Response of grasshoppers to the agricultural mosaics of the Cape Floristic Region biodiversity hotspot in South Africa

Adu-Acheampong, Samuel (2017-03)

Thesis (PhDAgric)--Stellenbosch University, 2017.


ENGLISH ABSTRACT: Agricultural production is one of the main drivers of the on-going biodiversity crisis. This has resulted in research on the impact of agriculture on biodiversity being at an all-time high. This is critical given that the world must produce food for the ever-growing human population. This growing demand for food often demands increasing production areas at the expense of protected ones. Such trade-offs can potentially lead to dire consequences on biodiversity and its associated ecosystem function. In an attempt to minimise this potential negative impact, and also to conserve biodiversity and its associated ecosystem function, scientists and producers have developed a system that integrates natural with production patches as part of making agriculture more sustainable. In most instances, decisions on agro-natural schemes for sustainable food production are based on research conducted on larger animals at the expense of smaller ones, especially arthropods, even though they constitute the largest group of animals. If humans are to achieve the aim of producing food to meet the growing demand at minimum cost to the environment and biodiversity, studies on smaller animals such as insects, which constitute more than 75% of all animals, and are also major contributors of terrestrial ecosystem function in the terrestrial world, must be considered a high priority. An insect group that has much value for the purpose of designing agro-natural schemes is grasshoppers (Orthoptera, Acridoidea). This is because they show high sensitivity to changes in vegetation type and structure, and have high potential for expressing changes in environmental conditions and vegetation. This is even more important in a biodiversity hotspot which is also known for intensive agricultural production, such as the Cape Floristic Region (CFR). In view of that, I embarked on a study to document the footprint of agricultural production types on biodiversity using grasshoppers as keystone species in four studies making up my four core chapters. Firstly, I compared species richness, abundance, composition, diversity and evenness of grasshoppers among 46 sites in four geographical areas in the CFR. Here, I investigated three land-use types: fynbos, vineyards and deciduous fruit orchards, the main production types in the region. Results showed that grasshopper abundance were significantly higher in vineyards than in fynbos or orchards. Species richness, diversity, and evenness were highest in fynbos followed by vineyards and then orchards. There was overall high species similarity among all three land-use types, with high species assemblage similarities between vineyards and orchards. Species that preferred fynbos were mostly flightless and endemic to the CFR. In the second chapter, grasshopper abundance was studied under agricultural land-use (vineyards) and in natural vegetation (fynbos) across two peak seasons (spring vs. summer). This study aimed at quantifying the level at which different grasshopper species utilise the different aspects of the landscape and how this range of utilisation among species relates to certain species’ traits. My results showed that species traits play a major role in grasshoppers’ ability to move between patches, and which also affects how they utilize various different patches on the landscape. Highly mobile, generalist species are able to utilise more aspects of the landscape. And depending on seasonality, these species will inhabit either vineyards or fynbos aided by their high ability to move between patches. On the other hand, low mobility, specialists lack the ability to move readily between patches, and as a result, they are confined to one or a few patches across the seasons. In the third chapter, I developed species distribution models for four localized, CFR endemic flightless grasshopper species, Euloryma larsenorum and E. lapollai, E. umoja and E. ottei. The first two are associated with fynbos only, while E. umoja and E. ottei, the second two, are both associated with both fynbos and vineyards. I used the Maximum Entropy algorithm, which showed that vegetation type and soil characteristics were the most important environmental factors affecting local distribution of Euloryma species in the CFR. My models also showed that Euloryma species have very narrow, predicted, suitable habitats in the CFR. I also showed that there are no significant differences in the distribution of species associated with fynbos only as well as those associated with both fynbos and vineyards. Lastly, in the fourth chapter, I investigated grasshopper species assemblage composition on three land-uses across the agro-natural mosaic landscape of CFR. This study documented species’ level of occupancy and abundances in relation to their life history traits in order to assess the amount of change occurring on the landscape in the CFR. My results show that very few species, and mostly from Acrididae, dominated the landscape. It also shows that the species that dominated the transformed landscape were generalists. There was also a high correlation between generalists, high to medium mobility and widespread species on one hand, and specialists, low in mobility, and localised species on the other. Conclusions My study shows that protected areas still remain vital for maintaining the full complement of CFR grasshopper species, especially flightless endemics. I also show that highly mobile, generalist species are better adapted to heterogeneous and novel landscapes compared to low mobility specialists. Surprisingly, agricultural production supports a wide variety of species, and hence contributes positively towards grasshopper conservation in the CFR. This study further shows that it is the poorly-mobile, specialist species that are particularly vulnerable to ongoing landscape change as they can only benefit from remnant patches of natural vegetation, unlike the highly mobile generalists which can move around the landscape and benefit both from anthropogenic patches and natural ones. To reduce future biotic erosion and homogenisation, there should be concerted efforts to protect grasshopper groups which occur in low abundance in this biodiversity hotspot.

