Beta diversity of Ephemeroptera, Plecoptera and Trichoptera on multiples spatial extents in Xingu River rapids

Abstract: Aim Additive diversity partitioning has been used to explain the accumulation of diversity at different spatial scales with relative success. In lotic ecosystems, the spatial extent is extremely relevant in studies of diversity accumulation, because it encompasses environmental variation that causes changes in the observed communities. Despite of previous knowledge on the effect of extent on biological communities and diversity accumulation, little is known about the topic in aquatic insect communities in large rivers. In this context, we studied the effect of spatial extent and environmental variation on diversity components, alpha and beta, in Ephemeroptera, Plecoptera and Trichoptera (EPT) groups in Xingu River rapids. Methods The sampling was carried out in October 2015 in the dry period of the region, in nine rapids in the Xingu, Bacajá and Iriri rivers. At each collection site, five Surber samples were taken. We also recorded pH, dissolved oxygen, electrical conductivity, water temperature, and geographic coordinates. We used additive diversity partitioning to separate the diversity components α and β. For the spatial component, we generated the spatial filters using PCNM (Principal Coordinates of Neighbour Matrices) and partitioned the variance between space and environment using partial Redundancy Analysis (pRDA). Results We collected 12,249 individuals in 27 genera within 11 families in the EPT orders. The greatest accumulation of diversity was observed among rapids of the river, when the β diversity in this spatial extent was greater than the expected. The spatial structure was an indirect effect at this extent, since it is a relevant drive to environmental variables. Conclusions The results indicate that the effect of spatial extent on rapids is a contributing factor in the diversity components of aquatic insect communities in large river rapids. To the conservation and management of this environment is necessary cover as many rapids as possible, since the preservation of only a few rapids can mean a substantial loss of regional diversity.


Introduction
Community ecology aims to explain the patterns of abundance distribution and species interactions and to understand how these patterns change at different spatial extent (Hastings et al., 2011;Hepp & Melo, 2013;Mykrä et al., 2007).An intrinsic component to understanding biological phenomena is the scale of effect, because the various environmental determinants affect biological communities at different spatial extents (Hamer & Hill, 2000;Moraga et al., 2019).However, the theories most often used to explain the patterns observed in communities assume a stability of the environment in the scale of study, observing how communities' structure themselves locally or regionally with little interaction between these levels of organization (Leibold et al., 2004).
Palavras-chave: partição de diversidade; diversidade beta aditiva; rios grandes.In such a way, the spatial scale would affect in a relevant way the rates of change of species among communities, because different spatial extensions would present rates of change in their environmental variables (Veech & Crist, 2007;Barton et al., 2013;Barros et al., 2022;Godoy et al., 2022a).Thus, it is necessary to observe which factors and to what spatial extent drive these changes in community structure in order to understand possible patterns of community distributions (Balvanera et al., 2002).The species distribution and how the community composition is spatially distributed is essential to understanding how biological diversity is maintained in ecosystems, and it is relevant to biodiversity planning and conservation (Balvanera et al., 2002;Veech et al., 2002;Godoy et al., 2017Godoy et al., , 2019)).Aquatic insects are good models for studies with alternating components of biological communities, because they respond strongly to environmental conditions at different scales, from microhabitats to watersheds (Baptista et al., 2014).This group constitutes about 90% of all macroinvertebrate fauna in freshwater environments, playing a relevant role in continental aquatic systems, with participation in various ecological processes, for example, nutrient cycling, leaf decomposition, and food for fish and other invertebrates (Merritt et al., 2008;Hamada et al., 2019).The orders Ephemeroptera, Plecoptera and Trichoptera (EPT) are predominant in terms of abundance which are commonly found in rivers and streams (Rosenberg & Resh, 1993;Bueno et al., 2003;Crisci-Bispo et al., 2007;Godoy et al., 2016).
Variations in river flow and current velocity influence food distribution, nutrient removal, and microhabitat availability, consequently contributing to variation in aquatic insect diversity (Godoy et al., 2016;Leal et al., 2023).Thus, variation in the physical characteristics of the river channel, such as the presence of rapids, can directly influence the structure of aquatic insect communities.If this dependence between the community and the rapids is high, it is expected that the accumulation of diversity will be greater at spatial scales that contain distinct rapids, since each rapids presents distinct environmental conditions.Other effect of space in community composition of aquatic insects in rapids on rivers is the possibility of interchange of individuals through drift movement (Leal et al., 2023).
We evaluated the effect of spatial scale and environmental variables on beta diversity components in the Ephemeroptera, Plecoptera and Trichoptera groups of Xingu River rapids.We used the rapids of the Xingu River, because this habitat was the most accessible to sample, because in the dry period, great portions of stones of the rapids emerge of water column.We tested the hypotheses that: 1) the accumulation of genera of EPT will be greater between than within rapids 2) the accumulation of EPT will be related with the environmental and spatial variables, since these elements influence the structure of EPT communities.

