Indirect effects of river regulation: consequences for landbirds of reduced numbers of aquatic insects
Darius Strasevicius
Umeå 2007
Department of Ecology and Environmental Science Umeå University Sweden AKADEMISK AVHANDLING
Som med vederbörligt tillstånd av rektorsämbetet vid Umeå universitet för erhållande av filosofie doktorsexamen i ekologi kommer att offentligen försvaras fredagen den 25 maj 2007, kl. 13.00 i Lilla hörsalen, KBC.
Examinator: Professor Christian Otto, Umeå universitet Opponent: Docent Tapio Eeva, Åbo universitet, Åbo, Finland ISBN: 978-91-7264-291-1 © Darius Strasevicius 2007
Printed by: VMC KBC Organization Document name Umeå University DOCTORAL Ecology DISSERTATION Department of Ecology and Environmental Science Date of issue SE 901 87 Umeå May 2007
Author : Darius Strasevicius Title: Indirect effects of river regulation: consequences for landbirds of reduced numbers of aquatic insects Abstract : The effects of river regulation on blackfly (Diptera: Simuliidae) abundances and consequences for the avifauna in terrestrial environments were studied along multiple rivers in northern Sweden. I found that impoundment of rivers has detrimental effect to blackfly abundances. The densities of large river breeding blackfly species were several fold higher along free flowing than along regulated rivers. The difference in abundances was much larger in males than blood seeking females. Blackflies attacked a variety of mammalian and avian hosts and showed different levels of host specificity between species. I found higher prevalence of haemosporidian blood parasites ( Leucocytozoon ) in birds along the free flowing Vindel River in comparison to the regulated Ume River, where the lower densities of ornithophilic blackflies were reduced. Blood seeking blackflies predominantly attacked large and/abundant hosts. Assemblages of birds differed between valleys of regulated and free flowing rivers. Densities of noninsectivorous birds tended to decrease along free flowing rivers in the post breeding season, but increased along regulated rivers at the same time. Insectivorous European pied flycatcher ( Ficedula hypoleuca Pallas) showed greater fledging success along free flowing than regulated rivers, which probably reflects the higher insect abundances found along free flowing rivers. Key words Boreal region, Simuliidae, Leucocytozoon , pied flycatcher, aquatic insects, breeding success, blood parasites, bird communities, river regulation, impoundment. Language: English ISBN: 978-91-7264-291-1 Number of pages: 31 + 5 papers Signature:……………….. Date: 20 th April 2007 To Jūrat÷
Medeina, Emilija and Kirnis
List of papers This thesis is based on the following papers, which will be referred to in the text by their Roman numbers. I. Malmqvist, B., Strasevicius, D. & Adler, P.H. Transfer to terrestrial ecosystems of an important aquatic insect prey and parasite vector decreases following human impact. (submitted manuscript) II. Strasevicius, D. & Malmqvist, B. Are avian blood parasites reduced because of degraded vector breeding habitats? (submitted manuscript) III. Malmqvist, B., Strasevicius, D., Hellberg, O., Adler, P.H. & Bensch, S. 2004. Vertebrate host specificity of wild caught blackflies revealed by mitochondrial DNA in blood. Proceedings of the Royal Society (Suppl.) 271: S152 S155. IV. Strasevicius, D. & Malmqvist, B. Influences of river regulation on upland bird assemblages in northern Sweden. (submitted manuscript) V. Strasevicius, D., Nyholm, E. & Malmqvist, B. Does river regulation reduce fledging success of European pied flycatchers via changed aquatic insect resources? (submitted manuscript)
Paper III is published with the kind permission of the publisher. CONTENTS INTRODUCTION ……………………………………………………..………..…..6 • River regulation……………………………………………………..………..6 • Aquatic terrestrial transfers………………………………………….……….7 • Blackflies……………………………………………………………..………8 • Leucocytozoon……………….……………………….………………..……10 • Bird communities………………………………………………………..…..10 • Pied Flycatcher………………………………………………………………12
AIMS OF THE THESIS ………………………………………….……………..…12 STUDY AREA ………………………………….…………………………...……...12 MAJOR RESULTS AND DISCUSSION ………………………………...………14 Densities of blackflies……………………………..………………….……..14 Blood sucking…………………………………………………..…….….….17 Leucocytozoon infection………………………………………….…………18 Bird densities…………………………………………………….………….19 Breeding success…………………………………………………….………20 CONCLUSIONS …………………………………………………………………...21 REFERENCES ……………………………………………….………………….....22 THANKS! …………………………………………………………………..…...…..30 Appendices: Papers I V
INTRODUCTION Humans have significantly influenced natural processes all over the world. Freshwater resources are among those having the greatest importance for human beings. The extent usage of the freshwater is often inseparable from the economic development of countries. Water resources are used for multiple purposes including consumption, irrigation, energy production, transport and recreation. And the riparian zone is often heavily used for residential, agricultural and industrial activities, which lead to disturbances, such as organic and chemical pollution, river regulation and canalization. The increasing electric energy usage forces us to seek new “ecologically acceptable” energy sources and hydropower is one of them. Hence, river regulation is one of the ways to exploit large rivers to meet the mentioned needs of human beings. River regulation However, hydropower has a reputation for being one of the most dramatic and widespread, deliberate impacts of man on the natural environments (Petts 1984, McCully 1996, Nilsson and Berggren 2000). Striking changes in river hydrology caused by hydropower development often lead to chain reaction effects on the surrounding ecosystems. The damming of rivers causes large scale impacts to aquatic ecosystems, which can be classified into: 1) Physical, chemical and geomorphologic consequences of blocking a river and altering the natural distribution and timing of river flow. 2) Changes in primary biological productivity of ecosystems including effects on riverine and riparian communities. 3) Alterations to fauna caused by both mentioned above. Although most large rivers in the world are regulated (Petts 1984), little is yet known about the long term ecological effects of regulating an entire river to the surrounding ecosystems (Nilsson et al. 1991). The impacts are often very complex and variable depending on the geographical location of a dam. Because of the complexity of its specific physical, chemical and biological features, each river system is to some extend unique (Nilsson and Berggren 2000). Therefore, it can be difficult generalize about the effects of river regulation. Commonly recognized effects of river impoundment causes some of the most dramatic changes to riparian plant communities (Nilsson et al. 1991, Jansson et al.
