The Spider and the Sea Effects of Marine Subsidies on the Role of Spiders in Terrestrial Food Webs

The Spider and the Sea Effects of marine subsidies on the role of spiders in terrestrial food webs

Kajsa Mellbrand ©Kajsa Mellbrand, Stockholm 2009 Illustrations and photos: Kajsa Mellbrand

ISBN 978-91-7155-877-0

Printed in Sweden by Universitetsservice, US-AB, Stockholm 2009 Distributor: Department of Botany, Stockholm University

“Jag vet var spindlarna spänna i vassen nät över vattnet”

-Dan Andersson

Doctoral dissertation Kajsa Mellbrand Department of Botany Stockholm University SE – 10691 Stockholm Sweden

The Spider and the Sea Effects of marine subsidies on the role of spiders in terrestrial food webs

Abstract – Marine inflows to terrestrial ecosystems have been suggested as an important factor for the structure and function of shore ecosystems. The overall aim of this thesis is to increase the understanding of how marine subsidies affect shore ecosystems, with focus on the role of spiders in shore food webs. The thesis includes five papers. In Paper I, a bottom-up food web is constructed based on carbon sources of coastal arthropods, in Paper II relationships between arthropod densities and edge and dispersal effects are examined, in Paper III top-down effects in the coastal food web is examined, Paper IV investigates variation in spider carbon and nitrogen stabile isotope ratios in relation to eutrophications on shores, and Paper V quantifies the inland reach of marine subsidies in Swedish shore meadows and Australian sandy beaches and examine processes behind the inland transport of marine subsidies. The studied marine inflows consist of marine algae and emerging phantom midges (Chironomidae) with marine larval stages. The results show that spiders utilize marine subsidies to a larger extent than other arthropod predators on shores. A large-scale removal experiment showed that spiders had a negative effect on densities of insect predators, but no top-down effects could be measured on lower levels of the food web. Responses of density to island size differed between different arthropod groups on small islands, implicating that the relative importance of dispersal and edge effects differ between taxa. Total niche width in wolf spiders decrease along an eutrophication gradient, and there is an individual variation in carbon stable isotope ratios of spiders on shores. Spiders and dipterans are important vectors for the inland transport of subsidies in both Swedish and Australian shore ecosystems, and the inland reach of subsidies is also affected by landscape characteristics of the shores.

Keywords: Marine subsidies, food webs, stable isotopes, shore ecosystems, predators, spiders, Pardosa, algae, emerging insects

List of papers

This thesis is comprised of a summary and five papers, which are referred to by their Roman numerals:

I Mellbrand, K. and Hambäck, P. A. Utilization of marine nutrients by coastal arthropod predators in the Baltic Sea area: a stable isotope study. Manuscript

II Östman, Ö., Mellbrand, K. and Hambäck, P .A. 2009. Edge or dispersal effects – Their relative importance on arthropod densities on small islands. Basic and Applied Ecology – In press

III Mellbrand, K., Östman, Ö. and Hambäck, P. A. Effects of subsidized predators on coastal food webs in the Baltic Sea area. Manuscript

IV Mellbrand, K., Enskog, M., Kautsky, L. and Hambäck, P. A. Individual variation between spiders on shores in the utilization of aquatic subsidies. Submitted

V Mellbrand, K., Lavery, P., Hyndes, G. A. & Hambäck, P. A. Linking land and sea – Arthropod vectors for marine subsidies. Manuscript

Paper II is reprinted in this thesis by permission of Basic and Applied Ecology.

Contents

Introduction ...... 9

Aims...... 11

Methods ...... 12

Papers ...... 20

Discussion ...... 31

Concluding remarks ...... 36

Acknowledgements ...... 37

References ...... 38

Svensk sammanfattning ...... 42

Tack...... 43

Introduction

As early as in the 1920´s, scientists (e.g. Elton 1927) had thoughts about the importance of cross-boundary flows of nutrients, matter and organisms for ecosystem function (Polis et al. 1997). However, spatial processes were rarely incorporated in food web theory before the 1990´s (Power & Huxel 2004) and these processes are still often neglected although we now know that the ecosystem is an arbitrarily defined unit and that movements of matter and organisms across ecosystem boundaries are common (Polis & Hurd 1996; Polis et al. 1996). Such cross-boundary flows often compromise an important nutrient and energy source for receptor ecosystems, and are suggested by Polis & Hurd (1996) to possibly be the dominant factor in shaping the dynamics of both consumers and resources in many ecosystems. One such ecosystem boundary where between-system processes may be of great importance is the marine shore-line (Polis & Hurd 1996; Polis et al. 1996; Hodkinson et al. 2001), a zone in which many organisms are almost exclu- sively found. Aggregation of predators on shores is a common and widespread phe- nomenon, and one often suggested explanation is that terrestrial predators are positively affected by aquatic subsidies (Polis et al. 1997; Nakano & Murakami 2001; Murakami & Nakano 2002; Henschel 2004; Power et al. 2004). The many predators found to aggregate along coasts include both species that naturally live close to water and species that are also found further inland. Many, if not most, of the shore-line predators belong to the latter group, for example many wolf spiders (Lycosidae) as well as other inverte- brates and many species of bats and lizards (Polis et al. 1997; Power et al. 2004). On bird-subsidized islands in the Gulf of California, terrestrial predators such as spiders, scorpions, lizards and ants were found to be 10-100 times more abundant than on the mainland (Polis 1994) and spider densities on islands were 6 times greater in the supralittoral area than in inland areas (Polis & Hurd 1996). In many systems, predators have also been found to move between beaches and inland habitats, thereby acting as vectors for marine inflows. Subsidies from marine to terrestrial systems may consist of marine or- ganic matter drifting ashore (Polis & Hurd 1996; Polis et al. 1997; Bastow et al. 2002), of sea birds feeding on marine food items but defecating and breeding on land (Polis et al. 1997, Sanchez-Piñero & Polis 2000; Anderson and Polis 2004), and of animals moving between aquatic and terrestrial habi-

