Species, Habitats & Niches (DP IB Environmental Systems & Societies (ESS))

Species, Habitats & Niches

Species

• A species is a group of organisms sharing common characteristics that interbreed to produce fertile offspring

  • Members of the same species share a gene pool, meaning that they can breed and produce offspring with similar traits

• The scientific name of a species consists of two words, the genus and the specific epithet (the second part of the name that identifies the species as unique), e.g. Homo sapiens (humans)

  • The naming system is called binomial nomenclature and is internationally recognised

Habitat

• A habitat is the environment in which a species normally lives

• Habitats can be characterised by abiotic and biotic factors

• Organisms adapt to their habitat through natural selection, in order to survive and reproduce successfully

Niche

• A niche describes the particular set of abiotic and biotic conditions and resources to which an organism or population responds

• A niche can only be occupied by one species, meaning that every individual species has its own unique niche

• If two species try to occupy the same niche, they will compete with each other for the same resources

  • One of the species will be more successful and out-compete the other species until only one species is left and the other is either forced to occupy a new, slightly different niche or to go extinct from the habitat or ecosystem altogether

• For example, the three North American warbler species shown below all occupy the same habitat (spruces and other conifer trees) but occupy slightly different niches as each species feeds at a different height within the trees

  • This avoids competition between the three species, allowing them to co-exist closely with each other in the same habitat

Although it appears as though these three species share the same niche, they actually spend their time feeding in different parts of spruces and other conifer trees

Fundamental vs Realised Niche

• The fundamental niche describes:

The full range of conditions and resources in which a species could survive and reproduce

• The realised niche describes:

The actual conditions and resources in which a species exists due to biotic interactions

• An example of a fundamental niche compared to a realised niche can be seen in the case of the barnacle species Chthamalus dalli

  • Its fundamental niche includes a wide range of rocky intertidal areas in the Pacific Northwest, where it can attach to a variety of substrates and tolerate a wide range of temperature and salinity conditions

  • However, in reality, the realised niche of this species is much smaller or 'narrower' due to competition with other barnacle species, such as Balanus glandula, for space and resources

  • As a result, the actual range of Chthamalus dalli is restricted to areas where Balanus glandula is absent or scarce, such as higher up on the shore, where it is exposed to air for longer periods of time and can avoid competition with Balanus glandula for space and resources

  • Therefore, the realised niche of Chthamalus dallia is smaller than its fundamental niche due to the biotic interactions with other species

An Example of a Fundamental Niche and a Realised Niche

Fundamental Niche	Realised Niche
The theoretical niche of a species	Where a species actually lives
The niche a species would occupy if there were no limiting factors on the environment or resources the species could use	The niche that a species actually occupies, in the presence of competitor species
No competition for resources, no predation	Competition for resources and predation occurs
Large in size	Small in size