BioRisk ie | ae 73 (20 | 0) Mees ea aaa ry doi: 10.3897/biorisk.847 RESEARCH ARTICLE & B | O R IS k http://biorisk-journal.com/ Changes in the range of dragonflies in the Netherlands and the possible role of temperature change Tim Termaat', Vincent J. Kalkman’, Jaap H. Bouwman? | Dutch Butterfly Conservation, De Vlinderstichting, PO. Box 506, 6700 AM Wageningen, The Netherlands 2 European Invertebrate Survey — The Netherlands, National Museum of Natural History Naturalis, RO. Box 9517, 2300 RA Leiden, The Netherlands 3 Groene Weide 62, 6833 BE Arnhem, The Netherlands Corresponding author: 7im Termaat (tim.termaat@vlinderstichting.nl) Academic editor: Jiirgen Ott | Received 5 August 2010 | Accepted 15 September 2010 | Published 30 December 2010 Citation: Termaat T, Kalkman VJ, Bouwman JH (2010) Changes in the range of dragonflies in the Netherlands and the possible role of temperature change. In: Ott J (Ed) (2010) Monitoring Climatic Change With Dragonflies. BioRisk 5: 155-173. doi: 10.3897/biorisk.5.847 Abstract The trends of 60 Dutch dragonfly species were calculated for three different periods (1980-1993, 1994— 1998 and 1999-2003). Comparing period 1 and period 3 shows that 39 of these species have increased, 16 have remained stable and 5 have decreased. ‘These results show a revival of the Dutch dragonfly fauna, after decades of ongoing decline. The species were categorized in different species groups: species with a southern distribution range, species with a northern distribution range, species of running waters, species of fenlands and species of mesotrophic lakes and bogs. The trends of these different species groups were compared with the all-species control group. As expected, a significantly higher proportion of the south- ern species show a positive trend than the all-species group. In the northern species group on the contrary, a significantly higher proportion of the species show a negative trend than the all-species group. Different explanations for these results are discussed, such as climate change, improved quality of certain habitats and degradation of other habitats. It is likely that the observed increase of southern species is at least partly caused by the increasing temperatures. The less positive picture of the northern species group is probably more influenced by other environmental factor than directly by climate change. Three out of six southern species which have become established since 1990 have done so during the aftermath of large invasions. It is concluded that dragonflies are well capable of using changing climate circumstances to colonise new habitats. Keywords dragonflies, Odonata, climate change, invasion, trends, conservation, Netherlands Copyright T.Termaat,V.J. Kalkman, J.H. Bouwman. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 156 Tim Termaat, Vincent J. Kalkman & Jaap H. Bouwman/ BioRisk 5: 155-173 (2010) Introduction During the last century, the Dutch dragonfly fauna has shown large changes. De- struction of habitats, canalisation of streams and rivers, desiccation, eutrophication, acidification and pollution led to an often strong decline of many species. This started in the first half of the 20" century, but was especially severe in the sixties and seventies of that century (Kalkman et al. 2002). Most affected were species of running waters and species of mesotrophic lakes and bogs (Wasscher 1994, 1999), some of which even disappeared from the Netherlands (Coenagrion mercuriale, Nehalennia speciosa, Gomphus flavipes, Ophiogomphus cecilia, Oxygastra curtisii, Leucorrhinia caudalis). The degradation of the Dutch dragonfly fauna reached a maximum in the 1980’s. Since the start of the 1990's, many species have increased. This is very obvious for some species of running water and ubiquistic species for which the Netherlands lie on the northern limit of their distribution range. These species seem to have profited from the improving water quality (RIVM 2003) and the recent warm summer seasons (KNMI 2006). However, a number of species of other habitats, such as mesotrophic lakes and bogs, have also increased during last decade. In this article we describe the revival of the Dutch dragonfly fauna, which seems to be happening. Special attention is given to the role of temperature change. Methods Database The database