J. Verboom

European Nuthatch Metapopulations in a Fragmented Agricultural Landscape

The European nuthatch Sitta europaea, which inhabits mature deciduous and mixed forest, has a fragmented distribution in the agricultural landscapes of Western Europe. Nuthatches have a high site fidelity, which makes them potentially sensitive to fragmentation. In earlier studies patch area and isolation were found to be related to nuthatch distribution pattern. In this paper, three times series of occurrence data are analysed to assess the effects of patch size (carrying capacity), habitat quality and isolation on the processes of local extinction and colonization.The results are interpreted in terms of a modified Levins metapopulation model, with patches of unequal size and habitat quality and effects of inter-patch distance and configuration.A method is presented to estimate the parameters of this model

Landscape cohesion: an index for the conservation potential of landscapes for biodiversity

In urbanising landscapes, planning for sustainable biodiversity occurs in a context of multifunctional land use. Important conditions for species persistence are habitat quality, the amount and configuration of habitat and the permeability of the landscape matrix. For planning purposes, these determinants should be integrated into simple indicators for spatial conditions of persistence probability. We propose a framework of three related indices. The cohesion index is based on the ecology of metapopulations in a habitat network. We discuss how an indicator for species persistence in such a network could be developed. To translate this network index into an area index, we propose the concept of spatial cohesion. Habitat cohesion and spatial cohesion are defined and measured for single species or, at best, for species profiles. Since species differ in their perception of the same landscape, different species will rate different values of these indices for the same landscape. Because landscapes are rarely planned for single species, we further propose the index of landscape cohesion, which integrates the spatial cohesion indices of different species. Indices based on these concepts can be built into GIS tools for landscape assessment. We illustrate different applications of these indices, and emphasise the distinction between ecological and political decisions in developing and applying such tools.

Introducing the key patch approach for habitat networks with persistent populations: an example for marshland birds

In landscapes where natural habitat is highly fragmented, any method for assessment of population persistence or potential for biodiversity should be based upon metapopulation theory, taking into account the spatial and temporal dynamics of species. We argue that methods based upon species distribution data, population viability analyses (PVA), or landscape indices alone all have severe flaws. We introduce an approach based upon a combination of the three methods, in which ecologically scaled landscape indices (ESLI) are compared to spatial standards derived from both analysis of distribution data and PVA-type simulations. We derive spatial standards, introducing the key patch approach. Key patches are large patches with a stabilizing role in habitat networks. Key patch standards were developed using spatial analysis of presence–absence data and calibrated metapopulation models for marshland bird species. We show examples of the application of this approach in land use management at both regional and national planning scales.

Management perspectives for populations of the eurasian badger (Meles meles) in a fragmented landscape

(1) In the modern agricultural landscape habitat patches for badgers are distributed like fragments in large suboptimal areas. In this paper the badger population in the Netherlands is considered as a metapopulation. A stochastic model is presented for a single badger clan. Subsequently, the model is extended to simulate a metapopulation consisting of badger clans that are connected through dispersal, while taking account of the present biological information. (2) The models are used to address the perspectives of management measures for badgers in the Netherlands. The results show that the viability of a single badger clan is especially sensitive to changes in adult mortality. (3) For a metapopulation of clans a similar result is obtained. In addition, the number of territories and the rate of dispersal between the clans are major factors that influence the viability of the metapopulation. (4) Management measures aimed at improving conditions for badgers should be directed at reducing the adult mortality and restoring or maintaining a large number of potential territories for clans while providing ample opportunity for dispersal between the clans.

An individual‐based approach to model spatial population dynamics of invertebrates in aquatic ecosystems after pesticide contamination

In the present study we present a population model (Metapopulation model for Assessing Spatial and Temporal Effects of Pesticides [MASTEP]) describing the effects on and recovery of the waterlouse Asellus aquaticus after exposure to a fast-acting, nonpersistent insecticide as a result of spray drift in pond, ditch, and stream scenarios. The model used the spatial and temporal distribution of the exposure in different treatment conditions as an input parameter. A dose-response relation derived from a hypothetical mesocosm study was used to link the exposure with the effects. The modeled landscape was represented as a lattice of 1- by 1-m cells. The model included processes of mortality of A. aquaticus, life history, random walk between cells, density dependence of population regulation, and, in the case of the stream scenario, medium-distance drift of A. aquaticus due to flow. All parameter estimates were based on expert judgment and the results of a thorough review of published information on the ecology of A. aquaticus. In the treated part of the water body, the ditch scenario proved to be the worst-case situation, due to the absence of drift of A. aquaticus. Effects in the pond scenario were smaller because the pond was exposed from one side, allowing migration from the other, less contaminated side. The results of the stream scenario showed the importance of including drift for the population recovery in the 100-m stretch of the stream that was treated. It should be noted, however, that the inclusion of drift had a negligible impact on numbers in the stream as a whole (600 m).

