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IB DP Biology Ecological niches Study Notes I IITian Academy

IB DP Biology Ecological niches Study Notes - New Syllabus

IB DP Biology Ecological niches Study Notes

IB DP Biology Ecological niches Study Notes at  IITian Academy  focus on  specific topic and type of questions asked in actual exam. Study Notes focus on IB Biology syllabus with guiding questions of

  • What are the advantages of specialized modes of nutrition to living organisms?
  • How are the adaptations of a species related to its niche in an ecosystem?

Standard level and higher level: 3 hours

IBDP Biology 2025 -Study Notes -All Topics

B4.2.1—Ecological niche as the role of a species in an ecosystem

The role of the species in an ecosystem
-includes: what it eats, when it’s active, its habitat
-includes all biotic & abiotic factors:
1. Biotic: any interaction w/ other living things
-competition, predation, cooperation/mutualism
2. Abiotic: anything that affects its range of tolerance
-temp, air quality

Compare fundamental vs. realized niche.

1. Fundamental niche: potential niche of a species based on its adaptation & tolerance limits
2. Realized niche: actual niche of a species when in competition w/ other species
-Range of tolerance: species have to be able to survive there in the first place
-Population interaction & chi squared: competition between species

B4.2.2—Differences between organisms that are obligate anaerobes, facultative anaerobes and obligate aerobes

Oxygen Requirements: A Spectrum of Tolerance

  • Obligate Aerobes: These organisms have an absolute requirement for oxygen for their metabolic processes. They rely on aerobic respiration for energy production and cannot survive in the absence of oxygen. Examples include most animals, plants, and many bacteria.
  • Obligate Anaerobes: These organisms are poisoned by oxygen. They have evolved metabolic pathways that do not require oxygen (anaerobic respiration or fermentation) and are inhibited or killed by the presence of oxygen. Examples include some bacteria, archaea, and protozoa.
  • Facultative Anaerobes: These organisms are flexible in their oxygen requirements. They can utilize oxygen for aerobic respiration when it is available, but they can also switch to anaerobic metabolism in the absence of oxygen. This flexibility allows them to survive in a wide range of environments. Examples include many bacteria and some yeast species.

Ecological Significance:

  • Oxygen as a Selective Force: The availability or absence of oxygen has played a significant role in shaping the evolution and distribution of organisms on Earth.
  • Diverse Metabolic Strategies: The different oxygen requirements of organisms reflect the diversity of metabolic strategies that have evolved to harness energy from the environment.
  • Ecological Niches: The oxygen requirements of organisms determine their ecological niches and influence the composition of microbial communities in various environments.

In essence, the varying oxygen requirements of organisms highlight the diverse metabolic strategies that have evolved to support life in environments with different oxygen availability. These differences have profound implications for the distribution and ecological interactions of organisms.

B4.2.3—Photosynthesis as the mode of nutrition in plants, algae and several groups of photosynthetic prokaryotes

Photosynthesis: Capturing Sunlight for Life

  • Foundation of the Food Web: Photosynthesis is the process by which organisms convert light energy into chemical energy, using carbon dioxide and water1 to produce organic compounds like sugars and amino acids. This process forms the foundation of most food webs on Earth.
  • Diverse Photosynthesizers: Photosynthesis is carried out by a wide range of organisms, including:
    • Plants: All plants, from mosses and ferns to conifers and flowering plants, are capable of photosynthesis.
    • Algae: This diverse group includes both multicellular seaweeds and unicellular algae like Chlorella.
    • Photosynthetic Prokaryotes: Several groups of bacteria, including cyanobacteria (blue-green bacteria) and purple bacteria, are also photosynthetic.
  • Evolutionary Distribution: Photosynthesis is present in two of the three domains of life: Eukaryotes and Bacteria. It is notably absent in Archaea.

Photosynthesis is a vital process that sustains life on Earth. It provides the energy and organic molecules that form the basis of the food web and supports the diverse ecosystems of our planet.

