@misc{WackervonElert2001,
  author    = {Wacker, Alexander and von Elert, Eric},
  title     = {Polyunsaturated fatty acids : evidence for non-substitutable biochemical resources in Daphnia galeata},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17587},
  year      = {2001},
  abstract  = {The factors that determine the efficiency of energy transfer in aquatic food webs have been investigated for many decades. The plant-animal interface is the most variable and least predictable of all levels in the food web. In order to study determinants of food quality in a large lake and to test the recently proposed central importance of the long-chained eicosapentaenoic acid (EPA) at the pelagic producer-grazer interface, we tested the importance of polyunsaturated fatty acids (PUFAs) at the pelagic producerconsumer interface by correlating sestonic food parameters with somatic growth rates of a clone of Daphnia galeata. Daphnia growth rates were obtained from standardized laboratory experiments spanning one season with Daphnia feeding on natural seston from Lake Constance, a large pre-alpine lake. Somatic growth rates were fitted to sestonic parameters by using a saturation function. A moderate amount of variation was explained when the model included the elemental parameters carbon (r2 = 0.6) and nitrogen (r2 = 0.71). A tighter fit was obtained when sestonic phosphorus was incorporated (r2 = 0.86). The nonlinear regression with EPA was relatively weak (r2 = 0.77), whereas the highest degree of variance was explained by three C18-PUFAs. The best (r2 = 0.95), and only significant, correlation of Daphnia's growth was found with the C18-PUFA α-linolenic acid (α-LA; C18:3n-3). This correlation was weakest in late August when C:P values increased to 300, suggesting that mineral and PUFA-limitation of Daphnia's growth changed seasonally. Sestonic phosphorus and some PUFAs showed not only tight correlations with growth, but also with sestonic α-LA content. We computed Monte Carlo simulations to test whether the observed effects of α-LA on growth could be accounted for by EPA, phosphorus, or one of the two C18-PUFAs, stearidonic acid (C18:4n-3) and linoleic acid (C18:2n-6). With >99 \% probability, the correlation of growth with α-LA could not be explained by any of these parameters. In order to test for EPA limitation of Daphnia's growth, in parallel with experiments on pure seston, growth was determined on seston supplemented with chemostat-grown, P-limited Stephanodiscus hantzschii, which is rich in EPA. Although supplementation increased the EPA content 80-800x, no significant changes in the nonlinear regression of the growth rates with α-LA were found, indicating that growth of Daphnia on pure seston was not EPA limited. This indicates that the two fatty acids, EPA and α-LA, were not mutually substitutable biochemical resources and points to different physiological functions of these two PUFAs. These results support the PUFA-limitation hypothesis for sestonic C:P < 300 but are contrary to the hypothesis of a general importance of EPA, since no evidence for EPA limitation was found. It is suggested that the resource ratios of EPA and α-LA rather than the absolute concentrations determine which of the two resources is limiting growth.},
  language  = {en}
}
@misc{BlenauScheinerPlueckhahnetal.2002,
  author    = {Blenau, Wolfgang and Scheiner, Ricarda and Pl{\"u}ckhahn, Stephanie and Oney, Bahar and Erber, Joachim},
  title     = {Behavioural pharmacology of octopamine, tyramine and dopamine in honey bees},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-44308},
  year      = {2002},
  abstract  = {In the honey bee, responsiveness to sucrose correlates with many behavioural parameters such as age of first foraging, foraging role and learning. Sucrose responsiveness can be measured using the proboscis extension response (PER) by applying sucrose solutions of increasing concentrations to the antenna of a bee. We tested whether the biogenic amines octopamine, tyramine and dopamine, and the dopamine receptor agonist 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (6,7-ADTN) can modulate sucrose responsiveness. The compounds were either injected into the thorax or fed in sucrose solution to compare different methods of application. Injection and feeding of tyramine or octopamine significantly increased sucrose responsiveness. Dopamine decreased sucrose responsiveness when injected into the thorax. Feeding of dopamine had no effect. Injection of 6,7-ADTN into the thorax and feeding of 6,7-ADTN reduced sucrose responsiveness significantly. These data demonstrate that sucrose responsiveness in honey bees can be modulated by biogenic amines, which has far reaching consequences for other types of behaviour in this insect. (C) 2002 Elsevier Science B.V. All rights reserved.},
