Population Ecology & Carrying Capacity

Population Ecology & Carrying Capacity - Population...

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Unformatted text preview: 1/15/12 Population Ecolog & Carr ing Capacit POPULATION ECOLOGY [Click he e to jum p to notes concerning Netting's T rbel stud for Oct 16th class] Intro P : 1) ( , , & .) 2) " I' " , . Population gro th R .T T M ( An Essa on the Principle of Population, 1798) " " " , ( " ), ( ) T , the rate of increase in population si e itself increases ( ) , E ) "C ) dN/dt = rN, t N )" N( T ( r( , , , , >0 N ( ) S , F - , E . co l i 20 , ; 36 , I , , ( , 100 A , courses.washington.edu/anth457/popnecol.htm , 1% S ( ); 70 ), 15,000 1/7 1/15/12 Population Ecolog & Carr ing Capacit yrs (the most recent possible date for colonization of the Americas) the resulting population would = 6.6x1066 (that is, 66 followed by 65 zeros); by comparison, present world population is approximately 7x109 (seven billion), and the estimated population of the Americas in 1492 was roughly 6 x 107 (sixty million) So exponential model with an annual growth rate (AGR) of 1% overestimates actual Amerindian population by 59 orders of magnitude! (for the mathematically challenged, 59 orders of magnitude = 1 followed by 59 zeros, not the much smaller 59 times) You might object that an AGR of 1% is unrealistic, and it certainly is over any sustained length of time (which is one of the conclusions we can draw here); but in the short run many expanding human populations have achieved AGRs of 4% or 5%; in fact, the current global AGR is about 1.2%, and reached 2.2% in 1962, and the AGR is currently well over 3% in many countries Indeed, a 1% AGR only requires that the average person produce 2.4 i ing (and reproducing) offspring over their lifetime; and keep in mind that a sustained average of <2 surviving offspring means inevitable population extinction As Maltlhus realized, it is a well-established fact that all species, humans included, have the physiological capacity to reproduce far above replacement rates Obviously the exponential model is highly unrealistic, since no population can reach infinite size or expand at infinite rate -- or even sustain 1% AGR indefinitely Long before this occurs, something must intervene to make growth rate zero or negative (by making births deaths), resulting in population stability or decline So a key question for population ecology is, what factors prevent exponential population growth from occurring unchecked? Pop la ion Reg la ion Malthus argued that as population got too dense, further growth was limited by factors causing increased mortality (which he termed "positive checks," such as war, famine, and disease), as well as factors decreasing fertility (the so-called "preventative checks," such as late marriage, sexual abstinence, etc.) A century and more later, population ecologists refined Malthus' basic argument and constructed a theory of population regulation One key element of this theory is a distinction btwn 2 kinds of population regulation, density-independen vs. density-dependen Characteristics of density-independen population dynamics: mortality or fertility rates unaffected by population density caused by factors such as climate, natural catastrophes, etc. typical of insects courses.washington.edu/anth457/popnecol.htm 2/7 1/15/12 Population Ecolog & Carr ing Capacit ead De e e ia i -dependent ai ad ai f c ai eg a i i fe i i a e (b&d) c ch fac ac eii f e eb a e c c ic ab e ai de ica ead e: e a ed / a i de i , eda i , e ce i i a i i e (i.e., Ma a g e i he ch a i e a e ab a ge, g- i ed, a d - e d ci g a i a de i -de e de d a ic a e ei a De i de e de ce c d be e fa P ai ai ec g dified e e ia Si e ei gi h f hi i e ai i ib i ) hich f he e i e ae ie e e , he ge e a c f he c a de ed he logistic e ic i d ic de f Ma h ia chec a e de f i a e, b f e i ha ai g i -de e de chec h: dN/dt = rN (K-N/K) N e ha he e a i ab e added he e e ia de i K = "ca i g ca aci ," defi ed a he equilibrium population si e achie ed he bi h = dea h , a d he ce dN/dt = 0 [ e ] L gi i c i f a i e idea ha a N i c ea e , fe i i dec ea e a d/ Th , gi ic de a habi a ), ai g ha he N i e h a e i highe A N i c ea e , (K-N)/K bec e a (i.e., a e , he ce Fi a , he N = K, (K-N)/K = 0, he ce g g i g, bi h = dea h ) ai ai g hc A h gh gi i c i de ) de , i i Ne e he e , gi ic de gi e ai ecie e a di g i M ec eh eadi g) e ia ea ab g d fi cc ied habi a ica ed (b i ea i e i e) de i i h da ed ci a i , cha ic beha i , i , a "e i ib a e ( e; i f K dec i e , i a " h ae h a e (dN/dt) = 0, a d N e L gi i c de d ce " ig id" (S- ha ed) g " bac a d S " a N d e a e fK e ea i ic ha e de a i i c ea e if e fi i ifica i ei e a a d a ai d ce (i e a a da a a i ec g d ce i i c c e , eh a d c a h ( ee C he 1995 Logistic Gro th In Human Populations courses.washington.edu/anth457/popnecol.htm 3/7 1/15/12 Population Ecolog & Carr ing Capacit Historical demography and archaeology indicate that whenever humans develop a new energy source, eliminate a major disease, or colonize unoccupied environments, we observe rapid population growth (up to 3% AGR = doubling each generation) for a period of time, followed by slowdown and approach towards equilibrium Precise demonstration of logistic growth in humans is elusive, because long-term demographic records not available except in situations where too many other variables intervene (e.g., emigration, rapid technological change, etc.) But some archaeological records give reasonably strong support for basic model For example, Hawaiian Islands colonized approx. 