(Otter introduction page 119- Read) 5-1 How Populations Grow Sea otters are important to populations of kelp, sea urchins, & killer whales.
CHARACTERISTICS OF POPULATIONS:1-Geographic distribution or range- the area inhabited by a population.
EX: A few cubic cm (bacteria in a rotting apple)…to millions of square km (Migrating whales)
2-Population Density- # of individuals per unit area.Density refers to HOW MANY…not where!!3-Growth Rate4-Age Structure-# of people in different age groups in the population.
POPULATION GROWTH 3 Factors That Affect Population Size: 1-# of births 2-# of deaths 3-# of individuals that enter or leave a population
A population will increase or decrease depending on how many individuals are added to it or removed from it. When birth rate = death rate…population stays the same size
When birthrate is GREATER than death rate…the population grows. When DEATHRATE is greater than birthrate…the population shrinks.
IMMIGRATION-(INTO a population)… movement of individuals into an area occupied by an existing population. Immigration can cause a population to grow. EX: Animals come into a territory in search of mates or food.
EMIGRATION-(EXIT from a population)… movement of individuals out of a population. Emigration can cause a population to decrease in size. EX: Young animals leave the area where they were born to find mates & establish territories. EX: shortage of food
EXPONENTIAL GROWTH- growth pattern in which the individuals in a population reproduce at a constant rate. At first, the # of individuals increases slowly. Over time the population becomes larger & larger at a very rapid rate!
Under IDEAL conditions…plenty of food, water, space; protected from predators & disease…a population will continue to grow… *Under ideal conditions with unlimited resources, a population will grow exponentially.
See Exponential Growth Curves on page 121…J-Shaped! How are these graphs alike? Besides showing different types of organisms, how do they differ? What do these differences indicate? What is another major difference between the reproduction of bacteria & that of elephants?
How are these graphs alike?Both plot time on the x axis & # of organisms on the y axis…curve on graph is “j” shaped. Besides showing different types of organisms, how do they differ? Population size is given in hundreds of thousands for bacteria & in millions for elephants. The elapsed time is in hours for bacteria & in hundreds of years for elephants.
What do these differences indicate?Bacteria reproduce very rapidly in a short period of time, but elephants reproduce much more slowly over a longer period of time.
What is another major difference between the reproduction of bacteria & that of elephants?Bacteria reproduce asexually, every bacterium is capable of producing 2 offspring. Elephants reproduce sexually- 2 parents- male & female- so two parents are needed to produce one offspring.
Bacteria double every 20 minutes under ideal conditions! ?Do ideal conditions usually exist in nature??
BIOTIC POTENTIAL- the size a population would reach if all offspring were to survive and produce young. In order for this to happen- ideal conditions would have to exist! 2 Elephants under ideal conditions would produce more than 20 million descendents after 750 years.
In reality- no population ever reaches its biotic potential. The factors that prevent this ideal growth are called Limiting Factors or Environmental Resistance
LOGISTIC GROWTH & THE LOGISTIC GROWTH CURVE… As resources become less available, the growth of a population slows or stops. Logistic Growth- growth pattern in which a population’s growth rate slows or stops following a period of exponential growth.
A logistic growth curve has a general “s” shape. Growth starts out slow, then hits a period of exponential growth. Exponential growth continues until the population reaches the “carrying capacity”.
Carrying Capacity- largest # of individuals of a population that a given environment can support. A horizontal line is drawn through the part of the graph where the population growth has leveled off…this is how carrying capacity is indicated on a logistic growth curve.
The average growth rate is = to zero at the carrying capacity. **Complete population trends on page 123….graphing & analyzing data.
5-2 Limits to Growth Page 124 LIMITING FACTOR- a factor that causes the growth of a population to decrease.
2 Types Of Limiting Factors: 1- Density-Dependent Factors-a limiting factor that depends on population size. EX: competition, predation, parasitism, & disease 2-Density-Independent Factors-limiting factors that affect all populations regardless of population size. EX: unusual weather, natural disasters, seasonal cycles, & certain human activities.
COMPETITION- when organisms compete/struggle with one another for food, water, space, sunlight, or other essentials of life. Competition usually occurs when populations become crowded. Competition is the major force behind evolutionary change!
PREDATION- interaction in which one organism captures & feeds on another organism. PREDATOR-PREY RELATIONSHIP mechanism of population control in which a population is regulated by predation. (See figure 5-7 page 126)
Periodic increases in the moose population are quickly followed by increases in the wolf population (predators!).
PARASITISM & DISEASE Parasites are similar to predators in many ways….they take nourishment from hosts and can cause them to become sick or die.
DENSITY INDEPENDENT FACTORS tend to be abiotic. They affect all populations the same way regardless of size.
5-3 HUMAN POPULATION GROWTH…page 129 The human population tends to increase with time. A long time ago, when life was harsh…limiting factors kept the human population sizes low.
Many years ago childhood diseases kept half of the children from surviving to adulthood. People would have several children because death rates were so high…this was to assure that some would survive!
Agriculture & industry made life safer & easier… -more reliable food sources -better sanitation -better healthcare -better medicine *Birth rates remained high & we experienced exponential growth.
See Figure 5-10 page 129 What would the graph look like if we were to extend the graph to thousands of years in the future? Why?
PATTERNS OF POPULATION GROWTH…. Demography-the scientific study of human populations. Demography examines characteristics of human populations & attempts to explain how these populations change over time.
Birth rates, death rates, & age structure of a population help predict why some countries have high growth rates & why others grow more slowly. DEMOGRAPHIC TRANSITION- change in a population from high birth rate & death rates to low birth & death rates.
The demographic transition is complete when the birthrate falls to meet the death rate…& population growth stops. This has happened only in a few countries.
AGE STRUCTURE Population growth depends on how many people of different ages makes up a population. AGE-STRUCTURE DIAGRAMS- population profiles which graph the #s of people in different age groups in the population.