B4.2Theme B — Form and function
Ecological niches — IB Biology HL Revision Notes & Topical Questions
10 min read 12 parts Lesson 11 of 14 1 quiz
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 HL notes: Explain niches, modes of nutrition, adaptations of predators, prey, herbivores and plants, and competition between species.Niche = the role of a species within its habitat.It includes what the species eats, which species depend on it …
- Obligate anaerobes
- Facultative anaerobes
- Obligate aerobes
- Heterotroph
- Holozoic nutrition
- Mixotrophs
Part 1 of 10Ecological niche and respiration types and niches
Ecological niche and respiration types and niches
Niche
Niche the role of a species within its habitat.
- It includes what the species eats,
- which species depend on it for food, when it is active, exactly where it lives and feeds, and the abiotic and biotic factors acting on it.
Competition
- Competition two species cannot fill the same niche, and one out-competes the other, which then dies out in that habitat.
- Apparent overlap hides subtle differences such as feeding time, food source or feeding location.
Ecological niche and respiration types and niches
Obligate anaerobes
- Obligate anaerobes single-celled organisms that respire only anaerobically and cannot tolerate oxygen.
- Early bacteria were obligate anaerobes, and now they live only in oxygen-free places such as deep soil, deep water and inside other organisms.
Facultative anaerobes
- Facultative anaerobes they mainly respire aerobically but switch fully to anaerobic respiration without harm when oxygen is absent.
- Examples are brewer's yeast (Saccharomyces cerevisiae) and Escherichia coli.
Obligate aerobes
- Obligate aerobes they cannot survive without oxygen and can respire anaerobically in some cells for only a few seconds.
- Examples are most animals, most fungi (not yeast) and Mycobacterium tuberculosis.
Part 2 of 10Modes of nutrition
Autotroph
Autotroph an organism that makes its own organic molecules from simple inorganic substances.
- Photoautotrophs use light energy and chemoautotrophs use energy from oxidising chemicals.
Heterotroph
Heterotroph an organism that gets organic molecules from the tissues of other organisms.
Photosynthetic organisms
- They use pigments such as chlorophyll to turn carbon dioxide into carbohydrates, so they are producers.
- Plants, algae and cyanobacteria are examples.
- Photosynthesis transfers light energy to chemical energy and releases oxygen for aerobic respiration.
- Energy is transferred, never produced or created.
Holozoic nutrition
Holozoic nutrition internal digestion by ingesting, digesting, absorbing and assimilating food, as in animals.
- Ingestion is eating, digestion is breaking down large molecules, absorption is transport into cells and assimilation is using the molecules to build cells and tissues.
- House flies secrete enzymes onto food, so they are heterotrophs but not holozoic.
Mixotrophs
Mixotrophs organisms using both autotrophy and heterotrophy.
- Obligate mixotrophs need both, and facultative mixotrophs use one supplemented by the other.
- Euglena takes in bacteria by endocytosis, digests them with lysosome enzymes and has an eyespot to orient to light for its chloroplasts.
- Carnivorous plants photosynthesise and digest insects.
- Corals get organic molecules from symbiotic algae and by filter feeding.
- Marine plankton such as dinoflagellates feed on bacteria and photosynthesise.
Saprotrophs
Saprotrophs heterotrophs that secrete enzymes onto dead material and waste, digest it externally and absorb the products.
- Fungi and bacteria are examples, and they are decomposers.
- They release mineral ions such as ammonium and phosphate, some of which stay in the soil for plants, so ecosystems depend on them.
- Detritivores such as earthworms digest dead material internally, so they use holozoic nutrition and differ from decomposers.
Part 3 of 10Nutrition in archaea
| Type | Energy source | Carbon source | Example or detail |
|---|---|---|---|
| Phototrophic (photoheterotrophs) | Light | Other organisms | Halobacteria use bacteriorhodopsin to pump H+ and drive ATP synthase, which is not oxygen-releasing photosynthesis |
| Chemoautotrophic | Chemicals (hydrogen, ammonia, methane, hydrogen sulfide) | Made by chemosynthesis | Energy from chemicals goes into carbon compounds |
| Chemoheterotrophic | Chemicals, used directly to make ATP | Other organisms | Gain carbon from other organisms |
| Heterotrophic | Organic compounds | Other organisms | Break down dead plant material |
Part 4 of 10Nutrition in Hominidae
Hominidae
- Hominidae humans, chimpanzees, gorillas, orangutans and gibbons, mostly omnivores.
