Population Dynamics in Ecosystems Bio.2.1.4, Bio.2.2.1, Bio.2.2.2

Population Dynamics Populations often change size over time. Some increase in size, others decrease. We will concentrate on population growth: How fast? For how long will growth continue? Population Density: # of individuals per unit area Population Growth Around the World since 1 A.D. http://desip.igc.org/mapanim.html

Population Dynamics Population growth can be exponential: Time # of Individuals J-Shaped Curve Population of Seagulls.. http://www.acclaimimages.com/_gallery/_pages/0018-0312-3010-5037.html

EXPLOSION Population Growth Exponential growth: when the number of organisms grows by a constantly increasing rate. Ideal situation with unlimited resources. Results in a population EXPLOSION

Population Dynamics R-selected: organisms that grow out of control, exponentially Exponential growth can occur for short periods of time, but cannot continue forever! Why? What limits exponential growth? http://www.sgnhs.org/mouse.html Mice and weeds are examples of r-selected organisms http://montana.plant-life.org/page_weeds.htm

Population Dynamics Population growth can be logistic: http://animaltrial.com/animals/Elephantpictures/africanelephantherdpict.html S-Shaped Curve Time # of Individuals Population of Elephants…. Logistic Growth: a population’s growth slows or stops following a period of exponential growth.

Population Dynamics Carrying Capacity: The number of organisms of one species that a habitat or environment can hold Once carrying capacity (k) is reached, the population maintains at that size. These populations of organisms are called k-selected. http://buten.net/max/My2001/10_monkeys/index_10_monkeys.html http://www.wildlife-pictures-online.com/image-files/xfamily.jpg Most primates and Elephants are k-selected

Population Dynamics Time # of Individuals k http://www.wildlife-pictures-online.com/image-files/xelecalf3a.jpg For logistic growth, population sizes always level out at the carrying capacity (k)

Characteristics of K and R selected organisms K-selected organisms: Big Usually mammals (parental care) Longer life span Stable environments Humans, bears, elephants R-selected organisms: Small bodied Often insects Short Life span Mature early, lots of offspring Mosquitoes, bacteria. http://www.theglobalroad.com/zoo/polar1/polar0025.shtml http://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?action=view&link=Animals/Insects/Ants&image=P7190888AB.jpg&img=&tt=

Population Dynamics Limiting Factors: Biotic or abiotic factors that restrict or prevent the existence, numbers, reproduction, or distribution of organisms. Ex. A predator such as a lynx is a limiting factor for a prey such as a hare. Ex. A cold snowy winter is a limiting factor for thousands of species that would die under those conditions. Ex. In brackish water, fish can’t pass from salt water to fresh water. The salinity of the water is a limiting factor. http://www.yukonman.com/pictures2-8.asp http://www.fotosearch.com/COR356/110000/

Population Dynamics Limiting Factors can be biotic or abiotic. *List examples of each! http://www.facethewind.com Abiotic Biotic http://www.spottycat.com/marlos/emporium/cougar/bigcat11.jpg

Population Dynamics Density Dependent Factors: Factors that limit the size of a population and only exist when populations get too big Ex. Disease, competition, parasites, and a limited amount of food. These would not have caused so many problems had the population remained small. http://gbgm-umc.org/umcor/00/eth6.stm

Population Dynamics Predation: One animal constantly consuming another, limits its’ population size Ex. Owls keeping a mouse population small, or hunters keeping deer numbers in check. Ex: Lynx and Hare Predator can’t eat all prey or food will be gone for good. http://www.naturia.per.sg/buloh/birds/Ardea_cinerea.htm http://www.colostate.edu/Depts/CoopExt/4DMG/Pests/spiders.htm

Lynx Chases Hare

Lynx and Hare Graph

Population Dynamics Competition: A density dependent factor. Individuals competing for limited food source or other resources. Crowding and Stress: Not completely understood, but causes: fighting Infertility decreased parental care decreased immunity to disease death Parasitism and Disease: parasites limit the growth of a population by causing diseases

Population Dynamics Floods Density Independent Factors: Limiting factors that would affect all populations regardless of size Most are abiotic factors. Ex. Floods, hurricanes, drought, habitat destruction. http://www.danieldesign.com/otherlinks.htm Volcanic Eruptions Fire http://www.arenal.net/ http://www.worldphotos.com/s/worldphotos/weather.html

Human Population Growth Demography: the study of human population growth characteristics. Scientists called Demographers. See Fig. 5.10 on p. 129 for graph of exponential human growth. Demographic transition: a dramatic change in birth and death rates

Human Population Growth Birth Rate: Usually it’s the number of babies that were born in the past year. # of births in a sample size of 1000 individuals Death Rate: Usually it’s the number of people who have died in the past year. # of deaths in a sample size of 1000 individuals http://www.ux1.eiu.edu/~cfruf/popfac.htm

Human Population Growth Fertility Rate: The number of babies each woman is having during her fertile years. Total Fertility rates in the U.S. from 1917 to2000. Note: Baby Boom After WWII http://www.ux1.eiu.edu/~cfruf/els_fertility_rates.htm

Human Population Growth Age Structure: can be used to determine how quickly a country or area is growing. Are most individuals post-reproductive? Are most individuals reproductive? Are most individuals pre-reproductive? Which of these would most likely be growing the fastest? The slowest?   Populations that are not growing have about the same numbers of each age group.    See p. Fig 5.13 pg. 131 Age Structure Diagram: population profiles, graphing the number of people in different age groups Age Structure Diagram http://www.ux1.eiu.edu/~cfruf/popagestruc.htm

Human Population Growth Immigration: movement by individuals into a country or area. Emigration: movement by individuals out of a country or area. Neither change world populations but both change populations of the countries involved. http://www.terragalleria.com/america/alaska/alaska-misc/picture.alas6416.html