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ASSESSMENT OF RIVERINE DRAGONFLIES (ODONATA: GOMPHIDAE) AND THE EMERGENCE BEHAVIOUR OF THEIR LARVAE BASED ON EXUVIAE DATA ON THE REACH OF THE RIVER TISZA IN SZEGED

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Abundance, phenology, sex ratio, emergence pattern, mortality and larval emergence behaviour of riverine dragonflies (Odonata: Gomphidae) were studied at the Lower-Tisza reach at Szeged (168–173 rkm) during the emergence period in 2011. Three 20 meter long sampling sites were chosen and searched systematically for exuviae, dead specimens and dragonfly wings, which were left behind by bird predators. At the studied reach of the river two species form stable populations: G. flavipes and G. vulgatissimus. G. flavipes was much more abundant than G. vulgatissimus. Exuviae indicated the excess of females in the G. vulgatissimus population (altough there were no significant difference between sexes), while in the case of G. flavipes the number of individuals in both sexes were almost the same. G. vulgatissimus started to emerge first as a 'spring species', while G. flavipes started to emerge about a month later showing the characteristics of a 'summer species'. The rate of mortality in the G. flavipes population during emergence was slight and quite normal compared to the abundance of the species. Selection of emergence support of G. flavipes showed that the significant majority of the larvae chose soil, but this could have been caused by the notable minority of other types of substrates at the sampling sites. The distance crawled by the larvae from the waterfront to the emergence site differed significantly between the two species, G. vulgatissumus crawled further, and in the case of G. flavipes the effect of the measured background variables to the distance had not been proven.
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TISCIA 39, 9-15
9
ASSESSMENT OF RIVERINE DRAGONFLIES (ODONATA:
GOMPHIDAE) AND THE EMERGENCE BEHAVIOUR OF THEIR
LARVAE BASED ON EXUVIAE DATA ON THE REACH OF THE
RIVER TISZA IN SZEGED
G. Horváth
Horváth, G. (2012): Assessment of riverine dragonflies (Odonata: Gomphidae) and the emergence
behaviour of their larvae based on exuviae data on the reach of the river Tisza in Szeged. Tiscia
39, 9-15
Abstract. Abundance, phenology, sex ratio, emergence pattern, mortality and larval emergence
behaviour of riverine dragonflies (Odonata: Gomphidae) were studied at the Lower-Tisza reach at
Szeged (168173 rkm) during the emergence period in 2011. Three 20 meter long sampling sites
were chosen and searched systematically for exuviae, dead specimens and dragonfly wings, which
were left behind by bird predators. At the studied reach of the river two species form stable
populations: G. flavipes and G. vulgatissimus. G. flavipes was much more abundant than G.
vulgatissimus. Exuviae indicated the excess of females in the G. vulgatissimus population (altough
there were no significant difference between sexes), while in the case of G. flavipes the number of
individuals in both sexes were almost the same. G. vulgatissimus started to emerge first as a ’spring
species’, while G. flavipes started to emerge about a month later showing the characteristics of a
’summer species’. The rate of mortality in the G. flavipes population during emergence was slight
and quite normal compared to the abundance of the species. Selection of emergence support of G.
flavipes showed that the significant majority of the larvae chose soil, but this could have been
caused by the notable minority of other types of substrates at the sampling sites. The distance
crawled by the larvae from the water-front to the emergence site differed significantly between the
two species, G. vulgatissumus crawled further, and in the case of G. flavipes the effect of the
measured background variables to the distance had not been proven.
Key words: Gomphus flavipes, G. vulgatissimus, collections of exuviae, abundance, emergence
pattern, sex ratio.
G. Horváth, Department of Ecology, University of Szeged, H-6726 Szeged, Közép fasor 52.,
Hungary
Introduction
If we want to examine Odonata (in this
particular case Gomphidae) populations, there are
three different methods to carry out the work:
The most difficult way is the imago based
examination because of the excellent manoeuvring
skills and hiding behaviour of the adults. The
collection of larvae is also not easy, sampling can be
problematic in large watercourses. In the case of
these two methods there is another disadvantage in a
conservational point of view, as imagines and larvae
may die during the collection.
Knowing all those, the most reliable and the
simplest method to define the population size and
emergence specificity of riverine dragonflies is the
regular quantitative collection of their exuviae. The
best time to estimate the accurate size of the
Gomphidae population is during the emergence
period (Suhling and Müller cit. Farkas et al.
2012a). Beside species composition and abundance,
exuviae provide information about phenology,
pattern of emergence, sex ratio, mortality during the
emergence, we could make statement about
morphological features or even about the moult-
strategy of the larvae (Berzi-Nagy 2011, Farkas et al.
10 TISCIA 39
2009, 2011, 2012a,b; Jakab 2006). The application
of the method is highly recommended, because it
does not require the collection of living animals so it
is not objectionable in a conservational point of view
either. Furthermore, exuviae of Anisopterans remain
intact for a long time, even under unsuitable weather
conditions (Jakab 2006) so there is no need for daily
collection.
During the past few years, many studies were
published about the riverine dragonfly populations of
the Upper- and Middle-Tisza regions (Bánkuti et al.
1997; Mátyus 2006 cit. Berzi-Nagy 2011; Berzi-
Nagy 2011; Farkas et al. 2009; Farkas et al. 2012a;
Jakab 2006). Nevertheless, this present study is the
first to discuss the Gomphid assemblages of the
Lower-Tisza region.
According to literature two Gomphidae species,
the River Clubtail (Gomphus flavipes) and the
Common Clubtail (Gomphus vulgatissimus) were
expected to occur with abundance big enough to
form stable populations along this region. In the light
of the current Gomphidae based works my goals
were to reveal the sex-ratio and emergence
characteristics (phenology, emergence pattern) of the
riverine dragonflies that inhabit the reach of the river
Tisza near Szeged. I also examined the emergence
behaviour (the distance larvae crawled from the
waterfront and correlation with the variables, and
substrate preference) and mortality during the
emergence.
Materials and Methods
Study sites and sampling
Sampling was carried out at the bank of the river
Tisza within the administrative territory of Szeged
(between 168-173 river kilometers).