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2000, Merritt and Cooper 2000), fish communities (Gehrke et al. 2002, Kruk and Penczak 2003), small mammals (Falck et al. 2003) and aquatic bird communities (Disler et al. 1990, Reitan and Sandvik 1996, Kingsford et al. 2004). Dams act as physical barriers for aquatic organisms disrupting the function of rivers as up downstream corridors (Nilsson et al. 1991, Shields et al. 2000, Malmqvist 2002), but surrounding ecosystems may also be effected indirectly. For example, large storage of water influences air temperature, humidity and fog formation in surrounding ecosystems (Sundborg 1977, Huntley et al. 1998). River damming inevitably increases water volume and inundates terrestrial and riparian areas, which leads to permanent loss of habitats (Nilsson and Berggren 2000). However, as pointed out above, the effects of river regulation to neighboring communities are to some extent unique for each river system. The impoundment of rivers in northern Sweden primarily has been for energy production and only partly for flood control (Nilsson 1986). This exploitation has been intensive, with most dams built between 1950 and 1970. Three out of the seven largest rivers in Västerbotten and Norbotten counties are heavily impounded; the Ume River by 17, and the Skellefte and Lule Rivers by 15 large dams each. These rivers has thereby become transformed into chains of lakes, with fast flowing stretches rarely present. For instance, the Ume River is about 450 km in length and drops about 445 meters, with the estimated fall inside hydropower stations is 440.5 meters. Those larger rivers that have remained unregulated were classified as “National Rivers” in 1993 and are since protected by law from hydropower exploitation. Several aspects of the aquatic ecology of these river ecosystems have been studied, but few extensive studies on bird communities or blackfly populations have been performed (but see Cuadrado and Hasselquist 1994, Malmqvist et al. 2001). The shift from flowing to standing water severely reduces otherwise extremely abundant filter feeding insects in northern rivers (Malmqvist et al. 2004a). Aquatic-terrestrial transfers A common feature of aquatic systems is the high primary and secondary production. Aquatic insects are one of the important links between aquatic and terrestrial environments, where emerged adults support and attract high diversity of riparian and terrestrial consumers. Several studies show the importance of the flux of aquatic insects to riparian communities. For instance, midges support high densities of
7 shoreline spiders (Henschel et al. 2001, Collier et al. 2002, Briers et al. 2005, Paetzold et al. 2005). Likewise, high densities of insectivorous birds often are found in riparian forests, where the concentration of aquatic insects is highest (Murakami and Nakano 2002, Iwata et al. 2003). Most aquatic insects disperse relatively short distances into the terrestrial surroundings (Jackson and Resh 1989, Kovats et al. 1996, Malmqvist 2002, Petersen et al. 2004), although blackflies (Diptera: Simuliidae) can disperse many kilometers (sometimes > 500 km) away from the breeding grounds (Davies and Roberts 1980, Crosskey 1990). However, the influence of aquatic prey on terrestrial biota often decreases rapidly with distance from the river (Naiman and Décamps 1997), and upland systems are therefore less studied. Blackflies The damming of rivers may have significant impacts on a variety of insects. For instance, in the boreal region filter feeding blackfly (Diptera: Simulidae) larvae are dominant insects in the rapids of large rivers (Malmqvist et al. 2004a) and may produce up to a billion of blackfly larvae per km of river (Malmqvist et al. 2004a). As larval blackflies depend on relatively fast flowing water, their populations and those of other current loving aquatic insects dwindle following river regulation, with predicted negative consequences for insect feeding arthropods and other consumers in the riparian zone that depend on this resource (Henschel et al. 2001, Sabo and Power 2002, Baxter et al 2005, Briers et al. 2005). About 1800 validly named species of blackflies are described in the world (Crosskey 2002). The Palearctic region is exceptionally rich with about 500 species described (over 60 in Sweden) (Crosskey 1990, Crosskey and Howard 2004). However, the taxonomy of blackflies is still under development and many more species are to be described. Blackflies differ markedly in terms of habitat used for reproduction (Malmqvist et al. 1999), fecundity (Malmqvist et al. 2004b) and preference of hosts (Crosskey 1990). According to their requirement of energy source for egg development blackflies can be divided into non haematophagous (not feeding on blood) and haematophagous. Haematophagous blackflies can be further subdivided into: Ornithophilic, feeding on blood of birds Mammalophilic, feeding on blood of mammals (except man) Antropophilic, feeding on human blood
