Functional heterogeneity of dry‐season fish refugia across a Mediterranean catchment: the role of habitat and predation

Abstract

SUMMARY 1. Fish in Mediterranean streams survive through the summer in residual surface waters, encompassing a broad range of abiotic and biotic conditions. Yet, the extent to which fish assemblages may be shaped by functional heterogeneity in dry‐season refugia is largely unknown. This study addresses this issue, by examining fish assemblage and population attributes, and predation patterns in residual summer habitats (12 pools and six runs) across a Mediterranean catchment in south‐west Portugal. 2. Species richness was fairly constant among runs but increased with pool size, with the addition of exotics and rare natives to large pools resulting in nested subsets. The four most common species (chub, nase, loach and eel) were considered generalists in terms of their use of dry‐season refugia. Conversely, rare species presented more specialised habitats, with barbel and exotics favouring pools and stickleback favouring runs. 3. Age and size of the two most common species varied among dry‐season habitats. Age 0 chub were restricted to runs, where spawning stages (age 2 and older fish) were also more represented. Age 0 nase also concentrated in runs, but the individuals collected in pools exhibited greater growth. Conversely, age 2 and older nase were proportionally more abundant in pools, but with greater growth and better condition in runs. 4. The otter was the main fish predator, consuming fish of all species and size classes, irrespective of habitat. Otter activity concentrated in pools, where predation risk for cyprinids seemed to be much higher than in runs. 5. Dry‐season refugia apparently vary in functional importance for different fish species and life stages, acting as complementary units in the landscape. Therefore, the presence of both pool and run refugia trough the summer dry season may play a critical role in promoting the persistence of native species in Mediterranean streams.

Fish-based groups for ecological assessment in rivers: the importance of environmental drivers on taxonomic and functional traits of fish assemblages

“…Accordingly, similar pattern in species diversity was observed. These results are in accordance with numerous previous studies (Godinho et al, 1997(Godinho et al, , 2000Carmona et al, 1999;Pires et al, 1999Pires et al, , 2004Mesquita and Coelho, 2002;Magalhães et al, 2002aMagalhães et al, , 2002bMagalhães et al, , 2007Clavero et al, 2004;Ferreira and Oliveira, 2004;Clavero and Garcia-Berthou, 2006;Mesquita et al, 2006;Ferreira et al, 2007aFerreira et al, , 2007b. In fact, increasing local species richness along the longitudinal stream gradient is a very well known pattern (e.g.…”

Interactions between invasive crayfish and native river shrimp

“…This value is apparently low, but it is important to remember that crayfish have not gone through any period of fasting and were well fed before the experiment. It is also important to note that the density of prey, five per container, is a low density compared to the river shrimp density values found in nature which are up to 1811 animals per m 2 (Meurisse-Génin et al, 1985;Fidalgo, 1990 Mediterranean freshwater systems are frequently confined to small areas due to drought during late summer and early autumn (Magalhães et al, 2002) and in those circumstances prey are heavily consumed by crayfish (Correia, 2003). Our field work was performed in early summer (late June to early July) when these confined conditions are beginning to emerge.…”

Fish fauna in Iberian Mediterranean river basins: biodiversity, introduced species and damming impacts

“…Most Iberian rivers follow a typical Mediterranean cycle, with autumn-winter floods and strong summer droughts (Gasith and Resh, 1999). This important seasonal instability, coupled with a huge interannual variability in the precipitation regime (Blondel and Aronson, 1999), are key factors in the structure of freshwater communities (Prenda and Gallardo, 1996;Pires et al, 1999;Magalhães et al, 2002).…”

“…In this environment, strong habitat or trophic specialisation, such as piscivorous diets, has not evolved (Poff and Allan, 1995). In general, Iberian freshwater fishes are habitat generalists very well adapted to survive in constantly changing environments (Magalhães et al, 2002). Reservoirs provide the stable lentic habitats in which introduced species, many of them predatory, can develop thriving populations.…”