Padrões de diversidade das assembleias de peixes de praias tropicais em diferentes escalas hierárquicas

Abstract

Ecologically, biodiversity refers to the variability and distribution of species and can be understood through biotic and abiotic variables that act at different hierarchical scales. The additive partitioning of diversity has received the attention of ecologists, and is a promising approach to understanding fish diversity patterns on beaches with different morphodynamics, with implications for the establishment of priority areas for conservation. Therefore, the main objective of this work was to evaluate the patterns of β diversity, at different spatial scales, of fish assemblages in three types-states of tropical mesotidal beaches, as well as to explore the components of beta diversity (species substitution and difference in richness) and the effects of the environmental conditions of these habitats on the observed patterns. Therefore, the following hypotheses were proposed: an increase in the dissimilarity in the species composition of fish assemblages as the studied spatial scale increases; and the replacement of species as the predominant mechanism that generates the partition of β diversity on beaches. Samplings were performed by the beach trawl method in three morphodynamic state-types: beaches dominated by waves (WD - Wave dominated), modified by tides (TM - Tide modified) and dominated by tides (TD - Tide dominated). A general hierarchical scope was also established, which presents the components: α, which corresponds to the diversity within the replicas/trawls, β1 the variation of the diversity between these replicas/trawls, β2 representing the variation of the diversity between the beaches and β3 the variation diversity among beach types-states. The standardized samplings correspond to excursions carried out between 2011 and 2018. In the present work, spatial differences in the structure of fish assemblages were demonstrated, through a Redundancy Analysis (RDA), between different types of beaches that are strongly influenced by wave action and tidal force. In general, the environmental variables acted as environmental filters for the assemblages, mainly salinity, time and wave height, resulting in changes in the diversity of fish found on the different beaches. The additive partition revealed a greater dissimilarity found at the highest hierarchical level (β3), indicating an increase in the dissimilarity in the species pool as the spatial scale increases and the tides replace the waves, playing the dominant role in the environment. Our results also showed that environmental and spatial factors contributed to species replacement and richness difference. Both were decisive in directing the diversity of fish assemblages. The environmental variations present can increase the variability of the environmental conditions to which different species are adapted. Environmental filtering, habitat heterogeneity and spatial connectivity can have different effects depending on the spatial scale. Therefore, future studies should be designed to incorporate existing knowledge and untangle such mechanisms underlying diversity, helping to guide conservation strategies.