September 2018

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English summaries

    • Fauna in the margins: chances around nutrient-poor nature areas
    • M.E. Nijssen, M. Geertsma, J.T. Kuper, G.A. van Duinen & R. Versluijs
    • Many animal species, mainly insectivores and flower visiting insects, which live in relative nutrient poor landscapes such as peat bogs and heathlands have a high need for food resources. Species like Red-backed shrike, Whinchat and Spotted crake live in deteriorated heathlands and bogs, where food availability is higher than under natural conditions. Restoration measures within the areas should be combined with restoration or development of rich borders on former arable land to facilitate these species. Within these borders most invertebrate prey biomass is found in mesotrophic grasslands, while flower abundancy is higher in more oligotrophic conditions. A variation in nutrient status of the borders is favourable for facilitating animal species in these landscapes.

    • Food chain reveals habitat demands of Dytiscus latissimus
    • H.H. van Kleef, G. van Dijk, I. Scholten, E. Schreurs & J. Brouwer
    • In recent years the Dutch population of the internationally threatened and protected dytiscid beetle Dytiscus latissimus has declined with approximately 85%, leaving only a few dozen adult individuals. Measures for protection, restoration and development of the species habitat are needed. However, its ecology was insufficiently known. Here we describe the habitat requirements using expert surveys, field and laboratory studies. Female beetles insert the eggs in macrophytes, mainly Menianthes trifoliata and Carex rostrata. Swards of these species are also present where the larvae grow up. The larvae need to grow faster than related species. This is possible because the larvae have a relatively high metabolism and are specialised hunters for caddisflies. These caddisflies are not eaten by other potential competitors. A beetle larva requires large numbers of caddisflies, we estimate around 200, to become a fully-grown water beetle. The caddisflies in turn require overhanging branches and the algae on leaf litter of birch and buckthorn as larval nourishment. Larval habitat of D. latissimus should therefor be near caddisfly habitat. Current threats are succession towards oligotrophic bog vegetation and nature management (i.e. clearing of shorelines from trees and shrubs) as both reduce caddisfly numbers. Nature management consisting of stimulating initial succession of macrophytes for ovipositioning and larval habitat, in combination with restoring shallow water with leaf litter input for a healthy prey population, is required to improve and restore habitat of D. latissimus and prevent the species extinction. 

    • From soil restoration to restoring heathland fauna in acidified heathland landscapes
    • J.J. Vogels, M.J. Weijters, H.L.T. Bergsma, R. Bobbink, H. Siepel, J. Smits & L. Krul
    • The traditional restoration tool to counteract soil acidification in Dutch heathland landscapes is the application of dolomite lime. Although proven effective in restoring soil buffering status and vascular plant species richness, invertebrate response to liming can be unfavourable. This is thought to arise from newly introduced nutrient imbalances at the micro- and/or macronutrient level. Therefore, alternative restoration methods using slow release soil buffering agents have been investigated. These slow release agents consist of finely ground igneous rocks (rock dust) and release a broad spectrum of cations and micro-nutrients more gradually to the soil through mineral weathering processes. We compared faunal response to addition of several slow-release agents, a control situation and liming. Three years after application, the first results regarding fauna response are promising. No consistent major negative side-effects of rock dust application have been identified in any of the field trials. Evidence for contrasting effects of rock dust application (positive) and liming (negative) on fauna were found in experiments performed in soils with low soil organic matter and hence, low soil CEC and overall nutrient availability. Here, detritivores decreased significantly as a result of liming treatment and herbivores increased significantly as a result of rock dust (Biolit) treatments. Under conditions of high soil organic matter content, effects on fauna were much less pronounced and not significantly different from control. Here, only a significant shift in Carabid beetle community composition was identified, most probably as a result of interactive effects of lime application with cattle grazing pressure, which unintentionally seemed to increase as a result of the lime and Biolit treatments. The first results indicate that it is beneficial to use rock dust as an alternative management practice. All experimental results as of now only encompass short term effects, treatment effects in the medium to long term are very much needed to draw definitive conclusions. It is becoming increasingly clear however, that traditional liming in soils poor in organic matter (i.e. sod cut soils) should be used with caution as unfavourable effects on fauna can hamper fauna conservation and restoration.

    • Year of the lapwing
    • W.A. Teunissen & H. van der Jeugd
    • Meadow birds have decreased at an alarming rate, including the northern lapwing. To draw more attention to this still numerous but rapidly declining species, 2016 was declared ‘the year of the lapwing’. We compared the survival of lapwing chicks from hatching to fledging in relation to land use (grassland versus arable land) and specific measures that are taken to improve the conditions for growing lapwing chicks. 300 and 613 lapwing chicks were fitted with plastic leg flags with an unique inscription in 2016 and 2017 respectively, to follow individual lapwing chicks during the fledging period. Volunteer ring readers as well as professional workers provided resightings that were analysed using a capture-mark-resighting model. Lapwing chicks were in slightly better condition on grassland with measures, but there was no difference on arable land. Survival was lower during the first week after hatching compared to later in the fledging period, and was somewhat higher on arable land compared to grassland, and marginally higher in control areas compared to areas with specific measures. The results were hard to interpret given many other factors and interactions that contributed to the model. Overall, survival until fledging was 10-14% in 2016 and 9-10% in 2017. Given a hatching success of 65% and a clutch size of 3.5, these figures are much below what is needed for a stable population. Availability of prey items was studied using pitfall traps. The number of prey items as well as the ash-free dry weight of prey declined during the season, but was always higher on grassland compared to arable land. A lack of food for the growing chicks may be a crucial factor explaining the consistently low survival of lapwing chicks and the population decline.

