DOI: 10.5061/dryad.685vq
title: Data from: Asynchronous changes in abundance over large scales are explained by demographic variation rather than environmental stochasticity in an invasive flagellate

description: Environmental stochasticity is important in explaining the persistence and
 establishment of invasive species, but the simultaneous effects of
 environmental and demographic factors are difficult to separate.
 Understanding how demography and environmental factors affect invasive
 species abundance over large temporal and spatial scales is essential to
 anticipate populations at risk of becoming established and setting
 appropriate management measures. Using a hierarchical mixed modeling
 approach we analyzed the spatial and interannual dynamics of the invasive
 raphidophyte Gonyostomum semen, a noxious flagellate which is spreading in
 northern Europe, in response to demographic and environmental variation.
 We used data from 76 lakes distributed across two biogeographical regions
 in Sweden (Central Plains in the south and Fennoscandian region in the
 north) and sampled during 14 years. We found a strong asynchrony in the
 density dynamics of G. semen populations between the two regions. G. semen
 showed positive trends (i.e. increasing frequency of high density peaks)
 in most southern lakes, forming established populations with recurrent
 blooms in successive years in some of them. In contrast, G. semen
 populations were smaller and more stochastic in the north. G. semen
 previous year's abundance, a proxy for cyst production and
 recruitment, had a strong control on the dynamics, likely contributing to
 the stability of high density populations in southern lakes. Conversely,
 the effects of climate and habitat were weaker and their influence varied
 across regions. Temperature was the limiting factor in the north whereas
 local habitat was more important in the south. Synthesis: A full
 understanding of the mechanisms driving abundance changes across large
 scales can only be gained if endogenous and environmental factors are
 analyzed together. For phytoplankton species, and specially, noxious
 microalgae, this implies that proxies for cyst production and recruitment,
 which are the inoculum for next year population, should be included in
 e.g. distribution, bloom formation and climate models, as these may modify
 establishment and population response to environmental variation.
 Asynchronous changes in abundance across regions also indicate that
 management plans should be developed for small regions, as inference at a
 large scale may obscure the mechanisms driving local population changes.
description: G. semen dynamics over
 large scalesData were collected in76
 lakes sampled annually between 1997 and 2010 as part of the Swedish
 National Monitoring program. Abbreviated headlines are as follows:
 "Limes_Norr" = Location south (1) or north (2) of Limes
 Norrlandicus; "number_cells" = number of cells L-1;
 "Temp_Aug"= mean temperature in August; "pH_Aug"= pH
 in August; "NH4-N_Aug" = Ammonia mg L-1 in August;
 "Tot_N_Aug" = total nitrogen mg L-1 in August;
 "PO4-P__Aug"= orthophosphate mg L-1 in August;
 "Tot-P_Aug"= total phosphorous mg L-1 in August;
 "Abs._F_Aug" = absorbance nm in August; "Temp_April"=
 mean temperature in April; "pH_April"= pH in April;
 "NH4-N_April" = Ammonia mg L-1 in April; "Tot_N_April"
 = total nitrogen mg L-1 in April; "PO4-P__April"= orthophosphate
 mg L-1 in April; "Tot-P_April"= total phosphorous mg L-1 in
 April; "Abs._F_April" = absorbance nm in April;
 "TGSL"= length of growing season as number of days;
 "area_geom"= total lake surface in ha; "perim_geom"=
 lake perimeter in Km; "avg_shore_slope"= mean shore slope;
 "LakeMeanDepth"= lake mean depth in m.Data to
 dryad.csv