Plants & Ecology

Effects of cormorants on species diversity and abundance of phantom midges and spiders by Caroline Essenberg

Plants & Ecology

Plant Ecology 2009/11 Department of Botany Stockholm University

Effects of cormorants on species diversity and abundance of phantom midges and spiders

by Caroline Essenberg

Supervisor: Peter Hambäck

Plants & Ecology

Plant Ecology 2009/11 Department of Botany Stockholm University

Plants & Ecology

Plant Ecology Department of Botany Stockholm University S-106 91 Stockholm Sweden

Abstract

Great cormorant (Phalacrocorax carbo) is a colonial seabird that transports loads of nutrients (e.g. nitrogen) from water to land. Contributed nitrogen may increase or kill the vegetation depending on cormorant density; it may also leach into the water affecting the algal growth in the surrounding water bodies. An increased algal growth may affect its consumers e.g. phantom midges, which enter the terrestrial food web as predator food when swarming over land. This study investigates how the terrestrial animal life is affected by nesting cormorants. Phantom midges and spiders were sampled on cormorant nesting islands, abandoned cormorant islands and non-cormorant islands to compare species richness and abundance in two trophic levels. The study was conducted in the archipelago of Stockholm, Sweden in 2008. The statistical analysis shows a negative trend, where phantom midge species richness decreases with higher cormorant density. Hunting and ground dwelling spider (e.g. Lycosidae) species richness and abundance decreases significantly with higher cormorant density. Contributed nitrogen in cormorant colonies may increase algal growth, but also cause a shift in the primary production where fast growing plants and algae may outcompete macrophytes. A decrease in species richness among primary producers may decrease species richness in higher trophic levels. Spiders may also be affected negatively by changed conditions and damaged habitats on cormorant islands and therefore decrease in species richness and abundance.

Introduction

Seabirds living in both aquatic and terrestrial ecosystems are important vectors in transferring nutrients from water to land (Lindeboom 1984; Polis and Hurd 1995, 1996; Sánches-Piñero and Polis 2000; Osono et al. 2002; Ellis et al. 2006). When the birds feed in water, they bring aquatic matter through their carcasses (Sanches-Pinero and Polis 2000) and guano (Anderson and Polis 1999; Sanches-Pinero and Polis 2000; Stapp and Polis 2003; Hobara et al. 2005; Wait et al. 2005) to their nesting places on land. The contributed nutrients are incorporated in the soil and alter the chemical composition, indirectly affecting plants (Smith 1978; Anderson and Polis 1999; Ellis 2005; Wait et al. 2005) and animals (Barrett et al. 2005). Seabird populations may have important consequences for plant and animal communities on islands and in the surrounding water bodies.

Great cormorant (Phalacrocorax carbo) is a colonial bird that is distributed almost all over the world (Cramp and Simmons 1977). Their colonies may be very big and contain up to 10,000 breeding pairs. They catch fish in lakes, rivers and coastal areas and are one of the top- predators in aquatic food webs (Hobson et al. 1994). By feeding in water and establishing breeding colonies on land, cormorants transport mainly two nutrients, phosphorus and nitrogen, from water to land (Kirkkala et al. 1998; Howarth and Marino 2006; Elser et al. 2007). Both phosphorus and nitrogen are important limiting factors of primary productivity (Kirkkala et al. 1998; Howarth and Marino 2006; Elser et al 2007). The effects of the increased nutrients in soil depends on cormorant nest density, it may either favour or kill vegetation (Ellis 2005). An increased input of nitrogen and phosphorus may lead to an increasing primary productivity (Onuf et al. 1977; Ryan & Watkins 1989; Anderson & Polis 1999; Wait et al. 2005), but when bird density is very high the nitrogen concentration in soil becomes toxic (Ellis 2005).

Phosphorus accumulates in the surface soil, while nitrogen instead is more mobile (Vitousek and Howarth 1991). Nitrogen in guano is uric acid and degrades microbiologically to ammonium. Ammonium may then follow different pathways: ammonia volatilization (Hobara et al. 2001; Lindeboom 1984), leach into the water (Wainwright et al. 1998) or be taken up by plants (Wainwright et al. 1998; Ellis 2005). Nitrogen leaching to the water may enter the

marine food web through aquatic plants. It can cause an increasing growth of algae which may affect their consumers, e.g. phantom midges (Chironomidae) (Wainwright et al. 1998).

The larval and pupal stages among phantom midges are constrained to aquatic habitats, while the adults are aerial (Wiederholm 1989). An increase in algae growth may lead to increased densities of phantom midges, which may re-enter the terrestrial food web as predator food. Stable isotope analysis (a tool for studying food-web interactions) in Mellbrand (2009) showed that spiders, which are the most abundant arthropod predators in seashores, mainly fed on phantom midges which have fed on green algae. Hodkinson et al. (2001) found a significant correlation between phantom midge density and spider density in coastal ecosystems, and Sanzone et al. (2003) showed that wolf spiders (Lycosidae) heavily relied on emerging adult insects. These studies support the hypothesis that insectivores are facilitating the transfer of energy from emerging aquatic prey along the water edge, which in turn increases the density of predators in seashores (Jackson and Fisher 1986).

