APES Ecosystem Fundamentals: Biomes, Food Webs, Cycles & Human Impact

Scientific Method

Steps (7 total): Observation → Question → Hypothesis → Experiment → Data Collection → Analysis → Conclusion

Independent Variable (IV)

Air pollution exposure

Dependent Variable (DV)

Dementia development

Control

Rate in less polluted areas

Constant

Age, nationality, initial complaint

Hypothesis

↑ Pollution → ↑ Dementia risk

Individual

One organism (elk)

Population

Same species group (elk herd)

Community

All living organisms in an area

Ecosystem

Living + nonliving things (plants, animals, soil, air, water)

Biome

Large area w/ similar climate → determines species (ex: rainforest)

Mutualism

(+/+) → Both benefit (coral & algae)

Commensalism

(+/0) → One benefits, other unaffected (bird nest in tree)

Parasitism

(+/−) → Parasite benefits, host harmed (tapeworms, mosquitoes)

Competition

Reduces population size

Predation

(+/−): True predators = kill prey (lion/zebra), Herbivores = eat plants (giraffe/tree), Parasites = energy from host, don't usually kill, Parasitoids = lay eggs in host, larvae kill host

Temporal Resource Partitioning

Different times (wolves at night, coyotes by day)

Spatial Resource Partitioning

Different spaces (roots at different depths)

Morphological Resource Partitioning

Different features (beak size for food type)

Tropical Rainforest

Warm, wet, high biodiversity

Tropical Dry Forest

Short rainy season, long dry, deciduous trees

Savanna

Seasonal rainfall & temp, grass + scattered trees

Desert

Driest (<25 cm rain), cacti, water storage

Temperate Grassland

Hot summers, cold winters, fertile soil, fire/grazing prevent trees

Chaparral

Hot/dry summers, cool/wet winters, fire-adapted shrubs

Temperate Deciduous Forest

4 seasons, deciduous trees

Temperate Rainforest

Mild temps, high rain, conifers, mosses

Boreal Forest (Taiga)

Cold, conifers, nutrient-poor soil

Tundra

coldest, permafrost, mosses & low plants

Biodiversity

measure of ecosystem health

Climate factors

temperature + rainfall → predict biome type & vegetation

Climate graphs (climatograms)

show rainfall + temp patterns

Great Rift Valley

a geographical feature impacting biomes

Woodland

a biome characterized by trees and shrubs

Grassland

biome covering large parts of Africa

Energy Pyramid Rule

~10% of energy moves to the next trophic level

Producers

organisms that use sunlight to make energy via photosynthesis

Photosynthesis

CO₂ + H₂O + sunlight → glucose + O₂

Respiration

All organisms convert glucose + O₂ → energy + CO₂ + H₂O

Consumers

organisms that cannot photosynthesize, rely on other organisms

Primary consumers

herbivores that eat producers

Secondary consumers

carnivores that eat primary consumers

Tertiary consumers

carnivores that eat secondary consumers

Food chains

show linear energy flow

Food webs

more realistic representation of energy flow in ecosystems

GPP (Gross Primary Productivity)

Total solar energy captured by producers

NPP (Net Primary Productivity)

GPP - energy used in respiration (energy available to consumers)

Hydrologic Cycle

Movement of water through evaporation, transpiration, precipitation, runoff.

Evapotranspiration

Evaporation + transpiration.

Carbon Cycle

Carbon moves via photosynthesis, respiration, decomposition, combustion.

Human Impact on Carbon Cycle

Humans add CO₂ by burning fossil fuels.

Nitrogen Cycle

Includes nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.

Nitrogen Fixation

N₂ → usable NH₃/NH₄⁺/NO₃⁻ (by bacteria, lightning, or fertilizers).

Nitrification

NH₄⁺ → NO₂⁻ → NO₃⁻.

Assimilation

Producers absorb nitrogen into tissues.

Ammonification

Decomposers turn waste/dead matter into NH₄⁺.

Denitrification

NO₃⁻ → N₂ gas, returns to atmosphere.

Human Impact on Nitrogen Cycle

Humans alter with fertilizers, pollution, eutrophication.

Phosphorus Cycle

No gas phase. Originates from rock weathering/mining, moves through soil and water.

Human Impact on Phosphorus Cycle

Fertilizers and detergents → algal blooms → hypoxia/dead zones.

Sulfur Cycle

Stored in rocks, released by weathering, volcanic eruptions, burning fossil fuels.

Sulfur in Atmosphere

SO₂ + H₂O → sulfuric acid → acid rain.

Ecosystem Resistance

How much a disturbance affects flows of energy/matter.

Ecosystem Resilience

How quickly an ecosystem recovers after disturbance.

Intermediate Disturbance Hypothesis

Moderate disturbances → highest biodiversity.

Human Impacts on Ecosystems

Deforestation → erosion, nutrient loss; Agriculture & runoff → fertilizer pollution, eutrophication; Fossil fuel combustion → CO₂ emissions (climate change), sulfur → acid rain; Overhunting & poaching disrupt food webs.

Ecosystem diversity

# of different habitats

Species diversity

# of species + evenness of populations

Genetic diversity

Variation of genes in a population

Richness (r)

# of species present

Evenness (E)

Balance in population sizes across species

Shannon Diversity Index (H)

Compares diversity levels; Higher H = more diverse ecosystem

Species Evenness (E)

E = \dfrac{H}{H_{max}}; Range 0-1 (closer to 1 = more balanced)

Resilience

Ability to bounce back after disturbance (fire, storm, deforestation, flood)

Bottleneck Events

Natural disasters or human habitat destruction that drastically reduce population size

Inbreeding Depression

Higher chance of related mating in small populations causing genetic defects

Diversity & Stability

More diversity → more stable food webs

Climate change drivers

Ranked: food production, power generation, manufacturing, deforestation, transportation, consumption, energy use

High richness

More quality resources (soil, H₂O)

High evenness

No one species dominates

Roles in Lab Field Study

Land Surveyor, Collector, Identifier

Quadrat method

Square/rectangular plot for counting species

Diversity tends to increase

Toward the equator

Higher biodiversity

Higher resilience (more species to regrow, stabilize soil, provide food & shelter)

High genetic diversity

Better survival under stress (drought, disease, famine)