Effects of deforestation on fish community structure in Ecuadorian Amazon streams

SUMMARY 1. There is little information on the impacts of deforestation on the fish fauna in neotropical streams, and on parameters influencing species diversity and community structure of fish. We analysed these aspects in 12 stream sites in the Ecuadorian Amazon. The stream sites represented a large gradient in canopy cover and were located in an area of fragmented forest. While some streams had been deforested, they had not suffered gross degradation of the habitat.
2. The species richness of stream fish was not related to deforestation. Local fish diversity (Fisher's Alpha) was positively related to the surface area of stream pools (m²). Beta diversity was higher among forested than deforested sites, indicating greater heterogeneity in species composition among forested than deforested sites. The percentage of rare species was positively correlated with canopy cover.
3. Total fish density increased with deforestation, and the fish community changed from dominance by omnivorous and insectivorous Characiformes at forested sites to dominance of periphyton-feeding loricariids at deforested sites.
4. Multidimensional statistical analysis of fish community structure showed that six environmental variables (the area of stream bottom covered by leaves, relative pool area, particulate organic matter, mean depth, conductivity and suspended solids) were related to the ordination axes. The presence of leaves, which was strongly correlated to canopy cover, was the variable most closely related to fish community structure, while relative pool area was the second strongest variable. Thus, fish community structure was strongly affected by deforestation.     

Disentangling the pathways of land use impacts on the functional structure of fish assemblages in Amazon streams

Agricultural land use is a primary driver of environmental impacts on streams. However, the causal processes that shape these impacts operate through multiple pathways and at several spatial scales. This complexity undermines the development of more effective management approaches, and illustrates the need for more in‐depth studies to assess the mechanisms that determine changes in stream biodiversity. Here we present results of the most comprehensive multi‐scale assessment of the biological condition of streams in the Amazon to date, examining functional responses of fish assemblages to land use. We sampled fish assemblages from two large human‐modified regions, and characterized stream conditions by physical habitat attributes and key landscape‐change variables, including density of road crossings (i.e. riverscape fragmentation), deforestation, and agricultural intensification. Fish species were functionally characterized using ecomorphological traits describing feeding, locomotion, and habitat preferences, and these traits were used to derive indices that quantitatively describe the functional structure of the assemblages. Using structural equation modeling, we disentangled multiple drivers operating at different spatial scales, identifying causal pathways that significantly affect stream condition and the structure of the fish assemblages. Deforestation at catchment and riparian network scales altered the channel morphology and the stream bottom structure, changing the functional identity of assemblages. Local deforestation reduced the functional evenness of assemblages (i.e. increased dominance of specific trait combinations) mediated by expansion of aquatic vegetation cover. Riverscape fragmentation reduced functional richness, evenness and divergence, suggesting a trend toward functional homogenization and a reduced range of ecological niches within assemblages following the loss of regional connectivity. These results underscore the often‐unrecognized importance of different land use changes, each of which can have marked effects on stream biodiversity. We draw on the relationships observed herein to suggest priorities for the improved management of stream systems in the multiple‐use landscapes that predominate in human‐modified tropical forests.     

Effects of habitat modification on coastal fish assemblages

The purpose of this study was to assess the influence of anthropogenic modification of coastal habitats on fish assemblages in Taiwan, comparing the abundance, species richness and taxonomic composition of fishes on natural v. artificial habitats. While there was no significant variation in the abundance or richness of fishes between natural and artificial habitats, the species composition of fishes in artificial habitats was significantly different from that of natural habitats. Natural reefs were characterized by greater abundance of Stethojulis spp. (Labridae), Abudefduf spp. (Pomacentridae) and Thalassoma spp. (Labridae), whereas anthropogenic habitats were dominated by Parupeneus indicus (Mullidae), Pempheris oualensis (Pempheridae) and Parapriacanthus ransonneti (Pempheridae). In general, it appears that specialist reef-associated species are being replaced with fishes that are much more generalist in their habitat-use. The loss of natural coastal habitats may threaten some species that cannot live in anthropogenically altered habitats, though the overall abundance and diversity of coastal fishes was not significantly different between natural and artificial habitats in Taiwan.     

