Aquatic Ecosystems: Factors, Niches, Biodiversity

Limiting Factors in Aquatic Ecosystems

In aquatic ecosystems, the following are the limiting factors:

Salinity

• Freshwater, as in rivers.
• Seawater, as in seas and oceans.
• Brackish water, as in marshes.

Living things are adapted to the salinity value of their aquatic environment. Very few species, such as salmon, can live in all of them.

Light Penetration

Filtered light entering the water decreases in intensity with depth. There are three zones:

• Photic zone: Sufficient light for photosynthesis.
• Oligophotic zone: Low light levels.
• Aphotic zone: Total darkness.

Temperature

Temperature determines the amount of dissolved oxygen; less oxygen at higher temperatures. Changes in ocean temperature are responsible for ocean currents that distribute nutrients.

Biotic Factors

a) Competition: Occurs when individuals struggle for food, living space, and reproduction. One individual benefits, and another is harmed.

b) Cooperation: Individuals work together towards a common goal. It is a win-win situation. Examples include:

• Social insects where there is a division of labor.
• Temporary groups that gather to find food, defend against predators, or migrate.

Relationships between different animal species are called interspecific.

c) Predation: One species (the predator) benefits by feeding on another. This includes true predators, grazers, and parasites.

d) Mutualism: Interacting species mutually benefit. This can occur when:

• Two species live separately.
• Two species unite to form a new individual (symbiosis).

Ecological Niche

An ecological niche is the function a species plays in an ecosystem. To explain a species' ecological niche, consider:

• Its environment (habitat).
• Its nutrition.
• Its relationships with other species.

There are two types of species according to their ecological niche:

• Specialists: Occupy a very specific ecological niche.
• Opportunists: Occupy a wide range of ecological niches.

Biodiversity

Biodiversity is the collection of all species on Earth. Human actions are causing a loss of biodiversity through:

• Destruction and fragmentation of natural habitats.
• Introduction of opportunistic exotic species.