used for this article is build and maintained by the Dutch Society for Dragonflies, Butterfly Conservation and the European Invertebrate Survey — the Netherlands. It contains over 307,000 records of 71 dragonfly species up to and in- cluding 2003, mainly submitted by volunteers. Each record constitutes a species on a date on a locality. The records are checked for mistakes by a committee of experts, based on the known distribution and flight period of the species. For records of rare species further documentation like a picture or a description is required. More than 279,000 records are available from the period 1980-2003. By far the largest number of these records was collected from 1994 onwards, but the number of records prior to this period is large enough to give a good impression of the distribu- tion of the species in that period. The database gives good information on the distribution of species. However it is subject to influences of the differences between fieldwork done by the volunteers and large-scale professional projects. Therefore, results based on the database can only be interpreted correctly with a good knowledge of the database itself. Changes in the range of dragonflies in the Netherlands and the possible role... 157 Calculation of trends The data set was divided in three periods: 1980-1993 (period 1), 1994-1998 (period 2) and 1999-2003 (period 3). Relatively few records are available from each year in period 1. Therefore, this period includes fourteen years while periods 2 and 3 only include five years. The 5x5 kilometre squares which had been visited at least in three different months in the period May till August were selected for each year (table 1). Only records from these squares were used for the analysis. For eleven of the 71 Dutch species this resulted in usable records for only one or none of the three periods. There- fore these species, all extinct or very rare, were not included in the trend calculation. Presence or absence of dragonfly species in the selected 5x5 kilometre squares was used, instead of the recorded number of individuals, as the latter is more prone to differ- ences in recording behaviour. The consequence of this method is that a decrease or increase in observed numbers or in localities within a 5x5 kilometre square will go unnoticed. For each species and period the relative abundance (RA) was calculated as follows: RA= (Number of squares in which a species is recorded)/(number of investi- gated squares) x 100%. The RA’s for each year were summed for each period and divided by the number of years. The relative change of a species was calculated as follows: Trend= (RA in recent period — RA in historical period)/(RA historical period x 100% The trends were divided in five trend categories (table 2). Southern and northern species group The Dutch dragonfly species were categorized as southern species, northern species or species without a typical southern or northern distribution pattern. ‘This categorization was based on distribution maps of Northwest Europe (NVL, 2002). A southern spe- cies was defined as a species of which the northern limit of its range runs through the southern tip of Sweden or more southwards. A northern species was defined as a species of which the southern border of its range runs through the Netherlands or Belgium and which is further south only found at higher elevations or in small, scattered populations. Habitat groups Next to the southern and northern species groups, three ecological species groups were se- lected: species of running water habitats (rheophilic species), species of mesotrophic lakes 158 Tim Termaat, Vincent J. Kalkman & Jaap H. Bouwman/ BioRisk 5: 155-173 (2010) Table |. The number of well investigated 5x5 kilometre squares Period 1 Period 2 Period 3 Well investigated Well investigated Well investigated Year squares Year uar Year squares 1980 235 1981 9 1995 260 2000 235 1982 16 1996 242 2001 241 1983 12 |e 205 2002 260 1984 180 372 1985 14 Total 1038 Total 1343 1986 19 1987 20 iss | 4 | 1989 20 1990 28 1991 23 OE Ee lo | 1993 68 1994 151 1995 260 1996 242 | | a |) 1997 205 Total 1342 and bogs and species of fenlands. For this categorization the habitat preference of Dutch dragonflies was used, as given in NVL (2002). Table 3 lists the species of the four selected