Population counting method line transect, point count, mark and recapture

Population Counting Method Line transect, Point count, Mark and recapture

1. Population Counting Method: Line transect, P oint count, Mark and recapture Submitted by: Tarique Bin Aziz BSc. (Honors) in Zoology MSc. In Wildlife and Biodiversity Conservation Jagannath University

2. Line transect Line transect is a tape or string laid along the ground in a straight line between two poles as a guide to a sampling method used to measure the distribution of organisms. E cologists use this method to investigate any community. This method surveys a small section of a natural area. Line transects can be walked, driven, swum or flown . Estimating abundance of a relatively large and conspicuous species, it is one of the best method.

3. Line transect cont. Assumptions No animals are missed Transect is a straight line Every detection is independent Points/objects are fixed at initial sightings and they do not move before being detected

4. Line transect cont. Advantages More economical Greater species turnover Larger area is covered in relatively shorter time Applicable throughout the year Permanent transects can be monitored for a longer period of time Can be used in most of the habitat types (except wetlands) With little care can also be used for hilly terrain Disadvantages       Distances are not correctly measured Movement of observer may disturb the animals Chances of missing rare or shy species are great

5. Line transect cont. Method: The essential feature of line transects is that one walks along a straight path and records the individuals seen and their perpendicular distance from the transect line. Line transects are best used for visible animals in open habitats. The sample size should be at least 40 sightings, and better results are obtained from 60–80 sightings. N ot all individuals need to be seen for this method to work.

6. Line transect cont. Plate No. 1: Method of Line transect

7. Line transect cont. An illustration of the basic measurements that can be taken for each individual sighted along a line transect in the direction indicated by the arrow. The key measurement is the perpendicular distance (x i ). If the sighting distance ( r i ) is easier to record in the field, the sighting angle (θ) must also be measured. The perpendicular distance x = r sinθ

8. Line transect cont . Strip transect Method: Strip transect method is a customize method of line transect method Plate No.2: Strip transect Method

9. Point count The simplest method of counting birds is called a "point count", in which a trained observer records all the birds seen and heard from a point count station for a set period of time. A series of point counts completed over a fixed route can then be compared to the results of the same point counts in other seasons or years. Point Counts can be imagined as transects of zero length conducted at zero speed. Types of Point Count: 1 . Plot Counts (fixed radii for all species) 2 . Point Counts with variable radii, by species 3 . Point Counts with unlimited radii (Total Counts)

10. Point count cont. Assumptions B irds do not approach the observer or flee. A ll the birds are detected at the point of the observer . B irds do not move much during the count period B irds behave independently of one another. D istance estimates are accurate B irds are fully and correctly identified.

11. Point count cont . Advantages L ess time consuming D uration can be controlled T otal attention to detect birds S mall homogenous habitats can also be studied   Disadvantages G enerating bird list is slower M any species are missed A rea sampled in one unit is small  

12. Point count cont. Methods Points to be counted are to be laid out systematically or selected randomly in the study area. Points should ideally be 200 meters apart to avoid double counting . In a small area, lesser points should be monitored to avoid duplication In small patches of habitat, inclusion of points near the edges should be done with caution depending on the objectives of the study. 

13. Point count cont . Count duration: It can vary from 2-20 minutes   Record only these birds seen during Count duration. Do not include for analysis those birds seen while walking between two points . How far Point counts should be done ? Not very far (> 200 m) Not very close (<20 m) Ideally 50 to 100 m apart

14. Point count cont . At what time it should be done ? 15-20 minutes after sunrise Evening counts can be done How to record distance ? Record bird’s distance from the observer (yourself) Record distance in categories (0-25m, 25-50m and >50m)

15. Point count cont . Plate No.3: Point count Method

16. Mark and recapture Mark and recapture is a method commonly used in ecology to estimate an animal population's size. A portion of the population is captured, marked, and released. Later, another portion is captured and the number of marked individuals within the sample is counted. Estimating Population Size = Number marked in first sample X Total caught in second sample Number marked in second sample

17. Mark and recapture cont. Assumptions Individuals with marks have the same probability of survival as other members of the population . Births and deaths do not occur between the time of release and the time of recapture. No immigration nor emigration between the time of release and the time of recapture. Marked individuals mix randomly with the population at large. Marked animals are neither easier, nor harder, to capture a second time. Marks do not come off of the marked organisms. Recapture rates are high enough to support an accurate estimate.

18. Mark and recapture cont. Advantages good method for detecting shy, skulking animals very rich source of information confirmed identification photographic evidence available very good learning process Disadvantages labour intensive exercise problems of permissions costly and time consuming ringing training and license required not good for short rapid surveys animals become net shy

19. Mark and recapture cont. This method can be expressed symbolically as follows- n1 = the number of animals first marked and released n2 = the size of the second sample m2 = the number of marked animals in that sample N = the total population size Then we expect that , m2/n2 = n1/N It is obvious that, since n1, n2, and m2 are known, N can be estimated. All mark–recapture methods rest on this basic idea, though most entail animals being caught and marked on several occasions.

20. Mark and recapture cont. No individuals enter or leave the population between surveys Survey 1 Survey 2 Population parameter estimation: Closed populations:

21. Mark and recapture cont. What makes a population closed ? Dispersal barriers Philopatry Large surveyed area Slow reproductive/death rate Short time between surveys Closed populations can estimate through these method- Petersen method Schnabel method Schumacher-Eschmeyer

22. Mark and recapture cont. Open populations: Individuals enter or leave the population between surveys. Open populations can estimate through Jolly Seber method. Survey 1 Survey 2

23. Mark and recapture cont. Variance and standard deviation Variance (and standard deviation) are measures of how spread out a set of results is. This is known as distribution (it is not how spread out the bees are in the environment ). Variance and mean: The Variance (σ 2 ) is calculated as the average squared deviation of each number from its mean. The formula (in summation notation) for the Variance in a population is-  

24. Mark and recapture cont. Here, Ʃ (summation) = sum of all values in range of series X = each value in the range μ = mean N = number of scores For example, for the numbers 1, 2, and 3, the mean is 2 and the Variance is : Standard Deviation: The Standard Deviation is the square root of the Variance .  

25. Conclusion Those are the population counting methods. So, which we can estimate abundance and density of population in an area.

26. Thank You….