Unit 3: Populations

• Organism/individual • Population • Community • Ecosystem • Biosphere

The study of factors that cause populations to increase or decrease

○ Size ○ Density ○ Distribution ○ Sex ratio ○ Age structure

The total number of individuals within a defined area at a given time

• The number of individuals per unit area at a given time ○ Helps scientists to determine if a species is rare or abundant

• A description of how individuals are distributed with respect to one another ○ Distributions can be random, uniform, or clumped

The ratio of males to females in a population

A description of how many individuals fit into particular age categories in a population

A factor that influences an individual’s probability of survival and reproduction in a manner that depends on the size of the population

A resource that a population can’t live without and that occurs in quantities lower that the population would require to increase in size

The maximum population of a particular species that a given habitat can support over a given period

A factor that has the same effect on the individual’s probability of survival and the amount of reproduction at any population size

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

The maximum potential for growth of a population under ideal conditions with unlimited resources

• 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

• 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

When a population becomes larger than the environment’s carrying capacity

A rapid decline in a population due to death

• 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

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

Graphs that represent the distinct patterns of species survival as a function of age

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

A pattern of survival over time in which there is a relatively constant decline in the survivorship throughout most of the life span

A pattern of survival over time in which there is low survivorship early in life with few individuals reaching adulthood