Spatial synchrony in microbial community dynamics: testing among-year and lake patterns

摘要

Quantifying the relative influence of forces that determine population and community dynamics is essential to our understanding of microbial function in lakes. Both intrinsic (sitespecific) and extrinsic (regional) factors have the potential to influence ecosystems, but the relative importance of each is currently the subject of considerable discussion (HUDSON & CATTADORI 1999, RUSAK et al. 1999, BJORNSTAD & GRENFELL 2001, LIEBHOLD et al. 2004, HESSEN et al. 2006). Lakes are model systems for examining the role of intrinsic and extrinsic drivers of microbial communities; distinct shoreline boundaries allow us to easily partition forces acting from within and outside the system. Regional extrinsic factors can impart synchrony to the dynamics of various ecosystem parameters (LIEBHOLD et al. 2004), and variables such as temperature and water chemistry have strong interannual synchrony across lakes in a region (MAGNUSON et al. 1990, KRATZ et al. 1998). Lake-specific intrinsic drivers, such as food-web interactions and stochastic population dynamics, typically dampen such patterns in plankton (RUSAK et al. 1999, BAINES et al. 2000, MAGNUSON et al. 2005). Earlier work exploring the relative importance of extrinsic and intrinsic factors in ecology has typically examined population synchrony (GRENFELL et al. 1998, Hu DSON & CATTAnon 1999, RUSAK et al. 1999). In this context, spatial synchrony (or temporal coherence; MAGNUSON et al. 1990) refers to correlated temporal variability in the abundance of a particular taxon among sites, usually within regions (DEBHOLD et al. 2004). In the absence of dispersal, synchrony among populations is often attributed to the "Moran effect," synchrony that is plausibly correlated with extrinsic climatic drivers (MORAN 1953) or to trophic interactions with populations that exhibit spatial synchrony (GRENFELL et al. 1998, HUDSON & CATTADORI 1999, LIEBHOLD et al. 2004). From a community perspective, concordance is an analogous concept that quantifies the degree to which spatial patterns in community structure are similar among locations or co-occurring taxonomic groups (PASZKOWSKI & TONN 2000, PERES-NETO & JACKSON 2001). Applied across time rather than space, `temporal concordance' implies that changes in community structure occur at the roughly the same time and pace among different communities, thus providing a very useful approach to quantifying synchrony from a community perspective (KENT et al. 2007). KENT et al. (2007) documented strong synchrony in the seasonal dynamics of microbial communities among 6 lakes in northern Wisconsin over the course of a single year using unaggregated intro-annual "species" level data. With generation times on the scale of days and the ability to adapt to environmental change over the course of a season, intra-annual time intervals for microbes may be somewhat analogous to annual dynamics for longer-lived organisms. We now have the opportunity to revisit this question of synchrony with another year of bacterial community composition (BCC) data in 2 of the same 6 lakes using a highly aggregated data set. Thus, using these data, we (1) test for ongoing synchrony in BCC among lakes with an additional year of data, and (2) compare patterns among years to explore both similarities and differences in the predictability and consistency of BCC and dynamics.