Environmental Science A Study of Interrelationships Tenth Edition

Environmental Science A Study of Interrelationships Tenth Edition Enger • Smith Chapter 7 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. 1

Population Principles Chapter 7 2

Outline • • • Population Characteristics Age Structure Diagrams Exponential Growth Carrying Capacity – Environmental Resistance Reproductive Strategies – (r and K) Human Population Growth – Doubling Time 3

Population Characteristics • Population - Group of individuals of the same species inhabiting the same area simultaneously. – Natality and Mortality v Natality - Number of individuals added through reproduction. Ø Birth Rate (Humans Born / 1, 000) – Mortality - Number of individuals removed via death. v Death Rate (Humans Died / 1, 000) 4

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Population Characteristics • • Population Growth Rate - Birthrate minus the death rate. Often expressed as a percentage of the total population. Survivorship Curve - Shows proportion of individuals likely to survive to each age. – High mortality in young. – Mortality equitable among age classes. – Mortality high only in old age. 6

Sex Ratio and Age Distribution • Sex Ratio - Age Distribution – Sex Ratio - Relative number of males and females in a population. v Females determine the number of offspring produced in sexually reproducing populations. – Age Distribution - Number of individuals of each age in the population. v Greatly influences population growth rate. 7

Age Distribution in Human Populations 8

Population Density and Spatial Distribution • Population Density - Number of individuals per unit area. – High population may lead to increased competition for resources. v Dispersal - Movement of individuals from densely populated locations to new areas. Ø Emigration - Movement from an area. Ø Immigration - Movement into an area. 9

Population Growth Curve • Biotic Potential - Inherent reproductive capacity. (Biological ability to produce offspring) – Generally, biotic potential is much above replacement level. v Natural tendency for increase. Ø All living populations follow an exponential growth curve. 10

Exponential Growth Curve • • • Lag Phase - First portion of the curve; slow population growth. Exponential Growth Phase (Log Phase)More organisms reproducing causing accelerated growth; continues as long as birth rate exceeds death rate. Stable Equilibrium Phase - Death rate and birth rate equilibrate; population stops growing. 11

Typical Population Growth Curve 12

Carrying Capacity • Carrying Capacity - Number of individuals of a species that can be indefinitely sustained in a given area without harming the habitat. 13

Environmental Resistance • Environmental Resistance - Any factor (limiting factor) in the environment limiting carrying capacity. – Four main factors: v Raw Material Availability v Energy Availability v Waste Accumulation and Disposal v Organism Interactions 14

Carrying Capacity 15

Reproductive Strategies and Population Fluctuations • Not all species reach a stable carrying capacity. – Species can be broadly lumped into two categories: v K-strategists v r-strategists 16

K - Strategists • • Large organisms Long-lived Produce few offspring Provide substantial parental care Populations typically stabilize at a carrying capacity. Usually occupy relatively stable environments. Reproductive strategy is to invest in a few, quality offspring. 17

K - Strategists • • Controlled by density-dependent limiting factors. – Factors that become more severe as the size of the population increases. v Diseases Deer - Lions - Swans 18

r - Strategists • • Small organisms Short-lived Produce many offspring Little if any parental care Usually do not reach carrying capacity (boom-bust cycles). Exploit unstable environments. Reproductive strategy is to produce large numbers of offspring to overcome high mortality. 19

r - Strategists • • Controlled by density-independent limiting factors. – Population size is irrelevant to the limiting factor. v Weather Conditions Grasshoppers - Gypsy Moths - Mice 20

Human Population Growth • Major reason for increasing human population growth rate is an increase in medical care, and a consequential decrease in death rates. 21

Historical Human Population Growth 22

Doubling Time • Doubling Time of a Population (years) : • 70 / Population Growth Rate (%) ( 70 / 2. 0% = 35 years ) 23

Doubling Time for the Human Population 24

Human Population Growth • Interactions Affecting Carrying Capacity – Available Raw Materials – Available Energy – Waste Disposal – Interaction With Other Organisms 25

Social Factors Influence Human Population • Humans are social animals who have freedom of choice. – People make decisions based on history, social situations, ethical and religious beliefs, and personal desires. v Biggest obstacles to controlling human population are not biological, but are the province of philosophers, theologians, politicians, and sociologists. 26

Ultimate Size Limitation • • If the world continues to grow at current rate, population will surpass 12 billion by 2060. Human population subject to same biological constraints as other species. – Human population will ultimately reach a carrying capacity and stabilize. v Disagreement about exact size and primary limiting factors. 27

Review • • • Population Characteristics Age Structure Diagrams Exponential Growth Carrying Capacity – Environmental Resistance Reproductive Strategies – (r and K) Human Population Growth – Doubling Time 28

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