Material and methods

Study species

Great cormorant is a species with increasing density in Europe. The number of cormorants has increased rapidly due to eutrophication of water bodies, protective measures, reduction of pesticides and alternation of water systems such as sluices and dams which facilitate foraging. Overfishing has caused changes in the size distribution of fishes; large predatory fishes have decreased which implicates an increase in the number of small fishes which enhancing the foraging conditions of cormorants (CARSS 2002).

The increasing number of cormorants has led to conflicts between interest groups (Suter 1995). The cormorants are blamed for many different negative effects in the environment e.g. for destruction of islands and reducing fish communities. Only a few studies investigate how cormorants influence the terrestrial ecosystems, and the ongoing public discussion about cormorants impact on the environment makes scientific studies about their ecological effects very important. This study investigates how the terrestrial animal life is affected by nesting cormorants. Abundance and species richness of phantom midges (Chironomidae) and spiders

(Araneae) on cormorant nesting islands and abandoned cormorant islands is analysed to examine the effects of cormorants.

Study area

This study was conducted in the archipelago of Stockholm, Sweden. The archipelago consists of 21,000 islands with varying sizes. The vegetation on the islands differ, some islands are covered with bare rocks, and others with herbs, grass and even forests. Bigger islands are built with houses, mainly summer houses.

In 2008, there were 21 cormorant colonies with 5,196 nests in the archipelago. In this study, five cormorant nesting islands and two abandoned cormorant island were examined (table 1). As control islands, neighbouring islands without nesting cormorants were used. Most of the study islands were small in size and covered with grass and low vegetation. Trees were present on most of the islands, and bigger islands contained forests. The control islands differed in size (800-4,500 m2) from the cormorant islands, but we have tried to find appropriate islands in relation to the study islands.

Methods

Hunting and ground dwelling spiders were captured using pitfall traps (plastic jars, 8 cm diameter and 6 cm height) in June 2008. The jars were placed in the ground, and collected two days after. Number of pitfall traps on each island was in relation with island size (table 1). Net building spiders and phantom midges were sampled by sweep netting in August 2008. Sweep netting was conducted in four gradients at two sides of the islands. Two of the gradients were placed one meter from sea, and two gradients at ten meters from sea. Each gradient had a distance of ten meters. Sampled spiders and phantom midges were stored in 70% alcohol until examination at laboratory.

Adult and subadult spiders were sorted out for examination. Adult spiders were identified to species, and subadult spiders to genus. Most of the spiders were examined by me with the keys by Roberts (1996) and Almqvist (2005; 2006), and some spiders were sent away for identification. Males of the sampled phantom midges were sorted into morpho-species, and

then sent away to Yngve Brodin at The Swedish National Environmental Protection Agency for species identification.

On some islands, the birds pulled out some pitfall traps, which resulted in a varying number of traps on each island (table 1) and made them therefore difficult to compare. To arrange this problem rarefaction was calculated in the program EstimateS Win 8.2, and abundance was calculated by dividing number of individuals with number of re-collected pitfall traps on each island.

Linear regression was used to analyse how species richness and abundance of phantom midges and spiders are affected by cormorant density. Cormorant density was calculated by dividing mean number of active cormorant nests in years 2005 - 2008 with island area (m2). All data was log-transformed and the statistical analysis was made in Statistica 5.5.

Table 1: summary of study islands. Area Time span of Number of active cormorant nests Mean density Number of Number of m2 colonisation 2005 2006 2007 2008 2005 - 2008 pitfall traps re-collected (nests/m2) pitfall traps Nesting islands Bergskäret 22,728 1998-2008 555 595 656 637 0.0269 200 46 Småholmarna "N" 8,550 2000-2008 410 591 538 448 0.0581 100 84 Marskärskobben 7,164 2003-2008 81 186 177 212 0.0229 100 68 Ryssmasterna "N" 3,224 2003-2008 65 171 127 183 0.0423 50 24 Alörarna 2,332 2007-2008 0 0 56 156 0.0227 50 40

Abandoned islands St. Trädskär 15,729 1996-2006 80 50 0 0 0.0021 150 75 St. Halmören 8,091 2002-2005 222 0 0 0 0.0069 100 71

Non-cormorant islands Mjölingsö 27,285 200 190 Ägglösen 17,357 150 118 Hannas holme 7,743 100 89 Nickesören 5,209 75 34 Fårören 3,286 50 48

Results

Phantom midges sampled by sweep netting

In this study, 6,141 male phantom midges were caught. A varying number of individuals were caught on the different island categories. On cormorant nesting islands, 4,942 individuals were caught, 140 individuals on abandoned cormorant islands and 1,059 individuals on non- cormorant islands (app. 1, table 1). The big difference in the number of sampled phantom midges is caused by the high number of individuals caught on the cormorant nesting island, Alörarna, where 4,039 individuals were caught.

Species determination resulted in 41 different species (app. 1, table 1). The number of species on each island varied between 9 and 24 species, and the most abundant species on the study islands were Paratanytarsus dissimilis, Tanytarsus usmaensis, Cricotopus bicinctus and Cricotopus caducus. Most of the sampled species are common in Sweden and Europe except for C. caducus, which was found in Sweden for the first time. The species is common in the rest of Europe and in my samples it was one of the four most abundant species. It was found on most of the study islands and is probably a quite common species in the rest of the archipelago. Linear regression analysis of cormorant density and phantom midges species richness (R2=0.32, F=4.78, N=12, p=0.054) (fig. 1), and abundance and cormorant density (R2=0.12, F=1.33, N=12, p=0.280) were not significant.

