L e c ture 2 L e c ture 2 Population E Population E c ology - PDF document

L e c ture 2 L e c ture 2 Population E Population E c ology c ology Po pula tio n Gro wth, Po pula tio n Gro wth, Co mpe titio n a nd Pre da tio n Co mpe titio n a nd Pre da tio n BF BF L L F F Bio lo g y Co nc e pts Bio lo g y Co nc e pts • Po pula tio n g ro wth • Po pula tio n g ro wth • I • I ntra spe c fic Co mpe titio n (I ntra spe c fic Co mpe titio n (I nte rspe c fic ) nte rspe c fic ) • Pre da tio n (Pa ra sitism/ Virule nc e ) • Pre da tio n (Pa ra sitism/ Virule nc e ) • Be ha vio r • Be ha vio r • E • E vo lutio n? vo lutio n? 1

T he T ra g e dy o f the Co mmo ns T he T ra g e dy o f the Co mmo ns • Ope n pa sture c a n suppo rt 10 c a ttle • Ope n pa sture c a n suppo rt 10 c a ttle • Curre ntly g ra ze d b y 10 he rdsme n • Curre ntly g ra ze d b y 10 he rdsme n e a c h with o ne e a c h with o ne • One o f the he rdsme n a dds • One o f the he rdsme n a dds o ne mo re if he c a n ma ke a o ne mo re if he c a n ma ke a pro fit. pro fit. • Adding o ne mo re a nima l = • Adding o ne mo re a nima l = le ss fo o d fo r e a c h a nima l, le ss fo o d fo r e a c h a nima l, b ut sinc e he o nly ha s o nly b ut sinc e he o nly ha s o nly 1/ 10 o f the he rd, he ha s to 1/ 10 o f the he rd, he ha s to pa y o nly 1/ 10 o f the c o st. pa y o nly 1/ 10 o f the c o st. T T he T he T ra g e dy o f the Co mmo ns ra g e dy o f the Co mmo ns • Shrinking pro fit ma rg ins ⇒ • Shrinking pro fit ma rg ins ⇒ e ithe r g o o ut o f b usine ss o r e ithe r g o o ut o f b usine ss o r a lso a dd mo re a nima ls. a lso a dd mo re a nima ls. • Mutua l e xplo ita tio n • Mutua l e xplo ita tio n c o ntinue s until o ve rg ra zing c o ntinue s until o ve rg ra zing a nd e ro sio n de stro y the a nd e ro sio n de stro y the pa sture syste m, a nd a ll the pa sture syste m, a nd a ll the he rdsme n a re drive n o ut o f he rdsme n a re drive n o ut o f b usine ss… b usine ss… • Ha rdin 1968 • Ha rdin 1968 2

St. Ma tthe w I sla nd Co lla pse St. Ma tthe w I sla nd Co lla pse • Sma ll numb e r o f • Sma ll numb e r o f re inde e r c o lo nize d re inde e r c o lo nize d the isla nd the isla nd • I nc re a se ra pidly • I nc re a se ra pidly • Use up a ll o f the • Use up a ll o f the re so urc e s re so urc e s • Po pula tio n • Po pula tio n c o lla pse s c o lla pse s Po pula tio n Gro wth Po pula tio n Gro wth • E • E xpo ne ntia l Gro wth xpo ne ntia l Gro wth dN/dt = rN dN/dt = rN dN/dt = rN rt N t N t = N 0 e rt = N 0 e rt N t = N 0 e Population Size Population Size N t N t = = popln popln @ time t @ time t N t = popln @ time t r = growth rate r = growth rate r = growth rate Time Time 3

Po pula tio n Gro wth Po pula tio n Gro wth • E • E xpo ne ntia l Gro wth xpo ne ntia l Gro wth dN/dt = rN dN/dt = rN dN/dt = rN high r high r Population Size Population Size moderate r moderate r low r low r Time Time Po pula tio n Gro wth Po pula tio n Gro wth • E • E xpo ne ntia l Gro wth xpo ne ntia l Gro wth – Disc re te T – Disc re te T ime N t+1 = N t * R ime N t+1 = N t * R • R = a ve ra g e re pro duc tio n • R = a ve ra g e re pro duc tio n 4

Po pula tio n Gro wth Po pula tio n Gro wth • L • L o g istic Gro wth (Ma lthus) o g istic Gro wth (Ma lthus) • I • I ntra spe c ific c o mpe titio n ntra spe c ific c o mpe titio n Carrying Capacity of Environment (K) Carrying Capacity of Environment (K) Population Size Population Size dN/dt = rN(1- N/K) dN/dt = rN(1- N/K) N 0 K N t = N 0 + (K − N 0 )e − r 0 t Period of Period of Exponential Exponential Growth Growth Time Time Density-Dependant Factors Regulate Population Size Density-Dependant Factors Regulate Population Size Density-dependent Density-dependent Density - dependent birth Density - dependent birth death rate - d death rate - d rate rate 1 dN 1 dN N dt N dt 1 dN 1 dN Density-independent Density-independent N dt N dt birth rate - b Density-independent birth rate - b Density-independent death rate death rate Population Density (N) Population Density (N) Population Density (N) Population Density (N) Equilibrium Equilibrium Density Density Density-dependent Density-dependent death rate death rate 1 dN 1 dN r = b-d N dt r = b-d N dt Density-dependent birth Density-dependent birth rate rate as N r as N r stabilizing stabilizing Population Density (N) Population Density (N) 5

