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