Søren Toft

Søren Toft
Aarhus University | AU · Department of Bioscience

About

150
Publications
30,781
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5,617
Citations
Citations since 2017
35 Research Items
1978 Citations
20172018201920202021202220230100200300
20172018201920202021202220230100200300
20172018201920202021202220230100200300
20172018201920202021202220230100200300
Additional affiliations
January 1998 - December 2012
Aarhus University

Publications

Publications (150)
Article
Full-text available
Interspecific exploitation and/or interference competition may be operating when a successful invasion of an animal species leads to decrease or disappearance of native relatives, in particular if inter-assemblage predation and other interactions are unlikely. The harvestman Opilio canestrinii arrived in Denmark around 1980 and quickly became a dom...
Article
Locomotion in animals follows simple mathematical rules: when active, most time is spent at lower velocities and exponentially decreasing time is spent at increasing velocities; when inactive, there is an abundance of short quiescence periods decreasing by an inverse power function towards longer quiescence periods. We investigated whether these ma...
Preprint
Full-text available
The harvestman Opilio canestrinii arrived in Denmark around 1980 and quickly became a dominant species in urban habitats. This was followed by nearly complete disappearance of the formerly co-dominant Leiobunum gracile . A second invasive species, Dicranopalpus ramosus , arrived in 2007 and is still under population increase. Old forests have been...
Article
Sperm competition drives traits that enhance fertilization success. The amount of sperm transferred relative to competitors is key for attaining paternity. Female reproductive morphology and male mating order may also influence fertilization, however the outcome for sperm precedence under intense sperm competition remains poorly understood. In the...
Article
Description of animals’ trophic niches help us understand interactions between species in biological communities that are not easily observed. Analyses of macronutrient niches, i.e. the range of macronutrient (protein:lipid:carbohydrate) ratios selected by generalist feeders, may be a useful alternative approach to inter‐species comparisons of diet...
Article
Predators are often food limited in their habitat, and some are limited by specific macronutrients (protein, lipid or carbohydrate). It is unresolved, however, to what extent and in what way food and macronutrient limitation are connected. Using a carabid beetle (Nebria brevicollis), we compared macronutrient self-selection of the animals three tim...
Article
Here, we investigate the spontaneous locomotor patterns in three spiders with different hunting strategies. The locomotor activity of adult wolf spiders Pardosa amentata, with a sit-and-move hunting strategy, has previously been demonstrated to follow strictly mathematical rules, with most time spent at lower velocities and exponentially decreasing...
Article
Spiders of the genus Dysdera are peculiar for their preying on terrestrial isopods though the preference for this prey type varies between species. We tested prey acceptance of two isopod and two non-isopod prey in 8 species endemic to the Canary Islands, and analyzed growth and metabolic parameters (growth efficiency; dry mass, lipid and N extract...
Article
1. Carnivores are often food and/or macronutrient limited in their natural habitats, but whether they are limited mostly by protein or lipid is still a matter of controversy. As many predators and carnivorous scavengers also include plant material in their diet (omnivory), carbohydrate limitation is also possible. 2. The authors used a recently des...
Article
The quality of biological control agents used in augmentative releases may be affected by rearing conditions due to inbreeding or laboratory adaptation, or to phenotypic effects of the rearing environment. We hypothesized that individuals from a wild population would be in better body condition and kill more prey than individuals from a commerciall...
Article
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Eradication of invasive plants from natural habitats may have positive side effects other than removal of the invasive species. The study describes an unintended but positive consequence of a program for eradication of Rosa rugosa in Danish coastal dunes. The measures undertaken leaves areas formerly covered by rose bushes as bare sandy patches. Ve...
Article
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In 2013-2014 flies (Diptera Brachycera exclusive Calyptratae) active on the sand surface (epigaeic) were collected in pitfall traps in yellow and grey coastal sand dunes in National Park Thy, Denmark. A total of 15,670 flies of 227 species representing 31 families were captured. Sphaeroceridae, Dolichopodidae, and Chloropidae were particularly spec...
Article
Full-text available
1. The presence of predators is known to suppress prey populations not only by consumptive but also by non‐consumptive effects, as it stresses the prey inducing costly changes to behaviour and physiology. However, there is recent evidence that disturbance from non‐predacious, non‐competing commensals can also negatively affect herbivore performance...
