Factors determining the structure of fish assemblages in Tarumã River, Jaru Biological Reserve, Machado River drainage, northern Brazil

ABSTRACT Few studies on fish assemblages and relations with environmental factors in aquatic systems in southeastern Amazonia have been carried out when compared to other areas in the Amazon. Therefore, which are the main environmental variables and processes responsible for structuring them remains unknown. We hypothesized that fish assemblages respond the variation in the physical-chemistry variables between seasons of the hydrological cycle in a pristine river in the Amazon. The study was performed on fish assemblages of the Tarumã River, Jaru Biological Reserve, Rondônia. Samplings were carried out in five sites along the river in March and September, 2015, which included fish collection and environmental data measurements. Principal component analysis was performed to ordinate the sites in high water and low water seasons, according to environmental variables. We used a similarity analysis in order to identify the individual contribution of species in hydrological period and a partial redundancy analysis for quantify the relative importance of environmental variables in the species composition. As predicted by our hypothesis, the species composition was influenced by dissolved oxygen and temperature. Myloplus rubripinnis, Serrasalmus compressus, and S. rhombeus were the most abundant during high water, while S. rhombeus, Myloplus lobatus, Prochilodus nigricans, and Hydrolycus armatus were the dominant species during the low water.

Spatial and temporal variation and the influence of environmental parameters in a fish community in the Una River, Paraíba do Sul Valley, São Paulo

Understanding of aspects of the structure of ichthyological communities and how these relate to the environment and its natural variation has been one of the principal objectives of ecological studies conducted in freshwater environments. The objective of this study was to evaluate the relationship between fish species composition in the Una River and environmental variables during dry and rainy seasons. Data collection was done along three stretches of the main channel of the Una River between April 2016 and March 2017. In general, the riverbed presented a high degree of silting in all study sites. A total of 1,534 fish specimens from thirty species were collected. There was greater richness and abundance of species during the rainy season in all sampled areas. A Partial Redundancy Analysis (pRDA) showed a significant correlation between the fish community, substrate composition, and concentrations of dissolved oxygen in the water. The qualitative structure of the ichthyofauna indicated a greater association with environmental structure than with seasonality, since there was a clear tendency for the three stretches of river to group together independent of the sampling period. There were no significant differences between the indices of diversity registered for the dry and rainy seasons. This is due to the dominance of the species Astyanax aff. bimaculatus (two spot Astyanax | lambari-do-rabo-amarelo) and Hypostomus cf. luetkeni (armoured catfish | cascudo), which represented more than half of the collected specimens during the rainy season.

Mosquito Community Composition, Seasonal Distributions, and Trap Bias in Northeastern Florida

Mosquito control agencies monitor mosquito diversity and abundance through a variety of trap types. Although various long-term ecological data sets exist, little work has been done to address the sampling effort required to capture mosquito community diversity by trap type and few spatiotemporal distributions of vector species have been described. Here, we describe the seasonal distributions of vector species of importance, assess trapping effort needed to capture the diversity of the mosquito community, and use a partial redundancy analysis to identify trap bias from four commonly deployed adult mosquito traps in Volusia County, Florida. Collections were made with American Biophysics Corporation (ABC) light traps, Biogents Sentinel (BGS) traps, chicken coop exit traps, and gravid traps. We collected a total of 238,301 adult female mosquitoes belonging to 11 genera and 36 species, 12 of which we deemed to be vector species of epidemiological importance. We found that ABC traps not only yielded the greatest abundance and diversity but also captured several nonvector species. BGS and gravid traps yielded the highest proportions of vector species; exit traps recorded the lowest abundances and species richness. Wintertime abundances of several species demonstrated a need for year-round surveillance in the study area; partial redundancy analysis revealed that trap type explained a significant proportion of the variance in our data set, with certain vector species associated with specific trap types. Increased awareness regarding the amount of trapping effort needed to detect vector species diversity will help to optimize efforts in the field, leading to more effective resource allocation.

Benthic Species Distribution Linked to Morphological Features of a Barred Coast

The composition of benthic species communities in the nearshore zone is closely related to the hydrodynamic and morphodynamic conditions. Sustainable management of the coastal ecosystem requires knowledge about the natural dynamics as well as human-induced changes on the ecosystem. To improve our knowledge of the benthic species distribution along a dissipative sandy shore with multiple breaker bars, an extensive dataset was collected in the nearshore zone of the barrier islands Ameland and Schiermonnikoog in the Dutch North Sea. From 2010 to 2014, every year, approximately 180 grab samples along 18 cross-shore transects were collected and analyzed for sediment characteristics and macrobenthic species composition. Mixed-effect-models and partial redundancy analysis were used to analyze the importance of morphological features (i.e., slopes, bar crests, and troughs) as an explanatory variable for the benthic species distribution. The results indicate that the morphological features in themselves explain three times more variation than the environmental parameters used. This demonstrates the importance of morphological features as a factor in explaining the distribution of benthic species communities in the nearshore. Detailed information on morphological features is easy to obtain from bathymetry maps or visual inspection. Incorporating morphological features in species distribution models will therefore help to improve sustainable management of our valuable sandy coastal systems.

