Review of de Castro & Bolker (2005) New stuff References

Mechanisms of disease-induced extinction

Ben Bolker, McMaster UniversityDepartments of Mathematics & Statistics and Biology

NCEAS

18 March 2013

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Outline

1 Review of de Castro & Bolker (2005)

2 New stuff

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Baseline: in a deterministic model . . .. . . of a specialist parasite . . .. . . with density-dependent transmission . . .the parasite can never drive the host completely extinctExceptions:

Inhomogeneous mixing(non-DD transmission, spatial structure)

Generalist pathogens(biotic or abiotic reservoir)

Stochastic extinction(small populations, or low troughs)

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Baseline: in a deterministic model . . .. . . of a specialist parasite . . .. . . with density-dependent transmission . . .the parasite can never drive the host completely extinctExceptions:

Inhomogeneous mixing(non-DD transmission, spatial structure)

Generalist pathogens(biotic or abiotic reservoir)

Stochastic extinction(small populations, or low troughs)

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

What is virulence?

Plant biology: ability to infect

Animal biology: pathogenicity

Evolutionary biology: loss of host fitness

Theoretical evolutionary biology: rate of host mortality Day(2002)

Popular media: generalized index of badness

G(host) × G(pathogen) × E (environment) interaction

Need to distinguish between individual impact andpopulation-level impact.

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

What is virulence?

Plant biology: ability to infect

Animal biology: pathogenicity

Evolutionary biology: loss of host fitness

Theoretical evolutionary biology: rate of host mortality Day(2002)

Popular media: generalized index of badness

G(host) × G(pathogen) × E (environment) interaction

Need to distinguish between individual impact andpopulation-level impact.

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Stochastic effects: predisposing conditions

small pre-epidemic population(endangered/endemic species)

low disease-present endemic equilibrium(intermediate virulence)

transient or periodic population troughs(?? virulence)

Allee effects

inbreeding depression (extinction vortex?)

fecundity-reducing parasites

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Stochastic effects: empirical examples

Host Impact ReferenceTree snail (Partula turgida) Extinction Daszak & Cunningham (1999)Thylacine (Thylacinus cynocephalus) Possible extinction Guiler (1961) (in McCallum &

Dobson 1995)Golden toad (Bufo periglenes) Probable extinction Pounds et al. (1997)Black-footed ferret (Mustela nigripes) Probable extinction Thorne & Williams (1988)Mednyi arctic fox (Alopex lagopus semenovi) Probable extinction Goltsman et al. (1996)African wild dog (Lycaon pictus) Population crash Burrows et al. (1994)Boreal toad (Bufo boreas) Population crash Muths et al. (2003)Noble crayfish (Astacus astacus) Population crash Taugbol et al. (1993)Spanish Ibex (Capra pyrenaica hispanica) Population crash Fandos (1991),Leon-Vizcaino et

al. (1999)Big-horn sheep (Ovis canadiensis) Population crash (model) Gross et al. (2000)Florida torreya (Torreya taxifolia) Population crash and pre-

dicted extinction (model)Schwartz et al. (1995,2000)

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Inhomogeneous mixing: predisposing conditions

frequency-dependent transmission

sexually transmitted diseases

vector-borne disease

social behaviour

spatially localized populations

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Inhomogeneous mixing: empirical examples

Host Impact ReferenceKoala/Chlamydia Possible population crash

(model)Augustine (1998)

Eupatorium makinoi Asteraceae Population crash Funayama et al. (2001)Rabbit/Rabbit haemorrhagic disease Possible population crash

(model)White et al. (2003)

Common flax (Linum marginale) Possible population crash(model)

Thrall et al. (2003)

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Reservoirs: predisposing conditions

biotic: apparent competition (local congenerics??)

abiotic: amplification in environment (saprophytic stages)

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Reservoirs: empirical examples

Host Impact ReferenceIiwi (Vestiaria coccinea) Population crash Atkinson et al. (1995)Amakihi (Hemignathus virens) Population crash Atkinson et al. (2000)White-tailed deer (Odocoileus virginianus) /moose (Alces alces)

Population reduction Schmitz & Nudds (1994)

Red squirrel (Sciurus vulgaris) Population reduction Rushton et al. (2000)Ethiopian wolf (Canis simensis) Population reduction

(model)Haydon et al. (2002)

Tussock moth (Orgya antiqua) Population crash Richards et al. (1999)

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Outline

1 Review of de Castro & Bolker (2005)

2 New stuff

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Interactions between mechanisms

Effect of reservoirs on R0/equilibrium density/trough density

Detailed modeling of density/frequency-dependence?

