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Population Dynamics in Ecosystems Bio.2.1.4, Bio.2.2.1, Bio.2.2.2 K. Nifong 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 Growth Around the World since 1 A.D. • Population Density: # of individuals per unit area http://desip.igc.org/mapanim.html 2 Population Dynamics # of Individuals • Population growth can be linear: Time Population of lions. http://www.fotosearch.com/DGV119/029069/ 3 Population Dynamics • Population growth can be exponential: # of Individuals J-Shaped Curve Population of Seagulls.. Time http://www.acclaimimages.com/_gallery/_pages/0018-0312-3010-5037.html 4 Population Growth 5 • Exponential growth: when the number of organisms grows by a constantly increasing rate. • Ideal situation with unlimited resources. • Results in a population Population Dynamics • R-selected: organisms that grow out of control, exponentially • Exponential growth can occur for short periods of time, but cannot continue forever! http://www.sgnhs.org/mouse.html • Why? • What limits exponential growth? Mice and weeds are examples of r-selected organisms http://montana.plant-life.org/page_weeds.htm 6 Population Dynamics Population growth can be logistic: http://animaltrial.com/animals/Elephantpictures/africanelephantherdpict.html # of Individuals S-Shaped Curve Population of Elephants…. Logistic Growth: a population’s growth slows or stops following a period of exponential growth. Time 7 Population Dynamics • Carrying Capacity: The number of organisms of one species that a habitat or environment can hold http://buten.net/max/My2001/10_monkeys/index_10_monkeys.html • Once carrying capacity (k) is reached, the population maintains at that size. • These populations of organisms are called k-selected. http://www.wildlife-pictures-online.com/image-files/xfamily.jpg Most primates and Elephants are k-selected 8 # of Individuals Population Dynamics k http://www.wildlife-pictures-online.com/image-files/xelecalf3a.jpg Time For logistic growth, population sizes always level out at the carrying capacity (k) 9 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: http://www.theglobalroad.com/zoo/polar1/polar0025.shtml • • • • • Small bodied Often insects Short Life span Mature early, lots of offspring Mosquitoes, bacteria. 10 http://classroomclipart.com/cgibin/kids/imageFolio.cgi?action=view&link=Animals/Insec ts/Ants&image=P7190888AB.jpg&img=&tt= • Limiting Factors: Biotic or abiotic factors that restrict or prevent the existence, numbers, reproduction, or distribution of organisms. http://www.yukonman.com/pictures2-8.asp http://www.fotosearch.com/COR356/110000/ • 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. 11 Population Dynamics 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 12 Population Dynamics • Density Dependent Factors: Factors that limit the size of a population and only exist when populations get too big http://gbgm-umc.org/umcor/00/eth6.stm • Ex. Disease, competition, parasites, and a limited amount of food. • These would not have caused so many problems had the population remained small. 13 Population Dynamics http://www.naturia.per.sg/buloh/birds/Ardea_cinerea.htm • 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.colostate.edu/Depts/CoopExt/4DMG/Pests/spiders.htm 14 Lynx Chases Hare 15 Lynx and Hare Graph 16 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 17 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 18