species groups. Note that some species are appointed to more than one species group. Statistics y°-tests were conducted to test the differences between the all-species group and the se- lected distribution and habitat species groups. This was done by using Microsoft Excel 2000 software. Species with increasing (>20 %) and strong increasing trends (>100 %) were lumped together and tested as increasing species. Results The relative abundance for each period and the trend between the periods is given for each species in table 4. Table 2 gives the number of species showing a certain trend between the different periods. Changes in the range of dragonflies in the Netherlands and the possible role... 159 Table 2. Categories of trend and the number of species showing this trend between periods Trend In table 4 as | period 1 to 2 | period 2 to 3 | period 1 to 3 Strong increase | >100% ++ 19 (32%) 6 (10%) 13 (25%) Increase >20% and <100% | + 9 (15%) 19 (32%) 14 (25%) Stable -20% to 20% 0 19 (32%) 28 (47%) 16 (31%) Decrease <-20% 7 (12%) 9 (17%) Trends between the first and the third period could be calculated for 60 species. 39 species (65%) show a positive trend, 16 species (27%) remained stable and 5 species (8%) show a negative trend. Most increasing species show the strongest positive trend between the first and second period (see figure 1). The results of the y7-tests are given in table 5. Species with a southern distribution pattern Within the southern species group, significantly more species show a positive trend than the all-species group, when period 1 is compared to period 2 and when period 1 is compared to period 3. Furthermore, a significantly lower proportion of the southern species remained stable, when period 1 is compared to period 3 (figure 2). Species with a northern distribution Within the northern species group, significantly more species show a negative trend than the all-species group, when period 1 is compared to period 2. Furthermore, a significantly lower proportion of the northern species remained stable, when period 2 is compared tot period 3 (figure 3). Differences in trends between habitats Within the species group of mesotrophic lakes and bogs, significantly less species show a positive trend than the all species group and significantly more species show a stable trend, when period 1 is compared to period 3 (figure 4). Within the ecological species groups of running waters and fenlands, no significant differences are found for the three trend categories. Discussion The results show that the Dutch dragonfly fauna has recovered since the start of the 1990's, which is in sharp contrast with some other groups of invertebrates as but- 160 Tim Termaat, Vincent J. Kalkman & Jaap H. Bouwman/ BioRisk 5: 155-173 (2010) Table 3. Categorisation of the species in five different species groups. Species Aeshna affinis Southern Northern Running waters Lakes and | Fenlands bogs Aeshna grandis Aeshna isoceles Aeshna juncea Aeshna mixta Aeshna subarctica Aeshna viridis Anax imperator Anax parthenope Brachytron pratense Calopteryx splendens Calopteryx virgo Ceriagrion tenellum Coenagrion hastulatum Coenagrion lunulatum Coenagrion puella Coenagrion pulchellum Cordulegaster boltonii Cordulia aenea Crocothemis erythraea Enallagma cyathigerum Erythromma lindenii Erythromma najas Erythromma viridulum Gomphus flavipes Gomphus pulchellus Gomphus vulgatissimus Ischnura elegans Ischnura pumilio Lestes barbarus Lestes dryas Lestes sponsa Lestes virens Lestes viridis Leucorrhinia dubia Leucorrhinia pectoralis Leucorrhinia rubicunda Libellula fulva Libellula quadrimaculata Ophiogomphus cecilia Orthetrum brunneum Orthetrum cancellatum Orthetrum coerulescens x ~ 1X ~* * * ~ 1s * »* ~* ~* ~ 1s |x » ~* ~ |x | |X »* » »* ~* ~ 1X ~ ~ 1X Changes in the range of dragonflies in the Netherlands and the possible role... 161 Species Southern [Northern |Running | Lakes and | Fenlands waters bogs Platycnemis pennipes Pyrrhosoma nymphula Somatochlora arctica Somatochlora flavomaculata ny el x Sympecma fusca x — Sympecma paedisca —s =_——s Sympetrum danae Sympetrum flaveolum Sympetrum fonscolombii x Sympetrum pedemontanum Sympetrum sanguineum Sympetrum vulgatum terflies and bees (Peeters and Reemer 2003; Swaay and Groenendijk 2005). Only 5 dragonfly species have declined, while a majority