WEWeb EcologyWEWeb Ecol.1399-1183Copernicus PublicationsGöttingen, Germany10.5194/we-16-13-2016Relations between environmental gradients and diversity indices of benthic
invertebrates in lotic systems of northern ItalyAschonitisV. G.schvls@unife.ithttps://orcid.org/0000-0003-4852-5992CastaldelliG.FanoE. A.Department of Life Sciences and Biotechnology, University of Ferrara,
Ferrara, V. L. Borsari 46, 44121, ItalyV. G. Aschonitis (schvls@unife.it)1February2016161131519September201529December201519January2016This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://we.copernicus.org/articles/16/13/2016/we-16-13-2016.htmlThe full text article is available as a PDF file from https://we.copernicus.org/articles/16/13/2016/we-16-13-2016.pdf
The relations between environmental gradients, as measured by 19 independent
variables, and traditional diversity indices (taxonomic richness, diversity
and evenness) of benthic macroinvertebrate communities in the lotic systems
of northern Italy were analyzed. Redundancy analysis (RDA) was used to
describe the response of taxa to environmental gradients. Diversity indices
were analyzed using generalized linear models (GLMs) with explanatory
variables the first two major RDA axes. The results from RDA showed that taxa
variance is mostly explained by altitude/latitude and combined pollution
gradients. Taxonomic richness and diversity was higher in the low polluted
upland sites (LPUs) in comparison to high polluted lowland sites (HPLs),
suggesting that headwater streams have higher taxonomic richness than
downstream reaches. On the other hand, evenness was lower in LPUs, probably
due to the dominance of some taxa (e.g., Plecoptera) that are more tolerant
of colder conditions.
RDA ordination graphs: (a) environmental gradients,
(b) sampling stations, (a–f) taxa in parts,
(g) richness S′, (h) diversity H′ and
(i) evenness J′ (for abbreviations, see Tables S1 and S2).
GLMs for species richness S′, diversity H′ and evenness J′.
Benthic macroinvertebrates are considered extremely sensitive to
environmental changes and gradient analysis is a suitable method for
analyzing the effects of various environmental stressors on their communities
and consequently on their diversity indices (taxonomic richness, diversity
and evenness) (Feld and Hering, 2007). The aim of the study was to combine
gradient analysis and GLMs in order to describe the effects of environmental
stressors on traditional diversity indices of macroinvertebrates in lotic
systems of northern Italy.
Materials and methods
Field surveys between 2003 and 2013 yielded 98 taxa and 31 micro–meso scale
parameters of water quality, hydromorphology and land use (Tables S1 and S2
in the Supplement) from 585 sampling stations of northern Italy (Fig. S1 in
the Supplement). The data were analyzed using redundancy analysis (RDA) with
CANOCO 4.5 (ter Braak and Smilauer, 2002). Detailed description about the
taxa and environmental parameters, and RDA analysis is given in detail in
Aschonitis et al. (2016). Initial RDA simulations were performed to identify
collinear variables. The analysis showed 19 non-collinear environmental
variables that were used in the final RDA. All the ordination plots were
created using as a base the triplot graphs (env.parameters, taxa,
sampl.stations) that provide axis values between -1 and 1. Considering as a
base the RDA results, further analysis was performed on diversity indices
such as species richness S′= ln(S), Shannon's diversity index H and
the Pielou evenness index J. The first two ordination axes of RDA for taxa
were used as independent variables in generalized linear models (GLMs) in
order to describe the diversity indices. The analysis was performed using the
GLM module that is incorporated into the CanoDraw-CANOCO testing linear,
quadratic and cubic degree models and following the options “stepwise
selection using F statistics for p < 0.05” and “the maximum
value for binomial total settings”. For S′ and H, a linear model with
“Gaussian distribution” was used, while for the J index a quadratic model
with “Binomial distribution” was used. The models were used to construct
isolines of the diversity indices on the same RDA ordination graphs. The
selection of GLMs was made taking into account the deviance and Akaike's
information criterion (AIC).
Results and discussion
The results of RDA analysis using the two major ordination axes showed that
the cumulative proportion of taxa variance explained by environmental
variables and the taxa–environment relation was 30.0 and 82.2 %,
respectively (Tables S3 and S4). According to Fig. 1a, b, a clear division of
sampling stations is observed in two distinct groups along the first axis:
(a) the lower latitude/altitude areas that are highly impacted by
anthropogenic activities (high pollution lowland stations – HPLs) and
(b) the low impacted areas of higher latitude/altitude (low pollution upland
stations – LPUs) (Fig. 1b). The latitudinal/altitudinal gradient (surrogate
of climate and hydromorphology) and the combined pollution gradient
(surrogate of water quality parameters) are the main environmental regulators
of taxa distribution. Figure 1c–f shows the response of different groups of
taxa to environmental gradients.
The two major ordination axes of RDA (Fig. 1b) were used as independent
variables to describe the taxonomic richness S′, diversity H′ and
evenness J′ using GLMs. The statistics of the GLMs are given in Table 1
and the isolines graphs of each diversity index are given in Fig. 1g–i,
respectively. The Fig. 1g–i in conjunction with Fig. 1a, b showed that
taxonomical richness and diversity are mostly regulated by the first major
axis of RDA (see coefficients in Table 1). The higher richness and diversity
of the LPUs suggests that headwater streams have higher taxonomic richness
than downstream reaches, verifying Clarke et al. (2008).
In the case of evenness, the second ordination axis had the more significant
contribution, especially in the low polluted upland sites (LPUs), while the
first ordination axis had the opposite impact with respect to richness and
diversity. These effects leaded to lower evenness in the LPUs in comparison
to HPLs, probably due to the dominance of some taxa (e.g., Plecoptera) that
are more tolerant of colder conditions. Such cases of species-taxa dominance
are well documented for the Alpine rivers by Brittain and
Milner (2001).
The Supplement related to this article is available online at doi:10.5194/we-16-13-2016-supplement.
Acknowledgements
This study was supported by national, regional, and local public funds in the
context of national programs concerning freshwater quality monitoring and
environmental impact assessment in the regions of Veneto, Lombardy, and
Trentino-Alto-Adige. Edited by:
S. Navarrete Reviewed by: two anonymous referees
References
Aschonitis, V. G., Feld, C. K., Castaldelli, G., Turin, P., Visonà, E.,
and Fano, E. A.: Environmental stressor gradients hierarchically regulate
macrozoobenthic community turnover in lotic systems of Northern Italy,
Hydrobiologia, 765, 131–147, 2016.
Brittain, J. E. and Milner, A. M.: Ecology of glacier-fed rivers: current
status and concepts, Freshwater Biol., 46, 1571–1578, 2001.
Clarke, A., Mac Nally, R., Bond, N., and Lake, P. S.: Macroinvertebrate
diversity in headwater streams: a review, Freshwater Biol., 53, 1707–1721,
2008.
Feld, C. K. and Hering, D.: Community structure or function: effects of
environmental stress on benthic macroinvertebrates at different spatial
scales, Freshwater Biol., 52, 1380–1399, 2007.
ter Braak, C. J. F. and Smilauer, P.: CANOCO Reference Manual and CanoDraw
for Windows User's Guide Version 4.5. Wageningen and České
Budějovice, 2002.