I chose 3 different sampling sites, one on the left
bank [L.I. (46°12'46.71"N, 20° 7'42.43"E)], and two
on the right bank of the river [R.II. (46°14'25.53"N,
20°8'57.53"E); R.III. (46°13'31.74"N, 20°8'23.20"E)],
each site was 20 m long.
Each sampling site differed from the others in
their characteristics. L.I. site was sunny, cover of
vegetation was low, and the inclination angle of the
riverbank was little. The R.II. site was shaded the
whole day, cover of vegetation was low, and the
inclination angle of the riverbank was high. The
R.III. site had sunny and always shaded parts too,
cover of vegetation was relatively high, the
inclination angle of the riverbank was medium
compared to the other two sites.
Sampling was performed between 6 May and 18
August in 2011 twice a week, usually in the third and
the fifth day.
I checked the bank of the river carefully twice
(the soil and the vegetation) in a 4-5 m zone from the
water-front. I recorded the emergence support and
the distance crawled from the water-front to the
emergence support, then I collected the exuviae with
tweezers and stored them in boxes in dry conditions.
To study the substrate-preference I determined 8
different support-types (artificial objects in the
watercourse, dead fallen leaves, exuviae, green
leaves, objects washed up by the river, roots, soil and
thin branches).
To study the mortality during the emergence, I
recorded data of individuals that were captured by
predators (wings near the exuviae indicate bird
predation), or died during the emergence due to other
reasons (e.g. abnormal moulting or abnormal wing
decompression). To determine total mortality, I also
paid attention to young adult dragonflies that were
damaged. These individuals would not live enough
to mate, they usually die shortly after emergence. I
did not count these imagines in the total number of
individuals, because in most cases I found their
exuviae next to them.
Processing of the exuviae took place at the
laboratory of the Department of Ecology of the
University of Szeged. Identification of the specimen
to species and gender level had been carried out with
a stereomicroscope. I used the keys and descriptions
of Askew (1988), Gerken and Sternberg (1999) and
Raab et al. (2006). To separate the sexes I used the
work of Berzi-Nagy (2011).
The water level and water and air temperature
data came from the on-line database
www.vizadat.hu, data of the measure station in
Szeged (173,6 river kilometer) were used as
background variables.
Statistical analysis
PAST (Hammer et al. 2001) and R (R
Development Team 2009) softwares were used to the
statistical analysis of the dataset.
To the comparison of the sex ratio of G.
vulgatissimus and G. flavipes, χ2 test was used.
To compare the distance crawled from the
waterfront to the place of emergence by G.
vulgatissimus and G. flavipes larve, Kruskal-Wallis
test was used.
The number of G. vulgatissimus larvae was so
low that if the data of this species were used by
ANOVA and linear regression the results would be
quite questionable, so during the following statistical
methods I used only the data of G. flavipes exuviae.
Linear regression was used to examine the
relationship between the amount of emerged G.
flavipes specimens and that of captured by birds.
TISCIA 39 11
The analysis of the substrate-preference of G.
flavipes was carried out with one-way ANOVA, and
Tukey-test was used to the pairwise comparisons.
Multiple linear regression was used to reveal the
connection between the distance crawled by G.
flavipes larvae and the background variables (water
level, water temperature and air temperature) and
between the number of the exuviae and the
background variables. The best model had been
chosen with Stepwise models election based on
Akaike information criterion (AIC).
Results
Abundance of species
During the examination period, 1217 exuviae
were found. Thirty two (2,6%) of them were G.
vulgatissimus, 1183 (97,2%) G. flavipes and 2
(0,2%) were Green Snaketail (Ophiogomphus
cecilia). The 1217 exuviae come from 3 study sites,
so the average number on a 20 meter long study site
is 406. In the case of G. vulgatissimus exuviae this
number is 11 and the G. flavipes is 394. In the case
of O. cecilia, there is no point talking about
population density, because of their low number.
In the case of G. vulgatissimus, there was no big
difference between the number of the individuals at
the three study sites. However, in the case of G.
flavipes, the number of the exuviae in the L.I. site
exceeded the combined number of the individuals of
the R.II. and R.III. (Fig. 1.).
Figure 1. Distribution of G. vulgatissimus (dark grey columns) and
G. flavipes (light grey columns) exuviae between the sampling
sites.
Sex ratio
From the 32 G. vulgatissimus exuviae there were
19 (59,4%) female and 13 (40,6%) male specimens. In
the case of the 1183 G. flavipes exuviae, there were
590 (49,8%) female and 591 (49,9%) male, while the
sex of 2 individuals were uncertain. There was no
significant difference between the ratio of sexes either
in case of G. vulgatissimus (χ2=0,0008; df=1; p=0,98)
or G. flavipes (χ2=1,125; df=1; p=0,29).
Pattern o f the emergen ce
G. vulgatissimus started to emerge on the 6th
May. The emergence of G. flavipes started on the
25th May.
The pattern of the emergence is fundametally
different between the two Gomphid species (Fig. 2.).
In the case of G. vulgatissimus the whole population
emerged within a month (19 days), the EM50 value
(the time needed for the 50% of the population to
emerge) is 4 days, the curve of the emergence is
steep the species act as a ’spring species’. In the
case of G. flavipes, however, the emerging of the
total population took more than two months (72
days), the EM50 value is 17 days the species act as
a ’summer species’.
If we examine the pattern of the emergence on
the basis how many exuviae had been found each
day, two peaks can be seen in the case of G. flavipes
(Fig. 3.).
Figure 2. The emergence curve of G. vulgatissimus and G. flavipes
at the investigated reach of the river Tisza at Szeged in 2011
(EM50 :the time needed for the 50% of the population to emerge;
▲–G. vulgatissimus ■–G. flavipes).
Figure 3. The emergence pattern of G. vulgatissimus and G.
flavipes at the investigated reach of the river Tisza at Szeged in
2011 (▲–G.vulgatissimus ■–G.flavipes).
12 TISCIA 39
Mortality of G. flavipes during the
eme rgence
Total mortality of G. flavipes during the
emergence period was 5,58%. According to the
literature (Farkas et al. 2011, 2012b) this is a normal
value by this abundance of the species. Larvae
consumed by predators (4,9%) make up the largest
proportion of the total value, and within predation
birds are liable for the most consumed larvae
(4,48%). These specimens can be easily
distinguished from those that were consumed by
other, unknown predators (0,42%) in most cases.
