- Title
- Modelling locust foraging
- Creator
- Georgiou, Fillipe
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Locusts are short horned grasshoppers that exhibit two diametrically opposed behavioural types depending on their local population density. These are: solitarious, where they will actively avoid other locusts, and gregarious where they will seek them out. It is in this gregarious state that locusts can form massive and destructive flying swarms or plagues. However, these swarms are usually preceded by the aggregation of juvenile wingless locust nymphs. In this thesis we develop a mathematical model to understand how and why the distribution of food resources affect the group formation process. We do this by first deriving a multi-population partial intergro-differential equation model that includes non-local locust interactions, local locust and food interactions, and gregarisation dynamics. The model is studied using a combination of analytical techniques, such as linear stability theory and gradient flow methods, and numerical simulations. The numerical solutions are obtained using an adaptive time-stepped finite volume based scheme combined with fast Fourier transforms to efficiently solve the non-local component. Our initial results suggest that food acts to increase the maximum density of locust groups, lowers the percentage of the population that needs to be gregarious for group formation, and decreases both the required density of locusts and time for group formation around an optimal food width. Further, by considering foraging efficiency within the numerical experiments, we find that there exists a foraging advantage to being gregarious. Next, we explore this foraging advantage of gregarisation within increasingly heterogeneous environments. We consider a single two dimensional simulation of a spatially heterogeneous environment to understand the mechanics of gregarious/solitarious foraging. We also investigate the steady state foraging advantage in environments ranging from homogeneous to very spatially heterogeneous. Finally, we perform a parameter sensitivity analysis to determine the model parameters that have the greatest effect on foraging advantage. We find that during the aggregation stage, prior to the onset of marching, in increasingly heterogeneous food environments it is better for a locust to be gregarious than solitarious. In addition, we find that this is intrinsic to the gregarious/solitarious behavioural dynamic as it occurs almost regardless of the model parameters. In the final part of this thesis, we expand the model to include the effect of hunger on locust interactions and repeat our analyses. We find that the results are consistent with the less complex model and that hunger acts to decrease the maximum density of locust groups and raises the percentage of the population that needs to be gregarious for group formation. Overall, this thesis demonstrates the advantages and power of continuum models in providing insights into biological systems. The results presented here provide avenues of future exploration both in the mathematical and experimental spaces. Finally, it is our intention that this thesis will provide a guide for the creation and analysis of future models of collective behaviour.
- Subject
- locusts; collective behaviour; non-local PDEs; nonlocusts
- Identifier
- http://hdl.handle.net/1959.13/1467621
- Identifier
- uon:47859
- Rights
- Copyright 2022 Fillipe Georgiou
- Language
- eng
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 5 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 230 KB | Adobe Acrobat PDF | View Details Download |