C1.4 ecological niches
B4.2.1— Ecological niche as the role of a species in an ecosystem.
Define a niche.
A niche refers to the specific role an organism plays within its ecosystem, encompassing all of its interactions with the biotic (living) and abiotic (non-living) components of its environment. It includes what an organism eats, where it lives, when and how it reproduces, and its interactions with other species.
State factors that determine the niche of a species.
Abiotic factors: Temperature range, pH, water availability, light intensity, soil type, salinity.
Biotic factors: Food availability, predators, competitors, parasites, diseases, symbiotic relationships, nesting sites, suitable mates.
Physiological tolerances: The range of environmental conditions an organism can survive and reproduce in.
Compare niche generalists and specialists.
Niche Generalists:
Have broad niches, capable of utilizing a wide variety of resources and tolerating a broad range of environmental conditions.
Often found in changing or unstable environments.
Examples: Raccoons (eat diverse foods), cockroaches (live in various habitats).
Niche Specialists:
Have narrow niches, relying on specific resources or restricted to specific environmental conditions.
Often found in stable environments where competition is high.
More vulnerable to environmental changes or resource depletion.
Examples: Koalas (feed primarily on eucalyptus leaves), pandas (feed almost exclusively on bamboo).
B4.2.2— Differences between organisms that are obligate anaerobes, facultative anaerobes and obligate aerobes.
Compare the different oxygen requirements of obligate anaerobes, facultative anaerobes and obligate aerobes.
Obligate Aerobes:
Require oxygen (O_2) for cellular respiration and survival.
Cannot survive without O_2, as their metabolic pathways (e.g., electron transport chain) depend on it as the final electron acceptor.
Examples: Most animals, plants, fungi, and many bacteria.
Obligate Anaerobes:
Cannot survive in the presence of oxygen (O_2), which is toxic to them.
Perform anaerobic respiration or fermentation to generate energy.
Lack enzymes (e.g., superoxide dismutase, catalase) to detoxify reactive oxygen species.
Examples: Clostridium botulinum (causes botulism), many methanogens (Archaea).
Facultative Anaerobes:
Can survive and grow in both the presence and absence of oxygen (O_2).
Utilize O_2 for aerobic respiration when available, which is more energy-efficient.
Switch to anaerobic respiration or fermentation when O_2 is absent.
Examples: Escherichia coli (E. coli), yeast (Saccharomyces cerevisiae).
B4.2.3— Photosynthesis as the mode of nutrition in plants, algae and several groups of photosynthetic prokaryotes.
State the energy and carbon sources utilized in photosynthesis.
Energy Source: Light energy (primarily from sunlight).
Carbon Source: Inorganic carbon in the form of carbon dioxide (CO_2).
List three groups of photosynthetic autotrophs.
Plants
Algae
Cyanobacteria (a group of photosynthetic prokaryotes)
B4.2.4— Holozoic nutrition in animals.
Outline the acquisition of energy and matter by holozoic animals.
Holozoic nutrition involves the intake of solid or liquid organic food particles, which are then processed internally. Animals acquire energy and matter by consuming other organisms (plants, animals, or both).
Distinguish between ingestion, digestion, absorption and assimilation.
Ingestion: The process of taking food into the body, typically through the mouth.
Digestion: The mechanical and chemical breakdown of complex food molecules into simpler, smaller molecules that can be absorbed.
Absorption: The passage of digested food molecules from the digestive tract into the bloodstream or lymphatic system (and then into cells).
Assimilation: The process by which absorbed food molecules are incorporated into the body's cells and utilized for energy, growth, repair, or storage.
B4.2.5— Mixotrophic nutrition in some protists.
Outline the acquisition of energy and matter by mixotrophic protists.
Mixotrophic protists acquire energy and matter by combining different nutritional strategies, typically photosynthesis (autotrophy) and phagocytosis or absorption of organic compounds (heterotrophy). This allows them to switch between modes depending on environmental conditions.
State an example of a mixotrophic protist.
Euglena
Distinguish between obligate and facultative mixotrophs.
Obligate Mixotrophs: These organisms require both autotrophic and heterotrophic nutrition for survival and growth.
Facultative Mixotrophs: These organisms can survive and grow by solely using either autotrophic or heterotrophic nutrition, but can switch between modes to gain an advantage when conditions allow (e.g., photosynthesizing when light is available, or heterotrophically feeding when nutrients are scarce).