When birds eat the emerging dragonflies they leave
the uneatable wings of the insects behind, so if the
wings are found nearby the exuviae that refers to
bird predators. Linear regression shows that there is
a significant and positive correlation between the
amount of emerged dragonflies and mortality caused
by birds (β=0,52; F=15,4; df=1 and 12; p=0,002,
n=12).
The remaining proportion of mortality was
caused by abnormal moulting (0,34%) and the
abnormal decompression of the wings (0,34%).
Substrate perefe rence of G. flavipes
I used data of 763 specimen of G. flavipes
exuviae to the examination of substrate preference,
because the original support could be identified
without doubts by that many exuviae (in the other
420 case the exuviae were found lying on their back,
or due other reasons I could not identify the original
support). According to one-way ANOVA there is a
significant difference between the support choice
(F=7,832; df=7,16; p<0,0003), the majority of the
larvae chose soil as an emergence support (Table 1.).
Tukey’s pairwise comparison shows (Table A.1.)
that soil is significantly differ from any other
supports and between other support types there are
no significant difference in terms of preference.
Table 1. Substrate types chosen by G. flavipes larvae at the reach
of the river Tisza in Szeged.
support type
number of
individuals
percentage of
individuals
fallen leaves
14
1,83
exuviae
5
0,66
roots
6
0,79
artificial object
10
1,31
washed up objects
7
0,92
soil
687
90,04
branches
12
1,57
green leaves
22
2,88
Total
763
100
Distance crawled from waterfront, number
of exuviae and connecti on with
background variables
According to the distance data crawled by
larvae, there is a significant difference between G.
vulgatissimus and G. flavipes populations (Kruskal-
Wallis-test: H=13,35; Hc=13,35; p<0,0005). G.
vulgatissimus crawl greater distance
(horizontal+vertical) from the waterfront than the
other species, although there was no vertical
movement observed of G. vulgatissimus specimens.
(Figure 4. and Table 2.).
Water level, water temperature and air
temperature (investigated their effects individually)
have no significant effect on the distance crawled by
G. flavipes larvae (Linear regression: β=-0,24;
F=0,35; df=7,3; p=0,79; n=12), and they have no
significant effect if we assume interaction between
them either (Linear regression: β= 0,07; F=1,11; df=
7,3; p=0,51; n=12). None of the models were
supported by the AIC.
Nevertheless, marginally significant positive
connection was found between water temperature
and the number of exuviae (Linear regression:
β=0,52; F=14,1; df= 1,11; p=0,003; n=13).
Figure 4. Distance crawled by the larvae of G. flavipes and G.
vulgatissimus from the waterfront to the emergence substrate at
the reach of the river Tisza in Szeged.
Discussion
At the investigated reach of the river Tisza G.
vulgatissimus and G. flavipes seem to form stable
populations. Although there is a huge difference
between the abundance of the two species this
phenomenon seems to be normal along the river
Tisza and every other places where the two species
occur together. (Jakab and Dévai 2008). In 2011 at
Szeged the abundance of G. flavipes was 36 times
bigger than G. vulgatissimus, many authors inform
about a similar result, nevertheless, the differences in
TISCIA 39 13
abundance quoted by these papers are greatly
variable. According to Jakab (2006) at the reach
between Tiszafüred and Tiszacsege in 2001 the
abundance of G. flavipes was 8 times greater, during
the following years the abundance of G. flavipes was
much more greater than the abundance of G.
vulgatissimus: 11 times greater in 2002; 23 times
greater in 2003 and 26 times greater in 2012 (Farkas
et al. 2012a). At Vásárosnamény in 2008 the
abundance of G. flavipes was 2 times greater than the
abundance of G. vulgatissimus (Farkas et al. 2008).
As we can also see the differences increase toward
the south greatly, it could be possible that the
southern regions of the river Tisza can provide better
conditions for the populations of G. flavipes, as this
species, in his paper Berzi-Nagy (2011) made the
same conclusions.
In the case of O. cecilia it is quite sure that the
species has no stable population at the investigated
reach of Tisza. This species, as well as the Small
Pincertail (Onychogomphus forcipatus), the fourth
occurring Gomphid in Hungary, prefers small rivers
and streams with high oxygen level and moderate
flow (Raab et al. 2006). The two specimens might
have drifted from the river Maros, where they form
populations (Jakab and Dévai 2008).
The result of the investigation shows that in
2011 at Szeged there was no significant difference
between the ratio of sexes either in case of G.
vulgatissimus or G. flavipes. In the case of G.
flavipes the number of individuals in both sexes are
almost the same. Although, for the subgenus
Anisoptera it is general that the number of females is
higher than the number of males (Berzi-Nagy 2011;
Farkas et al. 2009; Jakab 2006) similar result may
occur (Jakab 2006). It is also an example that the sex
ratio of a certain species differ at the same reach of a
river between years (Corbet 1999 cit. Farkas et al.
2009), so it is possible that next years the sex ratio of
the G. flavipes also will change.
In 2011 at Szeged the G. vulgatissimus acted as
a ’spring species’ (the species emerged strongly
synchronized within a short time) the G. flavipes as a
’summer species’. (the emergence was less
synchronized and stretched in time) This
phenomenon can be observed at other regions of the
river Tisza during the last decade as well. According
to Berzi-Nagy (2011) the emergence pattern of G.
flavipes showed the trait of a ’spring species’ at the
Middle-Tisza region near Szolnok. Jakab (2006)
reported the same phenomenon from that region, but
during his three year long investigation the pattern of
the emergence of G. flavipes varied between years,
too, and the differences were significant. Similarly to
sex ratio, the pattern of emergence can vary between
years, and also between different reaches of one
certain river. Variability could be caused by water
temperature: lower water temperature in winter and
higher one during summer caused more synchron-
ized emergence (Suhling 1995 cit. Jakab 2006).
The emergence pattern of G. flavipes shows two
peaks, but this cannot be explained with weather
conditions, because these peaks do not coincide with
the highest air temperatures. So in this case, cohort
splitting seems to be the best explanation to the
emergence pattern as cohort splitting and unsuitable
weather conditions can cause a long-drawn
emergence period too. The reason of cohort splitting
is that females lay eggs during the entire emergence
period and some larvae winter in the final (F0)
larval, while some in the penultimate (F-1) larval
stage. Those that winter in F-1 stage will emerge a
few days or weeks later and they cause the second
peak in the emergence pattern.
