Linking zooplankton richness with energy input and insularity along altitudinal and latitudinal gradients

Abstract

Altitudinal and latitudinal gradients are excellent venues for investigating the direct and indirect effects of air temperature, solar irradiance, and insularity on spatial patterns of aquatic biodiversity. The findings can be used to predict how lake communities will respond to increasingly extreme climate events. We explored hypotheses of energy/climate, geography, and glacial history explaining patterns in species richness in a historical dataset of crustacean zooplankton communities from 436 lakes in the Canadian Rocky Mountains. GIS-based estimates of solar and thermal energy inputs combined with habitat area and insularity provided the best prediction of local species richness. Energetic and geographic factors explained a moderate proportion of the total variation in species richness (Generalized R 2 5 0.50), and were sufficient to account for both altitudinal and latitudinal gradients in zooplankton diversity. History of deglaciation was not supported as a predictor of patterns in species richness. A post hoc analysis with a smaller dataset also found strong support for lake pH, and some support for fish presence as predictors of species richness, but these only increased the proportion of the total variation explained very slightly relative to the model including only energetic and geographic factors (Generalized R 2 5 0.55 vs. 0.53). Our findings highlight the multiplicity of local and regional factors of zooplankton species richness in mountain lakes, forecasting that it will increase under a scenario of warmer and drier (i.e., less cloud cover) conditions, especially in high connectivity lakes that cease to be fed by rapidly disappearing glaciers.Lakes and ponds are increasingly viewed as sentinels of global change as they integrate the cumulative impacts of local and regional anthropogenic perturbations (i.e., stressors) on their whole catchments (Williamson et al. 2009). Remote mountain lakes are particularly useful because of the absence of local stressors, which can often obscure the effects of larger-scale human pressures, which can be subtle, but potentially more powerful and persistent in the long-term (Catalan et al. 2013). Moreover, their characteristic cold temperature, dilute chemistry, insularity, and low biocomplexity cause alpine lakes to be acutely sensitive to anthropogenic stressors (Hauer et al. 1997;Vinebrooke and Leavitt 2005).Understanding the factors of past and current spatial patterns of aquatic biodiversity is key to accurate forecasting how these patterns will respond to future environmental changes. Many hypotheses exist to explain how the interplay between immigration, speciation, and extinction determines patterns of species richness; there are more than 30 potential explanations for latitudinal gradients in species richness and hypotheses for altitudinal gradients are similarly diverse (Willig et al. 2003;McCain and Grytnes 2010). Recently, several hypotheses relating species richness to energy and climate have become prominent in the ecological literature, reflecting meta...

Macroecological drivers of zooplankton communities across the mountains of western North America

“…As chief herbivores of the pelagic zone, zooplankton both regulate primary production and support higher aquatic organisms, including planktivorous fish and insect larvae. Given sufficient time, chance dispersal should permit zooplankton species sorting over vast geographic extents (Lyons andVinebrooke 2016, Heino et al 2017a); however, species may be differentially affected by dispersal limitation based on their functional traits. Given sufficient time, chance dispersal should permit zooplankton species sorting over vast geographic extents (Lyons andVinebrooke 2016, Heino et al 2017a); however, species may be differentially affected by dispersal limitation based on their functional traits.…”

“…In addition, we expected that spatially structured catchment features would account for a significant fraction of the residual variation in community composition not captured by climate, given the high degree of natural environmental heterogeneity characterizing our study region. Further, since many mountain lakes are remote and insular because of large topographic barriers (Lyons and Vinebrooke 2016), we hypothesized that habitat connectivity would explain a substantial portion of beta-diversity attributable to species dispersal limitation. Further, since many mountain lakes are remote and insular because of large topographic barriers (Lyons and Vinebrooke 2016), we hypothesized that habitat connectivity would explain a substantial portion of beta-diversity attributable to species dispersal limitation.…”

“…Mountain ecosystems are fertile grounds to test fundamental hypotheses in macroecology and the biogeographic origins of species diversity patterns (Fjeldså et al 2012, Lyons and Vinebrooke 2016, Liu et al 2018. Environmental heterogeneity is pronounced in mountain regions, as climatic shifts along elevational gradients amplify spatial variations in temperature, precipitation, solar radiation, and regional land cover characteristics.…”

“…Passive overland dispersal by wind and animal vectors maintains connectivity among isolated habitats (Vanschoenwinkel et al 2008), especially along major migratory routes such as the Pacific Flyway over western North America (Viana et al 2016b). Given sufficient time, chance dispersal should permit zooplankton species sorting over vast geographic extents (Lyons andVinebrooke 2016, Heino et al 2017a); however, species may be differentially affected by dispersal limitation based on their functional traits. For instance, species capable of cyclic parthenogenesis (i.e.…”

“…Localized stocking of mountain lakes with sportfish (Crawford and Muir 2008) was also expected to help explain zooplankton variation owing to intensive size-selective predation (Loewen and Vinebrooke 2016). Further, since many mountain lakes are remote and insular because of large topographic barriers (Lyons and Vinebrooke 2016), we hypothesized that habitat connectivity would explain a substantial portion of beta-diversity attributable to species dispersal limitation. Thus, we applied a functional approach to explore the roles of key species' traits (body size and reproductive potential) in explaining community composition patterns in the context of hypothesized ecological mechanisms involving metabolic theory, predation, and dispersal limitation.…”