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Chumak, V., Duelli, P., Rizun, V., Obrist, M.K., Wirz, P. (2005) Arthropod biodiversity in virgin and managed forests in Central Europe. Forest, Snow and Landscape Research. 79:101-109.
The species composition of arthropods was used for a pair-wise comparison of the biodiversity in virgin forests of the Ukrainian Carpathians and managed Swiss forests with similar tree species composition. In both countries, pure beech forests and fir-spruce-beech forests were assessed at comparable altitudes and exposures. Both types of extensively managed forests in Switzerland yielded slightly more species and considerably more individuals in most arthropod taxa than their virgin counterparts in Transcarpatia. On the other hand, the Shannon index of diversity and evenness were almost consistently higher in the Ukrainian virgin forests. Separating the collected arthropods into trophic groups highlights the Saprophaga and Xylophaga as indicators for natural or virgin forests. The size spectrum of the predatory carabid beetles was much broader in virgin forests than in managed forests; both large and very small species were lacking in the managed forests in Switzerland, indicating a limited potential for ecosystem functions.
Duelli, P., Chumak, V., Obrist, M.K., Wirz, P. (2005) The biodiversity values of European virgin forests. Forest, Snow and Landscape Research. 79:91-99.
The species composition of arthropods was used for a pair-wise comparison of the biodiversity in virgin forests of the Ukrainian Carpathians and managed Swiss forests with similar tree species composition. In both countries, pure beech forests and fir-spruce-beech forests were assessed at comparable altitudes and exposures. Both types of extensively managed forests in Switzerland yielded slightly more species and considerably more individuals in most arthropod taxa than their virgin counterparts in Transcarpatia. On the other hand, the Shannon index of diversity and evenness were almost consistently What makes virgin forests better forests? Biodiversity evaluation depends on the value systems of the stakeholders involved. Indicators for conservation value, ecosystem functions, wilderness, uniqueness, or species richness may not correlate, or even correlate negatively. Based on arthropod data from a comparative study in two types of virgin forests in core areas of the Carpathian Biosphere Reserve in Ukraine and managed forests in Switzerland with matching tree species composition, several biodiversity aspects and their underlying value systems are presented and discussed. There were no significant differences in species richness between virgin and managed forests. Most arthropod groups tended to be more divers in managed forests, while saproxylic beetles, and fungi, millipedes and molluscs were more divers in virgin forests.The most obvious assets of virgin forests in terms of biodiversity values are wilderness and uniqueness. The conservation value, focussing on rare and threatened species, seems to be of lesser importance in Central European virgin forests. Other values of forest biodiversity such as species richness and ecosystem functions are unsuitable for valorising virgin forests in comparison to managed forests.
Moretti, M., Obrist, M.K., Duelli, P. (2004) Arthropod biodiversity after forest fires: Winners and losers in the winter fire regime of the Southern Alps. Ecography. 27:173-186.
Since prehistoric times, natural and man made fires have been important factors of natural disturbance in many forest ecosystems, like those on the southern slopes of the Alps. Their effect on scarce, endangered or stenotopic species and on the diversity of invertebrate species assemblages which depend on a mosaic of successional habitat stages, is controversially discussed. In southern Switzerland, in a region affected by regular winter fires, we investigated the effect of the fire frequency on a large spectrum of taxonomic groups. We focussed on total biodiversity, taxonomic groups specific to certain habitat types, and on scarce and endangered species. Overall species richness was significantly higher in plots with repeated fires than in the unburnt control sites. Plots with only one fire in the last 30 yr harboured intermediate species numbers. Fire frequency had a significantly positive effect on species richness of forest edge specialists. Species of open landscape, open forests and interior forests were not influenced by fire frequency. A positive effect of fire on species richness was observed for ground beetles (Carabidae), hoverflies (Syrphidae), bees and wasps (Hymenoptera aculeata, without Formicidae), and spiders (Araneae). True bugs (Heteroptera), lacewings (Neuroptera) and the saproxylic beetle families Cerambycidae, Buprestidae and Lucanidae showed positive trends, but no statistically significant effects of fire on species numbers or/and abundances. Negative effects of fire on species numbers or/and abundances were found only for isopods and weevils (Curculionidae). A compromise for forest management is suggested, which considers the risk of damage by fire to people and goods, while avoiding the risk of damage to biodiversity by imitating the effects of sporadic fires and providing a mosaic forest with open gaps of different successional stages.
