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Do pinch points and barriers affect functional connectivity for butterflies and grasshoppers across networks of conservation corridors?
Thesis (PhDConsEcol)--Stellenbosch University, 2025.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613899522572288 |
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| access_status_str | Open Access |
| author | Davids, Liaam |
| author2 | Pryke, James Stephen |
| author_browse | Davids, Liaam Pryke, James Stephen |
| author_facet | Pryke, James Stephen Davids, Liaam |
| author_sort | Davids, Liaam |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhDConsEcol)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/134583 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:43:28.625Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/134583 Do pinch points and barriers affect functional connectivity for butterflies and grasshoppers across networks of conservation corridors? Davids, Liaam Pryke, James Stephen Samways, Michael John Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology & Entomology. Butterflies -- Ecology -- South Africa -- KwaZulu-Natal Midlands Grasshoppers -- Ecology -- South Africa -- KwaZulu-Natal Midlands Biodiversity conservation -- South Africa Insects -- Effect of habitat modification on Landscape ecology -- South Africa -- KwaZulu-Natal Corridors (Ecology) -- South Africa -- KwaZulu-Natal Midlands UCTD Thesis (PhDConsEcol)--Stellenbosch University, 2025. Davids, L. 2025. Do pinch points and barriers affect functional connectivity for butterflies and grasshoppers across networks of conservation corridors? Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/5fe20427-34e8-4c56-a4c5-cb95d174d9b2 ENGLISH ABSTRACT: Commercial forestry production landscapes have transformed and fragmented natural and semi-natural grasslands in South Africa, putting insect biodiversity at risk. However, these landscapes have incorporated large and extensive conservation corridor networks to mitigate the effects of timber stands. These set-aside networks of corridors provide natural habitat that allows movement and dispersal. The structural layout of these corridors may not be enough for long-term persistence of insects such as butterflies and grasshoppers. Corridors are wide for much of their length, although there are localized reductions in corridor width (pinch points) as well as structurally disconnected corridors (cul-de-sacs) which have the potential to restrict movement of species by funnelling individuals through smaller spaces or even acting as a physical barrier. This thesis investigates the role that these two localized structural changes have on shaping butterfly and grasshopper diversity and functional connectivity within a timber-grassland mosaic. Specifically, I assess whether there are changes in butterfly and grasshopper taxonomic diversity when exposed to different corridor local configurations (i.e., the pinch points and cul-de-sacs) through local changes in environmental conditions. I also investigate the effect of corridor configuration and composition on butterfly behaviour, trait selection, and functional diversity. Lastly, I use satellite derived imagery in combination with machine-learning algorithms to model butterfly species distribution and functional connectivity across these conservation corridors. Sampling was undertaken across various Pinus plantation estates within the KwaZulu-Natal Midlands, South Africa. Pinch points were categorized in narrow or wide based on their average width, while cul-de-sacs were characterized by only having one entrance/exit (i.e. a dead end). Extensive open grassland patches were used as reference for comparison. Potentially important environmental variables within sites were vegetation cover type and extent, and the presence of certain landscape features. Cul-de-sacs significantly reduced butterfly and grasshopper taxonomic diversity by decreasing overall structural connectivity and habitat quality. In contrast, narrow and wide pinch points supported more butterfly functional groups and promoted key resource and movement behaviours, while open grassland patches were critical for grassland-specific butterflies. Regardless of pinch point width, structural connectedness provides more microhabitats, encourages resource use, and facilitates movement better than cul-de-sacs. Overall, I provide evidence that these corridors provide adequate levels of functional connectivity. However, cul-de-sacs may act as an ecological trap due to their less available habitat and higher cover of invasive plants, especially Rubus cuneifolius. Additionally, I show that habitat heterogeneity is an important predictor for butterfly assemblages, especially in relation to floral cover, rockiness, topography, and vegetation productivity. Here I demonstrate the importance of using multiple measures of diversity (taxonomic and functional) while staying contemporary with recent advancements in ecological methods (deep-learning modelling of remotely sensed data), to fully understand insect responses to landscape change. There is value in maintaining a landscape mosaic that contains both configurational and compositional heterogeneity but only when there is sufficient structural connectivity. Not only does this heterogeneity promote resource use and movement (i.e., functional connectivity) for variety of species and functional groups, but it also potentially allows their long-term persistence in the landscape. AFRIKAANSE OPSOMMING: Kommersiële bosbouproduksielandskappe het natuurlike en semi-natuurlike grasvelde in Suid-Afrika hervorm en gefragmenteer, wat die biodiversiteit van insekte in gevaar stel. Hierdie landskappe het egter groot en uitgebreide bewaringsgang-netwerke inkorporeer om die effekte van boomplantasies te versag. Hierdie