Habitat Networks Research Articles

The relationships between the structure of paddy levees and the plant species diversity in cultural landscapes on the west side of Lake Biwa, Shiga, Japan

Paddy levees form networks of narrow linear habitats and play various roles in cultural landscapes. Traditional landscapes on the west side of Lake Biwa consist of paddy field terraces and both “stone” and “soil” levees that have been maintained by paddy field management using local resources. Paddy levees in this study site are principally classified into five different types. Our study points out how differences in paddy levee structure as well as in management practices influence the plant species. Seventeen paddy levee transects were split into four habitat types based on their species components by TWINSPAN. Spatial characteristics and physical structures of paddy levees depended on natural conditions and human activities. The species–area curves of each levee type showed a clear distinction: the “soil”, “stone” and “abandoned” curves were steep, while the “concrete” and “consolidated” ones were gentle. The vegetation on “consolidated” levees was utterly different from the vegetation on traditional levee types from the aspect of species richness and species components. “Soil” type levees contained various woody plant species and included more diverse and indigenous plant species than “abandoned” type levees.

Inferring persistence of indigenous mammals in response to urbanisation

The number and extent of human settlements around the world are increasing as the human population grows and people move from rural to urban areas. The decline and ultimately the local extinction of many indigenous species from a range of taxonomic groups within urbanised areas is a recurring theme from cities around the world. However, determining whether a species has become extinct can be difficult because sufficient survey effort may be too costly and expert opinion may involve considerable subjective bias. In this study, we compared the results of four quantitative assessments of the probability of persistence of indigenous mammals within Melbourne, Australia. Our comparisons were methodological, taxonomic and spatial. Less than half (26) of the original 54 species that occurred in Melbourne prior to European settlement have a greater than 95% probability of being extant at the end of 2000. Mammals occurring in local government areas (LGAs) within 10km of the central business district of Melbourne were less likely to be extant, with 29% of species having a greater than 95% probability of persisting, compared to 48% in the outer LGAs. The group of species most negatively affected by urbanisation were the small, ground-dwelling mammals, with just two out of 15 species having a greater than 10% probability of persisting. All four methods gave broadly similar results, with the Bayesian approach consistently suggesting higher probabilities of species persistence. The decline in the number of species is likely to continue with the ongoing expansion of Melbourne. The greatest opportunity to conserve the maximum number of species of mammal within Melbourne is in the outer LGAs where they remain extant. We recommend that state and local governments design and adopt a comprehensive strategy for managing habitat networks that cross jurisdictional boundaries and encompass the greater Melbourne area to enhance prospects for the survival of mammals.

Gap‐crossing decisions of woodland songbirds in Scotland: an experimental approach

Summary Recent declines in woodland birds in Britain have been linked to increasing habitat fragmentation. To understand the effects of fragmentation, data on avian dispersal across woodland gaps are essential but often lacking. We used song thrush Turdus philomelos mobbing calls to attract songbirds across gaps ranging from 5 to 120 m in width and along comparable woodland edges. Responses were modelled against distance using generalized linear models. Such models have clear applied value for connecting fragmented landscapes. We also calculated response indices and compared these with bird morphology. The gap‐crossing results were applied to a real landscape in central Scotland and landscape metrics were calculated to judge how perception of habitat connectivity varies interspecifically. The chaffinch Fringilla coelebs and the robin Erithacus rubecula both responded more readily across gaps than through woodland. There was no difference between gap and edge response for the coal tit Parus ater, while the goldcrest Regulus regulus responded more readily along edges than across gaps. Maximum gap‐crossing distances ranged from 46 m (goldcrest) to 150 m (chaffinch). There was a positive linear trend between mass of bird and the difference in the maximum response for gap and control experiments. Likewise there was a positive curvilinear relationship between wing area and the difference in probability of response between gap and control experiments at 50 m. These results may be interpreted in terms of manoeuvrability and ability to escape avian predation. For the central Scotland landscape, the perceived number of patches in the landscape decreased exponentially with increasing gap‐crossing distance, while the median patch size and mean patch fractal dimension increased linearly with gap‐crossing distance. Synthesis and applications. Our results show that an experimental approach using playback can be used to obtain data on avian gap crossing and the results applied to real landscapes to visualize interspecific differences in habitat perception. This has practical management applications, especially for designing forest habitat networks to maximize avian biodiversity, and potentially could help reverse the recent declines in woodland birds.