Effects of reduced‐impact logging on physical habitat and fish assemblages in streams of Eastern Amazonia

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Local-scale species-energy relationships in fish assemblages of some forested streams of the Bolivian Amazon

Productivity (trophic energy) is one of the most important factors promoting variation in species richness. A variety of species-energy relationships have been reported, including monotonically positive, monotonically negative, or unimodal (i.e. hump-shaped). The exact form of the relationship seems to depend, among other things, on the spatial scale involved. However, the mechanisms behind these patterns are still largely unresolved, although many hypotheses have been suggested. Here we report a case of local-scale positive species-energy relationship. Using 14 local fish assemblages in tropical forested headwater streams (Bolivia), and after controlling for major local abiotic factors usually acting on assemblage richness and structure, we show that rising energy availability through leaf litter decomposition rates allows trophically specialized species to maintain viable populations and thereby to increase assemblage species richness. By deriving predictions from three popular mechanistic explanations, i.e. the 'increased population size', the 'consumer pressure', and the 'specialization' hypotheses, our data provide only equivocal support for the latter.     

Biogenic habitat structure and characteristics of temperate reef fish assemblages

Assemblages of non-cryptic, substrate-oriented species of fish were compared on a series of reefs in Southern California, USA. Reefs were grouped according to algal cover: dense beds of giant kelp (Macrocystis pyrifera) with turf understorey; sparse beds of giant kelp with foliose algae understorey: foliose algae < 1 m in height; and open barrens. Despite affinities to particular algal substrates by many individual species, we detected no differences in fish species richness and only weak differences in species composition among reefs of different habitat types. Planktivores and species that consume macro-invertebrates were less likely to occur on reefs that supported giant kelp; the frequencies of occurrence of three other trophic groups (piscivores, herbivores and micro-carnivores) were unaffected by giant kelp. Algal composition on reefs in Southern California is temporally highly dynamic. Changes in macro-algal composition of reefs influenced population dynamics of two fish species (black surfperch and striped surfperch) examined. Overall, the weak spatial variation in fish assemblages on reefs in Southern California appears to result from relatively unspecialized ecological requirements of many species combined with temporal changes in algal structure on reefs that are rapid relative to generation times of the fish. We hypothesize that the degree of spatial differentiation in assemblages of substrate-associated species of fish may be inversely related to the temporal constancy of biogenic reef structure.     

Effects of habitat structure on habitat use by Gammarus pulex in artificial streams

1. The influence of coarse substratum and flow, coarse substratum and food, and predation risk and flow on habitat use by Gammarus pulex was studied in three experiments conducted in artificial stream channels. Each stream channel consisted of a riffle and pool habitat.
2. Location of coarse substrata and food was manipulated by placing cobbles (coarse substratum) and leaf packs (food) in different habitats. Predation risk was varied by running experiments in the presence and absence of sculpins ( Cottus gobio ), and flow was varied by pumping water with one or two pumps.
3. In all experiments Gammarus were most abundant in pools but placement of cobbles in riffles increased use of the latter. An even greater percentage of Gammarus used riffles if leaf packs were also placed there. Decreased discharge and the presence of sculpins ( Cottus gobio ) also caused Gammarus to increase use of riffles. These data indicate that Gammarus is able to evaluate differences in habitat quality and respond accordingly.     

Effects of habitat structure on habitat use by Gammarus pulex in artificial streams

1. The influence of coarse substratum and flow, coarse substratum and food, and predation risk and flow on habitat use by Gammarus pulex was studied in three experiments conducted in artificial stream channels. Each stream channel consisted of a riffle and pool habitat.
2. Location of coarse substrata and food was manipulated by placing cobbles (coarse substratum) and leaf packs (food) in different habitats. Predation risk was varied by running experiments in the presence and absence of sculpins ( Cottus gobio ), and flow was varied by pumping water with one or two pumps.
3. In all experiments Gammarus were most abundant in pools but placement of cobbles in riffles increased use of the latter. An even greater percentage of Gammarus used riffles if leaf packs were also placed there. Decreased discharge and the presence of sculpins ( Cottus gobio ) also caused Gammarus to increase use of riffles. These data indicate that Gammarus is able to evaluate differences in habitat quality and respond accordingly.     