AFRIKAANS OPSOMMING: Landbouproduksie is een van die dryfvere agter die huidige biodiversiteitskrisis. Navorsing oor die impak van landbou op biodiversiteit is belangrik aangesien die wêreld moet aanhou om kos te produseer wat daartoe lei dat produksie areas dikwels groei ten koste van bewaarareas. Dit kan potensieel tot verdere verliese in biodiversiteit en ekosisteem funksie lei. In ‘n poging om die potensiele negatiewe impak van landbou te minimeer, het wetenskaplikes en produsente ‘n stelsel ontwikkel wat natuurbewaring en landbouproduksie integreer om landskappe meer volhoubaar te maak. In die meeste gevalle word besluite oor sulke agri-natuurskemas vir volhoubare voedselproduksie geneem op grond van groter diere eerder as kleineres, soos geleedpotiges, selfs al vorm laasgenoemde meer as 75% van alle diere op aarde, en speel hulle ‘n belangrike rol in die funksionering van terrestriële ekosisteme. As mense graag die doel wil bereik om die groeiende vraag na kos te beantwoord sonder om die omgewing beduidend te benadeel, moet studies oor kleiner diere soos insekte ‘n hoër prioriteit word. ‘n Groep insekte wat groot waarde het vir die ontwerp van agri-natuurstelsels is springkane (Orthoptera, Acridoidea). Hulle is sensitief vir veranderinge in plantegroeitipe en –struktuur, en weerspieël ook veranderinge in omgewingstoestande. In ‘n biodiversiteitshittekol wat bekend is vir sy intensiewe landbouproduksie, soos in die Kaapse Floristiese Streek (KFS), is dit selfs nog belangriker om hierdie klein diertjies in ag te neem wanneer ‘n mens na die integrasie van natuurbewaring en landbouproduksie kyk. In die lig hiervan, kyk hierdie studie na die effek van verskillende landproduksietipes op biodiversiteit deur te fokus op springkane as ‘n sleutel takson. In die eerste hoofstuk het ek spesiesrykheid, talrykheid, spesiesamestelling, diversiteit en getalgelykheid van springkane tussen 46 areas in vier geografiese areas in die Kaapse Floristiese Streek (KFS) vergelyk. Ek het na drie landsgebruiktipes gekyk: fynbos, wingerde, en vrugteboorde. Laasgenoemde twee landsgebruiktipes is ook die hoof produksietipes in die streek. Resultate dui aan dat springkane se talrykheid beduidend hoër is in wingerde as in fynbos of in vrugteboorde. Spesiesrykheid, diversiteit en getalgelykheid was egter die hoogste in fynbos, gevolg deur wingerde en dan vrugteboorde. Vrugteboorde het geen unieke spesies gehad nie, maar wingerde het twee, en fynbos het 14 unieke spesies gehad. Nogtans was daar ‘n hoë soortgelykheid in spesiessamestelling tussen die drie landsgebruiktipes, veral tussen wingerde en vrugteboorde. Spesies wat fynbos verkies het was meestal vlugloos en endemies tot die KFS. Ek wys uit hoe landboustreke nie die volle komplement van spesies in natuurlike fynbos ondersteun nie, maar dat wingerde wel meer divers as vrugteboorde is. Ek wys ook hoe wingerde ‘n goeie geleentheid bied vir harmonie tussen landbouproduksie en natuurbewaring deur verbetering in grondbedekking en ander landboupraktyke. Minder geleenthede bestaan in vrugteboorde aangesien hulle ‘n digte blaredak het, en nie gekenmerk word deur ‘n gras grondbedekking of fynbosplante nie. In die tweede hoofstuk het ons gekyk hoe springkane se talrykheid van wingerde en natuurlike plantegroei (fynbos) varieer oor twee piek seisoene (lente vs. somer) in die Kaapse Floristiese Streek (KFS). Die doel van die studie was om te bepaal watter springkaanspesies watter dele van die landskap gebruik, en hoe dit verband hou met spesiespesifieke kenmerke in die KFS. My resultate toon dat spesiespesifieke kenmerke ‘n groot rol speel in springkane se vermoë om te beweeg en verskillende