Do aquatic macrophytes co-occur randomly? An analysis of null models in a tropical floodplain

Abstract

One of the main issues in community ecology is the detection of structure and the identification of its related causes. In this study, co-occurrence null models were used to identify possible spatio-temporal patterns in the assemblage of aquatic macrophytes in the Upper Paraná River floodplain. The samples were obtained through the Long Term Ecological Research (LTER) Program at two different grains: (1) a coarser spatial grain in January and August 2001 (entire floodplain lagoons); (2) and a finer spatial grain in November 2006 (1 m(2) quadrats). The study was conducted in 36 lagoons, both connected and disconnected to the main river channel, located in the sub-basins of the Baía, Ivinheima and Paraná rivers. Two null models of species co-occurrence, the C-Score and Checkerboard indices, were used to test the null hypothesis of random structure of the aquatic macrophyte assemblages. The null models showed that the aquatic macrophyte assemblages were spatially structured in the distinct spatial grains. However, despite this general pattern, macrophyte assemblages are organized differently depending on the degree of connectivity, seasonal period and, at a finer grain, depth. Species co-occurrences were random in the disconnected lagoons during flood periods, in deep zones of the lagoons of the Baía River and in the shallow littoral zone in the lagoons of the Paraná River. Analysis of the patterns of co-occurrence indicated that competition and/or habitat preferences are probably important influences on the nonrandom structure of assemblages. However, we suppose that at least three important factors (disturbances by water level fluctuation, dispersion and facilitation) counteract potential effects of competition in specific situations, leading macrophyte assemblages to assume random structure.

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

“…), that were restricted to shallow localities (E. tenellus) or that occurred in exposed sites (N. guadalupensis). Thus, it is unlikely that co-occurrence patterns emerged from strong competitive interactions; again, it seems to be related to specific habitat affinities (Boschilia et al, 2008). Fernandes et al (2009), studying the temporal organization of fish assemblages in floodplain lagoons, also evoked the presence of rare species and/or geographical segregation as potential explanations for patterns of segregation.…”

The role played by aquatic macrophytes regarding CO2 balance in a tropical coastal lagoon (Cabiúnas Lagoon, Macaé, RJ)

“…AIC selected models to explain CO 2 diffusion through the Cabiúnas water surface. macrophyte assemblages tend to have a spatial segregation (Boschilia et al, 2008), the amount of CO 2 assimilated may differs among the littoral zone of lakes due to the change in species cover. Thus, C cycling in lakes' littoral zones may be strongly determined by species identity when estimating C balance in aquatic ecosystems.…”

Invasion of Water Hyacinth (<i>Eichhornia crassipes</i>) Is Associated with Decline in Macrophyte Biodiversity in an Ethiopian Rift-Valley Lake—Abaya

“…A clear understanding of time of infestation and direction of invasion certainly will help us understand better the level of impact and direction of impact progression in the context of local environmental conditions. Macrophyte assemblages are indicated to be impacted by competition [20].…”