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Ecological correlates of wildlife diseases
M ilind W atveIISER, Pune
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• W hy study wildlife diseases? Disease: an intrinsic component of natural
ecosystems W ildlife health and conservation Potential reservoir for emerging diseases,
• W hy ecological correlates? conditions for endemism/epidemics
• W hich diseases should we look at? micro/macroparasites endemic/epidemicNat
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Parasites in host ecologyParasites in host ecologyN
atur
e P
rece
ding
s : d
oi:1
0.10
38/n
pre.
2010
.483
4.1
: Pos
ted
29 A
ug 2
010
Wildlife Sanctuaries of India.
Sanctuaries visited for sample collection
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What decides parasite load?
• Host population density
• Host body size and home range
• Host phylogeny
• Gregariousness
• Anatomical niche diversity
• Host diet
• Predatory pressure
Host ecological variables potentially affecting parasite loads and diversity
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Four levels of analysis for testing the hypotheses
• Individual as a unit. (2551 individual samples com ing from 29 species from 20 wildlife sanctuaries)
• Species as a unit. (mean or median parasite loads of 24 host species, grouped ecological variables)
• Species as a unit. (non parametric correlations with demographic data in Tadoba National Park, 9 host sp).
• Intraspecific patterns – across different habitats (2 host sp.)
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Effect of host variables on parasite loadsAnalysis with species as a unit Pooled data from all sanctuaries
Predation freedom index Vs mean parasite load Kendall’s =0.53
Blackbuck
haremuskdeer
Sambar
wildboarLangur
rhesus
buffalo
gaur
slothbearcivetporcupine
lion
Barsingha
chital
hogdeer
muntjac
nilgai
elephant
rhinoWildass
leopard
wild dogtiger
0.001
0.01
0.1
1
10
100
1000
0 2 4 6
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Barsingha
Blackbuck
hogdeerSambar
Langur
rhesus
buffalo
gaur
slothbear
civet
elephant
porcupine
rhino
Wildass
leopardwild dog
lion
tiger
chital
hare
muntjac
muskdeer
nilgai
wildboar
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 2 4 6
Predation freedom index Vs prevalence Kendall’s =0.4264
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Kendall’s =0.54
0= herbivore 1= omnivore 2= carnivore
food Vs. mean parasite load
Barsinghabuffalo
civet
gaur
hare
muntjac
muskdeer
rhino
Sambar
slothbear
Blackbuck
chital
elephant
hogdeer
Langur
leopard
lion
nilgai
porcupine
rhesus
tiger
wild dog
Wildass
wildboar
0.001
0.01
0.1
1
10
100
1000
0 0.5 1 1.5 2 2.5
food
mea
n pa
rsite
load
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food vs prevalence
Barsinghabuffalo
Langurleopard
muntjac
porcupine
rhesus
rhino
slothbear
tigerwild dog
wildboarblackbuck
chital civet
elephant
gaur
hare
hogdeer
lion
muskdeer
nilgai
Sambar
wildass
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 0.5 1 1.5 2 2.5
food
pre
vale
nce
Kendall’s =0.33
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Species as a unit.Non param etric correlations with dem ographic data in Tadoba National Park.
Density densityF:F ratio
adult sex ratio
pred index (num)
predation index (biomass)
average eggs
average proto
egg + proto
Female:fawn ratio
-0.022
Adult Sex Ratio
-0.200 -0.511 predation index (numbers)
0.452 0.181-0.22
6
predation index (biomass)
0.542 0.000 0.136 0.598
average eggs -0.223 -0.313 0.045 -0.432 -0.432
average protozoa
-0.536 -0.268 0.089 -0.250 -0.523 0.292
egg + protozoa -0.447 -0.447 0.268 -0.477 -0.341 0.562 0.697
Sex ratio in Tiger Kills
0.400 -0.400 0.200 0.600 0.800 0.200 0.200 0.200
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Turning the question upside down
W hat decides the standing density of a species?• Birth rate – fem ale:fawn ratio, sex ratio
no correlation
• Predation rate – predation index, sex ratio in killsPositive correlation contrary to expection
• Disease, starvation, malnutrition etc – reflected in fecal parasite counts
Negative correlation
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Testing predation hypothesis in Chital
Bharatpur Sariska & Ranathambhor
No. of observations
79 130
Average of ranks 51.85 23.57
Wx =4096 Wy = 3064 U=3057 Z=12.35 P<0.001
Bharatpur (predator free habitat) compared with others
Bharatpur Other wet habitats
No. of observations
79 243
Av. Of ranks 70.03 43.68
Wx= 5533 Wy=10616 U=5533
Z=10.05 P< 0.01
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Predator – prey – parasite dynamics Chital – Dhole- Sarcocystis
(Jog et al 2005)
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Predation hypothesis:
ecological Vs evolutionary
• Ecological: predators remove infective individuals from the population (removal of predator should reverse the effect quickly)
• Evolutionary: prey species experience greater selection for parasite resistance.(removal of predator not expected to reverse the effect for several generations)
• Both effects seen, evolutionary stronger.
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Possible im plications
• Density regulation by diseases and parasites
• Predator regulation of diseases and parasites
• Disturbance of predatorprey dynamics may lead to unpredictable changes in parasite dynamics
• Species/populations devoid of predators need to be watched more carefully as a potential source of emerging diseases
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