Ecology

Concept of ecology and ecosystem

Ecology is the branch of biology that studies the interrelationship between organisms and their environment, and among organisms themselves. The environment of an organism has two components:

• Abiotic (physical) factors: non-living components such as temperature, light, water, soil, air and minerals, which determine where an organism can live and how it functions.
• Biotic factors: the living components, that is, all the other organisms (plants, animals, microbes) sharing the same habitat.

An ecosystem is a structural and functional unit of nature in which a community of living organisms (biotic component) interacts with its physical environment (abiotic component) through a continuous exchange of matter and energy. Ecosystems can be natural (a pond, a forest, a river) or artificial (an aquarium, a crop field).

Species interactions

Organisms sharing an ecosystem interact in several characteristic ways:

• Competition: two species/individuals struggle for the same limited resource (food, space, light).
• Predation: one organism (predator) kills and feeds on another (prey).
• Parasitism: one organism (parasite) lives on or in another (host) and derives nutrition at the host's expense, generally harming it.
• Commensalism: one species benefits while the other is neither helped nor harmed (e.g. epiphytic orchids growing on a tree).
• Mutualism (symbiosis): both interacting species benefit (e.g. Rhizobium bacteria and legume roots).

Structural and functional aspects of the pond ecosystem

A pond is a small, self-contained, standing (lentic) freshwater ecosystem, and is one of the simplest complete ecosystems to study. Structurally it has:

• Abiotic component: water, dissolved gases and minerals, sunlight, and the mud/soil substrate.
• Producers: photosynthetic organisms that trap solar energy and manufacture food.
  • Macrophytes: rooted or floating plants with differentiated stems and leaves, e.g. Pistia, Trapa, lotus.
  • Microphytes (phytoplankton): minute floating or suspended algae, e.g. Volvox, Nostoc, Spirogyra.
• Consumers: heterotrophic animals that depend directly or indirectly on producers.
  • Primary consumers (herbivores): feed on producers, e.g. tadpoles, small crustaceans, mites.
  • Secondary consumers (carnivores): feed on primary consumers, e.g. small fishes, predatory insects.
  • Tertiary consumers (top carnivores): feed on secondary consumers, e.g. large fishes, frogs, crocodiles.
• Decomposers: saprophytic bacteria and fungi that break down the dead remains of producers and consumers into simple inorganic substances, returning nutrients to the water and mud for reuse by producers.

Functionally, the pond ecosystem works through the one-way flow of energy (entering as sunlight, leaving as heat) and the cyclic exchange of nutrients between the biotic and abiotic components.

Structural and functional aspects of the forest ecosystem

A forest is a larger, more complex terrestrial ecosystem dominated by trees.

• Abiotic component: soil, humus, light, temperature and rainfall of the region.
• Producers: trees, shrubs, herbs and grasses of several storeys/layers (canopy, understorey, shrub and ground layer).
• Consumers: herbivores (deer, insects, rodents), carnivores (leopards, birds of prey, snakes) and omnivores, arranged in several interconnected trophic levels.
• Decomposers: fungi, bacteria and detritivores (earthworms, termites) that break down the large amount of leaf litter and dead wood, recycling nutrients back into the soil.

Because a forest has many more species and food links than a pond, it is structurally more complex but works on the same functional principle: fixation of solar energy by producers, its transfer through several consumer levels, and its final dissipation as heat, along with cyclic recycling of nutrients by decomposers.