Populations Biology – Ch 5

Population Characteristics Geographic distribution Density Growth rate Age structure *Characteristics used to describe any population found in nature*

Geographic Distribution Area where the population is found (“range”) Geographic distribution is also a function of WHEN. Tiger population range change over 90 years (click) Grizzly bear population range

Population Density The number of individuals in a unit area Density is also dependant on WHEN.

Growth rate Populations tend to stay somewhat the same size from year to year. However, populations may change due to three factors: Number of births Number of deaths Immigration & emigration Immigration = “in” (individuals entering a population). Emigration = “exit” (individuals exiting/leaving a population)

Growth Rate Representations Unlimited resources and ideal conditions allow a population to grow without limits = exponential growth (Click for bacterial growth example)

Logistic Growth Curve Realistic population growth in nature Population growth is limited by resources, competition & natural events The largest number of individuals that a given environment can support = carrying capacity

Reality WHAT kinds of things might cause RESISTANCE to population growth?

Limits to Population Growth Limiting factor = a factor that causes population growth to decrease Parasitism Predation Population SIZE Competition Click to watch a bunny love story… Density Dependent Disease Human interaction Density Independent Climate extremes

Density Dependent Factors Limiting factors that depends upon population size Factors that are limiting only when a population reaches a certain size Don’t affect smaller populations as strongly as larger populations Biotic: competition, predation, parasitism, disease

Density-Independent Factors Limiting factors that do NOT depend upon population size Factors that limit population size regardless of how large a population might be Affects both large and small populations Abiotic: unusual climate, natural disasters, seasonal cycles, certain human activities (damming rivers, clear-cutting forests)

Human Population Growth Human population growth exhibited the same characteristics as any organism population growth in nature EXPONENTIAL Is there a “carrying capacity” for the human population? If so, what is it? Have we reached it? What happens if we do reach this?

Human Population Growth Patterns Demography = the scientific study of human population growth, including: Birth rates Death rates Age structures (This helps predict world population needs) A dramatic change in birth and death rates may be caused by a demographic transition in a country. A dramatic change due to economic/cultural changes

WHY does each group shown above exhibit the particular growth rate patterns?

Age Structure Diagrams WHY/HOW does each graph describe each type of growth (rapid, slow, declining)? Populations described by age groups

Just for information – do NOT need to remember

Future Population? How does world population growth affect QUALITY OF LIFE?

Epilogue One of the most obvious characteristics of human evolution and history has been the exponential growth in the world-wide human population. As such exponential population growth continues, it will have a significant impact upon every aspect of human existence from increasing demand on natural resources to the proliferation of mega-cities and the infrastructure needs of an increasingly urbanized world population. Despite having one of the lowest population growth rates of any country, according to the U.S. Census Bureau, the U.S. population is nevertheless projected to growth from the current 300 million to somewhere between 422 to 458 million by the year 2050. The United States and most of the developed nations are also likely to experience an increased aging of their populations, with the current 15 percent of the population that is age 65 or older expected to increase to approximately 20 percent by 2050. At the same time, however, the United States is expected to experience an even greater surge of young workers as the U.S. population between the ages of 15 to 64 years old is projected to grow by 42 percent. This is in contrast to other countries such as China where the same age group is expected to decline by 10 percent and Europe where the working age population is expected to decline by 25 percent. Japan faces an even more severe problem as the working age population is expected to decline by 40 percent by the year 2050. But population is not affected just by growth rates – but is also affected by the migration of people. As a consequence, another factor that is likely to affect the population of countries are such variables as quality of life, cost of living, availability of jobs, and wars that displace people and cause migrations of people. Just food for thought…..