9 tats as part of their life history (Hodkinson et al. 2001; Murakami & Nakano 2002; Power et al. 2004). Most studies in this thesis were made in the Baltic Sea area, and while inflows here are not truly marine since the Baltic Sea is a brackish sea, they will still be referred to as marine subsidies in this thesis. The Baltic Sea is one of the largest brackish water bodies on the planet and includes elements of both a marine and a freshwater ecosystem. Species diversity in the Baltic Sea is low compared to both freshwater and strictly marine habitats, since few species are adapted to brackish habitats, and species composition is mostly a mix of marine and freshwater species. Species composition also changes along the salinity gradient from south to north in the Baltic Sea, with a decrease in marine species along the gradient (Nielsen et al.1995). Inflows of aquatic algae and plants are common subsidies in marine shore ecosystems, and may in arid areas with little primary production be the only available nutrient source on shores (Polis and Hurd 1996; Polis et al. 2004; Catenazzi & Donnelly 2007). While inflows of aquatic algae and plants exist in freshwater ecosystems, their role as a subsidy to terrestrial ecosystems is not well studied. Emerging insects is on the other hand a very common and often important subsidy to shores of freshwater ecosystems, but insects are less common in true marine ecosystems and the few “marine” insects are typically found in habitats in ecotones between marine and terrestrial habitats, such as estuaries, salt marches and intertidal zones (Cheng 1976). The role of emerging insects as a subsidy to shore ecosystems have been well studied in particular in stream ecosystems (Hodkinson et al. 2001; Murakami & Nakano 2002; Power et al. 2004), but have been given much less attention in for example lakes. The Baltic Sea shores thereby provide an opportunity to study relative roles of different inflow types in the same receptor system.

10 Aims of the thesis

The overall aims of this thesis were to understand the effects of marine subsidies on the role of spiders in shore food webs, and to examine the relative importance of two subsidy types: algal inflows and emerging insects. To achieve this, more specific questions were asked. In Paper I, the aims were to quantify the extent to which arthropods on Baltic Sea shores utilize marine subsidies, and to construct a bottom-up food web for Baltic shores including marine inflows. This knowledge would make it possible to further examine ecosystem processes in relation to marine subsidies using Baltic Sea shores as a study system. The aim of paper II was to investigate the relative importance of dispersal and edge effects on subsidized small islands, while in Paper III the roles of subsidized arthropod predators and the occurrence of top-down effects in the shore food web is examined. In Paper IV, the aim was to investigate variation in spider stable isotope ratios along an eutrophication gradient. This paper thereby addresses both underlying causes of variation in spider stable isotope ratios, and meth- odological concerns when handling large variations in stable isotope ratios. The aim of Paper V was to quantify the inland reach of marine subsidies in relation to factors such as inflow type, landscape characteristics and arthropod vectors. Paper V is a comparative study of two types of shore ecosystems, Baltic shore meadows and Australian sandy beaches, and important questions here were the relative importance of different subsidy types and the relative importance of different vectors. In addition to these aims, studies of marine subsidies can also provide a better understanding of underlying ecosystem processes and food web interactions in ecosystems.

11 Methods

The study system

Study area The focal ecosystems in this thesis are coastal ecosystems in the northern Uppland archipelago in the Baltic Sea, Sweden (Fig. 1; Fig. 2). The Austra- lian parts of Paper V were carried out on three sandy beaches on the Indian Ocean coast in South-western Australia (Lat: N 37 º 25.82', Long: W 122º 05.36'): Hillary´s Beach and Two Rocks north of Perth, and Sulphur Beach on Garden island in the Shoalwater marine reserve south of Perth (Fig. 2). Arthropods, terrestrial plants, filamentous green and perennial brown algae were collected for stable isotope analysis (Paper I & V) on the coast of the Swedish mainland and on the coast of the island of Gräsö (16º45’E, 67º10’N, size about 150 km2) in the northern Uppland archipelago. The studies in Paper II and Paper III were made on small islands in two areas on the northern and north-eastern coasts of Gräsö. The study of individual variation in spiders (Paper IV) was made in Norrtäljeviken in northern Uppland.

Figure 1. The Uppland coast, Sweden .

12 Most of the Swedish study shore-lines, on both mainland shores and islands, are shore meadows separated by rocky areas (Fig. 2). The shore meadows are mostly kept open by flooding during parts of the year and none of the study sites in this thesis are grazed by domestic animals. Water level fluctuations are mainly due to meteorological and hydrological factors in the atidal Baltic Sea and change both between and over the year (Johannesson 1989; Winsor et al. 2001). Typically, mean water levels in the Baltic Sea are high- est in January, lowest in late winter-early spring, and rise again in late- summer-autumn (Jerling 1999). Many of the studied shore meadows are flooded from autumn to early spring and occasionally during late spring and summer, depending on wind conditions. The vegetation on shore meadows in the Baltic Sea show a gradient inland, due to factors such as salinity and water content in the soil, water fluctuations and duration of flooding (Johan- nesson 1989; Jerling 1999). Closest to the sea, reeds and sedges often form more or less large stands. Further inland, plants less tolerant of salinity and water content may establish, and eventually trees replace the meadow vegetation. The study shores in this thesis often have reeds (Phragmites australis) and sedge (Bolboschoenus maritimus) closest to water. In rockier areas without reeds, salinity tolerant herbs such as Triglochin maritima, Plantago maritima, Aster tripolium and Glaux maritima are often found close to the waterline. Further inland on shore meadows, usually a turf of grasses, often dominated by Agrostis stolonifera, interspersed with plants such as Eleocha- ris uniglumis, Carex nigra, Carex distica, Plantago maritima, Glaux maritima, Spergularia media, Blysmus rufus, Juncus gerardii, Ophioglossum vulgatum, Rhinantus serotinus, Pedicularis palustris, Orchis maculata, Fili- pendula ulmaria and Mentha aquatica. On the rocky beaches vegetation is scarcer and typically consist of species such as Lythrum salicaria, Sedum acre, Sedum telephium, Ophioglossum vulgatum, Matricaria maritima, Viola tricolor, Vicia cracca and Allium schoenoprasum. The Australian study systems in Paper V (Fig. 2) are sandy beaches and dunes where marine subsidies to shores consist of seagrass (mainly Posido- nia species) and algal detritus (mainly Sargassum spp.) washed ashore during winter. On beaches little or no vegetation is found, though sometimes scattered succulents (mainly Tetragonia decumbens) grow in the upper part of the beach. Further inland dunes are colonized first by grasses (mainly Spinifex longifolius) closest to the beach and then by shrubs further inland. Common plants are various Acacia species, Scaevola crassifolia, Leuco- phyta brownii, Tetragonia decumbens, Lepidospermum gladiatum, Spinifex longifolius and veldt grass (Ehrarta spp.).

Figure 2. Shore meadow on Gräsö, northern Uppland, Sweden (left) and sandy beach north of Perth, Western Australia (right).

Figure 3. Marine inflow types (left to right): Chironomid midges (Sweden), filamentous green algae (Sweden) and brown algae and seagrass (Australia).

Figure 4. Wolf spiders Pardosa amentata (Sweden) and Tetralycosa oraria (West- ern Australia), and web weaving spider Larinioides cornutus (Sweden).

