POPULATION GROWTH & MEASUREMENT AP Environmental Science Chapter 6 WHAT IS A POPULATION? POPULATION SIZE is A group of determined by: interbreeding individuals within a. #of births (based a geographical on fertility rates) location. b. # of deaths c. # of indiv that enter or leave the population Population Graphs measure status of populations J-curve or Exponential Growth Curve S-Curve or Logistics Curve POPULATION DENSITY DENSITY: number of individuals per unit area or volume Ex: Suppose there are 150 bullfrogs living in a pond that covers an area 3 square km. What is the population density? Population density Population Density = Number of Individuals (150 frogs) Unit Area (3 sq KM) = 50 bullfrogs per square kilometer! Populations Dynamics Population Modeling http://www.hippocampus.org/course_locato r?course=AP%20Biology%20II&lesson=63 &topic=1&width=600&height=454&topicTitl e=Population%20Ecology:%20Overview&s kinPath=http://www.hippocampus.org/hipp ocampus.skins/default CARRYING CAPACITY Max population that a habitat can support (Level line) D I S E A S E D I S A s T E R S = P R E D A T O R S F O O D Carrying Capacity Factors These limiting pressures keep a population in check such as carrying capacity: 1. # of Predators 2. Amount of Food & Water Resources Disease Natural Disasters Reproductive ability Other factors – H I P P O can decrease in population!! H=Habitat I= Invasive species P= Pollution P=Other interacting populations O=Overconsumption Exponential Increase (J-curve) In a J-curve, the popul keeps growing quickly (exponentially over time). What causes J-curve to occur? Conditions: 1. No enemies 2. No competition. 3. Plenty of food & water 4. Low % of disease J-curve is usually a temporary situation=Population crash. Exponential Growth Math Model Change in N Initial Population Change in time Rate of reproduction Time dN/dt = rN Time (dt) N (dN) Rate (r)* rxN Exponentially how does it look for a J-curve T1 2 10 10x2 = 20 2x10 T2 20 10 10x20=200 2x10x10 T3 200 10 10x200=2,000 2x10x10x10 T3 2000 10 10x2,000=20,000 2x10x10x10x10 T4 20,000 10 10x20,000=200,000 2x10x10x10x10x10 N=2 cockroaches (male and female) r= 2 cockroaches can produce 20 offspring in 3 months a. The rate of growth (r) 20/2 adults or 10 per 1 adult. b. The growth rate (r) equals 10 Figure 06_03 Exponential Growth can Crash When population can no longer sustain itself without food resources, pop decrease beneath the carrying capacity. Population Crash Isle Royale, Michigan National Park Moose pop quickly in 1991-1995. Wolf pop due to Parvovirus passed on from domesticated dogs visiting the National Park. Moose population Due to tick infestation. S-curve (Logistics curve) S-curve or Logistics Population 1. Population at equilibrium. 2. S-curve may change (increase & decrease) slightly, but is constant near the carrying capacity. 3. May be considered “restricted growth”. Factors that keep populations within carrying capacity Migration Logistics Curve Model dN = dt rN 1-N K dN = change of population over time dt N = Population K= Current Carrying Capacity r= rate of change or reproductive rate of a speciesd Logisitics/Carrying Capacity Connection If the carrying capacity (K) = 100 wolves If the N = 100 wolves (wolves bred successfully to increase population) Look at the 1-N/K part: 1 - 100 100 1- 1 = 0 dN/dt = rN(0)=0!!! Logistics & CC (continued) There is no change in dN/dt-no population growth! What if N=50? Plug it into 1-N/K to see how it affects the reproductive rate for a population. 1-50/100 = 1-1/2 = 1/2rN or half of the maximum reproductive rate for the wolves. Logistics & CC (continued) If N = 10…plug into 1-N/K (1- 10) = (1-.10) = .90 100 dN = rN(.90) or dN is at a rate of dt dt 90% as fast as the max possible reproductive rate for the wolves! Lincoln Peterson Population Estimate Model Estimating population size by random sampling an ecosystem. Focus on population density or animal abundance. Est Population Model: n1 = m2 OR N= n1 x n2 N n2 m2 n1=#animal marked & released 1st time n2=# animals captured during 2nd session m2-# animals captured during 2nd session & are marked. Population Measurement in Review J-curve •Exponential Curve S-curve •Logistics Curve •Carrying Capacity Population Equilibrium Equilibrium: the balance between births and deaths within a population Other Population Considerations Environmental Resistance Population Dispersal Reproductive Potential Environmental Resistance Factors/pressures that limit a population’s ability to increase (CC) Density Dependent Density Independent Parasites Temperature Disease Moisture, light, pH salinity Competitors Weather Predators Natural Disasters Human Intervention Lack of habitat/territory Population Dispersal Definition Different patterns of how a species or population will inhabit a certain geographical location. Population Dispersal is determined by: Population Dispersal Uniform Clumped Random POPULATION DISPERSAL A. RANDOM: 1. Least Common 2. Found anywhere in envir. 3. High mobility such as wind blown Ex: Dandelions POP DISPERSAL B. Uniform 1. Rare Occurrence but does occur in nature! (Hawks, wolves) 2. Can indicate human impact a. Plantations, orchards, etc. UNIFORM POPULATION DISP. Red-Tailed Hawk Orchards CLUMPED POP DISPERSAL C. CLUMPED: 1. Patchy, most common 2. Protection, avail of natural resources, to survive 3. Ex: Allelopathy, fish, plants, trees, etc. Clumped Dispersal – Purple Loosestrife Patterns in US Reproductive Potential …Is an organism’s ability to grow at the fastest rate. (To replenish the species—innate!) REPRODUCTIVE POTENTIAL COMPARISON 1. R-selected Hint: Rapid Repro 2. K-selected Hint: Longer Repro a. b. c. d. a. b. c. d. e. Early reproduction Short life span Hi mortality Little/no parental care e. Large # of offspring produced f. Inhabit lower trophic levels (1st order consumers) Late reproduction Long life span Low mortality High parental care Small # of offspring produced REPRODUCTION TYPES K-SELECTED TYPE R-SELECTED TYPES Reproductive potential – “R” Bacterium can produce 19 million descendants in a few days!! Mosquitoes live 10-14 days laying eggs every 3 days. Mosquito rafts have 200-300 eggs;. hatch in 48 hours Reproductive potential – “K” Some species have higher reproductive potential!! K-Potential Gestation Times: Human= 9 months Elephants= 22 months Oppossum = 12-13 days (marsupial) CRITICAL NUMBERS Survival & recovery of population depends on a minimum population base—its critical number. Factors Affecting Critical Number C1. IMMIGRATION: movement of indiv into an area C2. EMIGRATION: movement of individuals which leave an area. Plus Environmental Resistance Factors Critical Numbers If pop falls below critical number, breeding may fail and extinction could occur. Threatened: species whose pops are declining rapidly Endangered: near critical number and may become extinct.