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Haematophagous blackflies may have two opposing effects on animals: they may serve as a food resource (positive) for insectivorous, but also act as predators (negative) for all endothermic vertebrates (Crosskey 1990). Many birds are insectivorous and are therefore expected to experience the dual effect of blackflies (Fig. 1). Aquatic Terrestrial Free flowing Rivers SIF Regulated Rivers Blackflies LISF Smaller streams Figure 1. A schematic view over the main effects of rivers to bird communities. White arrows indicate positive, black negative, effects. SIF stands for small prey insectivores, LISF for large insect and/or seed eaters. Many blackflies emerge at the beginning of summer, when most boreal bird species breed. Therefore, the transfer of aquatic prey to terrestrial environments may potentially have high importance for reproductive success of insectivorous passerines, as for example the pied flycatchers ( Ficedula hypoleuca ) (Fig. 1). However, high abundances of blackflies may cancel or even reverse this positive effect by harmful blood sucking (Ojanen et al. 2002, Malmqvist et al. 2004a), harassment, and transmission of haemosporidian blood parasites (Bennett et al. 1991(a,b), Valkiunas et al. 2003, Scheuerlein and Ricklefs 2004). Approximately half of the blackfly species present in Scandinavia are ornithophilic, i.e. they require bird blood for egg development (Adler et al. 1999), and attack a variety of terrestrial birds (Fig. 1 and Paper III ). Blackflies are able to transmit bacteria, nematodes, protozoa, and viruses to a variety of hosts, but are relatively poorly studied as vectors of several of these agents (Reeves et al. 2007).
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Leucocytozoon Haemosporidians are blood parasites having important consequences for the evolution and ecology of many host species (Clayton and Moore 1997) and potentially for ecosystems (cf. Loreau et al. 2005). They can be serious pathogens of both domestic (Kreier and Baker 1987, Crosskey 1990, Atkinson and van Riper 1991, Bennett et al. 1993) and wild birds (Hatchwell et al. 2000). For instance, negative effects on the life history have been manifested in host reproductive effort (Siikamäki et al. 1997, Figuerola et al. 1999, Fargallo and Merino 2004), fledgling success (Hunter et al. 1997, Merino et al. 2000) and post breeding condition (Fargallo and Merino 1999, Merino et al. 2000, Tomas et al. 2005). Leucocytozoon is one of the most common haemosporidian parasites, predominantly transmitted by blood sucking blackflies (Kiszewski and Cupp 1986, Crosskey 1990), and therefore is largely limited largely to blackfly inhabited areas. Several factors may influence the transmission of Leucocytozoon . If different blackfly species are responsible for transmission of the different Leucocytozoon species, the variation in the prevalence of Leucocytozoon across landscapes is expected, because the larvae of different blackfly species inhabit different types of streams (Malmqvist et al. 1999) and blood seeking females are partly host specific (Paper III). In addition, high densities of hosts increase the probability of the parasite to encounter a host (Hudson et al. 2001, Tella 2002) and are important for the parasite to successfully complete its life cycle, because each species of Leucocytozoon is typically specific to family or single host species (Crosskey 1990). Bird communities River regulation affects the local climate, riparian vegetation structure and production of aquatic organisms, which consequently may affect the entire bird community in surrounding ecosystems. Changes in local climate may affect the breeding conditions of birds and the activity of insects; increased ground water levels affect vegetation structure and hence breeding habitats; reductions in the production of aquatic insects may affect the breeding success of insectivorous birds. Therefore, most of the effects of river regulation on terrestrial bird communities can probably be considered as secondary.
