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Understanding Population Estimation Methods in Amphibians and Reptiles

This document covers vital concepts from Chapter 9 on Population Distribution and Abundance, focusing on estimation methods for amphibians like frogs, salamanders, and reptiles. Key topics include mark-recapture techniques, evaluation of mobile and cryptic populations, and methods for calculating population density. Emphasis is placed on understanding variables affecting estimates, and practical examples such as using tagged largemouth bass to demonstrate the mark-recapture method are provided. Additionally, critical information about Missouri's lizards and salamanders is highlighted.

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Understanding Population Estimation Methods in Amphibians and Reptiles

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  1. Monday 2/24 • Pop Quiz #6 • Review Prickly Pear math questions • See Salamanders and Lizards – Quiz M 3/3 • Chapter 9 – L-P population estimates • Due today: all of Prickly Pear Case Study • Exam postmortem due Wednesday!!

  2. Class Amphibia • Order Anura – frogs and toads • Order Caudata – salamanders and newts • Order Apoda – caecilians Class Reptilia • Order Testudines - turtles, terrapins, and tortoises • Order Squamata - lizards and snakes • Order Crocodilia - crocodiles and alligators

  3. Missouri Lizards and Salamanders All images are from Wikimedia Commons, unless otherwise identified

  4. Common mudpuppyNecturusmaculosus

  5. HellbenderCryptobranchusalleganiensis

  6. Ringed salamanderAmbystomaannulatum

  7. Tiger salamanderAmbystomatigrinum

  8. Spotted SalamanderAmbystomamaculatum

  9. Eastern newt, red-spotted newtNotophthalmusviridescens

  10. Broad-headed skinkPlestiodonlaticeps

  11. American five-lined skinkPlestiodonfasciatus

  12. Little brown skinkScincellalateralis

  13. Prairie lizard, eastern fence lizardSceloporusundulatus

  14. Not on quizAxolotlAmbystomamexicanum

  15. Chapter 9 – Population Distribution and Abundance • What are some methods of counting populations?

  16. Chapter 9 – Population Distribution and Abundance • What are some methods of counting populations? • What if the individuals are mobile? • Hidden/“cryptic”? • What if we only have a sample?

  17. Required variables • N = n1n2/m2 • N = estimated population size • n1 = number of individuals marked in first sample. • n2 = number of individuals marked in second sample. • m2 = number of individuals captured in second sample, that were marked in the first.

  18. This method only works IF: • Probability of survival is equal • Births and deaths are insignificant between release and recapture • Immigration and emigration are nonexistent or insignificant • Marked individuals re-mix randomly • The mark makes it no easier or more difficult to recapture • Marks are permanent

  19. Practice A biologist nets 45 largemouth bass from a farm pond, tags their fins, and releases them unharmed. A week later, she nets 58 bass from the pond, including 26 tagged. Based on the L-I index, estimate the size of the population.

  20. Mark-Recapture • m2 / n1 = probability that an animal will be captured. • So, how large is the population? • n2 is really the portion of N that we expect to capture. • This is N*p = n2 where p is m2/n1.

  21. Population Density • So, N*p = n2 • N = n2 / p • N = n2 / (m2 / n1) = n1n2 / m2 • But, this is only part of the problem. We also need some estimate of area since Density, D = N / A.

  22. Population Density • Imagine we study rodents using a trapping grid w/ 15m trap spacing. • We trap the animals over a series of nights, always noting the identity and location of each animal. • Then, we can estimate how far each individual moved between captures.

  23. Population Density • Now, if an organism can travel from one station to the next, we can assume that it could travel half the distance to the next station as well. • Thus, the ‘effective area’ of our sample is the area of our grid, plus a border region around the grid, with a width of half the distance between stations.

  24. Population Density

  25. Area? • What is the area of the grid? • Ag = W2 • How about the 4 rectangles? • Ab= 4 * W * (0.5 * D) • How about the 4 corners? • This is essentially the area of a circle. • Ac = (0.5D)2

  26. Population Density • Finally, density can be estimated as

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