MICROHABITAT USE BY FISHES IN SMALL STREAMS: METHODS AND PERSPECTIVES

Abstract

Physical microhabitat use studies describe the features of areas occupied by fishes.

That information has been often used to address the central themes of ecological research in the last decades (resource partitioning, mechanisms of community organization, ecomorphology, optimal foraging, historical and landscape ecology). The spatial scales and methods of description are diverse, reflecting the different aims of research projects, species involved, study sites and logistical constraints. Nonetheless, some parameters have received attention consistently. At a larger scale, authors have assessed fish distribution relative to physiognomically homogeneous units (riffles, pools, runs) of the stream banks (midstream vs. margins). At a smaller scale, they have measured water velocity, water depth, streambed substrate and cover. Data on habitat use require information on available habitat. No sampling method for either kind of data is absolutely tree of bias. Capture methods can displace fish and can not supply a totally accurate location, while observation may not perform equally well in all habitat types. In any case, the distribution in space of sampling points should be done according to randomized a priori designs. The frequent covariation among microhabitat parameters has led researchers to use multivariate statistics to uncover multivariate gradients. However, categorical variables are not easily incorporated into these techniques ar authors have focused in single parameters for diverse reasons. Thus, univariate analyses are also common. More research into the mechanisms behind observed habitat use is still needed. Recent developments such as historical and landscape ecology provide conceptual frameworks that offer exciting research opportunities in is. The biogeographic conditions of neotropical streams ensure the interest of descriptive studies of the little known microhabitat use of their fishes.