Patterns and drivers of terrestrial arthropod biodiversity in northern Canada

The overarching goal of this thesis was to describe patterns of terrestrial arthropod biodiversity and community structure in northern Canada, and to explore the underlying drivers and mechanisms that are responsible for these patterns. The term “biodiversity” is used here in a broad sense that includes both taxonomic (TD) and functional (FD) diversity. Ground-dwelling arthropods, especially beetles (Coleoptera), were used as model taxa, and were collected using standardized methods from twelve locations in the three northernmost ecoclimatic zones of Canada. Beetle biodiversity changes over time and space. Over the course of one active season, rapid species and functional turnover were observed in two major habitats in one subarctic location (Kugluktuk, Nunavut). While some functional groups were apparent only for brief periods of time, entomophagous predators consistently dominated the assemblage structure in biomass and abundance. This dominance by carnivores was observed consistently throughout the study, regardless of spatial or taxonomic scope. This inverted trophic structure suggests that predators may rely on alternative, non-epigeic prey items. A natural history study of previously unknown host-parasite interactions between beetles and nematomorphs (Gordionus n. sp.) suggests that beetles use alate insects with aquatic larval stages as an important nutrient subsidy. Across the entire study region, beetle TD and FD, as well as overall assemblage structure, display strong negative relationships with latitude, which conforms to the classical latitudinal gradient of diversity. After considering many spatial, environmental and climatic variables, the most significant driver of beetle biodiversity and assemblage structure over time and space was climate, particularly temperature. When the taxonomic scope of the research was expanded to include all ground-dwelling macroarthropod taxa, and the functional scope refined with a multidimensional functional trait-based approach, the same patterns and processes were observed. Additionally, it was found that functional redundancy was greater in the high arctic than in the warmer ecoclimatic zones further south, despite a paucity of taxa in the high arctic. This supports the hypothesis that environmental constraints are more important in regions with harsh climates, and play a greater role in diversity and community assembly processes than niche differentiation. The biodiversity (TD and FD) and structure of terrestrial macroarthropod communities in northern Canada have several consistent patterns: (1) large-scale negative relationships between biodiversity/assemblage structure and latitude; (2) strong correlations between TD and FD; and (3) the dominance of active predatory taxa. The most important finding of this study is that climate (temperature) gradients provide the best explanation for the variability observed in arthropod biodiversity and assemblage structure over time and across space. Lastly, the effects of climate on biodiversity and community assembly seem to be more pronounced in the high arctic than in more southerly biomes. Given the rapid and significant rise in temperature projected for northern biomes and the fact that predatory taxa are often more sensitive to changes in their environments, major changes to arthropod diversity are expected in the north, with implications for the stability of northern ecosystems.  

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