Lecture 8: Population Structure, Distribution, Exponential Growth Flashcards
Describe population
A group of potentially interbreeding individuals of the same species that occupies a particular place at a particular time
Individuals in a population use common resources, cope with similar environmental factors, and interact with one another and with their environment
How do population size and structure vary?
Through time and space as a result of
BIRTHS
DEATHS and
MIGRATION
What 5 characteristics are populations associated with?
- distribution
- abundance
- structure
- dispersion
- dynamics
Describe distribution
the geographic range that a population inhabits
Describe abundance
population size or number of individuals in a population
- closely related to density (part of population structure)
Describe structure
The structure of the population can be classified by
- density (# individuals/unit area)
- sex ratio
- age class (ex. sexually immature individuals vs. sexually mature individuals)
Describe dispersion
the pattern of spacing or smaller habitat patches between individuals within the geographic range
Describe dynamics
Changes in population size and structure over time (ex. number of individuals, density, age structure, etc.)
Give some examples of factors that affect the distribution of populations
abiotic factors such as:
- physical/geographic barriers (ocean, mountains, etc.)
- latitude change alters temperature and precipitation (as you move away from the equator)
- moving east to west = the precipitation gradient from east to west (ppt. will decrease from coast to inland)
Define fundamental niche
the range of physical/chemical conditions over which a population of particular species COULD persist
Define realized niche
the observed range of conditions over which a species ACTUALLY does persist
What sorts of factors constrain populations to their realized niche?
climatic factors such as precipitation and temperature
But also interactions with other organisms that have the same or similar fundamental niche
- such as competition, predation, etc.
Describe ecological niche modelling
the process of determining the suitable habitat conditions for a species
How does it help ecologists?
Helps ecologists make predictions
- to determine where to reintroduce endangered species
- where an invasive species may spread once introduced
- about how species distribution will change in response to climate change
What are the steps involved in ecological niche modelling?
- mapping locations where species has been recorded in literature (ie., find actual populations)
- collect range of meteorological (precipitation and temperature) that is favourable to the species
- create ecological envelope
- map favourable conditions onto geographic space
- predict for the thing of interest (ex. invasive species distribution)
- check if the prediction is accurate by doing field work
Describe ecological envelope
the range of conditions
Describe ecological envelope
the range of conditions that is predicted to be suitable based on the current distribution that was mapped out in the first step of ecological modelling
Define density
a component of population structure:
the number of individuals per unit area
How do ecologists estimate population size when the populations are relatively small?
all individuals in the population can be counted
ex. the goats on Saturna Island
How do ecologists estimate population size when the populations are relatively large?
size can be often estimated using sampling techniques
used often when there is high density or very small organisms
Define sampling
counting a portion of a population to estimate the total number of individuals present
When do ecologists use quadrat sampling?
used to estimate population size or density for sessile or slow moving organism
- ex. plants
How do ecologists estimate population size when the populations are relatively large?
size can be often estimated using sampling techniques
used often when there is high density or very small organisms
What is a quadrat?
sampling area of any size or shape
What is a quadrat?
sampling area of any size or shape
What is the formula for estimating population size? What do each of the variables mean?
N = A(n/a)
N: population size
A: whole area of population
n: average # individuals per quadrat
a: quadrat area
What is the formula for estimating population size from quadrat sample? What do each of the variables mean?
N = A(n/a)
N: population size
A: whole area of population
n: average # individuals per quadrat
a: quadrat area
T or F: Dispersion affects the reliability of our population estimates? Explain
True
Because there might be varying patterns of dispersions of individuals within the sampling area which will effect the data
What are the 3 patterns of dispersion?
random
uniform
clumped
How do ecologists estimate population size when the populations consist of fast moving organisms or organisms that hide?
Population indices
What are population indices? Give some examples
evidence of occurrence in an area
ex. counting number of nests, number of dens, counting fecal matter left behind, counting tracks
Used as a method of estimating population size when organisms are fast moving or hard to find
Describe mark-recapture and give an example
A method of estimating population sizes of motile organisms
ex. estimating the number of seed bugs in lodgepole pine orchards
What are the steps of mark-recapture?