- Chimps are mainly frugivores and gorillas are mainly herbivores.
Dentition fits diet.
- Chimps have small incisors and long canines to bite and tear soft fruit and meat, with weak jaw muscles.
- Gorillas have strong jaw muscles and large premolars and molars to grind tough vegetation.
- Incisors cut and bite, canines hold and tear, and premolars and molars grind.
Extinct species
- Extinct species jaws and teeth preserve well and can show diet and ecosystem structure.
- Paranthropus robustus had a robust gorilla-like skull with attachments for large jaw muscles, large molars and premolars and thick enamel for tough plants.
- Homo floresiensis had large premolars, small canines, a robust square jaw, tooth abrasion showing a fibrous plant diet and tools showing some meat eating.
Limits of teeth as evidence
- Humans eat much meat but have teeth like plant-eaters.
- Orangutans and gorillas have pointed canines but eat no meat.
- Male chimps have longer canines than females but the same diet.
- Teeth also serve in defending territory and competing for mates, so tooth abrasion under a microscope helps.
Nature of science
- Nature of science deductions from theory must be revised when evidence such as modern mismatches appears.
Part 5 of 10Herbivores and plant defences
Herbivory adaptations
- Aphids have stylets that pierce plant tissue to reach phloem sap.
- Caterpillars, grasshoppers and beetles have mandibles to cut leaves.
- Grazers such as sheep and horses have flat teeth for grinding.
- Ruminants such as cattle and deer have multi-chambered stomachs, regurgitate and re-chew food,
- and host bacteria with the cellulase enzymes herbivores lack.
- Some deer have saliva proteins that bind tannins, and proboscis monkeys have gut bacteria that neutralise toxins.
- Mammals use cautious sampling of new plants so toxins are not eaten in dangerous amounts.
Plant defences
- Plant defences herbivory reduces leaf area and transport, and plants cannot flee.
- Mechanical deterrents are cactus spines, nettle hairs that contain skin-irritating toxins, thick bark and tiny leaf hairs.
- Toxic compounds include digitalis from foxgloves, which affects the heartbeat.
- Atropine from deadly nightshade blocks neurotransmitter binding and paralyses muscle.
- Tannins taste bitter and reduce digestion efficiency.
- Alkaloids such as caffeine and nicotine are toxic to insect growth and nerve impulses.
Part 6 of 10Predator adaptations
- Predators hunt and eat other animals or recently dead animals.
| Type | Adaptations |
|---|---|
| Chemical | Venom: adders and rattlesnakes have haemotoxic venom that damages blood and clotting, mambas and cobras have neurotoxic venom that blocks nerve impulses, and scorpions and spiders also use venom |
| Chemical | Chemical mimicry: bolas spiders release moth pheromones to attract male moths |
| Chemical | Chemical crypsis (scent camouflage): pirate perch prey seem unable to detect them |
| Physical | Excellent vision in birds of prey, and forward-facing eyes for depth perception |
| Physical | Snakes' Jacobson's organ detects chemicals, and bats use echolocation |
| Physical | Cheetahs have long limbs and flexible spines, swordfish are streamlined, mantis shrimps have fast front limbs, and carnivores have large canines |
| Behavioural | Ambush: puff adders stay still for weeks, mantis shrimps hide in cracks, crocodiles approach underwater |
| Behavioural | Pack hunting: orcas, wolves and lions cooperate |
| Behavioural | Pursuit: cheetahs use bursts of speed, wolves and painted dogs use persistence over long distances |
Part 7 of 10Prey adaptations
| Type | Adaptations |
|---|---|
| Chemical | Toxins: poison dart frogs, bad-smelling skunks and tiger moths that taste unpleasant to bats |
| Chemical | Scent camouflage: puff adders hide from mongooses and harlequin filefish take on the scent of corals |
| Physical | Eyes on the sides of the head give a wide field of vision |
| Physical | Camouflage: insects that look like leaves or sticks |
| Physical | Mimicry: owl butterflies have owl-eye wing patterns, and king snakes mimic venomous coral snakes |
| Physical | Aposematism: bright warning colours signal chemical defences, as in poison dart frogs |
| Physical | Mechanical defences: tough exoskeletons, turtle shells, and spines in porcupines and hedgehogs |
| Behavioural | Innate preference for dark places, such as woodlice |
| Behavioural | Fleeing, as rabbits run to burrows when they see predator wing shapes |
| Behavioural | Avoiding predator places or times, such as desert rodents emerging at night |
| Behavioural | Grouping in shoals or flocks, which confuses predators and reduces the chance of being caught |
| Behavioural | Mobbing, as gulls do, and warning calls |
| Behavioural | Bluffing: opossums, some snakes and some sharks feign death, and frill-necked lizards look larger |
Part 8 of 10Plant adaptations for harvesting light
1Form adaptations
- Form adaptations whole-organism adaptations that help plants compete for light in a forest.