of 39 species has increased and 16 species remained stable. Out of the 27 species placed on the red list in 1999 (Wasscher 1999) 17 show an increase, 4 a decrease, 1 remained stable and 3 are still extinct. For the remaining 2 red-listed species (Coenagrion armatum and Leucorrhinia albifrons) no trend was calculated, as they were only recorded in one period. Populations of both species have recently been rediscovered (Van der Heijden 2001; De Boer and Wasscher 2006) in the Netherlands and although they are extremely rare, there is no evidence for an actual decline. Two different causes can be pointed out for the increase or decrease of the differ- ent species. The first is climate change, the second is changes in the quality of habitats. Climate change The average temperature in the Netherlands in the last twenty years of the 20" century was 0,7 degree higher than the average temperature of the first twenty years of the 20" century (KNMI 2006). Especially the spring temperature has shown a strong increase. This increase in temperature caused several southern species to expand their range northwards, becoming more common in the Netherlands. ‘This is at least the case for Lestes barbarus, Aeshna affinis, Anax parthenope, Crocothemis erytraea, Orthetrum brunneum and Sympetrum fonscolombii. Coenagrion scitulum ex- panded its range in northern France and Belgium and was first found in the Neth- erlands in 2003 (Goudsmits 2003). Also for more common southern species like Lestes virens and Ceriagrion tenellum a positive effect of increasing temperatures is expected. Whether or not higher temperatures also play a role in the negative trend shown by some northern species is difficult to say, because the habitats of northern species are 162 Tim Termaat, Vincent J. Kalkman & Jaap H. Bouwman/ BioRisk 5: 155-173 (2010) Table 4. Relative abundance (RA) and trends for each species. Species Aeshna affinis Vander Linden, 1820 Aeshna cyanea (O.F. Miller, 1764) 47,1 Aeshna grandis (Linnaeus, 1758) 36,3 Aeshna isoceles (O.E Miller, 1767) PD 12,3 ++ Aeshna juncea (Linnaeus, 1758) 18,1 D335 0 Aeshna mixta Latreille, 1805 21,9 +4 Aeshna subarctica Walker, 1908 0,4 0,9 ts Aeshna viridis (Eversmann, 1836) 1 4,2 0 ++ Anax imperator Leach, 1815 2555 59,5 0 ++ Anax parthenope (Selys, 1839) + ++ Brachytron pratense (O.E. Miller, 1764) 17,8 + + Calopteryx splendens (Harris, 1782) 33 = é 0 0 Calopteryx virgo (Linnaeus, 1758) 552 : ye - 0 - Ceriagrion tenellum (de Villers, 1789) 4, + Coenagrion armatum (Charpentier, 1840) Coenagrion hastulatum (Charpentier, 1825) + - Coenagrion lunulatum (Charpentier, 1840) + - Coenagrion puella (Linnaeus, 1758) 0 0 Coenagrion pulchellum (Vander Linden, 1825) 0 0 Coenagrion scitulum (Rambur, 1842) Cordulegaster boltonii (Donovan, 1807) - - Cordulia aenea (Linnaeus, 1758) 0 0 Crocothemis erythraea (Brullé, 1832) ++ ep Enallagma cyathigerum (Charpentier, 1840) 0 0 Erythromma lindenii (Selys, 1840) + +4 Erythromma najas (Hansemann, 1823) 0 + Erythromma viridulum (Charpentier, 1840) 0 ++ Gomphus flavipes (Charpentier, 1825) ++ ++ Gomphus pulchellus Selys, 1840 0 + Gomphus vulgatissimus (Linnaeus, 1758) + ++ Hemianax ephippiger (Burmeister, 1839) Ischnura elegans (Vander Linden, 1820) 0 0 Ischnura pumilio (Charpentier, 1825) ++ ++ Lestes barbarus (Fabricius, 1798) 0 ++ Lestes dryas Kirby, 1890 0 0 0 Lestes sponsa (Hansemann, 1823) 0 0 0 Lestes virens (Charpentier, 1825) ? r + ++ Lestes viridis (Vander Linden, 1825) 32,0 0 Leucorrhinia dubia (Vander Linden, 1825) 18,6 # Leucorrhinia pectoralis (Charpentier, 1825) Ty 12 9: 1 + aac Leucorrhinia rubicunda (Linnaeus, 1758) 20,4 [bos 22,9 - + 0 Changes in the range of dragonflies in the Netherlands and the possible role... 163 Species RA RA RA trend |trend | trend period | period | period | 1st to | 2nd Ist to 1 2 3 2nd to 3rd_ | 3rd period | period | period Libellula depressa Linnaeus, 1758 23,9 + i Libellula fulva O.F. Miller, 1764 6,8 6,5 0 0) Libellula quadrimaculata Linnaeus, 1758 65,8 56 0 0 Ophiogomphus cecilia (Fourcroy, 1785) 0,3 ++ + ++ Orthetrum brunneum (Fonscolombe, 1837) 1,6 : +4 Orthetrum cancellatum (Linnaeus, 1758) ADR 80,2 + 0 a Orthetrum coerulescens (Fabricius, 1798) Ve7 4,1 3:2 ph 0 ++ Platycnemis pennipes (Pallas, 1771) | leat 18,6 0 Pyrrhosoma nymphula (Sulzer, 1776) 69,4 + Somatochlora arctica (Zetterstedt, 1840) 0,2 0,4 ++ re ++ Somatochlora flavomaculata (Vander Linden, 1825) 0,1 OFF ee + ++ ++ Somatochlora metallica (Vander Linden, 1825) 18,7 15,7 0 0 Sympecma fusca (Vander Linden, 1820) 0,4 6,2 + ++ Sympecma paedisca (Brauer, 1877) 0,3 ++ ++ Sympetrum danae (Sulzer, 1776) 51,4 45,6 0 0 Sympetrum depressiusculum (Selys, 1841) 1 ea a eae - - Sympetrum flaveolum (Linnaeus, 1758) 24,4 - + Sympetrum fonscolombii (Selys, 1840) 0,4 0 ++ Sympetrum pedemontanum (Allioni, 1766) 1,4 1,7 0 x if Sympetrum sanguineum (O.F. Miiller, 1764) S741 0 + Sympetrum striolatum (Charpentier, 1840) 13,2 41,8 + 0 ri Sympetrum vulgatum (Linnaeus, 1758) 38 44,5 48,3 0 0 + more prone to negative influences of other environmental factors. Five out of seven northern species occur in mesotrophic lake and bog habitats, while there are no north- ern species occurring in running waters. It is clear that habitat degradation is an impor- tant factor to explain the results of the northern species group, possibly climate change makes this decrease more severe. The northern distribution of many southern species seems to be directly limited by the summer temperatures, resulting in a direct expansion of their range when tempera- ture permits (Appendix1). The southern border of northern species on the other hand does not seem to be limited directly by temperatures, but seems to be determined by habitats being absent more southerly and by competition with other species prevailing in warmer climates. The decrease of northern species as a result of increasing temperatures would in that case be caused by degradation of habitats and by increasing competition from southern species. This would result in a slow decline, which is far more difficult to detect than the rapid increase shown by southern species. Another negative effect of increasing summer temperatures is increasing evapora- tion, resulting in lower surface and ground water tables. ‘This can lead to desiccation of 164 Tim Termaat, Vincent J. Kalkman & Jaap H. Bouwman/ BioRisk 5: 155-173 (2010) All species, period 1-2 All species, period 2-3 All species, period 1-3 Dincreased Bdecreased Ostable Figure |. Distribution of all tested species over the trend categories. Three different periods were compared. Period 1 = 1980-1993, period 2 = 1994-1998, period 3 = 1999-2003. important vegetation structures in the riparian zone of lakes and the upstream stretches of streams. This happens especially in late summer, when the first and most vulnerable larval instars of most species are present in the water. Furthermore, desiccation leads to the stagnation of ground water in seepage fed lakes and streams, causing acidification. Also the turn-over rate of organic matter increases when lake shores dry out, causing nutrient enrichment. Coenagrion hastulatum, Cordulegaster boltonii and Somatochlora arctica are examples of threatened species which are known to react negatively on desic- cation caused by human influences (e.g. intensive drainage in agricultural areas and drinking water collection) (Groenendijk 2002; Groenendijk 2005; Ketelaar 2001a; Ketelaar 2001b; Wasscher 1999). It is expected that hot summers con- tribute to this problem. On the other hand, temporary water specialist like Lestes barbarus and Sympetrum flaveolum might have profited from waters becoming shallower. Changes in quality of habitats The test failed to show that the species group of running water contains a signifi- cantly higher portion of increasing species than the all-species group. However, this is probably due to the low number of species included in the group, making it difficult to find significant results. Of the ten included species five show a strong increase, two a moderate increase, one is stable and two show a decrease when the first period is compared with the third. Most striking is the comeback of Gomphus flavipes, which from 1996 onwards reoccupied all large river systems in the Nether- lands (figure 5), after an absence of more than 90 years (Kleukers and Reemer 1998; Changes in the range of dragonflies in the Netherlands and the possible role... 165 Table 5. Results of y2-tests of the observed proportions of trend categories within the different species groups. *p<0,05; **p<0,01. Northern species n=19 ae served pected. Period 1 compared to period 2 Number