Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Both taxonomic diversity and diversity of species interaction networks are experiencing
declines as a result of agricultural intensification at habitat and landscape scales. Reversing
this trend is a key conservation issue, particularly for important functional groups such as
flower-visiting insects and the networks within which they interact. This is of great concern
in regions of high conservation priority such as the Cape Floristic Region (CFR), known for
its high level of floral and faunal endemism and exceptional species turnover. Holistic
approach to conservation in agricultural landscapes involves both preservation of natural land
and wildlife friendly management of the farm land to achieve conservation targets. The value
of these extensive management approaches is yet to be fully assessed, especially in perennial
systems such as vineyards.
I examined here the effects of vineyard management and landscape context on species
richness and abundance of flower-visiting insects and their species interaction networks.
Possible taxon specific effects were verified. I also investigated whether vineyards under
organic and conventional management homogenized insect-flower interaction networks and
whether vineyards with different management practices vary in patterns of species turnover. I
sampled flower-visiting insects and their interactions in organic and conventional vineyards,
and in natural reference sites. Inclusion of natural reference sites enabled me to make
management recommendations for patches of natural vegetation in CFR agricultural
landscape.
Statistical models showed taxon-specific benefit of organic farm management, and of
landscape (distance to natural habitat). There was benefit to monkey beetles (Scarabaeidae)
but not to bees (Apidae). Organic vineyards had a higher number of insect-flower interactions
than conventional ones, but vineyards under the two types of management were similar in
terms of other important network indices. However, networks of the vineyards were more nested than the natural sites, indicating that they may be potentially more stable to
perturbation and random extinctions. Multivariate dispersion tests revealed insect-flower
interaction networks were not homogenized by both organic and conventional vineyards
across the landscapes. I also found, through additive partitioning, that organic and
conventional vineyards were similar in terms of species turnover of bees and flowering
plants.
The findings of this study provide heuristic value to current debates on the value of
vineyard habitats for insect conservation. Both organic and conventional vineyards that
promote sustainable management of the non-crop floral vegetation between vineyard rows
are potential solutions for conservation of flower-visiting insects and their interactions. Also,
attention has to be paid to the quality and connectivity of the natural habitat patches that are
within CFR agricultural landscape. Site specific management and assessment of the value of
these landscape elements is important. Management approaches such as carefully controlled
burning may be beneficial, as the CFR natural vegetation is a fire-driven community. / AFRIKAANSE OPSOMMING: Taksonomiese diversiteit en diversiteit van spesies-interaksie netwerke ondervind beide
afnames as gevolg van landboukundige intensifikasie op habitat en landskap skaal. Om die
neiging terug te swaai, is ’n sleutel bewaringsaangeleentheid, veral vir belangrike funksionele
groepe soos blom-besoekende insekte en die netwerke waarbinne hulle op mekaar inwerk.
Dit is van groot kommer in streke met hoë bewaringsprioriteite soos in die Kaapse Floristiese
Streek (KFS), bekend vir sy hoë vlak van plant- en dierendemisme en buitengewone spesies
kentering. ’n Holistiese benadering tot bewaring van landboukundige landskappe behels
beide die bewaring van natuurlike land en natuurlewe-vriendelike bestuur van die plaasgrond
om bewaringsdoelwitte te bereik. Die waarde van hierdie ekstensiewe bestuursbenaderings
moet nog volledig bepaal word, veral in meerjarige sisteme soos wingerde.
Ek het die uitwerkings van wingerdbestuur en landskapsamehang op spesiesrykheid en
volopheid van blombesoekende insekte en hulle spesies interaksie netwerke ondersoek.
Moontlike takson-spesifieke uitwerkings is nagegaan. Ek het ook ondersoek ingestel of
wingerde onder organiese en gebruiklike bestuur ooreenstemmende insek-blom interaksie
netwerke met wingerde met verskillende bestuurspraktyke in patroon van spesies kentering
gewissel het. Ek het blom-besoekende insekte en hulle interaksies in organiese en
konvensionele wingerde, asook in natuurlike verwysingsgebiede gemonster. Insluiting van
natuurlike verwysingsgebiede het my in staat gestel om bestuursvoorstelle vir gebiede van
natuurlike plantegroei in KFS landboulandskappe voor te stel.
Statistiese modelle toon takson-spesifieke voordeel van organiese plaasbestuur en van die
landskap (afstand van natuurlike habitat) self. Daar was voordeel vir bobbejaankewers
(Scarabaeidae), maar nie vir bye (Apidae) nie. Organiese wingerde het ’n groter getal insek-blom interaksies as konvensionele wingerde gehad, maar wingerde onder beide tipes van
bestuur was soortgelyk in terme van ander belangrike netwerk aanduiders. Netwerke van
wingerde was egter meer geklomp dan natuurlike gebiede wat aandui dat hulle potensieel
meer stabiel betreffende versteuring en lukrake uitsterwings is. Multivariate
verspreidingstoetse het aangetoon dat insek-blom interaksie netwerke by beide organiese en
konvensionele wingerde oor landskappe nie eenvormig was nie. Ek het ook bevind deur
aanvullende verdeling dat organiese en konvensionele wingerde gelykwaardig was in terme
van spesies kentering van bye en blomplante.
Die bevindings van hierdie studie verskaf heuristise waarde tot huidige debatte oor die
waarde van wingerdhabitatte vir insekbewaring. Beide organies en konvensionele wingerde
wat volhoubare bestuur van die nie-gewas plantegroei binne wingerdrye bevorder, is
moontlike oplossings vir die bewaring van blom-besoekende insekte en hulle wisselwerkings.
Bykomend moet aandag gegee word aan die kwaliteit en verbindings van en tussen natuurlike
habitat gebiede binne die KFS landboulandskap. Plekspesifieke (plaaslike) bestuur en
bepaling van die waarde van hierdie landskapelemente is belangrik. Bestuursbenaderings,
soos noukeurig beheerde brand, mag voordelig wees aangesien die KFS natuurlike
plantegroei ’n vuurgedrewe gemeenskap is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17980 |
| Date | 12 1900 |
| Creators | Kehinde, Temitope Olatayo |
| Contributors | Samways, Michael J., Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 155 p. : ill., maps |
| Rights | Stellenbosch University |
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