Chapter 5 Populations

members of the same species that reside in the same area

Characteristics of populations 1. Geographic distribution: Where do they live? 2. Density: How many are found in a given unit of area? 3.Growth rate: How quickly do they grow? Daisy population

Factors affecting population growth? 1.Birth rate: number of offspring per time period 2.Death rate: number of deaths per time period 3.Migration rate movement in and out of populations in a period of time Immigration: in Emigration: out

Exponential growth Occurs when individuals in a population reproduce at a constant rate Only under ideal conditions

Activity Assume 2 flies (one male and one female) start reproducing. Assume constant rate reproduction. Assume each female lays 120 eggs (½ male ½ female). Calculate the total population at the end of 6 cycles. Graph your results. Create a curved fit.

Result? 1.2 flies offspring (60 females) 3.14, , ,840, ,110,400,000

Logistic growth Occurs when a population’s growth rate slows or stops, following a period of exponential (geometric) growth Carrying capacity: largest number that a given environment can support

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What can slow down exponential growth?

Limiting factors cause population growth to stop Density-dependent factors depend upon population size: –Competition –Predation –Parasitism –Disease

Competition Occurs when 2 species occupies the same niche & habitat What are some things they compete for?

Competition Using this 1990 census map of US population densities, what can one deduce at resource competition between the different parts of the country? How can competition explain population size in nonhuman species?

Predation Predator: one that consumes or exploits a particular species for self gain Prey: one that is consumed or exploited What would you expect to happen to prey populations if the predator numbers increased or if predator numbers decreased?

Figure 5-7 Wolf and Moose Populations on Isle Royale MooseWolves Describe the relationship between the wolf and moose populations shown in the graph.

Predator-Prey relationships

Parasitism and Disease Both deplete the host organism of vital minerals and nutrients to sustain life. Death of the organism results in the decline of population size. Heart worms (roundworms) as exposed by a veterinarian

Density-independent factors Limiting factors on population size, regardless of the number of individuals in the population –Weather –Natural disaster –Seasonal cycles –Human activities (habitat destruction) Corals that have died from weather changes, leading to increased water temperature and pollution.

Historical Human Population Growth Agriculture begins Plowing and irrigation Bubonic plague Industrial Revolution begins It took 500,000 years to reach 1 billion & less than 200 years to reach 5 billion. What might be some reasons why?

What’s the carrying capacity for the human population? What if it’s right here?  But, what if it’s right here?  (We do know it lowers when pollution occurs)

Age structure diagrams (population profiles): graphs showing numbers of people in different age groups in the population U.S. PopulationRwandan Population Males Females What conclusions can be drawn from these graphs?

Why do the population growth curves look different between developing and developed countries?

Demography Study of human population size, density and distribution, movement, and its birth and death rates Birth rate is the number of live births per 1000 population in a given year. Death rate is the number of deaths per 1000 population in a given year.

Calculating how fast populations grow Birthrate – Death rate = Population Growth Rate (PGR) If PGR > 0, then the population is growing. If PGR < 0, then the population is declining.

R/K Selection R-strategists the ability to reproduce quickly, small body size, early maturity onset, short generation time and short gestation period. Results in unstable or unpredictable environmentsreproducebody size K-strategists large body size, long life expectancy, and the production of fewer offspring that require extensive parental care until they mature, long gestation period. Results in stable or predictable environmentslife expectancy

Animal Gestation or incubation, in days (average) Longevity, in years (record exceptions) Ass36518–20 (63) Bear180– –30 (47) Cat52–69 (63)10–12 (26+) Chicken227–8 (14) Cow2809–12 (39) Deer197– –15 (26) Dog53–71 (63)10–12 (24) Duck21–35 1 (28)10 (15) Elephant510–730 1 (624)30–40 (71) Fox51–63 1 8–10 (14) Goat136–160 (151)12 (17) Groundhog31–324–9 Guinea pig58–75 (68)3 (6) Hamster, golden15–172 (8) Hippopotamus220–255 (240)30 (49+) Horse329–345 (336)20–25 (50+) Human253– (120) Kangaroo32–39 1 4–6 (23) Lion105–113 (108)10 (29) Monkey139– –15 1 (29) Mouse19–31 1 1–3 (4) Parakeet (Budgerigar)17–20 (18)8 (12+) Pig101–130 (115)10 (22) Pigeon11–1910–12 (39) Rabbit30–35 (31)6–8 (15) Rat213 (5) Sheep144–152 1 (151)12 (16) Squirrel448–9 (15) Whale365–547 1 n.a. Wolf60–6310–12 (16)