Regional zooplankton dispersal provides spatial insurance for ecosystem function

Abstract

Changing environmental conditions are affecting diversity and ecosystem function globally. Theory suggests that dispersal from a regional species pool may buffer against changes in local community diversity and ecosystem function after a disturbance through the establishment of functionally redundant tolerant species. The spatial insurance provided by dispersal may decrease through time after environmental change as the local community monopolizes resources and reduces community invasibility. To test for evidence of the spatial insurance hypothesis and to determine the role dispersal timing plays in this response we conducted a field experiment using crustacean zooplankton communities in a subarctic region that is expected to be highly impacted by climate change - Churchill, Canada. Three experiments were conducted where nutrients, salt, and dispersal were manipulated. The three experiments differed in time-since-disturbance that the dispersers were added. We found that coarse measures of diversity (i.e. species richness, evenness, and Shannon-Weiner diversity) were generally resistant to large magnitude disturbances, and that dispersal had the most impact on diversity when dispersers were added shortly after disturbance. Ecosystem functioning (chl-a) was degraded in disturbed communities, but dispersal recovered ecosystem function to undisturbed levels. This spatial insurance for ecosystem function was mediated through changes in community composition and the relative abundance of functional groups. Results suggest that regional diversity and habitat connectivity will be important in the future to maintain ecosystem function by introducing functionally redundant species to promote compensatory dynamics.

Can dispersal buffer against salinity‐driven zooplankton community change in Great Plains' lakes?

“…The same pattern of rising salinity levels during periods of draught can be found for other lakes on the Great Plains, with some reaching values >20 g/L (Laird et al, 1998;Michels et al, 2007). In addition, past studies have shown that dispersal can be important for maintaining community structure and function in the face of environmental change (Cottenie & De Meester, 2004;Strecker & Arnott, 2010;Thompson & Shurin, 2012;Symons & Arnott, 2013). Although we were unable to reach firm conclusions about the role of dispersal in our study, our results suggest that dispersal may allow cladocerans to persist in lakes experiencing moderate salinity increases.…”

“…As a result, the magnitude of the salinity changes tested in previous studies were quite small (<1 g/L), paling in comparison to the spatial and temporal heterogeneity in salinity levels experienced for prairie lakes (Symons & Arnott, 2013;Thompson & Shurin, 2012). As a result, the magnitude of the salinity changes tested in previous studies were quite small (<1 g/L), paling in comparison to the spatial and temporal heterogeneity in salinity levels experienced for prairie lakes (Symons & Arnott, 2013;Thompson & Shurin, 2012).…”

“…For example, one species of Daphnia could be replaced by another, or a salinity-tolerant phenotype of a Daphnia species could replace a salinity-intolerant member of the same species. Manipulative experiments also provide some support for the idea that dispersal can act to buffer against community change in the case of small increases in salinity (Symons & Arnott, 2013;Thompson & Shurin, 2012) or when zooplankton are exposed to other stressors such as nutrient enrichment (Forrest & Arnott, 2006), acidification (Steiner et al, 2011) and introduced predators (Howeth & Leibold 2010). The likelihood that dispersal could act to counter salinity-driven changes in this manner depends on two assumptions: (1) that dispersal occurs at a temporal and spatial scale that is significant enough to compensate for losses; and (2) that variation in salinity tolerance among populations and species occurs among lakes with varying salinity levels.…”

Effects of dispersal and environmental heterogeneity on the replacement and nestedness components of β‐diversity

“…Increased nutrient loading and reduced dispersal rates owing to fragmentation are amongst the major drivers of species extinctions worldwide and can undermine ecosystem functioning and stability both in terrestrial and aquatic systems (Kruk et al 2009, Symons and Arnott 2013, Hautier et al 2015, Hooftman et al 2015. Our study additionally suggests that nutrient loading and dispersal limitation synergistically enhance each other's effects on β-diversity.…”

Biodiversity and Resilience of Ecosystem Functions

“…Recent definitions of resilience encompass aspects of both recovery and 84 resistance, although different mechanisms can underpin these, and in some cases there 85 might be trade-offs between them [24]. However, some mechanisms can promote both 86 resistance and recovery depending on the timeframe in which a system is observed (e.g. 87 very rapid recovery can look like resistance).…”