- Capture random sample of individuals
- mark captured individuals
- release marked individuals and allow time to mix back into population
- capture 2nd random sample after some time has passed
- count number of marked and unmarked individuals within the second sample
What is the formula for estimating population size using the mark recapture method? What do each of the variables mean?
M/N = R/C
N = CM/R
M: # marked individuals in first sample
R: # marked individuals recaptured in 2nd sample
C: total # individuals captured in second sample
N: estimated population size
What is the formula for estimating population size using the mark recapture method? What do each of the variables mean?
M/N = R/C
N = CM/R
M: # marked individuals in first sample
R: # marked individuals recaptured in 2nd sample
C: total # individuals captured in second sample
N: estimated population size
What are the assumptions of the mark-recapture method?
- marked and unmarked individuals have the same probability of being captured
- this is dependent on how the experiment is designed
- ex. if you use traps baited with food it will affect the likelihood of recapture and can cause trap-seeking or trap-avoidance behaviour - marked organisms mix completely back into the population before 2nd sampling event
- this also depends on experimental design
- ex. if you have a slow moving organism, you will have to wait longer vs. if you have quick moving organisms, you will have to wait less time so they don’t leave the area completely - no individuals are born, die, immigrate or emigrate before second sampling
- need to know lifespan and when to do experiment
What factor needs to be considered when marking organisms in mark-recapture?
Some markers can be harmful/toxic to organisms so experiments need to be done to make sure of this
certain colours or using bright colour tags/marks can make organisms more vulnerable to predation
need to consider whether the marks will cause undue harm to the individuals in the experiment
How are density and body size related?
negatively correlated
As body mass increases, an individual will require more resources and therefore less individuals can exist per unit area
as body mass increases, the number of individuals per unit area decreases
Describe dispersal
the movement of individuals or gametes away from their original population
How can dispersal be monitored?
using radio collars, tags, permanent tags (ex. leg/wing bands on birds)
T or F: density can vary locally within population boundaries?
True because there are different dispersion patterns
What does dispersion tell ecologists?
with information regarding social interactions and environmental associations
Describe clumped dispersion patterns
Individuals are aggregated in patches
this is the most common pattern in nature
Which pattern of dispersion is the most common in nature?
clumped
Give examples of clumped dispersion patterns
Prides of lions with 1-2 males and 5-6 females and offspring will cluster together and avoid other prides due to territoriality
mechanism of predator avoidance, fish swim in schools for protection in numbers
plants and fungi aggregate in areas with suitable abiotic conditions which may not be distributed evenly
Describe uniform dispersion patterns
individuals evenly spaced
common in desert plants with severe competition for abiotic conditions
less common in nature
Give examples of when uniform dispersion patterns occur
When there is not enough water to support another plant individual any closer
nesting birds, like king penguins, will disperse within pecking distance of each other
Describe random dispersion patterns
Unpredictable spacing
Which is the most uncommon pattern of dispersion in nature?
rare
Give an example of random dispersion pattern
will happen for plants with wind dispersed seeds if there isn’t a lot of variation in the habitat
ex. dandelion seeds
What are the 4 parameters that influence population growth?
- natality
- mortality
- immigration
- emigration
What two parameters that influence population growth are not considered when measuring? Why?
immigration and emigration because we assume they usually balance each other out because they are incredibly difficult to measure
What is the formula for modelling population growth? What do the variables represent?
B: # births
D: # deaths
N: population size (# of individuals)
What determines the population size in modelling population growth?
- gains to the population through births
2. losses to the population through deaths
If births are higher than deaths, what happens to N?
N population size increases
If births are lower than deaths, what happens to N?
N population size decreases
If births are equal to deaths, what happens to N?
N population size does not change
What is the formula for modelling the change in population growth? What do the variables represent?
change in population size during a fixed time interval = birth during time interval - deaths during time interval
dN/dt = rN dN/dt = b-d