Metapopulation models for impact assessment of fragmentation

In Western Europe, fragmentation of natural habitat types is a considerable problem for nature conservation (Opdam et al., 1993, this volume). Guidelines for landscape design and management are badly needed. To develop these guidelines, we need a better understanding of the quantitative relation between landscape characteristics (such as size and configuration of natural elements) and the prospects for survival of plant and animal populations restricted to those elements. Moreover, we need to assess the effects of mitigating measures (e.g. restoring linear landscape elements) or measures that add to fragmentation (e.g. construction of roads and railways). Metapopulation models are an indispensable tool for understanding the dynamics of fragmented populations and for impact assessment of (de)fragmentation.

Effect of local weather on butterfly flight behaviour, movement, and colonization: significance for dispersal under climate change

Recent climate change is recognized as a main cause of shifts in geographical distributions of species. The impacts of climate change may be aggravated by habitat fragmentation, causing regional or large scale extinctions. However, we propose that climate change also may diminish the effects of fragmentation by enhancing flight behaviour and dispersal of ectothermic species like butterflies. We show that under weather conditions associated with anticipated climate change, behavioural components of dispersal of butterflies are enhanced, and colonization frequencies increase. In a field study, we recorded flight behaviour and mobility of four butterfly species: two habitat generalists (Coenonympha pamphilus; Maniola jurtina) and two specialists (Melitaea athalia; Plebejus argus), under different weather conditions. Flying bout duration generally increased with temperature and decreased with cloudiness. Proportion of time spent flying decreased with cloudiness. Net displacement generally increased with temperature. When butterflies fly longer, start flying more readily and fly over longer distances, we expect dispersal propensity to increase. Monitoring data showed that colonization frequencies moreover increased with temperature and radiation and decreased with cloudiness. Increased dispersal propensity at local scale might therefore lower the impact of habitat fragmentation on the distribution at a regional scale. Synergetic effects of climate change and habitat fragmentation on population dynamics and species distributions might therefore appear to be more complex than previously assumed.

Population dynamics under increasing environmental variability: implications of climate change for ecological network design criteria

There is growing evidence that climate change causes an increase in variation in conditions for plant and animal populations. This increase in variation, e.g. amplified inter-annual variability in temperature and rainfall has population dynamical consequences because it raises the variation in vital demographic rates (survival, reproduction) in these populations. In turn, this amplified environmental variability enlarges population extinction risk. This paper demonstrates that currently used nature conservation policies, principles, and generic and specific design criteria have to be adapted to these new insights. A simulation shows that an increase in variation in vital demographic rates can be compensated for by increasing patch size. A small, short-lived bird species like a warbler that is highly sensitive to environmental fluctuations needs more area for compensation than a large, long-lived bird species like a Bittern. We explore the conservation problems that would arise if patches or reserve sizes would need to be increased, e.g. doubled, in order to compensate for increase in environmental variability. This issue has serious consequences for nature policy when targets are not met, and asks for new design criteria.

Sacrificing patches for linear habitat elements enhances metapopulation performance of woodland birds in fragmented landscapes

It is generally assumed that large patches of natural habitat are better for the survival of species than the same amount of habitat in smaller fragments or linear elements like hedges and tree rows. We use a spatially explicit individual-based model of a woodland bird to explore this hypothesis. We specifically ask whether mixtures of large, small and linear habitat elements are better for population performance than landscapes that consist of only large elements. With equal carrying capacity, metapopulations perform equally or better in heterogeneous landscape types that are a mix of linear, large and small habitat elements. We call this increased metapopulation performance of large and small elements “synergy”. These mixed conditions are superior because the small linear elements facilitate dispersal while patches secure the population in the long run because they have a lower extinction risk. The linear elements are able to catch and guide dispersing animals which results in higher connectivity between patches leading to higher metapopulation survival. Our results suggest that landscape designers should not always seek to conserve and create larger units but might better strive for more variable landscapes with mixtures of patch sizes and shapes. This is especially important when smaller units play a key role in connecting patches and dispersal through the matrix is poor.

Applying ecological knowledge in landscape planning: a simulation model as a tool to evaluate scenarios for the badger in the Netherlands

The distribution of the Eurasian badger (Meles meles, L.) in the Netherlands is fragmented and adult mortality is high in many places because of traffic casualties. Both these facts affect the survival and dispersal of badgers in a negative way and are suggested to be the main causes of the decline of this species. For this reason the species receives special attention from the government in the national Nature Policy Plan and also from the lower administration in the provinces in their policy on physical planning and nature conservation. To evaluate changes in land use by means of spatial scenarios and conservation strategies in favour of the species, an individual-based simulation model was built that describes population dynamics in space and time. The model was used to evaluate three scenarios. The results indicate that the survival of groups benefits strongly from measures directed at lowering adult mortality. Also the (re)colonization of suitable but not inhabited areas increases the survival and is favoured by measures that encourage dispersal. The results indicate that simulation models as described are useful tools for establishing the comparative effectiveness of plans or measures aimed at increasing the viability of the species.