BackPopulation Growth Models and Life History in General Biology
Study Guide - Smart Notes
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Population Growth Models
Exponential Growth Model
The exponential growth model describes how a population increases when resources are unlimited and environmental conditions are ideal. The population grows at a constant rate over each time period, resulting in rapid expansion.
Key Assumptions:
Resources (such as food, space, etc.) are unlimited.
All individuals have equal chances of survival and reproduction.
No immigration or emigration occurs.
Birth and death rates remain constant.
Growth Pattern: Population grows at a constant rate (r).
Curve Shape: Produces a J-shaped curve.
Equation:
Where:
N = population size
r = intrinsic rate of increase
Logistic Growth Model
The logistic growth model considers resource limitations and describes how population growth slows as the population approaches a maximum sustainable size, known as the carrying capacity.
Key Features:
Considers resource limitations.
Growth slows as population approaches a maximum size.
Produces an S-shaped (sigmoidal) curve.
Equation:
Where:
K = carrying capacity (maximum population size the environment can support)
Comparison of Exponential and Logistic Models
The following table summarizes the main differences between the exponential and logistic models:
Feature | Exponential Model | Logistic Model |
|---|---|---|
Resource Limitation | Not considered | Considered |
Growth Rate | Constant | Decreases as population nears carrying capacity |
Curve Shape | J-shaped | S-shaped (sigmoidal) |
Carrying Capacity | Not included | Included |
Life History and Natural Selection
Definition of Life History
Life history is the pattern of growth, reproduction, and survival that an organism follows throughout its life. It encompasses traits such as age at first reproduction, number of offspring, frequency of reproduction, and lifespan.
Key Traits:
Age at first reproduction
Number of offspring produced
Frequency of reproduction
Lifespan
Life History Traits and Natural Selection
Life history traits influence how well an organism survives and reproduces, affecting its overall fitness. Natural selection acts on these traits, favoring those that help organisms leave more offspring in their environment. Over time, populations evolve life history strategies that are best suited to their ecological conditions.
Fitness: The ability of an organism to survive and reproduce in its environment.
Natural Selection: The process by which traits that improve survival and reproduction become more common in a population.
Adaptation: Life history strategies evolve to match ecological conditions, such as resource availability and predation pressure.
Example: Species with high predation risk may reproduce earlier and produce more offspring, while species in stable environments may invest more in fewer offspring and longer lifespans.
