Populations and Life Cycles

What is a population?  Population – a group of the same species that occupies the same geographical space

What is a community?  Community- a group of interacting populations occupying the same area

How do populations grow? 1. Linear Growth - population grows by set increments (for example 2 feet per year) # time

How do populations grow? 2. Exponential Growth (J Curve) - Doubling of population by each time increment # time Where is the… Lag Phase? Exponential Phase? What is biotic potential?

How do populations grow? 3. Logistic Growth Curve (S-Curve) - the population grows exponentially up to a point, then levels off due to resource availability Where is the… Lag Phase? Exponential Phase? Stationary Phase? What is the carrying capacity?

So…how do populations actually grow? BIDE Model (Births + Immigration) – (Deaths + Emigration) = Example: A population of chimpanzees has 150 births a year and 10 immigrants per year. During the same year 25 chimpanzees died and 15 left the population. Is this population growing or declining? ( ) – (25 +15) = +120 chimpanzees Population Growth or Decline

Terms to know when talking about populations  Biotic factors – A factor created by a living thing or any living component within an environment that effects the action of another organism, for example a predator consuming its prey.  Abiotic factors – A factor that is non- living in an environment that effects the action of another organism, for example rain or soil

N t+1 = R x N t N t = number individuals now N t+1 = number of individuals next year where R is the finite rate of increase If R > 1 the population grows If R < 1 the population declines A More Sophisticated Look: Exponential growth In problems you may be asked to figure out what R is. The general equation is R = 1 (+/-) ___ % (in decimal form) You would use a + sign when the population is increasing You would use a – sign when the population is declining

Examples of the Exponential Growth Model Example 1: A population of humans has 50 individuals. If the rate of increase is 4% (R = ), what will the population be next year? N t+1 = 50 x people next year! Example 2: A population of lemmings is currently at 100. If the rate of decline is 15% (so R = ) in the current year, how many will be present next year in the population? N t+1 = 100 X lemmings next year!

What factors influence population growth? Density Independent Factors - abiotic factors that effect each member of the population, no matter how many are present Density Dependent Factors - biotic factors that influence population size that is influenced by the number of individuals

One other factor that has not been accounted for…. Assumption for exponential growth model was that all individuals are equal. That is, the population is unstructured Is the human population unstructured??

Most organisms have structured populations

Stage and Size predict survival and fecundity Plants- seed, seedling, adult Invertebrates- number of molts, larva-pupa-adult Amphibians- egg-tadpole-adult Birds- egg-chick-adult Mammals- newborn, juvenile, adult

Exponential growth with structure N 0 (t+1) N 2 (t+1) N 1 (t+1) = F0F0 0 S0S0 F1F1 S1S1 0 F2F2 0 0 N 0 (t) N 2 (t) N 1 (t) N t+1 = R x N t Unstructured exponential growth model Structured growth model

Management of the pest plant, Garlic mustard Exotic plant (from Europe)- highly invasive weed in USA Biennial life cycle- seed, rosette, adult…also has seed dormancy

Life cycle graph for garlic mustard Seed RosetteAdult

Life cycle graph for garlic mustard Seed RosetteAdult Drayton and Primack 1999 Biological Invasions 920

Transition matrix for garlic mustard seedrosadult seed ros adult Now Next Year

N S (t+1) N A (t+1) N R (t+1) = N t+1 = A x N t Ten seeds are introduced to Fullersburg Woods in How many plants will be there in 2001? = (0.09*10) + (0*0) + (80*0) (0.01*10) + (0*0) + (920*0) (0*10) + (0.50*0) + (0*0) Pattern to multiply by: Each number in the column labeled “1” must be multiplied by the number beside the letter “A”. Each number in the column labeled “2” must be multiplied by the number beside the letter “B”. Repeat for column “3”. All rows must be added at the end.

The Results for 2001! It may look like the population is dying, but looks can be deceiving…let’s do it another year! N S (t+1) N R (t+1) N A (t+1).9 0.1

N S (t+1) N A (t+1) N R (t+1) = N t+1 = A x N t 2001 to = (0.09*.9) + (0*.1) + (80*0) (0.01*.9) + (0*.1) + (920*0) (0*.9) + (0.50*.1) + (0*0) Notice that the matrix is the same, but this is from our results from 2001!

The Results for 2002! Hmmm…look adults!...1 more year! N S (t+1) N R (t+1) N A (t+1)

N S (t+1) N A (t+1) N R (t+1) = N t+1 = A x N t 2002 to = (0.09*.081) + (0*.009) + (80*.05) (0.01*.081) + (0*.009) + (920*.05) (0*.081) + (0.50*.009) + (0*0) Notice that the matrix is the same, but this is from our results from 2002!

The Results for 2003! Ummm we have a problem here…. N S (t+1) N R (t+1) N A (t+1)

E+07 1E+09 1E Seed Rosette Adult Population Size (log scale) Time A BIG Problem…..

We see cycles between rosette and adult years in the field

How do we manage Garlic mustard? Seed RosetteAdult

Explore effects of management  Turning over the seed bank = reduce number of seeds present  Spray rosettes with herbicide = reduce rosettes (R) by some amount  Pull adults = Reduce adults (A) by some amount

Managing Only Rosettes Look at the end of the graph. Why does killing rosettes increase the total number? What information are we missing?

Managing Only Adults How much do we need to eliminate to make an impact?