Data from: Lake and catchment-scale determinants of aquatic vegetation across almost 1000 lakes and the contrasts between lake types

Aim: The factors controlling macrophyte (aquatic plant) composition are
complex, recent research showing that the well-studied filtering effects
of lake environmental factors are constrained by hydrological and
landscape factors. We investigated the factors determining macrophyte
composition in lakes over water body and catchment- scales and the
transferability of this pattern across lake types. Location: Almost 1000
lakes distributed across Britain. Taxon: Lake macrophytes. Methods: Lakes
were partitioned into five types based on subdivision of alkalinity and
elevation gradients. Data from botanical surveys were used to compare
spatial turnover and nestedness components of beta diversity between lake
types. The relative importance of lake environment (based on local
physicochemical data), hydrology (e.g. lake and stream density), landscape
(e.g. fragmentation indices, land cover) and spatial autocorrelation in
explaining macrophyte composition were derived from variance partitioning.
Results: Species composition showed strong spatial structuring, suggestive
of overland dispersal, enhanced by spatially-correlated abiotic factors
such as alkalinity and elevation. Catchment-scale factors (e.g. land use,
connectivity) promoted the establishment of different communities (more or
less diverse, or differing in composition) but were of secondary
importance. Turnover in composition between upland lakes was lower than in
other lake types, reflecting a more specialist flora and increased
potential for propagule exchange due to spatial aggregation and
hydrological connectivity. Main conclusions: Vegetation composition in
lakes is more spatially-structured than previously appreciated, consistent
with the importance of dispersal limitation, but this does not apply
evenly to all lakes, being most acute in lowland high alkalinity lakes.
Thus, spatially-structured abiotic factors, such as alkalinity, influence
macrophyte composition most (suggestive of niche filtering) in those lakes
where human impacts tend to be greatest, although nestedness was also
lowest there. By contrast, hydrological connectivity has a proportionally
stronger structuring role in upland lakes.