Population Growth and Regulation
Characteristics of Populations
Demographics are characteristics of populations
Populations can be characterized by their: Population Size
Population Density
Population Distribution
Age structure
Reproductive base # Reproductive and younger
Age Structure Diagram
Green - Pre-reproductive yearsDark Blue- Reproductive yearsLight blue - Post- reproductive years
Age Structure Diagram U.S.
Zero growth:
#births = #deaths and #immigrate = #emigrate
Regarding Population Density:
The same area may be home to many species but they may vary by density
Density refers to the number of individuals in an area but not how they are dispersed
Population density variations are largely due to ecological relationships and organism interactions in an area
Population Size and Exponential Growth:
How population size changes
Size depends on births, immigration, deaths, emigration and migrations
Zero population growth is a near balance between all the positive and negative factors
Ground Zero to Exponential Growth
J Shaped Growth CurveIncrease in population of field mice
Effects of Deaths on Populations
The effects of deaths on the rate of increases in 2
bacterial populations
Regarding the Biotic Potential:
The biotic potential of a population is its maximum rate of increase under ideal conditions
Biotic potentials vary from species to species based on: What age reproduction begins How frequent reproduction is How many offspring are born at a time
Limits on the Growth of Populations:
The actual rate of growth depends on the environmental conditions
Limiting factors are collectively called environmental resistance and include: Nutrient supply Predation Competition for space Pollution Metabolic wastes
Limiting Factors on Growth
The sustainable supply of resources defines the carrying capacity for a population in an environment
The capacity can vary over time
Note the S shaped logistic growth
Carrying Capacity
Density - Dependent Controls:
The main controls are: Competition for resources
Predation
Parasitism
Disease
They exert their effects in proportion to the number of individuals present
Density - dependent factors
Events resulting in more deaths
Fewer births
Fig. 48.4, p. 856
Paramecium caudatum
Paramecium aurelia
Fig. 48.7, p. 858
PREY POPULATION
PREDATOR POPULATION
Fig. 48.8, p. 859
Density Independent Factors:Some events such as weather tend
to increase the death rate without respect to the number of individuals present
Lightning, floods, snowstorms affect both large and small populations!
Life History Patterns:Life Tables
Demography is the study of the age-specific patterns of particular populations
Life tables follow the fate of a group (cohort) and calculate survivorship schedules
A note on… Human Population Growth
Increase in growth rate Expansion of habitat
Increased capacity in existing habitats
Population has sidestepped limiting factors
Technology
Medicine
Population Growth Rate in Different Regions
Population Growth Rate in Different Regions
1996 - Orange2025 - Blue