Community ecology of moths in floodplain forests of Eastern Austria

In der vorliegenden Arbeit habe ich Nachtfaltergemeinschaften aus Wäldern unterschiedlicher Überflutungsregime in drei verschiedenen Auenregionen (Donau, March und Leitha) im Tiefland Ost-Österreichs untersucht. Für die Erfassung der Falter wurden, über einen Zeitraum von 2 Jahren, einmal pro Monat Lichtfallen betrieben. Obwohl der Lichtfang die am häufigsten verwendete Methode ist, um Nachtfalter zu erfassen, weiß man immer noch erstaunlich wenig über die Entfernungen, aus denen Falter zum Licht fliegen. Um den Attraktionsradius einer schwachen Lichtquelle (2 × 15 W UV-emittierende Leuchtstoffröhren) zu untersuchen, wurden zwei Fang-Wiederfang-Experimente durchgeführt. Insgesamt wurden 2.331 Nachtfalter aus 167 Arten gefangen, individuell markiert und aus Entfernungen von 2–100m zur Lichtquelle erneut freigelassen. Von diesen Nachtfaltern kamen nur 313 Tiere innerhalb von 5 Minuten wieder zum Leuchtturm zurück. Generell war die Wiederfangrate mit 13,4 % gering und nahm mit steigender Entfernung immer mehr ab. Die Ergebnisse bestätigen, dass der Attraktionsradius einer schwachen Lichtquelle für Nachtfalter sehr klein ist und oft sogar unter 10 m liegt. Mit solchen Fallen erhobene Stichproben bilden daher die Artengemeinschaften, aus denen sie gezogen wurden, mit der erforderten hohen räumlichen Auflösung ab, um auch in einer heterogenen Landschaft kleinräumige Unterschiede zwischen Habitaten beurteilen zu können. Da eine Hauptfrage dieser Untersuchung dem Einfluss von Überflutung auf die Nachtfalter-Diversität gewidmet war, war es zunächst wichtig, ein geeignetes Maß für lokale Arten-Diversität auszuwählen. Dieses Maß sollte auf den betrachteten räumlichen und ökologischen Skalen ausreichend hohe Auflösung erbringen. Ich habe anhand eines großen empirischen Datensatzes (448 Nachtfalter-Arten und 32.181 Individuen) eine Reihe von Alpha-Diversitätsmaßen miteinander verglichen. Für ähnliche Vergleiche wurden bisher überwiegend modellierte Datensätze verwendet. Die betrachteten Auwälder umfassten sowohl regelmäßig überflutete als auch heute nicht mehr (bzw. nur kaum) überflutete Bereiche. Ich erwartete daher, dass regionale wie auch lokale Einflüsse die Artendiversität der Nachtfalter beeinflussen. Überraschenderweise ließen sich weder mittels beobachteter Artenzahlen noch mit acht verschiedenen Extrapolationsmethoden für die Gesamtartenzahlen Unterschiede zwischen den Regionen oder zwischen überfluteten und nicht überfluteten Habitaten abbilden. Rarefaction-Analysen und der Formparameter der logarithmischen Reihe (Fisher's alpha) zeigten Unterschiede zwischen den Regionen auf, nicht aber zwischen den beiden Habitattypen. Nur mittels Shannons Diversität konnten alle erwarteten Differenzierungen auf hohem Signifikanzniveau abgesichert werden. Dabei machte es wenig Unterschied, ob Shannons Diversität in ihrer ursprünglichen Form oder unter Berücksichtigung einer kürzlich entwickelten Bias-Korrektur für kleine Stichproben zum Einsatz kam. Letztere vermied aber die Unterschätzung der lokalen Diversität an Stand¬orten mit kleinen Fangzahlen, weshalb ich die Bias-korrigierte Fassung für alle weiteren Analysen verwendete. Sodann verglich ich die Artendiversität und -zusammensetzung der Nachtfalter-Faunen zwischen den drei Auenregionen und den beiden Überflutungsregimen. Heutige Auwaldreste in Ost-Österreich sind kleinräumig in eine waldarme Kulturlandschaft eingebettet. Daher – und angesichts der hohen Mobilität vieler Nachtfalter – enthalten auch Stichproben, die im Inneren eines Waldes gezogen werden, stets einen beträchtlichen Anteil von Individuen, die aus der umgebenden Landschaftsmatrix zugeflogen sind. Um den Einfluss solcher Irrgäste zu testen, wurden die Nachtfalter anhand der spezifischen Ressourcenansprüche ihrer Raupen in „Residente“ und “Irrgäste” eingeteilt. Irrgäste waren zahlreich vertreten (17 % der beobach-teten Arten, 6 % der Individuen), beeinflussten aber die Muster der Artendiversität nur marginal. Residente wurden in weiterer Folge unterteilt in Tiere, die ihre Larvalentwicklung in der Baum- und Strauchschicht vollziehen, und jene, die sich bodennah entwickeln. Damit sollte festgestellt werden, ob diese Gruppen unterschiedlich von der Überflutungsdynamik beeinflusst werden. Überraschenderweise war weder die Gesamtdiversität der Nachtfalter noch die Diversität der Arten mit bodennaher Entwicklung in überfluteten Waldanteilen vermindert. In zwei der drei Auenregionen war die Artendiversität dieser terrestrischen Insekten sogar in Waldgebieten mit Überflutungsdynamik höher. Ich erkläre dies mit der größeren Heterogenität und Natürlichkeit überfluteter Waldbereiche wie auch mit dem hohen Wiederbesiedlungspotenzial mobiler Nachtfalter nach Störungen durch Hochwasserereignisse. Die Diversität der