topic 2

Question 1

what is absolute density

Answer 1

• Number of individuals per unit area or volume
• Can be a total count of the entire population
Can be estimated by sampling and extrapolating (must still conduct total counts within some defined area)

Question 2

what is relative density

Answer 2

• Indirect measure of population size
• Use variable with relatively constant, but unknown relationship to population size
e.g. scat frequency, no. of individuals in timed count

Question 3

when to use absolute density?

Answer 3

• Often impractical (especially for small or mobile organisms)
• May be possible for larger and/or immobile organisms
Ex. northern fur seal breeding colonies - larger, dont move too far

Question 4

how to sample? types?

Answer 4

• Count a small proportion of population and extrapolate to estimate total population size or density
  
  • Two types: quadrat sampling and mark-recapture sampling

Question 5

describe quadrat sampling

Answer 5

○ Count the number of individuals in several quadrats of known size and extrapolate the average across the total area
ex. 11 individuals in 12m2 = 92 indviduals/100m2

Question 6

what does quadrat sampling require?

Answer 6

§ Accurate counts within each quadrant
§ Didn’t miss any individuals
§ Known quadrat area
Quadrats must be representative of whole area (random sampling)

Question 7

describe mark-recapture sampling

Answer 7

○ Important for mobile animals
○ Capture - mark individuals - release - recapture
Various models
two sampling periods: 1.capture then mark all individuals (record #)
2. recapture, assuming second sample will contain same % of marked animals as the whole pop.

Question 8

how to calculate total pop size w mark recapture

Answer 8

marked animals in 2nd sample/ total caught in 2nd = marked animals in 1st/total pop size
cross multiply

Question 9

assumptions of cross recapture and why

Answer 9

○ Closed population (no immigration or emigration)
○ No recruitment/births of new animals in sampling period
○ Marked and unmarked indiviuduals are captured randomly
§ Small mammals might become trap happy or trap shy
§ Trap happy = underestimation of pop sized
§ Trap shy: over estimation of pop size
○ Marked animals are neither lost or overlooked
§ May be stressed and have higher mortality
§ Some fishermen keep tags as good luck charms
Tags can fall off

Question 10

how to calculate relative density

Answer 10

traps (#caught per day)
no of fecal pellets/ area (ex. hares, mice, deer, rabbits)
vocalization frew. (frogs, birds, calls per 30 mins ex)
pelt records (trappers)

Question 11

how to choose a sampling tehnique

Answer 11

depends on organism density, size, and mobility

Question 12

what determines pop abundance?

Answer 12

• Birth and immigrations, death and emigration

BIDE equation - balance of these four parameters

Question 13

BIDE equation variables

Answer 13

• births (b or B)
  -immigration (i or I): movement of individuals into area
  -mortality: d or D
  -emigration: e or E
  uppercase = absolute #, lowercase = per capita rate

Question 14

how to convert absolute values to rates and vise versa?

Answer 14

• Convert absolute values to rates and vice versa?
○ Convert to rate by dividing by number of individuals
○ Convert to absolute by multiplying by number of individuals

Question 15

look at bide demopgraphic model infographic thing. what is the open pop. formula

Answer 15

Nt+1= Nt+ B+ I - D- E
• Nt+1 = number of individuals at a given time
• Nt = number of individuals at a previous time

Question 16

bide demographic model for rates?

Answer 16

bNt = # of individuals added to the population via births (find it by multiplying b by N)
Nt+1=Nt+(b-d)Nt (closed)

Question 17

describe importance of immigration and emigration

Answer 17

• Important to maintain gene flow, prevent inbreeding
• Sets limits to geographic distribution
• Basis of metapopulation (source/sink) dynamics
• Rarely accounted for in population studies
• Assumed to be equal (immigration = emigration) or absent
(closed population)

Question 18

what are life tables? questions they answer?

Answer 18

• Populations are composed of different types of individuals with different vital rates
• Life tables: technique to summarize the mortality and reproduction schedules of a populations
• Originally developed by insurance
At what age are organisms most vulnerable? Most important for future survival and reproduction?

Question 19

how to make a life table (general)

Answer 19

Classify - determine appropriate age intervals or stage intervals (ex. Insect life cycle)

Question 20

describe cohort tables

Answer 20

• Identify individuals born at same time (cohort)
• Follow over time, recording deaths (& sometimes births)
• Easy to interpret
• Difficult (or impossible) to collect these data in nature
Assumes cohort represents population

Question 21

describe static life tables

Answer 21

• Stationary; time-specific; cross section of population at a given time
• Can use age at death data
• Record age at death of large number of individuals (requires accurate estimate of age at death), ex. Trees, sheep (horns), coral (growth rings)
• Can use age distribution data (assumes differences between age classes is due to mortality)
Assumes population is stationary (b & d constant), which would lead to a stable age class distribution over time

