Ecology and Ecosystem Dynamics: Key Concepts and Cycles

Ecology

The scientific study of how organisms interact with each other and their environment.

Levels of Ecological Organization

Organism, Population, Community, Ecosystem, Biome, Biosphere.

Biotic factors

Living components of an ecosystem (plants, animals, fungi, bacteria).

Abiotic factors

Nonliving components of an ecosystem (temperature, water, sunlight, soil, climate).

Habitat

The physical environment where an organism lives.

Niche

The role an organism plays in its environment (its job, how it gets food, how it interacts).

Interspecific interactions

Interactions between different species (e.g., competition, predation).

Intraspecific interactions

Interactions within the same species (e.g., mating, competition for mates).

CHNOPS

The six most common elements in organic molecules (Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur).

Macromolecules

Four major biomolecules: carbohydrates, lipids, proteins, nucleic acids.

Biogeochemical cycles

Pathways by which elements and matter move through living and nonliving systems.

Water cycle

Evaporation, condensation, precipitation, infiltration, transpiration.

Carbon cycle

Photosynthesis, respiration, decomposition, fossil fuels, combustion.

Nitrogen cycle

Nitrogen fixation, nitrification, assimilation, ammonification, denitrification.

Phosphorus cycle

Weathering of rocks, absorption by plants, movement through food webs, return to soil.

Reservoirs

Major storage areas of nutrients (Water: oceans; Carbon: atmosphere/fossil fuels; Nitrogen: atmosphere; Phosphorus: rocks/soil).

Predation

One organism kills and eats another.

Herbivory

Consumption of plants by animals.

Defense mechanisms

Adaptations to avoid predation (camouflage, mimicry, toxins, spines, shells, behavior).

Resource partitioning

When species divide resources to reduce competition.

Competitive exclusion principle

Two species competing for the same niche cannot coexist indefinitely.

Species richness

Number of different species in a community.

Species abundance (evenness)

Proportion of each species in a community.

Simpson's diversity index

A measure of biodiversity and ecosystem health.

Symbiosis

Long-term biological interaction between two organisms.

Mutualism

Both benefit from the relationship.

Commensalism

One benefits, other unaffected.

Parasitism

One benefits, one harmed.

Lichen

Symbiosis between fungus and photosynthetic algae/cyanobacteria.

Keystone species

Species that have a disproportionate impact on community structure.

Invasive species

Non-native species that disrupt ecosystems.

Succession

Predictable changes in community composition over time.

Primary succession

Occurs where no soil exists (bare rock).

Secondary succession

Occurs where soil remains after disturbance (fire, hurricane).

Pioneer species

First species to colonize barren environments (lichens, mosses).

Climax community

Stable, mature community at the end of succession.

Energy flow vs matter cycle

Energy flows one way (sun → producers → consumers → heat); matter cycles.

Autotrophs

Producers that make their own food (plants, algae).

Heterotrophs

Consumers that rely on others for food.

Herbivores

Eat plants.

Carnivores

Eat animals.

Omnivores

Eat both plants and animals.

Detritivores

Eat detritus/dead matter.

Decomposers

Break down organic material (fungi, bacteria).

Scavengers

Consume carcasses of dead animals.

Food web

Shows feeding relationships in an ecosystem.

Food chain

Linear sequence of energy transfer.

Trophic levels

Positions in a food chain (producers, primary consumers, secondary consumers, etc.).

Ecological pyramids

Show energy, biomass, or numbers at each trophic level.

Eutrophication

Nutrient enrichment → algal blooms → oxygen depletion.

Acid precipitation

Rain with low pH due to sulfur/nitrogen oxides.

Biomagnification

Increasing concentration of toxins up the food chain.

Population size (N)

Total number of individuals in a population.

Population density

Number of individuals per unit area.

Population dispersion patterns

Clumped, uniform, or random spacing of individuals.

Density-dependent factors

Limiting factors that increase with population size (disease, competition, predation).

Density-independent factors

Affect populations regardless of size (natural disasters, climate).

Carrying capacity (K)

Maximum population size the environment can sustain.

Exponential growth (J-curve)

Growth without limits.

Logistic growth (S-curve)

Growth slows near carrying capacity.

Survivorship curves

Type I: low early death; Type II: constant death; Type III: high early death.

Age distribution patterns

Show structure of population: growing, stable, declining.

r-selected species

High reproduction, low parental care, unstable environments.

K-selected species

Low reproduction, high parental care, stable environments.

Innate behavior

Inherited, instinctual behaviors (migration, reflexes).

Learned behavior

Modified by experience (tool use, language, problem-solving).

Taxis

Directed movement toward/away from a stimulus.

Kinesis

Random movement in response to stimulus.

Altruistic behavior

Behavior that reduces individual fitness but increases fitness of relatives.

Kin selection

Altruism toward relatives to pass on shared genes.

Habituation

Learning to ignore repeated, harmless stimuli.

Imprinting

Irreversible learning during a sensitive period (ducklings following mother).

Classical conditioning (Pavlov)

Learning to associate a neutral stimulus with a response.

Operant conditioning (Skinner)

Learning through rewards and punishments.