2Chapter 26 begins with the Mystery of Easter Island Chapter 26 begins with the Mystery of Easter Island. At one time, Easter Island was forested, and supported a large population of humans who carved huge stone statues. Today the island has no forests, is sparsely populated, and the people have no memory of the culture that created the statues. What possible connections are there between the disappearance of the forests and the disappearance of the statue-carving culture?WORKTGEH
3Why study populations?In the field, populations tend to be the unit of study. A population is a natural grouping, so studying populations reflects what is going on in nature.Even so – it’s not always easy to define a population!
4Population ScienceStudying growth rates of populations helps us understand:the effects of rapid overpopulation.how population growth is regulated.We can derive important lessons for humans from studies of populations in nature.
5General PrinciplesA population consists of members of the same species living in the same ecosystem at the same time.Total population increases or decreases according to the number of births, deaths, immigration, and emigration that occurs.
6DistributionIndividuals distribute themselves in a population in three general patterns:ClumpedUniformRandom
7DistributionClumped distribution is typical of organisms that move in groups (herds, flocks, etc.), or that cluster around resources, such as plants near a water source.
8DistributionUniform distribution is typical where resources are scarce. Individuals compete to claim enough territory to support them and keep a distance from others.
9DistributionRandom distribution is rare. Organisms may distribute randomly if resources are abundant and the organisms do not form social groups. Trees in a diverse forest may distribute randomly.
10They live in social groups. Male marine iguanas are highly territorial. They also compete for females. Male iguanas tend to be distributed uniformly throughout their territory. Why?They live in social groups.Each male has its own distinct breeding territory.The iguana’s resources are localized.
11Which pattern of distribution do human populations tend to show? ClumpedUniformRandom
12Growth RateTo determine the actual change in numbers of a population in a given unit of time, we look at the difference between losses (deaths and emigration) and additions (births and immigration)(births - deaths) + (immigrants - emigrants) = change in population size.
13What is the change in a population over a ten-year period if in that time there are 9,000 births, 2,000 deaths, 800 immigrants, and 400 emigrants?1220660070007400
14Falklands Conservation Growth RateIf we want to know the rate (r) at which a population is increasing, we need to know:Birth rate (b) = number of births in a population during a certain time period.Example: 150 births in a gull population of 1000 = 150/1000 = 0.15 per year.Falklands Conservation
15Falklands Conservation Growth RateWe also need to know:Death rate (d) = number of deaths in the same time period.Example: 50 deaths in a gull population of 1000 = 50/1000 = per year.Falklands Conservation
16Growth Rate Growth rate (r) = birth rate – death rate r = b – d Ex: 0.15 – 0.05 = 0.1 (10% per year)minus=percent increase
17Growth RateIf we want to know the actual number of individuals by which the population increased, we use this formula:G = r x NG = 0.1 x 1000 = an increase of 100 individuals per year.
18Try this:You are studying a population of 30 ferns. This year you saw six new fern plants become established, and 3 fern plants died. Calculate the growth rate of the population.Remember: r = b – d G = r x NWORKTGEH
19What is the annual growth rate of a population of 10,000 sea turtles if there are 500 deaths and 1,500 births per year?5%10%15%20%
20Choice A: $1,000,000 on your birthday. Suppose your eccentric uncle says that for your birthday, he will give you your choice between two presents:Choice A: $1,000,000 on your birthday.Choice B: A penny on your birthday, two pennies the next day, four the next, and so on for 30 days.Which would you take? Why?WORKTGEH
21What happened? Why did Choice B give you so much more money? Choice A yields $ 1,000,000Choice B yields $10,737, (Why? See: pennies.html)What happened? Why did Choice B give you so much more money?What does this have to do with population growth?WORKTGEH
22What happens to r and G when b gets big and d gets little? Exponential GrowthBiotic potential = Maximum growth possible. This assumes a maximized birth and minimized death rate Calculated as: r = b - d G = r x NWhat happens to r and G when b gets big and d gets little?
23Exponential growth produces a J-shaped population graph.
24Age of first reproduction affects the rate of population growth. Why? Exponential GrowthAge of first reproduction affects the rate of population growth. Why?
25Death rates and average lifespan also affects growth rate. Why? Exponential GrowthDeath rates and average lifespan also affects growth rate. Why?
26Under what conditions can exponential growth occur in nature? You’ve probably guessed that exponential growth can’t go on forever. What factors limit population growth?WORKTGEH
27Environmental resistance Population LimitsTwo opposing forces act on population growth.Environmental resistanceBiotic potential
28Environmental Resistance Species introduced to a new environment may experience exponential growth.Environmental resistance will eventually limit growth.Some populations experience “boom and bust” cycles.Others stabilize and show logistic growth.
29Population Limits K = Carrying Capacity: # births = # deaths The upper limit for population growth is determined by the carrying capacity of the environment.
30Available space limits barnacle populations. Population LimitsAvailable space limits barnacle populations.Where there are many natural controls, populations tend to demonstrate logistic growth.
