Ecology Notes: Populations and Communities

Definition: A population is defined as all organisms of the same species within a specified area.
Emphasis: Focuses on factors affecting population growth and regulation.
Ecology: Studies factors affecting population growth, regulation, size, and distribution of organisms (where & why in a particular place at a particular time).

Population Size: The number of individuals contributing to the population's gene pool at a specific time.

Balance: Population size depends on the balance between natality (births), mortality (deaths), emigration (movement out), and immigration (movement in).
Diagrammatic Representation: Increase in population size (natality, immigration); decrease in population size (mortality, emigration).
Life Events: Life events add individuals to or remove them from the population.
Change in Population Size Equation: $\text{Change in Population size} = (\text{Natality} + \text{Immigration}) – (\text{Mortality} + \text{Emigration})$

Graph: A graph illustrating exponential population growth, showing phases like lag phase, exponential growth phase, deceleration phase, stable equilibrium phase and carrying capacity.

Impact: Species interactions can significantly impact the distribution and abundance of species.
Symbiotic Relationship: Members of two different populations may interact in a symbiotic relationship.
Forms of Symbiosis:
- Parasitism: One organism (parasite) derives nourishment from another (host), similar to predation. Examples: viruses (HIV), protists (malaria), bacteria (Streptococcus sp.).
- Commensalism: One species benefits, and the other is neither benefited nor harmed. Examples: provision of home, transportation, protection.
- Mutualism: Both species benefit from the relationship. Example: bacteria in the human gastrointestinal tract.

Definition: A biological community is an assemblage of populations interacting within the same environment.

Elements: Size, boundary, diversity, and abundance.
Size Differences: No two communities have the same size.
Fluctuation: Community size and composition fluctuate over time.
Boundaries: Clear boundaries between different communities are sometimes difficult to define.
Composition: Refers to the listing of various species in that community.
Diversity: Includes the number of species and the relative abundance of individuals of different species.

Change Over Time and Space: Species in a community may change in time and space, affecting their number and abundance.
Competition (C) and Predation (P): Particularly by dominant species, may lead to the extinction or removal of other species from the community.
Competition: Species utilize the same food source with no specialization.
Predation: Dominant and efficient species monopolize available prey, preventing one prey species from eliminating others through competition.
Maintaining Species Diversity:
1. Resource Subdivision: When species are in potential competition for food, the resource may be subdivided (e.g., specialization).
2. Habitat Variety: A variety of habitats in a community, each with its diversity, may attract different species.
Periodic Disturbance: Creation of different habitats within a region by periodic disturbance.
Climax Community: A community that forms if the land is undisturbed and perpetuates itself. Disturbance leads to ecological succession.
Ecological Succession: The process of returning to its original state after a disturbance, producing a climax community again.
Types of Ecological Succession:
- Primary Succession: Takes place in barren land with limited or no soil (very slow).
- Secondary Succession: Community changes in disturbed areas with soil (more common, faster).
Climate: Another cause of diversity of species within communities.