Soil entomology

Section 13 - Talks
Soil entomology
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Section 13 - Keynote
Tools to open the black box – biochemical markers unravel soil food webs
L. Rueß
Soils harbour an enormous diversity of organisms connected by multitrophic
interactions that are central to nutrient cycling. Microarthropods, in particular
microbial grazers such as Collembola, are important determinants for the energy and
carbon flow through belowground food webs. Regardless of their significance, trophic
relationships in soil are still poorly understood. Due to the cryptic habitat and the
small size of the fauna, feeding strategies are difficult to address, either
experimentally or by direct observation.
Over the last decade, stable isotopes have increasingly been used as biomarkers.
The isotopic ratios of 15N/14N and 13C/12C in animal tissues were employed to
reconstruct food webs, with nitrogen assigning relative trophic levels and carbon food
resources. Recently, lipid pattern were applied to unravel trophic interactions. Food
derived fatty acids are conserved and transferred in the food chain, a fact called
“dietary routing”. Several marker fatty acids have been defined for Collembola
feeding strategies hitherto. To increase resolution, lipid and stable isotope techniques
were combined, and, by comparison of the 13C in fatty acids of consumer and diet,
specific trophic links were determined.
In conclusion, biochemical markers offer new insight into feeding habits of soil
animals in situ. The relative simplicity of chemical analysis, which uses widely
available equipment, provides a high potential for food web studies. A prospect for
the future is the combination of stable isotope probing (SIP) in nucleic acids (DNASIP) and fatty acids (FA-SIP) to link identity and function in soil key biota.
Liliane Rueß, Institute of Biology, Ecology Group, Humboldt-Universität Berlin, Germany,
[email protected] (Presenting Author)
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Section 13 - Talk
Using easily identified macrofaunal taxa for soil zoological site assessments
C. Kantner, A. Bruckner
During the last 100 years, limnologists have established an indicator system which
evaluates water quality by analyzing the occurrence of aquatic organisms using
representative taxa from nearly all animal and plant groups. In soil zoology, single
taxa like Collembola or Carabidae are established as indicators, however,
evaluations are based on only on a very limited fraction of animals present in the soil
(taxocoenoses). A more comprehensive use of the diversity of soil organisms is
hampered by tremendous identification problems in many of the groups.
The aim of this diploma thesis was to test whether single taxa - when identified to a
level which can be achieved without expertise and with reasonable time effort - are
indicative for soil analyses. The most important requirement for a taxon to qualify as
an indicator was that it had to be identified unambigously, rapidly, and without
preparation. To test this, the macrofauna of 20 sites belonging to four forest types
(beech, acidic beech, oak and pine stands) and 5 non wooded sites as a contrast to
the forest types (2 grasslands and 3 forest clearing sites) were sampled, all of them
situated in the biosphere reserve Wienerwald in Lower Austria. Three different
sampling methods were applied: (i) pitfall traps (ii) a manual search on the ground
and (iii) soil samples. Taxa sampled on the sites that did not meet the requirements
above were not counted. To test the indicativeness of the selected taxa, various
parameters were surveyed at the sites (density of canopy, stand density, deadwood
density, Ellenberg indicator values of vegetation). The results showed that the factor
sitetype (this factor included the 4 forest types and the non-forest type) had a
significant influence on the similarity of the indicator assemblages, however,
contributed little to total variability (approxiamately 12%). It was not possible to
analyze the influence of individual taxa on this result, due to the low explained
variability. Of the three methods, the pitfall traps best represented the site
assemblages, regardless of the data transformation used. In further analyses the
method could be improved by more sampling dates or a overworked taxa set.
Christian Kantner, Department of Evolutionary Biology, University of Vienna, [email protected]
(Presenting Author)
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Section 13 - Talk
Überlebensstrategien und Kosten-Nutzen-Bilanzen einer räuberischen
Insektenlarve (Euroleon nostras FOURCROY, Myrmeleontidae)
K. Meißner, M. Feike, C. Pires & J. Stetzkowski
Bei 200 Arten, deren Larven im Boden Trichterfallen bauen, ist der
Entwicklungszyklus evolutionsbiologisch stabil. Aber nach der Eiablage entwickeln
sich drei Larvenstadien in etwa 24 Monaten unter schwierigsten Konditionen. Die
Larven leben in Extremwerthabitaten: Die Trichter sind stabil als auch instabil, sie
sind rieselfähig, werden verweht und erneuert oder beim Beutefang beschädigt. Die
Bodentemperatur erreicht Werte über 50° C, die Bodenfeuchtigkeit geht gegen Null,
aber nach Regenfällen sind die Trichterhorizonte durchnässt. Und Beute gibt es für
die sit-and-wait-Predatoren selten und unregelmäßig. Obwohl sie z. B. erst nach 3
oder 25 Tagen und seltener wieder Beute machen, nimmt ihre Biomasse von der
geschlüpften Larve (L1: 0.5mg) mg) bis zum Bau des Kokon (L3: 140mg) auf das
280-fache zu. Wir untersuchen die Überlebensstrategien im Freiland wie im Labor
und kontrollieren dabei die Populationsökologie, Bodentexturen, Beutespektrum und
Wachstum, Bau und Parameter der Trichterfallen, die Ausnutzung der Beute, den
Wasserhaushalt und Stoffwechselraten. Mit Optimalitätsmodellen zu Kosten und
Nutzen des Trichterbaues werden quantitative Voraussagen geprüft. Alle Larvenstadien bauen den Trichter in ca. 0:25 h (n= 257, Textur 0.2-0.5 mm), in 23:35 h des
24 h-Tages sind sie i. w. inaktiv. Larven von 20 bis 30 mg haben in dieser Aktivitätszeit eine Stoffwechselrate, die 8-fach über dem Niveau des Ruhestoff-wechsels liegt.
