Unit 3: Populations Flashcards
The five levels of nature
- Organism/individual
- Population
- Community
- Ecosystem
- Biosphere
Population ecology
The study of factors that cause populations to increase or decrease
Basic characteristics of populations
○ Size
○ Density
○ Distribution
○ Sex ratio
○ Age structure
Population size (n)
The total number of individuals within a defined area at a given time
Population density
- The number of individuals per unit area at a given time
○ Helps scientists to determine if a species is rare or abundant
Population distribution
- A description of how individuals are distributed with respect to one another
○ Distributions can be random, uniform, or clumped
Population sex ratio
The ratio of males to females in a population
Population age structure
A description of how many individuals fit into particular age categories in a population
Density-dependent factor
A factor that influences an individual’s probability of survival and reproduction in a manner that depends on the size of the population
Limiting resource
A resource that a population can’t live without and that occurs in quantities lower that the population would require to increase in size
Carrying capacity (K)
The maximum population of a particular species that a given habitat can support over a given period
Density-independent factors
A factor that has the same effect on the individual’s probability of survival and the amount of reproduction at any population size
Population growth rate
The number of offspring an individual can produce in a given time period, minus the deaths of the individual or its offspring during the same period
Instrinsic growth rate (r)
The maximum potential for growth of a population under ideal conditions with unlimited resources
Exponential growth model
- A growth model that estimates a populations future size after a period of time based on the intrinsic growth rate and the number of reproducing individuals currently in the population, without considering limiting factors
□ This model produces a J-shaped curve
□ Exponential growth is a density-independent factor
Logistic growth model
- A growth model that describes a population whose growth is initially exponential, but slows as the population approaches the carrying capacity of the environment
□ This model produces a S-shaped curve
□ Logistic growth is a density-dependent factor
Overshoot
When a population becomes larger than the environment’s carrying capacity
Die-off
A rapid decline in a population due to death
K-selected species
- A species with a low intrinsic growth rate that causes the population to increase slowly until it reaches carrying capacity
○ Large mammals and most birds are K-selected species
r-selected species
A species that has a high intrinsic growth rate, which often leads to population overshoots and die-offs
○ These species reproduce often and produce many offspring
○ Small organisms are r-selected species
Survivorship curves
Graphs that represent the distinct patterns of species survival as a function of age
Type I survivorship curve
A pattern of survival over time in which there is a high survival throughout most of the life span, but then individuals start to die in large numbers as they approach old age
Type II survivorship curves
A pattern of survival over time in which there is a relatively constant decline in the survivorship throughout most of the life span
Type III survivorship curve
A pattern of survival over time in which there is low survivorship early in life with few individuals reaching adulthood
