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snail Presentation



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  • 1.
  • 2. INTRODUCTIONRegression Analysis of Fresh-water Gastropods Distribution Along the San Marcos River
    Existing State of Knowledge
    Most invasion gastropods were introduced by humans in aquarium trade
    Snails are an intermediate host for liver fluke parasite which is fatal to small native fish
  • 3. Snails of the San Marcos River
    • 12 different species of snails (Diaz and Alexander)
    • 4. For our study’s focus:
    • 5. Melanoidestuberculata
    • 6. Tarebiagranifera
    • 7. HydrobiidaeAmnicolalimosa
    • 8. Marisa cornuarietis
  • Melanoidestuberculata
    • Were first called “Philippine Horn of Plenty” ion 1937
    • 9. From southern Asia
  • Tarebiagranifera
    • Makes up 60% if bottom-dwelling invertebrates of the river
    • 10. Displaces native snails
    • 11. Also from southern Asia
  • HydrodiidaeAmnicola
    • Spire has four whorls
    • 12. Aperture is dextral
    • 13. Pathenogenic: females produce eggs without involvement of males
  • Marisa cornuarietis
    (giant ram-horn)
    • From South America
    • 14. About 1 inch in diameter
  • Snail Anatomy
    • The shell:
    • 15. Grows by secreting shell material at the edge of the mantle
    • 16. Opening of the shell is called the aperture
  • 17. Snail Anatomy
    • Movement:
    • 18. The foot is the muscle that projects from the shell
    • 19. Slime track of mucous
    • 20. Not known if movement is dependent on waves of muscular contractions
    • 21. “hunching” used foot to pull shell forward
  • Snail Anatomy
    • Feeding and Digestion
    • 22. Vegetarian: eating chiefly off lawns of living algae, dead plant material and some dead animal matter
    • 23. Greater activity and food intake at higher temperatures
  • Predators/Parasites
    • Greatest enemy are the fish: suckers, perch
    • 24. Some ducks
    • 25. Invertebrates
    • 26. Leeches
    • 27. Ostracods
    • 28. Intermediate host for parasite: Centrocestusformosanus
    • 29. Fatal to fountain darter
    • 30. Originates in Asia
  • 31.
    • Broader Ecology Context
    • 32. Invasive species drive out native species
    • Research Questions
    How do snails feed? breed? respire? move?
    Do these aspects determine where the snail resides in the river, and to how much effect?
    What significant do the invasive species pose on the native species of the ecosystem?
    There will be no difference in snail abundances among
    different flow regimes, substrate type/size, and/or depth.
  • 33. Materials and Methods
    San Marcos River at the falls of Spring Lake near Salt Grass
    3 separate days in March
    From 11am-4pm
  • 34.
    • How
    • 42. Technique
    • 43. Measure average depth
    • 44. Measure surface flow
    • 45. Photograph plot for snail count
  • 46.
    • Statistical Design
    • 47. Regression analysis:  analyzing several variables, with a focus on the relationship between the dependent (number of snails and an independent variable (depth, current, substrate size) 
    Fig. 1. Regression analysis, number of snails present as a function of water depth
  • 48. Fig. 2. Regression analysis, number of snails present as a function of water current
  • 49. Fig. 3. Regression analysis, number of snails present as a function of substrate size
  • 50. Fig. 4. Regression analysis of all three variables compared.
  • 51. Fig. 4. Number of snails present in areas with and without vegetation. Note, only 14 of the 35 sites had vegetation.
    There will be no difference in snail abundances among different flow regimes, substrate type/size, and/or depth.
    Compared Results
    Found in abundance by Kimmel, and Diaz and Alexander.
    Grantham showed results that support rams-horn have a preference for macrophytes
  • 53.
    • Limitations of the study
    • 54. Time
    • 55. Limited space
    • 56. Knowledge
    • 57. Equipment
    • 58. Broader Ecology Meaning
    • 59. Insight to why this invasive species is so successful
    • 60. Influence to endangered fountain darter