of increased oh 92 0.027* 3.4 0.641 species Number of stabel / 2 5 9.8 3 3.6 decreased species Number of decreased 8 1 a 0.301 e) 0.9 0.022* species Number of stabel / 52 16.5 6.1 increased species Number of stabel species pas 4 is 0.121 0 2.7 0.037* Number of increased / 37 15 Le. 7 4.3 decreased species Period 2 compared to period 3 Number of increased species Number of stabel / decreased species 2:7 0.072 Number of decreased species Number of stabel / increased species 0.7 0.705 Number of stabel species 31 3.6 0.048* Number of increased / decreased species Period 1 compared to period 3 bbe 3.4 Number of increased 39 19 4.6 0.663 species Number of stabel / 21 0 25 decreased species Number of decreased species Number of stabel / increased species Number of stabel species 1S 0.459 Number of increased / decreased species Period 1 compared to period 2 Number of increased species Species of running Species of lakes and 5.1 Species of fenlands waters n=10 bogs n=24 n=19 p Ob- | Ex- p Ob- | Ex- p served | pect- served | pect- 166 Tim Termaat, Vincent J. Kalkman & Jaap H. Bouwman/ BioRisk 5: 155-173 (2010) Species of running | Species of lakes and | Species of fenlands waters n=10 bogs n=24 n=19 Number of stabel / decreased species Number of de- 8 creased species Number of stabel / 52 increased species 8.7 18 20. 8 Number of stabel 8 1 species 22. 3 1 / decreased species Period 2 compared to period 3 Number of increased species Number of stabel / decreased species Number of de- creased species Number of stabel / increased species Number of stabel species Number of increased / decreased species species Number of stabel / decreased species Number of de- 2.0 creased species 8 0.233| 10 | 9.2 | 0.737 7.3 | 0.079 4 | 14.8 1 ; Number of stabel / increased species Number of stabel species Number of increased / decreased species Bouwman and Kalkman 2005). One extinct species (Ophiogomphus cecilia) and one absent species (Onychogomphus forcipatus) were found reproducing in the 1990's, in the river Roer in the south of the Netherlands (Geraeds 2000; Geraeds and Van Schaik 2004). Platycnemis pennipes, Gomphus vulgatissimus, Orthetrum coerulescens, Orthetrum brunneum and Sympetrum pedemontanum increased (van Eijk and Ket- Changes in the range of dragonflies in the Netherlands and the possible role... 167 Southern species, period 1-2 Southern species, period 1-3 -0 _0 4 1 14 19 OD increased @ decreased O stable Figure 2. Distribution of the tested southern species over the trend categories. Three different periods were compared. Period 1 = 1980-1993, period 2 = 1994-1998, period 3 = 1999-2003. Northern species, period 1-2 Northern species, period 2-3 0 4 1 4 5 Dincreased Hdecreased Ostable Figure 3. Distribution of the tested northern species over the trend categories. Three different periods were compared. Period 1 = 1980-1993, period 2 = 1994-1998, period 3 = 1999-2003. elaar 2004; van Delft 1998; Mensing 2002), while Calopteryx splendens remained stable. Calopteryx virgo and Cordulegaster boltonii are the only rheophilic species showing negative trends, however the observed numbers of these species have in- creased recently and several new localities were found (Groenendijk 2002; Termaat 168 Tim Termaat, Vincent J. Kalkman & Jaap H. Bouwman/ BioRisk 5: 155-173 (2010) Species of mesotrofic lakes and bogs, period 1-3 Gincreased HMdecreased Ostable Figure 4. Distribution of the tested species of mesotrophic lakes and bogs over the trend cat- egories. Three different periods were compared. Period 1 = 1980-1993, period 2 = 1994-1998, period 3 = 1999-2003. and Groenendijk 2005). In our opinion, these findings leave no doubt that species of running water have increased strongly since 1980. Water quality improvement and restoration of the natural morphology of streams and rivers are likely to be the important causes for it. Some species probably profited from the higher summer temperatures as well. This is at least very likely for Orthetrum brunneum, O. coerule- scens and Sympetrum pedemontanum. Whereas the quality of running water habitats has improved, the threats for stagnant water habitats such as mesotrophic lakes and bogs are still present. Eutrophication, dessi- cation and habitat fragmentation are still factors which explain why relatively few species in this species group