Ecology of Freshwater Fish 2015 Ó 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd ECOLOGY OF FRESHWATER FISH Fish assemblages in Atlantic Forest streams: the relative influence of local and catchment environments on taxonomic and functional species Bianca de F. Terra1,2, Robert M. Hughes3, Francisco G. Araujo 2 1Departamento de Biologia, Laboratorio de Ecologia de Rios do Semiarido, Centro de Ci^encias, Universidade Federal do Ceara (UFC), Campus do Pici, Caixa postal 6021, CEP 60455-970, Fortaleza, Ceara, Brazil 2Departamento de Biologia Animal, Laboratorio de Ecologia de Peixes, Instituto de Biologia, Universidade Federal Rural do Rio de Janeiro, Rodovia 465, km 7, CEP 23897-000 Seropedica, Rio de Janeiro, Brazil 3Amnis Opes Institute and Department of Fisheries & Wildlife, Oregon State University, 2895 SE Glenn, Corvallis, OR 97333, USA Accepted for publication April 16, 2015 Abstract – Streams are under environmental pressures acting at different scales that influence the ecological organisation of their fish assemblages. However, the relative influence of the different scale-related variables on assemblage composition and function is poorly understood. We evaluated the importance of local- and catchment- scale environmental variables, as well as the spatial structure of the sampling sites, in shaping fish assemblages in Atlantic Forest streams. Local-scale variables were those measured at the sampling sites, describing the local habitat conditions (e.g. depth, substrate type, altitude). Catchment-scale variables were those integrating the upstream landscape of the sampling sites (e.g. catchment land use). Spatial distances were calculated from watercourse distance using principal coordinates of neighbour matrices. Altogether, 28 local and seven catchment variables were initially subjected to two processes of eliminating co-linearity. Redundancy analysis was applied to the three matrices (spatial, local and catchment) to quantify the variance in the structure of the fish assemblages explained by each matrix. Local variables explained more variability in both taxonomic and functional assemblage structure, than catchment and spatial variables. Local variables also changed along the longitudinal gradient, which consequently influenced fish assemblage structure. This pattern was also influenced by anthropogenic alteration and non-native species, which were more abundant in downstream sites. These results highlight the need to assess Atlantic Forest streams under different environmental scales, especially through the use of quantitative local-scale metrics, and to consider the effects of longitudinal patterns in structuring fish assemblages when developing and implementing monitoring programmes, impact studies and conservation plans. Key words: stream habitat; variance partitioning; fish ecology; longitudinal gradient; tropical streams haus et al. 2007). Local variables, such as water Introduction quality, energy source, substrate and channel mor- Characterising fish assemblage structure at different phology, help to determine the structure and compo- scales increases our ability to comprehend ichthyofa- sition of fish assemblages and are influenced by unal organisation, which is important for conserving catchment-scale factors, such as surficial geology, aquatic systems. Studies have indicated that fish soil type, bedrock type and depth, watershed topogra- assemblage organisation may be determined not only phy, land cover and climate (Tonn 1990; Wang et al. by local processes, but also by large-scale environ- 2003). Moreover, local habitat characteristics and mental variables (e.g. Magalh~aes et al. 2002; Hoeing- catchment environmental factors mediate biotic inter- Correspondence: Bianca de F. Terra, Departamento de Biologia, Laboratorio de Ecologia de Rios do Semiarido, Centro de Ci^encias, Universidade Federal do Ceara (UFC), Campus do Pici, Caixa postal 6021, CEP 60455-970, Fortaleza, Ceara, Brazil. E-mail: [email protected] doi: 10.1111/eff.12231 1 Terra et al. actions, which are inherently local in scale, and may Ontogenetic segregation of some fish species is limit the ability of species to persist in a local com- also observed in Atlantic Forest streams. In some munity (Hoeinghaus et al. 2007). Because rivers are populations, small individuals are found in lower one of the most threatened ecosystems in the world reaches, whereas larger individuals and adults con- (Dudgeon et al. 2006), with projected high faunal centrate in upper reaches (Abilhoa et al. 2011). Dur- extinction rates, it is vital to develop a consistent ing the wet season, eggs, larvae and small individuals understanding of the patterns and processes that of those species are carried to lower reaches, and as determine aquatic