Untangling mechanisms structuring insect diversity patterns in the Cape Floristic Region : the Restionaceae and their herbivores

Kemp, Jurene Ellen (2014-12)

Thesis (MSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: Research into the patterns and drivers of insect diversity in the Cape Floristic Region (CFR) lags far behind that of plants. Here I sample insect herbivore communities on a dominant plant family (Restionaceae), and use a spatially nested sampling design and network analysis to evaluate the association between plant and insect diversity in the CFR. I find that plant species richness predicts insect richness better than environmental factors. Turnover in insect communities is strongly associated with turnover in plant (both species and phylogenetic) communities at both local and regional sampling scales, suggesting insect host specificity. Plant communities unsurprisingly show significant turnover at small spatial scales (i.e. communities situated 0.1-3 km apart show significant turnover and may be tied to ecological niches). Insects show a similar pattern, but the decrease in community overlap is more gradual, suggesting many insects can utilise multiple (possibly closely related) hosts while plants are tied to particular niches. The emergent structure of multiple interaction networks is spatially and temporally invariant, despite high compositional change. However, the internal structure of the networks shows variation (i.e. interactions show spatial and temporal turnover). Seasonal interaction turnover is driven by a turnover in herbivores and by herbivore host switching. Spatially the turnover in interactions is driven by simultaneous turnover in both plants and insects, either suggesting that insects are host specific, or that both groups exhibit parallel responses to environmental gradients. Spatial interaction turnover is also driven by a turnover in plants, showing that many insects can utilise multiple (possibly closely related) hosts and have wider distribution ranges than their host plants. Results point toward insect host specificity, but probably not at the species level, as the primary mechanism structuring insect communities associated with the Restionaceae in the CFR.

AFRIKAANSE OPSOMMING: Navorsing wat verband hou met die patrone en meganismes wat insekdiversiteit in the Kaapse Blommeryk (KBR) hou nie pas met dié van plante nie. In hierdie studie neem ek insekmonsters binne een van die dominante plantfamilies (Restionaceae), en gebruik ‘n ruimtelik geneste ontwerp en netwerkanalise om die verbintenis tussen plant- en insekdiversiteit te evalueer. Ek vind plantrykheid voorspel insekrykheid beter as enige omgewingsfaktore. ‘n Omset in in insekgemeenskappe is sterk verbind aan ‘n omset in plantgemeenskappe (beide spesie en filogenetiese) by beide plaaslik en vir die hele streek. Hierdie dui op insekgasheerspesifisiteit. Plantgemeenskappe wys omset teen kort ruimtelike skale (0.1-3 km). Insekte wys ‘n soortgelyke patron, maar die afname in oorvleueling tussen gemeenskappe is meer geredelik. Dit dui dat insek meer as een gasheer kan gebruik, terwyl plante streng tot sekere nisse verbind is. Die ontluikende struktuur van menigde interaksienetwerke wys geen ruimtelike of tydelike variasie nie, ten spyte van hoë gemeenskapsomset. Nietewel, die interne struktuur van die netwerke wys veranderinge (interaksies in netwerke wys omset). Seisonale interaksie-omset kan toegeskryf word aan ‘n omset van herbivore en insekgasheerverandering. Ruimtelike interaksie-omset word toegeskryf aan gelyktydige insek- en plantomset, wat óf deur insekgasheerspesifisiteit veroorsaak word óf deur parallele reaksies tot omgewingsveranderinge. Ruimtelike interaksie-omset word ook deur plantomset beïnvloed, wat aandui sommige insekte kan meer as een gasheer benut en insekte het weier verspreidings as hul gasheer. Resultate dui daarop dat insekgasheerspesifisiteit, maar waarskynlik nie op die spesievlak nie, moontlik die primêre meganisme is wat insekgemeenskappe verbind aan die Restionaceae in die KBR struktureer.

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