31Population LimitsIf a population overshoots the carrying capacity of the environment, the result is a population crash.
32Population LimitsWhere there are few natural controls, a population may rise rapidly, exceed carrying capacity, then crash as most of the population starves.
33Which population is most likely to experience exponential growth? Algae introduced into a small pond in North Dakota.A migrating herd of pronghorn antelope in Eastern Oregon.Chinook salmon in the Columbia River.
34Cyanobacteria population boom How can this be represented graphically? In July growth conditions for cyanobacteria become favorablepopulation boomThe population grows rapidlyBy early September the nutrient supply has been depleted and competition for what is left is fierce. Most cyanobacteria can’t get enough and die.How can this be represented graphically?
35How can the cyanobacteria example be represented graphically? _numbertime
36What caused the cyanobacteria to crash was environmental resistance that was: Dependent on the density of the population.Independent of the density of the population.
37This graph shows human population over the last 14,000 years This graph shows human population over the last 14,000 years. What kind of curve is this? What implications does this have for humans?WORKTGEH2012*2006DateBillionsTime to addeach billion(years)199918041All of humanhistory198719272123196033319751974414billions of people19875131999612bubonic plague196020127*131930*projected1830Technical andcultural advancesAgricultural advancesIndustrial andmedicaladvances
38A growing population may become self-limiting. Population LimitsA growing population may become self-limiting.In fruit flies, reproduction rate drops in response to crowded conditions.lifespanoffspring per daydayspopulation density
39Seasonal weather changes Population LimitsDensity-independent factors limit populations regardless of how large or small the population is. Usually abiotic.Examples:Seasonal weather changesNatural disastersPollution
40Population LimitsDensity-dependent factors affect a population more strongly the larger it grows. Usually biotic.Examples:PredationParasitesDiseaseResource competition
41Which of these is a density-dependent factor? Harsh, cold winters with lots of snow and ice.A sudden tornado.An outbreak of cholera in a refugee camp.A violent earthquake.
42Density-dependent factor Density-independent factor A population of Bluebirds is displaced when a new housing development destroys the meadow where they nested. They move to another meadow where other nine male bluebirds live. The males compete intensely for nesting sites. At the end of the season, there are still only nine successful males. Competition for nesting sites is a:Density-dependent factorDensity-independent factor
43Density-dependent factor. Density-independent factor. A squirrel population is isolated on the Capitol grounds in Salem. Heavy traffic on all sides makes it hard for squirrels to leave the grounds. Squirrel fatalities happen as squirrels try to cross the streets. Is traffic a density-dependent or density-independent factor for these squirrels?Density-dependent factor.Density-independent factor.
44For each of these scenarios, list both density-independent and density- dependent factors that could be involved.During a drought, a thick stand of young pine trees is attacked by pine bark beetles.A large herd of deer is caught by a winter storm that buries much of their food supply. Several of the deer, suffering from parasites as well as lack of food, are caught and killed by wolves.WORKTGEH
45SurvivorshipPopulations show different patterns in survival at different ages, which in turn can affect population growth.Early loss – many young dieConstant loss – equal loss at all agesLate loss – high survivor of young, most deaths in old age
46Survivorship curves very for different species, depending on their reproductive strategy.
47(a) Developed countries 20062025205075 and oldermalefemalepostreproductive (45–79 yr)agereproductive (15–44 yr)0 - 14prereproductive (0–14 yr)millions of people(b) Developing countries75 and oldermalefemaleage0 - 14millions of peopleDifferent survivorship curves can have different consequences for populations, even of the same species.
48Birth rates do slow down as nations become more industrialized Birth rates do slow down as nations become more industrialized. However, the world population is not evenly developed, and in developed nations, resource consumption per capita is high.
49Based on what you have learned in Chapter 26, how can you explain the disappearance of the ancient, statue- carving culture on Easter Island?WORKTGEH
50Deer and WolvesUsing the worksheets provided, calculate the population change in the deer population for each year.Population changes = births – deathsIn this case, deaths are due to both starvation and predation.
51Deer population change YearWolvesDeerDeer offspringPredationStarvationDeer population change1997102,0008004001003001998122,3009204802402001999162,5001,000640500-1402000222,360944880180-1162001282,2249961,12026-1502002242,0948369602-1262003211,968788840-522004181,916766720462005191,9527807602020061,97279030
54braconid wasp (predator) How does this graph relate to your deer/wolf graph?bean weevils (prey)braconid wasp (predator)A high predatorpopulationreduces the preyThe prey populationpeaks when thepredator populationis low
56On the back of your graph: Describe what happened to deer and wolf populations between 1997 and 2006.What might have happened if wolves had NOT been introduced to the island?Some people think it was cruel to introduce wolves. Some think it would have been cruel NOT to. Is there another management plan that would have been as good or better?
57RecapPopulation size changes through birth, death, immigration, and emigration.Population size is regulated by environmental restraints that increase deaths or decrease births.Populations are distributed in various patterns for social reasons or because of resource availability.