3.4

3.2

Two points 3.0

2.8

2.6

Number of species Number 2.4

(scale is log-transformed)

2.2

2.0 0.00 0.01 0.02 0.03 0.04 0.05 0.06

Cormorant density (nests/m2)

Figure 1: Species richness of phantom midges.

Spiders sampled by pitfall traps

In a total, 39 spider species (app. 1, table 2) and 598 individuals were sampled. The most abundant species on the study islands were Pardosa amentata, Pardosa agricola, Trochosa ruricola and Pachygnatha degeeri. On most of the islands, P. amentata was the most abundant species, but P. agricola was very common on three of the study islands. Many spiders of the group “money spiders” were also caught in the pitfall traps. Because of the difficulty of species identification of these spiders, they were all sorted out and are not included in this study.

On cormorant nesting islands 92 individuals were caught, 206 individuals on abandoned cormorant islands and 300 individuals on non-cormorant islands (app.1, table 2). Rarefaction resulted in a variation between 1 and 9.53 species on each island. Linear regression analysis shows that abundance (R2=0.47, F=8.76, N=12, p=0.014) (fig. 2) and species richness (R2=0.56, F=12.67, N=12, p=0.005) (fig. 3) of hunting and ground dwelling spiders decreases with higher cormorant density.

1,0

0,5

0,0

-0,5

-1,0

-1,5

Abundance -2,0

(scale is log-transformed) -2,5

-3,0

-3,5 0,00 0,01 0,02 0,03 0,04 0,05 0,06

Cormorant density (nests/m2)

Figure 2: Abundance of hunting and ground dwelling spiders (e.g. Lycosidae). Abundance was estimated on number of individuals / pitfall trap.

2,4

2,0

Two points 1,6

1,2

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Number of species

(scale is log-transformed) 0,4

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0,00 0,01 0,02 0,03 0,04 0,05 0,06

Cormorant density (nests/m2)

Figure 3: Species richness of hunting and ground dwelling spiders (e.g. Lycosidae). Number of species is rarefied. 10

Spiders sampled by sweep netting

With sweep netting, 344 individuals and 21 species were sampled. Species list can be found in appendix 1, table 3. Tetragnatha montana was the most abundant species on the study islands, Larinioides cornutus, Tetragnatha dearmata and Xysticus cristatus were also common species. On cormorant nesting islands 119 individuals were caught, 85 individuals on abandoned cormorant islands and 140 individuals were caught on non-cormorant islands (app. 1, table 3). Linear regression analysis of species richness and cormorant density (R2=0.03, F=0.27, N=12, p=0.616), and abundance and cormorant density (R2=0.009, F=0.09, N=12, p=0.771) were not significant.

Correlation analysis

To test if hunting and ground dwelling spider species richness are depending on phantom midge species richness, a correlation analysis was made (r=0.57, p=0.053) (fig. 4).

3,4

3,2

3,0

2,8

2,6

2,4

(scale is log-transformed)

Number of phantom midge species 2,2

2,0 0,0 0,4 0,8 1,2 1,6 2,0 2,4 Number of spiders species (scale is log-transformed)

Figure 4: Correlation analysis of phantom midges species richness and hunting and ground dwelling spider (e.g. Lycosidae) species richness. Spider species richness is rarefied.

Discussion

The cormorants bring loads of nutrients to their nesting places, affecting the surrounding environment. They nest in big colonies on small areas and bring nutrients (phosphorus and nitrogen) from water to land (Kirkkala et al. 1998; Howarth and Marino 2006; Elser et al. 2007). The nutrients incorporate in soil, and nitrogen may also leach into the water and affect the aquatic plants and indirectly its consumers (Wainright et al. 1998). Contributed nitrogen may increase algal growth (Wainright et al. 1998), but also cause a shift in primary producers. Fast growing macroalgae, epiphytes and phytoplankton will out-compete macrophytes by exploiting the nutrients and by reducing light penetration for submerged plants (Sand-Jensen and Borum 1991; Short et al. 1995; Taylor et al. 1995; Wear et al. 1999). High species diversity among primary producers allows rare consumer species to become abundant and, therefore, increases species richness of the consumers (Hutchinson 1959). A decrease in diversity of primary production consequently leads to a decrease in consumer diversity (Siemann 1998; Haddad et al. 2000). This study shows a negative trend (p=0,054) between phantom midge species richness and cormorant density probably caused by a decrease in diversity of primary producers due to a high input of nitrogen.

Phantom midges are aerial as adults (Wiederholm 1989) and enter the terrestrial system when swarming over land (Wainright et al. 1998). Spiders are the most abundant arthropod predators on seashores and mainly feed on phantom midges (Jackson and Fisher 1986; Hodkinson et al. 2001; Sanzone et al. 2003; Mellbrand 2009). A decrease in herbivore diversity may also decrease the diversity in higher trophic levels (Siemann 1998; Keats et al. 2004), and this study shows that hunting and ground dwelling spiders (e.g. Lycosidae) significantly decreases in abundance and species richness with higher cormorant density. Another important factor that may affect species diversity and abundance of spiders on cormorant islands is the terrestrial vegetation. When the high input of nutrients is incorporated in the soil, it affects the terrestrial plants by increasing biomass and by decreasing species richness (Smith 1978; Anderson and Polis 1999; Ellis 2005; Wait et al. 2005). In seabird colonies, annual and biennial plant species increase while perennial species decrease (Smith 1978; Vidal et a. 1998; Garcia et al. 2002), and when the bird densities are very high the nutrient concentration in soil becomes toxic and may kill the vegetation (Ellis 2005). Spiders

may be sensitive to changed conditions and damage habitats and consequently decrease in abundance and species richness (Greenstone 1984; Siemann 1998; Haddad et al. 2000).

