Table of contents |
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Population Attributes |
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Population Growth |
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Growth Models |
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(i) Exponential Growth |
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(ii) Logistic Growth |
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Life History Variation |
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Birth and death rates are crucial attributes of a population. While an individual organism may experience births and deaths, a population is characterized by birth rates and death rates, which are expressed per capita. These rates reflect the change in numbers (increase or decrease) concerning the members of the population.
Example:
A population's sex ratio indicates the proportion of males and females within it. For instance, if 60 percent of the population are females and 40 percent are males, this distribution reflects the sex ratio of the population.
Representation of age pyramids for human population
Understanding these population attributes is essential for studying ecological processes, such as competition with other species, the impact of predators, or the effects of pesticide applications, all evaluated in terms of changes in population size.
Population growth refers to the change in the number of individuals in a population over time. It is influenced by factors such as birth rates, death rates, immigration, and emigration. Understanding these factors helps us analyze whether a population is increasing, decreasing, or stable.
Population density varies over time due to factors like food availability, predation, and weather.Changes in density indicate whether a population is thriving or declining.
Four basic processes affect population density:
Population Density Key Processes
So, if N is the population density at time t, then its density at time t +1 is
Nt+1 = Nt + [(B + I) – (D + E)]
Understanding how populations grow over time can help us learn about controlling population growth.
There are two main models to explain how populations grow:
Exponential growth occurs when a population increases rapidly over time without any limits on resources like food and space.
Population growth curve a when responses are not limiting the growth, plot is exponential, b when responses are limiting the growth, plot is logistic, K is carrying capacity
Key Equation: The change in population size over time can be expressed with the formula:
dN/dt = (b - d) × N where:
dN/dt: Change in population size over time
b: Birth rate
d: Death rate
N: Population size
Intrinsic Rate of Natural Increase (r): This is a crucial factor in understanding population growth. It is calculated as r = b - d. For example, the Norway rat has an r value of 0.015, the flour beetle 0.12, and in 1981, India's human population had an r value of 0.0205.
J-shaped Curve: When plotted on a graph, exponential growth creates a J-shaped curve, indicating rapid population increase over time.
Integral Form: The integral form of the exponential growth equation is:
Nt = N0ert
where:Nt: Population density after time t
N0: Population density at time zero
r: Intrinsic rate of natural increase
e: Base of natural logarithms (approximately 2.71828)
Anecdote: To illustrate exponential growth, consider the story of a king and a minister playing chess. The minister bets on receiving wheat grains placed on the chessboard in a doubling pattern. This story highlights how quickly populations can grow when resources are unlimited, similar to how a tiny organism like Paramecium could multiply rapidly under ideal conditions.
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Population Attributes & Growth
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1. What is exponential growth in population dynamics? | ![]() |
2. How does logistic growth differ from exponential growth? | ![]() |
3. What factors influence population growth rates? | ![]() |
4. What is the concept of carrying capacity in logistic growth? | ![]() |
5. How do life history traits affect population growth? | ![]() |