arborealen Arten zeigte überhaupt keine Unterschiede zwischen überfluteten und nicht überfluteten Habitaten. Es gab eine starke Differenzierung der Artenzusammensetzung bezüglich der Regionen und schwächer, aber trotzdem signifikant, zwischen überfluteten und nicht überfluteten Waldanteilen. Allerdings war die Arten-zusammensetzung der überfluteten Gebiete in den drei Regionen unterschiedlich, so dass man, anders als erwartet, keine Nachtfalterfauna ausmachen kann, die typisch für überflutete Habitate wäre. Die Differenzierung der Artengemeinschaften war im Wesentlichen durch Verschiebungen der Abundanzverhältnisse eurytoper Arten verursacht, Spezialisten für Feuchtgebiete spielten nur eine untergeordnete Rolle. Weiters wurde untersucht, ob verschiedene Teilgruppen einer Nachtfaltergemeinschaft sich in dem betrachteten Habitatmosaik unterschiedlich verhalten bzw. ob es Teilgruppen gibt, die als Stellvertreter (und damit ggf. als Indikatoren) des Gesamtmusters dienen können. Damit verbunden war die Frage nach dem Ausmaß struktureller Redundanz im Datensatz. Drei taxonomisch definierte (Überfamilien Noctuoidea, Geometroidea und Pyraloidea) und 10 funktionell definierte Teilgruppen spiegelten das Gesamtmuster in unterschiedlichen Graden wider. Zwar reflektierten die Noctuoidea die Beta-Diversität am besten, doch aufgrund ihrer hohen Arten-und Individuenzahl sind sie als Stellvertreter nicht optimal. Die Geometroidea hingegen reduzieren den Arbeitsaufwand (sie machen 31.25% der Arten und 21.22% der Individuen aus) und bilden die Beta-Diversität fast genauso gut ab wie die Noctuoidea. Der gesamte Datensatz konnte auf 8–15 Arten (das sind 1.5–3,35% aller gefundenen Arten) reduziert werden, die das Gesamtmuster nahezu genauso gut abbildeten wie der vollständige Datensatz. Interessanterweise waren nicht unbedingt die abundantesten Arten als Stellvertreter bedeutsam, sondern es scheint wichtiger zu sein, dass alle (häufigen) funktionellen Typen eines Ökosystems in einer Indikatorgruppe vertreten sind. Diese Beobachtungen führen zu der Hypothese, dass Nachtfaltergemeinschaften in Auwäldern ein hohes Ausmaß auch an funktioneller Redundanz aufweisen könnten. Insgesamt zeigen die Ergebnisse meiner Studie, dass für Nachtfalter – eine sehr artenreiche und durchaus repräsentative Gruppe terrestrischer herbivorer Insekten – Auwälder nicht unbedingt als ‚Hotspots’ der Biodiversität zu betrachten sind. Artendiversität und Artenzusammensetzung dieser Insekten wurden zudem stärker von regionalen Faktoren moduliert als von der lokalen Hochwasserdynamik.In this thesis I investigated moth communities in relation to flood regime across three riparian regions of lowland Eastern Austria (viz. Danube, Morava and Leitha rivers) using light traps once a month over a period of two consecutive years. Although light trapping is the most widely used method to survey nocturnal moths, little is still known about the distances at which moths respond to an artificial light source. Two community-wide mark-release-recapture experiments were carried out in order to investigate the attraction radius of a weak artificial light source (2 × 15 W UV-light tubes). Altogether 2,331 moths belonging to 167 species were caught at light traps, individually marked, and released again at distances of 2–100 m. Of these only 313 moths returned to the light trap within 5 min of release. Percentage recapture was generally low (gross rate 13.4%) and strongly decreased with increasing the distance at which they had been released. The data confirm that the attraction radius of low-power light traps for moths is very small, often even below 10 m. Therefore, moth samples assembled with such light traps reflect the communities from which they are drawn at a sufficiently high spatial resolution (in the range of tens of meters) to allow for comparisons in a finely grained forest landscape. As one major question of this thesis was the impact of flooding on moth species diversity, it was important to select an appropriate measure of local diversity which is sensitive at precisely the ecological scales under study. I used a large data set of 448 moth species and 32,181 individuals, collected in the three floodplain forests mentioned above, to empirically explore the performance of a range of alpha-diversity measures. Earlier comparisons of diversity measures have mostly been made using modelled data sets. The studied forests comprised regularly flooded and non-flooded habitats, thus, I expected that local moth diversity should be shaped by both, regional differences and local flood effects. Surprisingly, observed species numbers as well as eight methods to extrapolate species totals completely failed to reflect differences between the three study regions or between flooded and non-flooded habitats. Rarefied species numbers and Fisher’s