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Birds constitute the majority of the terrestrial vertebrates in most boreal communities (Niemi et al. 1998). In Finland, for instance, birds make up about 75% of all terrestrial vertebrates (Mönkkönen 1994). Therefore, the conservation of bird populations is particularly important for the maintenance and sustainability of boreal ecosystems. Brawn et al. (2001) in their review postulated that proximate cues used by birds to discriminate among habitats probably involve factors that influence the availability of food, risk of predation and availability of nest sites. In addition, natural ecological processes and, increasingly, anthropogenic disturbance can modify the landscape framework and therefore influence species diversity at landscape or regional scales (Brawn et al. 2001). Large scale studies involving entire bird communities are important for understanding the consequences of natural and anthropogenic impacts. Many studies have produced models relating bird species distribution or richness to environmental variables, highlighting a variety of factors across different environmental scales, covering small scale habitats to broader land use scale (Buckland and Elston 1993, Tucker et al. 1997, Siriwardena et al. 1998, Saab 1999). The studies from different landscapes and geographical zones indicate greater species richness and total abundance of birds in riparian versus non riparian zones, which is probably related to higher food and habitat diversity (Woinarski et al. 2000, Iwata et al. 2003). Floodplains create an extraordinary diversity of habitats and therefore have the richest bird communities (Terborgh et al. 1990). Bird species richness and abundance are higher along large than smaller rivers (Lock and Naiman 1998). Particular plant species associated with avian nesting and feeding needs may highly influence breeding bird communities. For instance, willow cottonwood plant communities are highly dependent on flood disturbance and reduction of disturbance by damming cause a decline in many bird species depending upon these communities (Strong and Bock 1990, Askins 2000). Preferences of trees used for foraging were also documented in floodplain forests, where twelve of 13 studied bird species foraged selectively with respect to tree species (Gabbe et al. 2001). However, little attention has been paid to the impacts of aquatic ecosystems to more remote terrestrial environments.
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Pied flycatcher The Pied flycatcher is a small (12 13g), exclusively insectivorous and a common migratory species, breeding extensively in European woodlands (Lundberg & Alatalo, 1992). Pied flycatchers feed on a variety of insects, such as caterpillars, flies, bees, beetles, woodlice, millipedes and ants, catching them in the air or picking them from vegetation. They are widespread in deciduous or mixed forests and especially common in areas where nest boxes are provided. The preference for nest boxes over natural cavities makes the pied flycatcher a suitable and popular species for testing ecological hypotheses (Lundberg & Alatalo, 1992). AIMS OF THE THESIS The purpose of this thesis was to gain a better understanding of the processes underlying river regulation effects on upland bird communities, by affecting breeding possibilities for otherwise highly abundant insect species in the boreal zone. The main questions addressed are as follows: • Does river regulation affect densities and species composition of blackflies? If they do, river regulation may be seen as a manipulation of blackfly communities ( Papers I, II, IV and V) • Do blackflies have influences bird communities negatively by biting and transmitting blood parasites? ( Papers II and III ) • Do bird communities differ between valleys of regulated and free flowing rivers? ( Paper IV ) • Can river regulation indirectly reduce the breeding success of insectivorous birds due to reduction of food resources? ( Paper V ) STUDY AREA All studies were conducted in northern Sweden (64 66 0 N), where bird and blackfly sampling (Paper I, II and IV ) was performed along seven large rivers: Ume, Vindel, Skellefte, Pite, Lule, Kalix and Torne (data from Torne River was not included in Paper I) (Fig. 2). The nest box experiment ( Paper III ) was conducted along four rivers (Ume, Vindel, Skellefte and Pite), whereas the study on Leucocytozoon parasitism ( Paper V ) was done along two rivers (the Ume and Vindel). Three of the studied rivers are highly regulated, with large reservoirs in the mountains and run of river regulation in
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N LK T U P S 1 2 V 200 km 20 km 3 Figure 2. Locations of study areas (black boxes) and rivers: Ume (U), Vindel (V), Skellefte (S), Pite (P), Lule (L), Kalix (K) and Torne (T). downstream parts, while four rives are free flowing. Every other river is regulated allowing us to study them as a pair with one regulated and one free flowing river. The rivers in the southernmost pair (the Ume and Vindel Rivers) run parallel to each other for about 450 km, less than 56 km apart. They join 30 km before entering the Gulf of Bothnia. The 17 large dams have changed the Ume River considerably, while the Vindel River remains free flowing. In addition, these rivers have similar catchments area, water discharge and proportion of forest cover (Table 1.). Given the similar background (SMHI 1999), these two rivers offer an excellent opportunity to investigate the effects of large river regulation within one watershed. Table1. Catchment characteristics of studied rivers. Data from Raab (1995) and SMHI (1999). Water Forest Hydro electric Catchment discharge cover Lakes power stations Rivers Status area (km 2) (m 3 s 1) (%) (%) (No.) Ume Regulated 13 838 231 60 10 17 Vindel Free flowing 12 625 173 63 6 0 Skellefte Regulated 11 731 155 58 15 15 Pite Free flowing 11 285 160 58 8 1 Lule Regulated 25 240 490 44 10 15 Kalix Free flowing 18 130 290 55 4 0 Torne Free flowing 40 157 390 53 5 0
