Why life history information matters: drought refuges and macroinvertebrate persistence in non-perennial streams subject to a drier climate

In some arid, semi-arid or Mediterranean climate regions, increased water extraction combined with climate change will prolong periods of drought in non-perennial streams, but the effects on macroinvertebrate populations are poorly understood. Drought refuges allow species to survive drying but their use depends on species’ traits, and refuge availability depends on landscape structure. This review evaluates the utility of existing ecological concepts for predicting the role of drought refuges for sustaining biodiversity in non-perennial streams. We also suggest traits that may determine invertebrate species’ resistance or resilience to prolonged drying. Parts of the likely responses by populations to increased stream drying are described by existing ecological concepts, such as the biological traits of species and their interaction with the habitat templet, barriers to dispersal and metapopulation dynamics, the use of drought refuges, habitat fragmentation and population and landscape genetics. However, the limited knowledge of invertebrate life histories in non-perennial streams restricts our ability to use these concepts in a predictive manner. In particular, reach or pool occupancy by species cannot be accurately predicted, but such predictions are necessary for evaluating potential management actions such as the use of environmental flows to sustain drought refuges during dry periods.

Spatial and temporal heterogeneity of an epilithic streambed community in relation to the habitat templet

The microbial community of river sediments and their relationship to environmental factors is largely unknown. In this study, the abundance of bacteria, flagellates, ciliates, and Micrometazoa was investigated for eight different sediment types. The sediment types were classified by discharge (stable versus flood period), location (upper versus lower reach), and depth (superficial versus deep sediment layer). Abundances in the lower reach were more than two times higher than in the upper reach but decreased markedly at both sites after flooding. Organism densities were similar between the two sediment layers, although deeper habitats served as potential refugia, as indicated by reduced transport of coarse particles into the deep sediment layer. The organism abundances correlated with concentration of fine organic particles. A habitat templet model was used to classify favourableness and disturbance of the sediment types. For an empirical placement of sediment types in the model, results on abundances, fine organic particles, nutrient concentrations, particle transport, and flood frequency were integrated. Local processes, mainly related to sediment transport, decreased the predicticability of the habitat templets.