2.1C Ecological Niche and Population Interactions Notes

The Ecological Niche

1. Every species in an ecosystem has a unique ecological niche, its role and position within that system.
2. The niche describes the set of abiotic and biotic conditions that determine where and how a species lives, survives, and reproduces.
3. It includes all environmental requirements and interactions necessary for an organism’s growth, survival, and reproduction, such as food sources, temperature tolerance, and behavioral adaptations.

Components of a Niche

1. Habitat: The physical environment where the species lives (e.g., forest floor, coral reef, tundra).
2. Feeding habits: Type of food consumed and method of obtaining it (e.g., carnivore, herbivore, detritivore).
3. Temporal activity: When the species is active (diurnal, nocturnal, seasonal).
4. Interactions: Symbiotic relationships, competition, and mutualistic partnerships.
5. Physiological range: Tolerance limits for temperature, salinity, pH, and humidity.
6. Reproductive strategy: Mating behavior, breeding season, and parental investment.

Types of Niches

1. Fundamental niche: The full range of environmental conditions under which a species could survive and reproduce.
2. Realized niche: The portion of the fundamental niche that a species actually occupies, considering competition and other limiting factors.

Competitive Exclusion Principle

1. Proposed by G.F. Gause (1934), this principle states that no two species can occupy the exact same niche indefinitely in a stable ecosystem.
2. If two species compete for identical resources, the superior competitor will eventually exclude the other.
3. Some species avoid this by resource partitioning, i.e., dividing resources spatially or temporally.

Population Interactions

1. Populations interact in various ways within ecosystems, shaping ecological balance, population sizes, and evolutionary adaptations.
2. These interactions drive natural selection, influencing species behavior and survival.
3. These interactions create complex food webs and energy flows within ecosystems.
4. The major interaction types include herbivory, predation, parasitism, mutualism, disease, and competition.

1. Herbivory

1. Herbivory occurs when an animal feeds directly on plant material.
2. It influences both the plant population (by reducing biomass) and the herbivore population (through food availability).
3. Effect on Population Dynamics:
   1. Overgrazing reduces plant availability, limiting herbivore populations.
   2. Plants develop chemical defenses, reducing herbivore feeding success.

2. Predation (Predators vs. Prey)

1. Predation is an interaction in which one organism (predator) kills and eats another (prey).
2. Predator-prey relationships regulate population sizes through negative feedback loops, maintaining ecological balance.
3. Effect on Population Dynamics:
   1. High parasite loads reduce host survival and reproduction.
   2. Infected populations may develop partial immunity over generations.

3. Parasitism (Parasite vs. Host)

1. Parasitism involves one organism (parasite) benefiting at the expense of another (host).
2. The parasite depends on the host for nutrients or habitat, often weakening but not immediately killing it.
3. Types:
   1. Ectoparasites live on the surface (e.g., ticks on dogs).
   2. Endoparasites live inside the host (e.g., tapeworms in humans).
4. Effect on Population Dynamics:
   1. High parasite loads reduce host survival and reproduction.
   2. Infected populations may develop partial immunity over generations.

4. Mutualism (Both Species Benefit)

1. Mutualism is a symbiotic interaction where both species benefit.
2. It enhances survival, reproduction, and carrying capacity for both participants.
3. Mutualisms can be obligate (necessary for survival) or facultative (beneficial but not essential).

Example

• Bees collect nectar for food while pollinating flowers, enhancing plant reproduction.
  • Ecological effect: Increases productivity and biodiversity.
  • Behavioural effect: Species develop interdependent behaviors (e.g., flower recognition).
  • Evolutionary effect: Coevolution enhances mutual benefits as floral structures evolve to suit pollinators.
• Effect on Population Dynamics:
  • More bees = higher plant reproduction rates.
  • More flowering plants = higher bee populations due to nectar availability.

5. Disease (Pathogens vs. Hosts)

1. Disease is caused by pathogens (bacteria, viruses, fungi, protozoa) that infect a host, reducing its health and fitness.
2. Diseases can act as selective pressures, favoring individuals with natural immunity.
3. Effect on Population Dynamics:
   1. Outbreaks reduce host populations, sometimes leading to local extinction.
   2. Some populations develop resistance, preventing mass die-offs.

Example

• White-nose syndrome in bats is a fungal disease that disturbs hibernation, leading to starvation and massive population declines.
  • Ecological effect: Alters community dynamics and food web balance.
  • Behavioural effect: Populations adopt avoidance strategies or develop immunity.
  • Evolutionary effect: Acts as a selective pressure favoring resistant individuals.

6. Competition (Interspecific & Intraspecific)

1. Competition occurs when organisms vie for limited resources such as food, space, water, or mates.
2. It can be:
   1. Intraspecific: Among individuals of the same species.
   2. Interspecific: Between different species.
3. Effect on Population Dynamics:
   1. Dominant individuals breed more, shaping population genetics.
   2. Limited resources lead to territorial behaviors and population control.