Study area
The study was carried out on the Xingu, Bacajá and Iriri Rivers (02°51′33.1′′Sand 52°19′28′′W), near the city of Altamira, Pará, during the dry period, October 2015 (Figure 1).The Bacajá and Iriri Rivers are tributaries of the Xingu River, in the Amazon River Basin, located on the right side of the river.With an extension of 1500 km from its source in the Brazilian Central Plateau until its mouth in the Amazon River, the Xingu River drains an area of 531,250 km 2 (CPRM, 2023).The pH ranges from 5.5 to 7.0 with a mean conductivity of 30 μS.cm -1 , as well as high concentrations of oxygen (Sioli, 1968;Salomão et al., 2007).
The average flow rate during the flood period varies from 8,000 to 10,000 m 3 s -1 and in the dry period the average is 2,000 m 3 .s - (Norte-Energia, 2016).The flood period occurs between December and April and the dry season occurs between July and November.Because it is located near the equator, the Xingu River basin presents a warm climate and according to Köppen classification the climate is tropical and predominantly humid [Am, Sheffield et al. (2006)].The mean annual temperature in the Altamira-PA region is 27°C, the rainy season starts in November and the dry season in July (Norte-Energia, 2016).The Xingu River is characterized by a significant number of rapids its course, something not commonly found in other large Amazonian rivers.The rapids of the Xingu are predominantly consolidated substrate formed by rocks of varying sizes [large, medium, small, and even gravel; Salomão et al. (2007)].
The sampling period (October 2015) was chosen because it presents the lowest water discharges facilitating the sample procedure.The dry period has the characteristic of favoring the colonization of high densities of invertebrates, since fast and oxygenated water are favorable conditions for organisms that occur in this environment (Frissell et al., 1986;Bispo et al., 2001).
Acta Limnologica Brasiliensia, 2023, vol. 35, e23 We sampled nine rapids, six in the Xingu River, two in the Bacajá River, and one in the Iriri River.The average distance between samples units in each rapid was five meters, and between rapids was 66.65 km.

Sampling
We measured in locus the environmental variable pH, dissolved oxygen (DO, mg.L -1 ), electrical conductivity (µS.cm -1 ) and temperature (°C) in each sampling site using a probe (Hanna HI98194/10).After we measured the environmental variable, we sampled the benthic aquatic insects.We used a Surber sample (mesh size of 250 µm, with a 60 cm height and 0.5 m 2 of area) to collect the insects attached in the rocks on the rapids, in five subsample units.The collected insects were identified to the genus level.