diversity at different spatial scales they grow, they increase their swimming capability (Ibanez~ et al. 2007). and then explore upstream habitats, where they repro- The Atlantic Forest biome has high levels of biodi- duce (Abilhoa et al. 2011). Such human interventions versity and is considered one of the 25 global biodi- as dam building, clear-cutting of riparian vegetation versity hotspots in regard to endemism and degree of and contaminant discharges may create structural, threat (Myers et al. 2000). One of the biggest threats thermal and chemical migration barriers leading to is urbanisation, considering that 58.1% of the Brazil- declines of natural populations (Casatti et al. 2006a), ian population lives in the Atlantic Forest, and more dominance of generalist species (Casatti et al. than 80% of the original vegetation cover has been 2006b), establishment of non-native species (Cucher- removed (SFB 2014). Streams are one of the most ousset & Olden 2011) and modifications in natural threatened components of this biome; most of which longitudinal patterns. However, the wide range in are small, highly isolated coastal systems harbouring natural variability along the longitudinal gradient numerous endemic species (Abilhoa & Bastos 2009; confounds our ability to detect the effects of human- Nogueira et al. 2010). Of the 260 species of fish cur- induced changes in these streams. rently identified in this region, 70% are endemic The most influential drivers of fish assemblage (Abilhoa et al. 2011). organisation in Atlantic Forest streams have been pre- In these small Atlantic Forest streams, environmen- sumed to be local habitat characteristics such as tal conditions vary considerably longitudinally over cover, water velocity, substrate, riparian vegetation, relatively short distances (200 km, altitudes from 0 depth, current velocity and water quality. In tropical to 2000 m) (Aranha & Caramaschi 1999; Lowe- environments, that may be because most studies have McConnell 1999). Headwater streams have high focused on local environmental influences on fish velocities, waterfalls, boulder substrates, small pools, assemblages or populations (e.g. Ferreira & Casatti cool clear water and dense riparian vegetation. Mid- 2006a; Rezende et al. 2010). Catchment-scale vari- dle reaches have moderate velocities, gravel sub- ables (e. g. geomorphology, annual precipitation, dis- strates, runs and larger pools, warmer water and tance to the estuary, area above the sampling site and disturbed riparian vegetation. Lower reaches have land cover) have been pointed out as those that alto- low velocities, sand and silt substrates, many large gether define lower-level, instream properties (Poff pools, warm turbid water and highly fragmented 1997). However, some studies suggest that land- riparian vegetation. In other words, these streams fol- scape-scale properties, such as catchment land cover, low the river continuum concept (RCC; Vannote better predict local stream conditions (see Kautza and et al. 1980), but with little change in stream order. Sullivan 2012). Human influences, particularly land According to the RCC, changes in food sources use and land management practices, also influence along the fluvial continuum constrain the trophic reach-scale habitat (Richards et al., 1996). Because groups of aquatic organisms within communities. the catchment-scale studies are less common, and Based on this concept, fish species that are general- mostly focused on determinants of species richness ised invertebrate feeders are expected in upstream (Hoeinghaus et al. 2007; Macedo et al. 2014), our reaches, whereas omnivores, detritivores, herbivores ability to understand catchment-scale controls is lim- and piscivores become more abundant in larger ited. However, catchments are the chief management reaches downstream (Vannote et al. 1980). Some focus in Brazil and are needed for effective manage- tropical stream studies have corroborated this pattern ment intervention for protecting and recovering eco- using taxonomic species data (Mazzoni & Lobon- system integrity (Lake et al. 2007). Cervia 2000; Mazzoni & Iglesias-Rios 2002; Suarez The use of functional groups along with taxonomic & Petrere-Junior 2007; Suarez & Lima-Junior 2009; data can be helpful, but they are still largely unde- Goncßalves & Braga 2012). These studies suggest that rused for understanding fish assemblage organisation differences along longitudinal gradients in tropical in tropical ecosystems. Some functional groups (e.g. rivers are among the main determinants of fish spe- trophic guilds, water column habitat) have been cies distribution (Mazzoni et al. 2006; Araujo et al. applied in multimetric biotic indices (Ferreira & Cas- 2009; Ferreira & Petrere 2009) and their