Ecological structure of tropical fish assemblages in wet-zone streams of Sri Lanka

The introduction of four fish species into a depauperate stream system in central Sri Lanka provided a 'natural experiment' that enabled us to determine the ecological structure of wet-zone stream fish assemblages. All the species indigenous to this 'introduction' stream system also co-occur naturally with the introduced species in nearby streams. Analyses of habitat use and dietary requirements revealed that most species in the assemblages were segregated on the basis of macrohabitat, microhabitat and food, regardless of origin of the fishes. Macrohabitat and microhabitat utilizations by species were similar in each stream of the 'introduction' system despite differences in stream conditions. Thus species distributions, relative to each other in ecological space, were consistent among streams, and with the combined data. High overlaps along the resource axes of velocity, depth, substratum and food were few. A major proportion of the high overlaps was due to associations with introduced species; especially Barbus nigrofasciatus and Barbus cumingii. The other two introduced species, Barbus titteya and Rasbora vaterifloris , were more specialized, and interacted relatively less with indigenous species. The indigenous species, however, exhibited pronounced complementarity along three resource axes representing depth, velocity and food. Rasbora vaterifloris and B. nigrofasciatus grew to larger sizes in one stream which had fewer indigenous species, suggesting competitive release. In this stream, the most common indigenous species was a dietary specialist that fed on diatoms, and B. nigrofasciatus , which fed heavily on diatoms in other streams, switched to feeding more on macrophytes. Overall, the data suggest that these assemblages are predictable, co-evolved systems with competition serving as an important structuring force that reinforces species segregation.     

Effects of multi-year droughts on fish assemblages of seasonally drying Mediterranean streams

1. This study analysed changes occurring in Mediterranean stream fish assemblages over a sequence of dry years followed by a generally wet period (1991–98). Variations in assemblage attributes were quantified at the basin and stream reach scales, and related to variables reflecting the occurrence of unusually dry or wet conditions. 2. Assemblage variability increased along with the resolution of analysis, with little changes in species richness, composition and rank abundances, but significant variation in individual species abundances. Fluctuations in relative abundances were significantly affected by variables reflecting the severity of summer droughts and the occurrence of rainy springs. These patterns were evident at the basin scale, while variability at individual stream reaches tended to be higher and less related to rainfall patterns. 3. At least three response guilds to rainfall variation could be identified: two of the four abundant and widespread species (chub and loach) declined following dry years, whereas the two other core species (nase and eel) declined after rainy spring; one scarce native species (stickleback) increased in dry years. 4. Except at the two most upstream reaches, the assemblages tended to recover quickly to previous configuration after the changes occurring during the sequence of dry years. 5. Temporal variability of local assemblages was concordant among reaches but did not follow any consistent spatial pattern. Instead, spatial patterns in assemblage attributes changed over time in response to environmental variability, with a tendency for a disruption of upstream–downstream gradients following dry years. 6. Results supported the view that present‐day droughts cause relatively small and transient changes to Mediterranean stream fish assemblages. However, longer and more severe droughts expected under altered future climates, may result in declines or local extinctions of the most sensitive species and their potential replacement by more resistant species. Changing drought regimes thus need to be duly considered in the development of conservation strategies for Mediterranean stream fish.     

Decreased habitat specialization in macroinvertebrate assemblages in anthropogenically disturbed streams

