topic 2 Flashcards by Maya T

what is absolute density

• 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)

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what is relative density

• 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

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when to use absolute density?

• 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

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how to sample? types?

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

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describe quadrat sampling

○ 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

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what does quadrat sampling require?

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

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describe mark-recapture sampling

○ 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.

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how to calculate total pop size w mark recapture

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

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assumptions of cross recapture and why

○ 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

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how to calculate relative density

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)

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how to choose a sampling tehnique

depends on organism density, size, and mobility

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what determines pop abundance?

• Birth and immigrations, death and emigration

BIDE equation - balance of these four parameters

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BIDE equation variables

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

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how to convert absolute values to rates and vise versa?

• 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

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

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

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bide demographic model for rates?

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

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describe importance of immigration and emigration

• 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)

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what are life tables? questions they answer?

• 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?

how to make a life table (general)

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

describe cohort tables

• 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

describe static life tables

• 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

what leads to a stable age class distribution

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

how could cohort and static tables be identical

• 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

cohort table variables

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

life table 0 find nx ?

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

find lx on life table?

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

find gx on life table?

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

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

find dx on life table?

dx=nx-nx+1 | number dying at each cohort

find qx on life table | age specific mortality

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

steps to build a static life table?

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

what are survivor ship curves? what do they plot

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)

3 common survivorship curves? look at graph in notes

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)

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

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)

what is GRR - survivroship schedule

sum of bx column = gross reproductive rate | GRR = average # of offspring produced by an individual that survives through all reproductive ages classes

survivorship schedule - R0?

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

increasing vs declining pop based on R0?

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

what is reproductive value

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

significance of reproductive value irl?

• 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

Look at formula for Vx. what are the assumptions

• 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)

Vx calculation - find present progeny

bx = # of offpsring produced per individual at age x

Vx calculation - find future progeny

``` 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 ```

what is ltbt in the Vx equation

``` 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) ```

what does lx do for Vx equation

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