Friday, 11 December 2015

BioMaths Colloquium - 11/12/2015

BioMaths Colloquium Series - 2015/16

11 December 2015 - 3pm Maths Seminar Room 

(room 224 Talbot Building 2nd floor)

Effects of spatial structure on a cyclic herbivore populations

Dr Christina Cobbold

From: Hughes, Cobbold et al. (2015) Am. Nat. 185(5): E130-E152

Our final BioMaths Colloquium seminar of this term will be by Dr Christina Cobbold from the School of Maths & Stats at the University of Glasgow. Christina is Senior Lecturer in Applied Mathematics and member of the Boyd Orr Centre for Population and Ecosystem Health.  Her keen interest in Mathematical Biology concerns especially the mathematics of biological interactions, such as host-parasitoid interactions, the evolution of developmental timing, and modelling dynamics of rapid evolutionary processes. Examples of the latter include antigenic variation in trypanosomes and mutation leading to myotonic dystrophy. 

Understanding how cycles of forest-defoliating insects (herbivores) are affected by forest  structure is of major importance for forest management. Achieving such an understanding with data alone is difficult. We therefore constructed mathematical models to investigate the effects of forest structure on herbivore cycles, focusing on herbivore cycles driven by parasitoids.  
Forest tent caterpillar moth
Pic from Wikipedia

Typically when we think of spatially structured habitat we think of a habitat fragmentation and a mosaic of suitable and unsuitable habitat. However, suitable habitat can be uniformly distributed, but still show spatial structure  via spatial variation in the  plant genotype. It has been shown the plant genotype can strongly affect not only individual herbivore performance, but also community composition and ecosystem function. In this talk I will examine the impact of two these types of spatial heterogeneity (fragmentation and genotype variation) on the population cycles of forest-defoliating insects.

Forest tent caterpillar.
Pic from Wikipedia
Our integrodifference equation model shows that forest destruction can increase herbivore density when parasitoids disperse much farther than the herbivores because the benefits of reduced herbivore mortality due to increased parasitoid dispersal mortality exceed the costs of increased herbivore dispersal mortality. This novel result can explain observations of increased outbreak duration with increasing forest fragmentation in forest tent caterpillar populations.

A Tachinidae parasitoid, genus Leschenaultia.
Pic from
I will also show how plant genotype, the relative size of genotypic patches, and the rate of herbivore dispersal between them, affect the frequency, amplitude, and duration of herbivore outbreaks. We found that coupling two different genotypes does not necessarily result in an averaging of herbivore dynamics. Instead, depending on the ratio of patch sizes, when dispersal rates are moderate, outbreaks in the two- genotype case may be more or less severe than in forests of either genotype alone.

The discussions will continue over biscuits and tea/coffee after the seminar. 
Hope to see many of you!