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General Ecology > Life tables > Flashcards

Life tables Flashcards

1
Q

populations have a spacial structure which includes:

A
  1. their range
  2. spatial arrangement of individuals within and among the range
    - density
    - patterns of movement among individuals
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2
Q

Populations also have genetic variation
among individuals throughout the population
… or represented in

A

subpopulations

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3
Q

Another component of populations is

associated with age structure

A

and the
rates at which births and deaths occur
within a population

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4
Q

who invented life tables and why

A

the Insurance and Health Care Industry to monitor mortality and survivorship in human populations

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5
Q

When was the first life table developed

A

in 1921 by Pearl and Parker

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6
Q

In order to construct a life table in the first place,

one must have some knowledge of the

A

age structure within a population

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7
Q

the first column of the life table is

A

x

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8
Q

x usually represents

A

age (could be in days, weeks, years, hours, etc.)

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9
Q

individuals that make up x are referred to as a

A

cohort

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10
Q

two inherent weaknesses in life tables

A
  1. only age is considered when allocating individuals to classes (not size, social status, and genotype)
  2. life tables almost always include only females for species having distinct males and females. This is because one of the key parameters in a life table is the rate of production
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11
Q

the male’s contribution to sexual reproduction

A

difficult to measure in terms of the numbers of young produced

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12
Q

how is birth accounted for in life tables

A

by counting the number of female offspring produced per breeding season or age interval per female in the population (fecundity)

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13
Q

Life tables

A

tables that contain class-specific survival and fecundity data

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14
Q

x

A

age class

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15
Q

nx

A

the number of individuals in each age class immediately after the population has produced offspring

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16
Q

sx

A

the survival rate from one age class to the next age class

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17
Q

bx

A

the fecundity of each age class

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18
Q

what is the fecundity of each age class denoted by

A

bx (b for birth)

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19
Q

what does the column bx indicate

A

new offspring cannot reproduce, but 1-year-olds can each produce one offspring, 2-year-olds can each produce three offspring, and 3-year-olds can each produce two offspring

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20
Q

Number surviving to next age class

A

(nx) x (sx)

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21
Q

Number of new offspring produced

A

(nx) x (sx) x (bx)

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22
Q

if we do these calculations for every age class…

A

we can find the number of individuals that we will have after one time interval

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23
Q

the number of individuals in a population after one time interval divided by the initial number of individuals provides…

A

lambda

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24
Q

A POPULATION WITH A FIXED LIFE TABLE
ASSUMES A STABLE AGE DISTRIBUTION AND
GROWS

A

at a constant rate

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25
Q

When age-specific birth bx and survival, sx, rates remain
unchanged for a sufficient length of time, a population
will assume

A

a stable age distribution

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26
Q 
Under such conditions, each age class in the population 
grows or declines at the same rate; and so, therefore, 
does the
A

total size of the population

27
Q

lambda

A

the growth rate of the population

28
Q 
Under stable age distribution conditions, each 
age class grows at the
A

same rate from year to year

29
Q

Stable age distribution

A

when the age structure of a population doesn’t change over time

30
Q

when does a stable age distribution occur

A

when survival and fecundity of each age class stays constant over time

31
Q

survivorship

A

the probability of surviving from birth to any later age class (lx); survivorship in the first age class is always set at 1

32
Q

survivorship to the second year (l2) is calculated as

A

l1s1

33
Q

net reproductive rate (R0)

A

the total number of female offspring that we expect an average female to produce over the course of her life

34
Q

R0 =

A

Sigmalxbx

35
Q 
lx is the number at the beginning of
a particular age class divided by
A

the number at the beginning of the cohort

36
Q

Generation time (T)

A

the average time between the birth of an individual and the birth of its offspring

37
Q

T =

A

Sigma X x X lx X bx / Sigma X lx X bx

38
Q

When λ or r is estimated from a life table, it is assumed that the life table has

A

a stable age distribution

39
Q

Age distributions fluctuate due to environmental conditions, so any approximation of λ or r is restricted to

A

the environmental conditions that the population experiences at the time of measurement

40
Q

To calculate an approximate (denoted as a) λ

λa =

A

R0^(1/T)

41
Q

to calculate an approximate r

A

ra = logeR0 / T

42
Q

populations grow when

A

R0 > 1

43
Q

populations decline when

A

R0 < 1

44
Q

Net reproductive rate (R0)

A

the total number of
female offspring that we expect an average female to
produce over the course of her life

45
Q

Generation time (T)

A

the average time between the birth

of an individual and the birth of its offspring.

46
Q

We can provide close approximations, denoted as λa and ra (where the letter “a”
indicates an approximation), based on our estimates of net reproductive rate (R0 )
and generation time (T):

A

λa = R0^(1/T)

47
Q

Kinds of Life Tables

A
  1. cohort/dynamic life tables

2. static/time-specific life table

48
Q

Cohort life table

A

a life table that follows a group of individuals born at the same time from birth to the death of the last individual

49
Q

Cohort life tables are readily applied to

A

sessile organisms that can be tracked over the course of their life

50
Q

Environmental changes can affect survival and fecundity of a cohort

A

it is difficult to separate the effects of age and the environment

51
Q

Rosemary and Peter Grant

A

1978 marked 210 cactus finch fledglings and followed them for 15 years

52
Q

The cohort life table does not work well for

A

species that
are highly mobile or for species with very long life spans,
such as trees

53
Q

One of the problems in using a cohort life

table is that

A

a change in the environment during one year
can affect survival and fecundity of the cohort that year.
This makes it difficult to disentangle the effects of age from
the effects of changing environmental conditions

54
Q

Static life table

A

a life table that quantifies the survival and fecundity of all individuals in a population during a single time interval

55
Q

age is not confounded with

A

time

56
Q

Static life tables can be applied to

A

highly mobile organisms, and species with long life spans

57
Q

Life tables may not be representative of years with different environmental conditions

A

tables for multiple years should be constructed

58
Q

A life table may also be constructed from the

distribution of the ages at death in a population

A

For example, one could obtain the age of death for
each person in a local cemetery by examining the
headstones. Using the total number of occupants of
the cemetery, we could determine the number of
individuals surviving at the beginning of each age
interval, and from that, survivorship

59
Q

Some biases though (life table)

A

For example, it assumes that an
equal number of newborns forms the basis for each
age class. This assumption is violated in expanding
and declining populations in which younger and older
age classes, respectively, are over-represented.

60
Q

Sea turtle populations have declined by more than

A

99% over the past several centuries

61
Q

Once life tables were created, population modelers realized that

A

few hatchlings survive in nature anyway, so protecting eggs would not benefit the population

62
Q

Instead, life tables indicated that

A

improving the survivorship of adult turtles would grow the population

63
Q

what has been proven to be a tremendous success in conserving the sea turtles

A

turtle excluder devices on fish trawling nets

General Ecology (16 decks)

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