The natural drivers and the effects of landscape transformation for dragonflies of the Cape Floristic Region

Kietzka, Gabriella Joy (2016-03)

Thesis (MSc)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: The Cape Floristic Region (CFR) is a biodiversity hotspot. The region has three established biosphere reserves, which all aim to alleviate the impacts that land transformation has on ecosystem integrity, without jeopardizing basic human needs. In addition to its unique plant diversity, the CFR has high endemism levels of other taxa, including dragonflies. Dragonflies are useful bioindicators of freshwater quality, which has led to the development of the Dragonfly Biotic Index (DBI), a biomonitoring tool for freshwater. The combined pressures of urbanisation and agricultural expansion in the CFR are a major concern for rare, endemic dragonfly species, as well as for overall river ecosystem integrity. In view of this, my study aims to determine which variables drive lotic dragonfly diversity in the CFR, and to assess the effects that land transformation has on this diversity. I first determined which environmental parameters were consistently important so that they could be used as mesofilters to conserve dragonfly diversity (Chapter 2). Dragonfly assemblages and various environmental variables were recorded along the untransformed reaches of three CFR rivers. Heterogeneity of water parameters was found to be the most crucial variables for dragonfly assemblages and for affecting species richness. Here, heterogeneity is defined by the natural spatial and temporal variation of water temperature, dissolved oxygen, conductivity and pH. This differed from previous studies, which strongly suggest vegetation-related variables are the primary drivers of dragonfly diversity. However, these studies took place in transformed landscapes where the strong effects related to anthropogenic disturbances could override the importance of other more subtle natural variables. The maintenance of a gradient of water parameters, which accounts for the natural range of each of the selected water variables, would thus aid in the conservation of dragonflies in the CFR. I also investigated the effects of urbanization and agricultural development on dragonfly diversity and DBI scores. Land transformation homogenized dragonfly assemblages as some endemic species could not persist in these areas. However, species richness was not always reduced, because disturbance allowed for additional widespread, generalist species to enter the system. Dragonfly assemblages differed between agricultural and urban sites but these sites were more similar to each other than to undisturbed sites. Each river supported a unique dragonfly assemblage, making it important to conserve each individual river. Mitigating the adverse influences of landscape transformation is essential for the conservation of rare and endemic taxa, particularly in areas of high conservation value, and the DBI provided an effective way to assess ecosystem integrity in the region. In conclusion, land transformation negatively affects dragonfly diversity and ecosystem integrity in CFR rivers. Conservation efforts should aim to rehabilitate the natural heterogeneity of riparian ecosystems. However, conservation plans should not only focus on restoration of riparian vegetation, but also incorporate variation in water quality parameters. There is not a high possibility of reducing land transformation, with the requirements of an ever-increasing human population. An important alternative option, as I show here, is to protect ecological integrity within a biosphere reserve. The proclamation of more biosphere reserves in the CFR, that include other, additional river catchments, will allow for the conservation of more rare, endemic dragonflies and other taxa. Dragonfly assemblages and the DBI should be used in future monitoring programs and to guide conservation actions.

AFRIKAANSE OPSOMMING: Die Kaapse Floristiese Streek (KFR) is 'n biodiversiteit kernarea. Die streek besit drie gevestigde biosfeerreservate, wat poog om die impak van landtransformasie op die integriteit van ekosisteeme te verlig, sonder om basiese menslike behoeftes in gevaar te stel. Benewens sy unieke plantdiversiteit, het die die KFR ook besonderse hoë vlakke van ander endemisme taxa, insluitend naaldekokers. Naaldekokers is uiters nuttig as bioindikatos van varswater gehalte. Dit het geleei tot die ontwikkeling van die naaldekoker biotiese indeks (NBI), 'n biomoniterings hulpmiddel. Die gekombineerde druk vanaf verstedeliking en landbou-uitbreiding in die KFR is 'n groot bron van kommer vir die bewaring van skaars, endemiese naaldekokerspesies, sowel as vir algehele rivierekosisteem integriteit. In lig hiervan, het my studie gepoog om te bepaal watter spesefieke faktore naaldekokerdiversiteit dryf in die KFR. Die gevolge van land transformasie op hierdie diversiteit was ook geevalueer. Eerstens het ek bepaal watter omgewingsfaktore deurgaans belangrik is om naaldekoker diversiteit te bewaar (Hoofstuk 2). Naaldekoker gemeenskappe en verskeie omgewings-veranderlikes was aangeteken langs die ongetransformeerde areas van drie KFR riviere. Heterogeniteit van waterveranderlikes was bevind as die mees kritieke faktore wat naaldekoker gemeenskappe en spesierykheid bepaal. Hierdie resultate verskil van vorige studies wat gewys het dat plantegroei verwante veranderlikes die primêre oorsake van verandering van naaldekoker diversiteit is. Hierdie vorige studies was egter gefokus op getransformeerde landskappe waar die sterk effekte van menslike versteurings die belangrikheid van ander, meer subtiele, natuurlike faktore kon oorheers. Die instandhouding van 'n wye verskeidenheid water veranderlikes blyk dus om die behoud van die naaldekoker gemeenskappe in die KFR the bevorder. Ek het ook die gevolge van verstedeliking en landbouontwikkeling op die diversiteit van naaldekokers en die NBI bepaal. Landtransformasie het naaldekoker gemeenskappe gehomogeniseer deurdat sommige endemiese spesies nie kon bestaan in hierdie gebiede nie. Dit het egter nie altyd gepaard gegaan met ‘n vermindering in spesierykheid nie, want aandui dat addisionele, wydverspreide, generiese spesies versteurde habitatte binnedring. Naaldekoker gemeenskappe het tussen landbou en stedelike areas verskil, maar was steeds meer soortgelyk aan mekaar as aan ongestoorde areas. Elke rivier ondersteun 'n unieke naaldekoker gemeenskap, wat daarop wys dat dit belangrik is om elke individuele rivier te bewaar. Verligting van die negatiewe invloede van landskaptransformasie is noodsaaklik vir die bewaring van skaars en endemiese spesies, veral in gebiede van hoë bewaringswaarde. Die NBI verskaf 'n doeltreffende manier om die integriteit van die ekosisteem te evalueer in hierdie streek. Ten slotte, land transformasie beïnvloed naaldekoker diversiteit en die integriteit van die ekosisteem in KFR riviere negatief. Bewaring moet poog om die natuurlike heterogeniteit van die rivieroewer ekosisteme te rehabiliteer. Bewaring moet egter nie uitsluitlik fokus op die herstel van oewerplantegroei nie, maar moet ook poog om variasie in water faktore te inkorporeer. Vermindering van transformasie area is nie werklik haalbaar in die streek nie aangesien 'n toenemende menslike bevolking se vereistes ook toeneem. 'n Belangrike alternatiewe opsie, soos ek hier uitwys, is om te verseker dat die ekologiese integriteit binne biosfeerreservaate beskerm word. Die proklamasie van meer biosfeerreservate in die KFR, wat bykomende rivieropvanggebiede insluit, sal voorsiening maak vir die bewaring van meer seldsaame en endemiese naaldekokers, asook ander taxa. Naaldekoker gemeenskappe en die NBI behoort gebruik te word in toekomstige moniterings programme en kan dus bewaringsoptredes lei.

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