B4.2 Ecological Niches

• Define a niche. 

A niche is the functional role of a species within an ecosystem. It includes the full range of biotic and abiotic conditionsunder which the species survives and reproduces, as well as the resources it uses, the interactions it has with other organisms, and its mode of life. A niche therefore describes how an organism lives, not just where it lives.

• State factors that determine the niche of a species.​

The niche of a species is determined by a combination of:

• Abiotic factors, including temperature range, water availability, oxygen availability, light intensity, pH, and salinity

• Biotic factors, including food availability, predators, parasites, pathogens, competitors, and mutualistic relationships

• Resource use, such as type of food consumed, method of feeding, and timing of activity

• Physiological tolerances, such as tolerance to temperature or oxygen levels

• Behavioral patterns, including activity cycles and habitat selection

• Compare niche generalists and specialists.

• Niche generalists occupy a broad niche, using a wide range of resources and tolerating a wide range of environmental conditions. They are often adaptable and resilient to environmental change but may be less efficient at exploiting any single resource.

• Niche specialists occupy a narrow niche, relying on specific resources or environmental conditions. They are often highly efficient in stable environments but are more vulnerable to environmental change or resource loss.

• Compare the different oxygen requirements of obligate anaerobes, facultative anaerobes and obligate aerobes.

• Obligate anaerobes cannot survive in the presence of oxygen, as oxygen is toxic to them. They obtain energy exclusively through anaerobic metabolic pathways.

• Facultative anaerobes can survive with or without oxygen. They use aerobic respiration when oxygen is available but switch to anaerobic respiration or fermentation when oxygen is absent.

• Obligate aerobes require oxygen for survival, as they depend on aerobic respiration to generate sufficient ATP.

• State the energy and carbon sources utilized in photosynthesis. 

• The energy source for photosynthesis is light energy, typically from sunlight.

• The carbon source is carbon dioxide (CO₂), which is fixed into organic molecules during the Calvin cycle.

• List three groups of photosynthetic autotrophs. ​

• Plants

• Algae

• Cyanobacteria

• Outline the acquisition of energy and matter by holozoic animals. 

Holozoic animals acquire energy and matter through ingestion of organic material. Food is taken into the body, digested internally into simpler molecules, absorbed across the gut wall, and assimilated into tissues. Energy is obtained by cellular respiration of absorbed organic molecules, while matter is used for growth, repair, and reproduction.

• Distinguish between ingestion, digestion, absorption and assimilation.​

• Ingestion is the intake of food into the body.

• Digestion is the mechanical and chemical breakdown of food into small, soluble molecules.

• Absorption is the movement of digested molecules across the gut wall into the blood or body fluids.

• Assimilation is the incorporation of absorbed molecules into cells for metabolism, growth, or storage.

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• Outline the acquisition of energy and matter by mixotrophic protists. 

Mixotrophic protists acquire energy and matter through a combination of autotrophic and heterotrophic nutrition. They can photosynthesize using light energy and carbon dioxide, and also ingest or absorb organic matter from their environment when light or inorganic nutrients are limiting.

• State an example of a mixotrophic protist.

Euglena

• Distinguish between obligate and facultative mixotrophs.​

• Obligate mixotrophs require both autotrophic and heterotrophic modes of nutrition to survive.

• Facultative mixotrophs can switch between autotrophy and heterotrophy depending on environmental conditions.

• Outline the acquisition of energy and matter by saprotrophic organisms. 

Saprotrophic organisms obtain energy and matter by external digestion. They secrete digestive enzymes onto dead organic material, break it down outside the body, and absorb the resulting soluble products. Energy is obtained by respiration of absorbed organic compounds.

• Compare location of digestion in saprotrophs and detritivore animals. 

• In saprotrophs, digestion occurs externally, outside the organism’s body.

• In detritivore animals, digestion occurs internally, within a digestive tract after ingestion of detritus.

• List two example saprotrophic organisms.

• Fungi

• Saprotrophic bacteria

• Explain why all saprotrophs are decomposers but not all decomposers are saprotrophs.

All saprotrophs are decomposers because they break down dead organic matter through extracellular digestion. However, not all decomposers are saprotrophs because some decomposers, such as detritivores, ingest organic matter and digest it internally rather than externally.

• List the three domains of life.

• Bacteria

• Archaea

• Eukarya

• Outline the characteristics of archaea.

Archaea are prokaryotic organisms that:

• Lack a nucleus and membrane-bound organelles

• Have unique membrane lipids distinct from bacteria

• Often inhabit extreme environments

• Possess metabolic pathways not found in other domains

• Compare the energy source and carbon source in chemoautotrophs and photoautotrophs.

• Photoautotrophs use light as an energy source and carbon dioxide as a carbon source.

• Chemoautotrophs use chemical energy from inorganic compounds and carbon dioxide as a carbon source.

• List extinct and extant representatives of the Hominidae family of primates.

• Extinct: Australopithecus, Homo habilis, Homo erectus, Homo neanderthalensis

• Extant: Homo sapiens, chimpanzees, gorillas, orangutans

• Outline the physiological, morphological and/or behavioral adaptations of mammalian teeth for different diet types.

• Carnivores: sharp canines, carnassial teeth for slicing meat

• Herbivores: broad molars with ridges for grinding plant material

• Omnivores: combination of incisors, canines, and molars

• Deduce the diet of an organism given dentition patterns.

• Prominent canines and sharp molars indicate a carnivorous diet

• Flat molars and reduced canines indicate a herbivorous diet

• Mixed dentition indicates an omnivorous diet

• Outline the physiological, morphological and/or behavioral adaptations of leaf eating insects  for feeding on plants.

• Specialized mouthparts for cutting or piercing leaves

• Digestive enzymes or symbiotic microbes to break down cellulose

• Behavioral adaptations such as feeding at night to avoid predators

• Outline the physiological, morphological and/or behavioral adaptations of plants for resisting herbivory.​

• Chemical defenses such as toxins or bitter compounds

• Physical defenses such as thorns, spines, or thick cuticles

• Structural adaptations such as tough leaves or silica deposits

• Outline the chemical, physical and/or behavioral adaptations of predators for finding, catching and killing prey.

• Keen sensory systems

• Camouflage or stealth behaviors

• Specialized teeth, claws, or venom

• Outline the chemical, physical and/or behavioral adaptations of prey animals for resisting predation.​

• Camouflage or mimicry

• Behavioral defenses such as grouping or alarm calls

• Physical defenses such as shells, spines, or toxins

• Describe examples of adaptations for harvesting light, including height, lianas, epiphyte, shade-tolerance, and leaf surface area. ​

• Height to access light above competitors

• Lianas use other plants for support

• Epiphytes grow on other plants to reach light

• Shade tolerance allows survival at low light

• Large leaf surface area increases light absorption

• Distinguish between the fundamental and realized niche. ​

• The fundamental niche is the full range of conditions a species could occupy in the absence of competition.

• The realized niche is the portion actually occupied due to competition and other biotic factors.

• Explain competitive exclusion as a factor that can limit the distribution of a species in an ecosystem.   

Competitive exclusion occurs when two species compete for the same limited resources, resulting in one species being outcompeted and excluded from the habitat, thereby limiting its distribution.

• Explain why two species cannot survive indefinitely in the same habitat if their niches are identical.

If two species occupy identical niches, they compete directly for the same resources. Over time, one species will outcompete the other, leading to local extinction of the less competitive species.

• State that organisms that can adapt to extreme niches encounter less competition and predation.​

Organisms adapted to extreme niches experience reduced competition and predation because fewer species possess the physiological adaptations necessary to survive under extreme conditions.