Abstract
Many macroecological patterns of biodiversity, including the relationship between latitude and species richness, are well-described. Data collected in a repeatable, standardized manner can advance the discipline beyond the description of patterns and be used to elucidate underlying mechanisms. Using standardized field methods and a hyper-diverse focal taxon, viz. Coleoptera, we aim to (1) describe large-scale latitudinal patterns of taxonomic diversity, functional diversity, and assemblage structure across northern Canada, and (2) determine which climatic, spatial, and habitat variables best explain these patterns. We collected terrestrial beetles at twelve locations in the three northernmost ecoclimatic zones in North America: north boreal, subarctic, and high arctic (51–81°N, 60–138°W). After identifying beetles and assigning them to a functional group, we assessed latitudinal trends for multiple diversity indices using linear regression and visualized spatial patterns of assemblage structure with multivariate ordinations. We used path analysis to test causal hypotheses for species and functional group richness, and we used a permutational approach to assess relationships between assemblage structure and 20 possible climatic and environmental mechanisms. More than 9,000 beetles were collected, representing 464 species and 18 functional groups. Species and functional diversity have significant negative relationships with latitude, which are likely explained by the mediating effects of temperature, precipitation, and plant height. Assemblages within the same ecoclimatic zone are similar, and there is a significant relationship between assemblage structure and latitude. Species and functional assemblage structure are significantly correlated with many of the same climatic factors, particularly temperature maxima and minima. At a large spatial extent, the diversity and assemblage structure of northern beetles show strong latitudinal gradients due to the mediating effects of climate, particularly temperature. Northern arthropod assemblages present significant opportunities for biodiversity research and conservation efforts, and their sensitivity to climate make them ideal targets for long-term terrestrial diversity monitoring.
Highlights
Macroecologists have successfully described large-scale spatial patterns of biodiversity and species distributions
Our data have provided a valuable test of macroecological diversity patterns and their underlying processes across the three northernmost ecoclimatic zones of North America
We collected over 9,000 beetles from diverse taxonomic and functional groups, and demonstrated that beetles conform to classical latitudinal gradients of diversity
Summary
Macroecologists have successfully described large-scale spatial patterns of biodiversity and species distributions. The latitudinal gradient of species richness, in which fewer species are found at high latitudes compared to at the equator, has captivated researchers for many decades [1]. The search for likely mechanisms has been challenging, and a broad range of climatic, evolutionary, biotic, and spatial hypotheses have been put forth, reviewed by [3], no single factor has been identified as a key mechanism. It is highly likely that the number of species found at different latitudes, and the way these species assemble over space and time, is the result of multiple interacting ecological and evolutionary factors [6, 7]. Despite the challenge of teasing apart the relative contributions of different factors to patterns of diversity, climate—in particular, temperature—has been broadly recognized as a key element in both terrestrial and aquatic systems [8,9,10] and is worthy of additional testing
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