Gradients within gradients: The mesoscale distribution patterns of palms in a central Amazonian forest

Abstract

Questions: What are the relative contributions of environmental factors and geographic distance to palm community structure at the mesoscale, and how do they depend on the length of the environmental gradient covered? How do soil and topography affect variation of the canopy and understory palm community structure at the mesoscale? How does fine‐scale variation within the broad edaphic/topographic classes affect palm community composition? Location: Reserva Ducke, terra‐firme forest, Manaus, Brazil. Methods: Palms were sampled in 72 plots 250 m × 4 m, systematically distributed over an area of 100 km2. Soil, topography and distance to watercourses were measured for all plots. The relationship between community structure axes, summarized by NMDS ordinations, and environmental predictors, was analysed with multivariate regressions. Matrix regressions were used to determine the proportions of variance explained by environmental and geographic predictors. Results: Floristic variation at the mesoscale was mostly related to environmental variation, and the proportion of variance explained depended on the amplitude of the environmental gradient. Soil was the main predictor of floristic change, but its effects differed between life forms, with the understory palm community structured within one of the edaphic/topographic classes, in association with distance to watercourses. Conclusions: Dispersal limitation does not explain palm composition at the mesoscale, and the amplitude of environmental gradients covered by the analysis can be as important as the scale of analysis, in determining the relative contributions of environmental and geographical components to community structure. Soil and topography can predict a large proportion of palm composition, but gradients differ in scale, with some environmental gradients being nested within others. Therefore, although all environmental gradients are nested within distance, they do not necessarily coincide.

A comparison between time of exposure, number of pitfall traps and the sampling cost to capture ground-dwelling poneromorph ants (Hymenoptera: Formicidae)

“…In tropical rainforest, soil clay content has also been shown to affect the distribution of palms (Costa et al, 2009), frogs (Menin et al, 2007), oribatid mites and ants (Oliveira et al, 2009;Vasconcelos et al, 2003;Souza et al, 2007;2016). The effect of each environmental factor varies depending on the scale of analysis (total area surveyed and the number of sampling units).…”

Palm community transitions along a topographic gradient from floodplain to terra firme in the eastern Amazon

“…Similarly, the two sympatric Attalea species, A. attaleoides and A. microcarpa are locally segregated in the terra firme forest close to Manaus, A. attaleoides occurs more often on upland plateaus, whereas A. microcarpa is confined to bottomlands (Costa et al 2009). Freitas et al (2012) investigated and found no evidence that seed removal or seed germination patterns in relation to topography or abundance of adults explained the topographic separation between the two species.…”

Influence of a topographic gradient on the occurrence, abundance and composition of nine species of palms (Arecaceae) in the Central Amazon

“…Another factor that can be considered favorable to the increase of changes in species composition is the soil type found in plateaus, that is more fertile than the soil of valley and slope areas (Vormisto et al, 2004;Costa et al, 2009), where nutrients leaching in the surface horizons is more intense and constant. Since soil conditions are good in plateau areas, competition by space becomes important.…”

“…Most of the studies conducted at Ducke Reserve, near Manaus, are about communities (Tello, 1997;Zuquim et al 2007). In the same area, the species composition of the palm community varied significantly in relation to environmental and geographical gradients (Costa et al, 2009). The distribution of populations of more abundant palm species can be influenced by several components of the forest structure, like litter quantity, canopy opening, tree density, soil types, etc (Cintra et al, 2005).…”