Po pula tio n Gro wth Po pula tio n Gro wth • L • L o g istic Gro wth o g istic Gro wth – Disc re te T ime N t+1 = N t (1+r(1-N t / K )) – Disc re te T ime N t+1 = N t (1+r(1-N t / K )) • R = a ve ra g e re pro duc tio n • R = a ve ra g e re pro duc tio n • K • K = c a rrying c a pa c ity = c a rrying c a pa c ity Whic h g ra ph o f po pula tio n g ro wth Whic h g ra ph o f po pula tio n g ro wth c o uld not b e g e ne ra te d b y this c o uld not b e g e ne ra te d b y this e q ua tio n? N t+1 = N t (1+r(1-N t / K e q ua tio n? N t+1 = N t (1+r(1-N t / K )) )) • A • A • C • C • B • B • D • D • E • E - T - T he y c o uld all b e g e ne ra te d he y c o uld all b e g e ne ra te d • F • F - None c o uld b e g e ne ra te d - None c o uld b e g e ne ra te d 6

Po pula tio n Gro wth Po pula tio n Gro wth • L • L o g istic Gro wth o g istic Gro wth – Disc re te T ime N t+1 = N t (1+r(1-N t / K )) – Disc re te T ime N t+1 = N t (1+r(1-N t / K )) • L imit Cyc le s • L imit Cyc le s • Cha o s • Cha o s Re a l Po pula tio n Gro wth Re a l Po pula tio n Gro wth 7

• Huma n • Huma n po pula tio n po pula tio n g ro wth g ro wth 8

Human Population Age Distribution Human Population Age Distribution More Developed Countries More Developed Countries Age Interval Age Interval Long periods of Long periods of no net growth lead to no net growth lead to 80 - 90 80 - 90 even distribution even distribution 70 - 80 70 - 80 60 - 70 60 - 70 50 - 60 50 - 60 40 - 50 40 - 50 30 - 40 30 - 40 20 - 30 20 - 30 10 - 20 10 - 20 0 -10 0 -10 Females Females Males Number of people (Millions) Males Number of people (Millions) Po pula tio n Summa ry fo r Po pula tio n Summa ry fo r the US the US 2000 2025 2050 http://blue.census.gov/ 9

Population Age Distribution Population Age Distribution Less Developed Countries Less Developed Countries Age Age 300 300 300 300 Females Females Males Number of people (Millions) Males Number of people (Millions) Po pula tio n Summa ry fo r Po pula tio n Summa ry fo r Ug a nda Ug a nda 2000 Very high reproductive rate 2025 2050 http://blue.census.gov/ 10

6,432,150,287 Human Population Growth Now projected to Human Population Growth (4/22/05) reach 9 Billion 6,363,174,549 and level off (4/28/2004) 6,289,870,258 * 6 6 (4/30/2003) 5 5 Population (Billions) Population (Billions) 6 Billion 6 Billion 4 Modern Medicine (1999) 4 Modern Medicine (1999) (reduced mortality) (reduced mortality) Agriculture & Agriculture & (1900) (1900) 3 3 domestification of domestification of Fossil animals Fossil animals Hunter Hunter Industrial Revolution Industrial Revolution Fuel Fuel Gatherers 2 Gatherers 2 (1800) (1800) Bubonic Plague Bubonic Plague 1 4 million 7 million 1 4 million 7 million (1400) (1400) 10,000 BC 8,000 BC 4,000 BC 0 2,000 AD 10,000 BC 8,000 BC 4,000 BC 0 2,000 AD Year Year Adapted from: Cohen, “How Many People Can the Earth Support” http://www.census.gov/main/www/popclock.html Adapted from: Cohen, “How Many People Can the Earth Support” http://www.census.gov/main/www/popclock.html http://www.census.gov/ipc/prod/wp02/wp02-1.pdf 11

Demographic Transition Demographic Transition Stage 1 Stage 2 Stage 3 Stage 4 Stage 1 Stage 2 Stage 3 Stage 4 High birth rate Declining death rates Declining birth and Low death rate High birth rate Declining death rates Declining birth and Low death rate High, but fluctuating Continuing high birth death rates Low, but fluctuating High, but fluctuating Continuing high birth death rates Low, but fluctuating death rate rates birth rate death rate rates birth rate Wha t do yo u think is the huma n Wha t do yo u think is the huma n c a rrying c a pa c ity o f e a rth? c a rrying c a pa c ity o f e a rth? • A - 6 b illio n • A - 6 b illio n • B - 9 b illio n • B - 9 b illio n • C - 12 b illio n • C - 12 b illio n • D - 15 b illio n • D - 15 b illio n 12