B4.2.6- Saprotrophic nutrition in some fungi and bacteria.
Outline the acquisition of energy and matter by saprotrophic organisms.
Saprotrophic organisms (saprotrophs) obtain energy and matter by secreting digestive enzymes onto dead organic matter (detritus, decaying organisms, waste products) externally. These enzymes break down complex organic molecules into simpler soluble compounds, which are then absorbed by the saprotroph.
Compare location of digestion in saprotrophs and detritivore animals.
Saprotrophs: Digestion occurs externally. Enzymes are secreted outside the organism, and digested products are then absorbed.
Detritivore animals: Digestion occurs internally (holozoic-like). Detritivores ingest the dead organic matter and then break it down within their digestive systems.
List two example saprotrophic organisms.
Mushrooms (fungi)
Many soil bacteria
Explain why all saprotrophs are decomposers but not all decomposers are saprotrophs.
All saprotrophs contribute to decomposition by breaking down dead organic matter. Therefore, all saprotrophs are decomposers.
However, decomposers also include detritivores (e.g., earthworms, dung beetles), which internally ingest and digest dead organic matter. Since detritivores do not externally digest like saprotrophs, not all decomposers are saprotrophs.
B4.2.7- Diversity of nutrition in archaea.
List the three domains of life.
Bacteria
Archaea
Eukarya
Outline the characteristics of archaea.
Prokaryotic: Lack a membrane-bound nucleus and other membrane-bound organelles.
Unique Cell Walls: Contain pseudopeptidoglycan or other protein/glycoprotein cell walls, unlike bacterial peptidoglycan.
Membrane Lipids: Possess unique membrane lipids (ether linkages, branched hydrocarbon chains) which are distinct from bacterial and eukaryotic lipids (ester linkages, unbranched chains).
Extremophiles: Many species are adapted to extreme environments (e.g., high temperatures, high salinity, acidic conditions) but also found in moderate environments.
Diverse Metabolism: Exhibit a wide range of metabolic pathways, including chemoautotrophy (e.g., methanogenesis) and photoautotrophy (using bacteriorhodopsin, not chlorophyll).
Genetic Machinery: More closely related to Eukarya in terms of genetic replication, transcription, and translation machinery than to Bacteria.
Compare the energy source and carbon source in chemoautotrophs and photoautotrophs.
Chemoautotrophs:
Energy Source: Chemical reactions involving the oxidation of inorganic compounds (e.g., hydrogen sulfide, ammonia, ferrous iron).
Carbon Source: Inorganic carbon (carbon dioxide, CO_2).
Photoautotrophs:
Energy Source: Light energy (from the sun).
Carbon Source: Inorganic carbon (carbon dioxide, CO_2).
B4.2.8- Relationship between dentition and the diet of omnivorous and herbivorous representative members of the family Hominidae.
List extinct and extant representatives of the Hominidae family of primates.
Extant (Living): Humans (Homo sapiens), chimpanzees (Pan troglodytes), bonobos (Pan paniscus), gorillas (Gorilla gorilla, Gorilla beringei), orangutans (Pongo pygmaeus, Pongo abelii, Pongo tapanuliensis).
Extinct (Examples): Australopithecus afarensis, Homo habilis, Homo erectus, Homo neanderthalensis.
Outline the physiological, morphological and/or behavioral adaptations of mammalian teeth for different diet types.
Incisors: Sharp, chisel-like teeth at the front for biting, cutting, and nipping food. Prominent in herbivores (for clipping vegetation) and omnivores.
Canines: Pointed, cone-shaped teeth located next to incisors for piercing, tearing, and holding food. Very prominent in carnivores, less so in herbivores, and moderate in omnivores.
Premolars and Molars: Broad, flattened teeth at the back with cusps or ridges for grinding, crushing, and pulping food. Well-developed and flatter in herbivores (for fibrous plant material) and omnivores, and sharper/shearing in carnivores.
Deduce the diet of an organism given dentition patterns.
Herbivores: Generally have highly developed incisors (for clipping) and large, flat, ridged molars and premolars (for grinding fibrous plant material). Canines may be reduced or absent. Gaps (diastema) may allow separate processing of leaves/stems from molars.
Carnivores: Characterized by prominent, sharp canines (for killing and tearing), sharp incisors, and specialized blade-like premolars/molars (carnassials) for shearing flesh and crushing bone. Grinding surfaces are minimal.
