1. Population Ecology

2. Learning Outcome Define population and its parameter
Describe the approaches to estimate population density
Distinguish between potential and realized of natality and mortality
Distinguish between population distribution pattern
Explain the demographic technique

3. Population as a Unit of Study
A group of organisms of the same species occupying a particular space at a particular time
Deme
Groups of interbreeding organisms, the smallest collective unit of a plant or animal population
Individual that have possible chances to mate with each other
Deme- share a distinct gene pool.

4. Population as a Unit of Study
Population has group and not individual characteristics
Basic characteristics of a population:
Density (no/area; no/vol)
Size (numbers) of the defined area
Age structure (based on age distribution) of the population group
Dispersion (the spread of individuals in relation to one another)

5. Four basic population parameters emigration mortality natality DENSITY
immigration

6. Immigration and Emigration = Migration
Density: no of organisms per unit area or
per unit volume
Natality: the reproductive output of a population
(birth, reproduction)
Mortality: the death of organisms in a population
Immigration: the no of organisms moving into
area occupied by the population
Emigration: the no of organisms moving out of
the area occupied by the population
Immigration and Emigration = Migration

7. Population parameters
Population parameters affect population density

8. How to estimate population density?
Techniques differ between organisms such that the technique to estimate deer cannot be applied to plant sp. or barnacles or vice versa.
There are 2 fundamental attributes that affect and ecologists choice of technique for population estimation.

9. 2 attributes affecting the choices of estimation technique
1) Mobility
- based on movements of the organisms
Animal- mobile
Plant- sessile
2 attributes affecting the choices
of estimation technique
2) Size
- small animals/plants are usually more abundant
than large animals/plants
- Elephant vs ant population

10. Why do we need to estimate population density?
Estimates of population are made for two reasons:
To quantify nature
2. Allows for comparisons between different populations in terms of space and time measure

11. 2 approaches to estimate pop density
1) Absolute density
No of individual per area/ volume
Important for conservation and management
2 approaches to estimate pop density
Absolute data- total count method
As for relative density, comparison done not by using total count method but we used other parameter to estimate the population density
2) Relative density
Comparative no of organisms
Which area has more organism
e.g, between area x and y
Area x has more organism than area y

12. Absolute density Total counts Sampling methods a) Quadrat
b) Capture-recapture method

13. Absolute density- Total count
Total counts - direct counting of populations.
e.g:
human pop census,
trees in a given area,
breeding colonies can be photographed then later counted
in general, total counts are possible for few animals eg. cat, butterfly, grasshoppers, bugs.

14. Absolute density- sampling method
Sampling methods
to count only a small proportion of the population - sample
Using the sample to estimate the total population
2 general sampling techniques:
a) Quadrat
b) Capture-recapture method

15. Absolute density- sampling method (quadrat)
a) Quadrat
Definition – An ecological sampling unit consisting of a small
square area of ground within which all species of interest are
noted or measurements taken.
2. Method- Count all individuals on several quadrats of known size,
then extrapolate the average count to the whole area by using
diversity index or relative density formula.
3. Requirements:
area of the quadrat must be known
the pop in the quadrat must be determined exactly
iii) quadrat/s must be representative of the area
- achieved by random sampling
Quadrat may be placed over a larger area to form an overall view when a total survey impracticable or it can be used to sample along a transect.

16. What is random sampling?
Absolute density- sampling method (quadrat)
What is random sampling?
Done many times at different points within the habitat to give a large number of different samples.
Toss coin/or small objects into the square or draw lots
Usually carried out when the area under study is fairly uniform, very large, and/or there is limited time available.
The quadrate frame is placed on the ground (or on whatever is being investigated) and the animals and/or plants inside it counted, measured, or collected.

17. b) Capture recapture method
Absolute density- sampling method (capture-recapture)
b) Capture recapture method
Capture, marking, release, and recapture- important for mobile animals
Why?-it allows not only an estimate of density but
also estimates of birth rate
and death rate for the population being studied
Peterson method
Involves 2 sampling periods:
Time 1- Capture, mark and release
Time 2- Capture and check for marked animals
Time intervals between the 2 samples must be short because this method
assumes a closed population with no recruitment of new individuals into the
population between time 1 and 2 and no losses of marked individuals

18. Absolute density- sampling method (capture-recapture)
What is the formula?
Marked animals in 2nd sample = Marked animals in 1st sample
Total caught in 2nd sample Total population size

19. e.g of capture-recapture method
Absolute density- sampling method (capture-recapture)
e.g of capture-recapture method
Dahl marked trout in small Norwegian lakes to estimate the size of the population that was subject to fishing.
He captured, marked and released 109 trout, and in 2nd sample a few days later caught 177 trout, of which 57 were marked.
From the data, what is the estimate population size?