  language  = {en}
}
@misc{HeinkenRaudnitschka2002,
  author    = {Heinken, Thilo and Raudnitschka, Dorit},
  title     = {Do wild ungulates contribute to the dispersal of vascular plants in central European forests by epizoochory?},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5850},
  year      = {2002},
  abstract  = {The external dispersal ("epizoochory") of vascular plant diaspores (seeds and fruits) by roe deer and wild boar, i.e. the most common wild large mammals with a large home range in central Europe, was investigated in a 6.5-km² forest area in NE Germany dominated by mesic deciduous forests. The study involved brushing out the diaspores from the coats and hooves of 25 shot roe deer and nine wild boar. The results were compared with the forest vegetation of the study area. Whilst wild boar transported large amounts of various diaspores in the coat, the significance of roe deer for epizoochory was low due to their sleek fur and different behaviour compared to wild boar. Altogether, 55 vascular plant species were transported externally. Since only a limited number of seeds came from woodland habitats, the open landscape was at least as important as a source of attached seeds as the forest vegetation. Thus, most plant species occurring in the studied forest area, especially characteristic woodland herbs, showed no adaptations to epizoochorous dispersal, although being very abundant in the herb layer. We conclude that hoofed game play a particular role concerning the dispersal of ruderal and grassland species in the agricultural landscape of central Europe. However, the actual spread of some herb species in forests of northern Germany, e.g. Agrostis capillaris, Brachypodium sylvaticum, Deschampsia flexuosa, Galium aparine and Urtica dioica, may be mainly facilitated by wild ungulates. Though dispersal by large mammals is an important mechanism for long-distance dispersal of plants in general, our results suggest that most of the characteristic herb species of mesic deciduous forests have only low epizoochorous dispersal potentials. The implications for nature conservation and silviculture are discussed.},
  language  = {en}
}
@misc{WackervonElert2002,
  author    = {Wacker, Alexander and von Elert, Eric},
  title     = {Strong influences of larval diet history on subsequent post-settlement growth in the freshwater mollusc Dreissena polymorpha},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17627},
  year      = {2002},
  abstract  = {Significant seasonal variation in size at settlement has been observed in newly settled larvae of Dreissena polymorpha in Lake Constance. Diet quality, which varies temporally and spatially in freshwater habitats, has been suggested as a significant factor influencing life history and development of freshwater invertebrates. Accordingly, experiments were conducted with field-collected larvae to test the hypothesis that diet quality can determine planktonic larval growth rates, size at settlement and subsequent post-metamorphic growth rates. Larvae were fed one of two diets or starved. One diet was composed of cyanobacterial cells which are deficient in polyunsaturated fatty acids (PUFAs), and the other was a mixed diet rich in PUFAs. Freshly metamorphosed animals from the starvation treatment had a carbon content per individual 70\% lower than that of larvae fed the mixed diet. This apparent exhaustion of larval internal reserves resulted in a 50\% reduction of the postmetamorphic growth rates. Growth was also reduced in animals previously fed the cyanobacterial diet. Hence, low food quantity or low food quality during the larval stage of D. polymorpha lead to irreversible effects for postmetamorphic animals, and is related to inferior competitive abilities.},
  language  = {en}
}
@misc{BlenauGrohmannErberetal.2003,
  author    = {Blenau, Wolfgang and Grohmann, Lore and Erber, Joachim and Ebert, Paul R. and Str{\"u}nker, Timo and Baumann, Arnd},
  title     = {Molecular and functional characterization of an octopamine receptor from honeybee (Apis mellifera) brain},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-44293},
  year      = {2003},