14 Study organisms The two types of marine subsidies included in this thesis are marine algae and phantom midges (Chironomidae) (Fig. 3). Most of the studied shores and islands in paper I and III are located in shallow bays, and the inflow of algae to many of these shores is low. The algal inflow mainly consists of filamentous green algae (Cladophora spp., Mougeotia spp., Spirogyra spp. and Ulva spp.) which are very fast degradable, providing an ephemeral and less stable habitat for detritivores than driftwalls consisting of perennial slowly degrading species (Paper I, III, IV and V). In the Baltic Sea study sites in Paper III, an inflow of brown (Fucus) algae only occurred to four of the 19 islands in the study. In the Australian part of Paper V, wrack is the only type of marine inflow to shores and consists of brown algae, mainly Sargassum spp., and seagrasses, e.g. Posidonia spp., all relatively slowly degradable. Several insect families with aquatic larval stages are common on the Swedish study shores, such as dragonflies (Odonata), damselflies (Zygop- tera), mayflies (Ephemeroptera), caddisflies (Trichoptera) and various dipterans, but the most abundant are chironomid midges. The midges emerge in swarms throughout summer and rest in vegetation when not flying. A dominant group of chironomids in the area are Orthocladinae species that are generally herbivorous (Wiederholm 1989), but various Chironominae species, of which several species are detritivores, are also abundant. In the terrestrial ecosystem my main study organisms are spiders, in particular wolf spiders (Lycosidae) in the genus Pardosa (Fig. 4), which are the by far most common and abundant spiders (and predators) on shores in the Baltic Sea area. Of the arthropod fauna on shores, about 80% of all ground- living arthropod predators are spiders, about 50% of the spiders are wolf spiders, and about 80% of the wolf spiders are Pardosa wolf spiders (Fig. 4) of which the most common species is Pardosa amentata (50% of all wolf spiders). Other common spiders on shores are web weaving spiders in families Araneidae (Fig. 4), Linyphiidae and Tetragnathidae, though most Swed- ish spider families are represented. Other arthropod predators common on Baltic Sea shores are shore bugs (Saldidae), nabid bugs (Nabidae), carabids (mainly Dyschirius) and staphylinid beetles (Staphylinidae). Common herbivores on the shores are planthoppers (Homoptera; Cercopidae, Cicadellidae), grasshoppers (Orthoptera), mirids (Heteroptera), butterfly larvae and beetles such as weevils (Curculionidae) and chrysomelids. The most common detritivores are springtails (Collembola; mostly Podura aquatica). Dipterans are also a common and abundant group on the shores. In the Australian study sites, common wrack fauna are mainly dipterans and weevils but also predators such as wolf spiders (in wrack only Tetraly- cosa oraria (Fig. 4)), small web weaving spiders and staphylinid beetles. Spiders, in particular wolf spiders but also web weaving spiders and jumping spiders are common predators both on the beach and in the dunes. Insect

15 predators in dunes include staphylinid beetles, carabids, predatory heterop- terans, mantids and scorpions (Two Rocks only). Lizards and snakes, though not included in this study, are also very common predators on shores. Com- mon herbivores are mainly plant hoppers (Homoptera) and weevils (Curculi- onidae).

16 Methods

Data collection For the papers in this thesis I used a variety of sampling methods for density estimates of arthropods and for collection of samples for stable isotope analysis: glue traps, pitfall traps, and d-vac sampling using a vacuum sampling device, a Stihl® BG85 Leaf Blower/VAC. Plants, marine algae and often wolf spider stable isotope samples were sampled by hand. Not included in any of the papers are several smaller studies aimed at examining intraguild predation, fitness, and movement and stable isotope turnover rates in wolf spiders. For all these studies, spiders were collected on shore meadows on the Gräsö. To examine intraguild predation among wolf spiders on shores, Pardosa and Trochosa wolf spiders were collected and separated into two size classes each; with small Trochosa being roughly the same size as large Pardosa. Four spiders of two size classes were placed together in 2 l containers. Five replicates were used for each of the six combinations of size classes, and containers were continuously supplied with plentiful alternative prey throughout the experiment (mainly various dipterans and plant hoppers). Surviving spiders were counted after three weeks, and individuals not found (any spiders found dead but intact were assumed dead from other causes than predation) were considered eaten by its cohabitants. To examine fitness related to distance from the waterline in wolf spiders, female Pardosa wolf spiders carrying egg sacs were collected along inland transects at 0 m, 20 m and 160 m from the waterline in five shores on the island of Gräsö. The number of eggs (or spiderlings) in egg sacs were counted, and egg number divided by cephalothorax width was used as a measure of fecundity. To examine stable isotope turnover rates and to get realistic fractionation rates, Pardosa wolf spiders (N=62) were fed on a diet of bred dipterans (Drosophila melanogaster) of known stable isotope composition for 13 weeks. Once a week four spiders were sampled for stable isotope analysis. To examine the scale of wolf spider movement on shores, a mark- recapture study was performed in a 60*20 m area (60 m along the waterline, 20 m inland) on two shores, one long shore (open shore meadow with short vegetation) and one short shore (forest about five meters from the waterline). On each shore, Pardosa wolf spiders were captured, marked and released in three 5 m2 squares 30 m apart along the waterline during two subsequent days. Spiders were captured using pitfall traps and hand capture. Marking was made using water based acrylic dye, with one colour being used for each release point and each day. The third day spiders were captured using pitfall traps set 2 m apart in the 60*20 m grid.

Stable isotope analysis Stable isotope analysis has become a widely used tool for the study of energy and nutrient flows in food webs and for the study of long-term differences in feeding behaviour between consumers. While stable isotope analysis, as all methods, has its drawbacks, one of its many advantages is the abil- ity to distinguish between local production and inflows from other systems, as long as there is a detectable difference in isotopic ratios between sources. Stable isotope analysis has been used for this purpose in a large number of studies concerned with aquatic subsidies (for example Collier et al. 2002; Barrett et al. 2005; Briers et al. 2005; Ballinger & Lake 2006; Catennazzi & Donnelly 2007; Paetzold et al. 2008), and is used in four out of the five papers in this thesis in order to understand variation among organisms in their usage of marine subsidies. Separating marine and terrestrial carbon sources is possible since basal resources in marine and terrestrial environments typically differ in carbon stable isotope composition. Due to differences in pho- - tosynthetic apparatus and carbon sources (CO2 vs CO3 ), terrestrial plants are typically much more 13C-depleted than marine plants and algae (Fry 2006), though different algal species and marine plants also differ in carbon isotope composition (Fredrikssen 2003, Edward et al. 2008; Paper I, V). Stable isotope composition of plant and animal tissues is a combination of stable isotope ratios within sources and of fractionation processes. Fractiona- tion occurs during chemical reactions since different stable isotopes of the same element behave somewhat differently in chemical reactions (though the magnitude of the fractionation differs a lot between elements): The lighter isotope of an element typically reacts faster than the heavy isotope, which requires more energy for the formation or breaking of chemical bonds (Fry 2006). This causes heavy isotopes to have slower incorporation rates in tissues than lighter isotopes of the same element. As a result stable isotope ratios of carbon and nitrogen (δ13C=13C/12C and δ15N=15N/14N) differ between carbon dioxide and nitrogen in the air on one hand and the carbon and nitrogen composition in plant tissues on the other hand. Also, plants using different modes of photosynthesis, as well as different carbon sources, may differ in stable isotope ratios (Fry 2006). Fractionation will occur for every chemical reaction as elements travel up the food chain, resulting in the heav- ier isotope being retained longer in an open system, and enriched at higher levels of the food chain. For carbon, only minor fractionation of carbon isotopes typically occur for each trophic step (typically <0.1 %), but this is much smaller than the known difference in carbon isotope ratios between the primary carbon sources in this thesis (typically >0.8%, Fry 2006; McCutchan et al. 2003). While fractionation rates may vary not only between groups, species or populations, but also between tissues and individu-