Effects of Habitat Suitability and Landscape Patterns on Tick (Acarina) Metapopulation Processes

Tick density and population dynamics are important factors in the ecological processes involved in pathogen circulation in a habitat. These characteristics of tick populations are closely linked to habitat suitability, which reflects the limiting ecological factors and landscape features affecting tick populations; however, little work has been done on the regional assessment of habitat suitability. In this study, a regional model for the distribution and abundance of the tick Ixodes ricinus in central Spain is developed. An occurrence and an abundance model were constructed; climate and vegetation variables were found to be the main predictors of both occurrence and density in a relatively homogeneous matrix of habitat patches, whereas topographical variables were found to have small contributions and were therefore discarded. The residuals of the abundance model showed good correlation with the isolation of each patch. The predictive power of the abundance model was greatly enhanced by inclusion of the traversability (a measure of the permeability of each patch to the propagules of the metapopulation) and recruitment (an index of the relative importance of each patch to the traffic through the entire habitat network). The removal from the landscape of the patches whose recruitment values were in the top 10% has a critical effect on tick density, an effect not observed when patches are removed at random. These results indicate that permanent tick populations can be sustained only in landscapes containing a minimum network of viable sites. Graph theory and measurements of patch isolation should prove to be important elements in the forecasting of tick abundance and the management of the features underlying the landscape ecology of tick populations and pathogen circulation in the field.

Survival of the Black bog ant (Formica transkaucasica Nasanov) in relation to the fragmentation of its habitat

In the past, extensive areas in Drenthe (The Netherlands) were covered by peat bogs and wet heath lands, but nowadays only relatively small fragments are left. During the second half of the 20th century the quality of these fragments decreased, due to lowering of the water table and the input of nutrients. These factors will have a negative effect on the survival of species which are adapted to these stable type of biotopes, like the Black bog ant. The distribution pattern was analysed within a study area of 750 km2, in order to find out if this species will survive in a landscape where its habitat is severely fragmented. Using multiple logistic regression analysis it appears that size and quality of the habitat patches, as well as openness of the environment, contribute significantly to patch-occupancy. No correlation was found between the probability of a patch being occupied and its distance to the nearest occupied patch. It appears that the spatial cohesion of local populations by means of flying queens is weak or absent on the scale of the study area. Only in parts of the area, where the distance between habitat patches is less than 3 km in open field, a habitat network may still exist. However, with ongoing habitat loss a threshold will be passed and the species will ultimately become extinct.

Afforestation Planning and Biodiversity Conservation: Predicting Effects on Habitat Functionality in Lithuania

Habitat re-creation is one of the multiple faces of biodiversity restoration and encompasses the attempts to reconstruct an ecosystem on severely disturbed sites with little left to restore. Afforestation of abandoned or marginal agricultural land is an important tool for the re-creation of forest ecosystems and re-establishment of functional habitat networks for the maintenance of biodiversity. This study was performed in the context of the Danish-Lithuanian project ‘Afforestation of abandoned agricultural land based on sustainable land use planning and environmentally sound forest management’. The study assessed how habitat re-creation as designed in alternative afforestation plans for two administrative regions in Lithuania will affect the functionality of the landscapes for bird species of conservation concern. Spatial analysis of the forest cover was performed under existing and proposed conditions using general landscape ecological principles concerning core and edge habitats as well as nearest-neighbour metrics. The results show that the use of general criteria may result in proportionally negative changes in the availability of some forest habitats relative to changes in total forest cover, thus leading to less significant improvements in the habitats of many naturally occurring (and even protected) species compared to what would be expected from changes in forest cover alone. To solve this dilemma it is suggested that the requirements of focal species and quantitative conservation objectives should be considered in a spatially explicit – each main forest type. It is concluded that to ensure functionality of habitat networks, knowledge and experience from the fields of landscape ecology and conservation biology should be more commonly incorporated into afforestation planning.

