Population Dynamics Chapter 4 Section 1

Main Idea Populations of species are described density, spatial distribution, and growth rate.

How does carrying capacity affect reproductive rates? Thinking Questions What are the characteristics of populations and how they are 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?

Populations are groups of the same species in the same area. Population Characteristics Populations are groups of the same species in the same area. Characteristics of populations that are used to classify them include density, distribution, and growth rate

Population Characteristics Population density The number of organisms per unit area is the population density.

Spatial distribution Dispersion is the spacing pattern of a population. Can be uniform, clumped groups, or random Uniform- bears, bald eagles, corn Clumped- bison, lions Random- deer, dandelions Pattern primarily driven by resources such as food Population Characteristics

Population ranges No population occupies all habitats in the biosphere Population Characteristics Population ranges No population occupies all habitats in the biosphere A species’ range is its distribution across the environment. Hawaiian Honeycreeper has limited population range while the Peregrine Falcon has vast population range A species might not be able to expand its population range because it cannot survive the abiotic conditions found in the expanded region.

Limiting factors are either density-independent or density-dependent. Population- Limiting Factors Limiting factors are biotic or abiotic forces that keep populations from increasing indefinitely. Limiting factors are either density-independent or density-dependent.

Density-independent factors Population- Limiting Factors Density-independent factors Any factor in the environment that does not depend on the number of members in a population per unit area is a density-independent factor. Usually abiotic, and include: Weather events Fire Human alterations of the landscape-land development, dams, fishing practices Air, land, and water pollution

Density-dependent factors Population- Limiting Factors Density-dependent factors Any factor in the environment that depends on the number of members in a population per unit area is a density-dependent factor. Often biotic, and include: Predation Disease ~When population density is high, diseases can spread more quickly Competition ~Increases as density increases Parasites

Population growth rate Population- Limiting Factors Population growth rate The population growth rate (PGR) explains how fast a given population grows. Natality: birthrate of a population in a given year (number of individuals born) Mortality: the number of individuals who die in a given year Emigration: number of individuals moving away from a population Immigration: number of individuals moving into a population

Population growth rate Population- Limiting Factors Population growth rate Exponential growth model: J-shaped growth curve Occurs when growth rate is proportional to population size Begins with a lag phase, or slow growth rate phase All populations grow exponentially until they encounter a limiting factor.

Population growth rate Population- Limiting Factors Population growth rate Logistic growth model: S-shaped growth curve Occurs when a population’s growth slows or stops following exponential growth, at the population’s carrying capacity A population stops increasing when the number of births < number of deaths, or when emigration > immigration.

Population growth rate Population- Limiting Factors Population growth rate Carrying capacity Carrying capacity is the maximum number of individuals in a species that an environment can support.

Reproductive patterns Population- Limiting Factors Reproductive patterns Species vary in the number of births per reproduction cycle, age that reproduction begins, and in the life span. Plants and animals are placed into groups based on their reproductive factors. r-strategists or k-strategist

Reproductive patterns Population- Limiting Factors Reproductive patterns r-strategy k-strategy Rate strategy Carrying-capacity strategy Adapted for fluctuating environment Adapted to stable environment Generally small Generally large Short life span Long life span Many offspring Few offspring Expend little energy to raise young Invest more energy into nurturing young

How does carrying capacity affect reproductive rates? Thinking Questions What are the characteristics of populations and how they are 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?