The fact that more than 90% of the larvae chose
soil as emergence support does not necessarily mean
that there is a specific attachment to the soil as
substrate. 92% of the 763 G. flavipes larvae emerged
within 2 meters from the waterfront and 78% of
them within 1,5 metres. There is a possibility that the
over-representation of the soil has caused this
phenomenon, as during most of the emergence
period there were no or was in very low proportion
of other substrates in the first 1,5-2 meter zone
from the waterfront. Former studies (Farkas et al.
2009, 2011) claim that in the case of G. flavipes
larvae there is no substrate-specific attachment, but
they choose supports that are available within a
certain distance from the waterfront. This idea is
supported by the observation that larvae that chose
Table 2. The mean, standard deviation and maximum values of distances (horizontal, vertical and total) crawled by the larvae of G.
flavipes and G. vulgatissimus.
Species
Horizontal distance
Total distance
N
Mean±SD
Max.
Mean±SD
Max.
Mean±SD
Max.
G.flavipes
104 ± 63
420
1 ± 6
72
105 ± 62
420
763
G.vulgatissimus
174 ± 114
506
0
0
174 ± 114
506
26
14 TISCIA 39
green leaves (second most frequently chosen
emergence support) did not crawl further than the
mean distance but most of them emerged in late June
and July, when the vegetation had grown in this zone
too (68% of them emerged within 2 metres; 68 %
emerged in July and 54% of them emerged within 2
metres in July).
During the emergence period in 2011 there were
66 G. flavipes exuviae, larvae or young imagines
found consumed by predators or wounded mortally
at the investigated reach of the river. This proportion
at this density is quite normal (Farkas et al. 2011,
2012a,b). Due to the emergence strategy of the
species [larvae emerge close to the waterfront and
the entire process takes 15-59 minutes, which is very
short compared to other Anisoptera taxa (Farkas et al
2012b)] the major factor for mortality is predators,
especially birds as common blackbird (Turdus
merula) and white wagtail (Motacilla alba) (personal
observation and Farkas et al. 2012a,b).
Results of the present study shows that G.
vulgatissimus larvae crawl greater distances from the
waterfront than G. flavipes larvae, as there is a strong
significant difference between the crawled distance
(from the waterfront to the emergence support) of the
two species. This seems to be general along the river
Tisza (Farkas et al. 2009, 2011, 2012a,b), and the
explanation is that G. vulgatissimus starts emerging
in late April or early May when greater fluctuations
of the water-level is possible, while in late May or
early June, when the G. flavipes starts the
emergence, there is a less chance of the fluctuation
of the water level (Farkas et al. 2012b).
The background variables could have a strong
effect to the emergence of the Gomphidae species:
Berzi-Nagy (2011) claims that the level and
temperature of water could influence the rate of
synchronization and the timing of emergence.
Moreover, according to former studies (Farkas et al.
2009) water level has a positive and water
temperature has a negative effect on the crawled
distance. In the case of this present study, the fact
that none of the background factors showed to effect
the distance, might be due to the low sample size.
Aknowledgement
My sincere thanks go to Judit Márton and Róbert
Gallé for the English language corrections and for
their indispensable professional guidance and useful
insights that helped me in data processing.
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TISCIA 39 15
Appendix
Table A.1
. Tukey’s pairwise comparisons for the substrate types (* marks the significant differences).
fallen leaves
exuviae
roots
artifical ob.
washed ob.
soil
branches
green leaves
fallen leaves
1
1
1
1
0,001*
1
1
exuviae
0,1053
1
1
1
0,0009*
1
1
roots
0,0936
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... Until now, studies on the selection of emergence sites have been conducted on single species [23][24][25], while most studies on the ecological niches of coexisting species have focused more on temporal rather than spatial segregation. Considering larvae, in most cases a spatial segregation was observed [26,27], while a temporal separation in the emergence patterns occurs when several congeneric species coexist in the same habitat [28][29][30]. For instance, two congeneric species, Anax imperator Leach 1815 and A. parthenope Sélys 1839, share similar environmental requirements but avoid competition through a temporal shift of their emergence peak [31]. ...
... Based on our results, the preservation of the aquatic vegetation, and especially of aquatic plants, is therefore crucial not only to guarantee the complex habitat structure that favors the emergence of A. grandis but also to permit the coexistence of the two congeneric species of Aeshnidae in the investigated sites. Although the coexistence of multiple dragonfly species is often mediated by a temporal segregation in the emergence peaks [28][29][30], the structure of the vegetation could enhance species coexistence through spatial segregation. ...
... Until now, studies on ecological preferences in the selection of emergence sites by dragonflies have mainly been conducted on single species [20,23,25]. At the same time, the potential niche overlaps among congeneric species coexisting in the same habitat have always been resolved by examining the temporal segregation [27,28,31], even if spatial segregation among Gomphus flavipes and G. vulgatissimum was observed [30]. In our case, we took advantage of the simultaneous emergence peak of the two coexisting Aeshnidae species to highlight potential spatial rather than temporal segregation. ...
Article
Full-text available
We investigated the ecological requirements in the emergence phase of two congeneric species of Aeshnidae, Aeshna grandis (Linnaeus 1758) and A. juncea (Linnaeus 1758), occurring in syntopy at the southernmost limit of their range. We sampled the exuviae of the two species at the peak of their emergence in three lakes in NW Italy. In each lake we defined 30 to 50 sampling plots along the lake borders where we checked for the presence of exuviae and collected data on the microhabitat composition. By modeling the response of the exuviae presence and abundance against the environmental parameters, we could highlight a partial differentiation in the ecological requirements of the two species at emergence. In particular, A. grandis is more influenced by the structure of the aquatic vegetation than A. juncea and the niche space occupied by A. grandis is wider, almost totally encompassing the one of A. juncea. We argue that A. grandis exploits microhabitats rich in aquatic plants to avoid competition with A. juncea. We suggest the preservation of well-structured aquatic vegetation as a key management practice to preserve the three studied populations of A. grandis, a species which has been recognized as Vulnerable for Italy according to the IUCN criteria.
