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

Abstract

Quantifyingtherelativeinfluenceofforcesthatdeterminepop-ulation and community dynamics is essential to our under-standing of microbial function in lakes. Both intrinsic (site-specific) and extrinsic (regional) factors have the potential toinfluence ecosystems, but the relative importance of each iscurrently the subject of considerable discussion (Hudson C distinct shorelineboundaries allow us to easily partition forces acting fromwithin and outside the system. Regional extrinsic factors canimpartsynchronytothedynamicsofvariousecosystemparam-eters(Liebholdetal.2004),andvariablessuchastemperatureandwaterchemistryhavestronginterannualsynchronyacrosslakes in a region (Magnuson et al. 1990, Kratzet al. 1998).Lake-specific intrinsic drivers, such as food-web interactionsand stochastic population dynamics, typically dampen suchpatterns in plankton (Rusak et al. 1999, Baines et al. 2000,Magnuson et al. 2005).Earlier work exploring the relative importance of extrinsicand intrinsic factors in ecology has typically examined popu-lation synchrony (Grenfell et al. 1998, Hudson & Catta-dori 1999, Rusak et al. 1999). In this context, spatial syn-chrony (or temporal coherence; Magnuson et al. 1990)refers to correlated temporal variability in the abundance of aparticular taxon among sites, usually within regions (Lieb-hold et al. 2004). In the absence of dispersal, synchronyamong populations is often attributed to the “Moran effect,”synchrony that is plausibly correlated with extrinsic climaticdrivers (Moran 1953) or to trophic interactions with popula-tions that exhibit spatial synchrony (Grenfell et al. 1998,Hudson & Cattadori 1999, Liebhold et al. 2004). Froma community perspective, concordance is an analogous con-cept that quantifies the degree to which spatial patterns incommunity structure are similar among locations or co-occurring taxonomic groups (Paszkowski & Tonn 2000,Peres-Neto & Jackson 2001). Applied across time ratherthan space, ‘temporal concordance’ implies that changes incommunity structure occur at the roughly the same time andpace among different communities, thus providing a veryuseful approach to quantifying synchrony from a communityperspective (Kent et al. 2007).Kent et al. (2007) documented strong synchrony in theseasonal dynamics of microbial communities among 6 lakesin northern Wisconsin over the course of a single year usingunaggregated intra-annual “species” level data. With genera-tion times on the scale of days and the ability to adapt to envi-ronmental change over the course of a season, intra-annualtime intervals for microbes may be somewhat analogous toannual dynamics for longer-lived organisms. We now havethe opportunity to revisit this question of synchrony withanother year of bacterial community composition (BCC) datain 2 of the same 6 lakes using a highly aggregated data set.Thus, using these data, we (1) test for ongoing synchrony inBCC among lakes with an additional year of data, and (2)compare patterns among years to explore both similaritiesand differences in the predictability and consistency of BCCand dynamics.