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37 Cards in this Set
- Front
- Back
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What does population growth represent?
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It represents the difference between rates of birth and deat.
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What is r? Write out the equation to determine r.
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The intristic rate of population growth.
r= (b-d) dN/dt= rN |
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r= (b-d)
dN/dt = rN --> What does this equation represent? |
The model of exponential population growth.
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What is characteristic of populations inhabiting favorable environments at low population densities (colonization).
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Exponential growth
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Give an examples of exponential growth.(2)
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(1) St. Pauls Island, which is considered one of the Probilof's Islands in Alaska, orginally was introduced to a reindeer herd that consisted of 4 males and 22 females. From 1910- to 1940 on the chart, the growth rate of the deers continued to grow to about 2000 in 1940.
(2) Whooping Crane- This species in 1941 was near extinction and since then has recovered (considered endangered) from about 20 to 190 in 2000. These estimates were based on the count of adult birds over-wintering in the southern USA. |
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What do life tables provide?
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A schedule of age-specific mortality and survival.
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Define cohort.
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A group of individuals born in the same period of time.
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What variables make up a life table and briefly describe each one. (5)
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(1) x= years
(2) Nx= the number of individuals from the original cohorts that are alive at the specified age x. (3) Lx= probability at birth of surviving to any given age (4) Dx= the number of individuals that have died during a given time interval. A measure of age specific mortality. (substract years) (5) Qx= age-specific mortality rate. The rate at which individuals died in that age class. (d/n) |
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Different life tables reflect....?
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different approaches to defining cohorts and age structure
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What are the two kinds of life tables?
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Cohort or dynamic
Time specifc |
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What is a cohort or dynamic life table?
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a cohort of organisms is followed from birth until death
---> dynamic composite life: combined results of several distinct cohorts. |
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What is a time specific life table?
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A table that represents a population which is sampled at one point in time to obtain a distribution of age classes.
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This kind of table provides date for mortality and surviorship curves.
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Life Table
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What does a mortality curve plot?
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The mortality rates (Qx) against age
Examples: Gray squirrels- Mortality is high (~0.7) at birth and then drops around 2 years to ~0.4 and then from there mortality increases with age. Sedum Smalli(annual plant, Elf Orpine)- Shows 0 mortality in summer and then mortality increases as fall approaches and then decreases in the december and rises again slightly from there but its major (fast) increase in spring until June and then drops. |
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What does a survivorship curve plot?
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It plots the survivorship rate (lx) against age:
Examples: Gray Squirrel- decreases with age Sedum smallii (annual plant, Elf Ordine)- deceases a little from july to end of sept. then drops fast until end of december where the survivorship rate drops more slowly until there is about a ~0 survival rate in April. |
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What are the three categories that a survivorship can fall into?
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(1)- Type 1--> convex, typical of humans (goes out for a little steady and then drops towards older age)
(2) Type II--> (straight), typical of adult birds, rodents and reptiles; aslo many perennial plants (3) Type III--> (concave..scooplike) high mortality when young. typical of oysters, fish, many invertebrates and plants |
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What organism typically has a type I survivorship curve?
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Humans
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What organism(s) typically has a type II survivorship curve?
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adult birds
rodents reptitles many perennial plants |
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What organism(s) typically has a type III surviorship curve?
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oysters
fish many invertebrates many plants |
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How is birthrate expressed?
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births per 1000 individuals in the population per unit time. Crude birthrate.
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True/False:
Birthrate is age-specific |
True
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Age-specific Birth rate is defined as?
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It considers only the females of a given age, since only the females give birth and since birthrate does very with the age of the female.
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What is Gross reproductive rate?
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The number of female offspring born to a female over her lifetime.
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What two factors determine net reproductive rate?
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(1) Birthrate
(2) survivorship |
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Explain a Fecundity Table (fertility).
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Combine age-specific birthrates with survivorship to give mean number of females born in each age group, adjusted for survivorship.
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Net reproductive net (Ro) describes what?
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The number of female left during a lifetime by a newborn female. Provides a way to examine individual fitness and the population consequences of specific life history characteristics.
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What Ro(net reproductive rate) is greater than one, the population is:
a. increase b. decreasing (not replacing itself) |
Increasing
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What two factors can be used to project population growth?
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(1) age-specific mortality
(2) birthrates |
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What does a population projection table do?
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Allows the calculation of age distribution for each year and results in a stable age distribution by year 7.
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What is Lambda on a population projection table?
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finite multiplication rates. greater than 1 the population is growing.
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Example of the population projection table showed what pattern among the gray squirrels?
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The pattern that resulted was a geometric population growth by comparing the population growth over discrete time intervals. It was similar to the exponential growth model.
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Give a disadvantage of both the population projection table ( geometric population growth model of squirrels) and exponential growth model.
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Nature is not consistent, therefore both systematic and stochastic (random) processes an influence population dynamics.
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Name two ways random processes can influence population dynamics
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(1) Demographic Stochasticity: random variation in birth and death rates
(2) Environmental Stochasticity: variation in the environment (climate and natural disasters) can influence birth and death rates. |
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Give an example of extinction via exceeding resources
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Reindeer introduced onto St. Paul's Island in Alaska. it produced a classic J shaped curve which is typical of population crashes
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Give an example of a smaller population being more suceptible to extinction.
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American Ginseng:
Population size decreased and and then the fruit production decreased due to less visits by pollinators with the smaller population. " Allee Effect after W.C. Allee." |
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What is the Allee Effect after W.C. Allee
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Small population associated with less reproduction
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Name two other factors besides decline in reproductive rate that lead to extinction in smaller population.
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(1) Genetic Drift- Some alleles become fixed in population so alternative alleles are lost.
(2)- Inbreeding: Increased homozygosity and resulting expression of rare recessive and deleterious alleles. |
