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Disease (Ch. 10)

Disease (Ch. 10). ConBio. Parasite Spillover/Spillback. Parasite spillover : exotic parasite shared with native host Ex., Native bumblebees ( Bombus ) vs. commercial Bombus in greenhouses Protozoan pathogen jumps to natives outside. Bumblebee box. Parasite Spillover/Spillback.

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Disease (Ch. 10)

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  1. Disease (Ch. 10) ConBio

  2. Parasite Spillover/Spillback • Parasite spillover: exotic parasite shared with native host • Ex., Native bumblebees (Bombus) vs. commercial Bombus in greenhouses • Protozoan pathogen jumps to natives outside Bumblebee box

  3. Parasite Spillover/Spillback • Parasite spillback: native parasite boosted by exotic host NIS: non-native invasive species

  4. Parasite Spillover/Spillback • Parasite spillback: native parasite boosted by exotic host • Ex., ??

  5. Parasite Spillover/Spillback • Parasite spillback: native parasite boosted by exotic host • Ex., Cane toad • Myxosporean parasites increasing native frogs (spillback from cane toads)

  6. Solutions • 1) Make/enforce quarantine rules • 2) Minimize interspecies interactions in conservation programs

  7. Solutions • 3) Monitor for disease • 4) Maintain populations at appropriate densities/conditions • 5) Treat disease directly • Ex, who am I? • Vaccinate feral dogs: control canine distemper Hotspot: Eastern Afromontane

  8. Enlightened Self-Interest • Diseases can cause human difficulties • Ex, Lyme disease and deer ticks. Deer ticks Lyme disease bacteria Others: Hantavirus, west Nile…

  9. 4 major threats in Ch. 9 • 1) Habitat destruction • 2) Habitat fragmentation • 3) Habitat degradation • 4) Global climate change • Ch. 10, overexploitation, invasive species, disease.

  10. The LARGE problems of small populations (Ch. 11) • Cheetahs

  11. ConBio & small pops. • ConBio species: habitat fragmented, population number small, population sizes small Threatened U.S. species in various groups MVP concept?

  12. Minimum Viable Population (MVP) • Concept: smallest population that will survive long-term • Def’ns vary • Ex, smallest population with 99% chance surviving 1000 yr • Challenge: survive catastrophes!

  13. Minimum Viable Population (MVP) • Catastrophes: Gila Trout. • Gila River (NM/AZ) • Federally endangered, recovery established new populations • New Mexico moved to de-list species

  14. Minimum Viable Population (MVP) • Next 6 months: • Flood eliminated 80% 1 pop’n. • Fire + flood eliminated “type locality” (species first described from specimen collected there) • Drought + fire eliminated 90% third population.

  15. Minimum Viable Population (MVP) • Associated concept: Minimum Dynamic Area (MDA) • Area habitat needed by MVP • How determine MVP & MDA?

  16. MVP and MDA • How determine? Hard! Lots research • Guesses: • Vertebrates: 500-5000 individuals • Invertebrates/annual plants: 10,000 individuals. My middle daughter’s kind of Guess

  17. Figuring out MVP • Ex, Desert bighorn sheep • Long-term records • MVP >50

  18. Problems of Small Populations • 1) Genetic drift • Effective population size • 2) Founder effect • 3) Demographic variation (stochasticity) • Allee effect • 4) Environmental variation (stochasticity) Genetic drift…….

  19. Loss of Genetic Variability • Genetic drift: Chance elimination rare alleles • Major problem when population small

  20. Loss of Genetic Variability Discoverer David Noble said…. • Ex, Wollemi “Pine” (Australia) • Living fossil: Extinct 2 mya, 2 stands found 1994. 40 plants!

  21. Genetic Variability • Models: Genetic variability decreases if population size small (N<100)

  22. Genetic Variability • 50/500 rule: Isolated pops. need 50 (better 500) individuals (maintain genetic diversity) • Biological Conservation 2009 paper: probably 10-fold too low!

