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Mark Recapture lecture 1

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1 Mark Recapture lecture 1
An example from Sockeye salmon….

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5 Mark recapture lectures
Petersen method Schnabel method Schumacher-Eschmeyer Jolly Seber Closed population Open population Overview of methods to help your reading of Krebs Chp 2

6 Closed populations No individuals enter or leave the population between surveys Survey 1 Survey 2

7 Individuals enter or leave the population between surveys
Open populations Individuals enter or leave the population between surveys Survey 1 Survey 2

8 What makes a population closed?
Dispersal barriers Philopatry Large surveyed area Slow reproductive/death rate Short time between surveys

9 What type of population are snow geese?

10 Snow Goose La Pérouse Bay

11 Recording which birds are marked, and marking new birds

12 LPB Colony size Year

13 Petersen method: Closed population
Survey 1: Survey 2: Catch several animals Catch C animals Count recaptures (R) Mark all M animals Return animals to population Return animals to population

14 Survey 2: C = 15 R = 4 Survey 1: M = 12

15 What is the total population size (N)?
Note that the proportion marked in the population equals the proportion marked in the 2nd sample M = R N C N = M C R M = 12 C = 15 R = 4

16 What is the total population size (N)?
Note that the proportion marked in the population equals the proportion marked in the 2nd sample N = 13 * 16 5 -1 N = (M+1) (C+1) (R+1) -1 M = 12 C = 15 R = 4

17 When would Petersen give you a bad estimate?
Population not closed Marked animals likely to be re-trapped Marked animals likely to die Marks fall off

18 Schnabel method: closed population
Survey 1 Survey 2 Survey 3 Survey 4 Survey 5 Essentially, Petersen estimates on multiple surveys

19 Schnabel method: closed population
Catch Ct animals Survey t: Mark Ut unmarked animals Return animals to population Record Rt recaptures

20 Schnabel method: closed population
Survey t: Catch Ct animals What’s the relationship between Ct, Rt, and Ut ? Record Rt recaptures Mark Ut unmarked animals Ct = Rt + Ut Return animals to population

21 Schnabel method: example
Time (t) Ct Rt Ut 1 20 2 5 3 13 4 10 How many individuals marked by beginning of time 5?

22 Schnabel method: example
Time (t) Ct Rt Ut 1 20 2 5 15 3 7 13 4 10 How many individuals marked by beginning of time 5?

23 Schnabel method: example
Time (t) Ct Rt Ut 1 20 2 5 15 3 7 13 4 10 Σ = 58

24 Schnabel method: example
Time (t) Ct Rt Ut 1 20 2 5 15 3 7 13 4 10 In general: Mt = U1 + U2..Ut-1 Σ = 58

25 Schnabel formulas: N = Σ (Ct Mt) Σ Rt N = Σ (Ct Mt) Σ Rt+1
Marked > 10% of population N = Σ (Ct Mt) Σ Rt+1 Marked < 10% of population ( just weighted average of Petersen estimates!)

26 Schnabel method: example
Time (t) Ct Rt Ut Mt CtMt 1 20 2 5 15 3 7 13 35 4 10 48

27 Schnabel method: example
Time (t) Ct Rt Ut Mt CtMt 1 20 2 5 15 400 3 7 13 35 700 4 10 960 48 Σ = 22 Σ = 2060

28 Schnabel method: example
Time (t) Ct Rt Ut Mt CtMt 1 20 2 5 15 400 3 7 13 35 700 4 10 960 N = Σ (Ct Mt) = 2060 = 94 Σ Rt 48 Σ = 22 Σ = 2060

29 Schnabel method: example
Time (t) Ct Rt Ut Mt CtMt 1 20 2 5 15 400 3 7 13 35 700 4 10 960 What proportion of total population marked by end? 48 Σ = 22 Σ = 2060

30 Scumacher-Eschmeyer method (for Schnabel experiment)
N = C M R R = 1 * M C N y = mx + b

31 Scumacher-Eschmeyer method (for Schnabel experiment)
N = C M R R = 1 * M C N R C Slope = ? M


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