    • How nutritious is food in our forests?
    • A.B. van den Burg
    • Animal life depends on food of sufficient quality. One important aspect of food quality is that an animal should be able to extract sufficient essential nutrients from its entire diet. These are compounds which animals cannot produce by themselves, more specifically minerals, vitamins and some of the amino acids. However, as a result of soil acidification and nitrogen deposition, forest ecosystems on nutrient-poor soils have become increasingly mineral limited whilst facing excessive amounts of nitrogen. These unnatural conditions result in changing plant physiology and deteriorating food quality for herbivores. In some cases, such food quality issues are further propelled into the food chain up to the level of top-predators. Problems concerning food quality are in this paper illustrated centered upon a mineral (calcium), a vitamin (B2) and amino acids. Calcium shortages due to acidification and mineral leaching result in declining snail numbers and hence poor egg formation and poor fledgling numbers in some bird species. Other species, which differ only slightly in diet, supplement their diet with alternative calcium-rich prey, as to avoid calcium deficiency. Whereas top predators such as Sparrowhawks in nutrient-poor forests showed signs of vitamin B2 deficiency, the  underlying mechanism was failure to accumulate vitamin B2, which depends on amino acids. Amino acid and protein formation were reduced in forests which were mineral limited and received high levels of nitrogen deposition. As amino acids are irretrievably used at each level in the food chain, also (or especially) top-predators are vulnerable to amino acid deficiencies. Sparrowhawks declined greatly in numbers and were limited in their reproduction by particular amino acids, especially cysteine. Whereas diurnal birds of prey incur amino acid deficiencies, this is not the case in owls. Unlike raptors, owls possess caecal blind sacs in which uric acid is transformed to amino acids, the composition of which benefits egg formation better compared to other protein sources available to owls. So, soil acidification and nitrogen deposition cause alterations of food quality throughout the forest ecosystem, but the vulnerability of particular species depends on ‘details’ in their ecology, behavior and physiology. Food quality in nutrient poor forests  is declining and we know enough to conclude that pressures of soil acidification and nitrogen deposition should be lifted to ensure future restoration and survival of our forest wildlife communities.

    • Protecting species of higher trophic levels is a puzzle
    • D. Bal
    • Vertebrates and other species of higher trophic levels play an important role in the protection of Natura 2000 sites. In management plans the requirements for all the different species are taken seriously. The knowledge summarized in the recovery strategies proved to be of key importance for that process. But combining necessary measures forms a difficult puzzle.

    • Are bats disturbed by festival music?
    • J.T. Oudega, R. Janssen, A. van Hooff & R. Delbroek
    • Humans may experience music festivals as disturbing noises, specifically when it concerns a high volume of low frequency sounds. Low frequencies, such as the thumping of the bass, have a large noise transmission, and are perceptible from long distances. Humans can hear these tones, but bats cannot. It is, however, not the case that bats are never disturbed by noise. Experiments in which bats were allowed to choose whether to forage in rooms with noise or without noise, have indicated that bats preferred the noise-free room. Noise also affected prey detection and capture rate (Schaub et al., 2008; Siemers & Schaub, 2011). However, a field study towards the behavior of the common long-eared bat (Plecotus auritus), at the time of the Airforce Festival 2017, has concluded that these bats were not disturbed by the music festival (Janssen et al., 2017). The most noticeable difference between the experiment in laboratory setting and the field work was that the sounds used in the experiment were of much higher frequency and at louder volume than the music at the festival. Additionally, during the festival, the range of perceptible frequencies for bats (from 8 KHz) was limited. The authors have not been able to show the existence of a threshold for the volume (dB) at the 8 kHz frequency at which the bats may be disturbed. The conclusions from the field study cannot be generalized to other festival situations, as circumstances like sound range, lightning, terrain set-up and presence of alternative foraging areas may differ. An assessment of possible negative influence remains crucial. Our study provides a good basis for judgement of noise effects on bats. It highlights that it is necessary to distinguish the sound volumes and ranges of frequencies audible for bats.  

    • Towards a base-level for habitat quality
    • R.G.M. Kwak, A.B. van den Burg, G.J.G. Dommerholt, A.R. van Kreveld, A.H.F. Stortelder & R.P.A. van Wijngaarden
    • Populations of (formerly) common species, from insects to birds, are declining in the Netherlands. Apparently, the quality of their habitats has become insufficient across large surface areas. To counteract these declines, we should have a base-level for habitat quality for all landscapes in the Netherlands, so besides nature reserves also agricultural and build-up areas. We define this base-level per landscape type as the set of environmental and landscape characteristics which allows the development of the plant and animal community which typically belongs to that landscape. Many of the remedies to take away the bottlenecks to achieve a base level of habitat quality are no-regret measures, but are not incorporated in landscape management policies and practices. So, ecologists should get themselves more involved in the appropriate decision making processes. This includes the Dutch agricultural system, changes in which are crucial for the protection and restoration of biodiversity. In four municipalities it was investigated if the concept of a base-line for habitat quality was a useful framework for managers to direct their landscape conservation and restoration efforts. So far, this resulted in 18 issues which will be further addressed by concrete action plans. Linking the prerequisites for biodiverse environments to all Dutch landscape types can direct and structure many existing and forthcoming initiatives for nature restoration in the Netherlands.