Modelling the effects of release timing on the wind-assisted dispersal of passive propagules

Modelling the effects of release timing on wind-assisted dispersal David Savage PhD Candidate (University of Western Australia) biosecurity built on science Cooperative Research Centre for National Plant Biosecurity

Introduction  Patterns in the timing of release can affect the direction of dispersal, the distance covered, and consequently, the resulting area of spread  Many fungal pathogens, including Leptosphaeria maculans display seasonal and diurnal patterns of release  Simple models of wind-assisted dispersal - aka mechanistically parameterised two-dimensional anisotropic dispersal kernels - can be easily constructed using wind data and knowledge of release timing biosecurity built on science

Timing of release affects windassisted dispersal

See Savage et. al. in Diversity and Distributions (2010) biosecurity built on science

Timing of release affects windassisted dispersal

See Savage et. al. in Microbial Ecology (in press) biosecurity built on science

Seasonal patterns in the release of ascospores Number of spores detected

Observed

Fitted

Time since rainfall is a significant variable

Time (hours, June - August 1972)

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Spores detected

Diurnal patterns in the release of ascospores

Hour of the day

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A mechanistically parameterised dispersal kernel  Joint density using half Cauchy and von Mises distributions  von Mises fit to wind data  Half Cauchy uses ballistic equation to represent median dispersal distance

hu µ= vt See Savage et. al. in Ecological Modelling (2011) biosecurity built on science

A mechanistically parameterised dispersal kernel

See Savage et. al. in Ecological Modelling (2011) biosecurity built on science

Integrating a release pattern into the dispersal kernel

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Integrating diurnal patterns into the dispersal kernel

n

k = ∑ ai ⋅ ki i=1

  ai > 0,

 ∑ ai = 1 n

i=1

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Integrating diurnal patterns into the dispersal kernel

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Integrating diurnal patterns into the dispersal kernel

h = 0.24 m, vt = 0.001 ms-1

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Integrating diurnal patterns into the dispersal kernel

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Conclusions  Timing of release does affect windassisted dispersal  Effect can be significant, and accumulates over a number of dispersal events  It’s not difficult to integrate the effects of timing into dispersal kernels biosecurity built on science

Thank you ď&#x201A;§ For more information, please email david.savage@uwa.edu.au

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Modelling the effects of release timing on the wind-assisted dispersal of passive propagules

Published on Sep 6, 2012

Plant Biosecurity CRC

Wind-assisted dispersal is an important ecological process that plays a significant role in the spread of invasive organisms. For passively dispersing propagules such as seeds, pollen and fungal spores, the wind-conditions experienced over the course of their journey define the distance and direction of their dispersal. Consequently, the time at which propagules are released influences the manner in which an invasive organism spreads from a particular location. In order to predict the spread of organisms that undergo wind-assisted dispersal, it is therefore necessary to integrate knowledge of release timing into models of wind-assisted dispersal. In this presentation we will outline a method for developing models of wind assisted dispersal that allows dispersal kernels to be easily constructed using meteorological data, knowledge of environmental triggers for propagule release and simple representations of diurnal patterns of propagule release.