Population (ecology)
In ecology, a population is a group of individuals of the same species living in the same geographic area at the same time and capable of interbreeding. Population ecology studies how populations change in size and composition over time, driven by birth rates, death rates, immigration, and emigration. Understanding populations is essential for conservation biology, fisheries management, and predicting the spread of invasive species.
Key Formula
N(t+1) = N(t) + B - D + I - E
LaTeX: N_{t+1} = N_t + B - D + I - E
| Symbol | Meaning | Unit |
|---|---|---|
| N_t | Population size at time t | individuals |
| B | Births during time interval | individuals |
| D | Deaths during time interval | individuals |
| I | Immigrants entering the population | individuals |
| E | Emigrants leaving the population | individuals |
Worked Example
Problem
A deer population in a forest reserve starts the year with 200 individuals. During the year, 40 deer are born, 15 die, 5 migrate in, and 10 migrate out. What is the population size at the end of the year?
Solution
Using the population change equation: N(t+1) = N(t) + B − D + I − E N(t+1) = 200 + 40 − 15 + 5 − 10 N(t+1) = 200 + 20 N(t+1) = 220
Answer
220 individuals at the end of the year
Key Population Parameters
| Parameter | Symbol | Definition | Units |
|---|---|---|---|
| Population size | N | Total number of individuals | individuals |
| Birth rate | b | Births per individual per unit time | individuals/time |
| Death rate | d | Deaths per individual per unit time | individuals/time |
| Growth rate | r | b − d (intrinsic rate of increase) | per time unit |
| Carrying capacity | K | Maximum sustainable population size | individuals |
Interactive Tools
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Related Terms
Ecosystem
An ecosystem is a biological community of interacting organisms together with the physical environment they inhabit, including all living (biotic) and non-living (abiotic) components. It represents a functional unit of ecology where energy flows and nutrients cycle between organisms and their environment. Ecosystems range in scale from a small pond to the entire Amazon rainforest and are the foundational units studied in ecology.
Community (ecology)
An ecological community is an assemblage of populations of different species that live in the same area and interact with one another. Communities are characterised by their species composition, diversity, and the web of interactions such as predation, competition, and mutualism. The study of communities examines how these interactions shape the structure and stability of ecosystems over time.
Ecological Niche
An ecological niche describes the functional role and position of a species within its ecosystem, encompassing all the physical, chemical, and biological conditions it requires to survive, reproduce, and maintain a population. Unlike a habitat (where an organism lives), a niche defines what an organism does — what it eats, when it is active, and how it interacts with other species. The competitive exclusion principle states that no two species can occupy exactly the same niche indefinitely in the same habitat.
From Latin populatio (a people, crowd), derived from populus (people). In ecological usage, the term was formalised in the early 20th century through the work of demographers and ecologists such as Raymond Pearl.