MYP Biology 6.1 Habitat Notes

What Is a Habitat?

1. A habitat is the specific environment where an organism lives, grows, and reproduces.
2. It includes abiotic (nonliving) and biotic (living) factors that determine whether a species can survive there.
3. Each species occupies habitats where conditions fall within its tolerance range, the limits it can survive and function.

What Abiotic Factors Define a Habitat?

1. Abiotic factors shape the physical conditions of an environment.
2. An organism can only survive where these conditions fall within its tolerance range.

Key abiotic factors

1. Temperature: affects enzyme activity and metabolic rate.
2. Light intensity: controls photosynthesis in plants and behaviour in animals.
3. Moisture levels: determine water availability for survival and reproduction.
4. pH: influences nutrient absorption and chemical reactions in soil or water.
5. Oxygen availability: essential for aerobic respiration.
6. Salinity: affects water balance in aquatic organisms.
7. Soil composition: determines nutrient levels and root stability.

What Biotic Factors Shape a Habitat?

1. Biotic factors involve interactions among organisms.
2. These determine population sizes, behaviour, and where organisms can live.

Key biotic factors

1. Food availability: limits population size and distribution.
2. Predation: influences behaviour and habitat choice.
3. Competition: occurs when species need the same resource.
4. Mutualism: both organisms benefit (e.g., bees pollinating flowers).
5. Parasitism: one organism benefits at the other's expense.

What Types of Habitats Exist?

1. Habitats can be grouped into terrestrial, aquatic, and extreme environments.
2. Each is shaped by a distinct combination of abiotic and biotic factors.

Terrestrial habitats

1. Forests
   1. High biodiversity and layered vegetation.
   2. Abiotic drivers: moderate temperature + moisture.
2. Deserts
   1. Very low rainfall and extreme temperature changes.
   2. Abiotic driver: low moisture.
3. Grasslands
   1. Dominated by grasses, few trees due to limited rainfall.
   2. Abiotic driver: seasonal drought.
4. Polar Regions
   1. Extremely cold, low plant diversity.
   2. Abiotic driver: temperature.

Aquatic habitats

1. Freshwater (rivers, lakes, ponds): Low salinity, oxygen levels vary with temperature.
2. Marine (oceans, coral reefs, estuaries): High salinity, stable temperatures.

Extreme habitats

1. Hot springs (thermophiles)
   1. Driver: very high temperature
   2. Adaptations: heat‑stable enzymes; reinforced proteins and membranes
2. Hydrothermal vents (deep sea)
   1. Drivers: high pressure, heat, toxic chemicals (e.g., hydrogen sulfide)
   2. Adaptations: barophile‑tolerant membranes; chemosynthetic bacteria form the food base
3. Hypersaline lakes
   1. Driver: extreme salinity
   2. Adaptations: halophilic ion pumps; intracellular salt balance
4. Acidic or alkaline waters/soils
   1. Driver: low pH (acidic) or high pH (alkaline)
   2. Adaptations: pH homeostasis, buffering systems
5. Polar/high altitude
   1. Drivers: extreme cold, low oxygen, high UV
   2. Adaptations: antifreeze proteins; compact body forms; UV‑screening pigments
6. Arid deserts
   1. Drivers: severe drought, high heat
   2. Adaptations: water storage; reduced water loss; dormancy during peak stress

What Is a Species’ Range of Tolerance?

1. The range of tolerance is the interval of an environmental factor (e.g., temperature, pH, salinity) within which an organism can survive, grow, and reproduce.
2. It has:
   1. Optimal range: conditions where performance is highest.
   2. Stress zones: sub‑optimal edges where survival is possible but reproduction or growth is reduced.
   3. Limits: beyond upper or lower thresholds, the organism cannot persist.

How Do Abiotic and Biotic Factors Influence Habitat Selection?

Organisms occupy environments where both abiotic and biotic factors allow maximum survival and reproduction.

Abiotic Influences

1. Organisms must live where physical conditions fall within their tolerance range.
2. For instance:
   1. Snakes bask to increase body temperature.
   2. Amphibians breed in moist environments to prevent egg drying.
   3. Carrots grow better in loose, sandy soil where roots can spread.

Biotic Influences

1. Living interactions also shape habitat choice.
2. For instance:
   1. Herbivores migrate to follow seasonal plants (food).
   2. Mice avoid open fields to reduce predation risk.
   3. Trees compete intensely for sunlight in dense forests.