Question 22

what leads to a stable age class distribution

Answer 22

all pops with a constant schedule of b and d rates will approach a fixed/stable age distribution, no matter initial distribution - constant b and d rates lead to it

Question 23

how could cohort and static tables be identical

Answer 23

• Would be identical if: 
	• Cohort used represents population 
	• Environment is constant 
	• Population is at equilibrium (constant b & d, stable 
	age-class distribution) 
— Almost never true; can vary widely

Question 24

cohort table variables

Answer 24

x = age.chorot 
nx= # alive at age x = survivorship schedule 
lx = proportion of orgs. surviving from start of life table to age X = standardized survivorship 
dx= number of individuals dying during age interval x to x+1 
qx= per capital mortality rate during interval x to x+1 = age-specific mortality rate

Question 25

life table 0 find nx ?

Answer 25

# of individuals surviving at each age class/survivorship schedule
n0 can only stay the same or decline in subsequent age classes

Question 26

find lx on life table?

Answer 26

l0 is always 1, l(last age class) is always 0

Question 27

find gx on life table?

Answer 27

probability that an individual who has already survived to a certain age (x) will survive to the next age class (x+1)
gx=1-qx
gx=nx+1/nx
gx= lx+1/lx

Question 28

look at graph for n0, nx, and nx+1 under subscripts in notes

Answer 28

ok

Question 29

find dx on life table?

Answer 29

dx=nx-nx+1

number dying at each cohort

Question 30

find qx on life table

age specific mortality

Answer 30

qx=1-gx
qx=(nx-nx+1)/nx
qx= dx/nx

Question 31

steps to build a static life table?

Answer 31

1. determine # that die in each age class (dx)
2. use (1) to determine # alive at beginning of age class (nx) - do nx=nx-1-dx-1
3. use nx to find lx
4. calculate qx and gx

Question 32

what are survivor ship curves? what do they plot

Answer 32

common pop. demographic technique
plot (log) survivorship (nx or lx) on y axis vs age on x axis
if using nx data, n0 is standardized (100 or 1000)

Question 33

3 common survivorship curves? look at graph in notes

Answer 33

type I: low mortality for most of lifespan; higher loss of older orgs.
type II: constant per capita mortality rate (independent of age)
type III: high mortality rates early in life, followed by lower and relatively constant mortality of older age classes (high adult survivorship)

Question 34

what do we need to determine how likely a pop id to change in abundance over time?

Answer 34

Life tables give us lots of information about age-specific
survival/mortality
• To determine how a population is likely to change in
abundance over time, we also need:
Age-specific schedule of births (bx)

Question 35

what is GRR - survivroship schedule

Answer 35

sum of bx column = gross reproductive rate

GRR = average # of offspring produced by an individual that survives through all reproductive ages classes

Question 36

survivorship schedule - R0?

Answer 36

net reproductive/replacement rate
sum of per capita birth rates adjusted for mortality
average # of offspring per individual in their life time

Question 37

increasing vs declining pop based on R0?

Answer 37

R bigger than 1 = increasing
R less than 1 = declining
R=1 = unchanged

Question 38

what is reproductive value

Answer 38

contribution that an individual of a certain age makes to future pop
Vx = present progeny + expected progeny

Question 39

significance of reproductive value irl?

Answer 39

• Conservation, wildlife and fisheries management, forestry, etc
• Tells us:
○ Which age classes contribute most to present and future population growth
○ Which age classes to focus on protectiong
○ For which age classes should we allow harvesting
• Pest management
○ Efficacy of the control agent will depend on the reproductive value of the targeted stage
○ e.g. if a biocontrol agent targets prey with low reproductive value (old individuals) it may not be effective as a biocontrol agent
• Implications for natural selection and evolution
○ Natural selection acts more strongly on age classes with higher Vx (bigger contribution to future population growth)
• Helps us understand the evolution of life history traits

Question 40

Look at formula for Vx. what are the assumptions

Answer 40

• Assume population is stable in size
• In a growing population: present offspring will be worth more than future progeny (in terms of proportionate contribution to future pop growth)
Declining population: future progeny are worth more than present offspring (in terms of proportionate contribution to future pop. Growth)

Question 41

Vx calculation - find present progeny

Answer 41

bx = # of offpsring produced per individual at age x

Question 42

Vx calculation - find future progeny

Answer 42

it is the Residual reproductive value - avg. # progeny produced for rest of individuals lifetime 
sum of (lt*bt)/lx for age classes x+1 to last age class (w) after current age class

Question 43

what is ltbt in the Vx equation

Answer 43

bt = # offspring produced per individual 
in each age class for ages (x + I) to w 
(last age class) 
Adjusted for mortality occurring in age 
classes (x+1) to w (multiplied by It)

Question 44

what does lx do for Vx equation

Answer 44

adjust for mortality occuring in age class x 
denominator will always be the same for a given vx calc