Habitat specialists are considered to be more sensitive to anthropogenic disturbance than habitat generalists. However, a number of studies have shown that habitat specialists can be tolerant to or even benefit from environmental degradation, suggesting that the effect of disturbance on distributions and abundances of habitat generalists and specialists can be unpredictable. In this study, we assessed the effects of anthropogenic disturbance on the degree of specialization of stream macroinvertebrates in boreal streams. We first measured the niche width for each macroinvertebrate species using the Outlying Mean Index (OMI) analysis and then, using independent data sets of near-pristine and anthropogenically altered streams, we examined the effects of human disturbances on stream macroinvertebrates with different tolerances to environmental conditions. As expected, human disturbance significantly decreased the level of the specialization in stream macroinvertebrate assemblages, and taxa with narrow environmental tolerances were more sensitive to disturbance than taxa with wide tolerances. Despite being more sensitive to disturbance, taxa with narrow environmental tolerances were locally more abundant than tolerant taxa in near-pristine streams, indicating their better performance in their optimal environments. However, many tolerant taxa decreased in their occurrence in disturbed streams, suggesting that habitat generalists also tend to negatively respond to disturbance. Species-rich assemblages harboured more taxa with narrow tolerances compared with species poor assemblages, suggesting a high conservation value of streams with diverse macroinvertebrate assemblages. Consistent with findings for many biological groups, our results indicate that macroinvertebrate species specialised in certain habitats are more sensitive to environmental degradation than habitat generalists. However, contrary to many previous studies, our results suggest that only a few species are likely to benefit from anthropogenic disturbance and, therefore, environmental degradation does not necessary result in macroinvertebrate assemblages composed of a few tolerant taxa.     

Effects of livestock exclusion on in‐stream habitat and benthic invertebrate assemblages in montane streams

1. Stream and riparian ecosystems in arid montane areas, like the interior western United States, are often just narrow mesic strands, but support diverse and productive habitats. Meadows along many such streams have long been used for rangeland grazing, and, while impacts to riparian areas are relatively well known, the effect of livestock grazing on aquatic life in streams has received less attention. 2. Attempts to link grazing impacts to disturbance have been hindered by the lack of spatial and temporal replication. In this study, we compared channel features and benthic macroinvertebrate communities (i) between 16 stream reaches on two grazed allotments and between 22 reaches on two allotments where livestock had been completely removed for 4 years, (ii) before and after the 4‐year grazing respite at a subset of eight sites and (iii) inside and outside of small‐scale fenced grazing exclosures (eight pairings; 10+ year exclosures) in the meadows of the Golden Trout Wilderness, California (U.S.A.). 3. We evaluated grazing disturbance at the reach scale in terms of the effects of livestock trampling on per cent bank erosion and found that macroinvertebrate richness metrics were negatively correlated with bank erosion, while the percentage of tolerant taxa increased. 4. All macroinvertebrate richness metrics were significantly lower in grazed areas. Bank angle, temperature, fine sediment cover and erosion were higher in grazed areas, while riparian cover was lower. Regression models identified riparian cover, in‐stream substratum, bank conditions and bankfull width‐to‐depth ratios as the most important for explaining variability in macroinvertebrate richness metrics. 5. Small‐scale grazing exclosures showed no improvements for in‐stream communities and only moderate positive effects on riparian vegetation. In contrast, metrics of macroinvertebrate richness increased significantly after a 4‐year period of no grazing. 6. The success of grazing removal reported here suggests that short‐term removal of livestock at the larger, allotment meadow spatial scale is more effective than long‐term, but small‐scale, local riparian area fencing, and yields promising results in achieving stream channel, riparian and aquatic biological recovery.     

The influence of habitat homogenization on the trophic structure of fish fauna in tropical streams

Habitat homogenization is one of the most important drivers of change in riverine fauna. Therefore, the aim of this study was to determine whether habitat homogenization influences the trophic structure of fish assemblages in tropical streams. We sampled 78 streams located in pasture and crop lands to examine habitat variables and fish. Principal coordinates analysis, canonical analysis of principal coordinates, and a distance-based test for homogeneity of multivariate dispersions revealed two groups of streams, designated homogeneous and heterogeneous, based on the habitat variables. We determined trophic guilds according to the frequency and biovolume of food items. Seven guilds were identified: aquatic insectivores, terrestrial insectivores, detritivores, herbivores, omnivores, algivores, and detritivores–algivores. Homogeneous streams showed higher abundance and biomass of aquatic insectivores, detritivores, and algivores. Heterogeneous streams showed greater diversity of trophic guilds and higher abundance and biomass of terrestrial insectivores and herbivores than homogeneous streams. Our results demonstrate that trophic structure is influenced by habitat condition. Additionally, the riparian canopy and nearshore vegetation have a modulating role in the trophic structure of stream fishes due to their influence on resource supply and promotion of the physical heterogeneity of the channel.     