18 als, the large differences between aquatic and terrestrial carbon sources in this thesis enable tracing of primary carbon sources up the food chain even without detailed knowledge of carbon fractionation rates of consumers. Still, several studies have shown that intrapopulation variation in δ13C (δ13C =13C/12C) may lead to under- or overestimations of dietary variation (Bolnick et al. 2003; Matthews & Mazumder 2004; Araújo et al. 2007) which is a reason for caution in the use of stable isotope analysis. One aspect of this topic is addressed in Paper IV. Nitrogen stable isotope ratios similarly show different signals in marine and terrestrial environments, but with a much larger spatial variability and a larger and more variable nitrogen isotopic fractionation in relation to differences both among sites and among organisms (Vanderklift & Ponsard 2003; Jennings & Warr 2003, Caut et al. 2009). Nitrogen stable isotope ratios are therefore less useful than carbon stable isotope ratios for delineating trophic links. Variability in 15N between primary producers and consumers may nevertheless provide information on the relative length of trophic chains (Post 2002), but due to the problem with larger and more variable fractionation rates, particularly for generalist predators, few conclusions in this thesis are based on nitrogen stable analysis. In generalist predators with a high prevalence of behaviours such as intraguild predation and cannibalism and a large number of prey species in their diet (such as many spiders) (Foelix 1996; Wise 2006), fractionation rates are often difficult or impossible to determine since the feeding on multiple trophic levels cause large variations in stable isotope composition.

19 Papers

Paper I

Utilization of marine nutrients by coastal arthropod predators in the Baltic Sea area: a stable isotope study.

The aim of paper I was to examine which arthropods on shores, in particular which predators, utilize carbon of marine origin and to what extent, and to use stable isotope analysis to construct a bottom-up food web (Fig. 5) based on the three main types of available and distinguishable carbon sources on these shores: marine algal detritus, marine prey (chironomid midges) and terrestrial material (plants, prey, detritus).

Spiders

Insect predators

Small spiders (<3mm)

Chironomidae Herbivores

Terrestrial detritivores Collembola Marine algae Terrestrial plants

Algal detritus Terrestrial detritus

Nutrients

Figure 5. Suggested coastal food web of Baltic Sea shores.

20 Diets of arthropods on shores were examined using stable isotope analysis. The results show that spiders are the terrestrial predators in my study system mainly utilizing nutrients, while most insect predators (Fig. 6) and all herbivores mainly utilize carbon of terrestrial origin. This indicates that marine subsidies in the area may be more important when arriving as an inflow of prey rather than as an inflow of detritus. However, since terrestrial plants cannot utilize aquatic carbon sources but can still benefit much from algal detritus as a nutrient source, our methods were insufficient to determine the extent to which plants, and thereby also herbivores feeding on shore vegetation, utilize marine subsidies.

Predator groups

Theridiidae 3

Tetragnathidae 13

Salticidae 12 Pisauridae 4 Philodromidae 5 Lycosidae 57 Linyphiidae Gnaphosidae 9 Dictynidae 1 Clubionidae 7 Araneidae 6 Staphylinidae 7

Silphidae 1 Saldidae 4 Nabidae 18

Chrysopidae 7 Carabidae 5 Opiliones 13 Acarina 6

00.20.40.60.81 0 0.2 0.4 0.6 0.8 1 Marine carbon proportion

Figure 6 Carbon mixing model with fractionation of either -0.5 (A) or 0.5 (B) at a family level. Grey bars show proportions of marine carbon in terrestrial arthropod diets (± confidence intervals).

It is clear from this study that the predators that benefit most from an inflow of marine prey are spiders, indicating that eventual effects of marine subsidies for the coastal ecosystem are likely to be mediated by spiders.

21 Paper II

Edge or dispersal effects – Their relative importance on arthropod densities on small islands.

In Paper II the relative importance of edge effects and dispersal effects was examined on small islands of different sizes and isolation. Carbon stable isotope analysis of wolf spiders was also made to examine utilization rates of carbon of marine origin both within and between islands. Different responses of density to island size were observed for different taxa. There was a negative relationship between density and island size for leaf hoppers, and a positive relationship for ants, while dipteran and web spider densities did not show any response to either island size or isolation. An interactive effect of island size and isolation was found for wolf spiders and parasitoids, whith a positive relationship between densities and island size on distant islands and a negative relationship on close islands. The results suggested that the relative importance of dispersal and edge effects differ between taxa, with dispersal behaviour being more important than edge effects in wolf spiders, parasitoid wasps and possibly leaf hoppers (Homoptera). Edge effects are more important in ants and collembolans, and results were inconclusive for web spiders and dipterans. The stable isotope analysis showed higher δ13C-values on islands closer to the mainland, but all spiders had a carbon stable isotope signal close to that of the two common subsidy types in the area, marine algae and emerging chironomid midges. The implications of this study are that both edge effects and dispersal should be considered when examining effects of patch size and isolation for density- area relationships.

22 Paper III

Effects of subsidized predators on coastal food webs in the Baltic Sea area.

