Chapter 14 notes By GiannaMarranca Period- 3
Section 1-populations and how they grow. Population-a group of organisms of a single species that live in a given area. Ex/ whitetail deer live in forests. Species-a group of organisms that reproduce fertile offspring. -populations mostly remain the same from year to year but they can vary Ex/ flooding will lower the population because most of the population will drown. -population will change in size depending on how many organisms are added to it and how many organisms are removed from it. This change in population size is called growth rate. Growth rate can be positive negative or zero. -a population will grow if more organisms are born than die. Populations living with ideal conditions(adequate food, shelter,and protection from predators.) 1-existing organisms reproduce 2-their offspring reproduce exponential growth 3-their offspring's offspring reproduce ex/ a bacteria divides every ½ hour. 30 minutes-2 bacteria 60 minutes-4 bacteria 90 minutes-8 bacteria 120 minutes-18 bacteria
Populations do not have exponential growth forever; growth will stop or atleast slow down. • Fig. 14-3 p.313 • -zero population growth- the size of a population stays the same because its growth rate is zero. • -Carrying capacity- the largest number of individuals that can survive over long periods of time in a given environment.. • [if the population gets larger then the carrying capacity its birth rate falls or death rate rises.] • Some organisms of a species reach a peak population size (boom) and then crash dramatically (bust) • known as boom and bust • fig. 14-4 p. 314
Section 2- why populations stop growing • Population growth may be limited by several factors ex/ size and density • Population density is the number of organisms in a given area. • Density-dependant limiting factors • 1-operate on large, dense population • 2-species whose populations are controlled by D.D.L.F.tend to have fairly stable populations • 3-competition, predation, parasitism and crowding are examples. • Competition • When populations become crowded, individual plants or animals may compete with one another for food, H20, space, sunlight, etc. • 3 outcomes of competition • 1- some individual may obtain enough of what they need to survive and reproduce • 2-others may obtain enough to live but not enough to enable them to raise offspring • 3- still others may starve to death or die from lack of shelter • -competition can thus lower birth rates, increase death rates, or do both. • - The more individuals there are in an area , the sooner they will use up the available resources.
-competition for limited resources is often one of the most important factors in determining the carrying capacity of an environment for a particular species. Predators 1-predators and their pray usually coexist over long periods of time 2-predators in turn develop their own defenses such as strong jaws and sharp teeth, powerful digestive enzymes or keen eyesight. Parasitism 1- a parasite is an organism that takes nourishment from its host. 2- parasite live at the expense of their host, weakening them and causing diseases and sometimes death. 3-parasites work most effectively when hosts are present in large numbers 4-parasites are often host-specific ; they grow best in members of a single species 5-crowding helps parasites travel from one suitable host to another. Crowding & stress 1-most animals have a builting need for space—hunting/nesting 2-organisms fight among themselves if they become overcrowded. 3-fighting causes high levels of stress, which can upset their hormone balance upsetting animals behavior so they neglect, kill or even eat their own offspring
Density-independent limiting factors 1-boom and bust 2-weather 3-human activities-toxic waste pesticides. predator vs. prey. parasite prey predator
Section 3- Human population growth • -Human populations grow slowly for most of human existence. • -about 300 years ago, the worlds human population started growing more rapidly. • 1- agricultural and industrial revolutions made human life easier • 2- foods became more nutrious • 3-doctors cured and prevented diseases • 4- better health care reduced infant mortality • -Birth rates became considerably higher than death rates • this led to the human population to grow exponentially • 1800- 1billion people • 1900-2 billion people global human population • 1950- 4 billion people • 1963-5 billion people • -2000’s – 180 people are born every minute (92 million new humans/year) • Controlling human population • Over the last century human population growth has slowed down dramatically in some countries • 1- biologists say that these populations passed through demographic transition( a change in growth rate resulting from changes in birth rate)
2-Demographic transition consists of three stages A- first stage- there is a high birth rate and a high death rate. B- second stage- improvements are made in living conditions C- third stage- birth rate decreases for a variety of reasons Birth rate Death rate
Section 4- population growth and carrying capacity • In most weastern countries and china, the global population is still growing exponentially. • because most people live in countries that have not yet completed the demographic transition. • U.S, Canada and Japan and countries of Europe have gone through all three stages of demographic transition- in these countries the population growth is slow. • Countries in Asia, Africa and South America have not yet completed the demographic transition. • - 80% of the worlds population live there • - this provides severe economic problems. • Future population growth • - this depends on how many people of different ages are living in that country today- this is called age-structure diagrams. • demographers- people who study population growth use age-structure diagrams to make predictions about future growth. • Rapid growth • Ex/ mexico- majority of the population is under the age of 15. • - the largest percentages of people has not yet reached their child bearing years • -this means that mexico can expect to grow even more.
Slow growth ex/ Sweden- there is almost equal numbers of people in each age group ex/ In the U.S.- the largest segment of the population belongs to people born after WWII – called the baby boomers. Earths carrying capacity what is the earths carrying capacity for humans? This is a hard question to answer. - some say that the earth can hold between 5-20 billion people.