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Final size curve (Ma & Earn, 2006)

1 2 3 4 5 6 7 8

0.0

0.2

0.4

0.6

0.8

1.0

R0

Fra

ctio

n ne

ver

infe

cted

Effect of non-amplifying environmental reservoir (Rohani et al., 2009): β︸︷︷︸direct

+ωρ

κη︸︷︷︸environmental

S0

γ

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Evolution of virulence

Tradeoff theory (Ebert & Bull, 2003a; Gandon & Day, 2003;Ebert & Bull, 2003b; Alizon et al., 2009)

Connections between virulence and population outcome

Factors affecting selection on virulence? Many . . . includingpresence of resting stages(Bonhoeffer et al., 1996; Gandon, 1998; Kamo & Boots, 2004)

resistance vs. tolerance vs. virulence(Carval & Ferriere, 2010)

capability of host to evolve resistance/tolerance:genetic variation, length of trough

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Open questions

understand transient trough depth (King et al., 2009)

general host-switching/emergence issues:virulence/population threat spectrum of novel pathogens

host vs. pathogen factors

ontogenetically structured models

effects of environmental variation (random, or seasonal)

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

reports by pathogen type

●

●

●

●

●

●

●

●

●

other

arthropod

helminth

protozoan

virus

fungus

0 4 8 12 16count

ref●

●

dCB2005Fisher+2012

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Meta- stuff

Ask not what modellers can do for you . . . (actually, do!)

Lumpers vs. splitters

Strategic vs. tactical models: Levins (1966); Mollison (1991)Why study detailed mechanism?

it’s really, really cool.treatmentleverage limited informationextrapolation across levels (multi-scale models)

What are models for? Analytical, statistical, predictive,synthetic, . . .

Ben Bolker NCEAS

Disease-induced extinction

Review of de Castro & Bolker (2005) New stuff References

Alizon, S, Hurford, A, Mideo, N, et al., 2009. Journal of Evolutionary Biology, 22(2):245–259. ISSN 1010061X.doi:10.1111/j.1420-9101.2008.01658.x. URLhttp://onlinelibrary.wiley.com/doi/10.1111/j.1420-9101.2008.01658.x/abstract.

Bonhoeffer, S, Lenski, RE, & Ebert, D, 1996. Proceedings: Biological Sciences, 263(1371):715–721. ISSN 0962-8452.doi:10.2307/50702. URL http://www.jstor.org/stable/50702.

Carval, D & Ferriere, R, 2010. Evolution, 64(10):2988–3009. ISSN 0014-3820. doi:10.2307/40863389. URLhttp://www.jstor.org/stable/40863389.

Day, T, 2002. Proceedings of the Royal Society B: Biological Sciences, 269(1498):1317–1323. ISSN 0962-8452.doi:10.1098/rspb.2002.2021.

de Castro, F & Bolker, B, 2005. Ecology Letters, 8:117–126. doi:10.1111/j.1461-0248.2004.00693.x.

Ebert, D & Bull, JJ, 2003a. Trends in Microbiology, 11(1):15–20.

Ebert, D & Bull, JJ, 2003b. Trends in Microbiology, 11(5):208–209. ISSN 0966-842X.doi:10.1016/S0966-842X(03)00072-6. URL http://www.sciencedirect.com.lp.hscl.ufl.edu/science/article/B6TD0-487DKNM-1/2/a73a504c3c242a5c72c5288af0221ba1.

Gandon, S, 1998. Proceedings of the Royal Society of London Series B-Biological Sciences, 265(1405):1545–1552.

Gandon, S & Day, T, 2003. Trends in Microbiology, 11(5):206–207.

Kamo, M & Boots, M, 2004. Journal of Theoretical Biology, 231(3):435–441.

King, AA, Shrestha, S, Harvill, ET, et al., 2009. American Naturalist, 175(4):446–455. doi:10.1086/597217.

Levins, R, 1966. American Scientist, 54:421–431.

Ma, J & Earn, DJD, 2006. Bulletin of Mathematical Biology, 68(3):679–702. ISSN 0092-8240.doi:10.1007/s11538-005-9047-7. URL http://www.ncbi.nlm.nih.gov/pubmed/16794950. PMID:16794950.

Mollison, D, 1991. Mathematical Biosciences, 107, Issue 2:255–287.

Rohani, P, Breban, R, Stallknecht, DE, et al., 2009. Proceedings of the National Academy of Sciences,106(25):10365–10369. ISSN 0027-8424, 1091-6490. doi:10.1073/pnas.0809026106. URLhttp://www.pnas.org/content/106/25/10365.

Ben Bolker NCEAS

Disease-induced extinction