Omnivores: Possess a balanced set of teeth, combining features of both herbivores and carnivores. Incisors are well-developed, canines are present but often smaller than in carnivores, and molars/premolars have flatter, rounded cusps suitable for both tearing and grinding a mixed diet.
B4.2.9- Adaptations of herbivores for feeding on plants and of plants for resisting herbivory.
Outline the physiological, morphological and/or behavioral adaptations of leaf eating insects for feeding on plants.
Physiological:
Detoxification enzymes: Produce enzymes (e.g., mixed-function oxidases) to break down plant toxins.
Specialized digestive enzymes: Possess enzymes to break down cellulose or other complex plant carbohydrates (e.g., cellulase in some).
Gut symbionts: Host symbiotic bacteria or protists in their gut to aid in digestion of plant matter.
Morphological:
Specialized mouthparts: Chewing mouthparts (mandibles) adapted for biting and grinding leaves (e.g., caterpillars, beetles).
Strong jaws/muscles: For processing tough plant material.
Adhesive structures: Some larvae have suckers or hooks to avoid being dislodged from plants.
Behavioral:
Selective feeding: Choose specific plant parts (young leaves often less toxic/tough) or plant species.
Avoidance: Migrate to avoid plant defenses, or feed at certain times of day when plant defenses are lower.
Galling: Induce gall formation, creating protective structures and concentrated nutrients.
Outline the physiological, morphological and/or behavioral adaptations of plants for resisting herbivory.
Physiological (Chemical Defenses):
Secondary metabolites: Produce a variety of toxic or deterrent compounds (e.g., tannins, alkaloids, terpenes, glycosides) that are unpalatable, toxic, or interfere with herbivore digestion.
Digestibility reducers: Produce compounds (e.g., tannins, lignin) that reduce the nutritional value or digestibility of plant tissues.
Induced defenses: Increase production of chemical defenses in response to herbivore attack.
Morphological (Physical Defenses):
Thorns, spines, prickles: Sharp, pointed structures to deter larger herbivores.
Trichomes: Hairy outgrowths on leaves that can physically impede small insects or release irritating chemicals.
Waxes and resins: Create a tough, indigestible coating on leaves.
Toughness/Lignification: Highly lignified tissues are harder to chew and digest.
Mimicry: Leaves designed to look unappetizing or like another species.
Behavioral (Indirect Defenses):
Attracting natural enemies: Release volatile organic compounds (VOCs) when damaged, which attract predators or parasitoids of the herbivores.
Rapid growth/tolerance: Grow quickly or tolerate damage, replacing lost tissue rapidly.
B4.2.10- Adaptations of predators for finding, catching and killing prey and of prey animals for resisting predation.
Outline the chemical, physical and/or behavioral adaptations of predators for finding, catching and killing prey.
Chemical:
Venom/Poison: For subduing prey (e.g., snakes, spiders, scorpions).
Scent detection: Highly developed sense of smell for tracking prey (e.g., wolves, bears).
Chemical lures: Some predators (e.g., some anglerfish) release chemicals to attract prey.
Physical:
Sharp claws/talons: For grasping and tearing (e.g., felines, raptors).
Sharp teeth/fangs: For piercing and tearing (e.g., sharks, wolves).
Camouflage: Blending with the environment for ambush predation (e.g., chameleons, snow leopards).
Speed and agility: For pursuit predation (e.g., cheetahs, falcons).
Strength and jaw power: To overpower larger prey (e.g., crocodiles, lions).
Specialized sensory organs: Excellent eyesight (e.g., eagles), echolocation (e.g., bats).
Behavioral:
Ambush hunting: Waiting for prey to come near (e.g., praying mantis, many snakes).
Pursuit hunting: Actively chasing prey (e.g., cheetahs, wolves).
Pack hunting: Cooperative hunting strategies to take down larger prey (e.g., wolves, lions).
Tool use: Using objects to obtain food (e.g., chimpanzees using sticks for termites, sea otters using rocks).
Mimicry: Mimicking other species to approach prey (e.g., some spiders mimic ants).
Outline the chemical, physical and/or behavioral adaptations of prey animals for resisting predation.
Chemical:
Toxins/Poisons: Producing compounds that are toxic when ingested (e.g., poison dart frogs, some plants).
Repellent sprays: Releasing noxious or irritating chemicals (e.g., skunks, bombardier beetles).
