Practical community ecology

1
Practical community ecology

• Complex networks of interactions
• Practical consequences
• Agriculture
• Fisheries
• Forestry
• Human health

2
Lyme disease

• Reading
• Ostfeld, R.S. 1997. Ecology of lyme-disease
  risk. American Scientist 85338-346
• Jones, C. G. et al. 1998. Chain reactions linking
  acorns to gypsy moth outbreaks and Lyme disease
  risk. Science 2791023-1026
• available on Ecology course web page

3
Lyme disease

• Disease symptoms
• red rash bulls eye shape
• fever, chills, muscle aches
• untreated arthritis, neurological disorders
• First identified in Europe 1909
• Cause Borrelia burgdorferi
• spirochaete
• idenitified in 1982

4
A common disease

• 1990-1999
• 122,651 cases
• Connecticut mean 63 cases per 100,000
• Reported in 48 states
• Most common vector borne disease in US

5
Lyme disease transmission

• Vector borne
• Ticks
• Northeast Black legged tick
• Ixodes scapularis
• Transmitted by bites while taking bloodmeals

6
Tick life cycle
Deer, rodents, birds, canids, humans
Rodents, birds, small mammals
7
Reservoir host

• Ticks become infected mainly as larvae
• Acquire spirochaete from Peromyscus leucopus
• Enzootic disease cycles between mouse and tick

8
Transmission to humans

• Both adults and nymphs can transmit spirochaete
  to people
• Nymphs believed to be greatest threat
• Epidemic disease outbreak in humans
• Principal risk factor Number of infected nymphs
  in areas frequented by people in early summer

9
Epidemic disease

• Lots of infected nymphs, adults
• High Tick population
• High infection rate
• Lots of human contact
• Human-tick spatial and temporal overlap

10
Tick populations

• High tick populations associated with abundant
  acorns
• Oaks
• boom / bust cycle of acorn production
• Mast years
• Deer
• eat twigs and leaves from woody plants
• Mast years, eat acorns
• Mast year, deer concentrated in oak woods

11
Deer and Ticks

• Concentration of deer in oak woods
• Adult ticks in oak woods
• Lots of tick eggs in oak woods
• Following summer lots of tick larvae in oak woods

12
Experiment

• 1995
• Acorn crop failure
• 3 experimental grids (2.25 ha each)
• added 800,000 acorns (3500 kg)
• 3 control grids
• 1996
• monitor mouse density, breeding, ticks/mouse
• monitor tick density

13
Experimental Results(Jones et al. 1998. Science)

• Addition grids
• Mouse densities 7x greater
• Winter more mice in breeding condition

14
ExperimentalResults(Jones et al. 1998. Science)

• Addition grids
• Tick abundance 8x greater
• Ticks / mouse 40 greater

15
High populations of infected ticks
Tick Larvae
Tick egg-laying
Infected tick nymphs, adults
Deer
Mice
Acorns
16
Predicting Lyme disease risk

• Two years after oak masting, expect greatest risk
  in oak forest
• Test will require long-term data
• several mast years
• monitor ticks, diseases incidence
• Where is risk in non-mast years?

17
Abundance of larval ticks
18
End 11th Lecture
19
Essay (20 pts)Mean 15.0 (74.8)SD 2.1
(10.5)
Overall (100 pts)Mean 72.8 (72.8)SD
10.7 (10.7)
Multiple choice (80 pts)Mean 57.9 (72.3)SD
9.4 (11.8) 
20
Fixed Quota Harvest_at_1/2 MSY
21
Fixed Effort Harvest_at_ MSY
22
Fixed Effort Harvest

• H g E N
• H harvest
• g efficiency (take per unit effort)
• E effort (e.g., trawler-days)
• N population
• If g is constant, H is linearly related to N,
  with slope dependent on E (But sonar changes g)
• With sonar, g is greater, so to maintain H at
  MSY, you need to reduce E

23
Answers

• Glass case on 3rd floor Felmley Annex
• Figure out what you did wrong
• Questions? see me

24
Lyme disease infection

• Experimental manipulation of acorns
• showed abundance of ticks increases after acorn
  addition
• Risk factor abundance of infected ticks
• data?

25
Longer time scale

• 1995 to 2000
• Acorn crop in year t-2
• Abundance of mice in year t-1
• Nymphal ticks in year t
• density of nymphs
• nymphal infection prevalence
• proportion infected
• density of infected nymphs

26
Effects of mice 1995 - 2000
Significant
Significant
Significant
27
Effects of acorns1995 - 2000
Significant
Significant
Not Significant
28
Acorn effects

• Combination of experiment and observation
• Mast years of acorns determine human risk of Lyme
  disease
• Community interactions in this case impact human
  health

29
Forest Fragmentation

• Alters habitat
• shrubby species
• edge
• Mammals
• reduces diversity of mammals
• eliminates some species
• increases abundance of certain species

30
Peromyscus leucopus

• abundance increases in small patches
• other mammal species decline in small patches
• number of mammal species declines in small
  patches
• effects on nymphal ticks and Lyme disease?
• sample patches of different area for tick
  populations

31
Ticks vs. fragment area
Significant
Significant
Significant
32
Conclusion

• Small fragments Greater risk of Lyme disease
• Human alteration of landscape alters community
  and affects human health
• Fragmentation often a result of development
• building homes
• human exposure
• Mechanism?

33
Possible mechanism 1Competition and predation
34
Possible mechanism 2Dilution effect
35
End 12th Lecture