alpha of the log-series distribution did capture differences in moth diversity between the regions, but failed to mirror flooding impact. Only Shannon’s diversity captured all expected diversity differences, at high significance levels. Whether using Shannon’s diversity in its original formulation, or a recently developed bias-correction for small sample sizes, did not affect conclusions about species diversity patterns, but the original formulation tended to underestimate species diversity in smaller samples. I therefore decided to adopt the bias-corrected Shannon diversity as the most meaningful species diversity measure for my subsequent analyses. I then proceeded to compare moth species diversity and species composition between the three floodplain forest regions and between differentially flood-impacted forest stretches. Today’s floodplain forests in Austria consist of small stretches embedded into non-forested cultivated landscape. Accordingly, and in view of the high mobility of these insects, moth samples taken inside forests always contain a fraction of non-breeding individuals that have immigrated from this landscape matrix. To test the impact of these stray species on diversity patterns, moths were segregated into resident and strays according to their larval resource and habitat requirements. Resident moths were further partitioned into arboreal and ground-layer species based on their larval habitat, to find out if flooding affects these groups differently. Stray species were quite numerous, accounting for 17 % of observed species and 6 % of sampled individuals, but they only marginally influenced diversity and species composition patterns. Contrary to expectation, total moth diversity and ground-layer moth diversity were generally not reduced in flooded habitats relative to non-flooded habitats. In two of three riverine regions species diversity of these terrestrial insects was even higher in flood-impacted habitat fractions. I attribute these patterns to the higher heterogeneity and naturalness of flood-impacted areas plus the strong re-colonisation potential of mobile moths after disturbances through floods. Species diversity of arboreal moths did not show any significant differences between flood regimes at all. With regard to species composition, there was a strong differentiation of moth communities between the three floodplain regions and to a lesser degree between flooded and non-flooded forests. Moth ensembles from flooded habitats in different riverine regions did not group together in ordination diagrams. This contradicts to the hypothesis that flooding would result in a characteristic moth community tolerant to frequent inundation. Differences in species composition were mostly caused by changes in abundance relations of eurytopic moths, and could not be attributed to specialist species bound to wetland habitats. I further investigated if subsamples of moth assemblages differ in their potential to reveal ecological patterns, i.e. such subsamples can serve as surrogates for overall beta-diversity. Concomitantly, I analysed the extent of structural redundancy in the dataset. Various taxonomically or ecologically defined moth subsamples mirrored total beta-diversity patterns to quite different degrees. For these analyses, I compared the three largest superfamilies (Noctuoidea, Geometroidea, and Pyraloidea) as well as 10 functional groups defined by their larval habitats and resource affiliations. Even tough the Noctuoidea showed the highest concordance with all moths, the Geometroidea provide a better surrogate for beta-diversity, because they scored almost as well as the Noctuoidea, but working effort is much lower since they are not that rich in species and less numerous in individuals (i.e. 31.25% of total species and 21.22% of total individuals). Regarding to structural redundancy I was able to reduce the dataset down to only 8–15 species (i.e. only 1.5–3.35 % of all recorded moth species) that were fully sufficient to reflect the species composition patterns in the overall moth community. The most abundant species did not necessarily carry the greatest weight in that regard. Rather, the results suggest that representation of all (common) functional types which may be expected within an ecosystem is more important to define surrogate groups to monitor species turnover. These observations also lead to hypothesize that floodplain forest moth assemblages likely show considerable functional redundancy. Overall, the results assembled in this thesis indicate that for moths, as a representative and species-rich group of terrestrial herbivorous insects, floodplain forests cannot be characterised as ‘hotspots’ of biodiversity. Moth species diversity and species composition were more strongly modulated by regional factors than by local habitat conditions