Obrist, M.K., Boesch, R., Flückiger, P.F. (2004) Variability in echolocation call design of 26 Swiss bat species: consequences, limits and options for automated field identification with a synergetic pattern recognition approach. Mammalia. 68:307-322.
Pattern recognition algorithms offer a promising approach to recognizing bat species by their echolocation calls. Automated systems like synergetic classifiers may contribute significantly to operator-independent species identification in the field. However, it necessitates the assembling of an appropriate database of reference calls, a task far from trivial. We present data on species specific flexibility in call parameters of all Swiss bat species (except Nyctalus lasiopterus and Plecotus alpinus). The selection of 'training-calls' for the classifier is crucial for species identification success. We discuss this in the context of echolocation call variability differing between species and its consequences for the implementation of an automated, species specific bat activity monitoring system.
Moretti, M., Obrist, M.K., Duelli, P. (2004) Arthropod biodiversity after forests fires: Winners and losers in the winter fire regime of the Southern Alps. Ecography. 27:173-186 Since prehistoric times, natural and man made fires have been important factors of natural disturbance in many forest ecosystems, like those on the southern slopes of the Alps. Their effect on scarce, endangered or stenotopic species and on the diversity of invertebrate species assemblages which depend on a mosaic of successional habitat stages, is controversially discussed. In southern Switzerland, in a region affected by regular winter fires, we investigated the effect of the fire frequency on a large spectrum of taxonomic groups. We focussed on total biodiversity, taxonomic groups specific to certain habitat types, and on scarce and endangered species. Overall species richness was significantly higher in plots with repeated fires than in the unburnt control sites. Plots with only one fire in the last 30 yr harboured intermediate species numbers. Fire frequency had a significantly positive effect on species richness of forest edge specialists. Species of open landscape, open forests and interior forests were not influenced by fire frequency. A positive effect of fire on species richness was observed for ground beetles (Carabidae), hoverflies (Syrphidae), bees and wasps (Hymenoptera aculeata, without Formicidae), and spiders (Araneae). True bugs (Heteroptera), lacewings (Neuroptera) and the saproxylic beetle families Cerambycidae, Buprestidae and Lucanidae showed positive trends, but no statistically significant effects of fire on species numbers or/and abundances. Negative effects of fire on species numbers or/and abundances were found only for isopods and weevils (Curculionidae). A compromise for forest management is suggested, which considers the risk of damage by fire to people and goods, while avoiding the risk of damage to biodiversity by imitating the effects of sporadic fires and providing a mosaic forest with open gaps of different successional stages.
Duelli, P., Obrist, M.K. (2003) Biodiversity indicators: the choice of values and measures. Agriculture, Ecosystems and Environment. 98:87-98
Ideally, an indicator for biodiversity is a linear correlate to the entity or aspect of biodiversity under evaluation. Different motivations for assessing entities or aspects of biodiversity lead to different value systems; their indicators may not correlate at all. For biodiversity evaluation in agricultural landscapes, three indices are proposed, each consisting of a basket of concordant indicators. They represent the three value systems 'conservation' (protection and enhancement of rare and threatened species), 'ecology' (ecological resilience, ecosystem functioning, based on species diversity), and 'biological control' (diversity of antagonists of potential pest organisms). The quality and reliability of commonly used indicators could and should be tested with a three-step approach. First, the motivations and value systems and their corresponding biodiversity aspects or entities have to be defined. In a time consuming second step, a number of habitats have to be sampled as thoroughly as possible with regard to one or several of the three value systems or motivations. The third step is to test the linear correlations of a choice of easily measurable indicators with the entities quantified in the second step. Some examples of good and bad correlations are discussed.
Duelli, P., Obrist, M.K. (2003) Monitoring biodiversity in agricultural landscapes: the dilemma of conflicting value systems and indicators. In: Proccedings of the Proceedings of the 5th meeting of the European Platform for Biodiversity Research Strategy, Brussels. 170-174.
Various biodiversity indicators are currently in use, but none of them have been tested for their correlation with the particular aspect or entity of biodiversity that they are meant to indicate. We propose a procedure to design value-specific indicator sets based on the main motivations of stakeholders to protect or enhance biodiversity in cultivated landscapes: species conservation, ecological resilience, and ecosystem functioning such as biological control or pollination. The approach includes the following steps: 1. Defining the value systems and measuring the appropriate aspects and entities as thoroughly and comprehensively as possible in national test areas for biodiversity assessment. 2. Measuring or calculating (by rarefaction) all kinds of indicators within the test areas and correlate their values with the "reality" of the assessed value systems. 3. Group the best concordant indicators into value baskets to form an index, e.g. the "biodiversity index for conservation".
