Exponential Growth: Occurs in an environment with unlimited resources, where the population size increases at a constant rate per individual, resulting in a J-shaped curve.
Logistic Growth: Describes population growth that slows as it approaches the carrying capacity of the environment, resulting in an S-shaped curve as resources become limiting.
Carrying Capacity (): The maximum number of individuals of a particular species that a specific environment can sustainably support without degrading the resource base.
Growth Rate Formula: The change in population size over time is often expressed as , where is the intrinsic rate of increase.
Life Tables: Tools used to track the fate of a cohort (a group of individuals born at the same time) from birth until the death of the last member, calculating age-specific mortality and life expectancy.
Type I Survivorship: Characterized by high survival rates in early and middle life, followed by a rapid decline in old age; typical of large mammals that provide extensive parental care.
Type II Survivorship: Shows a constant mortality rate throughout the individual's lifespan, where the probability of dying is independent of age; common in many bird species and small reptiles.
Type III Survivorship: Features extremely high mortality rates for the young, but those that survive to a certain age have much higher survival rates thereafter; typical of organisms that produce many offspring with little parental care.
| Factor Type | Description | Examples |
|---|---|---|
| Density-Dependent | Factors whose impact varies based on the population density. | Competition, predation, disease, waste accumulation. |
| Density-Independent | Factors that affect population size regardless of its density. | Natural disasters, weather extremes, pollution. |
Graph Interpretation: When looking at growth curves, identify if the slope is increasing (exponential) or leveling off (logistic). The point where the logistic curve flattens is the carrying capacity ().
Density Calculations: Always check units. If a question asks for density, ensure you divide the total population () by the specific area or volume provided.
Survivorship Identification: Remember that the y-axis of survivorship curves is usually logarithmic. A straight downward slope on a log scale indicates a constant percentage of death (Type II).
Common Mistake: Do not confuse 'zero population growth' with a 'dead population.' Zero growth means birth rates equal death rates, resulting in a stable population size.
