Chapter 52 Flashcards
Population
group of individuals in the same species that live in the same area at the same time
Population ecology
the study of how and why the # of individuals in a population changes over time
Number of individuals in a population
Four processes
Birth (growth)
Death (loss)
Emigration (leaving)
Immigration (entering/growth)
demography
The study and analysis of
Birthrates
Death rates
Emigration rates
Immigration rates
Or the study of factors that determine the size and structure of the population over time
If a population is mostly young individuals with a high survival and reproductive rate then
The population will increase
If the population is older and has a low reproductive rate and survival rate then
The population will decrease
Life tables
Summarizes the probability that an individual will reproduce in the given time interval in its timeline
fercundity
The number of female offspring produced by each female in the population
Males rarely affect population dynamics
There are almost always enough males to fertilize females
Survivorship
Proportion of offspring that survive on average to a particular age
Cohort
a group of individuals of the same age that can be followed through time
calculate survivorship
number of survivors versus age is calculated on a graph
forms a survivor ship curve
Three forms of the survivorship curve
humans - type 1
song birds- type 2
plants - type 3
survivorship
Type 1
survivorship is high throughout life, most hit the max life
survivorship
Type 2
individuals have the same probability of dying off every year ( songbirds)
survivorship
Type 3
extremely high death rates in juveniles or seedlings (plants)
Age specific fecundity
the average number of offspring produced in the age class X
Age class
group of individuals of a specific age
Given fecundity and survivorship
growth rate of population can be calculated
life table can show growth rate
If no immigration or emigration
Remember that life tables focus on females
Lx
symbol for survivorship
X
symbol for age class
Nx =
number of females in age class
No=
number of females existed as offspring
Growth rate
Lx=Nx/No
survivorship = number of females in age class divided by the number of females existed as offspring
Age specific fecundity is Mx =
(Total number of female offspring produced by females of particular age)/(the total number of females of that age class present)
LxMx=
the average number of female offspring produced by females in each stage of life
Net reproductive rate
Sum all of the LxMx values for a life span
The growth rate of a population per generation
If Ro is > 1 there is growth
Ro<1 there is a decline
Generation
the average time between the mother’s first child and the daughter’s first child
Females can’t seem to be able to have high fecundity and survivorship
Why?
Time and energy are restricted
Vicariance
more or less reproduction in each species
mechanical
Life history
Based on resource allocation
Or based on increases in fitness by natural selection
Exp egg size versus number changes according to optimization within the habitat
Life history continuum
Every animal or species can be placed on it
Growth rate=
change in the number of individuals in a population per unit time (∆N/ ∆ t)
Population growth
If there is no immigration or emigration occurring then a population’s growth rate is equal to the number of individuals in the population (N) times the difference between the birth rate (b)and death rate (d) per individual
difference in birth and death rate per capita (r )
If the per capita birth rate is less than the per capita death rate then r is negative
If the per capita birth rate is greater then r is positive
r can vary through time
N(b-d)
Per capita
for each individual
Intrinsic rate of increase
When the deaths are as low as possible and the births are as high as possible
rmax
growth rate
rmaxN = ∆ N/ ∆ t
r can be less than or equal too rmax
Exponential growth
For this the number of individuals is not influential
Density independent
Remember even if r is constant N is always changing
Only observed in nature if
It is a few individuals in a new population in a new habitat
Recovering population
Not possible indefinitely
Exponential growth limits
Eventually the habitat gets filled
When population density gets high then r will decrease
Birth rates will decrease and deaths will increase
This means that the r becomes density dependant
Logistic growth
To determine what happens when density becomes influential
K = carrying capacity or the max number of individuals that can be supported in a habitat for a sustained period of time
Depends on food, water, space, soil quality, resting/nesting sites
K can change from year to year
If the population size N is below K then the population will continue to grow
The equation for growth with a carrying capacity
∆N/∆ t = rmaxN(K-N/K)
(K/N/K) the proportion of unused resources and space
If N is small and (K-N/K) is close to 1 then the growth rate should be high
As N gets larger (K-N/N) gets smaller
When N is at Carrying capacity meaning K=N then (K-N/K)=0 and growth stops
So as N gets closer to k growth slows
The equation describes Logistic population growth or changes in growth rates that occur as a function of population size
To determine what happens when density becomes influential
K = carrying capacity or the max number of individuals that can be supported in a habitat for a sustained period of time
Depends on food, water, space, soil quality, resting/nesting sites
K can change from year to year
equation for growth with a carrying capacity
∆N/ ∆ t = rmaxN(K-N/K)
(K/N/K) the proportion of unused resources and space
If the population size N is below K then the population will continue to grow
If N is small and (K-N/K) is close to 1
then the growth rate should be high
As N gets larger
(K-N/N) gets smaller
When N is at Carrying capacity meaning K=N
then (K-N/K)=0 and growth stops
So as N gets closer to k
growth slows
Point where most of population reproduce
rmax
Competition
Exponential- looks like red but keeps going up
Logistic – growth that’s not exponential
R can be negative
Carrying capacity
max that can be hit to sustain continuously for a long time
Initially growth
is exponential meaning r is constant
N increases to the point
where competition or other density dependent factors kick in
When the population is at K
the growth is 0
Density independent
alter birth and death irrespective of the number of individuals
Changes to the abiotic(not living) environment
Density dependent factors
change in intensity as a function of population size
Usually biotic in nature
Population dynamics
how populations change over time
When studying populations
you have to understand that the population is going to reside in isolated patches within the range
metapopulations
A population of populations
Exp: butterflies in a large valley
Habitat fragmentation has lead to an increase in this
Used plant locations to study potential habitats
the subpopulations are going to die out eventually
Migration leads to repopulation of the potential areas
Assume: the percentage of marked and recaptured individuals in population studies
is equal to the percentage of marked in a population
need no bias in catching methods
Mark and recapture
(m2/n2)=(m1/N)
m2= number of marked animals in the second sample
n2= total number of animals in the second sample
N = total population
m1= marked individuals in the first sample
Population cycling
Helps determine interspecies factors
Note that there are more hares than lynx
Is the cycle food (the hare’s grasses) or predation (the lynx’s hares)
Age structure
the proportion of individuals at each stage in life also has a dramatic effect on the population growth
