Chapter 5 Population Biology

Describing Populations Geographic range – where they are located Density – how many organisms in a certain area Distribution – how they are spread out in the area -3 patterns *randomly *uniform *clumped

Population Growth 1. General A. Populations are groups of organisms of the same species B. Population growth is the change in the size of a population with time C. Scientists have found clear patterns of how and why populations grow -4 things change the populations size *births *deaths *immigration *emigration

2. How fast do populations grow A. Populations do not grow in a linear fashion B. Populations grow in an exponential fashion i. The initial increase in # is slow due to the small # of organisms able to reproduce, then the rate increases rapidly as the total # of organisms potentially reproductive organisms increases ii. Exponential growth occurs when the # of organisms increases by an ever increasing rate, this results in a population explosion iii. This results in a J shaped curve, see fig. 5.3 on page 115

3.Limits of the environment A. Populations cannot grow indefinitely B. Population size does have a limit C. Populations do have limiting factors in their environment. These limiting factors slow the growth of a population. i. Ex. Food availability and space C. This leveling off of population growth results in an s-shaped curve (this is called logistic growth) i. See fig. 5.4 page 118 ii. There is a plateau when the # of organisms the environment can support is reached

D. The # of organisms of a population that a particular environment can support over a period of time is known as its carrying capacity i. Often represented by the letter K E. When populations are under the carrying capacity, births will exceed deaths F. If the population overshoots the carrying capacity, deaths will exceed births until populations are once again at carrying capacity

*Life History Patterns 1. In nature, some populations remain in equilibrium (a state of rest or balance), some do not A. This occurs because there are 2 basic growth patterns, called life history patterns, that populations can follow i. Some populations reproduce very rapidly and produce many offspring (r-selected) 1. Ex. mosquitoes ii. Some populations have a slow rate of reproduction with few young (k-selected) 1. Ex. elephants iii. Which type a specie uses depends mainly on environmental factors

B. Species in an unpredictable and rapidly changing environment survive better with a rapid life history pattern (r-selected species) i. These organisms usually have similar adaptations 1. Ex. Small body size, mature rapidly, reproduce early, & have short life span, many young ii. Ex. Mosquitoes iii. Populations of these organisms increase and decrease rapidly as their environment changes 1. The small surviving population will begin reproducing exponentially when conditions are favorable again

C.Species that live in a more stable environment usually have a slow rate life history pattern (k-selected) i. Ex. Elephants ii. Are usually large in size, long lived, produce few young and mature slowly iii. These organisms usually maintain populations near the carrying capacity

Environmental limits to population growth a. Limiting factors regulate the size of a population b. Ecologists have recognized 2 types of limiting factors i. Density-dependent factors have an increasing effect on a population as the population increases in size 1. Ex. Disease, parasites, competition ii. Density-independent factors affect all populations regardless of their density 1. Usually abiotic factors 2. Ex. Temperature, storms, drought etc.

Interactions among organisms that limit population size Populations are also controlled by various interactions among organisms within the community -Predation/Herbivory -Competition *interspecific *intraspecific -Symbiosis -Disease -Overcrowding/Stress

Predation (animals killing and eating other animals) and Herbivory (animals feeding on plants) affects on population size A. necessary in a community, it ensures the continuation of the flow of energy throughout the ecosystem (animals have to eat) B. It also may be a limiting factor on a prey population size C. Most prey populations are controlled in some way by predators

D. Populations of predators and prey change over years, many in a cyclical fashion -Usually with the populations increasing and decreasing at the same times E. Predators help to weed out the sick, old, young and week i. This leaves the strong and well adapted left to reproduce

3. The effects of competition A. Organisms within a population compete for resources (food, water, shelter, etc) B. When population is low, resources are abundant C. As population increases the competition for resource increases and there may not be enough for everyone D. Density-dependent factor E. When the population becomes to big and the demand for the resources is greater than the supply of resources, the population size decreases F. Interspecific – between different species G. Intraspecific – within a species

4. The effects of overcrowding and stress A. When populations become crowded, individuals may exhibit stress B. Symptoms of stress from overcrowding include aggression, decrease in parental care, decreased fertility, and decreased resistance to disease C. All of these symptoms can lead to a decrease in population size (which relieves the overcrowding)

Section 2: Human Population *World Population 1. General A. Demography is the study of human population size, density and distribution, movement and birth/death rates 2. Human Population Growth A. humans consciously change their environment, so human population is different than other populations B. humans have reduced or eliminated many of their limiting factors which have allowed the human population to grow i. medical advances ii. agriculture advances iii. eliminate competition

3. Calculating growth rate A. 4 factors affect human population growth i. birth rate ii. death rate iii. immigration - movement into a population iv. emigration - movement out of a population B. to calculate population growth rate we must take all of these factors into account i. (birth rate + immigration) - (death rate + emigration ) = population growth ii. this just tells how many new individual are in a population iii. if the PGR is positive it means more individuals are entering the population than leaving it, if the PGR is zero it means that individuals are entering and leaving the population at the same rat, and if the PGR is negative it means that more individuals are leaving the population than entering it

4. Demographic Transition – page 144 A. Tracks birth rates and death rates as a country develops B. There is a general trend as the country develops *stage 1 = high birth and death rates *stage 2 = death rate begins to fall, birth rate remains high for a while *stage 3 = birth rate declines until it meets the death rate 5. Doubling time A. the time needed for a population to double in size B. a country with a slow doubling time is considered a developed country, while a country with a rapid doubling time is considered a developing country

6. Age Structure A. refers to the proportions of the population that are in different age levels B. shows the proportions of males and females in each age group and those within child bearing age and elderly (can help us predict trends in population growth) C. if the percentage of people in each age category is fairly equal the population is considered stable, rapidly growing populations have higher numbers in lower age groups (more people in child bearing age)

Chapter 6

Biodiversity The number of different types of organisms in an area -ecosystem diversity – different types of ecosystems -species diversity – different types of organisms -genetic diversity – different genetics within a population

Biodiversity is important because… -the ecosystem has value to humans *ex. materials that we use, medicines, food, etc. -it helps keep the ecosystem stable *if everything in the ecosystem is the same, then everything is susceptible to the same forces -aesthetic value (beauty)

HIPPO – five ways humans are decreasing biodiversity in nature H- habitat destruction I – invasive species P – population expansion P – pollution O – over-exploitation