20. e.g of capture recapture method
Absolute density- sampling method (capture-recapture)
e.g of capture recapture method
By using the formula:
Marked animals in 2nd sample = Marked animals in 1st sample
Total caught in 2nd sample Total population size =
Total pop size
Total pop size = (109 x 177) 57
= 338 trout

21. Some index used in relative density:
Traps – no caught per day per trap – animals caught will depend on their density, activity and range of movement, skill in placing traps – rough idea of abundance – night flying insects, pitfall traps for beetles, suction traps for aerial insects
Fecal pellets – rabbits, deer, field mice – provides an index of pop size
Vocalization frequency – bird calls per 10 mins, can be used for frogs, cicadas, crickets
Pelt records – trapper records dates back 300 years – of lynx

22. Questionnaires – to sportsmen (eg fish) and trappers
Relative density
Catch per unit effort – index of fish abundance – no of fish per cast net or no of fish per 1 hour trawling
Questionnaires – to sportsmen (eg fish) and trappers
Cover - % ground surface covered – in botany, invertebrate studies of the rocky intertidal zone
Feeding capacity – bait taken – for rats and mice – index of density
Roadside counts – birds observed while driving standard distances

23. Natality
The production of new individuals by birth, hatching, germination or fission
2 aspects of reproduction must be distinguished:
i) Fecundity- Potential
ii) Fertility- Realized

24. Natality- Fecundity vs Fertility
Fecundity -physiological concept that refers to an organism’s potential reproductive capacity
ii) Fertility -ecological concept based on the no of viable offspring produced during a period time

25. Natality
E.g.: the potential fecundity rate for humans is 1 birth per 10 to 11 months per female in the childbearing ages
realized fertility rate for a human pop may be only 1 birth per 15 years per female in the child-bearing ages

26. Mortality
Biologists-interested not only in why organisms die but also why they die at a given age
Longevity-the length or duration of life
2 types:
i) Potential longevity
ii) Realized longevity

27. Mortality- Potential longevity
i) Potential longevity
The maximum life span of an individual of a particular sp is a limit set by the physiology of the organism, such that it simply dies of old age
However, organisms rarely live under optimum conditions-most die from disease, or eaten by predators or succumb to a number of natural hazards
Can be measured only in labs or zoos
Can be measured in lab/zoo because they were protected from any circumstances that can minimize their longevity

28. Mortality- Realized longevity
ii) Realized longevity
The actual life span of an organism
Shorten from the potential longevity
Can be measured in the field/nature
In nature, many circumstances can minimizes their life span e.g. competition, predation, disease and parasitism.

29. examples
European robin has an average life expectation of 1 year in the wild, whereas it can live at least 11 years in captivity
1 yr in the wild= realized longevity
11 yrs in captivity= potential longevity

30. Population dispersion patterns
random
3 types
clumped
uniform

31. Population dispersion pattern

32. Example: plant population
Population dispersion pattern- random, uniform
Random-when the position of each individuals in a pop is independent of the others
Example: plant population
b) Uniform-it results as a form of some negative interactions
Common among animal pop where individuals defend an area for their own exclusive use (territoriality)
Example: penguin, lion population
If we compare between those three, in uniform dispersion type, the organisms location were far from each other.
Random and clumped- the organism were located closer to each other

33. c) Clumped-where individuals occur in groups
Population dispersion pattern- clumped
c) Clumped-where individuals occur in groups
Example: herd of cow, school of fish
Reason- suitable habitat or resources may be distributed as patches on a larger landscape

34. DEMOGRAPHIC TECHNIQUES
Patterns of survival

35. Patterns of Survival Three main methods of estimation:
1) Cohort life table
Identify individuals born at same time and keep records from birth.
2) Static life table
Record age at death of individuals.
3) Age distribution
Calculate difference in proportion of individuals in each age class.
Assumes differences from mortality.

36. Cohort Life tables
It is based on a single year class or cohort (e.g., all animals hatched or born in 2000).
We keep track of those individuals and recount them yearly, keeping records on them from birth to death
The cohort life table approach is generally not feasible for very longlived species
Most reliable way to identify a large number of individu that are born at the same time

37. e.g of cohort life table for the song sparrow
Age in years (x)
Observed no of birds alive
Proportion surviving at start of age interval x
No dying within age interval x to x+1
Rate of mortality
0 (2000)
115
115/115= 1.0
115-25= 90
90/115= 0.78
78%
1 (2001) 25
25/115= 0.217
25-19= 6
6/25= 0.24
24%
2 (2002) 19
19/115= 0.165
19-12= 7
7/19= 0.37
37%
3 (2003) 12
12/115= 0.104
12-2= 10
10/12= 0.83
83%
4 (2004) 2
2/115= 0.017
2-1= 1
1/2= 0.50
50%
5 (2005) 1
1/115= 0.009
1-0= 1
1/1= 1.0
100%
6 (2006)
0/115= 0.0 -
Colored the same figure

38. Static (Vertical) Life Table Based on Living Individuals
Record the age at death of a large number of individuals
The individuals in this sample were born at different times

39. The age of which individuals die
Tagging the newborn, recovering the tag after death and record the age at death
Estimation method:
i) Mountain sheep- can be aged by counting the growth rings on their horns
ii) carapaces of turtle
iii) trunks of trees

40. Age Distribution
Age distribution of a population reflects its history of survival, reproduction, and growth potential.
Miller published data on age distribution of white oak (Quercus alba).
Age distribution biased towards young trees.
Sufficient reproduction for replacement.
Stable population

41. Age Distribution

44. Population Age Pyramids

45. Survivorship curve summarizes the pattern of survival in a population

46. e.g: Humans and large mammals, dall sheep, annual plant, rotifer
Type 1- high survival in early and middle life, followed a rapid decline in survivorship in later life
e.g: Humans and large mammals, dall sheep, annual plant, rotifer
Type 2- constant mortality rate is experienced regardless of age
e.g: birds, squirrels, turtle, white-crowned sparrow, song bird
An annual plant is a plant that usually germinates, flowers, and dies in a year or season.
Perennial plant can lived for more than two years
Type 3- Greater mortality rate at early in life, followed by a period of much lower
and relatively constant loss
e.g: Fishes, invertebrates, parasites, perennial plant