Effects of limnological and morphometric factors upon Zmin, Zmax and width of Egeria spp stands in a tropical reservoir

Abstract

In this work, regression analyses were used to test the effects of fetch, littoral slope and

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

“…The positive relationship between depth and L. sedoides coverage apparently differs from the pattern found in the literature, since rooted macrophytes do not colonize deep areas (>3 m; Bini and Thomaz, 2005;Pierini and Thomaz, 2009), and emergent life forms usually colonize transitional shallow areas (Andersson, 2001). Indeed, Pott and Pott (2000) report that L. sedoides prefer shallow waters in natural lagoons.…”

“…Considering the non-linearity (i.e., uneven variability) in the relationship between macrophyte distribution and some environmental variables (e.g., Thomaz et al, 2003;Bini and Thomaz, 2005;Pierini and Thomaz, 2009), we explored the geometric shape of bivariate correlations (L. sedoides coverage versus biotic and morphometric variables; untransformed data). Using a null model, we tested if the observed geometric shape of each relationship could be produced by chance, comparing the observed pattern with simulations generated after 1000 randomizations of the original matrix.…”

“…Negative relationships between fetch and macrophyte distribution have been commonly reported, including several species of different life forms (Strand and Weisner, 1996;Rea et al, 1998;Riis and Hawes, 2003;Schutten et al, 2004;Bini and Thomaz, 2005;Azza et al, 2007). Disturbance is mainly mechanical, damaging plants and impairing colonization and development (Schutten et al, 2004;Pierini and Thomaz, 2009). This is typical in reservoirs, as these environments are large and extensive, with sites exposed to severe wave action.…”

“…Thus, exposed sites in the Lajeado reservoir, such as those located in the central canal, are unsuitable for L. sedoides, especially when fetch >1 km. However, the relationship between colonization and fetch showed a triangular distribution of data, i.e., high variability at one end of the gradient (envelope shape; Thomaz et al, 2003;Pierini and Thomaz, 2009). This high variability in plant distribution indicates that other variables contribute to minimize the probability of plant colonization when fetch is low, reducing the predictive power of the relationship.…”

“…When reservoirs are formed, therefore, society must be prepared to deal with potential tradeoffs between control, eradication and conservation of aquatic macrophytes. In this sense, studies that investigate the distribution of macrophytes (e.g., Neiff et al, 2000;Murphy et al, 2003;Bini and Thomaz, 2005;Pierini and Thomaz, 2009;Sousa et al, 2009) are crucial to provide management programs with information about the factors affecting colonization; a first step to build predictive models.…”