Scaling patterns and drivers of species richness and turnover across the Afrotropics

Bailey, Junior Curtis (2017-03)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Understanding the broad scale patterns and environmental determinants of amphibian richness (α-diversity) and turnover (β-diversity) is becoming ever more crucial as communities, ecosystems and landscapes are increasingly threatened by anthropogenic processes and climate change. Spatial scale, the grain at which sampling takes place or analysis occurs, confounds understanding of such diversity patterns and the relationships these exhibit with environmental processes. This is because various processes operate at different spatial scales resulting in different patterns emerging at different spatial scales. This is problematic, because patterns, and pattern-process’ relationships which emerge at one scale may not hold at another scale thereby confounding our understanding of how biotic patterns are generated and maintained, thus leading to misguided conservation strategies and policies. The focus of the present study was thus to examine the relationship between present patterns of anuran richness and turnover, the relationship of these with several contemporary environmental processes, and how these patterns and pattern-process relationships are influenced by spatial grain. Using IUCN range data for the Afrotropical region, amphibian richness and turnover patterns were generated using a Geographic Information System and quantified using the recently formulated zeta diversity partitioning method (ζ). These patterns were then related to several contemporary environmental variables/processes hypothesised to govern amphibian diversity across a range of spatial scales using both the global Ordinary Least Squares (OLS) method and local spatial Geographically Weighted Regression (GWR) across three nested spatial grains. The results show that amphibian richness and turnover patterns (visual & empirical) and the relationships these exhibit with environmental conditions were sensitive to spatial grain. Visually, spatial patterns were more distinct at finer grains, but visibly smooth at the coarser grains. The statistics describing these patterns suggest that the scaling behaviour follows an increasing linear and nonlinear trend across spatial grain. Results from both the OLS and GWR models confirm that contemporary environmental conditions are significant determinants of both anuran richness and turnover patterns across spatial grain. Precipitation was the strongest determinant of anuran richness while topographic complexity best explained turnover. The relationship between both diversity components and environmental conditions, however, was scale dependent with environmental conditions explaining a greater proportion of the variation in these biotic patterns at coarser than finer grains. Studies conducted across multiple grains is thus recommended to improve current understanding of biodiversity patterns and the relationship they exhibit with environmental processes.

AFRIKAANS OPSOMMING: Dit word al hoe meer noodsaaklik om die grootskaalse patrone en omgewingsdeterminante van amfibiese rykdom (α-diversiteit) en omset (β-diversiteit) te verstaan soos gemeenskappe, ekosisteme en landskappe bedreig word deur mensgemaakte prosesse en klimaatsverandering. Ruimetelike skaal, die grein waarteen monstering of analise plaasvind, verydel die begrip van sulke diversiteitspatrone en die verwantskappe wat vertoon word met omgewingsprosesse. Dit is omdat verskillende prosesse teen verskillende ruimtelike skale funksioneer wat daartoe lei dat verkillende patrone na vore kom teen verskillende ruimtelike skale. Dit is problematies omdat patrone en patroonproses verwantskappe wat teen ‘n sekere skaal na vore kom nie noodwendig teen ‘n ander skaal geld nie. Dit verydel die begrip van hoe biotiese gegenereer en in stand gehou word. En lei daartoe dat misleidende bewaringsstrategieë en -beleide geïmplementeer word. Die fokus van hierdie studie was dus om die verwantskap tussen huidige patrone van amfibiese rykheid en omset, die verhouding hiervan met verskeie kontemporêre omgewingsprosesse, en hoe hierdie patrone en patroonproses verhoudings in stand gehou word oor die ruimtelike grein te ondersoek. IUCN data vir die Afrotropiese gebied is gebruik om amfibiese rykheid en omsetpatrone te ondersoek met behulp van Geografiese Inligtingstelsels (GIS) en die onlangs-geformuleerde zeta diversiteit partisioneringstegniek (ζ). Hierdie patrone is dan verbind met verskeie kontemporêre omgewingsveranderlikes of omgwingsprosesse, wat veronderstel is om amfibiese diversiteit te reguleer, oor verskeie ruimtelike skale deur gebruik te maak van gewone kleinste kwadrate (GKK) en plaaslike geografies-geweegde regressie (GGR) oor drie ruimtelile skale. Die resultate toon dat amfibiese rykheid en omsetpatrone (visueel en empiries), en die verwantskap wat dit toon tot omgewingstoestande, sensitief is vir ruimtelike grein. Ruimtelike patrone was meer opmerklik teen ‘n fyner grein, maar word meer geleideli/gladder teen ‘n growwer grein. Die statistiek van die patrone dui daarop dat die skaleringseienskappe ‘n verhoogde lineêre-, mags- en eksponensiële neiging volg met verhoogde ruimtelike grein resultate van beide die GKK en GGR modelle bevestig dat kontemporêre omgewingstoestande beduidende determinante is van amfibiese rykheid en omsetpatrone. Reënval was die sterkste determinant van amfibiese rykheid en topografiese kompleksiteit het die beste verklaring gebied vir omset. Die verwantskap tussen diversiteitskomponente en omgewingstoestande was afhanklik van skaal met omgewingstoestande wat ‘n groter gedeelte van die afwyking in die biotiese patrone teen growwer as teen fyner greine verklaar. Dit word dus aanbeveel dat Stellenbosch toekomstige studies wat diversiteit patrone en hul verwantskap met omgwewingsprosesse ondersoek so doen oor verskeie ruimtelik skale om die huidiglike begrip daarvan te verbeter.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100911
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