Net building spiders showed no significant response to cormorant density in abundance and species richness. This is quite unexpected since these spiders may as well as hunting spiders utilize phantom midges as food resource to a high degree and persists in reduced vegetation. Web building spiders differ in hunting methods and ecology from ground dwelling spiders and may respond differently to damage habitats.

Conclusion

The cormorants bring loads of nutrients to their nesting places which affect the environment around them. Cormorant derived nitrogen leaching to the water affects the surrounding water bodies by changing species composition of aquatic plants. This study indicates that species richness of phantom midges (algae consumers) decreases with higher cormorant density as a result of low species richness among alage around cormorant islands. Phantom midges are aerial as adults and enter the terrestrial food web as predator food. Hunting and ground dwelling spiders (e.g. Lycosidae), which are common arthropod predators in seashores, decreases significantly in abundance and species richness with higher cormorant density. This may be a result of a decreased species diversity of prey and damaged habitats on cormorant islands.

Acknowledgements

I want to thank Peter Hambäck and Gundula Kolb for supervising this study, and Lenn and Eskil Jerling for their hospitality and helping in the field. I also want to thank Yngve Brodin for species identification of phantom midges, and Sandra Öberg, Torbjörn Kronstedt and Lars Jonsson for helping with species identification of spiders.

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Appendix 1

Table 1: list of phantom midge species and number of individuals Question mark between genus and species signifies that the genus is assured but not species. Subfamily Species Cormorant Abandoned Non - Total nesting cormorant cormorant islands islands island Chironominae Chironomus aprilinus 228 22 222 472 Chironomus plumosus 12 5 10 27 Dicrotendipes pulsus 213 4 78 295 Harnischia curtilamellata 1 1 Microchironomus tener 13 14 27 Microtendipes pedellus 220 26 57 303 Parachironomus arcuatus 7 8 15 Paratanytarsus dissimilis 466 10 139 615 Paratanytarsus natvigi 3 3 Paratendipes albimanus 2 2 Phaenopsectra flavipes 20 25 45 Polypedilum nubeculosum 52 36 88 Polypedilum scalaenum 253 40 24 317 Tanytarsus ? brundini 134 40 174 Tanytarsus usmaensis 927 4 74 1005 Xenochironomus xenolabis 11 4 15 Orthocladiinae Bryophaenocladius ? scanicus 5 11 16 Cricotopus annulator 4 4 Cricotopus bicinctus 1618 2 92 1712 Cricotopus caducus 458 58 516 Cricotopus flavocinctus 1 1 Cricotopus intersectus 10 8 18 Cricotopus ? ornatus 2 2 Cricotopus sylvestris 119 2 63 184 Halocladius variabilis 30 4 2 36 Limnophyes difficilis 6 23 29 Limnophyes minimus 3 3 Limnophyes pumilio 3 6 9 Limnophyes sp. A 1 1 Nanocladius dichromus 4 4 Nanocladius rectinervis 1 1 Orthocladius sp. A 1 1 Paratrichocladius rufiventris 6 1 7 Psectrocladius ? limbatellus 1 1 Psectrocladius ? oligosetus 7 7 Smittia sp. A 1 1 Tanypodiane Ablabesmyia monilis 56 13 69 Ablabesmyia longistyla 2 2 17

Procladius culiciformis 10 14 16 40 Procladius ? ferrugineus 4 4 7 15 Procladius ? sagittalis 41 3 14 58

Table 2: list of spiders species and number of individuals sampled by pitfall traps Family Species Cormorant Abandoned Non - Total nesting cormorant cormorant islands islands island Araneidae Larinioides patagiatus 1 1 2 Larinioides (imm.) 2 2 Clubionidae Clubiona (imm.) 1 1 2 Gnaphosidae Callilepis nocturna 3 3 Drassyllus praeficus 1 1 Gnaphosa montana 1 1 Haplodrassus signifer 3 3 Micaria nimosa 1 1 Micaria pulicaria 2 1 3 Zelotes petrensis 1 1 Zelotes subterraneus 2 1 5 8 Zelotes (imm.) 4 1 4 9 Hahniidae Antistea elegans 1 1 Linyphiidae Lepthyphantes flavipes 1 1 2 Lepthyphantes mengei 1 1 Stemonyphantes lineatus 1 1 Tenuiphantes flavipes 1 1 Lycosidae Alopecosa pulverulenta 8 8 Alopecosa (imm.) 1 1 Arctosa leopardus 1 1 10 12 Arctosa (imm.) 6 7 13 Pardosa agrestis 2 1 7 10 Pardosa agricola 14 49 80 143 Pardosa amentata 8 34 17 59 Pardosa fulvipes 3 5 8 Pardosa lugubris 3 3 Pardosa monticola 1 12 13 Pardosa nigriceps 2 2 Pardosa palustris 2 1 3 Pardosa prativaga 12 17 29 Pardosa pullata 2 2 4 Pardosa (imm.) 3 3 Pirata piraticus 1 1