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The catchments and discharges of the middle pair of rivers, the Skellefte (regulated) and Pite (free flowing), are somewhat smaller than others in the study. These two were distinguishable by the highest proportions of uniform conifer forest (predominantly pine Pinus sylvestris ) and mire when compared to the other studied pairs. Agriculture is generally rare along these two rivers. The Pite River does have one hydroelectric power station located near its outfall into the Gulf of Bothnia, but it is treated as an unregulated river here, because this construction is unlikely to influence our study area, which is located about 60 km upstream. The Lule (regulated), Kalix and Torne (free flowing) Rivers are the largest in the study (Table 1.). With the exception of the Kalix River, the catchment of which is dominated by pine forests, they all have a high proportion of mixed and deciduous forests, with birch ( Betula pendula ) being the dominant broadleaf tree. Also, similar to the Ume Vindel River basin, the Lule, Kalix and Torne Rivers flow through valleys used relatively extensive for agriculture. MAJOR RESULTS AND DISCUSSION Large scale studies often suffer from the problem of replication, and associated low statistical power, and my studies are no exception. The paucity of large unregulated rivers, as well as economic limitations restricted the study to three regulated and four free flowing rivers. The all seven rivers were used for studies of upland bird communities (Paper IV) , and six for study of blackflies (Paper I) . These two large studies confirmed similar patterns between rivers of the same status and differences between rivers of different status (regulated versus free flowing) in terms of the densities and community structure of blackflies and upland birds. Therefore, I believe that the patterns observed in smaller studies (e.g. Leucocytozoon infection, Paper II and breeding success, Paper V ) can also be expected in broader geographical area. Densities of blackflies ( Paper I ) Blackflies tend to occur in masses in both aquatic and terrestrial environments throughout the northern hemisphere ( Paper III ). Large rivers in northern Sweden provide favourable conditions for mass development of filter feeding larval blackflies. Such conditions are particularly well met in lake outlet streams (Carlsson et al. 1977, Wotton 1987), large river rapids (Crosskey 1990, Malmqvist 1999, Malmqvist et al.
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2001) and chalk streams (Ladle et al. 1972), where larval densities of blackflies may exceed one million per metre square (Wotton 1987, Malmqvist 1994) and exceed that of any other stream insects (Huryn and Wallace 2000). I found that blackflies are indeed very important insects in the terrestrial environment in northern Sweden. Three hundred and thirty two samples of flying
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12 Regulated Free-flowing 8 Insects/km 4
0 Ornith Mammal Others Figure 3. Densities (± SE) of blackfly males (BF M), blackfly females (BF F) and other flying insects along free flowing and regulated rivers. insects collected along studied rivers show that on average blackflies can account for up to 39% of all flying insects along free flowing rivers, whereas blackflies comprise only 12.9% (Fig. 3) along regulated rivers. Moreover, average densities of insects other than blackflies were similar at the two types of rivers (48 insects/km along regulated, vs. 52 insects/km along free flowing). Blackflies contributed the most to the 35.6% higher densities of flying insects that can be observed along free flowing rivers in comparison to regulated rivers (Fig. 3).
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40 Regulated 30 Free-flowing
Insects/km 20
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0 BF M BF F Other insects Figure 4. Densities (± SE) of ornithophilic (Ornith), mammalophilic (Mammal) and other (Others) blackflies along free flowing and regulated rivers.
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The ratio of mammalophilic and ornithophilic blackflies did not differ substantially with respect to river regulation, despite the differences in their densities observed between free flowing (59.7% and 39.5% respectively) and regulated rivers (61.9% and 36.3% respectively) (Fig. 4). Densities of non biting and unidentified blackflies were low generally. These results show, that river regulation has an equal effect on both mammalophilic and ornithophilic blackflies. Blackfly species breeding primarily in large rivers dominated samples: Metacnephia lyra , Simulium annulus , S. murmanum , S. reptans , S pusillum/subpusillum and S. vulgare/annulitarse/tuberosum (morphologically undistinguishable). In addition, non biting species were not abundant, comprising only about one percent of all sampled blackflies. Data for the entire blackfly material show that densities of males on average were about 14 times higher along free flowing then regulated rivers, whereas densities of females along free flowing rivers exceeded only 1.5 times those observed along regulated rivers. This pattern may be explained by the differences between male and female behavior. Males staying near the native rivers have a higher probability of meeting unmated females, and therefore the highest accumulations of male blackflies are found along rivers they originated from. In contrast, females, after mating, start their search for a blood meal needed for egg development, and to this end begin dispersing to a maximum distance of several hundred of kilometers. These observations suggest that, the breeding location of blackflies is better revealed by the presence of males then females.
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Regulated 20 Free-flowing Insects/km 10
0 Large river Medium stream Small stream Figure 5. D ensities (± SE) of males and females of blackflies according their habitat preferences.
