Chapter 8 Population Change

Overview of Chapter 8 Principles of Population Ecology Reproductive Strategies The Human Population Demographics of Countries Demographics of United States

Principles of Population Ecology Study of populations and why their numbers change over time Important for Endangered species Invasive species Population Group of individuals of same species living in the same geographic area at the same time

Population Density Population density The number of individuals of a species per unit area or volume at a given time Ex: minnows per Liter of pond water Ovals below have same population, and different densities

Change in Population Size

Change in Population Size

Calculating Population Change Birth (b), Death (d), Immigration (i) and Emigration (e) are calculated per 1000 people Death rate Growth rate Emigration rate r = (b – d) + (i – e) Birth rate Immigration rate

Maximum Population Growth Intrinsic Rate of Growth (Biotic Potential) Growth rate under ideal conditions J- Shaped Curve (exponential growth)

Environmental Resistance Environmental limits (resistance) Prevent indefinite reproduction Unfavorable food, water, shelter, predation, etc. Carrying Capacity (K) Maximum # of individuals an environment can support Causes leveling off of exponential growth S- shaped curve of logistic population growth

Population Crash Overshooting carrying capacity can lead to population crash Abrupt decline in population density

Factors That Affect Population Size Density Dependent Factor Factor whose effect on population changes as population density changes Examples: Predation Disease Competition Sometimes cause Boom-or-Bust Population Cycles

Boom-Or-Bust Population Cycles

Case Study- Predator Prey Dynamics on Isle Royale As wolf population increases, moose population decreases (and vice versa)

Factors That Affect Population Size Density Independent Factors Factors that affects population size, but is not influenced by changes in population density Examples: Killing frost Severe blizzard Fire

Reproductive Strategies r-selected species k-selected species -Small body size - Early maturity - Short life span - Large broods - Little or no parental care Probability of long term survival is low Mosquitoes and Dandelions Small broods Long life span Slow development Large body size Late reproduction Low reproductive rate Redwood trees and human beings

Survivorship

Some populations fit two curves Herring Gulls Type III & Type II

Human Population Demography Science of population structure and growth Human Population since 1980 is J-shaped curve

Human Population In 2011, world population increased to 7 billion 1800 2 Billion 1930 3 Billion 1960 4 Billion 1975 5 Billion 1987 6 Billion 1999 6.6 Billion 2006 In 2011, world population increased to 7 billion

Population Increase in Mexico

Projecting Future Populations Population is increasing Growth rate (r) has started to decline Projections for 2050 Low = 7.7 billion High = 10.6 billion Most likely = 9.1 billion

Demographics of Countries

Demographic Stages Pre-industrial Stage Transitional Stage Birth and death rates high Modest population growth Transitional Stage Lowered death rate Rapid population growth Industrial Stage Birth rate decline Population growth slow Post Industrial Stage Low birth and death rates Population growth very slow

Demographic Stages

Age Structure The number and proportion of people at each age in a population

Demographics of Specific Countries

World-wide 29% of human population is under age 15 Could cause large increase in birth rates

Education of Immigrants into US