Chapter 7 Populations: Characteristics and Issues

Population Characteristics  A Population is a group of individuals of the same species inhabiting an area.  Population characteristics include: Natality-Birth Rate Mortality-Death Rate Growth Rate Sex Ratio Age Distribution Population Density and Spatial Distribution

Natality and Mortality  Natality is the Birth Rate of a Population Measured in # of births per thousand individuals per year  Mortality is the Death Rate of a Population Measured in # of deaths per thousand individuals per year  Survivorship curves Show characteristics of deaths in the population and when they occur

Survivorship curves

Growth Rate, Sex Ratio and Age Distribution  Growth Rate Birth Rate minus Death Rate  Sex Ratio The number of males versus females  Age Distribution The number of individuals at each age in the population

Age Distribution Chart

Population Density and Spatial Distribution  Population Density The number of units (organisms) per unit area Density of the population  Spatial Distribution How closely the organisms in the population are to one another (dispersal) Varies based on immigration (moving into an area) and emigration (moving out of an area)  Often seasonal and based on competition and available resources

Population Growth Curve  Biotic Potential Reproductive capacity of a population  High in most populations  Results in growth of population  Growth occurs in predicable ways  Four phases

Growth Curves

Phases of a Growth Curve  Lag Phase Slow growth due to small population size  Offspring must mature to reproduce  Log Phase (exponential growth phase) Number of offspring increase quickly  Deceleration Phase Slowing of growth as birth rate and death rate become equal  Stable Equilibrium Phase Population levels off

Population Limiting Factors  Factors that act to limit the growth of a population Also known as Environmental Resistance  Extrinsic Limiting Factors Come from outside of the population  Predators, loss of food, lack of sunlight, immigration  Intrinsic Limiting Factors Come from within the population  Overcrowding, competition

Limiting Factors

Other Limiting Factors  Density Dependent Predator success, disease  Density Independent Catastrophic events, climate change  Availability of Energy  Accumulation of Waste Bacteria, results in death phase  Interaction Among Organisms Ecosystem balance

Carrying Capacity

 The maximum number of organisms in a population that can be supported by an environment. Level portion of the S curve after deceleration phase Not yet established for the human population

Environmental Resistance  The environmental factors that control the growth of a population.  See text illustration

Reproductive Strategies K and r  Strategies for survival in the environment

K-strategists  Put a great deal of energy into the offspring Stable Large Long lives, most live to reproduce Small number of offspring Parental Care provided Density dependent limiting factors Exponential growth followed by stablility

R-strategist populations  Put little energy into offspring but make lots Unstable Small Short life, most die before reproducing Large number of offspring Density independent limiting factors Exponential growth followed by crash Examples: Protozoa

Demographic Transition Model  The changing of the European and US human population over time to its current condition. Occurs in four stages  High birth rate, high death rate, low population size  High birth rate, low death rate, growing population  Tech development, slow birth rate, slow growth  High tech, low birth rate, low death rate, stable pop

Demographic Transition Model

Issues to be solved  Available Raw Materials  Available Energy  Waste Disposal  Interaction with other Species  Social Factors within the Human Population  Continued Population Growth

The Human RACE