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Blackfly species breeding in smaller streams, and therefore not directly affected by river regulation, may confound these results. In the present study, blackfly species breeding in small and medium streams were not very abundant (on average 8.8%), however, large river species might be overrepresented because of the selectivity of the method used (see Malmqvist et al. 2007). Males of species breeding in medium and small streams made up just 5.2% of all males caught along free flowing versus 37.5% along regulated rivers (Fig. 5). Females show a similar pattern, species breeding in medium and small streams comprised just 13.1% of all females caught along free flowing, versus 35.9% along regulated rivers (Fig. 5). Such high densities of adult blackflies as those shown in this study have a potentially great importance to terrestrial consumers. However, due to the host specificity of blackflies their importance to and effect on avian communities is difficult to study. While adult males simply can be seen as a food resource in the terrestrial environment, adult females have more complex effects: positive as food resource and negative because of their blood sucking, harassment, and transmission of haemosporidian blood parasites. Therefore, to some insectivorous species the positive effect of blackflies might be cancelled by negative ones, whereas only negative effects probably prevail among bird species which do not consume blackflies (Fig. 1). Blood sucking ( Paper III ) The search for hosts and the biting strategy of blackflies are still not very well understood. It is believed, that the host seeking blackfly female uses two main stimuli: chemical and visual. The stimulus used probably depends on the distance to the host
(Crosskey 1990). In long distance host location chemical stimulus (CO 2) is probably prioritized, whereas visual stimulus is used for exact location of the host (Bradbury and Bennet, 1974). It is thought that host finding by mammalophilic species depends more upon sight and less on the detection of CO2 as compared to ornithophilic species. DNA analysis of blood samples collected from engorged blackfly females showed that blackflies could be divided into either mammalophilic or ornithophilic species as suggested by Crosskey (1990). However, we also observed that some cross biting might occur, as some ornithophilic blackflies carried mammalian blood and vice versa. Moreover, mammalophilic species indicated higher host specificity than ornithophilic species, however the degree of specialization varied among species. This pattern might be a consequence of the potentially greater availability of avian than
17 mammalian host species. Another clear pattern was that both ornithophilic (see Fig. 1. in Paper III ) and mammalophilic (see Table 1. in Paper III ) blackfly species preferred the large hosts. Moreover, the density of the hosts also appeared to be important for ornithophilic blackflies. Moose, the largest animal in Sweden was attracted by all 10 investigated mammalophilic blackfly species, and 66% of identified blood samples indicated feeding on moose. An exception was Simulum tuberosum , which demonstrated high specialization on rodents (96% of samples). Similarly, large birds dominated the host list of ornithophilic species: capercaille (34%) and black grouse (18%). Interestingly, Metacnephia lyra , the most common blackfly species showed lowest host specificity (Shannon index 2.07), as 21 analyzed samples contained blood from nine bird species belonging to six families (one sample contained human blood). None of the investigated blackfly species specialized on humans. Therefore, the classification of haematophagous blackflies into three groups, as recommended by Crosskey (1990), has no foundation in this study. Interestingly, just two out of 132 samples (two blackfly species) of mammalophilic species were confirmed to have human blood (1.5%), whereas six out of 68 samples (five species) from ornithophilic blackflies contained human blood (~ 9%). Possibly, the lower host specificity among ornithophilic blackflies might explain why humans are more frequently attacked by this category of blackflies. Leucocytozoon infection ( Paper II ) The analysis of blood smears from 433 terrestrial birds sampled in the valleys of Ume and Vindel Rivers showed that over 15% of the birds were infected by Leucocytozoon parasite. Two main patterns were found. First, larger bird species had higher parasite prevalence (see Fig. 1. in Paper II ). This result is in line with the previous study (Paper III ), where females of blackflies more frequently attacked hosts of larger size. Host density on the other hand had no effect on parasite prevalence which contradicts the results in Paper III . However, this discrepancy emerged probably because different host species were investigated. In particular, I was not able to collect blood samples from capercaille, black grouse or other large bird species, which are the most common host of ornithophilic blackflies ( Paper III ). Therefore, birds screened for Leucocytozoon infection were much smaller than those most frequently attacked (Paper III) .
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The second main finding was that assemblages of birds living along the free flowing Vindel River tend to have a higher risk of Leucocytozoon infection than birds living along regulated the Ume River, despite short distance (~ 20 km) between the sampling sites compared. Higher infection prevalence, however not significant (Chi square [1] =2.195, P=0.098), was found for all four species, for which sample size was large enough (>20) to allow analysis: willow warbler ( Phylloscopus trochilus ), European pied flycatcher ( Ficedula hypoleuca ), European robin ( Erithacus rubecula ) and great tit ( Parus major ).
