Unit 2 Biodiversity: How Organisms Cope with Environmental Conditions

Ecological tolerance

The range of environmental (abiotic) conditions within which a species can survive, grow, and successfully reproduce.

Abiotic factors

Nonliving environmental conditions (e.g., temperature, pH, salinity, water availability, dissolved oxygen) that affect organisms.

Niche

A species’ role in an ecosystem, including the resources it uses and the environmental conditions it requires.

Limiting factor

An environmental variable that, when too low or too high, restricts the growth, abundance, or distribution of an organism or population.

Shelford’s Law of Tolerance

Principle that a species’ presence, abundance, and success depend on whether environmental conditions remain within its tolerance limits.

Tolerance range

The full span of conditions (for a specific abiotic factor) under which a species can persist by surviving and reproducing.

Tolerance curve

A graph showing species performance across a gradient of an environmental factor (x-axis = condition; y-axis = performance such as growth or reproduction).

Zone of intolerance

Part of a tolerance curve where conditions are too extreme for long-term survival or reproduction.

Zone of physiological stress

Range where a species can survive but with reduced growth and reproduction because energy is diverted to maintenance.

Optimal range (optimum)

The conditions under which a species performs best (highest growth, reproduction, and/or population density).

Generalist species

Species with broad tolerance and flexible resource/habitat use; often better able to persist under environmental change.

Specialist species

Species with narrow tolerance and/or specific habitat/resource requirements; often more vulnerable to disturbance or rapid change.

Dissolved oxygen (DO)

Oxygen gas available in water; a key limiting factor for many aquatic organisms, especially when water warms.

Thermal pollution

Human-caused warming of a water body (e.g., power plant discharge) that can reduce dissolved oxygen and stress aquatic life.

Estuary

Coastal ecosystem where freshwater mixes with seawater; salinity often fluctuates with tides and rainfall.

Osmoregulation

Physiological process of regulating internal water and salt balance; important for organisms living in changing salinity (e.g., estuaries).

Adaptation

An inherited trait that increases an organism’s survival and reproductive success in a particular environment.

Acclimation (acclimatization)

A short-term, non-inherited adjustment by an individual organism in response to environmental change.

Natural selection

Process where heritable traits that improve survival and reproduction become more common in a population over generations.

Structural (morphological) adaptation

A physical body feature that improves survival/reproduction in an environment (e.g., spines, thick fur, blubber).

Physiological adaptation

An internal functional trait that improves survival/reproduction (e.g., concentrated urine, salt regulation, CAM photosynthesis).

Behavioral adaptation

An action pattern that increases survival/reproduction (e.g., nocturnal activity, migration, burrowing).

Trade-off

A cost associated with an adaptation: improving performance in one context can reduce performance in another.

CAM photosynthesis

Plant pathway where stomata open at night to reduce water loss while still allowing carbon uptake; beneficial in hot, dry environments.

Mycorrhizae

Mutualistic association between plant roots and fungi that increases nutrient uptake, especially in nutrient-poor soils.