September Club Meeting Thursday, Sept. 16 7:30pm English Building Room 104 “To foster respect and compassion for all living things, to promote understanding of all cultures and beliefs and to inspire each individual to take action to make the world a better place for people, animals and the environment.” September & October Volunteering, Fundraising, and Social Events will be discussed. Snacks and juice will be served!

Fall 2010 IB Workshop Series sponsored by IB academic advisors IB Opportunities in C-U Thursday, Sept. 16 4:00-5:00pm G30 Foreign Languages Bldg. 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: Bring T + R LOs Complete: Problem Sets 1: 1-7 2: 1-2 Bring pg. 221 too!

Objectives Population Dynamics Growth in unlimited environment Geometric growth N t+1 = N t Exponential growth N t+1 = N t e rt 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 one graph of population growth contrasting: 1)Growth with unlimited resources 2)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)

Geometric growth: Individuals added at one time of year (seasonal reproduction) Uses difference equations Exponential growth: individuals added to population continuously (overlapping generations) Uses differential equations Both assume no age-specific birth/death rates Two models of population growth with unlimited resources :

Difference model for geometric growth with 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) N t+1 = N t + gN t =(1 + g)N t Let (lambda) =(1 + g), then N t+1 = N t = N t+1 /N t = finite rate of increase, /unit time

Values of, r, and R o indicate whether population is: *** R o < 1R o >1R o =1

Geometric growth over many time intervals: N 1 = N 0 N 2 = N 1 = · · N 0 N 3 = N 2 = · · · N 0 N t = t N 0 Populations grow by multiplication rather than addition (like compounding interest) So if know and N 0, can find N t.

Example of geometric growth (N t = t N 0 ) Let =1.12 (12% per unit time) N 0 = 100 N 1 = (1.12) N 2 = (1.12 x 1.12) N 3 = (1.12 x 1.12 x 1.12) N 4 = (1.12 x 1.12 x 1.12 x 1.12)

Complete Problem 2.1 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. 1.Does this species have overlapping generations? Explain. 2.What is for this population? Show formula with numbers; don’t solve. 3.Predict the population size after 3 yrs. Show formula with numbers; don’t solve. 4.What is one assumption you make in predicting the future population size?

Differential equation model of exponential growth:

dN / dt = r N rate of contribution number change of each of in = individual X individuals population to population in the size growth population Where r = (b - d) per individual per unit time

Problem 1.1 Calculate daily increase in 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 # per capita per unit time) r =intrinsic rate of increase

Problem 1.2 Calculate r.

E.g.: exponential population growth r =.247

Exponential growth: N t = N 0 e rt Continuously accelerating curve of increase Slope varies directly with population size N (slope gets steeper as size increases). r > 0 r < 0 r = 0

Problem 1.4 A. r B. population size in 6 mo.

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 r max for organisms in disturbed habitats Low r max 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 N t+1 = N t Exponential growth N t+1 = N t e rt 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 due to crowding N close to 0

Population growth predicted by the *** model. K = ***

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 in logistic model

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 = d Those rates can change with density.

Density-dependent factors: + or -?.

Population size is regulated by density- dependent factors affecting birth and/or death rates.

r (intrinsic rate of increase) decreases as a function of N. Population growth is negatively density- dependent.. rmrm r r0r0 N K slope = r m /K

Positive density-dependence Allee effect: greater pop size increases chance of recruitment.

Describes a population that experiences negative density-dependence. Population size stabilizes at K = carrying capacity dN/dt = r m N(K-N)/K where r m = 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 (Problem Set 2-2)

Logistic curve incorporates influences of decreasing per capita growth rate, r, and increasing population size, N. Specific (Problem Set 2-2)

Assumptions of logistic model: Population growth is proportional to the remaining resources (linear response). All individuals can be represented by an average (no change in age structure). Continuous resource renewal (constant E). Instantaneous responses to crowding.. *** K and r are specific to particular organisms in a particular environment.

Doubling time (Problem Set 1-6,1-7) t 2 = ln2 / ln t 2 = ln2 / r

Complete: Problem Set 1: 1-7 Problem Set 2: 1-2 Bring Thursday. (Also bring: Problem Set 3: 221-2)