Bio150 Exam 3

Ecology

Study of interactions between organisms and their environment

Biome

A region defined by dominant vegetation

Main factors that determine biomes

Temperature and precipitation

Abiotic factors

Nonliving environmental factors (temperature

Biotic factors

Living components of an ecosystem (organisms

Why are the tropics warmer than the poles?

Sunlight hits the tropics at a higher (more direct) angle

Why are polar regions colder?

Sunlight hits at a lower angle and is spread out

Earth’s tilt

23.5°

Effect of increased Earth tilt

More extreme seasons (hotter summers

Global air circulation

Movement of air that distributes heat and moisture around Earth

Rain shadow effect

Wet air rises and rains on one side of a mountain; dry air descends on the other side creating deserts

Wind direction for Atacama Desert rain shadow

East to west

How oceans influence climate

Water has high specific heat

Coastal vs inland climates

Coastal = mild temperatures/Inland = more extreme temperatures

Ocean currents (gyres)

Circular currents that move warm and cold water and affect climate

Biome definition (again

important)

Key abiotic conditions of biomes

Temperature

Net Primary Productivity (NPP)

Total biomass produced (energy available to consumers)

Niche

The role or “place” of an organism in its environment

Ecological niche (formal definition)

The range of environmental conditions where a species can survive

Tolerance range

Range of environmental conditions a species can survive in

Hutchinson niche concept

Niche is an n-dimensional hypervolume (many environmental factors combined)

Fundamental niche

All possible conditions a species could live in (no competition or limits)

Realized niche

Actual conditions where a species lives (limited by interactions)

Relationship between niches

Realized niche is always ≤ fundamental niche

What limits realized niche?

Biotic factors (competition

Example of niche limitation

Bird limited by disease → smaller realized niche

Community

Group of interacting species living in the same area

Species interactions are classified by

Their effect on fitness (+

Fitness

Ability to survive and reproduce

Fitness indicators

Population size

Mutualism (+/+)

Both species benefit

Competition (-/-)

Both species are harmed

Predation (+/-)

One benefits

Parasitism (+/-)

One benefits

Commensalism (+/0)

One benefits

Competitive exclusion principle

Two species with identical niches cannot coexist indefinitely

Result of competitive exclusion

One species outcompetes the other

Why species coexist in nature

They reduce competition

Niche partitioning

Species use different resources to reduce competition

Example of niche partitioning

Species feed in different areas or times

Character displacement

Evolutionary changes in traits that reduce competition

Example of character displacement

Different beak sizes in birds

Relationship between character displacement & niche partitioning

Character displacement can lead to niche partitioning

Main source of energy in ecosystems

The sun

Primary producers

Organisms that make their own food (plants)

Autotrophs

Another term for primary producers

Photosynthesis

Process where producers convert sunlight into chemical energy

GPP (Gross Primary Productivity)

Total energy captured by producers

What happens to GPP energy?

Used for respiration

NPP (Net Primary Productivity)

Energy remaining after respiration and heat loss

NPP formula

NPP = GPP − energy used in respiration

Why energy transfer is inefficient

Energy is lost as heat at each trophic level

Trophic levels

Positions in a food chain (producer → consumer)

Bottom-up control

Ecosystem controlled by resources (nutrients

Top-down control

Ecosystem controlled by predators

Decomposers

Organisms that break down dead material

Importance of decomposers

Recycle nutrients back into ecosystem

What happens without decomposers?

Nutrients would not be recycled → ecosystem collapse

Biogeochemical cycles

Movement of nutrients between biotic (living) and abiotic (nonliving) reservoirs

Biotic reservoirs

Living components of ecosystems (plants, animals, microbes)

Abiotic reservoirs

Nonliving components (air, soil, water, rocks)

Carbon cycle

Movement of carbon between atmosphere, organisms, and environment

How carbon enters ecosystems

Photosynthesis (CO₂ → organic molecules)

How carbon returns to atmosphere

Respiration, decomposition, combustion

Nitrogen cycle

Movement of nitrogen through atmosphere, soil, and organisms

Nitrogen fixation

Conversion of N₂ gas into usable ammonia (NH₃) by bacteria

Nitrification

Conversion of ammonia (NH₃) → nitrite (NO₂⁻) → nitrate (NO₃⁻)

Assimilation (nitrogen)

Plants take up nitrogen and incorporate it into tissues

Ammonification

Conversion of organic nitrogen → ammonia during decomposition

Denitrification

Conversion of nitrate (NO₃⁻) → nitrogen gas (N₂)

Key organisms in nitrogen cycle

Bacteria

Phosphorus cycle

Movement of phosphorus through rocks, soil, and organisms

Unique feature of phosphorus cycle

No atmospheric phase

Source of phosphorus

Weathering of rocks

Limiting nutrient

A nutrient that limits growth when scarce

Eutrophication

Excess nutrients cause algal blooms → oxygen depletion → organism death

Steps of eutrophication

• Nutrients increase

• Algae bloom

• Oxygen drops

• Fish die

Main human cause of eutrophication

Fertilizer runoff

Direct effects of climate change

Temperature increase, precipitation changes

Indirect effects of climate change

Changes in species interactions and food webs

Three species responses to climate change

Move, adapt, or go extinct

Biodiversity

Biological diversity of life

Species diversity

Combination of species richness and evenness

Species richness

Number of species in a community

Species evenness

How evenly individuals are distributed among species

High species diversity

High richness + high evenness

Low species diversity

Low richness or uneven distribution

Phylogenetic diversity

Evolutionary differences among species

High phylogenetic diversity

Species are distantly related

Low phylogenetic diversity

Species are closely related

Functional diversity

Range of ecological roles or traits in a community

High functional diversity

Many different functional roles

Low functional diversity

Few functional roles

Tradeoff in biodiversity conservation

Cannot always maximize both functional and phylogenetic diversity

Speciation

Formation of new species

Effect of speciation on biodiversity

Increases biodiversity

Extinction

Loss of species

Effect of extinction on biodiversity

Decreases biodiversity

Background extinction

Normal, low rate of extinction