  abstract  = {Biogenic amines and their receptors regulate and modulate many physiological and behavioural processes in animals. In vertebrates, octopamine is only found in trace amounts and its function as a true neurotransmitter is unclear. In protostomes, however, octopamine can act as neurotransmitter, neuromodulator and neurohormone. In the honeybee, octopamine acts as a neuromodulator and is involved in learning and memory formation. The identification of potential octopamine receptors is decisive for an understanding of the cellular pathways involved in mediating the effects of octopamine. Here we report the cloning and functional characterization of the first octopamine receptor from the honeybee, Apis mellifera . The gene was isolated from a brain-specific cDNA library. It encodes a protein most closely related to octopamine receptors from Drosophila melanogaster and Lymnea stagnalis . Signalling properties of the cloned receptor were studied in transiently transfected human embryonic kidney (HEK) 293 cells. Nanomolar to micromolar concentrations of octopamine induced oscillatory increases in the intracellular Ca2+ concentration. In contrast to octopamine, tyramine only elicited Ca2+ responses at micromolar concentrations. The gene is abundantly expressed in many somata of the honeybee brain, suggesting that this octopamine receptor is involved in the processing of sensory inputs, antennal motor outputs and higher-order brain functions.},
  language  = {en}
}
@misc{BlenauBaumann2003,
  author    = {Blenau, Wolfgang and Baumann, Arnd},
  title     = {Aminergic signal transduction in invertebrates : focus on tyramine and octopamine receptors},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-44271},
  year      = {2003},
  abstract  = {Electro-chemical signal transduction is the basis of communication between n eurons and their target cells. An important group of neuroactive substances that are released by action potentials from neurons are the biogenic amines. These a re small organic molecules that bind to specific receptors located in the target cell membrane. Once activated these receptors cause changes in the intracellula r concentration of second messengers, i.e. cyclic nucleotides, phosphoinositides , or Ca2+, leading to slow but long-lasting cellular responses. Biochemical, pha rmacological, physiological, and molecular biological approaches have unequivoca lly shown that biogenic amines are important regulators of cellular function in both vertebrates and invertebrates. In this review, we will concentrate on the p roperties of two biogenic amines and their receptors that were originally identi fied in invertebrates: tyramine and octopamine. },
  language  = {en}
}
@misc{BlenauMustardHamiltonetal.2003,
  author    = {Blenau, Wolfgang and Mustard, Julie A. and Hamilton, Ingrid S. and Ward, Vernon K. and Ebert, Paul R. and Mercer, Alison R.},
  title     = {Analysis of two D1-like dopamine receptors from the honey bee Apis mellifera reveals agonist-independent activity},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-44378},
  year      = {2003},
  abstract  = {Dopamine is found in many invertebrate organisms, including insects, however, the mechanisms through which this amine operates remain unclear. We have expressed two dopamine receptors cloned from honey bee (AmDOP1 and AmDOP2) in insect cells (Spodoptera frugiperda), and compared their pharmacology directly using production of cAMP as a functional assay. In each assay, AmDOP1 receptors required lower concentrations of dopamine and 6,7-ADTN for maximal activation than AmDOP2 receptors. Conversely, butaclamol and cis(Z)-flupentixol were more potent at blocking the cAMP response mediated through AmDOP2 than AmDOP1 receptors. Expression of AmDOP1, but not AmDOP2, receptors significantly increased levels of cAMP even in the absence of ligand. This constitutive activity was blocked by cis(Z)-flupentixol. This work provides the first evidence of a constitutively activated dopamine receptor in invertebrates and suggests that although AmDOP1 and AmDOP2 share much less homology than their vertebrate counterparts, they display a number of functional parallels with the mammalian D1-like dopamine receptors.},
  language  = {en}
}
@misc{HoppertReimerKemmlingetal.2004,
  author    = {Hoppert, Michael and Reimer, Rudolph and Kemmling, Anne and Schr{\"o}der, Annekatrin and G{\"u}nzl, Bettina and Heinken, Thilo},
  title     = {Structure and reactivity of a biological soil crust from a xeric sandy soil in Central Europe},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5872},
  year      = {2004},