... G. vulgatissimus, une espèce dite printanière, a été mieux détectée en 2016 grâce aux prospections avancées à fi n mai. Cette espèce, sensible à la qualité des eaux (GRAND & BOUDOT, 2006), est jugée rare sur le Rhône (LADET, 2013) et est régulièrement associée à S. fl avipes (GRAND et al., 2011 ;HORVÁTH, 2012). Habituellement plutôt signalé à l'amont des cours d'eau, vifs et oxygénés (GRAND & BOUDOT, 2006) : Onychogomphus uncatus a été trouvé (exuvies) sur le Gardon aval à Comps (30) en 2015. ...
... L'espèce est ainsi souvent rare à l'extérieur des méandres où l'accélération du courant chasse la fraction sablo-limoneuse (photographie 3) et en abondance à l'intérieur où elle se dépose (photographie 4). Le support d'émergence semble éclectique et surtout fonction des opportunités offertes sur la rive (MÜLLER, 1995 ;HORVÁTH, 2012). Sachant que la majorité des exuvies est trouvée à moins de 50 cm de hauteur, les phénomènes de ressac (vagues liées au vent), batillage (vagues liées à la navigation) et marnage (lâchers/ retenues d'eaux liées à l'exploitation hydroélectrique) entraînent non seulement une sous-détection des exuvies mais aussi une mortalité par noyade à l'émergence (photographie 5) (ELLWANGER et al., 2006). ...
Article
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Résumé - Le Rhône est un fleuve difficile à prospecter, parfois peu attrayant et où la connaissance odonatologique reste fragmentaire. Une étude ciblée a été lancée de 2014 à 2016, afin de confirmer l'autochtonie de 3 espèces protégées : Gomphus graslinii, Stylurus flavipes et Oxygastra curtisii et caractériser leurs habitats d'émergence sur des secteurs du Rhône méridional. Les sites suivis se situent sur 3 bras en aval de barrages hydroélectriques et sur des milieux annexes : affluents méditerranéens (Cèze et Gardon) et lônes. Les recherches d'exuvies en canoë ont été réalisées sur l'ensemble du linéaire en 2014 et sur 130 placettes de 50 m de rive en 2015 et 2016, avec 4 passages annuels. 3 495 exuvies d'Anisoptères ont été identifiées dont 43 % de S. flavipes, 31 % d'O. curtisii et 3 % de G. graslinii. S. flavipes est rarissime sur les affluents et lônes mais émerge abondamment sur le fleuve, sur des rives tant boisées qu'artificielles, sa présence étant surtout conditionnée par les zones d'accumulation de sédiments fins. Les émergences et exuvies, observées sur des supports variés, sont vulnérables au ressac et au marnage. G. graslinii émerge surtout d'un affluent, le Gardon et reste sporadique mais annuel sur le Rhône. O. curtisii émerge également rarement du fleuve mais est localement abondante sur les affluents et lônes. Cet article détaille et discute des cortèges d'espèces, habitats et supports d'émergences, phénologie, sex-ratio, détectabilité et menaces identifiés localement. ABSTRACT - The Rhône river is difficult to survey, not very appealing and odonatological knowledge remains fragmentary. A targeted study was launched from 2014 to 2016 to confirm the autochthony of 3 protected species: Gomphus graslinii, Stylurus flavipes and Oxygastra curtisii and to characterize their emergence habitats on sections of the southern Rhône. The monitored sites are located on 3 arms downstream from hydroelectric dams and on peripheral habitats: Mediterranean tributaries (Cèze and Gardon) and secondary arms. We carried out extensive searches for exuviae by surveying on a canoe both riverbanks in 2014 and on 130 plots with 50 m of riverbank in 2015 and 2016, with 4 annual passages. 3,495 exuviae of Anisoptera were identified including 43% of S. flavipes, 31% of O. curtisii and 3% of G. graslinii. S. flavipes is extremely rare on tributaries and secondary arms but emerges abundantly from the Rhône, on both wooded and artificial banks, its presence being mainly conditioned by the existence of areas where fines sediments accumulates. Emergences and exuviae, observed on various supports, are vulnerable to waves and water level variations. G. graslinii emerges mainly from a tributary, the Gardon, while on the Rhône it remains sporadic but annual. O. curtisii also rarely emerges from the Rhône but is locally abundant on tributaries and hydraulic annexes. This article presents the species assemblages, habitats, emergence supports, phenology, sex ratio, detectability and threats identified locally.
... The inter-year variations at the same site might have been attributed to the differences in annual fluctuations in the water temperature, indicating that rising temperatures may influence not only the onset of emergence but the synchrony as well. Abundance, phenology, sex ratio, emergence pattern, mortality and larval emergence behaviour of riverine dragonflies (Odonata: Gomphidae) at the Lower-Tisza reach at Szeged (168-173 rkm) was studied during the emergence period in 2011 [8]. Horváth (2012) [8] found 1,217 exuviae during the emergence period in 2011. ...
... Abundance, phenology, sex ratio, emergence pattern, mortality and larval emergence behaviour of riverine dragonflies (Odonata: Gomphidae) at the Lower-Tisza reach at Szeged (168-173 rkm) was studied during the emergence period in 2011 [8]. Horváth (2012) [8] found 1,217 exuviae during the emergence period in 2011. Differences in abundance increased towards the south greatly, it could be possible that the southern regions of the Tisza River can provide better conditions for the population of G. flavipes [2]. ...
Article
Full-text available
Till now, altogether 50 species of dragonflies have been found in the Danube and its arms in Slovakia. One of the most important indicator species is Gomphus (Stylurus) flavipes, listed as strictly protected by Appendix II of the Bern Convention. Large population of Gomphus flavipes was found in the Malý Dunaj (Small Danube), in the area called Danube’s “Inland Delta”, in 2000–2001. Watching of dragonflies in the Danube Delta (Romania) demonstrated another large population in 2007–2008. In contrast with these observations are our results, from long–term monitoring of dragonflies in the Danube, in the area influenced by the Gabčíkovo power plant (operational since 1992). Changes in hydromorphology in this section started in 19 th century and at present dam represents a significant impact on the functioning of the Danube ecosystem. During 20 years monitoring we found only one larva of Gomphus flavipes in the Danube at the site downstream of the dam. Another critically endangered species, mayfly Palingenia longicauda was found in the Danube Delta in 2009. We observed emergence of giant mayfly in the Danube ́s arm in Romania. Palingenia longicauda disappeared totally in the 1930s from many European rivers. At present it occurs in Tisza and Rába rivers (Hungary) and has been reintroduced in Lippe and Odra rivers (Germany). New findings of large populations of Palingenia longicauda in the Romanian Delta has been unknown till now. Findings of large population of Gomphus flavipes in deltas confirm that river deltas are of high importance for aquatic biodiversity conservati
... The inter-year variations at the same site might have been attributed to the differences in annual fluctuations in the water temperature, indicating that rising temperatures may influence not only the onset of emergence but the synchrony as well. Abundance, phenology, sex ratio, emergence pattern, mortality and larval emergence behaviour of riverine dragonflies (Odonata: Gomphidae) at the Lower-Tisza reach at Szeged (168-173 rkm) was studied during the emergence period in 2011 [8]. Horváth (2012) [8] found 1,217 exuviae during the emergence period in 2011. ...