Duelli, P., Obrist, M.K. (2003) Regional biodiversity in an agricultural landscape: The contribution of seminatural habitat islands. Basic and Applied Ecology. 4:129-138
An important goal of ecological compensation measures in agricultural areas is the conservation and enhancement of regional species diversity. However, some current European agri-environment schemes seem to be rather ineffective. A likely explanation is the lack of source populations in intensely cultivated landscapes. Remnants of natural and seminatural habitats can contribute to regional biodiversity in various ways: as essential habitats for specialised species, as stepping stones, and as temporary habitats for hibernation, larval development, or preovipository feeding. The overall percentage of arthropod species, for which seminatural habitats are an essential prerequisite for living in an agricultural landscape, was assessed with a 5 km long transect of 18 standardised trapping stations. The transect extended from an isolated area of wetland through intensely managed crop fields and grassland to an isolated semiarid meadow bordered by mixed forest. For more than 1000 arthropod species the spatial and temporal distribution of a one year's catch along the transect was interpreted with regard to their affinity to seminatural habitats. Experts were asked to judge questionable cases of apparent ubiquist species. All in all, more than 63% of all animal species (except for soil and water fauna) living in the agriculturally managed areas of the Limpach valley seem to depend on the presence of seminatural habitats. We conclude that remnant islands of natural or seminatural habitats provide the most important source populations for agri-environment schemes in order to enhance biodiversity in an otherwise depleted agricultural landscape.
Duelli, P., Obrist, M.K., Wermelinger, B. (2002) Wind-throw induces changes of faunistic biodiversity in alpine spruce forests. Forest, Snow and Landscape Research: "Special Issue 10 Years Windthrow Research After Vivian 1990". 77:117-131
After the severe windthrow caused by the storm Vivian in 1990 in the Alps, political conflicts arose over the question whether clearing of the resulting gaps in the forest should be promoted and publicly subsidised. One argument against clearing was that uncleared windthrow areas would be better for the enhancement and conservation of biodiversity. In three regions in the Eastern Swiss Alps, the fauna was assessed for up to ten years after the storm in pairwise comparisons between cleared and uncleared windthrow areas and an intact managed forest control plot. A total of 1856 species of invertebrates, reptiles, and small mammals were collected and identified. Windthrow areas yielded 35–69% more animal species than the intact forest plot. Neither the number of arthropod species collected in flight and pitfall traps, nor the number of red-listed species showed any significant differences between cleared or uncleared plots. However, extrapolation of rarefaction functions to estimate total species numbers per plot revealed that a combination of cleared and uncleared areas enhances biodiversity significantly more (by 21–26%) than a single treatment. Combining the data on the fauna recorded in both treatments with those of the surrounding forest shows that the species richness in the new mosaic of forest and gaps has increased by 100% since the storm. During the observed period of succession following the first assessment after the storm, the species richness further increased by 17% in both treatments. Within ten years after the storm there was no sign of ecological resilience in the sense of a faunistic convergence back to the original species composition. Moreover, the fauna in the two treatments did not become more similar. Rather, it became less similar. The best way, therefore, to enhance biodiversity after a windthrow is to do both, clear one half of the windthrow and leaving the other half uncleared.
Wermelinger, B., Duelli, P., Obrist, M.K. (2002) Dynamics of saproxylic beetles (Coleoptera) on windthrow areas in alpine spruce forests. Forest, Snow and Landscape Research: "Special Issue 10 Years Windthrow Research After Vivian 1990". 77:133-148
Storms are important disturbance factors in the development of forest ecosystems. They trigger definite changes in vegetation composition and hence also in the associated insect fauna. Three windthrow areas created by the storm Vivian in 1990 in alpine spruce forests were each subdivided into a cleared and an uncleared treatment. The abundance of the three most frequent beetle families (Scolytidae, Cerambycidae, and Buprestidae) was monitored with two different trap types during six summer periods within the first 10 years after the windthrow.The large supply of breeding substrate triggered a distinct increase in insect abundance and in the species richness of this guild (except for the number of buprestid species) over a period of approximately five years. The first group reaching peak numbers were the Scolytidae (in 1992), followed by the Buprestidae (1994) and then by the Cerambycidae (1996). Ips typographus, the most important bark beetle, peaked in the third season after the storm (1992). The maximum numbers of saproxylic species were trapped in June/early July. In uncleared windthrow areas beetle abundance as well as species numbers were generally higher than in cleared treatments. In the windthrow areas, cerambycid and buprestid species were 30–500 times more abundant than in an adjacent intact forest. Their species number exceeded that in the forest 2–4 times.To promote saproxylic species in general as well as endangered species of saproxylics, some parts of windthrow areas should be cleared and others left uncleared. The controversy about protecting the forest and promoting biodiversity is discussed.