Article
Full-text available
In 2013-2014 flies (Diptera Brachycera exclusive Calyptratae) active on the sand surface (epigaeic) were collected in pitfall traps in yellow and grey coastal sand dunes in National Park Thy, Denmark. A total of 15,670 flies of 227 species representing 31 families were captured. Sphaeroceridae, Dolichopodidae, and Chloropidae were particularly spec...
Article
Full-text available
In 2013-2014 flies (Diptera Brachycera exclusive Calyptratae) active on the sand surface (epigaeic) were collected in pitfall traps in yellow and grey coastal sand dunes in National Park Thy, Denmark. A total of 15,670 flies of 227 species representing 31 families were captured. Sphaeroceridae, Dolichopodidae, and Chloropidae were particularly spec...
Article
We studied the food quality of the aphid Rhopalosiphum padi to the pirate bug Orius majusculus using Ephestia eggs as high‐quality comparison prey. Several performance parameters were tested on individuals that had been reared and maintained on each of the two single‐prey diets or on a mixed diet. All fitness parameters were lower in individuals fe...
Article
1. Harvestmen are predators, although they suspected of being partly omnivorous by including fruits in their diet. 2. In the present study, the right‐angled mixture triangle (RMT) was used to analyse the macronutritional niche of the harvestman Opilio canestrinii, an invasive species in northern Europe. The study design followed a double‐test proce...
Article
Polyandry may occur in many species. In spiders when multiple males mate sequentially, conservative anatomical female traits largely, although not entirely, determine whether the first or last male gains precedence in siring the offspring. More flexible behavioural traits show remarkable variation among spiders, including the occurrence of extremel...
Article
Full-text available
Generalist predators potentially have access to a wide array of prey, but it is little studied how experience with specific prey affects preference for this prey. In particular, it is unknown how experience with pest prey affects predator foraging decisions in cases where the pest is nutritious but protected by a repelling, potentially deadly defen...
Article
The larvae of Hermetia illucens are known to successfully bio‐convert a vast range of organic substrates into high protein and fat biomass, but little is known about the larval instars. During this research, larval head capsules and biomass growth were measured daily and the specific metabolic rate of larger instars were considered. The head capsul...
Article
Full-text available
Habitats vary in food resources with carnivores often being prey limited, but it is unclear whether habitats facilitate a nutritionally balanced diet. Two paradigms in nutritional ecology, ecological stoichiometry and nutritional geometry, predict that carnivores are limited mainly by protein or lipid, respectively. Using the carabid beetle Anchome...
Article
Alternative mating tactics are expected to occur predominantly when mate competition is intense, resources are in short supply, or as a result of asymmetric power relationships between individuals. Males of the nuptial gift-giving spider Pisaura mirabilis use a prevailing tactic of offering a nutritive gift (insect prey) and a deceptive tactic of o...
Article
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1.Temperature influences biological processes of ectotherms including ecological interactions, but interaction strengths may depend on species‐specific traits. Furthermore, ectotherms acclimate to prevailing thermal conditions by adjusting physiological parameters, which often implies costs to other fitness‐related parameters. Both predators and pr...
Article
Full-text available
The two harvestmen Dicranopalpus ramosus and Odiellus spinosus were first recorded from Denmark in 2007 and 2006, respectively. Two nation-wide surveys of the species in urban habitats were conducted in 2010 and 2017 providing information on their initial colonization and subsequent establishment and spread. By 2017, D. ramosus occurred in all part...
Article
The prey choices of predators are determined, in part, by their hunting strategies. The sit-and-wait and the actively searching strategies seem designed for active and stationary prey, respectively. A supposedly intermediate strategy, the saltatory or sit-and-move strategy, combines sitting still, scanning for prey with frequent moves to new scanni...
Article
The opilionid fauna of Northern Europe, including Denmark, has become enriched by range expansion of several species originating from southern Europe, and this process is expected to continue into the future. I present data that describe the changing occurrence (relative abundance, locality representation) of invasive as well as native harvestman s...
Article
Bio-conversion of different organic waste streams in Hermetia illucens larval biomass suitable for animal feed is a promising sustainable solution across different sectors. However, environmental factors can affect the allocation of energy to fitness, survival and growth of insects in complex ways and can therefore impact the optimal functionality...
Article
We describe the remarkable egg sac of Benoitia lepida (O.P.-Cambridge, 1876) (Agelenidae) from the Negev Desert, Israel. It consists of four layers: (from outside) a papery envelope, an outer loose silk layer, a "dirt layer", and an inner flocculent silk layer surrounding the eggs. The dirt layer consists of loess soil, and may include stones, snai...
