Adriano S. Melo

Macroinvertebrates in neotropical streams: richness patterns along a catchment and assemblage structure between 2 seasons

We investigated macroinvertebrate richness in 10 streams of different sizes within the Carmo River catchment in Brazil. Specifically, we tested 2 predictions of the river continuum concept (RCC): 1) within the catchment, mid-sized streams (orders 3–4) have the richest biota, and 2) macroinvertebrate assemblage structure is more stable during the dry season than during the rainy season when natural spates are frequent. We sampled the streams using individual stones as sampling units. Observed and estimated values of richness did not follow the hump-shaped pattern of richness along a gradient of stream size as predicted by the RCC; the richest streams were smaller than those predicted. No difference in assemblage structure between seasons was found on the basis of observed and estimated richness or abundance. The similarity in assemblage structure between the rainy and dry seasons was also supported by multivariate analysis. Observed richness and species composition (reflected in multivariate analysis) were strongly correlated to stream size and the presence of fine sediments over rocks. Assemblage structure in these streams seems to be deterministic, in that richness and species composition are related to physical habitat characteristics.

Beta diversity in stream macroinvertebrate assemblages: among-site and among-microhabitat components

The benthic macroinvertebrate community is an important component of stream diversity, because its members are fundamental connectors among the different trophic levels of running waters. In this study, we assessed alpha and beta diversities of benthic macroinvertebrates in three stream sites and four microhabitats: (i) moss in the air-water interface; (ii) submerged roots of terrestrial plants; (iii) leaf litter deposited in pools; (iv) stones in riffles. We constructed rarefaction curves and compared species richness among microhabitats for each stream site. Additionally, we evaluated which factor, stream site, or microhabitat, was most important in determining variation in assemblage structure, i.e., beta diversity. There was no significant difference among microhabitats in terms of taxa richness evaluated by rarefaction curves. Using partial Constrained Correspondence Analysis (pCCA), we found that microhabitat was most important in determining community composition, accounting for 42.02% of the total variation. Stream sites accounted for 22.27%. In accordance with the pCCA, exploratory multivariate methods (ordination and classification) revealed four distinct groups, corresponding to the four microhabitats, independent of stream sites. Our results indicated that differences among environmental conditions are much more important in the determination of stream assemblage structure than are differences in spatial location. Accordingly, adjacent microhabitats in a single stream site harbor macroinvertebrate assemblages more dissimilar than those found in a single microhabitat at different stream sites.

Effects of taxonomic and numeric resolution on the ability to detect ecological patterns at a local scale using stream macroinvertebrates

With 3 figures and 3 tables Abstract: The increasing demand for methods of rapid stream bioassessment has stim- ulated the evaluation of data simplification. In particular, these studies have assessed how much power is lost when species/morphospecies identification is replaced by family identifications or use of EPT (Ephemeroptera, Plecoptera and Trichoptera) taxa only. A second simplifying factor commonly evaluated is the use of presence/absence data instead of density. These simplifications have provided valid results in most cases where differences among groups are large, particularly in studies comparing impacted vs. non-impacted stream sites and ecological studies involving large spatial scales. Here I evaluate whether data simplification, both in terms of taxonomic (families, mor- phospecies of EPT) and numeric (presence/absence) resolutions, is valid for ecological studies done at local scales, where differences among groups are subtle. Datasets used are derived from a five-year study of five stream sites situated in a catchment in south- east Brazil. Streams were sampled twice a year, in the rainy (summer) and dry (winter) seasons. I used Analysis of Similarity (ANOSIM) to evaluate if differences i) among stream sites and ii) between seasons within a stream site, revealed by using the full data set (morphospecies, quantitative data), were also detected when using the sim- plified datasets. The effect of taxonomic resolution was not significant; the two sim- plified levels of this factor (morphospecies of EPT, families) were able to recover the same groups revealed by the full dataset. However, the use of presence/absence data had a strong negative effect on the ability to distinguish groups, particularly when dif- ferences were small (between seasons within a stream site). The success in recovering groups using simplified taxonomic data agrees with previous evaluations done using datasets from applied fields and those from ecological studies involving large spatial scales. However, in contrast to results observed in applied and large-scale studies, use of simplified data quantification in local datasets resulted in significant loss of infor-

O que ganhamos 'confundindo' riqueza de espécies e equabilidade em um índice de diversidade?