B4.2.4—Holozoic nutrition in animals

Holozoic Nutrition: The Animal Way of Eating

  • Heterotrophs: Animals are heterotrophs, meaning they obtain their carbon compounds (like carbohydrates and proteins) by consuming other organisms.
  • Key Stages of Holozoic Nutrition:
    1. Ingestion: Taking in food through the mouth.
    2. Digestion: Breaking down large food molecules (like proteins and carbohydrates) into smaller molecules (like amino acids and simple sugars) through mechanical and chemical processes.
    3. Absorption: Transporting the digested nutrients across the intestinal lining into the bloodstream.
    4. Assimilation: Using the absorbed nutrients to build and repair tissues, and for energy production.
    5. Egestion: Eliminating undigested material from the body through feces.

Variations in Feeding Strategies:

  • Holozoic vs. Extracellular Digestion: While most animals exhibit holozoic nutrition, some, like spiders, digest their food externally. They inject digestive enzymes into their prey, break down the tissues, and then ingest the resulting liquid.

Holozoic nutrition is the characteristic mode of feeding in animals, involving the ingestion, digestion, absorption, assimilation, and egestion of food to obtain the necessary nutrients for survival and growth.

B4.2.5—Mixotrophic nutrition in some protists

Mixotrophy: A Flexible Feeding Strategy

  • A Combination of Strategies: Mixotrophs are organisms that can obtain energy and carbon through both autotrophic and heterotrophic pathways.
  • Facultative Mixotrophs: These organisms can switch between autotrophic and heterotrophic modes depending on environmental conditions. A well-known example is Euglena gracilis, which can photosynthesize in the presence of light but can also feed on detritus or other organisms.
  • Obligate Mixotrophs: These organisms must use both autotrophic and heterotrophic modes to survive and grow. This may be due to a requirement for specific nutrients that they cannot synthesize themselves. Some protists even obtain chloroplasts from other organisms and utilize them for photosynthesis until they degrade.

Ecological Significance:

  • Metabolic Versatility: Mixotrophy provides organisms with a flexible metabolic strategy, enabling them to thrive in environments with fluctuating resource availability.
  • Ecological Impact: Mixotrophic organisms can play important roles in aquatic ecosystems, influencing nutrient cycling and food web dynamics.

Mixotrophy represents a fascinating example of metabolic flexibility in unicellular eukaryotes. By combining autotrophic and heterotrophic modes of nutrition, these organisms can adapt to diverse environmental conditions and thrive in a variety of ecological niches.

B4.2.6—Saprotrophic nutrition in some fungi and bacteria

Saprotrophs: Nature’s Recyclers

  • Decomposers: Saprotrophs are organisms that obtain their nutrients by breaking down dead organic matter. They play a vital role in the ecosystem as decomposers, recycling nutrients back into the environment.
  • Extracellular Digestion: Saprotrophs secrete digestive enzymes onto the dead organic matter, breaking it down into smaller molecules. They then absorb these digested products for their own use.
  • Key Role in Nutrient Cycling: By breaking down complex organic matter into simpler compounds, saprotrophs release essential elements like carbon, nitrogen, and phosphorus back into the ecosystem, making them available for other organisms.

Examples:

  • Fungi: Many fungi, like mushrooms and molds, are saprotrophs. They play a crucial role in decomposing dead leaves, wood, and other organic debris.
  • Bacteria: Numerous bacteria are also saprotrophs, contributing to the breakdown of a wide range of organic materials.

Saprotrophs are essential for the functioning of ecosystems. They play a critical role in nutrient cycling, ensuring the continuous flow of nutrients through the food web and maintaining the health of the planet.

B4.2.7—Diversity of nutrition in archaea

Archaea: A Domain of Metabolic Diversity

  • Unique Domain: Archaea are a distinct domain of life, sharing some characteristics with bacteria (e.g., lack of a nucleus) but also exhibiting significant differences, particularly in their molecular biology and biochemistry.
  • Extremophiles: Many archaea are extremophiles, thriving in environments that would be inhospitable to most other organisms, such as hot springs, salt lakes, and deep-sea vents.
  • Diverse Metabolic Strategies: Archaea exhibit a remarkable diversity in their energy acquisition strategies. They can be:
    • Phototrophic: Utilize light energy for ATP production, but with pigments other than chlorophyll.
    • Chemotrophic: Obtain energy by oxidizing inorganic compounds, such as iron or sulfur.
    • Heterotrophic: Obtain energy by breaking down organic compounds from other organisms.

