3.2 Abiotic Environmental Factors

Abiotic features represent the non-living physical and chemical components of an ecosystem that influence the survival and reproduction of organisms.
These features are categorized into three primary domains:
- Climate
- Soil (substrate)
- Geography
Every organism possesses an optimum range and a tolerance range for various abiotic factors, which dictates where they can live and how well they thrive.

Optimal range: The specific range of environmental conditions (such as temperature or pH) within which an organism performs at its maximum physiological efficiency and the population density is generally at its highest.
Physiological stress: A state experienced by an organism when it is subjected to environmental conditions that fall outside of its optimal range but remain within its tolerance range. During this state, the organism may survive but will function less effectively.
Tolerance range: The total range of environmental conditions under which an organism can survive, encompassing the optimal range and the zones of physiological stress.
Cryptic organism: An organism that is difficult to observe or detect, often due to camouflage, behavior, or living in inaccessible habitats.
Marginal niche: The zone located at the edges of the optimal range where organisms experience physiological stress.
Lethal range: The environmental conditions that exist outside of an organism's tolerance range, where the organism cannot survive.

The distribution (where organisms are located) and abundance (how many there are) of species within an ecosystem are determined by a combination of biotic and abiotic factors.
Biotic Factors:
- Food availability: The presence and type of nutritional resources.
- Competition for resources: Interactions between individuals or species vying for the same limited assets.
- Predation: The impact of predators on prey populations.
- Disease: The presence of pathogens and their transmission through a population.
Abiotic Factors:
- Space: The physical area required for living and movement.
- Shelter: Protection from environmental extremes and predators.
- Availability of water: Access to potable water for hydration and biological processes.
- Nutrients: The presence of essential minerals and elements.
- Environmental conditions: General physical states such as temperature and humidity.

Temperature: The thermal energy within the environment.
Humidity: The amount of water vapor present in the air.
Wind: Atmospheric movement that affects evaporation and physical stability.
Air currents: Vertical or horizontal movements of air within a specific area.
Water currents: The movement of water in aquatic environments, influencing nutrient distribution and organism locomotion.
pH: The acidity or alkalinity of the environment, measured on a logarithmic scale from $0$ to $14$ .
Availability of light, water, and nutrients: Essential inputs for photosynthesis and cellular function.

pH levels of the soil
Mineral salts and trace elements: Essential inorganic compounds required for plant growth.
Water retention: The ability of the soil to hold water against the force of gravity.

Water currents
Salinity: The concentration of dissolved salts in water, typically measured in parts per thousand ( $\text{ppt}$ ).
Topography: The physical features and layout of the land.
Shelter: Specific structures or landforms used for protection.
Size and depth of an area: The total volume or surface area available to a population.

The relationship between an environmental variable and population size follows a bell-shaped distribution:
- High Population/Optimum Range: Found at the center of the curve where conditions are ideal.
- Low Population/Stressed Range: Occurs on either side of the optimum range; organisms survive but suffer from physiological stress.
- Zero Population/Lethal Range: The extreme ends of the environmental variable where conditions are too harsh for survival.
This model is universal and can be applied to any abiotic factor, such as temperature, salinity, or pH.

Identify: To distinguish, locate, recognize, or name a specific feature. To establish who or what something is or to provide an answer from several possibilities.
Classify: To arrange, distribute, or order items into specific classes or categories based on shared characteristics or qualities.
Compare: To recognize and display the similarities and differences between two or more items, while also recognizing the significance of those points of comparison.
Consider: To think carefully or deliberately about a subject before reaching a decision; to take something into account when forming a judgment; to scrutinize or view something attentively.