Time filter

Source Type

Nijmegen, Netherlands

Van Oosten H.H.,Bargerveen Foundation | Van Oosten H.H.,Radboud University Nijmegen | Emtsev A.A.,Surgut State University
Ardea | Year: 2013

The Yellow Wagtail Motacilla flava consists of about 18 taxa whose taxonomic relationships are unclear. Some authors elevate 11 taxa to species based on often characteristic nuptial plumages of males, whereas others recognize two species based on molecular data. Hybridization is a regular event but with intriguingly varying intensity between different taxa. In spite of breeding generally in damp fields, their breeding habitat is actually rather diverse, which offers an opportunity for ecological segregation by breeding habitat. Indeed, some authors describe habitat differences between taxa but others do not. Two sympatrically occurring taxa are thunbergi and beema in European Russia and Western Siberia. In this study we describe their breeding habitat and determine whether this differs between taxa. We aimed to determine whether breeding habitat could be an ecological factor for sub-specific segregation in this part of their breeding range. We found strong indications for segregated breeding, despite the rather limited dataset: thunbergi occurred in bogs as a breeding bird and beema was dominantly found breeding in floodplain meadows. On one location bog and floodplain were separated by only 1.5-2 km of forest, yet here too only thunbergi occurred on the bog and beema on floodplain meadows. Following recent molecular taxonomic findings our thunbergi might very well concern plexa, belonging to the eastern species. As beema is assigned to the western species, the observed spatial segregation between plexa and beema may be representative of habitat separation of the western and eastern species in areas where they occur sympatrically. Large scale segregated breeding due to different habitat preferences could have consequences for taxonomic interpretations within the M. flava complex. Source

van Kleef H.H.,Bargerveen Foundation | Jongejans E.,Radboud University Nijmegen
Aquatic Invasions | Year: 2014

Pumpkinseed (Lepomis gibbosus) is listed among the most invasive fish species and has been demonstrated to have adverse impact on native species when present in high numbers. However, not all introductions result in high density populations. There are several possible underlying mechanisms behind this variation in population density (e.g. water quality, availability of nesting substratum and biotic interactions), but their relative importance remains poorly known. With this in mind, we studied vital rates (i.e. growth, maturation and reproduction) of pumpkinseed in 19 isolated standing waters of different pumpkinseed density. The fish were collected in early summer to determine their density, sex, age, growth and reproductive effort as well as environmental variables (i.e. availability of nesting substratum, acidity, nutrient concentrations, fish assemblage structure). To construct a population projection model with which to assess the relative importance of each vital rate for the growth of the populations, a stable population structure was assumed. Most environmental variables that affected vital rates (e.g. pH effect on individual growth) had little effect on population growth, or the associations were spurious (e.g. the negative effect of nesting substratum availability on gonad production). The environmental effects were dictated by a strong density dependent feedback of pumpkinseed density on the growth of age 2 fish, and gonad size and maturation state. This finding has important repercussions for management of pumpkinseed invasions: if only part of the population is removed or if complete eradication is followed by a re-introduction, then the population will rapidly recover to its former size. It was not possible to identify environmental drivers of pumpkinseed survival because the data had to be pooled across populations in order to estimate survival rates. However, a negative correlation was found between pumpkinseed and predator density, indicating that predator-induced mortality may be key in determining pumpkinseed invasiveness. Although the measure still needs thorough evaluation, introduction of native piscivores, especially northern pike (Esox lucius), may be a suitable way to prevent pumpkinseed from becoming the dominant species and reduce damage to local biodiversity. © 2014 The Author(s). Journal compilation. Source

van Klink R.,University of Groningen | van der Plas F.,University of Groningen | van Noordwijk C.G.E.T.,Bargerveen Foundation | van Noordwijk C.G.E.T.,Radboud University Nijmegen | And 4 more authors.
Biological Reviews | Year: 2015

Both arthropods and large grazing herbivores are important components and drivers of biodiversity in grassland ecosystems, but a synthesis of how arthropod diversity is affected by large herbivores has been largely missing. To fill this gap, we conducted a literature search, which yielded 141 studies on this topic of which 24 simultaneously investigated plant and arthropod diversity. Using the data from these 24 studies, we compared the responses of plant and arthropod diversity to an increase in grazing intensity. This quantitative assessment showed no overall significant effect of increasing grazing intensity on plant diversity, while arthropod diversity was generally negatively affected. To understand these negative effects, we explored the mechanisms by which large herbivores affect arthropod communities: direct effects, changes in vegetation structure, changes in plant community composition, changes in soil conditions, and cascading effects within the arthropod interaction web. We identify three main factors determining the effects of large herbivores on arthropod diversity: (i) unintentional predation and increased disturbance, (ii) decreases in total resource abundance for arthropods (biomass) and (iii) changes in plant diversity, vegetation structure and abiotic conditions. In general, heterogeneity in vegetation structure and abiotic conditions increases at intermediate grazing intensity, but declines at both low and high grazing intensity. We conclude that large herbivores can only increase arthropod diversity if they cause an increase in (a)biotic heterogeneity, and then only if this increase is large enough to compensate for the loss of total resource abundance and the increased mortality rate. This is expected to occur only at low herbivore densities or with spatio-temporal variation in herbivore densities. As we demonstrate that arthropod diversity is often more negatively affected by grazing than plant diversity, we strongly recommend considering the specific requirements of arthropods when applying grazing management and to include arthropods in monitoring schemes. Conservation strategies aiming at maximizing heterogeneity, including regulation of herbivore densities (through human interventions or top-down control), maintenance of different types of management in close proximity and rotational grazing regimes, are the most promising options to conserve arthropod diversity. © 2014 The Authors. Biological Reviews published by John Wiley & Sons Ltd on behalf of Cambridge Philosophical Society. Source

