The relative importance of local conditions and regional processes in structuring aquatic plant communities

Abstract

1. The structure of biological communities reflects the influence of both local environmental conditions and processes such as dispersal that create patterns in species' distribution across a region. 2. We extend explicit tests of the relative importance of local environmental conditions and regional spatial processes to aquatic plants, a group traditionally thought to be little limited by dispersal. We used partial canonical correspondence analysis and partial Mantel tests to analyse data from 98 lakes and ponds across Connecticut (northeastern United States). 3. We found that aquatic plant community structure reflects the influence of local conditions (pH, conductivity, water clarity, lake area, maximum depth) as well as regional processes. 4. Only 27% of variation in a presence ⁄ absence matrix was explained by environmental conditions and spatial processes such as dispersal. Of the total explained, 45% was related to environmental conditions and 40% to spatial processes. 5. Jaccard similarity declined with Euclidean distance between lakes, even after accounting for the increasing difference in environmental conditions, suggesting that dispersal limitation may influence community composition in the region. 6. The distribution of distances among lakes where species occurred was associated with dispersal-related functional traits, providing additional evidence that dispersal ability varies among species in ways that affect community composition. 7. Although environmental and spatial variables explained a significant amount of variation in community structure, a substantial amount of stochasticity also affects these communities, probably associated with unpredictable colonisation and persistence of the plants.

Hydrologic connection between ponds positively affects macrophyte α and γ diversity but negatively affects β diversity

“…Our findings of a high contribution of b diversity and low contribution of a diversity to regional c diversity are consistent with previous studies of freshwater fishes and invertebrates (Stendera andJohnson 2005, Eros 2007) and terrestrial plants (Clough et al 2007). High dissimilarity between habitat patches has been explained by a strong dispersal limitation between the patches as well as a strong species-sorting process by environmental filters or competition (Capers et al 2010, Clarke et al 2010, Matthiessen et al 2010. For pond macrophytes in particular, differences in environmental conditions (Ray et al 2001, Capers et al 2010 as well as restrictions on propagule dispersal (Ray et al 2001, Akasaka andTakamura 2011) can strongly restrict species composition.…”

“…The coefficient for unconnected ponds was calculated with respect to that for connected ponds (i.e., the coefficient for connected ponds was set to zero). between unconnected habitat patches (Capers et al 2010). We found a greater similarity in macrophyte species composition between connected ponds than between unconnected ponds (Table 2).…”

“…High dissimilarity between habitat patches has been explained by a strong dispersal limitation between the patches as well as a strong species-sorting process by environmental filters or competition (Capers et al 2010, Clarke et al 2010, Matthiessen et al 2010. For pond macrophytes in particular, differences in environmental conditions (Ray et al 2001, Capers et al 2010 as well as restrictions on propagule dispersal (Ray et al 2001, Akasaka andTakamura 2011) can strongly restrict species composition. We therefore suggest that these factors limit the decrease in dissimilarity of species composition (i.e., b diversity) between connected ponds.…”

Ecological characteristics of plant species and associations along two Dinaric karstic rivers (Bosnia and Herzegovina, the Balkans)

“…Results from Bulgarian rivers (Gecheva et al 2013) or Slovak streams (Hrivnák et al 2010) and many others (cf. Capers et al 2010) corroborate the importance of water depth (or other measure of topography) for macrophyte composition and distribution. In this study, wa-ter and marsh associations were most highly developed in depths up to 1.8 m. This agrees with the findings of Sýkora (2008) for Dutch Nymphaeion albe communities, but only partly with Dimopoulos et al (2005) who found water lilies up to 2.5 m in Greek freshwater wetland.…”

“…These environmental variables are among those found almost universally to influence aquatic plant community composition (Capers et al 2010). Finally, Lukács et al (2009) showed that community-environment and species-environment relationship in nutrient rich water were similar to those found in nutrient poor waters and fens in Central Europe.…”