2Trees
- Trees they form the canopy, with emergent trees above and an understorey beneath, and maximising height gains the most light and allows fast growth.
3Lianas
- Lianas woody vines that germinate on the forest floor and climb tree trunks to reach the canopy.
- Their roots are in the soil, and they compete with trees for light, nutrients and moisture.
4Epiphytes
- Epiphytes they grow high on tree branches for light and do not spend energy on upward growth.
- Moss takes water and nutrients from rain running down bark.
- Bromeliads collect rainwater among their leaves.
- Some orchids have aerial roots that absorb moisture from the air.
5Strangler epiphytes
- Strangler epiphytes they start in the canopy and send roots down to the soil,
- as the strangler fig does,
- and may kill the host tree by taking its resources.
6Shade-tolerant shrubs and herbaceous plants
- Shade-tolerant shrubs and herbaceous plants they grow on the forest floor.
- They may have different photosynthetic pigments to absorb the limited wavelengths that reach the ground.
- Large leaves increase the area for light absorption.
- Bright or scented flowers attract pollinators in low light.
- Shrubs have woody stems, and herbaceous plants have soft stems supported by turgid cells.
Part 9 of 10Fundamental and realised niches
| Feature | Fundamental niche | Realised niche |
|---|---|---|
| Meaning | The full range of conditions and resources in which a species could survive and reproduce | The conditions and resources a species actually uses with competitors and predators present |
| Distribution | Potential | Actual |
| Interactions | No competition or predation | Competition and predation occur |
| Size | Large | Small |
- Barnacle example
- the fundamental niche of Chthamalus dalli covers the rocky intertidal zone and many conditions.
- Competition with Balanus glandula for space limits it to higher shore areas where Balanus is scarce and exposure to air is longer.
Part 10 of 10Competitive exclusion
Competitive exclusion
Competitive exclusion elimination of a species from a niche by a better competitor.
- The loser is forced into a slightly different niche, made locally extinct, or both species are pushed into a smaller part of their fundamental niches.
- Warblers competing for resources may be pushed into different feeding locations.
Paramecium example
- P. aurelia and P. caudatum thrive separately, but together P. aurelia out-competes and eliminates P. caudatum.
- This was in the laboratory, and two species rarely occupy exactly the same niche in nature.
Key terms
| Term | Meaning |
|---|---|
| Niche | the role of a species within its habitat. |
| Fundamental niche | the full range of conditions a species could use without competition. |
| Realised niche | the niche a species actually occupies with biotic interactions. |
| Competitive exclusion | elimination of one species from a niche by a competitor. |
| Saprotroph | a heterotroph that digests dead matter externally by secreted enzymes. |
| Mixotroph | an organism using both autotrophic and heterotrophic nutrition. |
| Aposematism | bright warning colouring that signals a chemical defence. |
| Epiphyte | a plant that grows on another plant, using its height for light. |
Avoid these mistakes
1
Habitat and niche are the same — a habitat is where a species lives and a niche is its role there.
2
Two species can share a niche indefinitely — one out-competes the other, or they separate into different niches.
3
Saprotrophs and detritivores feed the same way — saprotrophs digest externally and detritivores internally.
4
Energy is produced by photosynthesis — light energy is transferred to chemical energy.
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