IB MYP 4-5 Biology-Interdependency- Study Notes - New Syllabus
IB MYP 4-5 Biology-Interdependency- Study Notes – New syllabus
IB MYP 4-5 Biology-Interdependency- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Symbiosis (mutualism/commensalism/parasitism)
- Keystone species (e.g., wolves in Yellowstone)
- Human impacts on ecological relationships
- Symbiosis (mutualism/commensalism/parasitism)
- Keystone species (e.g., wolves in Yellowstone)
- Human impacts on ecological relationships
Interdependency in Ecosystems
Symbiosis: Mutualism, Commensalism, and Parasitism
What Is Interdependency?
Interdependency refers to the way organisms in an ecosystem rely on one another for survival. These interactions help maintain ecological balance and resource flow.
One of the most important types of interdependency is symbiosis.
What Is Symbiosis?
Symbiosis is a long-term biological interaction between two different species. At least one of the organisms benefits from the relationship. There are three main types of symbiosis:
1. Mutualism 
Both species benefit from the relationship. This cooperative interaction often enhances survival or reproduction for both organisms.
- Coral and zooxanthellae: Corals provide shelter, algae provide food via photosynthesis.
- Bees and flowering plants: Bees collect nectar, plants get pollinated.
- Humans and gut bacteria: Bacteria aid digestion, receive nutrients and habitat.
2. Commensalism
One species benefits while the other is unaffected (neither helped nor harmed).
- Barnacles on whales: Barnacles get mobility and food access, whale is unaffected.
- Epiphytic plants on trees: Orchids grow for sunlight, tree is not harmed.
- Birds nesting in trees: Shelter for birds, no impact on tree.
3. Parasitism
One organism benefits (parasite) at the expense of the host, which is harmed.
- Tapeworm in humans: Absorbs nutrients, causing malnutrition.
- Fleas or ticks on animals: Suck blood, may spread disease.
- Plasmodium (malaria parasite): Destroys red blood cells, causing illness.
Types: Endoparasitic (inside the host) e.g., tapeworm. Ectoparasitic (on surface) e.g., lice.
Comparison Table
| Symbiosis Type | Organism A | Organism B | Example |
|---|---|---|---|
| Mutualism | Benefits | Benefits | Coral and algae |
| Commensalism | Benefits | Unaffected | Barnacles on whales |
| Parasitism | Benefits | Harmed | Plasmodium in humans |
Summary:
Interdependency strengthens ecosystem structure through interactions such as symbiosis. Mutualism benefits both partners, commensalism benefits one without harming the other, and parasitism benefits one while harming the host. These relationships reflect evolutionary adaptations and contribute to biodiversity and ecological balance.
Keystone Species
What Is a Keystone Species?
A keystone species is a species that has a disproportionately large impact on its ecosystem relative to its abundance. Removing a keystone species can lead to a cascade of changes, often causing the ecosystem to become unstable or collapse.
Characteristics of Keystone Species
- Not always abundant, but highly influential
- Help maintain species diversity
- Control populations of other species
- Often involved in trophic interactions (e.g., predation, food chain regulation)
Types of Keystone Species
- Predators: Control herbivore populations and prevent overgrazing
- Ecosystem engineers: Modify the environment (e.g., beavers building dams)
- Mutualists: Form crucial relationships (e.g., pollinators, seed dispersers)
Case Study: Wolves in Yellowstone National Park
Background:
Wolves were removed from Yellowstone in the 1920s. This led to a sharp increase in elk populations, which caused:
- Overgrazing of young trees and shrubs
- Decline of species dependent on forest habitats (e.g., beavers, songbirds)
- Erosion and loss of biodiversity
Reintroduction in 1995:
When wolves were reintroduced:
- Elk behavior changed: they avoided open riverbanks and valleys
- Vegetation began to recover (willows, aspens, cottonwoods)
- Beavers returned, creating ponds and new habitats
- Increase in bird, fish, and amphibian populations
- Reduced coyote numbers allowed small mammals like rabbits to thrive
- Rivers became more stable due to increased vegetation
Conclusion:
Wolves regulated elk, which indirectly supported vegetation, biodiversity, and habitat structure. Their presence restored balance to the ecosystem.
Why Keystone Species Matter
- Maintain ecological balance
- Prevent dominance of single species
- Protect the structure of food webs
- Support habitat diversity
Keystone species are essential for the health and stability of ecosystems. Their removal can trigger ecological collapse through trophic cascades. The wolf reintroduction in Yellowstone is a classic case showing how one species can transform an entire ecosystem.
Human Impacts on Ecological Relationships
Introduction:
Human activities continuously shape the structure and dynamics of ecosystems. From urban development to industrial pollution, these impacts often weaken essential interactions such as feeding, reproduction, and species balance, making ecosystems more fragile.
1. Habitat Loss and Fragmentation
Clearing forests, expanding cities, and draining wetlands reduce or divide habitats. This limits species movement, food access, and reproduction. The disappearance of keystone species may destabilize entire ecosystems.
Example: Deforestation in tropical rainforests disrupts the lives of pollinators and tree-dwelling species, impacting plant reproduction and forest regeneration.
2. Pollution
Industrial waste, fertilizers, and plastics pollute air, water, and soil. These toxins can disrupt growth, symbiosis, and survival of many species.
Example: Fertilizer runoff causes algal blooms that reduce oxygen in water, suffocating fish and aquatic life.
3. Overharvesting and Exploitation
Excessive fishing, hunting, and harvesting remove species faster than they can recover. This affects predator-prey balance and ecosystem function.
Example: Overfishing of predators allows jellyfish populations to surge, which alters marine food webs.
4. Introduction of Invasive Species
Species introduced to new environments may outcompete local organisms and spread rapidly, disrupting native food chains and habitats.
Example: Cane toads in Australia have harmed native predators that die after consuming the toxic toads.
5. Climate Change
Rising temperatures, changing rainfall patterns, and seasonal shifts affect species behaviors and relationships. This can lead to mismatches in reproduction, feeding, and migration.
Example: Earlier spring blooms may miss the emergence of pollinators, reducing reproductive success in plants.
6. Disruption of Nutrient Cycles
Burning fossil fuels and using artificial fertilizers changes the flow of nitrogen, carbon, and phosphorus. This can lead to eutrophication and ecological imbalance.
Example: Excess nitrogen in lakes causes dense algal blooms that block sunlight and kill aquatic organisms.
Summary:
Human influences ranging from habitat destruction to climate change alter the delicate web of ecological relationships. Recognizing and mitigating these impacts are essential steps toward preserving biodiversity and ensuring long-term ecological health.