Article
In recent years, as economic globalization and long-distance trade have increased, so has the unintentional transport of non-human species. During the past 30 years, the species diversity of harvestmen (Opiliones) in northern Europe has changed dramatically due to the arrival of new species from southern Europe. Here we explore the changing harvest...
Article
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Biological control agents (BCA) are often mass reared at conditions very different from those at which they have to provide their service, especially if they are to be used under field conditions. It has been suggested that biocontrol efficiency might be enhanced by acclimating the BCA under near-field conditions for some time before release (benef...
Article
Full-text available
Ectotherms respond to their thermal environments by physiological acclimation, which increases tolerance to thermal extremes and may increase field performance. However, acclimation often has costs, and increased performance in some traits may be associated with reduced performance in other traits due to trade-offs. We investigated effects of therm...
Article
Male exploitation of female sensory or motivational biases has been proposed to account for the early evolution of nuptial gift-giving behaviour. The hypothesis is supported if females of a species positioned early in a clade respond positively to sexual signals from males of more recent species in the clade, and if these signals are not included i...
Article
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Restoration of fat stores is metabolic first priority for many insects that emerge from hibernation with depleted fat bodies. To some extent, the animals must be flexible and use whatever foods available irrespective of their nutrient composition. Previously, the carabid beetles Anchomenus dorsalis have been found to refill their fat stores to the...
Article
The spider genus Dysdera is considered to comprise specialist isopod feeders, although the degree of specialization varies between species, depending on morphological (shape of chelicerae), behavioural (attack tactics) and metabolic (food quality of prey) adaptations. Dysdera has radiated extensively in the Canary Islands (currently 47 endemic spec...
Article
Full-text available
Predators have been shown to alter their foraging as a regulatory response to recent feeding history, but it remains unknown whether trap building predators modulate their traps similarly as a regulatory strategy. Here we fed the orb web spider Nephila pilipes either live crickets, dead crickets with webs stimulated by flies, or dead crickets witho...
Article
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Several not mutually exclusive functions have been ascribed to nuptial gifts across different taxa. Although the idea that a nuptial prey gift may protect the male from pre-copulatory sexual cannibalism is attractive, it has previously been considered of no importance based on indirect evidence and rejected by experimental tests. We reinvestigated...
Article
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Carnivorous animals are known to balance their consumption of lipid and protein, and recent studies indicate that some mammalian carnivores also regulate their intake of carbohydrate. We investigated macronutrient balancing and lipid restoration following hibernation in the ground beetle Anchomenus dorsalis, hypothesizing that carbohydrates might b...
Article
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Pitfall trapping in the National Park Thy, north-western Jutland, Denmark, in 2011 and 2013 revealed 3654 specimens of the harvestman Nelima gothica. In most European countries, including Denmark, this species has been considered rare and little information is available on its biology. The species was found predominantly in the yellow dune habitat...
Article
We compared the arthropod fauna of Rosa rugosa patches to the adjacent native yellow dune vegetation by pitfall trapping in the National Park Thy at the Danish North Sea coast. R. rugosa changes the vegetation from a dune grassland (dominated by Ammophila arenaria) poor in flowering plants to a low monospecific shrubbery rich in large flowers. We p...
Article
Full-text available
Predators exhibit flexible foraging to facilitate taking prey that offer important nutrients. Because trap-building predators have limited control over the prey they encounter, differential nutrient extraction and trap architectural flexibility may be used as a means of prey selection. Here, we tested whether differential nutrient extraction induce...
Article
In species where females gain a nutritious nuptial gift during mating the balance between benefits and costs of mating may depend on access to food. This means that there is not one optimal number of matings for the female but a range of optimal mating numbers. With increasing food availability the optimal number of matings for a female should vary...
Chapter
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Nuptial gifts are an intriguing male sexually selected trait that has evolved in a wide range of forms among different animals. Wrapped prey gifts have been intensively studied in two spiders: Paratrechalea ornata (Trechaleidae), a neotropical species, and Pisaura mirabilis (Pisauridae), a Palearctic species. Interestingly, these species experience...
Article
Predators appear to be less frequently specialised (i.e. adapted to restricted diet) on their prey than herbivores, parasites or parasitoids. Here, we critically evaluate contemporary evolutionary hypotheses that might be used to explain the evolution of specialised foraging in predators. We propose a unifying concept within which we define four ty...