  abstract  = {The investigation was designed to explore the structure, composition and activity of a biological soil crust on an acidic, sandy soil from a temperate climate. The crust covers several hundreds of square meters on the hilltop of a large terminal moraine. The conjugate alga Zygogonium ericetorum forms the essential matrix for the crust, a dense web of algal filaments with interspersed lichens and mosses. The crust is composed of three layers, with an uppermost layer consisting nearly entirely of a dense algal mat. In lower layers, a parasitic fungus, penetrating the algal cells, is another important component of the crust community. In this soil crust, photosynthetic and respiratory activity is stabilized at low water activities.},
  language  = {en}
}
@misc{KoechyWilson2004,
  author    = {K{\"o}chy, Martin and Wilson, Scott D.},
  title     = {Variation in nitrogen deposition and available soil nitrogen in a forest-grassland ecotone in Canada},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5768},
  year      = {2004},
  abstract  = {Regional variation in nitrogen (N) deposition increases plant productivity and decreases species diversity, but landscape- or local-scale influences on N deposition are less well-known. Using ion-exchange resin, we measured variation of N deposition and soil N availability within Elk Island National Park in the ecotone between grassland and boreal forest in western Canada. The park receives regionally high amounts of atmospheric N deposition (22 kg ha⁻¹ yr⁻¹). N deposition was on average higher ton clayrich luvisols than on brunisols, and areas burned 1 - 15 years previously received more atmospheric N than unburned sites. We suggest that the effects of previous fires and soil type on deposition rate act through differences in canopy structure. The magnitude of these effects varied with the presence of ungulate grazers (bison, moose, elk) and vegetation type (forest, shrubland, grassland). Available soil N (ammonium and nitrate) was higher in burned than unburned sites in the absence of grazing, suggesting an effect of deposition. On grazed sites, differences between fire treatments were small, presumably because the removal of biomass by grazers reduced the effect of fire. Aspen invades native grassland in this region, and our results suggest that fire without grazing might reinforce the expansion of forest into grassland facilitated by N deposition.},
  language  = {en}
}
@misc{Heinken2004,
  author    = {Heinken, Thilo},
  title     = {Migration of an annual myrmecochore},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-5865},
  year      = {2004},
  abstract  = {A seed sowing experiment was conducted in a mixed secondary woodland on acidic soils in NE Germany with Melampyrum pratense, an annual ant-dispersed forest herb which lacks a natural population in the study area, but is abundant in similar habitats. Each set of 300 seeds was sown within one square metre at three sites in 1997, and the development of the populations was recorded from 1998 onward. Additionally, seed fall patterns were studied in a natural population by means of adhesive cardboard. All trials resulted in the recruitment of populations, which survived and increased in both individual number and area, up to the year 2001. Thus, local distribution of Melampyrum pratense is dispersallimited. Total individual number increased from 105 to 3,390, and total population area from 2.07 to 109.04 m². Migration occurred in all directions. Mean migration rate was 0.91 m per year, and the highest migration rate was 6.48 m. No individual was recorded beyond 7.63 m from the centres of the sawn squares after three years, suggesting exclusive short-distance dispersal. As primary dispersal enables only distances of up to 0.25 m, ants are presumed to be the main dispersal vectors. Despite differences in individual number and colonization patterns, migration rates did not differ significantly between the populations, but were significantly higher in 2001 due to an increased population size. Colonization patterns were characterized by a rapid, negative exponential decrease of population density with increasing distance from the sown plot, suggesting a colonization by establishment of more or less isolated outposts of individuals and a subsequent gradual infill of the gaps between. My results resemble myrmecochorous dispersal distances in temperate woodlands, and migration rates and patterns across ecotones from ancient to recent deciduous forests. They may function as a colonization model of Melampyrum pratense after accidental long-distance dispersal.},
  language  = {en}
}