Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Designing a mechanistic model that can give rise to realistic architecture of ecological
networks is central to the understanding of how species assemble and function in ecosystems.
As species are constantly adjusting their diets in an antagonistic network, we
here incorporate this adaptive behaviour of diet choice into a bipartite network model,
with the effect of antagonistic interactions between species depicted by Holling’s type
II functional response. Predictions of this model fit extremely well with the observed
levels of nestedness, modularity and node-degree distributions for 61 real host-parasitoid
and plant-herbivore networks. We further examined two specific scenarios of our model
(species with identical [neutral] demographic parameters and interactions with identical
[neutral] benefit in the network) and found that the demography-neutral scenario overestimated
observed modularity, whilst the benefit-neutral scenario over-estimate observed
nestedness. Relationships between nestedness, modularity and connectance were found
strong. Moreover, in contrast to the common belief of the high modularity in antagonistic
networks, most real networks (> 80%) are significantly nested, whilst nearly 40% of the
real networks are surprisingly less compartmentalized than random networks generated
from null models. Regardless of the controversy on whether antagonistic networks are
nested or compartmentalized, the proposed model captured the essence of the dynamic
nature of structural emergence in antagonistic networks. Due to its predictive power, this
model was further used to investigate robustness in antagonistic networks. Predictions
showed that the robustness of a network is determined by many factors, such as connectance,
resource degree distribution, resource-consumer ratio, diversity, nestedness and
compartmentalisation. Surprisingly, the manner of network response to species loss was
independent of the sequence followed while removing species from a network. Variations
were only noticed in the intensity of the effect resulting from the removals. In addition,
we also showed that species extinction procedures which ignore the interaction switch
underestimate the effect of any loss of species in these networks. We must therefore value
our knowledge of possible adaptive processes in the ecosystem as they may be important
for resolving the diversity-stability debate. / AFRIKAANSE OPSOMMING: Die ontwerp van ’n meganistiese model wat aanleiding kan gee tot realistiese argitektuur
van ekologiese netwerke is sentraal tot die begrip van hoe spesies bymekaar kom
en funksioneer in ekosisteme. Soos spesies voortdurend hul dieet aanpas in ’n antagonistiese
netwerk, het ons hierdie aanpasbare gedrag van dieet keuse in ’n bipartiet netwerk
model ingewerk, met die effek van antagonistiese interaksies tussen spesies wat uitgebeeld
word deur Holling se tipe II funksionele reaksie. Voorspellings van hierdie model pas
baie goed met die waargenome vlakke van nestedness, modulariteit en node-graad uitkerings
vir 61 ware gasheer-parasiet en plant-herbivoor netwerke. Verder het ons twee
spesifieke gevalle van ons model (spesies met identiese [neutrale] demografiese parameters
en interaksies met identiese [neutrale] voordeel in die netwerk) ondersoek en gevind
dat die demografie-neutrale geval waargenome modulariteit oorskat, terwyl die voordeelneutraal
geval waargenome nestedness oorskat. Verhoudings tussen nestedness, modulariteit
en konnektiwiteit is sterk bevind. Verder, in teenstelling met die algemene verwagting
van hoe modulariteit in antagonistiese netwerke, is oorhoofse werklike netwerke
(> 80%) aansienlik geneste, terwyl byna 40% van die werklike netwerke is verbasend
minder gekompartimenteerd as ewekansige netwerke gegenereer uit null modelle. Ongeag
van die omstredenheid oor of antagonistiese netwerke geneste of gekompartimenteerd is,
die voorgestelde model vang die essensie van die dinamiese aard van die strukturele opkoms
in antagonistiese netwerke. As gevolg van sy voorspellende krag, is hierdie model
verder gebruik om robuustheid te ondersoek in antagonistiese netwerke. Voorspellings
het getoon dat die robuustheid van ’n netwerk word bepaal deur verskeie faktore, soos
konnektiwiteit, hulpbron-graad verspreiding, hulpbron-verbruiker verhouding, diversiteit,
nestedness en kompartementasie. Verrassend, die wyse van die netwerk reaksie op die
verlies van spesies was onafhanklik van die reeks wat gevolg het toe die spesies verwyder
is uit ’n netwerk. Variasies is slegs opgemerk in die intensiteit van die effek van die verskuiwings.
Benewens, ons het ook aangetoon dat die prosedures van spesies se uitsterwing
wat die interaksie skakelaar geignoreer het, onderskat die effek van ’n verlies van spesies in
hierdie netwerke. Ons moet dus die waarde van ons kennis van die moontlike aanpassing
prosesse in die ekosisteem in agneem, aangesien dit belangrik kan wees vir die oplossing
van die diversiteit-stabiliteit debat.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/79849 |
| Date | 03 1900 |
| Creators | Nuwagaba, Savannah |
| Contributors | Hui, C., Stellenbosch University. Faculty of Science. Department of Mathematical Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xi, 95 pages : illustrations |
| Rights | Stellenbosch University |
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