Data analysis
The partition of the total diversity into alpha and beta components was done by the additive approach (Veech et al., 2002).The scales used for this study were: sample unit (α 1 ), rapid (α 2 ) and river (γ).The components of diversity accumulation considered in the partition were: average richness of the sample unit (α 1 ), difference between sample unit (β 1 ) and difference among rapids (β 2 ).To test the importance of each of the additive components of diversity, we use a randomization analysis and compared the observed values against the expected values in a null model for the components α, β 1 e β 2 (Veech, 2005).The communities simulated maintained the sums of row and columns to created communities comparable with the observed.
We used a Principal Coordinates of Neighbour Matrices [PCNM; Borcard & Legendre (2002)] to detect spatial relationships among the communities of the sampled points in the rapids.In order to reduce the number of spatial variables we ran a forward selection procedure in the PCNM filters to predict the community matrix (Blanchet et al., 2008).The distances between sampled points used in the PCNM calculations were estimated by the geographic coordinates.We used a partial redundancy analysis (pRDA) to assess the relative importance of environmental (pH, dissolved oxygen, electrical conductivity and temperature) and spatial (PCNM filters selected by the forward selection) variables for the structure of aquatic insect communities (Legendre & Legendre, 2012).The pRDA allows for the estimation of linear coefficients in the relation of spatial and environmental matrices with the aquatic insect community matrix, as well as the parameters of these relations.In the analyses we used two sources of variability, physical and chemical variables and pre-selected spatial filters.
We repeated the analysis two times, using the number of genera, and to the community composition (abundance per genera), to identify the effects of space and environment in distinctly components of aquatic insect communities (Godoy et al., 2017).In the analysis for genera richness the pRDA had the same characteristics of a partial regression, but we choose to use the pRDA only to standardize the results of partitioned variation in the study.The abundance of the community was standardized using Hellinger transformation, and all environment variables were standardized to normal distribution with mean equal zero and standard deviation equal one [z distribution; Legendre & Legendre (2012)].All analyses were carried out using the packages vegan and packfor in the statistical software R (Oksanen et al., 2012;R Development Core Team, 2020).

Addictive diversity partitioning
The observed values of the diversity components α 1 , α 2 e β 1 was lower than values estimated by the null model (Table 1).In other hand, the component β 2 , difference among rapids, had value greater than the expected by chance.In addition, we observed that all levels of diversity, both local and regional, had important contributions in the accumulation of genera along the Xingu River.Difference of diversity among rapids (β 2 ) were the highest, contributing the most to regional diversity.

Diversity partitioning in environmental and spatial components
The percentages of explanation of environmental and spatial variations were different for the number of genera and community composition (Table 2).Two drivers were important to the variation in the number of genera in the rapids, the spatially structured environment and the pure spatial effect.The water temperature variable was relevant in this model, representing the environment spatially structured.For community structure, only space had a relevant effect on the variance partition, although the dissolved oxygen variable was selected for the full model.The number in the parenthesis are the proportion for the total of diversity.The spatial filters selected for variance partitioning for the number of genera and community structure formed distinct sets.For genus numbers the best spatial arrangements were described by PCNM 3 and 9. Using the transformation of the axes into units of space (Guénard et al., 2010) the filters 3 and 9 represent spatial structures at distances of 92 and 36 km.For community composition the spatial filters were PCNM 2 and 3, with distances of 123 and 92 km respectively.

