B4.2 Ecological niches

• A niche is the role of a species in a community

• It includes habitat, activity, feeding, reproduction, and biotic and abiotic interactions

• Cormorants and shags illustrate different niches through diet and behaviour despite similar habitat

• Oxygen availability shapes microbial niches and respiration strategy

• Obligate aerobes require oxygen, such as Mycobacterium tuberculosis

• Obligate anaerobes are poisoned by oxygen; facultative anaerobes such as E. coli can switch pathways

• Photoautotrophs use light energy to make organic molecules from carbon dioxide

• Plants, algae, and cyanobacteria contain photosynthetic pigments

• Cyanobacteria were early oxygen-producing photosynthetic organisms

• Holozoic nutrition is heterotrophic feeding by ingestion of organic matter

• Food is digested internally, absorbed, and assimilated

• Herbivores, carnivores, and omnivores are consumers with holozoic nutrition

• Mixotrophs combine autotrophic and heterotrophic nutrition

• Euglena photosynthesizes using chloroplasts and can ingest bacteria by phagocytosis

• Mixotrophy may be obligate or facultative, including some plankton and symbioses

• Saprotrophs secrete enzymes onto dead organic matter and absorb digestion products

• Many fungi and bacteria are saprotrophic decomposers

• Saprotrophs recycle inorganic nutrients, but energy is lost as heat through respiration

• Archaea include photoheterotrophic, chemoautotrophic, and heterotrophic nutrition

• Halobacteria use light-driven ion pumps rather than oxygenic photosynthesis

• Methanogens and hydrogen-dependent archaea illustrate chemosynthesis and anaerobic niches

• Incisors slice, canines tear, and premolars and molars grind food

• Gorillas and Paranthropus robustus have robust jaws and large grinding teeth for tough vegetation

• Humans have smaller canines, smaller molars, and more gracile skulls linked to omnivorous diet

• Herbivores have adaptations such as chewing mouthparts, aphid stylets, or detoxifying gut bacteria

• Plants resist herbivory with spines, stinging hairs, or toxic compounds

• Examples include cacti, stinging nettles, deadly nightshade, oleander, and cassava

• Predators use binocular vision, specialized senses, speed, stealth, or venom to find and kill prey

• Prey use wide fields of view, camouflage, mimicry, armour, aposematic colouration, or toxins

• Examples include peregrine falcons, hedgehogs, chameleons, coral snake mimicry, poison dart frogs, and bombardier beetles

• Forest strata create intense competition for light from canopy to ground layer

• Canopy trees, lianas, epiphytes, and strangler figs reach light using different forms

• Shade-tolerant plants may have large leaves, different pigments, bright flowers, or strong scent

• Fundamental niche is where a species could live based on adaptations and tolerance limits

• Realized niche is where it actually lives after biotic and abiotic interactions

• Competition, predation, mutualism, dispersal, and climate can narrow realized niches

• Competitive exclusion occurs when one species outcompetes another for the same limiting resource

• Niche overlap increases interspecific competition

• Gause's Paramecium experiments showed P. aurelia excluding P. caudatum in mixed culture