  23. Problems of Decreased Genetic Diversity • 1) Loss evolutionary ability: Provides alleles valuable in future.

  24. Problems • 2) Inbreeding depression: loss vigor when mate close relative • Why? Rare harmful alleles expressed when homozygous recessive. (BGYNH: Be Glad You’re Not Haploid!) Fig. 11.6

  25. On the other hand…… • Outbreeding depression: mating with distant relative gives loss vigor • At population, subspecies, or species level

  26. The Goldilocks Effect On the other hand…… • Inbreeding depression greater ConBio challenge Fig. 11.8

  27. Countering genetic drift • 2 ways…..

  28. Countering genetic drift • 1) Mutation rate • Normally: 1/10,000 to 1/1,000,000 per gene/generation • Significant large populations • Negligible small populations.

  29. Countering genetic drift • 1) Mutation rate • Model: Mutation does not maintain diversity small pops. 120 individuals over 100 generations Fig. 11.4 What works?

  30. Countering genetic drift • 2) Immigration • Helpful! (low rates enough!) Give me Kwik E Mart! Apu

  31. Countering genetic drift • 2) Immigration • Model: 1 immigrant/generation maintains 90% genetic diversity 120 individuals over 100 generations Fig. 11.4

  32. Problems of Small Populations • 1) Genetic drift • Effective population size • 2) Founder effect • 3) Demographic variation (stochasticity) • Allee effect • 4) Environmental variation (stochasticity)

  33. Effective Population Size • Not all individuals contribute to next generation • Breeding individuals constitute effective population size (Ne) • Ne determines genetic diversity future generations

  34. What determines Ne? • 1) Maturity. Juvenile & senescent individuals don’t count! Juvenile Medically preserved (Dick Clark) Born 1929! Senescent

  35. What determines Ne? • 2) Unequal sex ratio (dioecious organisms: individuals male or female) • Ne= (4 Nm Nf)/(Nm + Nf) • Nm= # breeding males Nf= # breeding females (Fig. 11.10)

  36. What determines Ne? • 2) Unequal sex ratio • Ex, 6 males, 150 females (elephant seals) • Ne=23. • Ne= (4 Nm Nf)/(Nm + Nf)

  37. What determines Ne? • 3) Variable individual reproduction • Some more offspring: “stud factor” (joke) • Ex, many plants: few large ones make most seeds. Owl’s Clover (CA)

  38. What determines Ne? • 4) Population fluctuations/bottlenecks • Ne = t / (1/N1 + 1/N2 + 1/N3…+ 1/Nt) • t=time in yr N=# breeding in each yr Example…

  39. What determines Ne? • 4) Population fluctuations/bottlenecks • Ne = t / (1/N1 + 1/N2 + 1/N3…+ 1/Nt) • t=time in yr N=# breeding in each yr • N=10, 20, 100, 20, 10 • Mean=32 • Ne=16.1 Lesson?

  40. What determines Ne? • Short bottleneck better than long one!

  41. Last consideration on Ne • Can calculate Ne: measure loss heterozygosity • Study with Drosophila • N=5,000 • Ne=185 to 253 • Only 4% population!

  42. Problems of Small Populations • 1) Genetic drift (Done!) • Effective population size (Done!) • 2) Founder effect • 3) Demographic variation (stochasticity) • Allee effect • 4) Environmental variation (stochasticity) Defn

  43. Founder Effect • Founder Effect: Difference due to chance makeup establishing individuals (founders) • Few give rise to entire population Amish madonna

  44. Founder Effect • Good News! Few founders keep H high • Ne=10 individuals: 95% genetic variation NOTE SHAPE OF CURVE

  45. Founder Effect • Problem: populations often founded by few individuals (start w/ reduced H) Who am I? 18 animals as founders

  46. Problems of Small Populations • 1) Genetic drift • Effective population size • 2) Founder effect (Done!) • 3) Demographic variation (stochasticity) • Allee effect • 4) Environmental variation (stochasticity) Demography……

  47. Demographic Variation • General rule: Trouble when N<50 • Chance variation: birth/death rates, sex ratio Who am I? Sparrows…. Extinct!

  48. Demographic Variation • Ex, dusky seaside sparrow • Subspecies seaside sparrow (nigrescens) • Inhabited salt marshes FL • Last 5 individuals: males!

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