Vermonden K.,Radboud University Nijmegen | Vermonden K.,Copenhagen University | Brodersen K.P.,Copenhagen University | Jacobsen D.,Copenhagen University | And 4 more authors.
Journal of the North American Benthological Society | Year: 2011

Interest in the biodiversity value of urban waters is growing. Understanding key ecological processes is essential for effective management of these aquatic ecosystems. Our paper focuses on identifying the key factors that structure chironomid assemblages, such as water quality and dredging, in urban waters strongly influenced by seepage of large rivers. Chironomid assemblages were studied in urban surface-water systems (man-made drainage ditches) in polder areas along lowland reaches of the rivers RhineMeuse in The Netherlands. Multivariate analysis was used to identify the key environmental factors. Taxon richness, Shannon index (H′), rareness of species, and life-history strategies at urban locations were compared with available data from similar man-made water bodies in rural areas, and the effectiveness of dredging for restoring chironomid diversity in urban waters was tested. Three different chironomid associations were distinguished by Two-Way Indicator Species Analysis. Variation within and among chironomid associations were significantly related to substrate (sludge layer and substrate type: sand vs clay), % cover of lemnids, submerged vegetation, filamentous algae, and water transparency. Chironomid taxon richness and H′ were similar in urban and rural waters, probably because of their similar hydrologic, morphologic, and water-quality conditions and their similar dredging and weed-control regimes. Rareness was slightly higher in urban than in rural waters. In urban water systems, chironomid taxon richness was negatively related to sludge layer and % cover of lemnids. Dredging changed chironomid species composition, and increased taxon richness and life-history strategies indicative of good O2 conditions. Therefore, dredging can be regarded as an effective measure to restore diversity of chironomid communities in urban waters affected by nutrient-rich seepage or inlet of river water. © 2011 by The North American Benthological Society. Source

Van Noordwijk C.G.E.,Radboud University Nijmegen | Van Noordwijk C.G.E.,Ghent University | Verberk W.C.E.P.,Radboud University Nijmegen | Turin H.,Loopkeverstichting SFOC | And 16 more authors.
Ecology | Year: 2015

In the face of ongoing habitat fragmentation, species-area relationships (SARs) have gained renewed interest and are increasingly used to set conservation priorities. An important question is how large habitat areas need to be to optimize biodiversity conservation. The relationship between area and species richness is explained by colonization-extinction dynamics, whereby smaller sites harbor smaller populations, which are more prone to extinction than the larger populations sustained by larger sites. These colonization-extinction dynamics are predicted to vary with trophic rank, habitat affinity, and dispersal ability of the species. However, empirical evidence for the effect of these species characteristics on SARs remains inconclusive. In this study we used carabid beetle data from 58 calcareous grassland sites to investigate how calcareous grassland area affects species richness and activity density for species differing in trophic rank, habitat affinity, and dispersal ability. In addition, we investigated how SARs are affected by the availability of additional calcareous grassland in the surrounding landscape. Beetle species richness and activity density increased with calcareous grassland area for zoophagous species that are specialists for dry grasslands and, to a lesser extent, for zoophagous habitat generalists. Phytophagous species and zoophagous forest and wet-grassland specialists were not affected by calcareous grassland area. The dependence of species on large single sites increased with decreasing dispersal ability for species already vulnerable to calcareous grassland area. Additional calcareous grassland in the landscape had a positive effect on local species richness of both dry-grassland specialists and generalists, but this effect was restricted to a few hundred meters. Our results demonstrate that SARs are affected by trophic rank, habitat affinity, and dispersal ability. These species characteristics do not operate independently, but should be viewed in concert. In addition, species' responses depend on the landscape context. Our study suggests that the impact of habitat area on trophic interactions may be larger than previously anticipated. In small habitat fragments surrounded by a hostile matrix, food chains may be strongly disrupted. This highlights the need to conserve continuous calcareous grassland patches of at least several hectares in size. © 2015 by the Ecological Society of America. Source

Discover hidden collaborations