B4.2Theme B — Form and function
Ecological niches — IB Biology SL Revision Notes & Topical Questions
5 min read 12 parts Lesson 10 of 13 2 quizzes
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
B4.2 Ecological niches — IB BIOLOGY SL notes: Explain niches, competitive exclusion, modes of nutrition and the adaptations of herbivores, predators, prey and plants.Niche = the role of a species within its habitatIt includes what the species eats and what feeds on it.It includes…
- Habitat compared with niche
- Abiotic factors
- Unique niche
- Paramecium
- Early Earth
- Facultative anaerobes
Part 1 of 10Niche
Niche
Niche
Niche the role of a species within its habitat
- It includes what the species eats and what feeds on it.
- It includes when the species is active and exactly where it lives and feeds.
- It includes the abiotic and biotic factors acting on the species.
Habitat compared with niche
- Habitat compared with niche the habitat is where a species lives and the niche is what it does there
Abiotic factors
- Abiotic factors temperature, light, pH and water set limits on where a species can live
Biotic factors
- Biotic factors predators, prey, competitors and parasites shape the niche
Unique niche
- Unique niche no two species can permanently share exactly the same niche
- Species that seem to share one differ subtly, for example in feeding time or food source.
Part 2 of 10Fundamental and realised niches
| Feature | Fundamental niche | Realised niche |
|---|---|---|
| Definition | The full range of conditions and resources a species could use with no competitors | The range actually occupied |
| Biotic limits | Ignored | Competition and predation included |
| Size | Larger | Smaller or equal |
| Barnacle example | Much of the rocky shore | Upper shore only |
Barnacles
- Chthamalus dalli could live over a wide shore zone,
- but competition from Balanus glandula confines it to the upper shore where it is exposed to air longer
Competitive exclusion
Competitive exclusion the elimination of a competing species from its niche
- The loser is forced into a different niche or made locally extinct, or both species are restricted to part of their fundamental niches.
Paramecium
- P. aurelia and P. caudatum thrive alone, but when grown together P. caudatum dies out
- This was in laboratory conditions, and exactly shared niches are rare in nature.
Warblers
- Warblers related species feed in different parts of trees, which reduces overlap
Part 3 of 10Oxygen and respiration
| Feature | Obligate aerobe | Obligate anaerobe | Facultative anaerobe |
|---|---|---|---|
| Oxygen | Always needed | Never needed and harmful | Used if available |
| Respiration | Aerobic only | Anaerobic only | Both |
| Typical habitat | Air and surface water | Deep mud and guts | Soil, guts and food |
| Example | Humans and Mycobacterium tuberculosis | Clostridium | Yeast and E. coli |
Early Earth
- Early Earth early bacteria were obligate anaerobes in an atmosphere without oxygen
- Photosynthesis added oxygen, so obligate anaerobes now live in oxygen-free places such as deep soil, deep water and inside other organisms.
Facultative anaerobes
- Facultative anaerobes they switch to anaerobic respiration without ill effect, and aerobic respiration gives more ATP
Part 4 of 10Autotrophs
Nutrition
Nutrition how an organism gets the organic molecules that fuel respiration
Autotroph
- Autotroph makes its own organic molecules from simple inorganic substances
- Photoautotrophs use light energy.
- Chemoautotrophs use energy from the oxidation of chemicals, such as iron-oxidising bacteria turning Fe2+ into Fe3+.
Photosynthesis
- Photosynthesis pigments such as chlorophyll absorb light to turn carbon dioxide into organic molecules
- It transfers light energy to chemical energy and does not create energy.
- Producers include plants, algae and cyanobacteria.
- It released the oxygen that made aerobic respiration possible.
Hydrothermal vents
- Hydrothermal vents chemoautotrophs support food webs around deep-sea vents
Part 5 of 10Heterotrophs
Heterotroph
- Heterotroph gets organic molecules from the tissues of other organisms
Holozoic nutrition
Holozoic nutrition ingestion, digestion, absorption, assimilation and egestion, with digestion inside the body
- Ingestion is eating and digestion breaks large molecules into small ones.
- Absorption moves molecules from the gut into the cells and assimilation builds them into tissues.
- Humans and detritivores such as earthworms and woodlice use holozoic nutrition.
Saprotroph
Saprotroph a heterotroph that secretes enzymes onto dead matter and absorbs the products of external digestion
- Fungi and many bacteria are saprotrophs and decomposers.
- They release mineral ions such as ammonium and phosphate, and some stay in the soil for plant roots.
- Houseflies digest externally, so they are not strictly holozoic.
Mixotroph
- Mixotroph uses more than one mode of nutrition
- Obligate mixotrophs need both modes and facultative mixotrophs survive on one, boosted by the other.
- Euglena photosynthesises in light, engulfs bacteria by endocytosis and digests them in lysosomes, and an eyespot orients its chloroplasts to light.
- Other mixotrophs are sundews and pitcher plants, corals with symbiotic algae and filter feeding, and many dinoflagellates.
Part 6 of 10Nutrition in archaea
Phototrophic archaea
- Halobacteria use bacteriorhodopsin to absorb light and pump H+ across a membrane
- ATP synthase then makes ATP, but they take their carbon from other organisms.