Trochosa ruricola 9 10 10 29 Trochosa spinipalpis 1 1 2 Trochosa terricola 2 4 4 10 Trochosa (imm.) 8 31 33 72 Salticidae Heliophanus cupreus 1 1 Tetragnathidae Pachygnatha clercki 2 17 2 21 Pachygnatha degeeri 7 49 45 101 Theridiidae Crustulina guttata 1 1 Thomisidae Ozyptila praticola 3 3 Thanatus striatus 1 1 Xysticus cristatus 2 2 Zoridae Zora spinimana 1 1

Table 3: list of spider species and number of individuals sampled by sweep netting Family Species Cormorant Abandoned Non - Total nesting cormorant cormorant islands islands island Araneidae Araniella (imm.) 2 2 Larinioides cornutus 2 4 1 7 Larinioides patagiatus 1 1 2 Larinioides (imm.) 20 21 9 50 Clubionidae Clubiona (imm.) 3 3 Dictynidae Dictyna (imm.) 7 7 Linyphiidae Gongyliduim rufipes 3 3 Kaestneria dorsalis 5 8 13 Neriene (imm.) 1 1 Salticidae Heliophanus dubius 1 1 2 Heliophanus (imm.) 5 5 Tetragnathidae Meta mengei 1 1 Meta segmentata 9 1 10 20 Meta (imm.) 1 1 2 Pachygnatha degeeri 1 1 Tetragnatha dearmata 12 6 5 23 Tetragnatha extensa 2 4 6 12 Tetragnatha montana 32 24 18 74 Tetragnatha striata 3 1 11 15 Tetragnatha (imm.) 16 5 29 50 Theridiidae Anelosimus (imm.) 1 1 Theridion (imm.) 1 2 3 Thomisidae Philodromus (imm.) 2 4 6 Tibellus oblongus 1 1 19

Xysticus cristatus 1 1 4 6 Xysticus (imm.) 5 16 13 34

Serien Plants & Ecology (ISSN 1651-9248) har tidigare haft namnen "Meddelanden från Växtekologiska avdelningen, Botaniska institutionen, Stockholms Universitet" nummer 1978:1 – 1993:1 samt "Växtekologi". (ISSN 1400-9501) nummer 1994:1 – 2003:3.

Följande publikationer ingår i utgivningen:

1978:1 Liljelund, Lars-Erik: Kompendium i matematik för ekologer. 1978:2 Carlsson, Lars: Vegetationen på Littejåkkadeltat vid Sitasjaure, Lule Lappmark. 1978:3 Tapper, Per-Göran: Den maritima lövskogen i Stockholms skärgård. 1978:4: Forsse, Erik: Vegetationskartans användbarhet vid detaljplanering av fritidsbebyggelse. 1978:5 Bråvander, Lars-Gunnar och Engelmark, Thorbjörn: Botaniska studier vid Porjusselets och St. Lulevattens stränder i samband med regleringen 1974. 1979:1 Engström, Peter: Tillväxt, sulfatupptag och omsättning av cellmaterial hos pelagiska saltvattensbakterier. 1979:2 Eriksson, Sonja: Vegetationsutvecklingen i Husby-Långhundra de senaste tvåhundra åren. 1979:3 Bråvander, Lars-Gunnar: Vegetation och flora i övre Teusadalen och vid Auta- och Sitjasjaure; Norra Lule Lappmark. En översiktlig inventering med anledning av områdets exploatering för vattenkraftsändamål i Ritsemprojektet. 1979:4 Liljelund, Lars-Erik, Emanuelsson, Urban, Florgård, C. och Hofman-Bang, Vilhelm: Kunskapsöversikt och forskningsbehov rörande mekanisk påverkan på mark och vegetation. 1979:5 Reinhard, Ylva: Avloppsinfiltration - ett försök till konsekvensbeskrivning. 1980:1 Telenius, Anders och Torstensson, Peter: Populationsstudie på Spergularia marina och Spergularia media. I Frödimorfism och reproduktion. 1980:2 Hilding, Tuija: Populationsstudier på Spergularia marina och Spergularia media. II Resursallokering och mortalitet. 1980:3 Eriksson, Ove: Reproduktion och vegetativ spridning hos Potentilla anserina L. 1981:1 Eriksson, Torsten: Aspekter på färgvariation hos Dactylorhiza sambucina. 1983:1 Blom, Göran: Undersökningar av lertäkter i Färentuna, Ekerö kommun. 1984:1 Jerling, Ingemar: Kalkning som motåtgärd till försurningen och dess effekter på blåbär, Vaccinium myrtillus. 1986:1 Svanberg, Kerstin: En studie av grusbräckans (Saxifraga tridactylites) demografi. 1986:2 Nyberg, Hans: Förändringar i träd- och buskskiktets sammansättning i ädellövskogen på Tullgarnsnäset 1960-1983. 1987:1 Edenholm, Krister: Undersökningar av vegetationspåverkan av vildsvinsbök i Tullgarnsområdet. 1987:2 Nilsson, Thomas: Variation i fröstorlek och tillväxthastighet inom släktet Veronica. 1988:1 Ehrlén, Johan: Fröproduktion hos vårärt (Lathyrus vernus L.). - Begränsningar och reglering. 1988:2 Dinnétz, Patrik: Local variation in degree of gynodioecy and protogyny in Plantago maritima. 1988:3 Blom, Göran och Wincent, Helena: Effekter of kalkning på ängsvegetation. 1989:1 Eriksson, Pia: Täthetsreglering i Littoralvegetation. 1989:2 Kalvas, Arja: Jämförande studier av Fucus-populationer från Östersjön och västkusten. 1990:1 Kiviniemi, Katariina: Groddplantsetablering och spridning hos smultron, Fragaria vesca.