To examine top-down effects of spiders in coastal food webs in relation to marine subsidies, we performed a large scale removal experiment where spiders were removed from small islands and effects on densities of other arthropods and plants were measured. The results show that spider removal caused insect predator densities to increase (Fig 7), suggesting that insect predators are negatively affected by the high density of spiders on shores. Further studies are needed to understand the underlying mechanisms for this, but direct mortality from spider predation may have been a decisive factor. No treatment effects were found on either herbivore or detritivore densities (Fig 7) or on plant biomass, and we suggest that eventual negative effects of the high spider densities on control islands may be at least partly compensated by an increased effect of insect predators utilizing mainly terrestrial prey on treatment (removal) islands. This observation does not exclude the possibility of top-down effects on lower levels of the food web from spiders, but if they do exist, they are likely behaviour mediated rather than a result of predation. Behaviours such as cannibalism and intraguild predation are common in spiders and may dampen cascading effects, making top-down effects by spiders difficult to observe (Polis et al. 2000; Finke & Denno 2005). Behavioural effects may include decreased activity and switches in habitat and diet selection (Denno et al. 2003; Cronin et al. 2004; Moran et al. 1996; Schmitz 2004; Beckerman et al. 1997), and to find such effects necessitates a different experimental design. Without additional behavioural studies, the only conclusion that can be drawn is that spiders tend to affect other arthropod predators negatively, while top-down effects of spiders on lower trophic levels of the food web are either nonexistent or may be compensated by effects of insect predators on treatment islands, resulting in little or no measurable effect of spider removal on plants, herbivores or detritivores. Another possibility is that top-down effects are only apparent with a more complete spider removal treatment: as 50% of spiders remained on treatment islands.

100 a. web-spiders 10 b. carabid beetles

1 1

10 c. staphylinid beetles 10 d. predatory heteroptera

1 1

0.1 0.1

Density 10 e. parasitoid hymenoptera 10 f. herbivorous heteroptera

1 1

0.1 0.1 100 g. homoptera 1000 h. collembola

100

1 1 2004 2005 2006 2007 2004 2005 2006 2007 Year

Figure 7. Density responses by broad arthropod groups to removal of lycosid spiders (solid line = control islands, hatched line = spider removal islands).

24 Paper IV

Individual variation between spiders on shores in the utilization of aquatic subsidies

The aim of Paper IV was to examine variability in the utilization of marine subsidies in shore-dwelling spiders along an eutrophication gradient, using stable isotope analysis. The study was carried out inside and on islands outside Norrtäljeviken, a highly nutrient enriched eutrophicated bay in the Bal- tic Sea. The results showed that spiders inside the bay all utilized mainly terrestrial prey, while spiders outside the bay, in particular wolf spiders, were separated into individuals utilizing either terrestrial or aquatic prey (Fig. 8). The total population niche width was therefore larger outside than inside the bay. This individual specialization may be related to the differences in nutrient enrichment in the aquatic ecosystem and/or salinity between sites in- and outside the bay, but we could not fully explain the processes behind the narrowing niche width. We suggest that eutrophication in combination with a more variable habitat structure in the less nutrient enriched sites may affect trade offs in spiders, causing a decrease total niche width by affecting prey availability and prey choice of individual predators. Another important implication from this study is that large intrapopulation variation in isotopic values may lead to over- or underestimations of dietary variation between populations or species. Such large intraguild variation is common in spiders, which often are generalist predators, and our study underlines that while stable isotope analysis remains a useful tool for examining flows across ecosystem boundaries, caution is needed in the in- terpretation of data with large intrapopulation variation.

Aquatic algae and terrestrial plants 0.6 Brown algae 0.4 Green algae Terrestrial plants 0.2 Phragmites australis 0

Dipterans Frequency 0.6

0.4 Chironomid midges Brachycerid flies 0.2

Wolf spiders 0.6

0.4 Outside Inside 0.2

Web weaving spiders 0.6

0.4 Outside Inside 0.2

0 -30 -26 -22 -18 -14 -10 -6

13 δ C

Figure 8. δ13C of primary producers and dipterans across all sites,and δ13C of wolf spiders and web weaving spiders separated between sites inside and outside the bay.

26 Paper V

Linking land and sea –terrestrial arthropod vectors for marine subsidies

In Paper V we examined the inland reach of marine subsidies and the role of arthropod vectors in this inland transport. The study was carried out on Swedish and Australian shores (Fig.2), making it possible for us to use the large differences in shore type, vegetation, productivity and topography between the two study systems to study processes behind inland transport of subsidies. The results showed that spiders and dipterans are important vectors for the inland transport of marine subsidies. The large differences between our Swedish and Australian study systems (very different types of ecosystems both in the sea, on shores and further inland) allow us to draw general conclusions about the underlying processes of inland transport of marine subsidies. Emerging dipterans from the sea in Sweden and from wrack on beaches in Australia seem to fill a very similar role, with flying dipterans in both cases reaching further inland than wrack and subsidize spiders further inland as well as on the shores. While the effect decreases along inland transects, we still find a marine carbon stable isotope signal as far as 160 m inland in Sweden and 80-100 m in Australia (Fig. 9). This may not solely be related to the movement of dipteran vectors, but also to the movement of the spiders hunting them. In particular wolf spiders are cursorial and fast moving predators, and are both among the most common and abundant predators on shores and among the ones utilizing marine subsidies to the largest extent. While other spider groups on the shores may utilize marine subsidies to a similar extent, these spiders are often less mobile and less abundant than the wolf spiders, making the latter group better suited to function as a vector for the inland transport of subsidies. The study also indicate that landscape characteristics such as vegetation and topography can play an important role for the inland transport, and that these characteristics will affect different vectors differently. Both topography and higher vegetation will decrease the reach of wrack, but the vegetation may also contain the wrack longer on shores. The inland reach of dipterans will be less affected than wrack, but will still reach further inland in a flatter, more open landscape. The same is likely true for cursorial spiders that live in open habitats, such as many wolf spiders.

27 Sweden Australia Flies dipterans Wolf spiders Pardosa Web spiders Web spiders Jumping spiders 0 m Distance 0 10 (waterline) 20 (tideline) 8 15 6 10 4 2 5 0 0 -30 -25 -20 -15 -30 -25 -20 -15 -10 Distance 2 (upper beach, approx. 10 20 m 20 20 m from tideline) 8 15 6 10 4 2 5 0 0

N -30 -25 -20 -15 -30 -25 -20 -15 -10 15 δ 10 20 Distance 5 (dunes, approx. 80 m 80 m from tideline) 8 15 6 10 4 5 2 0 0 -30 -25 -20 -15 -30-25-20-15-10

Distance 6 (dunes, approx. 10 20 160 m 180-200 m from tideline) 8 15 6 10 4

2 5 0 0 -30 -25 -20 -15 -30 -25 -20 -15 -10 δ13C

Figure 9. δ13C and δ15N of dipterans and spiders along inland transects in Sweden and Australia.

