Chapter 4.1 Population Ecology

Population Characteristics Population Density: The number of living entities per unit of area

Population Characteristics Spatial Dispersion: the pattern of spacing of a population within an area Uniform Clumped (groups or herds) Random Dispersion patterns depend on the availability of resources

Limiting Factors Limiting Factors: any abiotic or biotic factor that restricts the number, reproduction, or distribution of organisms

Limiting Factors Two types of limiting factors: Density independent Density dependent

Chapter 4 Population Ecology 4.1 Population Dynamics Density-independent factor: Any factor (that limits population size) in an environment that does not depend on the number of members in a population per unit area.

Examples?

Density-Independent Factors Weather events – rainfall, flood, acidity, drought Fire Human alterations of the landscape Air, land, and water pollution

Can wipe out populations of species regardless if there are a few or a lot in a given area Density independent factors are unaffected by the number of individuals in a given area

The greater the number of species, the more that are wiped out Chapter 4 Population Ecology 4.1 Population Dynamics Density-dependent factor: Any factor, that limits population size, in an environment that depends on the number of members in a population per unit area The greater the number of species, the more that are wiped out

Examples?

Density-Dependent Factors Usually biotic factors and may include: Disease Parasites Competition for resources Predation

Density dependent factors are directly affected by the density of individuals in a given area.

Density-Dependent Factors Example: If one deer in a heavily populated community contracts tuberculosis, a communicable disease, what will happen to the deer population? Parasite?

Examples of Density-Dependent Factors: Competition: for food, space, mates Causes a lower birth rate (natality), increases death rate (mortality), or both

Density-Dependent Factors Predation: interaction between species on different trophic levels Almost every species is food for another species Predators (hunters) and prey (the hunted) have, in most cases, existed together for years

Predator-Prey Graph

What do you notice about the populations?

Population Growth Rate Chapter 4 Population Ecology 4.1 Population Dynamics Population Growth Rate Population growth rate (PGR) explains how fast a given population grows. What are some factors that would affect how quickly a populations grow?

Population Growth Rate Depends on several factors: Natality: birthrate (during a given time) Mortality: death rate (during the same given time) These two factors affect PGR the most

Emigration: the number of individuals moving away from a population Immigration: the number of individuals moving into a population These two factors are usually about the same

Two mathematical models that represent population growth rate: 1. Exponential Growth Model 2. Logistic Growth Model

Exponential Growth Model Chapter 4 Population Ecology 4.1 Population Dynamics Exponential Growth Model Exponential growth : the growth rate is proportional to the size of the population. All populations grow exponentially until some limiting factor slows the population’s growth.

If all offspring survive and reproduce, the population grows slowly at first Lag phase: slow growth period

The rate of population growth begins to increase rapidly Exponential growth phase: rapid population growth due to total number of organisms without any limiting factors Exponential growth creates a J-shaped curve

Second Model: Logistic Growth Model

Chapter 4 Population Ecology 4.1 Population Dynamics Logistic Growth Model The population’s growth slows or stops following exponential growth, at the population’s carrying capacity.

Carrying capacity: the maximum number of organisms in a population that an environment can support for the long term Carrying capacity is limited by the energy, water, oxygen, and nutrients available (resources).

Logistic Growth Model

Logistic Growth Model Similar to the exponential growth model, but with an S-shaped curve Occurs when the population’s growth slows or stops after exponential growth at the population’s carrying capacity

Chapter 4 Population Ecology 4.1 Population Dynamics Exceeding the carrying capacity of an area results in death to the organisms living there

Boom and Bust Graph

A = exponential growth B = massive death C = “new” carrying capacity

Reproductive Patterns Chapter 4 Population Ecology 4.1 Population Dynamics Reproductive Patterns Species vary in the number of births per reproduction cycle, in the age that reproduction begins, and in the life span of the organism. Two main patterns: R-strategy K-strategy

An r-strategist is generally a small organism. Chapter 4 Population Ecology 4.1 Population Dynamics R-strategy: (Rate Strategy) is a population pattern seen where fluctuations in biotic or abiotic factors occur in the environment. An r-strategist is generally a small organism. Short life span Produces many offspring

Examples of r-strategists: Fruit fly Mice Locusts

A k-strategist is generally a larger organism. Chapter 4 Population Ecology 4.1 Population Dynamics k-strategy : (carrying-capacity strategy) a population reproduction pattern that is adapted for living in stable environments. A k-strategist is generally a larger organism. Long life span Produces few offspring

Examples: Bears Elephants

Factors that Contribute to Biotic Potential Low (few babies) k-strategists High (lots of babies) r-strategists Maternal age older younger Number of offspring 1-2 (low) 1,000s (high) Maternal care months/years short/none Gestation period long short Organism’s size large small

Human Population 4.2

Chapter 4 Population Ecology 4.2 Human Population Human Population Growth Demography: The study of human population size, density, distribution, movement, and birth and death rates.

Technological Advances Chapter 4 Population Ecology 4.2 Human Population Technological Advances For thousands of years, the size of the human population remained relatively constant and below the environment’s carrying capacity. Why is it increasing in population now?

Populations are Increasing Because: Advances in technology: Farming and domestication of animals Medicine—antibiotics and vaccines Better shelter

Human Population Growth Rate Chapter 4 Population Ecology 4.2 Human Population Human Population Growth Rate Although the human population is still growing, the rate of its growth has slowed.

What might have happened in the 1960s? What might be responsible for the decline in percent increase in human population (world wide)?

Trends in Human Population Growth Chapter 4 Population Ecology 4.2 Human Population Trends in Human Population Growth Population trends can be altered by events such as disease and war. Human population growth is not the same in all countries. Why not?

Demographic Transition Demographic Transition: a change in growth rate resulting from high birth and death rates to low birth and death rates Consists of 3 stages

Most countries have not yet undergone a complete demographic transition 80% of the world’s population lives in these areas

Stage 1: high birth rate and a high death rate Families have lots of children

Stage 2: Improvements in living conditions Increased food production Medical advances Improved sanitation

Stage 3: The birth rate decreases Families have fewer children Population growth slows and may stabilize Undergone an industrial revolution

Future population growth depends somewhat on how many people of different ages are living in that country today.

Zero Population Growth Chapter 4 Population Ecology 4.2 Human Population Zero Population Growth Zero population growth (ZPG) occurs when the birthrate and immigration rate equal the deathrate and emigration rate.

pre-reproductive stage, reproductive stage, and post- Chapter 4 Population Ecology 4.2 Human Population Age Structure Age structure: the number of males and females in each of three age groups: pre-reproductive stage, reproductive stage, and post- reproductive stage.

At zero population growth, an age structure graph should appear more balanced with numbers at pre-reproductive, reproductive, and post-reproductive ages being approximately equal.

Human Carrying Capacity Chapter 4 Population Ecology 4.2 Human Population Human Carrying Capacity Scientists are concerned about the human population reaching or exceeding the carrying capacity. An important factor is the amount of resources from the biosphere that are used by each person.