1500 years ago, probably by small founding population of <1,000 people who came from Marquesas in several voyages First 700 yrs characterized by slow, steady growth (doubling ca. every 200 yrs), to population of ca. 15,000 Then a reorganization of settlement pattern, production system, & social organization led to rapid population growth This lasted for 400 years, followed by 200 years of little growth but much warfare, intensive competition for land At contact (1778), Hawaiian population = approx 225,000 Thus estimated annual growth rate averaged over entire period was less than 0.5% (.0425%) If AGR had been just a little higher (i.e., 0.7%), population at contact would have been 7.5 million (= entire population of No. America in 1780); but of course, there are good ecological reasons (not least of which is limited amount of arable land) why such a population density was not possible Global long-term population trends subject to lots of guesswork, but some reasonable estimates are: a) a few thousand or tens of thousand at outset of hominid lineage (ca. 5 million yrs ago) b) approx. 8 million worldwide at beginning of Neolithic (10,000 B.P.) c) world population increased 160x (5 mill. to 800 mill.) from 10,000 B.P. to A.D. 1750, doubling every 1,000 years (mean AGR = 0.1%) d) total AGR now 1.2% (= doubling every 60 yrs) e) big question is whether it will level off in sigmoid fashion (Cohen 1995: Fig. 4), or perhaps "overshoot" resulting in crash or oscillations courses.washington.edu/anth457/popnecol.htm 4/7 1/15/12 Population Ecolog & Carr ing Capacit Carr ing Capacit C AD ( , K= ) I , , (D ' "C ") M . : ) ) ) ( " - ") ) (" N ) ") ) , ) ) T : 1) ( , , .) & 2) F , , ' - ; , S , , T (1995:343), H K iche- : , , , ; , , (N J C - K) / K Calculating Carr ing Capacit S courses.washington.edu/anth457/popnecol.htm C 5/7 1/15/12 Population Ecolog & Carr ing Capacit F H-G, he e i c de a ia i , e c. ea e f a ef S e i e C c i e i a ed di ec f g e a e ce f NPP i i ed b h ech g ,a d ) F ag i c a ai The e e i a e a e e a , C c e i a ed ica d de ai eg a ed be 2) ai i i ed b N e ha a b F f da a 13 1 b i e ce-ag ic. ai fa be ai a d c i i /a ea gge i g ei he i ib i ei , di ea e) (Ma h ia a a i e da a h ie ) ie ) a ai i dica e ai e i a ed Cc, a d he e, he da a e hibi a e g i ea e a i a i (c e a i c efficie = 0.993, hich ea Cc, e e h gh N?Cc) e e ceed i hi b b e ed & edi c ed >98% f a ia ce i N ca be edic ed Thi gge ha ba ic i f ai bei g i i ed b e a ia c ec ; he i e e d e ec a a ai be i , a d a fa e " i " ea i hi be ee N a d Cc We ca a i e ha a g he e ag ic. g ; , a . ( e f- eg a i g e De i e fai e edi c N i h a eci i , c e g d c ea i b C c a d b e ed N Ga h h e i d, b e ed (e.g., i c a e, ea (NPP) f habi a , b ha e hic e e , e ce ch ice , i g a d a ea, fa b i e ce he fac ai ab e ie d, ca ia d ci ( hich de e d 30-50% highe ha 1) i, ce ba e (Cc) i a ea fa ab e diag a i e a e hi g in addi ion a ab e a d i ac i g ii he i e e d h N=Cc a he ha N<Cc Whi e agg ega e da a i e hi a e i i a i g, ea e a i e a ic a ca e i de ai -- a i Ne i g' a a de a d i f T be ai ai de i eg a i Case Stud : Sw iss Peasants (Netting) R be Ne i g' (1981) d i ea e f a ec Ne i g f c ed i g e a i h ce e e d a & he da a c e 3 ce ie g i ca a dS i ach hi a i e i age f T ica de ga h be ; ce Th , Ne i g' d e a i e hi ic hif i de g a h & b i e ce e gi e a d a a ca e e ( . a i a egi a agg ega i ae ed i hi ica de g a h ) S e ba ic fi di g f ec d a d: courses.washington.edu/anth457/popnecol.htm 6/7 1/15/12 Population Ecolog & Carr ing Capacit 1. Fe ili o e and fell in o gh balance i h mo ali a e (Ne ing, Fig. 6.1) ( ee foo no e 7 on p. 245 e apid eco e f om epidemic : "When an epidemic i pa , ho e ho emain ali e a e mo e igo o ; he dead ha e opened p ne place and lef behind hei inhe i ance , and fo hi ea on e e one ma ie ho can." -Wa e , 1700 ) 2. O e all, a ing b po i i e le el of pop la ion g o h mo of he ime; "e ce emig a e , o e iden pop la ion emain ela i el con an fo long pe iod 3. Fe ili limi a ion i p ima il ia e " pop la ion ic ion on ma iage: a. Linked o inhe i ance of ag ic l al e a e (common pa e n in E ope) b. Land ca ci lead o dela in age a ma iage, e en lifelong celibac (Ne ing no e on p 135 ha hen pop la ion den i inc ea ed, celibac en a high a 33%). I hi an e ample of den i -dependen pop la ion eg la ion? 4. Ne ing concl de ha inc ea e in pop la ion g o h a e in 19 h cen in fe ili han decline in mo ali d e mo e o inc ea e a. P e en da a ha le o a io po ible ca e (age a ma iage, ma iage d a ion, delibe a e fe ili con ol, e c.) b. A ib e hi p ima il o be e n i ion e l ing in ho e in e -bi h in e al c. S gge p o ima e ca e a in od c ion of po a o courses.washington.edu/anth457/popnecol.htm 7/7 ...
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