In Community Ecology and in many applications of Conservation Biology, diversity means variety of species, which may or not include information on the relative importance of each species. Diversity is one of the most important attributes in the study of communities and, as a result, many methods are available to its measurement. Among them, non-parametric diversity (or heterogeneity) indices such as Shannon and Simpson formulae are widely employed in a range of studies. These indices are composed of (or confound) two components, species richness and evenness. Different indices can be obtained combining the two components with different weights. The lack of an objective criteria to guide appropriate weighting of each component results in an arbitrary decision to use an index and not another. Additionally, depending on the weight the indices give to each component, an index may indicate that community A is more diversified than community B while a second index may indicate the contrary. Also, diversity indices applied to samples differing in species richness and evenness may produce similar values. Such problems can be avoided using alternative methods. One of them is diversity profile, which includes not one index but many diversity indices differing in the weight given to each component. Additional alternatives include the use of species richness only, Whittakers diagram (or of dominance) and scatter diagrams with axes defined by species richness and an evenness index. Except by species richness, the cited alternative methods show graphically much more information than that contained in a single value produced by a diversity index. In studies requiring a response variable to be modeled in relation to predictor variables (Linear Models such as Regression and Analysis of Variance), I suggest the separate use of species richness and evenness as each one may reflect different aspect of communities.

A comparative analysis reveals weak relationships between ecological factors and beta diversity of stream insect metacommunities at two spatial levels

The hypotheses that beta diversity should increase with decreasing latitude and increase with spatial extent of a region have rarely been tested based on a comparative analysis of multiple datasets, and no such study has focused on stream insects. We first assessed how well variability in beta diversity of stream insect metacommunities is predicted by insect group, latitude, spatial extent, altitudinal range, and dataset properties across multiple drainage basins throughout the world. Second, we assessed the relative roles of environmental and spatial factors in driving variation in assemblage composition within each drainage basin. Our analyses were based on a dataset of 95 stream insect metacommunities from 31 drainage basins distributed around the world. We used dissimilarity-based indices to quantify beta diversity for each metacommunity and, subsequently, regressed beta diversity on insect group, latitude, spatial extent, altitudinal range, and dataset properties (e.g., number of sites and percentage of presences). Within each metacommunity, we used a combination of spatial eigenfunction analyses and partial redundancy analysis to partition variation in assemblage structure into environmental, shared, spatial, and unexplained fractions. We found that dataset properties were more important predictors of beta diversity than ecological and geographical factors across multiple drainage basins. In the within-basin analyses, environmental and spatial variables were generally poor predictors of variation in assemblage composition. Our results revealed deviation from general biodiversity patterns because beta diversity did not show the expected decreasing trend with latitude. Our results also call for reconsideration of just how predictable stream assemblages are along ecological gradients, with implications for environmental assessment and conservation decisions. Our findings may also be applicable to other dynamic systems where predictability is low.

Responses of aquatic invertebrate assemblages and leaf breakdown to macroconsumer exclusion in Amazonian "terra firme" streams

Many authors have reported a lack of insect shredders in tropical streams and some have suggested that macroconsumers, such as fish and shrimp, are potential substitutes for insect shredders. We experimentally excluded macroconsumers (fish and shrimp) from leaf packs to examine their role in determining the rate of leaf breakdown and their effects on the associated invertebrate community. The experiment was designed in blocks and replicated in two reaches of four streams. Temperature of all stream reaches studied was 24 °C (without variation), and water conductivity was low, varying from 8.8 to 10.8 μs/cm. Fish were never observed near the leaf packs and therefore the effects of the macroconsumer treatment were attributed to shrimps. We found a significant effect on leaf breakdown, with greater leaf breakdown (i.e., less mass remaining after 17 days) in the control (65 % leaf mass remaining) compared to the macroconsumer exclusion (70 % leaf mass remaining). However, the mechanism for this effect was not clear. Considerable variation in leaf decomposition occurred among blocked stream sites, suggesting that some factors differing among these sites, perhaps macroinvertebrate shredder abundance, was contributing to decomposition. Leaves were visually inspected at the conclusion of the experiment and there was no sign of shrimp directly feeding on the leaves. There was no difference in insect shredder abundance between treatments. There was, however, a significantly greater amount of non-mining chironomids in the absence of macroconsumers. This is probably due to the release from predation by shrimp.