Parsons, S., Boonman, A.M., Obrist, M.K. (2000) Advantages and disadvantages of techniques for transforming and analyzing chiropteran echolocation calls. Journal of Mammalogy. 81:927-938
Bat researchers currently use a variety of techniques that transform echolocation calls into audible frequencies and allow the spectral content of a signal to be viewed and analyzed. All techniques have limitations and an understanding of how each works and the effect on the signal being analyzed are vital for correct interpretation. The 3 most commonly used techniques for transforming frequencies of a call are heterodyne, frequency division, and time expansion, Three techniques for viewing spectral content of a signal are zero-crossing, Fourier analysis, and instantaneous frequency analysis. It is important for bat researchers to be familiar with the advantages and disadvantages of each technique.
Duelli, P., Obrist, M.K., Schmatz, D.R. (1999) Biodiversity evaluation in agricultural landscapes: above-ground insects. Agriculture, Ecosystems and Environment. 74:33-64
In agriculture, sustainability can be linked to ecological resilience. In view of present or imminent environmental changes in agricultural landscapes, the diversity of species and genotypes, particularly of potential beneficials and alternative prey, may become of increasing importance. However, the available methods and empirical data concerning species diversity of above-ground insects in agricultural landscapes do not yet allow comprehensive evaluation. Standardized inventory methods must be used more rigorously and over longer time periods to detect significant differences in space and in time. Indicator groups for biodiversity estimates must be defined. Methods for optimizing the reliability and comparability of faunistic inventories are proposed, including rarefaction for reference functions and estimation of species numbers per unit area. Recommendations for optimum sampling periods and average empirical numbers for species diversity and abundance of major arthropod groups are given and compared to published data. In general, organismal biodiversity is higher in less intensely cultivated habitats. Apart from the impact of biocides, variation in species diversity often depends on the biodiversity of the surroundings (mosaic landscape) rather than on differing management regimes. The focus in preserving or enhancing, but also in evaluating biodiversity in cultivated areas thus should clearly be on the landscape level. Structural biodiversity in agricultural areas appears to be correlated with functional and organismal biodiversity of the above-ground insect fauna.
Duelli, P., Obrist, M.K. (1998) In search of the best correlates for local organismal biodiversity in cultivated areas. Biodiversity and Conservation. 7:297-309
Based on a transect consisting of 19 identical trap stations in cultivated areas and seminatural habitats, the correlation of species numbers of higher taxonomic groups with total species numbers of flowering plants and arthropods per trap site was calculated. A total of 191214 invertebrate specimens and 2221 species of plants and animals were analyzed. Considering both the height of the correlation coefficient R2 as well as the effort for sorting and identification, a "top twenty" list of indicator groups favors Heteroptera, flowering plants, Symphyta and aculeate Hymenoptera as the best choice for biodiversity evaluation. In general, flight traps rated better than pitfall traps. In most taxonomic groups, diversity indices such as the Shannon and the Simpson index were only weakly correlated with local species diversity.
Obrist, M.K., Wenstrup, J.J. (1998) Hearing and hunting in red bats (Lasiurus borealis, Vespertilionidae): Audiogram and ear properties. Journal of Experimental Biology. 201:143-154
We examined aspects of hearing in the red bat (Lasiurus borealis) related to its use of biosonar. Evoked potential audiograms, obtained from volume-conducted auditory brainstem responses, were obtained in two bats, and the sound pressure transformation of the pinna was measured in three specimens, Field-recorded echolocation signals were analysed for comparison, The fundamental sonar search calls sweep from 45 to 30 kHz (peak energy at 35 kHz), approach-phase calls sweep from 65 to 35 kHz (peak 40 kHz) and terminal calls sweep from 70 to 30 kHz (peak 45 kHz). The most sensitive region of the audiogram extended from 10 kHz to 45-55 kHz, with maximum sensitivity as low as 20 dB SPL occurring between 25 and 30 kHz, A relative threshold minimum occurred between 30 and 50 kHz. With increasing frequency, the acoustic axis of the pinna moves upwards and medially, The sound pressure transformation was noteworthy near 40-45 kHz; the acoustic axis was closest to the midline, the -3 dB acceptance angles showed local minima, and the pinna gain and interaural intensity difference were maximal, These results are related to the known echolocation and foraging behavior of this species and match the spectral components of approach-and final-phase calls, We conclude that coevolution with hearing prey has put a higher selective pressure on optimizing localization and tracking of prey than on improving detection performance.