uitgesette bewaringsgange bied natuurlike habitatte wat beweging en verspreiding van organismes moontlik maak. Vir insekte soos skoenlappers en sprinkane, mag hierdie gange egter nie voldoende wees vir hul langtermyn voortbestaan nie. Bewaringsgange is meestal wyd, hoewel daar soms plaaslike vernouinge (knelpunte), asook strukturele ontkoppelde bewaringsgange (doodlooppunte) is, wat die beweging van spesies kan beperk deur individue deur kleiner ruimtes te kanaliseer, of selfs as fisiese hindernisse op te tree. Hierdie tesis ondersoek die rol wat hierdie twee plaaslike strukturele veranderinge speel in die hervorming van skoenlapper- en sprinkaan-diversiteit, asook hul funksionele verbindings binne ’n boomplantasie en grasveld mosaïek-landskap. Spesifiek evalueer ek of daar veranderinge in taksonomiese diversiteit van skoenlappers en sprinkane is wanneer hulle blootgestel word aan verskillende plaaslike rangskikkings van bewaringsgange (d.w.s. knelpunte en doodlooppunte) deur middel van plaaslike veranderinge in omgewingstoestande. Ek ondersoek ook die effekte van gangrangskikking en -samestelling op skoenlappergedrag, kenmerkseleksie en funksionele diversiteit. Laastens gebruik ek satelliet-afgeleide beeldmateriaal gekombineerd met masjienleer-algoritmes om skoenlapperspesieverspreiding en funksionele verbindings oor bewaringsgange te modelleer. Monsters is ingesamel oor verskeie Pinus-plantasie landgoedere in die KwaZulu-Natalse Middellande, Suid-Afrika. Knelpunte is gekategoriseer as smal of wyd gebaseer op hul gemiddelde wydte, terwyl doodlooppunte gekenmerk is deur slegs een ingang/uitgang (d.w.s. ’n doodlooppunt). Uitgebreide oop grasveldgebiede is as verwysings gebruik tydens vergelykings. Moontlike belangrike omgewingsveranderlikes binne liggings was die tipe en omvang van plantebedekking, en die teenwoordigheid van sekere landskapskenmerke. Doodlooppunte het die taksonomiese diversiteit van skoenlappers en sprinkane aansienlik verminder deur algehele strukturele verbinding en habitatgehalte te verlaag. Daarteenoor het smal en wye knelpunte meer funksionele groepe van skoenlappers ondersteun en sleutelhulpbron- en bewegingsgedrag bevorder, terwyl oop grasveldgebiede krities was vir skoenlappers spesifiek tot grasvelde. Afgesien van die wydte van knelpunte, bied hierdie landskapselemente strukturele verbinding en meer mikrohabitatte, dit bevorder hulpbronbenutting, en ondersteun beweging beter in vergelyking met doodlooppunte. Oorheersend, verskaf ek bewyse dat hierdie bewaringsgange voldoende vlakke van funksionele verbinding bied. Doodlooppunte kan egter as ’n ekologiese lokval optree weens hul laer vlakke van beskikbare habitat en hoër bedekking van indringerplante, veral Rubus cuneifolius. Verder toon ek dat habitat-ongelyksoortigheid skoenlappergemeenskappe kan voorspel, veral met betrekking tot blombedekking, rotsagtigheid, topografie en plant-produktiwiteit. Hier demonstreer ek die belangrikheid van die gebruik van verskeie maatstawwe van diversiteit (taksonomies en funksioneel) terwyl ek tred hou met onlangse vooruitgang in ekologiese metodes (diep-leermodellering van satelliet-afgeleide beeldmateriaal data), om insektreaksies op landskapverandering ten volle te verstaan. Daar is waarde in die behoud van ’n landskapmosaïek wat ongelyksoortigheid van beide landskapsrangskikking en -samestelling bevat, maar slegs wanneer daar voldoende strukturele verbinding is. Hierdie ongelyksoortigheid bevorder nie net hulpbronbenutting en beweging (d.w.s. funksionele verbinding) vir ’n verskeidenheid van spesies en funksionele groepe nie, maar dit maak ook hul langtermynvoortbestaan in die landskap moontlik. Doctoral 2025-12-15T09:30:23Z 2025-12-15T09:30:23Z 2025-12 Thesis https://scholar.sun.ac.za/handle/10019.1/134583 en Stellenbosch University xvi, 138 pages : illustrations, maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Butterflies -- Ecology -- South Africa -- KwaZulu-Natal Midlands Grasshoppers -- Ecology -- South Africa -- KwaZulu-Natal Midlands Biodiversity conservation -- South Africa Insects -- Effect of habitat modification on Landscape ecology -- South Africa -- KwaZulu-Natal Corridors (Ecology) -- South Africa -- KwaZulu-Natal Midlands UCTD Davids, Liaam Do pinch points and barriers affect functional connectivity for butterflies and grasshoppers across networks of conservation corridors? |
| title | Do pinch points and barriers affect functional connectivity for butterflies and grasshoppers across networks of conservation corridors? |
| title_full | Do pinch points and barriers affect functional connectivity for butterflies and grasshoppers across networks of conservation corridors? |
| title_fullStr | Do pinch points and barriers affect functional connectivity for butterflies and grasshoppers across networks of conservation corridors? |
| title_full_unstemmed | Do pinch points and barriers affect functional connectivity for butterflies and grasshoppers across networks of conservation corridors? |
| title_short | Do pinch points and barriers affect functional connectivity for butterflies and grasshoppers across networks of conservation corridors? |
| title_sort | do pinch points and barriers affect functional connectivity for butterflies and grasshoppers across networks of conservation corridors |
| topic | Butterflies -- Ecology -- South Africa -- KwaZulu-Natal Midlands Grasshoppers -- Ecology -- South Africa -- KwaZulu-Natal Midlands Biodiversity conservation -- South Africa Insects -- Effect of habitat modification on Landscape ecology -- South Africa -- KwaZulu-Natal Corridors (Ecology) -- South Africa -- KwaZulu-Natal Midlands UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/134583 |
| work_keys_str_mv | AT davidsliaam dopinchpointsandbarriersaffectfunctionalconnectivityforbutterfliesandgrasshoppersacrossnetworksofconservationcorridors |