Chemoautotrophic archaea
- Chemoautotrophic archaea use hydrogen, ammonia, methane or hydrogen sulfide as an energy source and make their own carbon compounds
Chemoheterotrophic archaea
- Chemoheterotrophic archaea get ATP from inorganic chemicals but carbon from other organisms
Heterotrophic archaea
- Heterotrophic archaea absorb and break down carbon compounds, for example from dead plant material
Methanogens
- Methanogens release methane in anoxic habitats
Part 7 of 10Hominid diet and teeth
Hominidae
- Hominidae humans, chimpanzees, gorillas, orangutans and gibbons, mostly omnivores
- Chimpanzees are mainly frugivores with small jaw muscles and long canines.
- Gorillas are mainly herbivores with strong jaw muscles and large grinding premolars and molars.
Tooth roles
- Tooth roles incisors cut, canines grip and tear, and premolars and molars grind
Extinct hominids
- Extinct hominids skulls and teeth give clues to diet
- Paranthropus robustus had a skull crest for large jaw muscles, big molars and thick enamel for tough plants.
- Homo floresiensis had large premolars, small canines and fibrous wear, with tools suggesting some meat.
Caution
- Caution teeth do not always show diet
- Humans eat meat but have teeth like plant-eaters.
- Gorillas and orangutans have pointed canines but eat no meat.
- Male chimpanzees have longer canines for display or mate competition.
- Microwear patterns add evidence.
Nature of science
- Nature of science deductions made from theory must be tested against new evidence
Part 8 of 10Herbivores and plant defences
Insect herbivores
- Insect herbivores aphid stylets pierce the phloem, and caterpillar and beetle mandibles cut leaves
Mammal herbivores
- Grazers have flat grinding teeth.
- Ruminants have a multi-chambered stomach, re-chew the cud and rely on gut microbes that make cellulase.
Toxin handling
- Toxin handling some deer have salivary proteins that bind tannins, proboscis monkeys have gut bacteria that neutralise toxins and mammals sample new plants cautiously
Mechanical defences
- Mechanical defences cactus spines, stinging nettle hairs, thick bark and dense leaf hairs
Chemical defences
- Digitalis in foxglove.
- Atropine in deadly nightshade.
- Bitter tannins that also reduce digestion.
- Alkaloids such as nicotine and caffeine.
Arms race
- Arms race plants and herbivores show defences and counter-adaptations
Part 9 of 10Predator and prey adaptations
| Type | Predator | Prey |
|---|---|---|
| Chemical | Haemotoxic or neurotoxic venom, bolas spider moth pheromone mimicry, scent camouflage | Toxic frog skin, skunk spray, distasteful tiger moths, filefish smelling of coral |
| Physical | Forward-facing eyes, snake Jacobson's organ, bat echolocation, cheetah limbs, streamlined swordfish | Side-facing eyes, camouflage, eyespot mimicry, warning colours, shells and spines |
| Behavioural | Ambush, pack hunting, pursuit | Nocturnal activity, flocking, mobbing, alarm calls, playing dead, bluffing |
Predator and prey adaptations
Predator behaviour
- Ambushpuff adders and crocodiles.
- Packwolves, orcas and lions.
- Pursuitcheetahs and painted dogs.
Aposematism
- Aposematism bright warning colours advertise chemical defences, as in poison dart frogs
Mimicry
- Mimicry a king snake copies the pattern of a venomous coral snake, and owl butterflies have wing patterns like owl eyes
Group living
- Group living groups reduce the chance of capture and confuse predators
Bluffing
- Bluffing frill-necked lizards use a neck frill to look larger
Part 10 of 10Plant adaptations for light
Plant adaptations for light
Canopy and emergent trees
- Canopy and emergent trees they invest in woody height to get full sun
Lianas
- Lianas woody vines that germinate on the forest floor and climb tree trunks to the canopy
- They compete with trees for light, nutrients and moisture.
Epiphytes
- Epiphytes grow on branches, so they gain height without growing upward
- Moss gets water from rain running over bark.
- Bromeliads collect rainwater among their leaves.
- Some orchids have aerial roots that take moisture from the air.
Strangler fig
- Strangler fig begins in the canopy and sends roots down to the soil, and may kill the host tree
Shade-tolerant shrubs and herbs
- Shade-tolerant shrubs and herbs grow on the forest floor
- They have large leaves and pigments suited to filtered light.
- Their flowers are bright or strongly scented to attract pollinators.
Light partitioning
- Light partitioning different strategies let species occupy different niches
Key terms
| Term | Meaning |
|---|---|
| Niche | The role of a species within its habitat, including its biotic and abiotic interactions. |
| Fundamental niche | The full range of conditions and resources in which a species could survive and reproduce. |
| Realised niche | The range actually occupied, restricted by biotic interactions such as competition. |
| Competitive exclusion | The elimination of one species from a niche by a better competitor. |
| Saprotroph | A heterotroph that digests dead matter externally and absorbs the products. |
| Mixotroph | An organism that uses both autotrophic and heterotrophic nutrition. |
| Aposematism | The use of bright warning colours to advertise chemical defences. |
| Epiphyte | A plant that grows on another plant to reach light. |
Avoid these mistakes
1
Using habitat and niche as the same — a habitat is where an organism lives and a niche is its role
2
Saying decomposers and detritivores feed the same way — decomposers digest externally and detritivores internally
3
Saying the realised niche is larger than the fundamental niche — competition makes it smaller
4
Saying energy is produced by photosynthesis — light energy is transferred to chemical energy
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