Definition

Number of live births per thousand of population per year.

Death / Mortality Rate Definition

Ratio of deaths to population per area/period, usually per 1,000 people per year.

Population Density Definition

Measurement of population per unit area or unit volume.

Population Growth Rate Definition

Rate at which individual numbers increase in a given period, expressed as a fraction of initial population.

Age-sex Pyramid (Population Pyramid) Definition

Visual representation of the age and sex distribution of a population.

Expansive Pyramid Description

Broad base and narrow top.

Expansive Pyramid Characteristics

High birth rate, short life expectancy, rapid population growth.

Expansive Pyramid Examples

Developing countries (e.g., Philippines, Nigeria, Bangladesh).

Stationary Pyramid Description

Uniform width across age groups, tapering at top.

Stationary Pyramid Characteristics

Low birth and death rates; stable population with long life expectancy.

Stationary Pyramid Examples

Developed countries (e.g., USA, France).

Constrictive Pyramid Description

Narrow base and broader middle.

Constrictive Pyramid Characteristics

Low birth rate, aging population, declining growth rate.

Constrictive Pyramid Examples

Developed countries (e.g., Japan, Germany).

Survivorship Curve Definition

Graphic representation of individual numbers expected to survive at any specific age.

Type I Survivorship Description

High survivorship in early/middle life, rapid decline in later years.

Type I Survivorship Characteristics

Low death rate early; high death rate in old age.

Type I Survivorship Examples

Large mammals (e.g., human, lion).

Type II Survivorship Description

Relatively constant mortality rate throughout life.

Type II Survivorship Characteristics

Constant death/survivorship rate regardless of age.

Type II Survivorship Examples

Birds, mice, reptiles.

Type III Survivorship Description

High mortality rate immediately after birth, few survive to adulthood.

Type III Survivorship Characteristics

High early death rate; survivors live longer.

Type III Survivorship Examples

Fishes, inverts, trees.

Life History Definition

Describes lifespan, behavior, and reproductive strategy across a spectrum (r-selected vs K-selected).

r-Strategist Reproduction Rate

High

K-Strategist Reproduction Rate

Low

r-Strategist Offspring Number

Many

K-Strategist Offspring Number

Few

r-Strategist Parental Care

Little or none

K-Strategist Parental Care

Extensive

r-Strategist Maturation Time

Short

K-Strategist Maturation Time

Long

r-Strategist Lifespan

Short

K-Strategist Lifespan

Long

r-Strategist Survivorship Curve

Typically Type III

K-Strategist Survivorship Curve

Typically Type I

r-Strategist Population Growth

Rapid, exponential in ideal conditions

K-Strategist Population Growth

Slow, logistic (stabilizes near carrying capacity)

r-Strategist Adaptation

Thrive in unstable or unpredictable environments

K-Strategist Adaptation

Thrive in stable environments

r-Strategist Body Size

Generally small

K-Strategist Body Size

Generally large

r-Strategist Examples

Insects, bacteria, frogs, weeds, rodents

K-Strategist Examples

Elephants, humans, whales, oak trees

Mnemonic for r-strategist

r = reproduce, reproduce, reproduce; values quantity.

Mnemonic for K-strategist

k = kilo (heavy weight); values quality.

Distribution Patterns Definition

Describes how a species is spread out in the area they occupy (Clumped, Uniform, Random).

Clumped Distribution Description

Individuals are grouped in patches or clusters.

Clumped Distribution Factors

Affected by resource availability, social behavior, mating.

Clumped Distribution Examples

Schools of fish, elephant herds, fungi.

Uniform Distribution Description

Individuals are evenly spaced.

Uniform Distribution Factors

Affected by territoriality, competition, human organization.

Uniform Distribution Examples

Penguins nesting, territorial birds, planted crops.

Random Distribution Description

Individuals are spaced unpredictably and irregularly.

Random Distribution Factors

Affected by wind/animal dispersal, stable habitat, low competition.

Random Distribution Examples

Dandelions in a field, scattered forest trees.

Community Level Focus

Focuses on interactions and relationships between different species (competition, predation, symbiosis).

Niche Definition

An organism's role in an ecosystem, including physical space and interactions within that space.

Commensalism (+, 0)

One organism benefits; the other is neither helped nor harmed.

Commensalism Examples

Barnacles on whales, shark and remoras, hermit crab and snail.

Mutualism (+, +)

Both organisms benefit from the relationship.

Mutualism Examples

Lichen (fungus + alga), clownfish and anemone, bees and flowers.

Parasitism (+, -)

One organism (parasite) benefits; the other (host) is harmed but usually not killed immediately.

Parasitism Subtype: Parasitoidism

Host is killed. Example: Aphelinid wasps.

Ectoparasite Examples

Lice, tick, mite.

Endoparasite Examples

Roundworm (Ascaris sp.), tapeworm (Taenia sp.), Plasmodium sp.

Amensalism (0, -)

One organism harms another without any benefit to itself.

Amensalism Examples

Penicillin mold vs bacteria; elephant stepping on ant hill; humans walking on grass.

Predation (+, -)

One organism (predator) feeds on another (prey).

Predation Dynamic Equations

• prey = + predator; + predator = - prey; - prey = - predator; - predator = + prey.

Competition (-, -)

Organisms compete for limited resources (food, water, mates, space).

Competition Mechanics

• competition = + proximity, same resources; - competition = resource partitioning, niche differentiation.

Scavenging Definition

Organisms consume decaying or dead biomass instead of killing prey.

Scavenging Examples

Vultures and hyenas feeding on carcasses.

Saprophytism Definition

Organisms feed on dead and decaying organic matter, aiding nutrient cycling.

Saprophytism Examples

Fungi (mushrooms), some bacteria and plants.

Gause's Law (Competitive Exclusion Principle)

Two species competing for the exact same limited resources cannot coexist stably at constant population values.

Succession Definition

Sequential change in ecological community composition over time driven by disturbances, competition, and interactions.

Primary Succession Starting Point

Begins in lifeless areas with no soil (e.g., bare rock, lava).

Secondary Succession Starting Point

Begins in areas where a disturbance cleared life but left soil (e.g., after fire, flood).

Primary Succession Soil Presence

No initial soil; soil must be formed.

Secondary Succession Soil Presence

Soil already present.

Primary Succession Pioneer Species

Lichens, mosses (organisms that grow on bare rock).

Secondary Succession Pioneer Species

Grasses, herbs, fast-growing plants.

Primary Succession Time Required

Very slow (hundreds to thousands of years).

Secondary Succession Time Required

Faster (decades to centuries).

Primary Succession Biodiversity Development

Gradual increase over a long period.

Secondary Succession Biodiversity Development

Rapid recovery of biodiversity.

Primary Succession Examples

Volcanic islands, glacial retreats.

Secondary Succession Examples

Abandoned farmland, forest after wildfire.

Ecosystem Level Focus

Explores relationships between living organisms and their environment (energy flow, nutrient cycling, human impact).

Food Chain Definition

A linear sequence showing who eats whom.

Food Web Definition

A complex network of interconnected food chains.

Food Chain Structure & Pathways

Simple straight line; single pathway; less stable.

Food Web Structure & Pathways

Complex with multiple links/interactions; multiple pathways; more stable due to alternatives.

Food Chain Energy Flow

One direction, from producer to top consumer. Example: Grass -> Grasshopper -> Frog -> Snake -> Hawk.

Producers (Autotrophs) Definition

Produce food for themselves/others using energy and simple inorganic molecules.