show a positive trend. ‘The intensity of eutrophication has reduced in recent years (RIVM 2003), but in many cases this has not lead to the recovery of lakes and bogs that have already been spoiled. ‘The results of our analyses suggest that the nega- tive trend of the species group of mesotrophic lakes and bogs stopped, but that they fail to recover. Especially Coengrion hastulatum, a species of mesotrophic lakes and bogs, is still declining in the Netherlands and is becoming increasingly endangered (Termaat 2006). Conclusions The analyses of the trends in the period 1980 to 2003 shows that the 55 Dutch drag- onfly species for which a trend could be calculated remained stable or increased during Changes in the range of dragonflies in the Netherlands and the possible role... 169 + | x \ e-gees. _ e —eeeceececce’ " 8 ee poggoosegeay 8 i v ~ a, SS gee es SS eo it Figure 5. The distribution of Gomphus flavipes in the period 1996-2005. The species was not found in the Netherlands from 1902 to 1995. that time period and that only 5 species have declined. Habitat degradation during the larger part of the 20" century resulted in a degradation of the dragonfly fauna in the eighties of that century. Improved water quality and increasing summer temperatures in the last two decades resulted in a revival of the Dutch dragonfly fauna. Although our analyses failed to show that the species group of running water con- tains a significantly higher portion of increasing species than the all-species group, it is clear that especially species of running water have increased since 1980. This is prob- ably largely due to the improved water quality of running waters and the restoration of the natural morphology of these systems. The average temperature in the last twenty years of the 20" century was 0,7 °C higher than those of the first twenty years of the 20" century. As a result significantly more species with a southern distribution show a positive trend when compared with the all-species group. Seven species very rare or absent prior to 1990 became established in the Nether- lands, probably due to the increase in temperature. Three of these established them- selves by means of large invasions. These invasions were very effective, showing once more that dragonflies are highly capable of colonising new areas. No evidence could 170 Tim Termaat, Vincent J. Kalkman & Jaap H. Bouwman/ BioRisk 5: 155-173 (2010) be provided to state that species with a northern distribution are decreasing due to the higher temperatures. The habitats where these species live (mostly mesotrophic lakes and bogs) have been strongly influenced by eutrophication, acidification and desic- cation in the 1960" and 1970" resulting in a decline of most of these species. This decline might have masked the influence of climate change. References Boer EP de (2006) De Groene glazenmaker en de krabbescheerlevensgemeenschap in Friesland. Stichting Landschapsbeheer Friesland, Beetserzwaag. Boer EP de, Wasscher M (2006) Oostelijke witsnuitlibel (Leucorrhinia albifrons) herontdekt in Nederland. Brachytron 9 (1/2): 14-20. Bouwman JH, Kalkman V (2005) Eindrapportage inhaalslag libellen. Rapport VS2005.020. De Vlinderstichting, Wageningen. Corbett PS (1999) Dragonflies, behaviour and ecology of Odonata. Harley Books, Colchester. 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Bouwman/ BioRisk 5: 155-173 (2010) Appendix| Southern species and invasions Six southern species rare or absent in the 1980’s are now well recognised members of the Dutch odonate fauna: Lestes barbarus, Erythromma lindenii, Aeshna affinis, Croco- themis erytraea, Orthetrum brunneum and Sympetrum fonscolombii. Anax parthenope is expected to become established in the coming years, as it recently became a regular guest and has reproduced successfully. The way in which southern species became es- tablished in the Netherlands differs among the species. E. lindenii, C. erytraea (figure G6) and to a lesser extent O. brunneum gradually expanded the northern border of their range. The other three species L. barbarus, A. affinis, and S. fonscolombii became established after invasions, being rare in the years preceding these invasions (see table G6). The invasion of Lestes barbarus started in July 1994 (Ketelaar 1994) During the invasion records were made