The use of spatial concepts as a basis for designing a viable-habitat network: Conserving redstart (Phoenicurus phoenicurus) populations in Sherwood Forest, England

Summary This paper presents a method for the design of a habitat network in a fragmented landscape. It employs metapopulation dynamics and connectivity to develop spatial rules which, together with the requirements of a target species, can be used to guide the creation of a network to improve population persistence. Using these guidelines, two conservation strategies of patch enlargement and corridor creation are developed. The spatial models used to produce the habitat network are described. The resulting maps show the network consisting of the source patches that could be occupied by stable populations and a number of patches, which could support viable local populations, situated in the proximity of the sources or linked to them. The approach could be used to inform decision-making in nature conservation and landscape planning.

Urban comprehensive planning – identifying barriers for the maintenance of functional habitat networks

Maintaining biodiversity requires a wise combination of protection, management and recreation of habitats to secure representative and functional habitat networks. As urbanisation is increasing worldwide, town and cities are becoming the most common habitat for humankind. Accordingly, the urban landscape is becoming increasingly important for maintaining biodiversity on site, as well as for understanding the concept of biodiversity in general, and its maintenance in urban landscapes. We evaluated the extent to which Swedish urban planners experience barriers when using comprehensive planning as a tool for the maintenance of biodiversity through the provision of sufficient quantity and quality of green space. All of the six large Swedish cities, having had constant relative population growth since the beginning of the 19th century were chosen as case studies. We first defined a normative model for planning urban biodiversity and operationalised this concept by using landscape ecological principles. Structured in-depth interviews were then carried out with three planners in each city. The respondents were asked about their interest, ability, and knowledge concerning planning for functional networks of green spaces in relation to the normative model. The in-depth interviews with 18 urban planners indicated that legislation was an important driver for green space planning, that they paid attention to new knowledge concerning recreation values and public health, but that biodiversity maintenance was not a high priority. There was a general agreement that local governments lack necessary resources to plan for biodiversity. A majority of the respondents mentioned geographical information systems (GIS) as an important tool to integrate knowledge about biodiversity in the planning process, and to evaluate likely consequences caused by deviations from current structure plans related to an efficient use of urban green spaces to maintain biodiversity. However, an evaluation of the answers revealed that the respondents had actually overestimated their capacity to implement the normative model. To conclude, the unanimous view was that planners were interested in the maintenance of biodiversity, but were limited by knowledge and by personnel lacking suitable qualifications, as well as by inadequate organisations. Only a minority of the respondents thought that local governments should have resources for biodiversity conservation planning. Finally, we discuss how the implementation of biodiversity policies could be improved by better integration of natural and social sciences in education and policy implementation.

The re-expansion and improving status of the silver-spotted skipper butterfly ( Hesperia comma) in Britain: a metapopulation success story

Many specialist species are declining as a result of habitat loss and fragmentation, such that conservation actions typically aim to stem rates of decline rather than bring about genuine recovery. Here, we document the recovery of a species from former population refuges. An extensive survey of the entire British range of Hesperia comma, conducted in 2000, recorded over three times the number of tetrads (2 km × 2 km grid squares) occupied in 1982. This was accompanied by a fourfold increase in the number of populations and a 10-fold increase in the habitat area occupied. The improving status of H. comma is the product of good habitat management, recovering rabbit populations and climate warming, which have improved the quality, and increased the availability, of suitable habitat. This has enabled remnant metapopulations to expand, via distance-dependent colonisation, through large networks of habitat. Metapopulation recovery in H. comma demonstrates that landscape-scale conservation can be successful.

Long-distance plant dispersal and habitat fragmentation: identifying conservation targets for spatial landscape planning under climate change

Climate change presents a potentially severe threat to biodiversity. Species will be required to disperse rapidly through fragmented landscapes in order to keep pace with the changing climate. An important challenge for conservation is therefore to manage landscapes so as to assist species in tracking the environmental conditions to which they are adapted. Here we develop a stochastic spatially explicit model to simulate plant dispersal across artificial fragmented landscapes. Based on certain assumptions as to the dispersal mechanism, we assess the impact that varying potential for rare long-distance dispersal (LDD) has on the ability to move over landscapes with differing spatial arrangements of suitable habitat (clumped versus fragmented). Simulations demonstrate how the relative importance of landscape structure in determining migration ability may decrease as the potential for LDD increases. Thus, if LDD is the principal mechanism by which rapid large-scale migrations are achieved, strategically planned networks of protected habitat may have a limited impact on rates of large-scale plant migrations. We relate our results to conventional principles for conservation planning and the geometric design of reserves, and demonstrate how reversal of these principles may maximise the potential for conservation under future climates. In particular, we caution against the justification of large-scale corridors on grounds of climate change since migration along corridors by standard dispersal mechanisms is unlikely to keep pace with projected change for many species. An improved understanding of the dispersal mechanisms by which species achieve rapid migrations, and the way that these processes are affected by patterns of landscape fragmentation, will be important to inform future conservation strategies.