Bird densities ( Paper IV ) Average bird densities and species richness did not significantly differed between regulated and free flowing rivers in either breeding or post breeding. However, species richness was marginally higher along regulated rivers then free flowing rivers at both investigated seasons, whereas bird densities were marginally higher along free flowing rivers. After classifying birds into small prey insectivores (SIF) and large insect and/or seed eaters (LISF), a contrasting pattern between the regulated and free flowing rivers emerged. The accumulated densities of LISF markedly decreased in the free flowing river valleys in the post breeding season, while densities of SIF increased. In contrast, densities of both LISF and SIF species increased in the regulated river valleys in the post breeding season. These observations support our prediction that birds with different food requirements should respond differently to the summer emergence of aquatic insects, such as biting blackflies, although further investigations involving large host species would be required for the confirmation of this hypothesis. The MDS analyses based only on bird observations revealed a divergence in the positioning of regulated and free flowing rivers in space where regulated rivers appeared more in lower and left positions relative to their free flowing “partner” river. The divergence between rivers of different status increased even more in the post breeding season (see Fig. 3, in Paper IV ). The MDS analyses indicated, that terrestrial bird assemblages are more similar between rivers of the same status than between geographically proximal rivers. Therefore, a common factor seems to exist, that influences the divergence of bird communities at regulated and free flowing rivers, and although not shown, the bundance of blackflies might be a partly contributing factor. The CCA analyses indicated that habitat parameters, especially agriculture landscape
19 and vegetation structure, together with altitude, are the most important factors determining avian community structure. Nevertheless, the CCA analyses involving 31 environmental factors, showed that river regulation also has importance for the structure of bird species composition. Moreover, the impact of river regulation increased in the post breeding season, and therefore, indicated the existence of other, more dynamic factors than simply differences in habitat structure caused by river regulation (Nilsson and Jansson 1995). Once again, blackflies together with other aquatic insects may be good candidates to explain results from CCA analyses, because the post breeding season of birds coincides with the time when most aquatic insects are on their wings.
Figure 6. Mean survival (± SE) of nestlings at regulated and free flowing river sites in different years. Data from 2001 are based on sites from the Ume and Vindel Rivers only. Breeding success (Paper V ) I found that pied flycatchers breeding along free flowing rivers had higher fledging success than those breeding along regulated rivers. The better nestling survival along free flowing rivers, was consistent across years and river pairs and increased the success by 10 15% (Fig. 6). Despite the fact that birds breeding along regulated rivers initiated their earliest clutches two days earlier then those at free flowing rivers, the median clutch initiation date was on average one day earlier along free flowing rivers (Fig. 2 in Paper V ). Therefore, the time needed for pied flycatchers along free flowing rivers to lay their eggs was two days shorter, which indicates some uncertainty in flycatchers along regulated rivers when to lay eggs (Fig. 3 in Paper V ). On the other hand, shortage of food resources might also extend the time needed for egg development (Perrins 1970).
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There was no difference in clutch size or number of nestlings between regulated and free flowing rivers, however, I found significantly higher number of fledglings at the free flowing river sites. This difference emerged due to the higher mortality of nestlings along regulated rivers (Fig. 6). Survival of nestlings along free flowing rivers reached 97% at the Vindel River and 95.3% at the Pite River, as compared to 89.6% at regulated Ume River and 77.5% at regulated Skellefte River. Especially low fledgling success occurred along the Skellefte River (77.5%), where the breeding result (4.3 fledged youngs per pair) was just below the critical level for pied flycatcher populations to be self sustaining (4.4 per pair; Järvinen 1983). As, in most cases just a part of the nestlings died, I believe that the higher mortality of nestlings along regulated rivers could have been caused by food shortage. If all nestlings died at once, the predation or infection might be the cause, however, such mortalities were rare. Moreover, in extreme conditions, parents might abandon their youngs (Lundberg & Alatalo, 1992). The hypothesis that pied flycatchers along regulated rivers experience lower food availability was supported by the weight loss of females (Fig. 7 in Paper V ) and lower abundance of insects (Fig. 8 in Paper V ). I found that flycatchers breeding along regulated rivers at the end of the breeding season were on average by 9% lighter than those breeding along free flowing rivers. Also, a lower abundance of flying insects was observed along regulated rivers, especially at the period of feeding of nestlings. Better breeding success of pied flycatcher along free flowing rivers supports and partly explains the findings reported in the whole bird community study ( Paper IV ), where higher insectivorous bird density was found along free flowing rivers along with higher flying insect abundance. I believe that the findings on breeding success of pied flycatcher can also be valid for other insectivorous birds breeding in the boreal region. CONCLUSION Numerous studies have been conducted in order to evaluate the effects of river regulation to plant and animal communities in aquatic and riparian systems. Effects of river regulation that have been highlighted include reduction of floods and current velocity, fragmentation, changes in temperature and humidity etc. Such effects can be attributed to direct impacts, however, little is known about the secondary effects of river regulation, e.g. the effects of reduced productivity of river systems and associated
21 rates of transfer to terrestrial consumers. This study is a step forward in order to better understand linkages between different ecosystems and also the effects of large scale river regulation on processes taking place in uplands beyond the riparian zone. River regulation markedly reduces the densities of blackflies, the perhaps most abundant flying insects in the boreal region. Therefore, river regulation has a negative effect on the overall densities of flying insects. This effect appears to cascade on to breeding conditions and success of insectivorous birds. Hereby, river regulation plays an important role in the structuring of the entire bird community environment. Leucocytozoon were more frequently found in blood samples from birds breeding along the free flowing Vindel River, implying that a higher incidence of blackflies biting resulted in more frequent transmission of parasite. The larger size and most abundant hosts were prioritized by blood seeking females of blackflies. As, large sized hosts most likely are not small insect eaters, their relationship with blackflies is probably mainly negative, whereas smaller birds are more likely benefiting from the abundance of insects as a food resource and experiencing less negative effect of blackflies. Additional studies are required in order to better understand the consequences of river regulation to avian bird communities. We still have too limited data to be able to evaluate the consequences of river regulation for different bird communities in different landscapes. We also lack information on the importance of blackflies for a number of terrestrial consumers, and the effect of transmitted Leucocytozoon on the health of wild birds. The current study suggests that river regulation has an important effect for bird communities even in terrestrial environments distant from the rivers, and that the major part of this effect must be attributed to the reduced densities of aquatic insects, in particular blackflies. REFERENCES Adler, P.H., Malmqvist, B., and Zhang, Y.X. 1999. Black flies (Diptera: Simuliidae) of northern Sweden: taxonomy, chromosomes, and bionomics. Entomologica Scandinavica, 29: 361 382. Askins, R.A. 2000. Restoring North America’s Birds. Lessons from Landscape Ecology. New Haven, CT: Yale Univ. Press. 288 pp.
