Ch 5 Populations Students know how to analyze changes in an ecosystem resulting from changes in climate, human activity, introduction of nonnative species, or changes in population size. Students know how fluctuations in population size in an ecosystem are determined by the relative rates of birth, immigration, emigration, and death.

Content Objectives What characteristics are used to describe a population? What factors affect population size? What are exponential growth and logistic growth? What factors limit population growth?

Population Characteristics Three important characteristics of a population are its geographic distribution, density and growth rate. Population Density: The number of organisms per unit area 3

Population Growth How fast a given population grows Factors that influence this are: Birth Rate Death Rate Emigration (the number of individuals moving _________ a population) Immigration (the number of individuals _________ a population) away from moving to 4

Exponential Growth Under ideal conditions with unlimited resources, a population will grow exponentially. Populations reproduce at a constant rate. J-shaped curve

Understanding Exponentials 6

Logistic Growth As resources become less available the growth of a population slows or stops. Occurs when a population’s growth slows of stops following a period of exponential growth. Populations stop growing when the birth rate=death rate. S-shaped curve

Population Limiting Factors Population Ecology: Population Growth Models Population Limiting Factors Population growth models Logistic Growth Model Often called the S-shaped growth curve Occurs when a population’s growth slows or stops following exponential growth. Growth stops at the population’s carrying capacity Populations stop increasing when: Birth rate is less than death rate (Birth rate < Death rate) Emigration exceeds Immigration (Emigration > Immigration) 9

Population Limiting Factors Population growth models Limits to exponential growth Competition follows as nutrients and resources are used up The limit to population size that a particular environment can support is called carrying capacity (k) 10

Population Limiting Factors Density-independent factors Factors that limit population size, regardless of population density. These are usually abiotic factors They include natural phenomena, such as weather events Drought, flooding, extreme heat or cold, tornadoes, hurricanes, fires, etc. 11

Population Limiting Factors Density-dependent factors Any factor in the environment that depends on the number of members in a population per unit area Usually biotic factors These include Predation Disease Parasites Competition 12

Biodiversity What is Biodiversity? Biodiversity and Conservation: What is biodiversity? Biodiversity What is Biodiversity? The variety of life in an area that is determined by the number of different species in that area. There are 2 main types: Genetic Diversity Species Diversity

Community Ecology: Communities Review: A community is a group of interacting populations that occupy the same area at the same time.

Communities Limiting Factors Community Ecology: Communities Communities Limiting Factors Any abiotic or biotic factor that restricts the numbers, reproduction, or distribution of organisms.

Ecological Succession Community Ecology: Ecological Succession Ecological Succession Ecological Succession The change in an ecosystem that happens when one community replaces another as a result of changing biotic and abiotic factors