Aus einer Ameise von 9,45 mg (F. rufa, F. polyctena) kann ein Löwe 3,45 mg
Nahrung extrahieren und 0.37 mg Kohlenstoff gewinnen. Bei einem mittleren Niveau
des Grundstoffwechsels von 0,62 g C h-1 könnte er damit 25 d auskommen. Die
Ameisenlöwen optimieren außerdem die Fangleistung ihres Trichters, indem sie ihn
obligatorisch und periodisch erweitern (n=96, Periodenlänge 23.20±02.11 h). Für
einen erweiterten Trichter von 70 mm Durchmesser, der aus kleineren Dimensionen
entwickelt wird, werden z. B. nur 33 g statt 53 g Sand transportiert. Damit sind 38 %
der Transportkosten für den Stoffwechsel eingespart worden.
Karl Meißner, c/o Institut für Biowissenschaften, Universität Rostock, Deutschland, [email protected] (Presenting Author)
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Section 13 - Talk
Dipteran larvae as main decomposers in high alpine soils
A. Rief, M. Steinwandter, E. Meyer & J. Seeber
In alpine regions soil dwelling larvae of Diptera, which are important decomposer
species, take over the role as keyspecies of decomposition from earthworms, as the
latter recede in number and biomass. This is not only due to temperature conditions
and the short growing season, but also because of the reduction of habitat structure.
Dipterans are, however, a taxon which is among the least-studied groups of soil
animals, mostly because soil-dwelling larvae are challenging to be identified to
species level. Thus, only few studies have dealt with soil dwelling Dipteran larvae in
alpine regions.
In a first step the soil-macro fauna of alpine grasland sites in the Stubaier Alps
(Central Alps, Austria, 2.200 – 2.500 m a.s.l.) was detected and identified to family
level. Results from emergence trap sampling on the study site have shown that two
Dipteran families are predominate: the Sciaridae and the Chironomidae.
The second step is to identify the key decomposer species using stable isotopes.
The 15N/14N ratios will be used to clarify the relative trophic positions of the soil
animals: primary decomposer, secondary decomposer, and predator. As biochemical
reactions discriminate against the heavier isotope, 15N accumulates in the animals’
tissues the more the higher the trophic level. Primary decomposers will have the
lowest 15N value, followed by secondary decomposers, predatory species will be
on top of the range. Combined with molecular barcoding methods the identification to
species level and/or the assignment to taxonomical units (TUs) is allowed.
Alexander Rief, Institut für Ökologie, Universität Innsbruck, Österreich, [email protected]
(Presenting Author)
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Section 13 - Talk
Plant species effects on soil macrofauna density in grassy arable fallows of
different age
J.-A. Salamona, J. Wissuwa, S. Jagos, M. Koblmüller, O. Ozinger, C. Winkler & T.
Frank
The density of soil macrofauna groups in nine grassy arable fallows of different age
were investigated in a factorial design with the factors ‘plant species’ (legume:
Medicago sativa, herb: Taraxacum officinale, grass: Bromus sterilis) and ‘age class’
(2-3/3-4, 6-8/7-9, 12-15/13-16 years). Four plots were selected randomly at each
fallow. In May 2008 and May 2009, within each plot five M. sativa, T. officinale and B.
sterilis plants were extracted with their associated soil using steel cylinders. The
material from each plant species was used for extraction of soil macrofauna and for
determination of environmental parameters.
The main results were (May 2009) (i) the density of the saprophagous macrofauna
was significantly higher in B. sterilis than in M. sativa and T. officinale samples
indicating that this group benefited from the particularly high amount of fine roots in
the B. sterilis samples; (ii) the density of Gastropoda increased significantly with the
age of the fallows due to the increasing amount of fungal biomass; (iii) densities of
saprophagous macrofauna and predatory beetles were highest in the 7-9 yr old
fallows indicating that predators may have benefited from the increased availability of
their prey in the medium stage of grassland succession.
Jörg-Alfred Salamon, Institut für Zoologie, Department für Integrative Biologie und
Biodiversitätsforschung, Universität für Bodenkultur Wien, Austria, [email protected]
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