Fauna is the collective term used to describe all the animal life present in a specific region or during a particular time period. This word is often paired with flora, which refers to plant life, and both are collectively known as biota. Zoologists and paleontologists use the concept of fauna to characterize a typical assemblage of animals found in a specific geological layer or geographical area, such as the “Sonoran Desert fauna.”
Defining and Classifying Animal Life
The scientific framework for categorizing fauna places all animals within the Kingdom Animalia, also referred to as Metazoa. Members of this kingdom are multicellular organisms composed of eukaryotic cells, meaning their cells contain a nucleus and other membrane-bound organelles. A fundamental trait of fauna is that they are heterotrophs, meaning they must consume organic material from other organisms for nourishment. Animal cells also lack the rigid cell walls found in plants, which contributes to the mobility characteristic of most animal species.
The taxonomic classification system organizes this vast diversity using a hierarchy that moves from the broad Kingdom down through Phylum, Class, Order, Family, Genus, and finally to Species. The first major division in fauna separates animals into vertebrates and invertebrates. Vertebrates possess a backbone or spinal column and belong to the Phylum Chordata, a group that includes fish, birds, reptiles, amphibians, and mammals. In contrast, invertebrates lack a backbone and comprise the overwhelming majority of animal species on Earth, representing about 96% of all fauna. Major invertebrate phyla include Arthropoda (insects, spiders, crustaceans), Mollusca (snails, clams, squid), and Annelida (segmented worms).
Types of Fauna by Habitat and Size
Fauna can be categorized based on the environment they inhabit, leading to distinct groupings that reflect adaptations to specific conditions. Terrestrial fauna encompasses all animals living primarily on land, ranging from insects and reptiles to large mammals. Aquatic fauna covers animals that live in water, subdivided into marine fauna for oceans and limnofauna for freshwater bodies like lakes and rivers. A specialized group is avifauna, which refers specifically to the birds of a particular region or time period. Other specific ecological classifications exist, such as cryofauna for animals adapted to cold, icy environments, and troglofauna for small creatures that live permanently in caves.
Fauna are also classified according to size, a distinction that reveals important functional roles within ecosystems. Microfauna are microscopic animals, typically measuring less than 0.2 millimeters, and include organisms like rotifers and nematodes. Mesofauna are slightly larger, ranging from about 0.2 millimeters to 2 millimeters, and include springtails and mites. At the opposite end of the scale is megafauna, a term used for very large animals, such as elephants or whales. This term can also apply to soil animals larger than two centimeters, like burrowing rodents.
The Interdependent Role of Fauna in Ecosystems
Fauna plays a fundamental role in maintaining the function and stability of biological systems primarily through its position as consumers in the food web. Animals occupy various trophic levels, consuming other organisms to obtain energy. Herbivores, such as grazing mammals and many insects, consume plant life, forming the primary link between flora and the rest of the animal kingdom. Carnivores consume other animals, regulating prey populations, while omnivores maintain a varied diet of both plants and animals.
Detritivores, which include earthworms and millipedes, are responsible for breaking down dead organic matter and waste. This process is fundamental to nutrient cycling, returning essential elements like carbon, nitrogen, and phosphorus to the soil. The health of ecosystems relies heavily on the interdependent relationship between fauna and flora. Many plants depend on animals for their reproductive success, a key example being pollination, where insects, birds, and bats transfer pollen between flowers.
Animals also act as crucial seed dispersers, consuming fruits and then depositing the seeds elsewhere, enabling plant migration and colonization of new areas. Fauna contributes to the physical structure of the environment; for instance, burrowing animals like moles and termites mix and aerate the soil. This improves soil quality and water retention.