Ecological Niches (DP IB Biology)

An organism's mode of nutrition is the way in which it acquires organic molecules to fuel respiration.

Photosynthesis functions as a mode of nutrition by transferring light energy into a chemical form that can be used by living organisms.

Photosynthetic organisms include:

• plants

• algae

• photosynthetic bacteria, such as cyanobacteria

Holozoic nutrition is a form of heterotrophy where organisms ingest, internally digest, absorb, and assimilate organic molecules from the tissues of other organisms.

True.

All animals gain their organic molecules from the tissues of other organisms, meaning that they are all heterotrophic.

A mixotroph is an organism that can use both autotrophic and heterotrophic methods of nutrition.

Euglena is a mixotroph that gains organic molecules both by photosynthesis and by ingesting and digesting bacterial cells.

Obligate mixotrophs must constantly use both methods of nutrition, while facultative mixotrophs can survive on one method of nutrition, which may be supplemented by the other.

Saprotrophs are heterotrophs that digest food externally by secreting enzymes onto dead or waste material, then absorbing the digested products.

Fungi and bacteria are common examples of saprotrophs.

The archaea are a group of single-celled organisms that make up one of the three domains.

Archaea can provide energy for ATP production from:

• light (phototrophic)

• oxidation of inorganic chemicals (chemotrophic)

• oxidation of carbon compound (heterotrophic)

The following is suggested by the dentition of chimps and gorillas:

• small jaw muscles in chimps = softer foods, e.g. meat and fruit

• large jaw muscles in gorillas = tougher foods, e.g. plant material

True.

The dentition seen in fossils from extinct hominids can provide clues about their diet.

Teeth do not provide a perfect picture of the diets of extinct hominids because eating would not have been the only role played by teeth; they may also have been involved with, e.g. defending territory.

The presence of large molars in Paranthropus robustus suggests a diet of tough plant material.

Fossil evidence from Homo floresiensis that suggests information about their diet includes:

• Primarily plant eaters:

  • large grinding teeth

  • large jaw

  • tooth abrasions visible under microscope

• May have eaten some meat:

  • skull shape similar to modern humans

The use of fossil skulls to determine early hominid diet is an example of deduction because the deductive process starts with a theory, from which hypotheses can be developed. In the example of hominid dentition:

• There are theories about the relationship between dentition and diet that have been developed from studying living hominids

  • E.g. large molars = diet of vegetation

• These theories can be used to develop hypotheses about the diets of extinct hominids

  • E.g. P. robustus had large grinding teeth, so therefore had a diet of vegetation

A herbivore is a heterotroph that feeds on plants.

Adaptations of insect mouthparts for herbivory include:

• stylets that pierce plant tissue, e.g. in aphids

• mandibles that cut through plant tissue by chewing, e.g. in caterpillars

Mechanical defences against herbivory in plants include:

• cacti have sharp spines

• nettles have tiny hairs that contain toxins

• thick bark

• hairy leaves

Plants may use secondary compounds as a chemical defence against herbivory as follows:

• compounds such as digitalis, atropine and caffeine may be toxic

• compounds such as tannins may taste bitter

Mammals may avoid being harmed by plant toxins as follows:

• the ability to neutralise toxins, e.g. with neutralising proteins

• cautious sampling to determine whether a plant will have negative effects

Chemical adaptations in predators include:

• snakes, scorpions and spiders can produce venoms

• chemical mimicry may be used to attract prey animals

• chemical crypsis, or scent camouflage, allows ambush predators to lie in wait for prey without being detected

Examples of physical adaptations in predators include:

• long-distance vision

• eyes of predators located in the fronts of their skulls, giving good distance perception

• the ability to detect chemicals released by prey animals, e.g. a good sense of smell

• echolocation in bats

• the ability to move at high speed, e.g. being adapted to run or swim fast

• large canine teeth to catch and hold onto prey

Lying in wait for prey is an example of a behavioural adaptation in predators.

Examples of chemical adaptations in prey include:

• toxins that deter predators, e.g. poison dart frogs and skunks

• scent camouflage that allow prey to avoid detection

Eyes positioned in the sides of the head is an example of a physical adaptation in prey.

Behavioural adaptations in prey animals include:

• hiding

• moving away from predators

• living in a large group

• playing dead

• pretending to be larger than reality

Plant adaptations for harvesting light include:

• trees that grow tall to reach the canopy

• using other plants as a support to reach the canopy, e.g. lianas, epiphytes and

  strangler epiphytes

• being shade-tolerant

Strangler epiphytes begin their life in the canopy and grow both upwards and downwards to access resources, unlike lianas that germinate on the forest floor.

False.

Shade-tolerant plants often contain different photosynthetic pigments to absorb the limited light wavelengths that reach the forest floor.

Ground-dwelling plants have large leaves to maximise the surface area available for light absorption in the low-light conditions of the forest floor.

The fundamental niche of a species is the niche that it has the potential to fill, based on its adaptations and tolerance limits, while the realised niche is the niche that a species actually fills in reality, when in competition with other species.

Competitive exclusion is the elimination of a competing species from its niche.

False.

Competition for the same niche can lead to local extinction for the outcompeted species, but this is not the only outcome.

Possible outcomes of competitive exclusion include:

• one species becoming locally extinct

• one species being forced into a slightly different niche

• both competitors being forced into a smaller part of their fundamental niche