Population Ecology

Population Def. a group of individuals of a __________ species living in the same area Characteristics of a popl’n 1)Size 2)Density 3)Dispersion 4)Age Structure Dynamic Population Pyramid US vs. Swaziland single

Measuring Density Mark and Recapture Method x How would you find the value of x? Set up a proportion = x 4x = 3 x = 4/3 Apply same strategy of proportion for mark and recapture method

Mark and Recapture 40 fish are marked, captured and released. In 2 nd capture, 45 fish are caught, 9 of which were marked (recaptured) What is the estimated number of individuals in the population? = N = # of recaptures in 2 nd catch Total in 2 nd catch # of captures Total Popl’n (N) 9N = 1800 N = 200

Demography Def. The study of factors that affect the growth and decline of populations. Factors that affect growth: Factors that affect decline: Birth and Immigration Death and Emmigration

Survivorship Curves Describe how mortality of individuals in a species vary over time; gives survival pattern of popl’ns Type I: most survive to middle age before mortality rates increase; few offspring (high care of young) Type II: constant death rate; likelihood of death is equal at all ages Type III: most individuals die while still young; few survive to reproductive age

Life Histories Characteristics that describe an organism’s survival and reproductive schedule 1.Big Bang Reproduction / Semelparity Ex. Salmon Spawning Lower rate of offspring survival Unpredictable env’ts 2.Repeated Reproduction / Interoparity Ex. Lizards, humans Higher rate of offspring survival More dependable env’ts w/ limited resources

Population Growth Models 2 Models 1)Exponential Growth Model 2) Logistical Growth Models

What population do you think this is?

Exponential Growth Model 1)Also called geometric growth or J- shaped growth. 2)1st growth phase is slow (lag phase) 3)2nd growth phase is rapid (the exponential phase)

So, what do you think is going to happen to the human population? We will probably reach our carrying capacity. Our growth rate will start to look like most organisms, which is the Logistic Growth Model Carrying Capacity (k) What letter does this curve kind of look like?

1)Often called the S-shaped growth curve 2)Growth slows or stops following exponential growth at the population’s carrying capacity 3)Populations stop increasing when: Birth rate < Death rate Emigration > Immigration 4)Carrying capacity can be raised or lowered. How? Ex. 1: Artificial fertilizers have raised k Ex. 2: Decreased habitat can lower k Logistical Growth Model

Deriving Equations to Growth Models We will now derive the mathematical equations for both models First let’s define some variables: N = Population size K = Carrying capacity T = time r = reproductive rate B = # of births D = # of deaths