... Abundance, phenology, sex ratio, emergence pattern, mortality and larval emergence behaviour of riverine dragonflies (Odonata: Gomphidae) at the Lower-Tisza reach at Szeged (168-173 rkm) was studied during the emergence period in 2011 [8]. Horváth (2012) [8] found 1,217 exuviae during the emergence period in 2011. Differences in abundance increased towards the south greatly, it could be possible that the southern regions of the Tisza River can provide better conditions for the population of G. flavipes [2]. ...
Article
Full-text available
Till now, altogether 50 species of dragonflies have been found in the Danube and its arms in Slovakia. One of the most important indicator species is Gomphus (Stylurus) flavipes, listed as strictly protected by Appendix II of the Bern Convention. Large population of Gomphus flavipes was found in the Malý Dunaj (Small Danube), in the area called Danube’s “Inland Delta”, in 2000–2001. Watching of dragonflies in the Danube Delta (Romania) demonstrated another large population in 2007–2008. In contrast with these observations are our results, from long–term monitoring of dragonflies in the Danube, in the area influenced by the Gabčíkovo power plant (operational since 1992). Changes in hydromorphology in this section started in 19th century and at present dam represents a significant impact on the functioning of the Danube ecosystem. During 20 years monitoring we found only one larva of Gomphus flavipes in the Danube at the site downstream of the dam. Another critically endangered species, mayfly Palingenia longicauda was found in the Danube Delta in 2009. We observed emergence of giant mayfly in the Danube´s arm in Romania. Palingenia longicauda disappeared totally in the 1930s from many European rivers. At present it occurs in Tisza and Rába rivers (Hungary) and has been reintroduced in Lippe and Odra rivers (Germany). New findings of large populations of Palingenia longicauda in the Romanian Delta has been unknown till now. Findings of large population of Gomphus flavipes in deltas confirm that river deltas are of high importance for aquatic biodiversity conservation.
... We found no evidence of life-history plasticity along an altitudinal gradient or an alternative life cycle like that of another spring species, Gomphus vulgatissimus (Linnaeus, 1758) (Horváth 2012), which may extend the duration of its emergence (Farkas et al. 2012) or complete its larval development in two, three or four years (Müller et al. 2000). Thus, larval development of G. lucasii at the Seybouse River did not allow for a generation to be completed within a year and was similar to that of another semivoltine gomphid, Gomphus pulchellus Selys, 1840, which also exhibits an early mass emergence, typical of a spring species (Müller & Suhling 1990; Ferreras-Romero & García-Rojas 1995). ...
Article
Full-text available
We investigated the emergence and life cycle of the endangered Maghrebian en-demic Gomphus lucasii at the Seybouse River in northeastern Algeria. Starting in mid-April, their emergence, typical of spring species, was highly synchronized and was achieved within two to three weeks. EM 50 was reached in three days. Larval sampling indicated that the syn-chrony was achieved through larvae overwintering in the F-0 stage. Noteworthy was the concomitant presence of a junior cohort throughout the year demonstrating that the species completes a generation in two years. Thus, contrary to what has been reported previously, we argue that G. lucasii is a semivoltine species with a 'slow' developmental rate congruent with its distribution in high-risk permanent habitats. This finding has important conservation implications for this threatened endemic species which is facing severe anthropogenic pressures in the context of global changes.
... Anisoptera exuviae are valuable evidence of species' presence because they reveal a breeding site with certainty and demonstrate that the species was present at all stages of the life cycle (Aliberti Lubertazzi & Ginsberg, 2009;Oertli, 2008;Raebel, Merckx, Riordan, MacDonald, & Thompson, 2010). However, their value extends much beyond occurrence detection to include estimating larval population sizes, species distributions, and sex ratios, identifying diel and seasonal emergence patterns, and other ecological applications (Corbet, 1999, chapter 7.4;Foster & Soluk, 2004;Gibbs, Bradeen, & Boland, 2004;Horvath, 2012;Raebel et al., 2010). This broad range of usefulness led Corbet (1999, p. 244) to state that "it is impossible to exaggerate the value of exuviae collection for population studies." ...
Article
Full-text available
Exuviae collections have considerable value in population studies of Odonata, but methods for standardizing collections or estimating densities and detection probabilities have been little studied. I measured sampling rates for Anisoptera exuviae and used a maximum likelihood, four-pass, depletion population estimator to standardize collections and to estimate exuvial densities and detection probabilities along 10 riverbank stations in Wisconsin. First-pass sampling rates averaged slower than the overall average for experienced collectors (0.53 m min–1 compared to 0.90 m min–1) because more exuviae were present on the first pass, increasing picking and handling time. Neither bank vegetation type (grassy versus forested) nor amount of prior precipitation affected sampling rate. Exuviae detection probabilities for a single pass ranged from 0.49 to 0.75, and averaged 0.64. The mean cumulative probability of detection increased to 0.87 after two passes, 0.95 after three passes, and 0.98 after four passes. A strong negative relationship existed between detectability and the amount of prior precipitation. Bank vegetation type did not affect detection probability. Smaller exuviae had an 8% lower probability of detection than larger exuviae. If four sampling passes are cost-prohibitive for some exuviae studies, making just two passes may provide an adequate estimate of sampling efficiency. The assumption that exhaustive collecting efforts will find all or most of the exuviae along vegetated natural banks is unfounded.