Diatom-inferred aquatic impacts of the mid-Holocene eruption of Mount Mazama, Oregon, USA

High-resolution diatom stratigraphies from mid-Holocene sediments taken from fringe and central locations in Moss Lake, a small lake in the foothills of the Cascade Range, Washington, have been analyzed to investigate the impacts (and duration) of tephra deposition on the aquatic ecosystem. Up to 50 mm of tephra was deposited from the climactic eruption of Mount Mazama 7958–7795 cal yr BP, with coincident changes in the aquatic ecosystem. The diatom response from both cores indicates a change in habitat type following blanket tephra deposition, with a decline in tychoplanktonic Fragilaria brevistriata and Staurosira venter and epiphytic diatom taxa indicating a reduction in aquatic macrophyte abundance. Additionally, the central core shows an increase in tychoplanktonic Aulacoseira taxa, interpreted as a response to increased silica availability following tephra deposition. Partial redundancy analysis, however, provides only limited evidence of direct effects from the tephra deposition, and only from the central core, but significant effects from underlying environmental changes associated with climatic and lake development processes. The analyses highlight the importance of duplicate analyses (fringe and central cores) and vigorous statistical analyses for the robust evaluation of aquatic ecosystem change.

Effect of land use on mayfly assemblages structure in Neotropical headwater streams

The aim of this study was to test the effect of agricultural and forestry land use on the structure of mayfly assemblages in low-order streams. Twenty-nine headwater streams were investigated in the state of São Paulo. We analyzed 15 streams in pristine areas (mixed tropical rainforest, semideciduous forest and dense tropical rainforest), and 14 streams covered with sugarcane, eucalyptus and pasture. Mayfly richness obtained by rarefaction curves was higher in pristine areas (21 genera), especially in mixed and semideciduous forest when compared to land use (9 genera), where values were particularly low in sugarcane plantation (3 genera). The non-metric multidimensional scaling (NMDS) ordination showed clear difference in mayfly assemblages between land uses and pristine areas, supported by analysis of similarity (R=0.67, p=0.001). In partial redundancy analysis (pRDA), the environmental descriptors that best explained differences in assemblage structure were Riparian, Channel and Environmental Inventory (RCE) index score, percentage of fine sediment stream substrate, water pH and land elevation. Our results show that agricultural and forestry land use has a strong negative effect on the structure of mayfly assemblages. These results also support the use of mayflies as environmental indicators, as some genera were sensitive to changes in land use, while others responded to naturally occurring changes in the study area.

Climatic variables and altitude as predictors of anuran species richness and number of reproductive modes in Brazil

Because anuran species are highly dependent on environmental variables, we hypothesized that anuran species richness and the number of reproductive modes from different Brazilian localities vary according to climatic and altitudinal variables. Published data were compiled from 36 Brazilian localities and climatic and altitudinal data were extracted from an available database. A partial redundancy analysis (pRDA) showed that 23.5% of the data set's variation was explained by climatic and altitudinal data, while the remaining 76.5% remained unexplained. This analysis suggests that other factors not analysed herein may also be important for predicting anuran species richness and the number of reproductive modes in Brazil. Altitude and total annual rainfall were positively correlated with anuran species richness and the number of reproductive modes, and total annual rainfall was strongly associated with these two biotic variables in the triplot of pRDA. The positive association of total annual rainfall and the negative association of the concentration of annual rainfall were already expected based on physiological and reproductive requirements of anurans. On the other hand, temperature was not associated with richness or the number of reproductive modes.

Analytical methods for defining stand–clearcut edge effects demonstrated for N mineralization

Edge effects are becoming an important forest management consideration, but information regarding the influence of edges on N cycling variables has not been well documented. In addition, the quantification of edge effects can benefit from the application of complementary spatial analysis methods. Forest floor N mineralization and environmental variables were intensively measured 5 years after harvest along transects crossing the north and south edges of a 1-ha clearcut, in a high-elevation Engelmann spruce – subalpine fir forest. Wavelet analysis and depth-of-edge influence (DEI) methods were used to locate and measure the spatial extent of edge effects on N mineralization. Then variance partitioning (partial redundancy analysis) was used to examine the influence of edges on N mineralization relative to the influence of other environmental factors. Initial NO3-N content and net nitrification markedly increased in the opening within 2–6 m of each edge. Net ammonification did not exhibit obvious edge-related spatial patterns. Spatial patterns of nitrification appeared to be more closely related to spatial changes in substrate quality than to soil temperature and moisture. Results of the wavelet and DEI analyses provided quantification of locations and functional extents of edge effects.

Relationships among nutrients, phytoplankton, macrophytes, and fish in prairie wetlands

Phytoplankton abundance and nutrient concentrations in shallow-water ecosystems are influenced by submerged macrophytes, zooplankton, and fish, but few studies have simultaneously assessed the influence of all three variables. We sampled 18 semipermanent prairie wetlands for 5 years to assess influences of minnows, submersed macrophytes, cladocerans, and drainage history on phytoplankton abundance and concentrations of nitrogen (N) and phosphorus (P). Our macrophyte data reflect the abundance of three distinct species assemblages (Chara, Potamogeton, and Myriophyllum assemblages) typical of these wetlands. Partial redundancy analysis showed only the Chara and Potamogeton assemblages and fish to be significantly related to algal abundance, N, and P. Macrophytes and fish together explained 40% of the total variance, but the Chara assemblage explained threefold, and the Potamogeton assemblage twofold, more variance than did presence/absence of fish. However, relationships with N and P differed for the two groups of macrophytes: P showed a strong negative relationship with both plant assemblages, and N showed a weak negative relationship with Chara but no relationship with Potamogetons. Our results indicate that phytoplankton and nutrient concentrations in prairie wetlands are strongly influenced by submersed macrophytes, although influences may depend on plant community composition.