Morphometric and biotic variables as potential predictors ofLudwigia sedoides(Humb. & Bonpl.) Hara in a large Amazonian reservoir

Abstract

-Reservoirs cause hydrological changes (i.e., water level stabilization) that favor the colonization of aquatic macrophytes. Knowing the ecological factors that determine the occurrence of these plants is critical for water management (e.g., plant control) and biodiversity conservation. In this sense, the present study investigated colonization patterns of Ludwigia sedoides in Lajeado reservoir (Tocantins River, Amazon Basin), in order to identify variables that influence colonization at habitat scale. We investigated the relationship between colonization (coverage area and occurrence) and morphometric (fetch, slope, depth and distance from shoreline) and biotic variables (local diversity of macrophytes and co-occurrence patterns). Stepwise regression selected fetch, depth and slope as the best variables to explain the variation in L. sedoides coverage, which together explained 46% of data variability. Fetch and slope were negatively correlated with coverage, whereas depth showed a positive correlation. No biotic variable was included in the model (P > 0.05). However, the investigation of the geometric shape of bivariate correlations (null models) showed positive relationships with local species richness and richness of life forms (i.e., submerged, emergent, floating and epiphytic). In addition, an analysis of species co-occurrence (C-score) revealed that L. sedoides is negatively associated with some macrophyte species. We believe, however, that these results may be associated with species preferences for particular environmental conditions. In conclusion, the present study indicated that morphometric variables are potential predictors of the colonization of L. sedoides in Lajeado reservoir. Sheltered sites with low slope and moderate depths represent favorable environment for colonization and growth.

Distribution of aquatic macrophytes along depth gradients in Lajeado Reservoir, Tocantins River, Brazil

“…Our results confirm these biotic gradients in Lajeado Reservoir, but some species colonized the whole gradient, probably because the littoral zone in this reservoir favor the development of aquatic plants, i.e. extensive shore development, shallow depths (<2m), gentle slopes, stable water level, high water transparency and sites protected by wind/wave action (Lolis & Thomaz, 2011;Barbosa et al, 2014).…”

“…Slope is another important factor for emergent macrophytes, because it directly affects sediment grain size, chemical composition and stability; these conditions affect negatively plant anchoring and growth (Bornette & Puijalon, 2011). Barbosa et al (2014) observed that slope, together with fetch and depth, are the main factors regulating the coverage and distribution of L. sedoides in Lajeado Reservoir. The present study, however, included sites with gentle slopes, so this variable may have a secondary role influencing the distribution of emergent macrophytes.…”

“…emergent, submerged and floating plants (Thomaz & Bini, 1998;Thomaz, 2002). Among the factors that elicit macrophyte development in reservoirs, we can mention stable water levels, permanent shallow areas, gentle slopes, increased water transparency and nutrient availability (e.g., Bini et al, 1999;Bini & Thomaz, 2005;Pierini & Thomaz, 2009;Barbosa et al, 2014;Silva et al, 2014). Consequently, populations of submerged and emergent plants, in particular, have experienced significant development in Neotropical reservoirs (Cavenaghi et al, 2003;Martins et al, 2008;Pitelli et al, 2008).…”

“…The region is characterized by extensive shore development, shallow depths (usually < 100 cm), high underwater luminosity (Secchi > 150 cm), sediment enriched with organic matter, and several localities protected from wind and wave action. These conditions have favored aquatic macrophytes, and about 50 species have been recorded in this reservoir (Bianchini Junior et al, 2010;Lolis & Thomaz, 2011;Barbosa et al, 2014).…”

“…The large and shallow impoundment created by Lajeado Dam (UHE Luís Eduardo Magalhães hydropower plant), middle Tocantins, has favored the expansion of submerged and emergent plants. Few studies have been conducted to date, but they revealed general patterns of richness, composition and abundance (Bianchini Junior et al, 2010;Lolis & Thomaz, 2011), or the population response of Ludwigia sedoides to some environmental factors (Barbosa et al, 2014). No study, however, has investigated diversity patterns at small spatial scales, particularly the response of plants to depth gradients along the littoral zone.…”