A forest habitat network for the Atlantic Oakwoods in Highland region, Scotland

Summary The need to conserve biological diversity and ensure the future viability and integrity of Atlantic oakwoods in a fragmented landscape has led to strategies that facilitate a more holistic view of biodiversity conservation across extensive areas. The Scottish Forestry Strategy contains a major aspiration to develop forest habitat networks through the restoration and improvement of existing woodland and the expansion of new woodland. The Forest Research landscape ecology model BEETLE (Biological and Environmental Evaluation Tools for Landscape Ecology) uses a focal species approach to assess the functional connectivity of habitat within the wider landscape matrix. This model has been used to predict the current habitat network for Atlantic oakwood specialists in the Highland region of Scotland. The analysis outputs are presented with an approach to help practitioners and planners visualise the opportunities to target expansion, conversion or restoration of Atlantic oakwoods and their intrinsic biodiversity.

The German way to greenways and habitat networks

A prospective strategy is necessary to mitigate the negative impacts of habitat fragmentation in Germany. The traditional concept of protecting isolated remnants of endangered habitats as nature reserves could not stop the continuing decline of endangered species and the regional losses in biodiversity sufficiently. During the last century, different approaches to protect open space, species, and habitats have been developed. Based on a literature review, an analysis of the legal framework and a representative case study, this paper tries to characterise the development of greenways and habitat networks in Germany and to discuss the general possibilities and limitations in an European context. In Germany, greenways were first established to prevent urban sprawl, to separate settlements, to provide recreational opportunities and to improve air quality in industrialised urban areas. The increased relevance of nature conservation has led to the development of new types of habitat networks in addition to the greenway concept since 1980. Species-oriented habitat networks focus on the specific requirements of target species, while multifunctional habitat networks try to address many landscape functions when reconnecting the remnant habitats. The Kronsberg Project is an example of a local, multifunctional habitat network. It illustrates some of the implementation difficulties resulting from conflicting interests of the various user groups. In addition, the need became obvious to plan multifunctional networks which allow for spatial separation of conflicting site related objectives. The legal framework for habitat networks in Germany is, in principle, a sound legislation which requires that habitat networks cover a minimum of 10% of the total land area of the German states. The conceptualisation of the networks must not be restricted to the boundaries of the individual German states because the networks should have an interstate character and also contribute to the European network of Natura 2000. However, this national and European network cannot be presently implemented by the German national authorities. Instead, the framework legislation must be passed as nature conservation laws at the state level, while concrete implementation takes place at the regional and local levels. There the implementation is hampered primarily by property ownership considerations or conflicting interests of landowners. This situation hinders the implementation of national and European objectives for habitat networks. In order to create a forward looking network strategy for Germany, more authority should be transferred to the national level. In addition, a stronger link between the scientific and conceptual basis of habitat networks is needed. Prioritising landscape functions and the selection of target species require better coordination. Economic incentives could be used to reduce the conflicts with landowners. Hopefully, a change in the EU-agricultural policy will facilitate this development.

