Ribeiro J P N, Matsumoto R S, Takao L K, Lima M I S
Programa de Pós-graduação em Ecologia e Recursos Naturais, Universidade Federal de São Carlos, São Carlos, SP, BR.
Braz J Biol. 2015 Aug;75(3):511-6. doi: 10.1590/1519-6984.13314. Epub 2015 Aug 25.
Estuaries present an environmental gradient that ranges from almost fresh water conditions to almost marine conditions. Salinity and flooding are the main abiotic drivers for plants. Therefore, plant zonation in estuaries is closely related to the tidal cycles. It is expected that the competitive abilities of plants would be inversely related to the tolerance toward environmental stress (tradeoff). Thus, in estuaries, plant zonation tends to be controlled by the environment near the sandbar and by competition away from it. This zonation pattern has been proposed for regular non-tropical estuaries. For tropical estuaries, the relative importance of rain is higher, and it is not clear to what extent this model can be extrapolated. We measured the tidal influence along the environmental gradient of a tropical irregular estuary and quantified the relative importance of the environment and the co-occurrence degree. Contrary to the narrow occurrence zone that would be expected for regular estuaries, plants presented large occurrence zones. However, the relative importance of the environment and competition followed the same patterns proposed for regular estuaries. The environmental conditions allow plants to occur in larger zones, but these zones arise from smaller and infrequent patches distributed across a larger area, and most species populations are concentrated in relatively narrow zones. Thus, we concluded that the zonation pattern in the Massaguaçu River estuary agrees with the tradeoff model.
河口呈现出一种从几乎淡水环境到几乎海洋环境的环境梯度。盐度和洪水是影响植物的主要非生物驱动因素。因此，河口的植物分区与潮汐周期密切相关。预计植物的竞争能力与对环境压力的耐受性呈负相关（权衡）。因此，在河口，植物分区往往受沙洲附近的环境以及远离沙洲处的竞争控制。这种分区模式已被用于常规非热带河口。对于热带河口，降雨的相对重要性更高，尚不清楚该模型能在多大程度上外推。我们沿着一个热带不规则河口的环境梯度测量了潮汐影响，并量化了环境的相对重要性和共存程度。与常规河口预期的狭窄出现区域相反，植物呈现出较大的出现区域。然而，环境和竞争的相对重要性遵循与常规河口相同的模式。环境条件使植物能出现在更大的区域，但这些区域是由分布在更大区域的较小且不频繁的斑块形成的，并且大多数物种种群集中在相对狭窄的区域。因此，我们得出结论，马萨瓜苏河口的分区模式与权衡模型相符。
