Fundamentals of Population Ecology
📌 A population is defined as a group of individuals of the same species in the same place at the same time.
➕ Population size is affected by four key components: births (positive influence), deaths (negative influence), immigration (individuals moving in, positive), and emigration (individuals leaving, negative).

Methods for Counting Populations
🔢 For mobile organisms, the Mark and Recapture method is used with the formula $N = \frac{(M \times C)}{R}$, where $N$ is the estimated population.
* When calculating $N$, the resulting decimal number must always be rounded down to the nearest whole number because you cannot have a fraction of an organism.
* For slow-moving or stationary organisms, Quadrat Sampling involves using a standardized square area (e.g., $1 \text{m} \times 1 \text{m}$) to estimate density, requiring random placement of samples.
* When using quadrats, individuals on the edge are only counted if most of their body is inside the defined square.

Carrying Capacity and Population Dynamics
📉 Carrying capacity is the maximum number of individuals an ecosystem can sustainably support, limited by available resources like food and shelter.
⬆️ A population curve often overshoots the carrying capacity due to rapid reproduction before environmental resistance causes a dramatic dip; realistic curves fluctuate slightly above and below this maximum over time.
🛑 Environmental resistance is the force (linked to limited resources) that pushes down on a population, creating and maintaining the carrying capacity.

Factors Influencing Population Size
🧩 Density-Dependent Factors are linked to population size, such as food availability, shelter, predation, and disease; higher density increases the impact of these factors.
🌪️ Density-Independent Factors are not linked to population size and result from natural phenomena like climate changes (droughts, floods) or natural disasters (tsunamis), affecting all individuals equally regardless of density.

Key Points & Insights
➡️ Understand the four demographic factors affecting population size: Births, Deaths, Immigration, and Emigration.
➡️ When estimating population size using Mark and Recapture, always round the final result down to the nearest whole number.
➡️ Distinguish between density-dependent factors (like food scarcity) which are based on population density, and density-independent factors (like natural disasters) which affect populations regardless of size.

📸 Video summarized with SummaryTube.com on Nov 04, 2025, 20:42 UTC