Populations 1. How populations grow 2. Limits to growth 3. Human population growth

How populations grow 1.Describing populations a. Geographic range: the area inhabited b. Density and distribution Density is the number of individuals per unit area Distribution refers to how the population is spread out: randomly, uniformly, or concentrated in clumps c. Growth rate: increases, decreases, stays the same d. Age structure: the number of males and females of each age

How populations grow… 2.Population Growth a. Birthrate and death rate b. Immigration (move into population) and Emigration (move out of population) 3. Exponential growth: under ideal conditions with unlimited resources, a population will grow exponentially

3.Exponential growth a. Organisms that reproduce quickly: bacteria reproducing every 20 minutes b. Organisms that reproduce slowly: the time it takes for organisms to reach age of maturity prevents exponential growth (elephants) c. Organisms in new environments when first introduced, the population grows exponentially.

How populations grow… 4.Logistic Growth: the population grows exponentially at first, then slows down or decreases as resources are limited. a. Phases of growth 1. exponential 2. growth slows down 3. growth stops Carrying capacity: the maximum number of individuals of a particular species that a particular environment can support

Limits to growth 1.Density dependent factors competition predation herbivory: plant population fluctuations due to herbivores parasitism and disease stress from overcrowding 2.Density Independent Factors unusual weather natural disasters

Human Population Growth 1.Historic overview Exponential human population growth Industrial Revolution Reliable food supply Improved nutrition, sanitation medicine, and healthcare Malthus: war, famine, and disease would limit human populations

Patterns of Human Population Growth Demography: the study of human populations Birthrates, death rates, and age structure help predict growth rates The Demographic Transition Stage 1: high birth and death rates Stage 2: death rates begin to fall, birthrates remain high Stage 3: birth rate falls to meet death rate