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