ib topic 2

2.1 Species and Populations

Ecology: The branch of biology that studies how organisms interact with their environment and other organisms.

Significant Idea #1

• Species: A group of organisms sharing common characteristics that can interbreed and produce fertile offspring.

• Population: A group of the same species living in the same area at the same time, which are capable of interbreeding.

• Habitat: The environment in which a species normally lives.

• Niche: A particular set of abiotic and biotic conditions and resources to which an organism or population responds.

• The "role" or position a species has in its environment (how it makes a living).

• Fundamental Niche: The full range of conditions and resources in which a species could potentially survive and reproduce.

• Realized Niche: The actual conditions and resources in which a species exists due to biotic interactions (like competition).

• Abiotic Factors: Non-living, physical factors that influence organisms and ecosystems (e.g., temperature, sunlight, pH, precipitation).

• Biotic Factors: Interactions between organisms (e.g., predation, disease, competition).

Significant Idea #2 (Population Dynamics)

• Populations change and respond to interactions with the environment.

• Factors affecting population size:

1. Birth rates

2. Mortality (Death rates)

3. Migration:

• Immigration: Moving in.

• Emigration: Moving out.

2.2 & 2.3 Energy Flow and Matter

Significant Idea #1

• Ecosystems are linked together by energy and matter flows.

• Solar Radiation: Enters Earth's atmosphere; some becomes unavailable (absorbed by inorganic matter or reflected back).

• Pathways of energy:

• Loss of radiation through reflection and absorption.

• Only 1–4% of solar energy is available to plants for photosynthesis.

• Photosynthesis: Conversion of light energy into chemical energy.

Productivity Calculations

• Biomass: The living mass of an organism (measured in dry mass).

• GPP (Gross Primary Productivity): Total energy/biomass fixed by producers.

• NPP (Net Primary Productivity): GPP minus respiration (NPP = GPP - R). This is the energy available to the next trophic level.

• GSP (Gross Secondary Productivity): Total energy assimilated by consumers (GSP = Food\ eaten - Fecal\ loss).

• NSP (Net Secondary Productivity): GSP minus respiration (NSP = GSP - R).

Human Impact on Energy Flows

• Anthropogenic activities: Enhanced greenhouse effect \rightarrow Global warming.

• Energy Subsidy: Additional energy that humans have to put into a system (e.g., farming) to maximize yield.

• Simplification: Reducing biodiversity to increase NPP for human use (e.g., monoculture crops).

2.4 Biomes, Zonation, and Succession

Population Interactions

• Carrying Capacity (K): The maximum number of individuals that an environment can sustainably support.

• Limiting Factors: Resources (food, water, space) that slow population growth as it approaches K.

• Competition:

• Intraspecific: Between members of the same species.

• Interspecific: Between different species.

• Symbiosis:

• Parasitism: One benefits, one is harmed.

• Mutualism: Both species benefit.

Growth Curves

• S-Curve (Sigmoid): Shows exponential growth followed by a slowdown as the population reaches carrying capacity.

• J-Curve: Shows exponential growth that often leads to an "overshoot" of carrying capacity followed by a "die-back" (crash).

2.3 The Flow of Matter (Nutrient Cycles)

The Nitrogen Cycle

1. Nitrogen Fixation: N_2 gas from the atmosphere is made available to plants (via bacteria or lightning).

2. Nitrification: Bacteria convert ammonium into nitrites and nitrates.

3. Assimilation: Living organisms take up nitrogen to build proteins/DNA.

4. Ammonification: Decomposers turn organic nitrogen back into ammonium.

5. Denitrification: Bacteria convert nitrates back into N_2 gas.

The Carbon Cycle

• Storages: Fossil fuels, soil, oceans, atmosphere, organisms.

• Flows: Photosynthesis (carbon in), Respiration/Combustion (carbon out).

Human Impacts

• Carbon Budget: Humans are increasing the amount of carbon in the atmosphere by burning fossil fuels and deforestation.

• Eutrophication: Excess nitrates (from fertilizers/sewage) leach into water bodies, causing algae blooms, oxygen depletion (hypoxia), and fish kills.