Warning coloration (aposematism): Bright colors to advertise toxicity or bad taste (e.g., monarch butterflies, venomous snakes).
Physical:
Camouflage (cryptic coloration): Blending with the environment to avoid detection (e.g., stick insects, arctic foxes).
Armor/Spines: Protective coverings (e.g., turtles, armadillos, hedgehogs).
Speed: Running or flying away from predators (e.g., gazelles, many birds).
Size: Being too large to be easily consumed by many predators.
Startle displays: Suddenly revealing bright colors or patterns to surprise a predator.
Behavioral:
Flight/Escape: Running, flying, or swimming away.
Hiding: Seeking shelter (e.g., in burrows, dense vegetation).
Freezing/Playing dead (thanatosis): Remaining still to avoid detection or appear inedible (e.g., opossums).
Group living/Herding: Dilution effect, increased vigilance, confusing predators (e.g., schooling fish, herds of wildebeest).
Alarm calls: Warning other individuals of danger.
Mimicry (Batesian): Harmless species mimicking a dangerous or unpalatable one (e.g., hoverflies mimicking wasps).
B4.2.11- Adaptations of plant form for harvesting light.
Describe examples of adaptations for harvesting light, including height, lianas, epiphyte, shade-tolerance, and leaf surface area.
Height: Tall trees grow upwards to outcompete other plants for direct sunlight, especially in dense forests. This allows them to expose their leaves to maximum light intensity above the canopy.
Lianas: These are woody vines that use other plants (trees) for physical support to climb towards the canopy. This adaptation allows them to reach high light environments without expending energy on developing a thick, self-supporting trunk.
Epiphytes: Plants that grow on other plants, typically trees, but are not parasitic (e.g., some orchids, bromeliads). They use the host plant for physical support to elevate themselves into higher light zones, obtaining water and nutrients from rain, air, and debris rather than the host's vascular system.
Shade-tolerance: Plants adapted to low light conditions often have broader, thinner leaves with a larger surface area to capture as much diffuse light as possible. They may have more chlorophyll per chloroplast and lower respiratory rates, allowing them to survive with less light.
Leaf Surface Area: Generally, a larger leaf surface area allows for greater light interception. Plants in low light (shade plants) tend to have larger, thinner leaves, while plants in high light (sun plants) may have smaller, thicker leaves to reduce water loss and prevent photo-inhibition.
Arrangement of leaves: Leaves are often arranged in a mosaic pattern to minimize self-shading and maximize light exposure for all leaves on the plant.
B4.2.12- Fundamental and realized niches.
Distinguish between the fundamental and realized niche.
Fundamental Niche: The entire range of abiotic (e.g., temperature, light, pH, soil moisture) and biotic (e.g., food resources) conditions and resources that a species could potentially use and survive in, if there were no limiting factors from other species (e.g., competition, predation, disease). It represents the theoretical maximum niche width.
Realized Niche: The actual set of abiotic and biotic conditions and resources that a species actually occupies and uses in the presence of limiting factors such as competition, predation, and disease. The realized niche is typically smaller than or a subset of the fundamental niche.
B4.2.13- Competitive exclusion and the uniqueness of ecological niches.
Explain competitive exclusion as a factor that can limit the distribution of a species in an ecosystem.
Competitive exclusion (also known as Gause's Law) states that two species competing for the exact same limited resources cannot coexist indefinitely. Eventually, one species will outcompete the other, leading to the exclusion of the less successful competitor from that particular niche or habitat. This limits the distribution of species because the presence of a superior competitor can prevent a species from occupying parts of its fundamental niche.
Explain why two species cannot survive indefinitely in the same habitat if their niches are identical.
If two species have identical niches, it means they utilize the same resources in the same way, live in the same place, and have the same environmental requirements. This leads to direct and intense competition for those shared, limited resources. Even a slight advantage of one species in resource acquisition or utilization will eventually lead to it outcompeting the other species, driving the weaker competitor to local extinction or forcing it to adapt and shift its niche (resource partitioning).
State that organisms that can adapt to extreme niches encounter less competition and predation.
Organisms that are adapted to extreme niches (e.g., very high temperatures, high salinity, deep sea vents, highly acidic environments) often face less interspecific competition and predation because fewer other species are physiologically capable of surviving and thriving under such harsh conditions. This specialization allows them to exploit resources that are inaccessible to most other organisms.