Data from: Massive structural redundancies in species composition patterns of floodplain forest moths

Terrestrial arthropod communities usually consist of very large species numbers. Data from experiments or long time-series would be required to ascertain the functional significance of individual species. Both are largely unavailable for species-rich natural communities. Recognising structural redundancies in species composition allows for an alternative approach to address how strong functional redundancy might be in natural assemblages, if structural and functional redundancies are related to each other. Determining structural redundancies is a regular topic in aquatic ecology, but has rarely been applied to terrestrial communities. We explored the extent of structural redundancy in species-rich terrestrial insect assemblages and whether structural redundancies are contingent to species abundances or functional group affiliations. We used the BVSTEP algorithm to determine structural redundancies in a large data set of moth species (32 181 individuals; 448 species) that had been sampled with light-traps in three different floodplain forests in eastern Austria. We partitioned the moth species into 12 functional types based on larval host-plant affiliations to test if moth species included in reduced subsets represent functional groups in the same proportions as they occur in the entire fauna. We observed far more massive structural redundancies in moth assemblages than previously found in aquatic communities. Subsets containing only 8–15 species (1.8–3.3% of all recorded species) were still highly representative for the overall data. Subsets selected by the BVSTEP procedure performed better than equally small subsets that were defined solely by species abundances or by functional group affiliations. Effective ‘surrogate’ subsets contained only 6–9 of the 12 functional moth types. High abundance only loosely corresponded with the frequency at which a moth species was included in the subsets. Thus, certain uncommon species contribute importantly to species composition patterns. Our results show unexpectedly extensive structural redundancies in complex floodplain forest moth communities, which may also indicate strong functional redundancies

Classification of moth species into 12 functional groups according to larval feeding relationships.

Moths have been sampled in three floodplain forest regions in eastern Austria (along the rivers Danube, Morava and Leitha) which differ in flood regimes and forest vegetation. Each region contained two classes of forest habitats: ones that are regularly inundated once a year, and others that are not or only rarely flooded. In each forest habitat five light trap sites were selected at a distance of about 100 m from each other to avoid interference between traps. In the Leitha floodplain only four light traps were used because of the small size of remaining forest fragments. Automatic low-power light traps, each equipped with two 15 W lamps (Sylvania Blacklight-Blue, F15W/BLB-T8; and Philips TLD, 15W/05) and powered by a 12V car battery were placed about 1 m above ground under a closed forest canopy and run once a month during the vegetation period (March to November) at each of the 28 sites. Light traps within one habitat were operated simultaneously. At dusk the light was automatically switched on and run for about 6 hours. All 6 forest habitats were sampled on consecutive days, or as soon as possible if spells of unfavourable weather had to be avoided. Traps were never run during the 5 days before and after full moon to avoid any negative impact of moonlight on trap catches. Sampling did not take place during rainy weather, in which cases sampling was postponed until conditions improved, i.e. sampling was carried out on the next possible night with better weather conditions. Altogether, sampling was conducted over two complete annual cycles on 103 nights between 20.VIII.2006 and 24.VIII.2008. The sampling season ended with the first incidence of frost in autumn (last sampling dates: 26.XI.2006 and 08.XI.2007) and started again at spring time (first sampling dates: 26.III.2007 and 07.IV.2008). In all, data from 442 nightly trap samples were analysed. The number of moths caught during a single trap night ranged from 0 to 1092 (site MF5, 08.VIII.2007) individuals. Eighteen nightly trap samples did not contain any moths, likely due to cold temperatures and generally low moth activity in March, April, October and November. Three further samples did not contain moths due to equipment failure. Further information: Truxa, C. 2012. Community ecology of moths in floodplain forests of Eastern Austria. Doctoral dissertation, University of Vienna. URL: http://othes.univie.ac.at/25605