28 Studies not included in papers: Results

The intraguild predation experiment The intraguild predation experiment showed that larger wolf spiders prey on smaller wolf spiders to a high degree even when alternative prey is available. In 20 of the 30 containers, one or several of the four spiders were eaten by another spider. Intraguild predation was more common where the size difference between spiders were large; however, Pardosa was seemingly more aggressive and large individuals also killed small Trochosa spiders, despite the similarity in size.

Wolf spider fitness along inland transects There was a significant difference in Pardosa wolf spider egg production along inland transects, with lower production in spiders caught very close to the waterline (F=5.7; p<0.05) (Fig. 10).

12 10

8 Figure 10. Fecundity of female Pardosa 6

Fecundity wolf spiders along 4 inland transects. 2

0 020160 Distance (m)

Stabile isotope turnover time The experiment where spiders were fed a Drosophila diet showed that δ13C ratios of wolf spiders became more similar to prey ratios over time (Fig. 11), and at the end of the study (after 12 weeks) Dδ13C = 1.2 and Dδ15N = 1.6 between Drosophila flies and spiders. This remaining difference in δ13C ratios between spiders and prey after 12 weeks may be explained by the turnover time of spiders being longer than 12 weeks, but may also be related to a high carbon fractionation.

29 10.00

8.00 Drosophila 6.00 Pardosa week 1

N Pardosa week 13

15 4.00 δ

2.00

0.00 -25.00 -20.00 -15.00 δ13C

Figure 11. δ13C and δ15N of Drosophila flies and of Pardosa wolf spiders sampled week 1 (not fed on Drosophila flies) and week 13 (fed Drosophila flies for 12 weeks).

Mark-recapture of wolf spiders In the mark-recapture study, 410 Pardosa wolf spiders were marked and released on the long shore and 171 on the short shore; of these 39 were recaptured on the long and 21 on the short shore. 69% of the recaptured spiders on the long shore and 95% of the spiders on the short shore were captured within 5 m from the waterline, most in the vicinity of the original release, but a few individuals were recaptured on the opposite side of the 60*20 m grid, 60 m away. The results indicate that wolf spiders are able to move over large areas, but mainly move along the waterline rather than inland, even on the long shore. 12 10

8 long shore Figure 12. Average num- 6 bers of caught Pardosa wolf short shore 4 spiders per trap on one long Spiders/trap and one short Baltic Sea 2 shore. 0 0-5 5-10 10-20 Distance (m)

The total number of spiders caught in the 60*20 m grid was, including re- captures, 1562 on the long shore and 398 on the short shore. This study thereby also show that wolf spiders aggregate near the waterline on Baltic Sea shores and that densities decrease rapidly inland (Fig.12). Wolf spider densities were also much larger on the long shore (open shore meadow) than on the shore with forest close to the waterline.

30 Discussion

Stable isotope ecology of shore ecosystems The results from paper I provide a framework for closer examinations of feeding relationships in the coastal food web, some of which are addressed in Paper III, IV and V. We used information from carbon and nitrogen stable isotope analyses in Paper I to construct a bottom-up coastal food web (Fig. 6) based on terrestrial and marine carbon sources. Still, the picture remained obscure in some aspects, mainly because of difficulties in differentiating between the effects of the two inflow types: algae and the emerging chironomid midges. In paper I, we concluded that spiders are the main benefici- aries of the marine inflow, but we could not examine possible bottom up effects by algal inflow on herbivores and insect predators since we were unable to quantify this inflow. The algal inflow is likely important as a carbon and nutrient source for detritivores and as a nutrient source for terrestrial plants, but the importance of the algal subsidy to shore ecosystems in the Baltic Sea area is probably underestimated in this study due to the difficulties in differentiating between marine sources (Paper I). In this thesis, with the exception of Paper V, I therefore mainly discuss inflows consisting of emerging insects. On the predator level of the food web, a high inflow of alternative prey bypassing lower levels of the food chain and subsidizing predators directly could theoretically still be more important than the algal subsidy, and such direct subsidies to predators could also enhance top-down effects in the ecosystem (Polis et al. 1997; Henschel 2004). Another aspect not discussed in the papers in this thesis is temporal variation in inflow rates. One of the advantages of stable isotope analysis as a method is however that it provides long term dietary information rather than a "snapshot picture", and since the turnover rate for Pardosa wolf spiders is longer than 12 weeks, the marine carbon stable isotope signal found in wolf spiders on shores indicate that carbon of marine origin is a regular part of spider diets in this area. Results from the spider stable isotope analyses (Paper IV) show a large individual variation in spider diets (Fig. 9) beside the interspecific variation in stable isotope composition, and that this individual variation decreases along a gradient of decreasing salinity and increasing eutrophication. In- trapopulation variation is common in nature, and many generalist species

31 consists of individual specialists; such variation is however often (but not always) associated with differences in resource use between age classes, sexes and morphs (Bolnick et al. 2002; Bolnick et al. 2003; Svanbäck & Persson 2004). In our case, the increased individual variation in sites outside compared to inside the Norrtäljeviken bay is consistent with the mechanism for individual specialization suggested by Bolnick (2003), where the total niche width is expanded but individual niches are constrained by trade offs making it difficult for any single individual to utilize all available resources. We were unable in this study to separate between effects of salinity, eutrophication and habitat characteristics, but suggest that the effect of eutrophication on ecosystem dynamics may be influenced not only by species rich- ness per se, but by the narrowing of total niche width in consumers other- wise utilizing a wider range of resources. Individual variation in wolf spiders on shores may also explain some of the large variation in δ13C ratios of spiders on Baltic Sea shores found in Paper I and Paper V. Most studies of marine subsidies to shores have been made in areas with large differences in productivity between donor and receptor systems, where marine nutrient inflows greatly surpass local primary production (Polis and Hurd 1996; Polis et al. 2004; Orr et al. 2005; Catenazzi & Donnelly 2007; Ince et al. 2007; Marczak et al. 2007). This is true for the Australian shores (Paper V) as well, though the difference in this system is not as large (Ince et al. 2007) as in the studies by Polis & Hurd (1996), Polis et al. (2004) and Catenazzi & Donnelly (2007) of very arid, low productivity terrestrial systems and highly productive marine systems. In the Baltic study system (Pa- per V) there may be a difference in productivity, but it is likely much smaller, making effects of marine subsidies harder to find. This smaller productivity difference between systems is another factor setting the Baltic Sea area as a study system apart from previous studies of marine subsidies. In the only study previously made between systems of similar productivity, Paet- zold et al. (2008) found very little effect of subsidies on predator δ13C ratios above the intertidal zone on a temperate, productive, forested island subsidized by an inflow of algal detritus. Our results from Swedish study sites (Paper V) differ in this respect, with a larger inland reach of the subsidy, but also a larger variation in δ13C ratios. In the study by Paetzold et al. (2008), wrack was the only type of marine inflow, while in the Baltic Sea there is also a substantial inflow of emerging chironomid midges. The larger importance of marine subsidies in Baltic shore ecosystems may be due to a combination of a more efficient inland transport of subsidies (flying insects) and an inflow directly subsidizing predator levels of the food web rather than indirectly, through an increased primary production. Inflows of emerging insect have previously been studied mainly in stream ecosystems, and have been shown to be important for food webs in stream corridors (Murakami & Nakano 2002; Nakano & Murakami 2001; Power et al. 2004). Both Paetzold et al. (2008) and Marczak et al.