Obrist, M.K., Duelli, P. (1996) Trapping efficiency of funnel- and cup-traps for epigeal arthropods. Mitteilungen der Schweizerischen Entomologischen Gesellschaft. 69:367-369
Catches of six different groups of arthropods, collected in four habitat types, were analysed for the efficiency of two types of pitfall traps: plastic cups and plastic funnels. An ANOVA indicates influences of trap type, habitat and systematic group (spiders stand out) on capture success (Tab. 2). Correlation analysis of numbers captured per cm trap diameter shows significant dependence of catches in cup and funnel traps. A regression analysis confirms linear correlation of the number of specimens captured in cup and funnel traps (Tabs. 3+4, Fig. 2). The Linyphiidae (spiders) and the Formicidae differ significantly from all other investigated groups in the slopes of their regression lines. Both trap types catch these two groups about equally efficiently. However, all other groups (including lycosid spiders) are caught 2-3 times more efficiently per cm trap diameter with funnel traps. Potential reasons for the differential capture success of the two trap-types are discussed. We recommend funnel traps for the collection of epigeal arthropods.
Fenton, M.B., Audet, D., Obrist, M.K., Rydell, J. (1995) Signal strength, timing, and self-deafening: The evolution of echolocation in bats. Paleobiology. 21:229-242
We propose that the ancestors of bats were small, nocturnal, sylvatic gliders that used echolocation for general orientation. Their echolocation calls were short, low intensify, broadband clicks, which translated into a very short operational range. In the lineage that gave rise to bats, a switch to stronger, tonal signals permitted the use of echolocation to detect, track, and assess flying insects in subcanopy settings. We propose that these animals hunted from perches and used echolocation to detect, track, and assess flying insects, which they attacked while gliding. In this way, the perfection of echolocation for hunting preceded the appearance of flapping flight, which marked the emergence of bats. Flapping flight had appeared by the Eocene when at least eight families are known from the fossil record. Stronger signals and adaptations to minimize self-deafening were central to the perfection of echolocation for locating flying prey. Echolocation constituted a key innovation that permitted the evolution and radiation of bats. At the same time, however, its short effective range imposed a major constraint on the size of bats. This constraint is associated with flight speed and the very small time intervals from detection of, and contact with a flying target. Gleaning and high duty cycle echolocation are two derived approaches to hunting prey in cluttered situations, places where echoes from background and other objects arrive before or at the same time as echoes from prey. Both had appeared by the Eocene.
Obrist, M.K. (1995) Flexible bat echolocation: the influence of individual, habitat and conspecifics on sonar signal design. Behavioral Ecology and Sociobiology. 36:207-219
Acoustic signals which are used in animal communication must carry a variety of information and are therefore highly flexible. Echolocation has probably evolved from acoustic communication, still serves such functions and could prove as flexible. Measurable variability can indicate flexibility in a behaviour. To quantify variability in bat sonar and relate it to behavioural and environmental factors, I recorded echolocation calls of Euderma maculatum, Eptesicus fuscus, Lasiurus borealis and L. cinereus while the bats hunted in their natural habitat. I analysed 3390 search phase calls emitted by 16 known and 16 unknown individuals foraging in different environmental and behavioural situations. All four species used mainly multiharmonic signals that showed considerable intra- and inter-individual variability in the five signal variables I analysed (call duration, call interval, highest and lowest frequency and frequency with maximum energy) and also in the shape of the sonagram. A nested multivariate analysis of variance identified the influences of individual, hunting site, close conspecifics and of each observation on the frequency with maximum energy in the calls, and on other variables measured. Individual bats differed in multiple comparisons, most often in the main call frequency and least often in call interval. In a discriminant function analysis with resubstitution, 56-76% of a species' calls were assigned to the correct individual. Distinct individual call patterns were recorded in special situations in all species and the size of foraging areas in forested areas influenced temporal and spectral call structure. Echolocation behaviour was influenced by the presence of conspecifics. When bats were hunting together, call duration decreased and call interval increased in all species, but spectral effects were less pronounced. The role of morphometric differences as the source of individually distinct vocalizations is discussed. I also examined signal adaptations to long range echolocation and the influence of obstacle distance on echolocation call design. My results allow to discuss the problems of echo recognition and jamming avoidance in vespertilionid bats.
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