Ecological Significance:

  • Metabolic Versatility: The diverse metabolic capabilities of archaea have significant ecological implications. They play important roles in various biogeochemical cycles, such as the carbon and sulfur cycles.
  • Extremophiles as Models: The study of extremophiles can provide valuable insights into the limits of life and the potential for life to exist in extreme environments, including those found on other planets.

Archaea demonstrate a remarkable diversity in their metabolic strategies, showcasing the adaptability of life to a wide range of environmental conditions. Their unique metabolic capabilities and ability to thrive in extreme environments make them a fascinating and important area of research.

B4.2.8—Relationship between dentition and the diet of omnivorous and herbivorous representative members of the family Hominidae

Dentition: A Window into Diet

  • Hominidae Diversity: The family Hominidae includes humans, orangutans, gorillas, and chimpanzees. This diverse group exhibits a range of dietary preferences, from herbivory to omnivory.
  • Dental Adaptations:
    • Herbivores: Tend to have large, flat teeth designed for grinding tough plant material.
    • Omnivores: Exhibit a mix of tooth types, including flat molars for grinding plant matter and sharper canines and incisors for tearing meat.
  • Humans: A Mixed Diet: Humans, as omnivores, possess a combination of these dental features. We have flat molars for grinding plant-based foods and sharper canines and incisors for tearing and cutting meat.
  • Inferring Diet in Extinct Species: By studying the dental characteristics of extinct hominids like Homo floresiensis and Paranthropus robustus, scientists can infer their likely dietary habits.

The dentition of an organism provides valuable clues about its diet. By analyzing the size, shape, and wear patterns of teeth, scientists can reconstruct the feeding habits of both living and extinct species, including those within the Hominidae family.

B4.2.9—Adaptations of herbivores for feeding on plants and of plants for resisting herbivory

Plant-Herbivore Interactions: An Evolutionary Arms Race

Herbivore Adaptations:

  • Diverse Mouthparts: Herbivorous insects have evolved a wide variety of mouthpart adaptations for feeding on plants, reflecting the diverse plant structures and defenses.
    • Chewing Mouthparts: Insects like beetles have chewing mouthparts for biting off and chewing leaves.
    • Piercing-Sucking Mouthparts: Insects like aphids have specialized mouthparts for piercing plant tissues and sucking sap.

Plant Defenses:

  • Physical Defenses: Many plants have evolved physical defenses to deter herbivores, such as:
    • Spines and Thorns: These structures deter herbivores by causing injury or discomfort.
    • Tough Leaves: Thick, leathery leaves are difficult for many herbivores to chew and digest.
  • Chemical Defenses: Plants produce a variety of secondary metabolites that are toxic or unpalatable to herbivores. These compounds can deter feeding, disrupt digestion, or even kill herbivores.

An Evolutionary Arms Race:

The interaction between herbivores and plants is an example of an evolutionary arms race. As herbivores evolve adaptations to overcome plant defenses, plants evolve new defenses in response. This ongoing co-evolution results in a dynamic and diverse range of adaptations in both herbivores and plants.

The relationship between herbivores and plants is a complex and dynamic one, driven by continuous evolutionary pressures. Both herbivores and plants have evolved a wide range of adaptations to survive and thrive in this ongoing ecological interaction.

B4.2.10—Adaptations of predators for finding, catching and killing prey and of prey animals for resisting predation

Predators vs. Prey: An Evolutionary Arms Race

Predator Adaptations:

  • Sensory Adaptations: Predators have evolved a variety of sensory adaptations to locate and capture prey. These include keen eyesight, acute hearing, and a well-developed sense of smell.
  • Physical Adaptations: Predators possess physical adaptations for catching and subduing prey, such as sharp claws, teeth, and powerful jaws.
  • Hunting Strategies: Predators employ a range of hunting strategies, including ambush, pursuit, and cooperative hunting.

Prey Adaptations:

  • Physical Defenses: Prey animals have evolved various physical defenses to avoid predation. These include:
    • Camouflage: Cryptic coloration allows prey to blend in with their surroundings.
    • Armor: Shells, spines, and tough exoskeletons provide physical protection.
    • Speed and Agility: Enables prey to escape from predators.
  • Chemical Defenses: Many prey species produce toxins or other chemical deterrents to discourage predators.
  • Behavioral Defenses: Prey animals may exhibit behaviors such as hiding, fleeing, or forming groups to deter predators.