32 (2007) also stress that the productivity gradient alone is insufficient for ex- plaining variation in responses to spatial subsidies. This conclusion is supported by our results that densities are affected by other factors such as landscape characteristics (Paper V), edge effects and dispersal (Paper II). In Pa- per V we also discuss effects of landscape characteristics of the receptor ecosystem. We found that both higher shore vegetation (forest) and topography may decrease the inland reach of marine subsidies, factors that are not often discussed in literature (but see Marczak et al. 2007 and Stempniewicz et al. 2007). Stempniewicz et al (2007) found a much larger eutrophication effect of guano deposition of little auk (Alle alle) chickens compared to that of guillemots (Uria sp.), related to differences in shore topography of nesting sites.

Top-down effects in shore ecosystems The traditional approach for studying effects of arthropod predators on lower trophic levels is through small-scale enclosure studies (e.g., Schmitz 2003; Beckerman et al. 1997), or by selectively removing predators on focal plant individuals (e.g., Marquis & Whelan 1994). While such studies are well suited for examining underlying mechanisms, they may be less informative about large scale effects since small scale studies may impede natural movements and exclude population level feedbacks (Inouye et al. 2005). In our mark-recapture study of Pardosa wolf spiders on Baltic Sea shores, results indicate that Pardosa wolf spiders can move up to 60 m in a 48 h time period (Fig. 13). One of the aims in Paper III was to examine these processes on a larger scale, both temporally and spatially, than in traditional enclosure studies. Using islands as natural enclosures made differences due to treatment (spider removal) less apparent, perhaps due to the large variability both between islands and between years. No evidence of top-down effects on levels below predator levels of the ecosystem could be found (Paper III), in con- trast to previous small-scale studies (Polis et al. 1997; Schmitz et al. 2000; Halaj & Wise 2001; Denno et al. 2003; Anderson & Polis 2004; Schmitz 2004). Factors such as isolation, patch size and edge effects were also shown to affect arthropod densities on islands, and the importance of edge effects and dispersal differ between taxa (Paper II). While the investigated islands were all located close to the mainland (Paper III), the importance of edge effects may still vary between both islands and years and our observation of limited top-down effects may be partly related to the treatment not being effective enough considering the large natural variability in our study system. Still, we were able to show that insect predator densities are negatively affected by spiders on shores (Paper III), which may appear contradictory since nearly all common and abundant spiders on shores utilize mainly car-

33 bon of marine origin (Paper I), while most of the utilize mainly carbon of terrestrial origin (Paper I). The very high spider densities, however, may cause even a small inclusion of terrestrial prey in spider diets to affect densities of the less abundant insect predators. Competition from spiders for terrestrial prey may further reinforce the negative effect of spider intraguild predation on insect predator densities, even with terrestrial prey making up a very small part of the carbon signal of individual spiders. From this follows that the lack of top-down effects on herbivore and detritivore populations in this study may be explained by spider predation on control islands being compensated for by the increases in densities of more specialized insect predators on removal islands. If this is the case, removal of all arthropod predators would be necessary to discover top-down effects on herbivore and detritivore levels of the food web.

Density effects of marine subsidies Marine subsidies are often considered one of the main explanations for aggregation of predators on shores (Polis et al. 1997; Nakano & Murakami 2000; Murakami & Nakano 2002; Henschel 2004; Power et al. 2004). We found little evidence for aggregation of spiders on Baltic Sea shores (Paper V), but this result may be obscured by large variation, and densities may also be underestimated by the suction sampling method used for the density estimates. Suction sampling is considered a highly effective method for sampling terrestrial arthropods in short vegetation (Henderson 2003), but may be less effective for large, fast cursorial animals such as for example wolf spiders. In the Australian study sites, spider densities were higher on beaches than further inland, but here the density estimates were made using pitfall traps (Paper V). To examine the mobility of wolf spiders on Baltic Sea shores we did a mark-recapture study on two shores on the island of Gräsö (two of the five shores in paper V), one long and one short shore. The results suggest that wolf spider densities do decrease further inland also on Baltic Sea shores, even on a small spatial scale (20 m). The mark-recapture also indicated that densities are higher on long shores than short shores, though the difference in densities may be related to differences between sites. Wolf spider fitness is not included in Paper V, but fecundity of female Pardosa wolf spiders was measured along inland transects on the Swedish sites and the results indicate that fecundity is lower closer to the waterline. This may be related to higher densities, and thereby more competition and larger risk of intraguild predation and cannibalism. In this thesis I mainly discuss the role of spiders as predators in shore food webs, but in many shore ecosystem larger vertebrate predators such as birds, lizards and bats are important predators and often utilize marine subsidies to a high degree (Polis 1994; Power et al. 2004; Murakami & Nakano

34 2002; Barrett et al. 2005; Catenazzi & Donnelly 2007). The higher spider densities on shores both in the Baltic and Australia (Paper V) is likely related to higher prey availability closer to the waterline, but an additional factor affecting differences in spider density may be increased predation risk from larger insectivorous predators such as lizards further inland. In Australia (Paper V), lizards were often encountered in the dunes above beaches and often caught in our pitfall traps. We have not included any vertebrates in this study, but other studies found evidence of lizards utilizing inflows of marine prey both directly and by feeding on smaller terrestrial predators such as arachnids (Barrett et al. 2005; Catenazzi & Donnelly 2007). Lizards thereby also function as vectors in our Australian study systems. Other studies have found birds and bats to be important vectors for marine inflows (Murakami & Nakano 2001; Murakami & Nakano 2002; Power et al. 2004), and these groups are often seen hunting over water surfaces in Baltic shallow bays. The failure to include all levels of the food chain may lead to underestimations of the inland reach of marine subsidies, and in future studies it would be interesting to also include vertebrate predators.

