MYP Biology 7.1 Interdependency Notes

Why Do Organisms Rely On Each Other?

1. No species can meet all survival needs independently.
   1. Most organisms cannot produce their own food.
   2. Many organisms rely on other species for reproduction.
   3. Some organisms depend on others to maintain suitable living conditions.
2. These dependencies form biological links between populations.
   1. Removing one species can indirectly affect many others.
   2. Effects are often indirect rather than immediate.
   3. Changes can spread through multiple species even if they do not interact directly.

What Types Of Dependence Exist Between Organisms?

1. Feeding dependence
   1. Many organisms rely on other species as a food source.
   2. Herbivores depend on plant populations.
   3. Carnivores depend on prey populations.
2. Reproductive dependence
   1. Some plants rely on animals for pollination.
   2. Some plants rely on animals for seed dispersal.
   3. Without these interactions, reproduction success decreases.
3. Habitat dependence
   1. Some organisms create living spaces for others.
   2. Loss of habitat-forming species can affect many dependent species.
4. Decomposer dependence
   1. All ecosystems rely on decomposers to break down dead organisms.
   2. Without decomposers, nutrients would remain locked in dead biomass.

What Is Symbiosis?

1. Symbiotic relationships are classified by their effect on survival and reproduction.
2. Symbiosis represents a strong form of interdependency.
3. The relationship persists over long periods and the removal of one species directly affects the other.

Why Is Interdependency Not Fixed?

1. Interdependency exists on a spectrum.
   1. The balance of benefits and costs can change over time.
   2. Environmental conditions can shift outcomes.
2. A relationship can change category.
   1. Mutualism can shift toward parasitism if one species gains without contributing.
   2. Commensalism may become harmful if conditions change.

Why Do Changes In One Species Affect Others?

1. Species are connected through multiple dependencies.
   1. A change in one population alters the availability of resources for others.
   2. Indirect effects can spread beyond immediate interactions.
2. These effects are called ripple effects.
   1. One population change triggers changes in others.
   2. The full impact may take time to appear.

How Does Interdependency Prepare Us For Other Interactions?

1. Interdependency explains why interactions matter biologically.
   1. Competition occurs because species rely on shared resources.
   2. Predator–prey interactions exist because species depend on others for food.
   3. Parasitism exists because some organisms depend on hosts for survival.
2. Understanding interdependency makes later topics easier to analyse.
   1. It explains why population changes rarely affect only one species.
   2. It provides the logic behind ecosystem instability.