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Fall 2009 IB Workshop Series sponsored by IB academic advisors. IB Opportunities in C-U Tuesday, Sept. 15 4:00-5:00pm 135 Burrill There are many local opportunities for volunteering/internships! Representatives in fields from medicine to ecology will speak with students!.

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## Fall 2009 IB Workshop Series sponsored by IB academic advisors

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**Fall 2009 IB Workshop Seriessponsored by IB academic**advisors IB Opportunities in C-U Tuesday, Sept. 15 4:00-5:00pm 135 Burrill There are many local opportunities for volunteering/internships! Representatives in fields from medicine to ecology will speak with students!**Ch 11: Population Growth + Regulation dN/dt = rN**dN/dt = rN(K-N)/K For Thursday lecture, Bring lecture outline; Complete Problem Set 2-1 and 2-2 (see pg. 75). Bring pg. 73 too!**Objectives**• Population Dynamics • Growth in unlimited environment • Geometric growth Nt+1 = Nt • Exponential growth Nt+1 = Ntert • dN/dt = rN • Model assumptions • Growth in limiting environment • Logistic growth dN/dt = rN (K - N)/ K • D-D birth and death rates • Model assumptions**1.***Draw a graph of population growth constrasting:**Growth with unlimited resources Growth with limited resources Label axes. Indicate carrying capacity (K). 3) Add equations representing both types of growth: A) exponential B) logistic**Population growth predicted by the exponential (J) vs.**logistic (S) model.**Population growth can be mimicked by simple mathematical**models of demography. • Population growth (# ind/unit time) = recruitment - losses • Recruitment = Births + Immigrants • Losses = Deaths + Emigrants • Growth (g) = (B + I) - (D + E) • Growth (g) = (B - D) (in practice)**Two models of population growth with unlimited resources :**• Geometric growth: • Individuals added at one time of year (seasonal reproduction) • Uses differenceequations • Exponential growth: • individuals added to population continuously (overlapping generations) • Uses differential equations • Both assume no age-specific birth/death rates**Difference model for geometric growthwith finite amount of**time • ∆N/ ∆t = rate of ∆ = (bN - dN) = gN, • where b = finite rate of birth or per capita birth rate/unit of time • g = b-d, gN = finite rate of growth**Projection model of geometric growth (to predict future (or**past) population size) • Nt+1 = Nt + gNt • =(1 + g)Nt Let (lambda) =(1 + g), then • Nt+1 = Nt • = Nt+1/Nt • = finite rate of increase, /unit time**Geometric growth over many time intervals:**• N1 = N0 • N2 = N1 = · · N0 • N3 = N2= · · · N0 • Nt = t N0 • Populations grow by multiplication rather than addition (like compounding interest) • So if know and N0, can find Nt.**Example of geometric growth (Nt = t N0)**• Let =1.12 (12% per unit time) N0 = 100 • N1 = (1.12) 100 112 • N2 = (1.12 x 1.12) 100 125 • N3 = (1.12 x 1.12 x 1.12) 100 140 • N4 = (1.12 x 1.12 x 1.12 x 1.12) 100 157**2. Problem 2.1 on Pg 75 - due Thursday!**A moth species breeds in late summer and leaves only eggs to survive the winter. The adult dies after laying eggs. One local population of the moth increased from 5000 to 6000 in one year. Does this species have overlapping generations? Explain. What is for this population? Show formula with numbers; don’t solve. Predict the population size after 3 yrs. Show formula with numbers; don’t solve. What is one assumption you make in predicting the future population size?**If knowNt N0 and ,can calculate t (in future and past)**• Nt = t N0 • t = Nt/ N0 • = (Nt/ N0)1/t • t ln = ln (Nt/ N0) • t = [ln (Nt/ N0)]/ ln **3. Invasive insect:Geometric population growth:Calculate:A.**lambdaB. t when n = 1**Geometric growth (dots) and**exponential growth (lines) on regular and log scales (when >1 and r >0).**Values of , r, and Roindicate whether population is: *****Ro < 1 Ro =1 Ro >1**dN / dt = r N**rate of contribution number change of each of in = individual X individuals population to population in the size growth population**dN / dt = r N**• r = difference between birth (b) and death (d) • Instantaneous rate of birth and death • r = (b - d) so r is analogous to g, but instantaneous rates • rates averaged over individuals (i.e. per capita rates) • r =intrinsic rate of increase**E.g.: exponential population growth**r = .247**Exponential growth:Nt = N0ert**r > 0 • Continuously accelerating curve of increase • Slope varies directly with population size. • (N) (gets steeper as size increases). r = 0 r < 0**Environmental conditions and species influence r, the**intrinsic rate of increase.**Population growth rate depends on the value of r; r is**environmental- and species-specific.**Value of r is unique to each set of environmental**conditions that influenced birth and death rates… …but have some general expectations of pattern: High rmax for organisms in disturbed habitats Low rmax for organisms in more stable habitats**Rates of population growth are directly related to body**size. • Population growth: • increases inversely with mean generation time. • Mean generation time: • Increases directly with body size.**Assumptions of the model**• 1. Population changes as proportion of current population size (∆ per capita) • ∆ x # individuals -->∆ in population; • 2. Constant rate of ∆; constant birth and death rates • 3. No resource limits • 4. All individuals are the same (no age or size structure)**Objectives**• Growth in unlimited environment • Geometric growth Nt+1 = Nt • Exponential growth Nt+1 = Ntert • dN/dt = rN • Model assumptions • Growth in limiting environment • Logistic growth dN/dt = rN (K - N)/ K • D-D birth and death rates • Model assumptions**Populations have the potential to increase rapidly…until**balanced by extrinsic factors.**Population growth rate =**Intrinsic Population Reduction in growth X size X growth rate rate at dueto crowding N close to 0**On which island(s) is there evidence of**limited resources affecting population growth ?**Assumptions of the exponential model**1. No resource limits 2. Population changes as proportion of current population size (∆ per capita) ∆ x # individuals -->∆ in population; 3. Constant rate of ∆; constant birth and death rates 4. All individuals are the same (no age or size structure) 1,2,3 are violated *****Population growth rates become lower as population**size increases. Assumption of constant birth and death rates is violated. Birth and/or death rates must change as pop. size changes.**Population equilibrium is reached when b = dThose rates can**change with density.**Habitat quality affects reproductive variables affected (How**is K affected?)**Population size is regulated by density-dependent factors**affecting birth and/or death rates.**Density-dependence in plants first decreases growth. 2.**Size hierarchy develops. skewed**3) Density-dependence**thirdly decreases survival. Intraspecific competition causes “self-thinning”.**r (intrinsic rate of increase) decreases as a function of**N . Population growth is negatively density-dependent.. rm slope = rm/K r r0 K N**Positive density-dependence**Allee effect: greater pop size increases chance of recruitment.**2) (+) density-dependence secondly increases some components**of reproduction; decreases others…**Describes a population that experiences**negative density-dependence. Population size stabilizes at K = carrying capacity dN/dt = rmN(K-N)/K where rm = maximum rate of increase w/o resource limitation = ‘intrinsic rate of increase’ K = carrying capacity (K-N)K = environmental break (resistance) = proportion of unused resources Logistic equation**Logistic (sigmoid) growth occurs when the population reaches**a resource limit. Inflection point at K/2 separates accelerating and decelerating phases of population growth; point of most rapid growth

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