Discussion
The main sources for diversity of aquatic insects in Xingu River rapids were the differences among than inside communities in the rapids.At spatial scale comprising distances between rapids showing the greatest accumulation of EPT genera, and presenting the greatest difference between communities.The spatial effect (i.e., distances between sampling points) is an important factor for the structure of aquatic insect communities (Landeiro et al., 2012;Godoy et al., 2017Godoy et al., , 2019Godoy et al., , 2022a)).In our study, the spatial filters were similar in both the number of genera and the community composition both acting at greater distances between rapids.Thus, we can understand that at smaller spatial distances the greater the similarity between communities, as seen in studies in other environments (Heino, 2009;Godoy et al., 2022a).
Increasing diversity at different spatial scales allows us to understand the contributions of alpha and beta diversity over a range of spatial scales.Environmental and spatial factors are also important for aquatic insect community structure.In our study, water temperature and dissolved oxygen were relevant drivers to community of aquatic insects in the rapids.This is very characteristic of tropical regions, where temperature is a conditioning factor for the concentration of dissolved oxygen in water, becoming limiting factors for the stability of aquatic organisms (Thorp et al., 2006).Variations in physicochemical water parameters lead to functional responses of aquatic insect genera, changing the structure of these communities (Monteiro et al., 2008;Godoy et al., 2018Godoy et al., , 2019)).In addition, spatial distances need to be taken into consideration because it makes it possible to understand how elements such as spatial autocorrelation and dispersal effects can influence the aquatic insect community in rivers and streams (Peltonen et al., 1998;Ligeiro et al., 2010;Ferreira et al., 2017;Godoy et al., 2017).
The main source of variation in aquatic insect diversity in Xingu River rapids was at the meso-regional scale, since the accumulation of genera is greater when observed among different rapids in the river.The distances for selected axis of PCNM (for number of genera and community composition) was related to variation between rapids and also to all abiotic variation inside the river.Such distances would represent variations on a regional scale, suggesting dependence on abrupt physical-chemical variation in the river.The possible explanatory factor for the greater accumulation of EPT genera at the spatial distance covering the rapids may be the different characteristics of each site, creating differential environmental filters.Thus, we can infer that there is an effect of spatial scale on the structure, richness and composition of aquatic insects in the Xingu River.It can be seen that there is a relationship between environment and space, making the environment spatially structured and thus, taking into account how environmental variability is defined in the sample space, becomes important to have a real notion of the relationship between communities and the environment (Godoy et al., 2017(Godoy et al., , 2019(Godoy et al., , 2022b)).The distribution of aquatic insects is influenced by both overland dispersal (e.g., by flight) and aquatic dispersal (Landeiro et al., 2012).The structural patterns of communities of organisms that disperse by flight are clearer at larger spatial scales.Further studies are needed to observe whether the patterns found in this study are recurrent in communities where the main dispersal mode is passive by drift.In addition, the spatial scale at which the study was conducted has been identified as an important element in structuring aquatic insect communities.
The EPT orders need an environment with specific characteristics for their development, such as good oxygenation of the water and high current, so that the needs of these organisms are satisfied (Wallace & Webster, 1996;Baptista et al., 2001;Godoy et al., 2022b).The environments of rapids are highly utilized by some genera of Trichoptera, (i.e., Smicridea), and Ephemeroptera (i.e., Camelobaetidius and Baetodes) that have many representatives of omnivores or fine detritivores feeding organisms, which can only be found in places of rapid flow and which capture suspended or accumulated particles (Cummins & Klug, 1979;Wallace & Webster, 1996;Cummins et al., 2005;Ceneviva-Bastos et al., 2017).This resource is optimally obtained in rapids, highlighting the importance of flow and current velocity, and demonstrating the significance of conserving as many rapids as possible, since they are the point where diversity accumulates.In terms of conservation, the management of this environment should cover as many rapids as possible, since the preservation of only a few rapids can mean a substantial loss of regional diversity.
The Xingu River basin is undergoing major changes in its landscape characteristics due to the construction of the Belo Monte hydroelectric complex (UHEBL), which is drastically changing the water dynamics and affecting the functionality and diversity of the aquatic ecosystem (Freire et al., 2019;Godoy et al., 2023).One of the main environments affected by the damming of the river for the construction of UHEBL are the rapids, since the river level in some reaches has been reduced, causing the rapids to disappear and consequently affecting what was once recognized as an environment rich in species diversity (Araujo et al., 2014;Fearnside, 2014;Freire et al., 2019).Moreover, it can be observed that some environmental characteristics such as turbidity, temperature, riparian forest, among others that directly influence the distribution of genera have presented changes over time (Freire et al., 2019).However, this hypothesis had to be tested in the future, because these additional features lead to the formation of microhabitats that will also influence the structure of the aquatic insect community present there.The river environment is extremely sensitive to environmental changes (either man-made or natural), but the knowledge of its diversity has a deficit of studies in large rivers in the Amazon region, especially related to the EPT fauna.This raises an alert, since there are few public policies aimed at prioritizing these areas for conservation (Suring, 2022).

Figure 1 .
Figure 1.Rapids location in the Xingu, Bacajá and Iriri Rivers.Five Surber sampling units were obtained in each of the nine rapids.

Table 1 .
Observed and expected values of the addictive diversity partitioning of EPT orders in the Xingu River rapids.

Table 2 .
Variation partitioning results (R 2 ) based on pRDA analyses for different elements of aquatic insect communities.