35 Concluding remarks

This thesis has a dual theme: the importance of marine subsidies and the role of spiders in shore ecosystems. The results in Papers I, supported by results in paper II, IV and V, indicate that spiders on shores often utilize marine resources to a high degree, and different aspects of this relationship are examined in several of the papers. Paper I also showed that spiders utilize marine subsidies to a larger extent than other arthropod predators on shores. In Paper II, responses of density to island size differed between different arthropod groups on small islands, implicating that the relative importance of dispersal and edge effects differ between taxa. In Paper III, top-down effects were examined in a spider removal study using small islands as enclosures. The results showed that spiders have a negative effect on insect predators, but treatment had no measurable effects on lower levels of the food web. The results of Paper IV showed that there is an individual variation in spiders, in particular wolf spiders, on shores, and that total niche width of spiders decrease along an eutrophication gradient. In paper V the inland reach of marine subsidies was examined in a comparative study of Swedish shore meadows and Australian sandy beaches. The results indicate that spiders and dipterans are important vectors for the inland transport of marine subsidies in both these systems, and that the inland reach of subsidies is also affected by landscape characteristics of the shores.

36 Acknowledgements

Although this summary was written by me, it is based on the work of all authors and coauthors of the papers and manuscripts that it is based on (Paper I-V), and for that reason I would like to thank Peter Ham- bäck, Örjan Östman, Lena Kautsky, Paul Lavery, Glenn Hyndes and Maria Enskog. I also want to thank my supervisor Peter Hambäck and my assistant supervisor Lena Kautsky for valuable comments on this summary.

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41 Svensk sammanfattning

Denna avhandling syftar till att bättre förstå hur marina subsidier påverkar strandekosystem, med fokus på spindlars roll i strandfödoväven. Avhandlingen innehåller fem studier, som förutom en fältstudie på sandstränder i sydvästra Australien är utförda i Östersjöområdet, främst i Upplands skärgård. Den metod som främst använts för att studera betydelsen av marina näringsflöden är stabil isotopanalys av kol och kväve. I Paper I används isotopanalyser för att kvantifiera i vilken utsträckning leddjur på stränder utnyttjar marina näringsflöden och för att konstruera en födoväv för strandekosystem på Östersjöstränder. I Paper II undersöks hur kanteffekter och spridning påverkar tätheten av insekter och spindlar på små öar, i Paper III studeras top-down effekter i strandfödoväven. I Paper IV undersöks variationer i spindlars utnyttjande av marina susidier i relation till övergödning i Norrtäljeviken. I Paper V undersöks hur långt inåt land marina subsidier når, och hur olika typer av subsidiers räckvidd påverkas av egenskaper hos strandekosystemet. De marina subsidier som förekommer i avhandlingen är marina alger och växter som spolas upp på stränderna och insekter, främst fjädermygg (Chironomidae), med larvstadier i vattnet och vuxenstadier på land. Resultaten visar att spindlar utnyttjar marina näringsflöden till stor del, och att de gör det i högre grad än andra rovdjur (rovinsekter) på stränder. Ett storskaligt försök där spindlar togs bort från små öar visade att spindlar har en negativ effekt på tätheter av rovinsekter på stränder. Inga effekter av behandlingen kunde dock påvisas på lägre nivåer i födoväven (herbivorer, nedbrytare och växtbiomassa). Tätheterna av olika leddjur på stränder påverkas inte bara av subsidier, och en undersökning av tätheter på öar av olika storlek och på olika avstånd från fastlandet visade att kanteffekter och spridning har olika effekt på olika djurgrupper. Vargspindlars nischbredd minskar längs en gradient av ökande övergödning i den övergödda Norrtäljeviken, och denna undersökning visar också att det finns en stor individuell variation i spindlars utnyttjande av marina subsidier. Den jämförande studien mellan svenska och australiska strandekosystem visar att spindlar och tvåvingar är viktiga vektorer för transporten inåt land av marina subsidier i båda studiesystemen. Subsidiernas räckvidd påverkas också av landskapskaraktärer hos stränderna, som topografi och vegetationstyp.

42 Tack!

Det finns så många som på ett eller annat sätt, direkt eller indirekt, är delaktiga i den här avhandlingens tillblivelse, hoppas att jag inte glömmer någon! Först ett tack till min handledare Peter, för att du gav mig möjlighet att få jobba med spindelekologi och för att du är en kreativ forskningsmiljö i dig själv (jag hamnar ständigt ohjälpligt på efterkälken, såväl vetenskapligt som i fält)! Tack även till min biträdande handledare Lena, som alltid bidrar med ett välbehövligt marint perspektiv. Tack till alla andra forskare och doktorander på Botan som förgyllt doktorandtiden här, jag tänker inte nämna er allihop vid namn men ingen är glömd! Tack till Sonja för att du varit en så trevlig rumskamrat och för tips och råd under den första förvirrande tiden som doktorand. Tack till alla assistenter, kolleger och andra som varit med i fält de här åren, inte bara för arbetsinsatserna utan även för trevligt sällskap. Tack Örjan och Anna för alla trevliga fikastunder och middagar i Öregrund. Tack Torbjörn, för goda råd och trevliga samtal om spindlar i allmänhet och vargspindlar i synnerhet. Tack till Lars som på allvar väckte doktorandtankarna, även om det blev spindlar i stället för fiskar. Tack Marina, för alla trevliga luncher, quizpubs och diskussioner om doktorandlivet. Och naturligtvis insatsen som djur- och blomvakt medan jag var i Australien, något inte vem som helst tagit på sig! I synnerhet som jag vet att vissa av mina lägenhetsinvånare skrämde dig lite – du är nog den enda som kommit hem till mig, sett dig omkring bland fågelspindelterrarierna och sagt ”Åh nej, du har blommor!”. Thanks to all the nice people I met and worked with in Australia. Paul, Kathryn, Glenn, Peter, I had a wonderful time! Thank you Kathryn for all your hospitality, and thanks Paul for giving me the opportunity to do some field work “down under”. Tack mamma och pappa, ni har alltid stöttat och uppmuntrat mig att läsa och lära och undersöka, oavsett hur konstiga mina intressen än tett sig och hur illa ni än tyckt om alla spindlar och andra kryp jag dragit in. Och tack till mina systrar, som alltid ger mig nya och annorlunda perspektiv på vad jag sysslar med. Tack hela familjen för såväl uppmuntran som praktisk hjälp med fältjobb, bildbehandling med mera. Tack alla vänner nere i Skåne, ni vet vilka ni är och det är alltid lika trevligt att träffa er även om det inte blir ofta nog...

43 Sist men inte minst ett tack till alla trevliga människor i Sjövärnskårens Musikkår och Solna Brass. Ni har varit en viktig del av min doktorandtid – man blir så lätt så insnöad på sitt lilla lilla forskningsfält, och då behövs något som ger en lite perspektiv på tillvaron och påminner om att det faktiskt finns en värld utanför marina subsidier, strandfödovävar och spindlar, och att den världen är full av vacker blåsmusik!