B4.2 Ecological niches - UWCSEA - IB Biology 2025

B4.2.1—What is the ecological niche of an organism?

a niche includes the habitat in which the species lives

it includes the interactions with other species, such as competition, predation, and mutualism, are part of the niche;

abiotic factors like temperature, humidity, and light affect a species' niche;

a niche involves how a species obtains food, e.g., as a herbivore, carnivore, or decomposer;

B4.2.2—What are the different types of anaerobes?

Obligate anaerobes cannot survive in the presence of oxygen;

Facultative anaerobes can survive with or without oxygen;

Obligate aerobes require oxygen to survive; obligate anaerobes and aerobes have strict tolerance ranges for oxygen;

while facultative anaerobes are more adaptable;

B4.2.3—What is photosynthesis? How is it a mode of nutrition?

Photosynthesis is the process by which plants, algae, and some photosynthetic prokaryotes; convert light energy into chemical energy stored in glucose, using carbon dioxide and water;

This process releases oxygen as a byproduct and enables these organisms to be autotrophic, meaning they can produce their own food.

B4.2.4—What is holozoic nutrition?

Holozoic nutrition is a mode of feeding where animals ingest other organisms or organic matter to obtain nutrition;

The process involves several steps: ingestion (taking in food), digestion (breaking down food into simpler molecules), absorption (transporting nutrients into the bloodstream), assimilation (using nutrients within the body), and egestion (removing waste).

All animals, such as humans, lions, and birds, are heterotrophic and depend on holozoic nutrition for energy, growth, and maintenance.

B4.2.5— What is mixotrophic nutrition? What uses it?

Mixotrophic nutrition occurs in some protists, which can switch between autotrophic (photosynthetic) and heterotrophic modes of nutrition.

For example, Euglena can perform photosynthesis when light is available, but it can also ingest food particles in the absence of light;

Many oceanic plankton species are mixotrophic, playing significant roles in marine ecosystems.

Obligate mixotrophs require both modes of nutrition to survive;

while facultative mixotrophs can switch between modes depending on environmental conditions.

B4.2.6—What is saprotrophic nutrition? Which organisms use it?

In saprotrophic nutrition, organisms like fungi and bacteria decompose dead organic matter; by secreting enzymes externally to break down complex molecules into simpler substances;

These substances are then absorbed by the organism;

Saprotrophs act as decomposers, playing a critical role in nutrient cycling by recycling nutrients like carbon and nitrogen back into the ecosystem;

B4.2.7—Diversity of nutrition in archaea

Archaea are a diverse group of microorganisms that display a wide range of nutritional strategies;

Unlike other life forms, many archaea are extremophiles that thrive in extreme conditions, such as hot springs and salt lakes;

They may obtain energy through phototrophy (using light), chemotrophy (oxidising inorganic substances like hydrogen or sulfur), or oxidation of carbon compounds;

B4.2.8—Relationship between dentition and the diet of omnivorous and herbivorous representative

members of the family Hominidae

The study of dentition (the structure and arrangement of teeth) in the family Hominidae (great apes, including humans) reveals insights into their dietary habits;

For example, Homo sapiens (humans) have a mixed dentition suitable for an omnivorous diet, with incisors for cutting, canines for tearing, and molars for grinding.

Whereas Paranthropus robustus, a likely herbivore, had large, flat molars with thick enamel, adapted for grinding tough plant material;

B4.2.9—Adaptations of herbivores for feeding on plants and of plants for resisting herbivory

Herbivores have evolved adaptations such as specialised teeth or mouthparts (e.g., piercing and chewing mouthparts in insects) for feeding on plant material;

Plants have developed various defences against herbivory;

including physical defences e.g. thorns, spines, tough leaves;

and chemical defences e..g. toxic compounds (like alkaloids and tannins).

Some herbivores have developed counter-adaptations to detoxify or tolerate these plant defences, allowing them to consume otherwise toxic plants.

B4.2.10—Adaptations of predators for finding, catching and killing prey and of prey animals for resisting

predation

Predators have evolved specialised adaptations for hunting;

such as sharp claws, teeth, keen senses, and behaviours like ambush tactics or pack hunting;

Prey species have developed various defensive adaptations, including camouflage, mimicry, toxic secretions, and behavioural strategies like fleeing, hiding, or group living;

These adaptations enhance survival chances for both predators and prey in their ecological interactions.

B4.2.11—Adaptations of plant form for harvesting light

Canopy trees grow tall to reach direct sunlight; while lianas climb other trees to gain height;

Epiphytes, such as orchids, grow on tree branches to access light without rooting in the ground.

Shade-tolerant plants on the forest floor have broad leaves to capture light efficiently in low-light conditions.

B4.2.12—Fundamental and realized niches

The fundamental niche of a species is the potential range of conditions and resources it can utilise based on its adaptations and tolerance limits;

The realized niche is the actual range of conditions and resources the species occupies in the presence of competitors or other ecological factors;

B4.2.13—Competitive exclusion and the uniqueness of ecological niches

Competitive exclusion occurs when two species compete for the same resource, leading to the elimination of one species or a reduction in the niches of both species;

Each species' ecological niche is shaped by competition, resource availability, and environmental conditions, ensuring species coexistence through niche differentiation.