in most areas of the country with a strong emphasises on the dunes and the Pleistocene areas. At the majority of these localities several (up to 40) individuals were found. Almost all records were made at shallow, warm waters such as dried-out bogs and smaller dune lakes. In many cases the species established itself at these localities. Probably several smaller invasions occurred since 1994 but these went largely unnoticed as the species was already established. In the period since 1994 the species is found yearly in suitable habitat all over the Netherlands. Preceding the 1994 invasion the northern border of the distribution of L. barbarus was situated to the south of the Netherlands. ‘The invasion in 1994 therefore resulted in a northwards expansion of its range of well over 300 km. The invasion of A. affinis started mid July 1995. All 39 records from 1995 came from the southern part of the Netherlands, most of them from the coastal dunes or from the Pleistocene areas. Almost all individuals were found at drying or dried-out waters, with low reeds or bulrushes. Of the 81 sexed specimens only four were females. This might be partly due to the inconspicuous behaviour of the females. Since the 1995 * Stare 3 . a +* He . .* . fT a # o~«" . 7 : Figure 6. The distribution of Crocothemis erythraea in the periods 1980-1993, 1994-1998 and 1999-2003, showing its gradual northwards expansion. Changes in the range of dragonflies in the Netherlands and the possible role... 75 Table 6. Southern species rare during the eighties which have become established since 1990. The second column states whether or not the species became established during a large invasion or gradually expanded northwards. Established due to | Number of records| Number of records in the 10 years prior | in year of invasion to invasion Aeshna affinis Invasion in 1995 a) Anax parthenope Gradually (1) ——————l| Crocothemis erythraea Gradually Species Erythromma lindenii Gradually Lestes barbarus Invasion in 1994 Orthetrum brunneum Sane graduall iA Sympetrum fonscolombii_|Invasionin 1996 |1 [1385 (1) Anax parthenope is not yet established but has become a regular guest and is likely to become established in the future. invasion the species is found several times a year in all parts of the Netherlands. The first proof of successful reproduction was found in 2005 (Wasscher 2005) although it is likely that small (temporary) populations have existed since 1995. In end May and begin June of 1996 a massive invasion of Sympetrum fonscolombii reached Northwestern Europe (Lempert 1997; Dijkstra and Van der Weide 1997). As with Lestes barbarus the species was recorded all over the country with a strong emphasis- es on the dunes and the Pleistocene areas. Most records were made at unshaded, standing waters with sparse vegetation and often sandy banks. The species managed to establish itself at many of these localities. Since 1996 the species is found every year at numerous localities across the country, although it has become less abundant than in 1996. The invasions of L. barbarus, A. affinis, and S. fonscolombii have two things in common: 1 During the invasion almost all specimens were found at suitable habitats and not seldom successful reproduction was noticed in later years; 2 Most records during the years of the invasions referred to more than one specimen. The three species which invaded The Netherland in 1994, 1995 and 1996 were rarely seen at unsuitable sites. This stresses the fact that these species are highly capable of local- ising suitable habitats. This is further emphasised by the fact that in most cases more than one individual was found at a locality. These species do not fly in clustered groups mak- ing it likely that the individuals from one locality all located the habitat on their own. Probably these species used their ability to recognise polarized light combined with visual cues on vegetation structure to detect suitable habitat from some height as has been shown for some species of dragonflies (Corbett 1999). This makes that a relatively high portion of the individuals taking part in the invasion is able to reproduce at a po- tentially suitable location. These examples show that at least these species are capable of taking advantage of favourable circumstances in an extremely effective way.