... Based on sporadic observations in the Zselic Hills (30 km east of the Mecsek Mts.), Tóth (2006) noted in brief that C. heros exuviae were found no more than 2 m horizontal from the water line and usually located one and a half or 2 m above the ground on thick tree trunks. In Germany, C. bidentata and C. boltonii crawled various maximal horizontal distances in different studies (from 420 up to 1000 cm) and also vertically (from 350 up to 600 cm), while the average distances were 1 m horizontally and 2 m vertically, without well-defined species specific differences (Gerken and Steinberg 1999;Weihrauch 2003;Liebelt et al. 2011; Table 1). Given the variation in emergence behaviours among these congeners, it is difficult to apply these results to populations of C. heros, especially under different environmental circumstances and in a different ecoregion. ...
Article
Full-text available
In odonates, the emergence behaviour and finding suitable substrates for successful molting may influence the next generation and ultimately can determine the survival of the entire population. Understanding emergence behavior of endangered species and those granted special conservation status is particularly important. Despite this, little is known about the life history and emergence behaviour of Cordulegaster heros, a characteristic inhabitant of headwater streams. We hypothesised that the taxonomic composition and structure of the vegetation significantly affect the travel distance to the emergence site and the substrate choice. Two stream sections with different riparian zone vegetation were surveyed for exuviae in the emergence periods in two consecutive years, supported with detailed vegetation mapping. Significant differences were found between the vegetation characteristics at the two sites and differences were also found between emergences in edge zones within a site, indicating that the importance of vegetation structure operates within the scale of sites as well as between sites. At the site with more diverse vegetation, smaller horizontal but higher vertical travel distances and more varied emergence substrate choice were found. Habitat composition and complexity appears to determine the emergence behaviour of C. heros, so for the successful conservation of this species we recommend choosing appropriate forest management regimes and even maintaining riparian forests in near-pristine condition.
Thesis
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Understanding the consequences of past and future climatic changes on biodiversity has become one of the most important challenges of current ecological research. Due to the funda-mental importance of climate for determining the distribution and abundance of species, climatic changes have led to strong shifts of species’ ranges to higher altitudes and latitudes as well as to local changes in the phenology and abundance of species during the last decades. Nevertheless, most organisms are incapable of rapid responses to such changes as they are constrained by, for instance, phylogenetic conservatism in thermal adaptations and dispersal limitations. Therefore, a mechanistic understanding of the variation in functional traits of species is crucial for predicting biological responses to climate change. However, so far, most trait-based inferences focused on endotherm taxa, whereas the physiological processes shaping the diversity patterns of ectothermic organisms, particularly of insects, remain poorly understood. The overall objective of this PhD thesis is to investigate the importance of interactions between environmental factors and species’ functional traits across regions, scales and taxa, to improve forecasts of the ecological consequences of climate change as well as our understanding of the ecological and evolutionary processes that determine biogeographical patterns, the range size and the abundance of insects. Insects, like 99.9 % of the species on our planet, are ectothermic organisms that in contrast to endothermic organisms, mainly depend on thermal energy from their environment for their activity and for maintaining vital physiological processes. Ectotherms therefore evolved adaptations to the temperature regime in which they live. From a physiological perspective, strong arguments exist that biophysical principles link variation in species’ colour lightness and body size to heat gain and loss in endothermic animals. Larger species retain body heat more efficiently than smaller species owing to their lower surface-area-to-volume ratio, and darker coloured species heat up faster than lighter coloured species because they absorb more solar radiation. Other functions include enhanced immunocompetence of larger species and enhanced pathogen re-sistance (Gloger’s rule) as well as UV protection of darker species. Mechanistic links between these two morphological traits, species’ physiolo-gy and climate are hence probably important determinants of variation in the distribution and abundance of ectotherm organisms, but the limited availability of distributional and morphologi-cal data has so far hampered a large-scale perspective on the physiological processes that shape biogeographical patterns in insects. Constraints to the evolution of species’ morphological traits and dispersal abilities can limit the colonization of regions characterized by new climates or habitats and thereby influence geographical patterns in the phylogenetic diversity or geographical rarity of taxa. On the one hand, spatial concentrations of rare species are important conservation targets, because they indi-cate the distribution of species that are both particularly vulnerable to extinction in the future and unique elements of biodiversity. On the other hand, overall patterns of these facets of diversity provide information about past dispersal events and the ecological processes that shaped contemporary patterns of biodiversity. In six chapters of my thesis I investigate whether biogeographical patterns of insect assemblages are driven by variation in the colour lightness and the body size. I show that melanin-based thermoregulation, pathogen resistance and UV protection are important mechanisms that influence the distribution of dragonflies, butter-flies and moths at both local and continental scales. In all studies, species assemblages in cooler climates are on average darker coloured than assemblages in warmer climates. Furthermore, in line with the prediction that darker colouration is advantageous in regions with high humidity and in regions with high solar radiation due to the protective functions of melanin, colour lightness generally decreases with increasing precipitation and insolation. Body size clines are less strong and differ considerably among the considered taxa. In addition, I demonstrate that contrasting effects of the benefits and the energetic costs of an investment into body size and melanization on the range size and abundance of butterfly species can offset each other when their interactions with components of the energy budget are not taken into account. Thus, larger and darker butterfly species only have wider distributions and are more abundant if they compensate the costs of an investment into body size and melanization by reducing mobility costs or increasing energy uptake. In three additional chapters, I investigate whether evolutionary constraints on species’ thermal adaptations and dispersal ability influence the composition of insect assemblages and I assess the extent to which diversity patterns of insects are shaped by the contemporary climate and historical climatic changes. Using European dragonflies, I show that both phylogenetic conservatism of thermal adaptations and dispersal limitations constrain the recolonization of previously glaciated areas of Europe, resulting in a decrease of the endemism and phylogenetic di-versity of assemblages with decreasing tempera-ture and the increasing proportion of species with a high dispersal ability. In addition, I demonstrate that the climatic changes since the Last Glacial Maximum are consistently major drivers of the endemism and species richness of mammals, birds, amphibians and dragonflies across Africa. However, the results of this study also indicate that the signatures of species’ responses to historical climatic changes differ considerably between the considered taxa and are currently less effectively protected. Finally, using a group of flightless orthopterans endemic to Africa, I exemplify that the diversity of this group, and probability most of the insect diversity today found in the Eastern Arc Mountain biodiversity hotspot, has been generated by the interplay of humid periods that allowed the spread of forest-bound lineages across Africa with aridity-driven fragmentations of forests and their associated faunas. In conclusion, I demonstrate that both body size and colour lightness are major determinants of distribution and abundance of insects, across taxa, regions and scales. Despite the significant contributions of other functions of colour lightness, such as pathogen resistance and UV protection, as well as of the thermoregulatory function of body size, melanin-based thermoregulation is the most important and a strikingly general mechanism that shapes biogeographical patterns of insect. To understand and predict the effects of body size and colour lightness on ecological dynamics of insect species it is, however, crucial to account for their interactions with components of the energy budget, because the contrasting effects of an investment into body size, wing size and melanization on the range size and abundance of species can partly offset each other. Purely correlative approaches that predict spatio-temporal variation in the distribution and abundance of insect species based on easily measured morphological traits are therefore prone to false mechanistic conclusions and likely underestimate the functional importance of morphological traits. Furthermore, phylogenetic conservatism of thermal adaptations and dispersal limitations affect trait-environment relationships and species’ responses to historical climatic changes. Together these results highlight the potential of models that integrate morphological, climatic and phylogenetic data for improving predictions of species’ responses to climate change as well as our understanding of the processes that generated and maintain the remarkable diversity of insects on Earth.