Chapter
Full-text available
Though most spiders are generalist predators with extensive prey lists, the nutritional value of prey species varies over a continuum from complete food to useless or even detrimental food. Low food value of prey may be due to nutrient deficiencies or toxin content. Possibly, spiders in nature rely on a limited number of high-quality prey species f...
Article
In many species, condition-dependent secondary sexual traits are important for female choice. In the spider Pisaura mirabilis, males offer females a nuptial gift (prey wrapped in silk) during courtship. Gift construction may involve high costs for males, and those in low condition invest less time and silk in wrapping the prey. We investigated how...
Article
Full-text available
Spiders leave draglines, faeces and other secretions behind when traveling through their microhabitat. The presence of these secretions may unintentionally inform other animals, prey as well as predators, about a recent and possible current predation risk or food availability. For a wolf spider, other spiders including smaller conspecifics, form a...
Article
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Flies of the family Acroceridae are specialized internal parasitoids of spiders. We infected hatchlings of wolf spiders Pardosa prativaga (L. Koch 1870) (Araneae: Lycosidae) with larvae of Acrocera orbiculus (Fabricius 1787); most hosts were infected by a single larva, but others endured multiple infections of up to eight larvae. The infected spide...
Article
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Evolutionary theory predicts that animals should forage to maximize their fitness, which in predators is traditionally assumed equivalent to maximizing energy intake rather than balancing the intake of specific nutrients. We restricted female predatory ground beetles (Anchomenus dorsalis) to one of a range of diets varying in lipid and protein cont...
Article
Some ladybeetles are specialist predators of aphids, coccids or other prey, although they often eat a variety of species from their focal prey taxon. In addition, the diet is often supplemented with alternative prey. How larvae of the aphidophagous Coccinella septempunctata L. utilize a non‐aphid alternative prey (fruit‐fly larvae Drosophila melono...
Article
Full-text available
In nuptial gift-giving species, benefits of acquiring a mate may select for male deception by donation of worthless gifts. We investigated the effect of worthless gifts on mating success in the spider Pisaura mirabilis. Males usually offer an insect prey wrapped in silk; however, worthless gifts containing inedible items are reported. We tested mal...
Article
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The nutritional composition of prey is known to influence predator life histories, but how the life history strategies of predators affect their susceptibility to nutrient imbalance is less investigated. We used two wolf spider species with different life histories as model predators: Pardosa amentata, which have a fixed annual life cycle, and Pard...
Article
Full-text available
Pisaura mirabilis males offer a prey wrapped in silk as a nuptial gift that functions as a male mating effort. If nuptial gift construction is costly, males in poor feeding condition would invest less in this behaviour than males in good condition. We investigated frequencies and characteristics of gift construction in males under different sexual...
Article
Full-text available
Provisioning of nutrients to the young during parental care is one of the mechanisms by which parents can affect growth and survival of their young and thus their reproductive success. We examined the hypothesis that food quality, i.e., ratio of macronutrients, provided to the young via maternal care affects their performance and the female’s repro...
Article
Full-text available
Nutrient balancing is well known in herbivores and omnivores, but has only recently been demonstrated in predators. To test how a predator might regulate nutrients when the prey varies in nutrient composition, we restricted juvenile Pardosa prativaga wolf spiders to diets of one of six fruit fly, Drosophila melanogaster, prey types varying in lipid...
Data
Data for Jensen, K., Mayntz, D., Toft, S., Raubenheimer, D., and Simpson, S.J. 2011. Nutrient balancing in a predator, the wolf spider Pardosa prativaga. Animal Behaviour 81, 993-999
Article
Full-text available
Nutritional ecological theory predicts that predators should adjust prey capture and consumption rates depending on the prey's nutritional composition. This would affect the predator's functional response, at least at high prey densities, i.e. near predator satiation. Using a simple fruitfly-wolf spider laboratory system in Petri dishes, we found t...
Article
A specialist predator that has a specialized diet, prey-specific prey-capture behaviour and a preference for a particular type of prey may or may not be specialized metabolically. Previous studies have shown that jumping spiders of the genus Portia prey on other spiders using prey-specific prey-capture behaviour, prefer spiders as prey to insects a...