The trinity of ecological contrasts: a case study on rich insect assemblages by means of species, functional and phylogenetic diversity measures

Abstract Background The ‘classical’ concept of species diversity was extended in the last decades into other dimensions focusing on the functional and phylogenetic diversity of communities. These measures are often argued to allow a deeper understanding of the mechanisms shaping community assembly along environmental gradients. Because of practical impediments, thus far only very few studies evaluated the performance of these diversity measures on large empirical data sets. Here, data on species-rich riparian moth communities under different flood regimes and from three different rivers has been used to compare the power of various diversity measures to uncover ecological contrasts. Results Contrary to the expectation, classical metrics of species diversity (Hill numbers N1, N2 and Ninf) and evenness (Buzas-Gibson’s E and Pielous’s J) turned out to be the most powerful measures in unravelling the two gradients investigated in this study (e.g. flood regime and region). Several measures of functional and phylogenetic diversity tended to depict either only one or none of these contrasts. Rao’s Q behaved similarly as species diversity and evenness. NTI and NRI showed a similar pattern among each other but, were different to all the other measures. Functional Divergence also behaved idiosyncratically across the 28 moth communities. The community weighted means of nearly all individual functional traits showed significant ecological patterns, supporting the relevance of the selected traits in shaping assemblage compositions. Conclusions Species diversity and evenness measures turned out to be the most powerful metrics and clearly reflected both investigated environmental contrasts. This poses the question when it is useful to compile the additional data necessary for the calculation of additional diversity measures, since assembling trait bases and community phylogenies often requires a high work load. Apart from these methodological issues, most of the diversity measures related to communities of terrestrial insects like moths increased in forests that still are subject to flooding dynamics. This emphasizes the high conservation value of riparian forests and the importance of keeping and restoring river dynamics as a means of fostering also terrestrial biodiversity in floodplain areas

Additional file 1: of Stable isotope signatures reflect dietary diversity in European forest moths

Supplementary material. Table S1A. Number of substrate and moth samples taken per species and feeding guild. To level out variability between moth individuals, each sample consisted of the wings of 3–5 moth specimens (depending on body size of the species), so that each sample had a mass of 1–2 mg. The nomenclature of moths follows Fauna Europaea ( http://fauna.naturkundemuseum-berlin.de ). Figure S1A. Fraction of 15N relative to 14N for each moth species. Taxa are ordered by feeding guild and red coloration represents the overall mean for the respective guild aggregated across constituent species. Symbols represent the mean and whiskers the standard deviation for each group. Among the lichen-feeding species, L. quadra was evaluated separately from the remaining taxa due to its deviant nitrogen signature. Figure S2A. Fraction of 13C relative to 12C for each moth species. Taxa are ordered by feeding guild and red coloration represents the overall mean for the respective guild aggregated across constituent species. Symbols represent the mean and whiskers the standard deviation for each group. Among the lichen-feeding species, L. quadra was evaluated separately from the remaining taxa due to its deviant nitrogen signature. (PDF 860 kb

Stable isotopes - Raw data

<div>Raw Data  - stable isotopes (moths):</div>Stable isotope fractions (¹³C and ¹⁵N) and C/N ratios for 47 species of moth (Lepidoptera) caught by light trapping in the Danube floodplain forest near Vienna, Austria. specimens fall into eight larval dietary guilds (i.e. aquatic plants, grasses, herbaceous plants, lichens, decaying foliage of (mostly) woody plants, mosses, reeds, and roots).<div><br></div><div>Raw Data  - stable isotopes (substrate):</div><div>Stable isotope fractions (¹³C and ¹⁵N) and C/N ratios for 27 types of substrate corresponding to the eight dietary groups outlined above. Samples were likewise taken from the Danube floodplain forest near Vienna, Austria.</div