1990:2 Idestam-Almquist, Jerker: Transplantationsförsök med Borstnate. 1992:1 Malm, Torleif: Allokemisk påverkan från mucus hos åtta bruna makroalger på epifytiska alger. 1992:2 Pontis, Cristina: Om groddknoppar och tandrötter. Funderingar kring en klonal växt: Dentaria bulbifera. 1992:3 Agartz, Susanne: Optimal utkorsning hos Primula farinosa. 1992:4 Berglund, Anita: Ekologiska effekter av en parasitsvamp - Uromyces lineolatus på Glaux maritima (Strandkrypa). 1992:5 Ehn, Maria: Distribution and tetrasporophytes in populations of Chondrus crispus Stackhouse (Gigartinaceae, Rhodophyta) on the west coast of Sweden. 1992:6 Peterson, Torbjörn: Mollusc herbivory. 1993:1 Klásterská-Hedenberg, Martina: The influence of pH, N:P ratio and zooplankton on the phytoplanctic composition in hypertrophic ponds in the Trebon-region, Czech Republic. 1994:1 Fröborg, Heléne: Pollination and seed set in Vaccinium and Andromeda. 1994:2 Eriksson, Åsa: Makrofossilanalys av förekomst och populationsdynamik hos Najas flexilis i Sörmland. 1994:3 Klee, Irene: Effekter av kvävetillförsel på 6 vanliga arter i gran- och tallskog. 1995:1 Holm, Martin: Beståndshistorik - vad 492 träd på Fagerön i Uppland kan berätta. 1995:2 Löfgren, Anders: Distribution patterns and population structure of an economically important Amazon palm, Jessenia bataua (Mart.) Burret ssp. bataua in Bolivia. 1995:3 Norberg, Ylva: Morphological variation in the reduced, free floating Fucus vesiculosus, in the Baltic Proper. 1995:4 Hylander, Kristoffer & Hylander, Eva: Mount Zuquala - an upland forest of Ethiopia. Floristic inventory and analysis of the state of conservation. 1996:1 Eriksson, Åsa: Plant species composition and diversity in semi-natural grasslands - with special emphasis on effects of mycorrhiza. 1996:2 Kalvas, Arja: Morphological variation and reproduction in Fucus vesiculosus L. populations. 1996:3 Andersson, Regina: Fågelspridda frukter kemiska och morfologiska egenskaper i relation till fåglarnas val av frukter. 1996:4 Lindgren, Åsa: Restpopulationer, nykolonisation och diversitet hos växter i naturbetesmarker i sörmländsk skogsbygd. 1996:5 Kiviniemi, Katariina: The ecological and evolutionary significance of the early life cycle stages in plants, with special emphasis on seed dispersal. 1996:7 Franzén, Daniel: Fältskiktsförändringar i ädellövskog på Fagerön, Uppland, beroende på igenväxning av gran och skogsavverkning. 1997:1 Wicksell, Maria: Flowering synchronization in the Ericaceae and the Empetraceae. 1997:2 Bolmgren, Kjell: A study of asynchrony in phenology - with a little help from Frangula alnus. 1997:3 Kiviniemi, Katariina: A study of seed dispersal and recruitment of plants in a fragmented habitat. 1997:4 Jakobsson, Anna: Fecundity and abundance - a comparative study of grassland species. 1997:5 Löfgren, Per: Population dynamics and the influence of disturbance in the Carline Thistle, Carlina vulgaris. 1998:1 Mattsson, Birgitta: The stress concept, exemplified by low salinity and other stress factors in aquatic systems.

