Ch. 4 Population Ecology

Section 1--Essential Questions What are the characteristics of populations and how are they distributed? What are the differences between density- independent and density-dependent limiting factors? What are the similarities between the different models used to quantify the growth of a population? How does carrying capacity affect reproductive rates?

Characteristics of a population Population density—number of organisms per unit area (3 birds per sq. meter) Spatial distribution—(dispersion)—the pattern or spacing of populations with an area – Uniform, clumped (grazing animals), random (seed plants) – Depends on resources, such rainfall, sunlight, predators, parasites, food Growth rate—how fast a population grows – Emigration—members leave the population – Immigration—members enter a population

Population-Limiting factors Density-independent limiting factors—any factor in the environment that does not depend on the number of organisms in a population – Abiotic factors such weather, drought, flooding, natural disaster, extreme heat or cold, human activities (pollution, cutting forests) Density-dependent limiting factors—any factor in the environment that does depend on the number of organisms in a population – Biotic factors such as predation, disease, competition, parasitism, availability of food

Population Growth Rate Natality (birth rate)— increases population Mortality (death rate)---decreases the population Emigration—decreases the population Immigration—increases population

Population Growth Models Exponential growth (J shaped curve)—no limits on population by the environment Organisms must have unlimited resources. Bacteria, molds, small organisms Reproductive cycle is usually very fast.

Logistic Growth Model (S-shaped curve) After a population’s growth slows or stops following exponential growth, the population’s carrying capacity is reached Carrying capacity is limited to energy, water, oxygen, and nutrients available. A population stops increasing when the number of births is less than the number of death or when emigration exceeds immigration.

Reproductive Patterns r-strategists are organisms with the adaptation for living in an environment where fluctuation in biotic and abiotic factors occur, such as availability of food, changing temperatures. Usually small organisms such as fruit flies, mouse and locusts. Short life spans and produce many offspring. k-strategists are usually larger organisms that produce few offspring, have a longer life spans and invest time into caring for their young and are controlled by density-dependent factors

Section 2—Essential Questions What aspects affect human population growth? What are the trends in human population growth? What are the age structures of representative non-growing, slowly growing, and rapidly growing countries? What might be the consequences of continued population growth?

Human Population Growth Demography—study of human population size, density, distribution, movement, birth and death rates Human population was relatively stable until the 1300s when the bubonic plague killed about one- third of Europe’s population. 1804—one billion estimated population 1999—6 billion 2012—expected 7 billion 2050—9 billion

Technological advances Humans have learned to change environmental conditions and therefore altered the carrying capacity. Improved sanitation, domesticated animals and agriculture have increased the food supply. Technological advances and medicines have increased the chances of survival by reducing deaths from parasites and disease. Improvements in shelter have made humans less vulnerable to climatic impact.

Human population growth rate Although still growing, the human population growth rate has slowed. Sharp dip in 1960s because about 60 million people died in China due to a famine. Population models predict the overall population growth rate to be below 0.6 by The decline is due primarily to diseases such as AIDS and voluntary population control.

Trends in Human Population Growth Population growth trends are often similar in countries that have similar economics. Developed countries such as the US has technological capabilities and has a population with a high standard of living. The trend has shifted from high birth rate and high death rate to low birth rate and life expectancy is greater than 70 years. Demographic transition has occurred in the US. Demographic transition—shift from high birth and death rates to low birth and low death rates.

Undeveloped countries Add more people to the world population as compared to the amount of people added in the industrially developed countries.

Zero population growth – Births + immigration = deaths + emigration Age structure—number of males and females in each of three age groups: pre- reproductive, reproductive and post- reproductive stages. – Pre-reproductive: before age 20 – Reproductive: ages – Post-reproductive: after age 44

Human carrying capacity Many scientists suggest that the human population growth needs to be reduced. In many countries, voluntary population control is occurring through family planning. If human population continues to grow---as most populations do—and areas become overcrowded, disease and starvation will occur.

Factor that will keep the human population at or below the carrying capacity Use of resources—land used for production of crops, forests, housing