Abiotic factors such as temperature, pH, and salinity affect species distribution by determining whether organisms can survive, grow, and reproduce in a particular location. Each species has a range of tolerance for each factor, so its abundance usually decreases as conditions approach the limits of that range.
This is core SL and HL content in Subtopic 2.1, Individuals, populations, communities and ecosystems. An abiotic factor is a non-living physical or chemical component of an environment, while species distribution describes the geographical area or habitats in which a species occurs.
| Abiotic factor | Mechanism affecting distribution | Example |
|---|---|---|
| Temperature | Influences enzyme activity, metabolism, photosynthesis, reproduction, and water loss. Temperatures outside a species' tolerance range reduce survival or reproductive success. | Rising sea temperatures cause coral bleaching on the Great Barrier Reef because corals lose their symbiotic algae. |
| pH | Affects enzyme function, nutrient availability, and the toxicity or solubility of chemicals. Aquatic and soil organisms are often adapted to a limited pH range. | Ocean acidification reduces carbonate availability, making it harder for corals and molluscs to build calcium carbonate structures. |
| Salinity | Affects water movement across cell membranes and therefore osmoregulation. Species unable to maintain their water and ion balance cannot survive at certain salinities. | Along an estuary, freshwater species dominate upstream, while salt-tolerant species occur closer to the sea. |
These factors can act as limiting factors. If salinity exceeds a plant's tolerance, for example, increasing light or nutrient availability will not necessarily allow that plant to survive.
A common misconception is that abiotic factors alone determine distribution. They establish where survival is physically possible, but such as competition, predation, disease, and food availability also affect where a population is actually found.