kolle natuurlike plantegroei in die landskap te gebruik. Hoogs beweeglike, algemene voeder springkaanspesies kan meer dele van die landskap gebruik. Hulle kan tussen wingerde of fynbos beweeg, afhangende van die seisoensveranderinge. Aan die ander kant kan minder beweeglike spesialis springkaanspesies nie maklik tussen verskillende kolle nauurlike plantegroei beweeg nie. Hulle word grotendeels tot een of ‘n paar kolle beperk oor verskeie seisoene. In die derde hoofstuk, ontwikkel ek ‘n spesiesverspreidingsmodel vir vier gelokaliseerde, vluglose springkaanspesies (Euloryma larsenorum and E. lapollai, E. umoja and E. ottei) wat endemies is tot die Kaapse Floristiese Streek (KFS). Die eerste twee assosieer slegs met fynbos, maar die ander twee (E. umoja and E. ottei) bewoon fynbos sowel as wingerde. Ek het die Maksimum Entropie algoritme gebruik wat getoon het dat plantegroeitipe en grondkenmerke die belangrikste omgewingsfaktore was wat verspreiding van hierdie vier spesies beinvloed het. My modelle het voorspel dat hulle ‘n baie nou geskikte habitat in die KFS het. Daar was geen beduidende verskil in die verspreiding van spesies wat met slegs fynbos, of met fynbos en wingerde geassosieer is nie. Beduidende pogings tot die bewaring van Euloryma spesies is nodig in die KFS, veral aangesien hulle geskikte habitat mag krimp in die geval van globale veranderinge. Omdat E. larsenorum en E. lapollai baie sensitief is vir veranderinge in die landskap vanaf fynbos na landbou, behoort hulle bewaring geprioritiseer word. Dit is onwaarskynlik dat die ander twee spesies (E. umoja en E. ottei) tot dieselfde mate beïnvloed sal word aangesien hulle kan oorleef in die huidige landbou omgewing. Laastens, in die vierde hoostuk, oorweeg ek springkane se spesiesamestelling in drie landsgebruikstipes binne die agri-natuur mosaieklandskappe van die Kaapse Floristiese Streek (KFS). Ek het na spesies se vlak van okkupasie en talrykheid gekyk binne die konteks van spesiespesifieke kenmerke sodat ‘n mens ‘n beter idee kan kry van verandering wat binne die landskap gebeur. My resultate toon dat slegs ‘n klein hoeveelheid spesies (meestal Acrididae) die landskap domineer. Dit het ook getoon dat dominante spesies algemene voeders was. Daar was ‘n hoë korrelasie tussen algemene voeders, matige tot hoogs mobiele, en wydverspreide spesies aan die een kant, en spesialisvoeders wat minder beweeglik en gelokaliseerd is aan die ander kant. Gevolgtrekkings My studie het getoon dat bewaarareas belangrik bly om die volle komplement van springkane in die Kaapse Floristiese Streek (KFS) te bewaar. Dit is veral so vir vluglose endemiese spesies, want hulle het die nouste verspreidings en is baie sensitief vir antropologiese veranderinge. Ek het ook gewys dat hoogs beweeglike, algemene voeders beter aangepas is vir heterogene en nuwe landskappe as spesialisvoeders wat minder beweeglik is. Landbouproduksie areas ondersteun ‘n wye verskeidenheid spesies, en dra dus positief by tot die bewaring van springkane in die KFS. Hoogs beweeglike algemene voeders kan oor die hele landskap beweeg en baatvind by landbouproduksie en natuurlike kolle plantegroei, terwyl hulle optimeer vir seisoensveranderinge. Dit is meestal die minder beweeglike spesialisvoeders wat kwesbaar is vir veranderinge in die landskap, want hulle kan slegs oorblywende kolle natuurlike plantegroei bewoon. Die Euloryuma genus kan moontlik gebruik word as bio-indikatore vir grondstudies in die KFS. Om verdere vereenvoudiging van insekgroepe te verhoed moet daar gepoog word om springkaangroepe wat natuurlik teen lae getalle voorkom, te bewaar.

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