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An evaluation of latent Dirichlet allocation in the context of plant-pollinator networks

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dc.contributor.advisor Ali, Ayesha
dc.contributor.advisor Umphrey, Gary Callaghan, Liam 2013-01-08T16:49:47Z 2013-01-08T16:49:47Z 2012-12 2012-12-04 2013-01-08
dc.description.abstract There may be several mechanisms that drive observed interactions between plants and pollinators in an ecosystem, many of which may involve trait matching or trait complementarity. Hence a model of insect species activity on plant species should be represented as a mixture of these linkage rules. Unfortunately, ecologists do not always know how many, or even which, traits are the main contributors to the observed interactions. This thesis proposes the Latent Dirichlet Allocation (LDA) model from artificial intelligence for modelling the observed interactions in an ecosystem as a finite mixture of (latent) interaction groups in which plant and pollinator pairs that share common linkage rules are placed in the same interaction group. Several model selection criteria are explored for estimating how many interaction groups best describe the observed interactions. This thesis also introduces a new model selection score called ``penalized perplexity". The performance of the model selection criteria, and of LDA in general, are evaluated through a comprehensive simulation study that consider networks of various size along with varying levels of nesting and numbers of interaction groups. Results of the simulation study suggest that LDA works well on networks with mild-to-no nesting, but loses accuracy with increased nestedness. Further, the penalized perplexity tended to outperform the other model selection criteria in identifying the correct number of interaction groups used to simulate the data. Finally, LDA was demonstrated on a real network, the results of which provided insights into the functional roles of pollinator species in the study region. en_US
dc.language.iso en en_US
dc.subject pollination network en_US
dc.subject latent Dirichlet allocation en_US
dc.subject linkage rules en_US
dc.subject perplexity en_US
dc.subject model selection en_US
dc.subject BIC en_US
dc.subject AIC en_US
dc.subject DIC en_US
dc.title An evaluation of latent Dirichlet allocation in the context of plant-pollinator networks en_US
dc.type Thesis en_US Mathematics and Statistics en_US Master of Science en_US Department of Mathematics and Statistics en_US
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