B4.2 - Ecological Niches

Ecological niche

The role of a species in an ecosystem - has both biotic and abiotic elements

How species obtain food

By synthesis using light water, CO2 or taking it from other organisms.

To minimize competition, species must specialize, to compete effectively, they must develop adaptations for the mode of nutrition that is their specialism.

Obligate aerobes

Require a constant, continuous oxygen supply, only live in oxic environment

Obligate anaerobes

Inhibited or killed by oxygen so only live in anoxic environment (Clostridium tetani, methanogenic archaea)

Facultative anaerobes

Use oxygen if available so live in oxic or anoxic environment. (E coli)

Photosynthesis

Mode of nutrition in plants, algae and several groups of photosynthetic prokaryotes.

Holozoic nutrition

All animals are heterotrophic - In holozoic nutrition, food is ingested, digested internally, absorbed and assimilated.

Sequence of stage in holozoic nutrition

Ingestion - taking the food into the gut.

Digestion - breaking large food molecules into smaller molecules

Absorption - transport of digested food across the plasma membrane of epidermis cells and thus into the blood and tissues of the body

Assimilation - using digested food across the plasma membrane of epidermis cells and thus into the blood and tissues of the body.

Egestion - voiding undigested material from the end of the gut.

Mixotrophic nutrition

Some protists use both autotrophic and heterotrophic methods of nutrition

Facultative mixotrophs

Can be entirely autotrophic, entirely heterotrophic or use both modes.

Euglena gracilis - has chloroplasts and carries out photosynthesis when light is sufficient. It can also feed on detritus or smaller organisms.

Obligate mixotrophs

Cannot grow unless they utilize both autotrophic and heterotrophic modes of nutrition - the food they consume provides C compounds that they cannot synthesize themselves.

Saprotrophic nutrition

Secrete digestive enzymes into dead organic matter and digest it externally - then absorb the products of digestion.

Saprotrophs - decomposers

Break down C compounds in dead organism and release elements such as nitrogen

Diversity of nutrition in archaea

Metabolically diverse

Use either light, oxidation of inorganic chemicals or oxidation of C compounds to provide energy for ATP production (phototrophic, chemotrophic, heterotrophic)

Dentition and diet

Herbivore teeth - large, flat to grind down fibrous plant tissue

Omnivore teeth - mix of different types of teeth to break down both meat and plants in their diet.

Adaptation of herbivores - leaf eating insect

Have piercing and chewing mouthparts

Beetles - jaw-like mouth parts for biting off, chewing and ingesting leaf

Aphids - tubular mouth parts for piercing leaves or stems to reach phloem sieve tubes and feed on sap.

Adaptation of plants

resist herbivory by producing toxic secondary compounds in seeds and leaves. Some have tough, sharp-pointed spines, so herbivores risk injury

Adaptations of herbivores in response to adaptation of plants

Some herbivores have metabolic adaptations to detoxify these toxins.

Result in plant-herbivore specificity, with only a few species of herbivores adapted to feed on a particular plant.

Adaptation of plant form for harvesting light - tree

Dominant leading shoot that grows rapidly to great height.

Reach the forest canopy where they are unshaded by trees.

Adaptation of plant form - lianas

Climb through other trees (do not have to produce as much xylem tissue)

Adaptation of plant form - epiphytes

Grow on trunks and branches of trees, so they receive higher light intensity than if they grew on forest floors.

Adaptation of plant form - Strangler epiphytes

Climb up the trunks of trees encircling them and outgrowing their branches, to shade out the leaves of the tree.

Adaptation of plant form - Shade tolerant shrubs and herbs

Absorb light reaching the forest floor

Fundamental niche

Potential of a species based on adaptations and tolerance limits

Realized niche

Actual extent of a species niche when in competition with other species - the actual extent of the potential range that species occupies.

Competitive exclusion

If fundamental niches of two species overlap, one species is expected to exclude the other form the part of its range by competition.

Outcompeted species do not have a realized niche.

Every species must have a realized niche that differs from the realized niches of all other species if it is to survive an ecosystem.