Summary Resources In Ecosystems - Science for Grade 7

Introduction

Population dynamics is the study of how and why populations change. It examines key aspects such as:

• Population size
• Growth
• Distribution

Population changes affect economic, social, and environmental systems and influence resources like air, land, and water.

World Population

• Global population rose sharply over recent centuries, from under one billion in 1900 to over seven billion today.
• Most people live in developing countries and population distribution is uneven across regions.
• Population growth rate has slowed recently but future trends are uncertain.
• Health improvements can lower death rates and raise population; disease and conflict can reduce population locally.

Distribution of Population

• Population distribution shows where people live, often using maps of density.
• Population density is the number of people per square kilometre.
• Density varies by place; areas are classed as low, medium, or high density.
• Formula: Population density = Total population / Total land area in km².
• Density categories: Low (fewer than 10 per km²), Medium (10-50 per km²), High (more than 50 per km²).

Factors Responsible for Population Growth

• Major groups of factors: Physical, Economic, Social and cultural.

Physical Factors

• Landforms: Flat areas are more suitable for settlement; mountainous areas are less populated due to difficult terrain.
• Climate: Moderate climates attract people; extreme climates deter settlement.
• Soil fertility: Fertile soils support agriculture and attract larger populations.
• Water availability: Access to fresh water strongly influences population density.

Economic Factors

• Mineral wealth: Mineral resources attract industry and workers.
• Urbanization: Cities attract migrants for jobs, education, health services, and amenities.
• Industrialization: Industrial regions create diverse job opportunities and support larger populations.

Social and Cultural Factors

• Social and political stability: Stability attracts or retains people; unrest causes movement away.
• Religious significance: Cities with religious or cultural importance attract residents and visitors.

Factors Affecting Population Change

• Birth rate: Number of live births per 1,000 people per year; higher birth rates increase population.
• Death rate: Number of deaths per 1,000 people per year; higher death rates reduce population.
• Migration: Movement of people between places; emigration decreases and immigration increases a country's population.
• Natural Increase: Birth rate minus death rate; expressed as a percentage by dividing the difference by 10.

Overpopulation and Underpopulation

• Overpopulation occurs when resources are insufficient for the population, causing unemployment, pollution, and environmental damage.
• Essential resources that become scarce include food, shelter, clean water, fuel, and farmland.
• Reasons for overpopulation include migration to richer areas, illiteracy, poverty, and changes in birth and death rates driven by healthcare.
• Consequences of overpopulation: depletion of resources, environmental degradation, economic strain, and poor health and sanitation.
• Underpopulation occurs when a population is too small to use resources effectively; causes include low fertility, emigration, disease, and famine.
• Consequences of underpopulation: economic deflation from low demand, reduced resource pressure, increased burden on youth, and labour shortages.

Population Composition

• Rural-Urban composition: Agricultural countries have larger rural populations; industrialized countries have larger urban populations. Urban growth is rapid in many developing countries.
• Literacy: Literacy affects living standards and development. Globally, 17% remain illiterate. Global literacy rates: 90% for males and 82.7% for females. Developed countries around 99.2%. India overall 74.04%; Kerala 93.91%; Bihar 63.82%.
• Sex composition: Expressed as number of females per 1,000 males. More males are born, but females often live longer. Factors affecting sex ratio include differential mortality, migration patterns, and social practices. India's sex ratio (2011) was 940 females per 1,000 males. Issues affecting female numbers include female foeticide, gender discrimination, female infanticide, sex-selective abortions, and neglect of girls.
• Age composition: Population divided into three groups:
  • Children: 0-14 years (dependent)
  • Working age: 15-59 years (productive)
  • Old age: 60+ years (dependent)
  The dependent population includes children and the elderly who rely on the working-age group.

Population Pyramid

• Population pyramid is a chart showing population by age and sex; males left, females right.
• Main types: Progressive, Expansive, Stationary, and Constrictive (Stable or Declining).
• Progressive: broad base, narrow top - high birth and death rates, large child population.
• Expansive: wide base with more reaching middle age - high birth rates with lower child death rates and increasing life expectancy.
• Stationary: rectangular shape - similar numbers across age groups, high life expectancy, stable birth rates.
• Constrictive: narrow base and wider middle/top - low birth rates, high life expectancy, more elderly than youth, possible population decline.