Influence of riparian forests on fish assemblages in temperate lowland streams

Environmental Biology of Fishes - The characteristics of riparian vegetation along streams vary with natural and anthropogenic factors. Deforestation for agricultural purposes has consequences for...     

Assessing effects of water abstraction on fish assemblages in Mediterranean streams

1. Water abstraction strongly affects streams in arid and semiarid ecosystems, particularly where there is a Mediterranean climate. Excessive abstraction reduces the availability of water for human uses downstream and impairs the capacity of streams to support native biota. 2. We investigated the flow regime and related variables in six river basins of the Iberian Peninsula and show that they have been strongly altered, with declining flows (autoregressive models) and groundwater levels during the 20th century. These streams had lower flows and more frequent droughts than predicted by the official hydrological model used in this region. Three of these rivers were sometimes dry, whereas there were predicted by the model to be permanently flowing. Meanwhile, there has been no decrease in annual precipitation. 3. We also investigated the fish assemblage of a stream in one of these river basins (Tordera) for 6 years and show that sites more affected by water abstraction display significant differences in four fish metrics (catch per unit effort, number of benthic species, number of intolerant species and proportional abundance of intolerant individuals) commonly used to assess the biotic condition of streams. 4. We discuss the utility of these metrics in assessing impacts of water abstraction and point out the need for detailed characterisation of the natural flow regime (and hence drought events) prior to the application of biotic indices in streams severely affected by water abstraction. In particular, in cases of artificially dry streams, it is more appropriate for regulatory agencies to assign index scores that reflect biotic degradation than to assign ‘missing’ scores, as is presently customary in assessments of Iberian streams.     

Mycorrhizal status of epiphytes in Malaysian oil palm plantations

Epiphytic plants were collected from four oil palm plantations in Peninsular Malaysia and their mycorrhizal status determined. Conspecific plants with a terrestrial habit (16 species) and rhizosphere soils were also examined for mycorrhizal colonization and glomalean fungi, respectively. Twelve species of glomalean fungi were recovered from the four oil palm plantation soils. Of the 29 epiphytic species in 16 families belonging to the bryophytes, pteridophytes and angiosperms, only four species of angiosperms that were facultative epiphytes and a hemiepiphyte growing within 0.4 m of ground level had vesicular-arbuscular mycorrhizal (VAM) fungi. Bioassays of organic debris from oil palm trunks did not produce vesicular-arbuscular mycorrhizas on maize. Six epiphytic species grown in the greenhouse in pots containing oil palm rhizosphere soils rooted and had VAM fungi and thus may be facultative epiphytes. Five other epiphyte species failed to grow in pots and are probably obligate epiphytes. Seven epiphyte species that established themselves in pots failed to form vesicular-arbuscular mycorrhizas.     

Temporal variability in fish assemblages from disturbed and undisturbed streams

Fish assemblages were sampled by electrofishingover a two- to ten-year period in undisturbedand anthropogenically disturbed South Carolinacoastal plain streams. Jaccard similarity,Bray–Curtis similarity, and Spearman rankcorrelations among samples collected from thesame sites over time were significantly greaterat undisturbed sites than at disturbed sites,suggesting greater fish assemblage persistenceand stability at the undisturbed sites. TheIndex of Biotic Integrity (IBI) also exhibitedsignificantly less variation over time atundisturbed sites than at disturbed sites.Physical habitat structure changed more overtime at disturbed sites than at undisturbedsites, and this variability was directlyrelated to temporal variability in fishassemblage structure. Comparisons betweenmultiple and single pass electrofishing samplessuggested that only a small proportion of thetemporal variability observed at the studysites was caused by inefficient sampling.Assessment of temporal variation in fishassemblage structure can serve as an indicatorof environmental disturbance and facilitate thedistinction of substantive ecological changefrom normal background variation.