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ACKNOWLEDGEMENTS First off all, I would like to thank my supervisor Björn Malmqvist . I have been lucky to have a supervisor that from the start believed in me and this project. Your never ending enthusiasm kept me going through the tuff years off my PhD period. You introduced me to the wonderful world of Ecology, a world of never ending questions and complicated answers. Thanks for all encouragement, and always taking time to listen to me and even reading my “English”. All members, present and past, I would like to thank for sharing the years that I have been at EMG. The “old “ members of the group Per Ola Hoffsten (for all nice discussions), Åsa Eriksson (extra live in parties) and Micael Jonsson (never showing rarest birds) you introduced me into Stream Ecology group. Special thanks to Per Ola Hoffsten for sharing all secrets of fishing. The newer members of the group Zlatko Petrin (one of the most warm hearted persons I met), Fabio Lepori (fly fishing expert) and Brendan McKie (never ending humour), thank you so much for all the help through the last years. It was pleasure to work with all of you. Thanks to all dear friends and colleagues at the Ecology department. All the students at the department that I have met through the years and made this to the nice place it has been; it will be hard to find another bunch of nice people like you guys!!!!!!!!! Special thanks to my brother in arms, Tomas Brodin , without you all fun at department, parties and out in the fields will be minimal. Many thanks to all “ringers” at department; Katarina Stenman , Frank Johansson , Jonas Gustafsson , and other birders; Antoine Bos , Jörgen Olsson , Martin Lind for many hours spend with the BIRDS. Thank you Johanna Öhman and Karin Nilsson , my roommate and “labmate”, for stimulating and wild discussions on everything from …… to science. I definitively have enjoyed your presence in “my room and lab”. Thank every “Friday pub” member (especially Martin Frenkel ) for relaxation after long week. Many thanks to former and present members of the staff at the department, in the lead with Sussi and Ylva , without you will be not possible to swim in the lake of bureaucracy. Thanks to “old” friends from Micro, Åsa Gylfe for wonderful trip to Føroyar, Mikael Wikström for sharing “Bird Race” secrets.
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I am very grateful to past and present members of Lithuanian community Arūnas ir
Ramun÷ , Karolis and Rima , Ignas ir Kotryna , Ernestas ir Egl÷, Ramūnas ir
Kristina , Aidas ir Rūta, Algis , Jaunius , Aurelija , Aust÷ . D÷kingas už visus
susitikimus, vakarienes, balius ir keliones. Karoliui ir Rimai už vaiku priežiūrą, Ignui
ir Kotrynai už fantastiškus pasis÷d÷jimus , Ernestui ir Eglei už Kal÷das (žąsų dar bus),
Ramūnui už nuostabias žvejybas , Arūnui, Jauniui ir Aidui už krepšinį, Aurelijai už
linksmas kavos pertrauk÷les.
Thanks to Russian frends Gennady (Gena) and Olga ☺, Michael ( Miša) and Evgenya
(Ženia) ( for outstanding dinners ), Nina, Lena , Dennis for keeping my russian going.
My deepest thanks to Jūrat÷ and Medeina , Emilija and Kirnis . Thank you Jūrate for
all your love and support. Ačiū Tau už mano svajonių išpildymą – Kirnį ir Emiliją . O,
vaikučiams už nuolatinį rūpestį ”Kaip sekasi, t÷te?”
Didelis d÷kui t÷vams už tai, kad netrukdomai leidote dom÷tis paukščiais, už jūsų paramą ir supratimą, už tai, kad visuomet esame laukiami. Broliui , už rūpesti ir kartu praleistą vaikystę.
Thanks to all whom I did not mention, but have been a part of my life for six years. Thanks to all of you, Yours, Das
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