Article
Full-text available
1. Previous macrophysiological studies suggested that temperature-driven color lightness and body size variations strongly influence biogeographical patterns in ectotherms. However, these trait-environment relationships scale to local assemblages and the extent to which they can be modified by dispersal remains largely unexplored. We test whether the predictions of the thermal melanism hypothesis and the Bergmann's rule hold for local assemblages. We also assess whether these trait-environment relationships are more important for species adapted to less stable (lentic) habitats, due to their greater dispersal propensity compared to those adapted to stable (lotic) habitats. 2. We quantified the color lightness and body volume of 99 European dragon-and damselflies (Odonata) and combined these trait information with survey data for 518 local assemblages across Europe. Based on this continent-wide yet spatially explicit dataset, we tested for effects temperature and precipitation on the color lightness and body volume of local assemblages and assessed differences in their relative importance and strength between lentic and lotic assemblages, while accounting for spatial and phylogenetic autocorrelation. 3. The color lightness of assemblages of odonates increased, and body size decreased with increasing temperature. Trait-environment relationships in the average and phylogenetic predicted component were equally important for assemblages of both habitat types but were stronger in lentic assemblages when accounting for phylogenetic autocorrelation. 4. Our results show that the mechanism underlying color lightness and body size variations scale to local assemblages, indicating their general importance. These mechanisms were of equal evolutionary significance for lentic and lotic species, but higher dispersal ability seems to enable lentic species to cope better with historical climatic changes. The documented differences between lentic and lotic assemblages also highlight the importance of integrating interactions of thermal adaptations with proxies of the dispersal ability of species into trait-based models, for improving our understanding of climate-driven biological responses.
Article
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Monitoring of conservation status is an obligation arising from Article 11 of the Habitats Directive for all species of community interest. However, the development of monitoring methods for invertebrate species has received relatively little attention. Gomphus flavipes (Charpentier, 1825) and Ophiogomphus cecilia (Fourcroy, 1785) are two dragonfly species, listed in the annexes of the Habitats Directive, which suffered severe declines in the last century and have since recovered. Methods for the monitoring of these two gomphids have been proposed, but these have not been extensively tested and no abundance classes have been proposed for the evaluation of the conservation status of these species. A time-based standard sampling method is proposed for both species and results from numerous sites in Lombardy, northern Italy, are presented. Applying the standard method revealed that it is common for rivers that high water levels preclude sampling of exuviae through the summer and it is better to allow for two seasons when planning the monitoring. A further result is the fact that it was not always possible to sample the same stretches as the dynamic nature of the rivers and fluctuations in water level lead to some river banks becoming unsuitable for sampling during some visits. In these cases the time-based approach was advantageous, as the method did not need to be modified in response to the original bank section becoming unsuitable.
Article
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A comprehensive, but simple-to-use software package for executing a range of standard numerical analysis and operations used in quantitative paleontology has been developed. The program, called PAST (PAleontological STatistics), runs on standard Windows computers and is available free of charge. PAST integrates spreadsheettype data entry with univariate and multivariate statistics, curve fitting, time-series analysis, data plotting, and simple phylogenetic analysis. Many of the functions are specific to paleontology and ecology, and these functions are not found in standard, more extensive, statistical packages. PAST also includes fourteen case studies (data files and exercises) illustrating use of the program for paleontological problems, making it a complete educational package for courses in quantitative methods.
The Dragonflies of Europe Faunistical data on dragonfly (Odonata) exuvia from the active floodplain of river Tisza between Tiszabercel and Gávavencsellő (NE-Hungary). – Studia odonatol
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A sárgás szitakötő (Gomphus flavipes flavipes Charpentier, 1825) jellemzése és Tisza-menti populációinak összehasonlító elemzése (Characterization of river clubtails (Gomphus flavipes flavipes Charpentier, 1825) and comparative analysis of their populations along the river Tisza)
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Assessment of riverine dragonfly (Odonata: Gomphidae) on the basis of exuviae on the reach of the river Tisza at Vásárosnamény
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Farkas, A., Jakab, T., Dévai, Gy. (2009): Assessment of riverine dragonfly (Odonata: Gomphidae) on the basis of exuviae on the reach of the river Tisza at Vásárosnamény. -Acta Biol. Debr. Oecol. Hung. 20:65-78.
Emergence behaviour of riverine dragonfly (Odonata: Gomphidae) larvae along the Tisza river system based on exuviae surveys
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Emergence characteristics of riverine dragonflies (Odonata: Gomphidae) along the river Tisa between Tiszacsege and Tiszafüred
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Farkas, A., Jakab, T., Dévai, Gy. (2012a): Emergence characteristics of riverine dragonflies (Odonata: Gomphidae) along the river Tisa between Tiszacsege and Tiszafüred. -Acta Biol. Debr. Oecol. Hung. 27:39-50.
Mortality during emergence in Gomphus flavipes and G. vulgatissimus (Odonata: Gomphidae) along the Danube
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