Article
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Both hunger and body size differences increase the likelihood that an encounter between 2 predators turns into a cannibalistic event. Two hypotheses with opposite predictions can be proposed to explain how hunger influences cannibalism. The first claims that starvation weakens individuals, which then fall victim more easily to conspecifics that are...
Article
Prey quality can have large impacts on the survival, growth and behavior of predators. A number of studies have examined how different species of prey vary in quality. However, far less is known about intraspecific variation in the quality of prey for predators and even less about what nutrients are extracted from prey by predators. We examined how...
Article
Full-text available
In many animal species, mating behaviour is highly ritualised, which may allow us to relate some of its consequences, e.g. male paternity and female receptivity, to the progression of phases in the mating sequence; at the same time, ritualisation raises the question of to what extent the partners, especially the males, are able to influence the out...
Article
Larval nutrition may affect a range of different life history traits as well as responses to environmental stress in adult insects. Here we test whether raising larvae of fruit flies, Drosophila melanogaster, on two different nutritional regimes affects resistance to cold, heat and desiccation as well as egg production and egg-to-adult viability. W...
Article
In a 4 ha grass field in Denmark three separate plots of 15 times 25 m were cultivated with barley. In each plot a central area of 5 times 5 m were fenced off by a plastic barrier. Thus, each plot consisted of an unfenced area, accessible for predators immigrating from the grass field, and an unaccessible, fenced area. Numbers of polyphagous predat...
Article
Full-text available
Predator foraging may be affected by previous prey capture, but it is unknown how nutrient balance affects foraging behaviour. Here, we use a trap-building predator to test whether nutrients from previous prey captures affect foraging behaviour. We fed orb-weaving spiders (Zygiella x-notata) prey flies of different nutrient composition and in diffe...
Article
Full-text available
The development of male sexual ornaments and the intensity of male courtship behavior are often used by females as criteria for mate choice and by other males to evaluate the strength of a rival. We tested the hypotheses that courtship intensity and mating success depend on the males' nutritional status (enriched or deficient) and that courtship in...
Article
Full-text available
Climate change is advancing the onset of the growing season and this is happening at a particularly fast rate in the High Arctic. However, in most species the relative fitness implications for males and females remain elusive. Here, we present data on 10 successive cohorts of the wolf spider Pardosa glacialis from Zackenberg in High-Arctic, northea...
Article
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Diet composition of slow worms (Anguis fragilis) from a Danish population was recorded from May to September 2006. Slow worms were maintained in cool conditions (at 8°C) for a maximum of 126 h, which made approximately half of the animals regurgitate. The method worked equally well on juveniles and adults. The regurgitations revealed that the slow...
Article
Abstract Little attention is paid to the behavioural and physiological adaptations of ant-eating predators. It is expected that there should be a strong selection for traits related to prey handling, leading to the evolution of morphological, behavioural and nutritional adaptations. Such adaptations may then entail trade-offs in handling and utiliz...
Article
Many herbivores and omnivores can balance their intake of macronutrients when faced with nutritionally variable environments. Carnivores, however, are widely believed to optimize their rates of prey capture and energy intake rather than balancing nutrients. We tested nutrient balancing in captive mink and found a pronounced ability to balance and r...
Article
Full-text available
Two novel sampling techniques were used to survey the spider community of the leaf litter in a deciduous forest in Kentucky, USA. Using modified pitfall traps and litter-grab techniques, we sampled separately the top, middle and bottom litter layers from April–October. Our sampling program captured over 3,000 spiders encompassing 18 different famil...
Article
Males of the spider Pisaura mirabilis present a nuptial prey gift to the female during courtship as a mating effort. The gift is usually round and wrapped in white silk. It was suggested that the wrapped gift functions as a sensory trap by mimicking the female’s eggsac implying that males exploit the female maternal care instinct and not her foragi...
Article
The value of the cereal aphid species Metopolophium dirhodum (Wlk.), Sitobion avenae (F.) and Rhopalosiphum padi (L.) as prey for the linyphiid spider Erigone atra (Bl.) was assessed. Fecundity of females was determined for spiders fed on eight experimental diets: three single-species aphid diets, a mixed diet of all three aphid species, three mixe...
Article
We tested in a field experiment two hypotheses for why polyphagous predators aggregate at concentrations of aphids: 1) because they are attracted directly to aphids as prey, or 2) because they are attracted to alternative prey that aggregate around the honeydew produced by aphids. Small plots were established in the field with two experimental trea...