Evolutionary Arms Race:

The predator-prey relationship is an example of an evolutionary arms race. As predators evolve adaptations to capture prey more effectively, prey species evolve counter-adaptations to avoid predation. This ongoing co-evolution results in a dynamic and diverse range of adaptations in both predators and prey.

The interactions between predators and prey drive the evolution of a wide range of adaptations in both groups, shaping the structure and dynamics of ecosystems.

B4.2.11—Adaptations of plant form for harvesting light

The Struggle for Light: Plant Adaptations in Forests

  • Competition for Light: In dense forest ecosystems, where sunlight is a limited resource, plants have evolved a variety of strategies to capture as much light as possible.
  • Trees as Light Competitors: Trees exhibit several adaptations to reach the forest canopy and maximize light capture:
    • Rapid Growth: Many trees have a dominant leading shoot that grows rapidly to reach the canopy before being shaded by other trees.
    • Lianas: These climbing plants use other trees for support, reducing the need to invest heavily in producing woody tissues for structural support.
  • Other Strategies:
    • Epiphytes: These plants grow on the branches and trunks of trees, gaining access to higher light intensity.
    • Strangler Figs: These epiphytes eventually engulf their host tree, shading it out and taking its place.
    • Shade-Tolerant Plants: Shrubs and herbs in the understory have adapted to survive and thrive in low-light conditions.

The diverse plant forms observed in forests are a result of intense competition for light. These adaptations demonstrate the remarkable strategies that plants have evolved to maximize their access to sunlight and ensure their survival in these challenging environments.

B4.2.12—Fundamental and realized niches

The Niche Concept: Where an Organism Fits

  • Fundamental Niche: The fundamental niche represents the full range of environmental conditions and resources that a species could theoretically occupy in the absence of competition and other limiting factors. It is determined by the species’ physiological tolerances and adaptations.
  • Realized Niche: The realized niche is the actual range of conditions and resources that a species occupies in the presence of competitors, predators, and other interactions. It is often narrower than the fundamental niche due to these interactions.
  • Competition and Resource Partitioning: Competition with other species can restrict a species to a smaller portion of its potential niche. This leads to resource partitioning, where species evolve to specialize in using different resources or occupying different parts of the environment to minimize competition.

Example:

  • A bird species might have a fundamental niche that includes a wide range of food sources and nesting sites. However, in the presence of competitors, the bird may be restricted to a smaller realized niche, specializing in a particular type of food or nesting in specific locations to avoid competition.

The concept of fundamental and realized niches helps us understand how species interact with their environment and how competition shapes the distribution and abundance of organisms in ecosystems.

B4.2.13—Competitive exclusion and the uniqueness of ecological niches

Competitive Exclusion Principle

  • Overlapping Niches: When two species have overlapping fundamental niches (meaning they require similar resources and inhabit similar environments), they will compete for those shared resources.
  • Competitive Exclusion: If one species outcompetes the other in all aspects of the fundamental niche, the less competitive species will be excluded from that ecosystem. This is known as the competitive exclusion principle.

Evidence from Flour Beetles:

  • Experimental Demonstration: The image shows the results of an experiment with two species of flour beetles, Tribolium castaneum and Tribolium confusum.
  • Temperature and Humidity Influence: The outcome of competition varied depending on temperature and humidity levels. In some conditions, T. castaneum outcompeted T. confusum, while in others, T. confusum was more successful.
  • Pie Charts: The pie charts illustrate the percentage of trials where each species outcompeted the other under different environmental conditions.

Ecological Implications:

  • Resource Partitioning: To avoid competitive exclusion, species often evolve to specialize in using different resources or occupying different parts of their environment. This is known as resource partitioning.
  • Niche Differentiation: Every species must have a unique realized niche (the actual range of conditions and resources it occupies) to coexist with other species in the ecosystem.

The concept of competitive exclusion highlights the importance of niche differentiation for the coexistence of species within an ecosystem. By partitioning resources and occupying unique niches, species can minimize competition and ensure their survival.

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