1998:2 Forsslund, Annika & Koffman, Anna: Species diversity of lichens on decaying wood - A comparison between old-growth and managed forest. 1998:3 Eriksson, Åsa: Recruitment processes, site history and abundance patterns of plants in semi-natural grasslands. 1998:4 Fröborg, Heléne: Biotic interactions in the recruitment phase of forest field layer plants. 1998:5 Löfgren, Anders: Spatial and temporal structure of genetic variation in plants. 1998:6 Holmén Bränn, Kristina: Limitations of recruitment in Trifolium repens. 1999:1 Mattsson, Birgitta: Salinity effects on different life cycle stages in Baltic and North Sea Fucus vesiculosus L. 1999:2 Johannessen, Åse: Factors influencing vascular epiphyte composition in a lower montane rain forest in Ecuador. An inventory with aspects of altitudinal distribution, moisture, dispersal and pollination. 1999:3 Fröborg, Heléne: Seedling recruitment in forest field layer plants: seed production, herbivory and local species dynamics. 1999:4 Franzén, Daniel: Processes determining plant species richness at different scales - examplified by grassland studies. 1999:5 Malm, Torleif: Factors regulating distribution patterns of fucoid seaweeds. A comparison between marine tidal and brackish atidal environments. 1999:6 Iversen, Therese: Flowering dynamics of the tropical tree Jacquinia nervosa. 1999:7 Isæus, Martin: Structuring factors for Fucus vesiculosus L. in Stockholm south archipelago - a GIS application. 1999:8 Lannek, Joakim: Förändringar i vegetation och flora på öar i Norrtälje skärgård. 2000:1 Jakobsson, Anna: Explaining differences in geographic range size, with focus on dispersal and speciation. 2000:2 Jakobsson, Anna: Comparative studies of colonisation ability and abundance in semi-natural grassland and deciduous forest. 2000:3 Franzén, Daniel: Aspects of pattern, process and function of species richness in Swedish seminatural grasslands. 2000:4 Öster, Mathias: The effects of habitat fragmentation on reproduction and population structure in Ranunculus bulbosus. 2001:1 Lindborg, Regina: Projecting extinction risks in plants in a conservation context. 2001:2 Lindgren, Åsa: Herbivory effects at different levels of plant organisation; the individual and the community. 2001:3 Lindborg, Regina: Forecasting the fate of plant species exposed to land use change. 2001:4 Bertilsson, Maria: Effects of habitat fragmentation on fitness components. 2001:5 Ryberg, Britta: Sustainability aspects on Oleoresin extraction from Dipterocarpus alatus. 2001:6 Dahlgren, Stefan: Undersökning av fem havsvikar i Bergkvara skärgård, östra egentliga Östersjön. 2001:7 Moen, Jon; Angerbjörn, Anders; Dinnetz, Patrik & Eriksson Ove: Biodiversitet i fjällen ovan trädgränsen: Bakgrund och kunskapsläge. 2001:8 Vanhoenacker, Didrik: To be short or long. Floral and inflorescence traits of Bird`s eye primrose Primula farinose, and interactions with pollinators and a seed predator. 2001:9 Wikström, Sofia: Plant invasions: are they possible to predict? 2001:10 von Zeipel, Hugo: Metapopulations and plant fitness in a titrophic system – seed predation and population structure in Actaea spicata L. vary with population size. 2001:11 Forsén, Britt: Survival of Hordelymus europaéus and Bromus benekenii in a deciduous forest under influence of forest management.

2001:12 Hedin, Elisabeth: Bedömningsgrunder för restaurering av lövängsrester i Norrtälje kommun. 2002:1 Dahlgren, Stefan & Kautsky, Lena: Distribution and recent changes in benthic macrovegetation in the Baltic Sea basins. – A literature review. 2002:2 Wikström, Sofia: Invasion history of Fucus evanescens C. Ag. in the Baltic Sea region and effects on the native biota. 2002:3 Janson, Emma: The effect of fragment size and isolation on the abundance of Viola tricolor in semi-natural grasslands. 2002:4 Bertilsson, Maria: Population persistance and individual fitness in Vicia pisiformis: the effects of habitat quality, population size and isolation. 2002:5 Hedman, Irja: Hävdhistorik och artrikedom av kärlväxter i ängs- och hagmarker på Singö, Fogdö och norra Väddö. 2002:6 Karlsson, Ann: Analys av florans förändring under de senaste hundra åren, ett successionsförlopp i Norrtälje kommuns skärgård. 2002:7 Isæus, Martin: Factors affecting the large and small scale distribution of fucoids in the Baltic Sea. 2003:1 Anagrius, Malin: Plant distribution patterns in an urban environment, Södermalm, Stockholm. 2003:2 Persson, Christin: Artantal och abundans av lavar på askstammar – jämförelse mellan betade och igenvuxna lövängsrester. 2003:3 Isæus, Martin: Wave impact on macroalgal communities. 2003:4 Jansson-Ask, Kristina: Betydelsen av pollen, resurser och ljustillgång för reproduktiv framgång hos Storrams, Polygonatum multiflorum. 2003:5 Sundblad, Göran: Using GIS to simulate and examine effects of wave exposure on submerged macrophyte vegetation. 2004:1 Strindell, Magnus: Abundansförändringar hos kärlväxter i ädellövskog – en jämförelse av skötselåtgärder. 2004:2 Dahlgren, Johan P: Are metapopulation dynamics important for aquatic plants? 2004:3 Wahlstrand, Anna: Predicting the occurrence of Zostera marina in bays in the Stockholm archipelago,northern Baltic proper. 2004:4 Råberg, Sonja: Competition from filamentous algae on Fucus vesiculosus – negative effects and the implications on biodiversity of associated flora and fauna. 2004:5 Smaaland, John: Effects of phosphorous load by water run-off on submersed plant communities in shallow bays in the Stockholm archipelago. 2004:6 Ramula Satu: Covariation among life history traits: implications for plant population dynamics. 2004:7 Ramula, Satu: Population viability analysis for plants: Optimizing work effort and the precision of estimates. 2004:8 Niklasson, Camilla: Effects of nutrient content and polybrominated phenols on the reproduction of Idotea baltica and Gammarus ssp. 2004:9 Lönnberg, Karin: Flowering phenology and distribution in fleshy fruited plants. 2004:10 Almlöf, Anette: Miljöfaktorers inverkan på bladmossor i Fagersjöskogen, Farsta, Stockholm. 2005:1 Hult, Anna: Factors affecting plant species composition on shores - A study made in the Stockholm archipelago, Sweden. 2005:2 Vanhoenacker, Didrik: The evolutionary pollination ecology of Primula farinosa. 2005:3 von Zeipel, Hugo: The plant-animal interactions of Actea spicata in relation to spatial context. 2005:4 Arvanitis, Leena T.: Butterfly seed predation.

