SPATIAL AND TEMPORAL VARIATIONS' OF CHARACIDAE HABITAT, CASE STUDY IN ABRAS DE MANTEQUILLA WETLAND, ECUADOR

摘要

A central component of predictive ecology in wetlands is the analysis of species distribution as a function of their biotic and abiotic environment. Decision-makers in biodiversity conservation, species monitoring and environmental planning, among others normally use this analysis. Habitat suitability modelling is a major component of the process of making the analysis, however, temporal and spatial variations of hydrological, hydrodynamic and environmental variables are normally not well known and overall values are estimated. In Abras de Mantequilla wetland (Ecuador) we find a tropical situation where the hydrodynamics of inflows seem to play an important role on the stability of the ecosystem. The habitat suitability in wetlands is driven by hydrodynamic, physical and biological interactions that are not fully understood. This research explores the habitat changes in space and time of a littoral fish community (Characidae) in this tropical wetland, identifying extremes using a constant analysis (thresholds in a range), a one variable index, and a fuzzy combination of hydrodynamic model variables. The main goal was to quantify the extension of the habitat areas were the habitat index was high enough to be considered as suitable for this fish community. This analysis was based on the hydrodynamic features and on spatio-temporal variations of the habitat index. The hydrodynamic variables water depth and velocity were modelled with a 2D flow representation and information from hydrological models simulations at the inflows of the wetland. The hydrodynamic model of the wetland was built in Delft3D-FLOW software. A change of spatial distribution of the habitat for Characidae family was related to the velocity and water depth. Results from the Habitat model indicated that when only water depth was selected as unique variable for the analysis, the percentage of suitable areas was higher at the beginning and at the end of the wet season. Conversely, when velocity was selected as unique variable the percentage of suitable areas was higher during the middle of the wet season. A subsequent combination of both variables depth and velocity showed a similar trend to the one of velocity alone. The results from this Combined Habitat Index determined that a higher percentage of suitable areas for this fish assemblage occurred during periods of high flows (middle of the wet season), given the hydrodynamic variables selected. Thus, it would appear that the habitability of the Characids in the littoral areas decreased when low flows occurred. Despite this fact, it is essential to acknowledge that other physical, chemical and biotic variables may play an important role in the presence of this community and therefore should be gradually included in future studies for an integrated ecological habitat assessment.