Population Change Chapter 8

Principles of Population Ecology Population ecologists ask: 1) How many are in the population? 2) Are its numbers increasing / decreasing? 3) What is its pattern of reproduction? 4) What is its pattern of mortality?

Principles of Population Ecology Population Density (because you can’t count them all!): Not enough to know just how many. Need to know per unit area. Which environmental factors may influence population density? 20 / 100 m 2 20 / 25 m 2

Principles of Population Ecology How Do Populations Change in Size? On a global scale (closed system):

Principles of Population Ecology How Do Populations Change in Size? On a local scale (open system):

Principles of Population Ecology How Do Populations Change in Size? Global scale: Births and deaths per 1,000 people per year r = b/1,000 – d/1,000 Growth rate Birth rate Death rate

Principles of Population Ecology How Do Populations Change in Size? Local scale (all per 1,000 people): r = (b – d) + (i – e) Growth rate Birth rate Death rate Immigration rate Emigration rate What would a positive r or a negative r tell you about the population?

Principles of Population Ecology Maximum Population Growth- under ideal conditions = intrinsic rate of increase (biotic potential) Which factors could influence the intrinsic rate of increase? J-shaped curve (exponential growth) All species follow J-curve based on intrinsic rate. Major variable is pop. size and time!

Principles of Population Ecology Environmental Resistance- Exponential growth at intrinsic cannot occur forever. What factors prevent it from doing so? Crowding makes a pop. more susceptible to parasites, viruses, predators, waste, food / space shortage S-shaped curve (logistic growth) Environment influences K (ex. drought) How could one environmental influence have a “domino” effect on many species? Rate of population growth is proportional to the amount of resources

Principles of Population Ecology Overshooting the carrying capacity can lead to a population crash. Abrupt decline from high to low population density Over consumption of resources because of population size

Reproductive Strategies Life History Strategies - Trade offs! r-selected K-selected vs. high growth rate slow growth rate small body sizelarge body size early maturitylate maturity short life spanlong life span large broodssmall broods little / no parental carehigh parental care “perfect”: continual reproduction at intrinsic rate of increase with all offspring surviving to reproduce But… addt’l energy needed for their own survival

Reproductive Strategies Survivorship: proportion of individuals alive at a certain age (insurance companies used these!)

Factors that Affect Population Size Density-Dependent Factors- Factors that have a greater influence on population growth when density is high. Predation, competition, disease. Living space, food, cover, water, minerals, sunlight in high demand Large population: parasites and predators have more hosts / prey –survive longer / reproduce more In lab: control all factors except one

Factors that Affect Population Size Density-Dependence and Boom-or-Bust Population Cycles More prey - predator population increases Prey population decreases OR overwhelm food supply (plants=prey)

Factors that Affect Population Size Case-in-Point: Predatory Prey Dynamics on Isle Royale Canine parvovirus outbreak Tick outbreak

Factors that Affect Population Size Density-Independent Factors- Abiotic Regardless of population density, influences population growth. Frost, severe weather, fire. Example: Adult mosquitoes wiped out in winter. Species survives from hibernating larvae

The Human Population: Demography Human population size Would not have occurred if not for: Food production technology Medical advancements Water quality Decline in birth rate and death rate

The Human Population Current Population Numbers In 2004 = ~6.4 billion Check out:

The Human Population Current Population Numbers Rapid growth primarily due to drop in death rates

The Human Population Projecting Future Population Numbers When will zero population growth occur? K for Earth: 7.7 billion (most recent analysis) Past analyses: billion Assumptions: standard of living, consumption, tech. advancements, waste generation

Demographics of Countries Most Populous Countries Insert Table 8.1

Demographics of Countries Developed vs. Developing Countries Demographics (includes migration)

Demographics of Countries Developed vs. Developing Countries Demographics

Demographics of Countries Demographic Stages

Demographics of Countries Age Structure of Countries Generalized Age Structure: Factors are age distribution and male-female ratio Next Generation is larger Next Generation is almost same size Next Generation is smaller

Demographics of Countries Examples:

Demographics of Countries Examples:

Demographics of Countries Examples:

Demographics of Countries Population Under Age 15 (relative size of next generation):

Demographics of the US Case-in-Point: US Immigration Birth rate declining Increasing rate of immigration Consumption overpopulation Estimates 300,000 illegal per year, 1 million legal

Demographics of the US Case-in-Point: US Immigration Immigrate because of: Persecution High growth rate in developing countries reduces resources / jobs available Deteriorating environmental conditions in developing countries Top 5 immigrants: Mexico, Philippines, Vietnam, Dominican Republic, China 70% poor with few skills, 30% college graduates Should the US increase or decrease immigrants?