2005:5 Öster, Mathias: Landscape effects on plant species diversity – a case study of Antennaria dioica. 2005:6 Boalt, Elin: Ecosystem effects of large grazing herbivores: the role of nitrogen. 2005:7 Ohlson, Helena: The influence of landscape history, connectivity and area on species diversity in semi-natural grasslands. 2005:8 Schmalholz, Martin: Patterns of variation in abundance and fecundity in the endangered grassland annual Euphrasia rostkovia ssp. Fennica. 2005:9 Knutsson, Linda: Do ants select for larger seeds in Melampyrum nemorosum? 2006:1 Forslund, Helena: A comparison of resistance to herbivory between one exotic and one native population of the brown alga Fucus evanescens. 2006:2 Nordqvist, Johanna: Effects of Ceratophyllum demersum L. on lake phytoplankton composition. 2006:3 Lönnberg, Karin: Recruitment patterns, community assembly, and the evolution of seed size. 2006:4 Mellbrand, Kajsa: Food webs across the waterline - Effects of marine subsidies on coastal predators and ecosystems. 2006:5 Enskog, Maria: Effects of eutrophication and marine subsidies on terrestrial invertebrates and plants. 2006:6 Dahlgren, Johan: Responses of forest herbs to the environment. 2006:7 Aggemyr, Elsa: The influence of landscape, field size and shape on plant species diversity in grazed former arable fields. 2006:8 Hedlund, Kristina: Flodkräftor (Astacus astacus) i Bornsjön, en omnivors påverkan på växter och snäckor. 2007:1 Eriksson, Ove: Naturbetesmarkernas växter- ekologi, artrikedom och bevarandebiologi. 2007:2 Schmalholz, Martin: The occurrence and ecological role of refugia at different spatial scales in a dynamic world. 2007:3 Vikström, Lina: Effects of local and regional variables on the flora in the former semi-natural grasslands on Wäsby Golf club’s course. 2007:4 Hansen, Joakim: The role of submersed angiosperms and charophytes for aquatic fauna communities. 2007:5 Johansson, Lena: Population dynamics of Gentianella campestris, effects of grassland management, soil conditions and the history of the landscape 2007:6 von Euler, Tove: Sex related colour polymorphism in Antennaria dioica. 2007:7 Mellbrand, Kajsa: Bechcombers, landlubbers and able seemen: Effects of marine subsidies on the roles of arthropod predators in coastal food webs. 2007:8 Hansen, Joakim: Distribution patterns of macroinvertebrates in vegetated, shallow, soft-bottom bays of the Baltic Sea. 2007:9 Axemar, Hanna: An experimental study of plant habitat choices by macroinvertebrates in brackish soft-bottom bays. 2007:10 Johnson, Samuel: The response of bryophytes to wildfire- to what extent do they survive in-situ? 2007:11 Kolb, Gundula: The effects of cormorants on population dynamics and food web structure on their nesting islands. 2007:12 Honkakangas, Jessica: Spring succession on shallow rocky shores in northern Baltic proper. 2008:1 Gunnarsson, Karl: Påverkas Fucus radicans utbredning av Idotea baltica? 2008:2 Fjäder, Mathilda: Anlagda våtmarker i odlingslandskap- Hur påverkas kärlväxternas diversitet?

2008:3 Schmalholz, Martin: Succession in boreal bryophyte communities – the role of microtopography and post-harvest bottlenecks. 2008:4 Jokinen, Kirsi: Recolonization patterns of boreal forest vegetation following a severe flash flood. 2008:5 Sagerman, Josefin: Effects of macrophyte morphology on the invertebrate fauna in the Baltic Sea. 2009:1 Andersson, Petter: Quantitative aspects of plant-insect interaction in fragmented landscapes – the role of insect search behaviour. 2009:2 Kolb, Gundula: The effects of cormorants on the plant-arthropod food web on their nesting islands. 2009:3 Johansson, Veronika: Functional traits and remnant populations in abandoned semi-natural grasslands. 2009: 4 König, Malin: Phenotypic selection on flowering phenology and herbivory in Cardamine amara. 2009:5 Forslund, Helena: Grazing and the geographical range of seaweeds – The introduced Fucus evanescens and the newly described Fucus radicans. 2009:6 von Euler, Tove: Local adaptation and life history differentiation in plant populations. 2009:7 Tiderman, Dan: Sympatric speciation in Baltic Sea Fucus population- Is vegetative reproduction the key for evolution of F.radicans? 2009:8 Marteinsdóttir, Bryndis: Asembly of plant communties in grasslands: an overview. 2009:9 Herrström, Anna: Distribution and host plant selection of the Alcon blue (Maculinea alcon). 2009:10 Norrman, Karolina: Long-term exclusion of mammalian herbivores affect plant biomass in plant communities of the tundra in northern Norway.