Focando na variação: métodos e aplicações do conceito de diversidade beta em ecossistemas aquáticos

Ecologists usually estimate means, but devote much less attention to variation. The study of variation is a key aspect to understand natural systems and to make predictions regarding them. In community ecology, most studies focus on local species diversity (alpha diversity), but only in recent decades have ecologists devoted proper attention to variation in community composition among sites (beta diversity). This is in spite of the fact that the first attempts to estimate beta diversity date back to the pioneering work by Koch and Whittaker in the 1950s. Progress in the last decade has been made in the development both of methods and of hypotheses about the origin and maintenance of variation in community composition. For instance, methods are available to partition total diversity in a region (gamma diversity), in a local component (alpha), and several beta diversities, each corresponding to one scale in a hierarchy. The popularization of the so-called raw-data approach (based on partial constrained ordination techniques) and the distance-based approach (based on correlation of dissimilarity/distance matrices) have allowed many ecologists to address current hypotheses about beta diversity patterns. Overall, these hypotheses are based on niche and neutral theory, accounting for the relative roles of environmental and spatial processes (or a combination of them) in shaping metacommunities. Recent studies have addressed these issues on a variety of spatial and temporal scales, habitats and taxonomic groups. Moreover, life history and functional traits of species such as dispersal abilities and rarity have begun to be considered in studies of beta diversity. In this article we briefly review some of these new tools and approaches developed in recent years, and illustrate them by using case studies in aquatic ecosystems.

Dissimilarity of stream insect assemblages: effects of multiple scales and spatial distances

In addition to the effects of environmental conditions, biotic assemblages may exhibit spatial structure depending on the scale of study. We tested whether the dissimilarity of stream insect assemblages is related to two types of spatial distances (stream corridor and overland distance), and evaluated the relative importance of diversity components at multiple spatial scales. Field data included assemblages of Ephemeroptera, Plecoptera, and Trichoptera found in 16 streams in four microbasins. We evaluated the relationship of the dissimilarity of assemblages with the distance types, using Mantel tests. In addition, we evaluated the relationships among the diversity components at multiple spatial scales, using additive partitioning analysis. The biological dissimilarities were correlated only with the geographical distances. Additive partitioning showed that the values of richness observed in the β1 (among Surber), β2 (among riffles), β3 (among streams), and β4 (among microbasins) were higher than those expected. The highest variation of the richness was found in β3 (30.6%). We conclude that stream faunas are distributed in patches all over the studied spatial extent, causing a weak relationship of biological dissimilarity with distance but important beta components when compared to a completely homogenous distribution of the fauna.

Explaining dissimilarities in macroinvertebrate assemblages among stream sites using environmental variables

The relationship between community structure and environmental factors usually varies according to ecosystem type, group of organisms, and spatial scale. In this study I assessed whether dissimilarities among assemblages of stream macroinvertebrates are related to differences in environmental variables. Data consisted of macroinvertebrate samples of 10 stream sites during the dry season. Seven environmental variables were assessed. The relationship among dissimilarities in assemblage structure and dissimilarities in environmental variables was assessed using the BioEnv approach. Conductivity and measures related to stream size were the most important variables. However, part of the correlation with conductivity was due to the high value observed in a single stream site, which presented a relatively distinct macroinvertebrate fauna. There was an abrupt change in assemblage structure between 4th and 5th order streams. Although the study included a single 5th order site and thus only weak generalizations are possible, this finding corroborates scattered evidence observed in previous studies. The finding that nearby sites may harbor distinct macroinvertebrate assemblages implies whole-catchment conservation strategies. As most of the remaining Atlantic Rain Forest is restricted to small fragments, restoration projects near fragments should be implemented so as to properly conserve lotic ecosystems.

Diversity of tiger moths in a Neotropical hotspot: determinants of species composition and identification of biogeographic units

The Brazilian Atlantic Forest is a Biodiversity Hotspot, yet many biological groups in this biome are poorly known. We compiled information on the diversity of Atlantic Forest tiger moths (Arctiidae) and assessed the resemblance among localities, whether arctiid assemblages are concordant with major vegetation types, and the importance of environmental factors in structuring the variation among assemblages. Additionally, we developed a procedure composed of subsampling and procrustean analysis to assess the robustness of the results from community composition ordinations when localities differ in species richness. To do this, we built a database from specimens deposited in the ten most important Brazilian entomological collections, and mapped species richness in one-degree latitude/longitude grid cells. We employed Principal Coordinates Analysis to assess similarities among the best-sampled localities. We obtained 8,667 records including 1,193 species, representing 60 and 20% of the estimated Brazilian and Neotropical faunas, respectively. Our subsampling procedure indicated that the ordination was not greatly affected by differences in species richness, and was congruent with major vegetation types. Lowland localities on the seacoast were quite distinct in species composition. A second group included localities in montane areas in the southeast part of the biome. The last group included localities in the southern region and those with Araucaria forests, and was associated with long distances from the ocean, even distribution of precipitation throughout the year, and large annual temperature ranges.