Evaluating the effect of corridors and landscape heterogeneity on dispersal probability: a comparison of three spatially explicit modelling approaches

Spatially explicit simulation models of varying degree of complexity are increasingly used in landscape and species management and conservation. The choice as to which type of model to employ in a particular situation, is however, far too often governed by logistic constraints and the personal preferences of the modeller, rather than by a critical evaluation of model performance. We present a comparison of three common spatial simulation approaches (patch-based incidence-function model (IFM), individual-based movement model (IBMM), individual-based population model including detailed behaviour and demographics (IBPM)). The IBPM was analysed in two versions (IBPM_st and IBPM_dyn). Both assumed spatial heterogeneity of the matrix, but the IBPM_dyn in addition included temporal matrix dynamics. The models were developed with a shared minimum objective, namely to predict dynamics of individuals or populations in space given a specific configuration of habitat patches. We evaluated how the choice of model influenced predictions regarding the effect of patch and corridor configuration on dispersal probabilities and the number of successful immigrants of a simulated small mammal. Model results were analysed both at the level of the entire habitat network and at the level of individual patches. All models produced similar rankings of alternative habitat networks, but large discrepancies existed between absolute estimates of dispersal probabilities and the number of successful immigrants predicted by the different models. Generally, predicted dispersal probabilities were highest in the IBMM, intermediate in the IFM and the IBPM_st and lowest in the IBPM_dyn. Observed differences were due both to differences in implementation (e.g. raster versus vector-based movement algorithms), the chosen level of detail in landscape representation (e.g. matrix complexity) and the degree of behavioural realism included in the models (e.g. demography, differentiated mortality). The advantages and disadvantages of the three modelling approaches are discussed, as are the implications of the results for the recommended use of the three types of models in practical management.

Complex habitat requirements and conservation needs of the only extant Baroniinae swallowtail butterfly

AbstractThe unique butterfly species, Baronia brevicornis, perhaps the oldest taxon in the Papilionidae, is known to have a very restricted distribution in Mexico. Populations are restricted to southern Mexico in deciduous scrub forest where its host‐plants, Acacia trees (Leguminosae), are common and widespread. Little is known of the conservation implications of its relationship with its host trees. We recorded fine scale population data for larval and adult B. brevicornis in 22 km2 of fragmented landscape in southern Mexico. Habitat associations determined from over 1319 transect walks reveal that B. brevicornis exhibited an extremely localised distribution, occupying < 1% of the study area and being mostly associated with Acacia woodlots. Detailed analyses of habitat requirements for larva and/or adult B. brevicornis suggest that it lays its eggs on Acacia pennatula and A. macracantha (two newly recorded larval host‐plants), that eggs were laid disproportionately on Acacia trees with long branches (χ2= 17.7, P < 0.001) and that the probability of finding adult B. brevicornis between occupied and un‐occupied Acacia woodlots increased with host‐plant density (χ2= 18.4, P < 0.001). The results of this study suggest that conservation recommendations for B. brevicornis must consider the condition of the Acacia habitat network, given that Acacia is mostly associated with human‐managed grazing systems. Effective conservation will require the establishment of connected networks of patches where natural dynamics can produce new habitats, as well as the creation of new habitats within colonisation distance. This research provides a rare case study of conservation biology of a Neotropical insect, emphasising the importance of using ecological information to provide management recommendations.

The application of the biosphere reserve concept to urban areas: the case of green rooftops for habitat network in Seoul.

This article consists of two parts. The first shows how the principles of the ecosystem approach can be applied to green rooftops, and the second attempts to illustrate it through a case study. In particular, it suggests new approaches and techniques for creation of green rooftops in a perspective of urban habitat network and urban biosphere reserve. To endow urban rooftops with the roles and functions of urban habitat network and urban biosphere reserve, it is necessary to apply "an ecosystem approach to urban management." In this article, an ecosystem approach to urban management is illustrated with Seoul as an example. The Habitat Network in Seoul will be reviewed with a focus on the model suggested by MAB Urban Group. Then, the roles and functions of Myeongdong UNESCO Green Rooftop and its possible contribution to building the Seoul Urban Biosphere Network will be described. The UNESCO Green Rooftop is 628 m(2) and was created on the 12th floor rooftop of UNESCO Building in Myeongdong 2-ga, Jung-ku, Seoul. In the green rooftop, which was created with goals of securing green areas and biotopes in downtown, creating an urban econetwork, securing a base for urban ecosystem study and environment education, and disseminating an idea of coexistence between nature and humankind, wetland, meadow, scrub and woodland, wall revegetation, and a vegetable field are created. Also, rainwater recycling facilities and a solar energy water circulation system were set up. Rest facilities including observation and education facilities were built. Based on the Seoul example, as well as urban biosphere reserve models suggested by the MAB Urban Group, we suggest several principles to be applied for a green rooftops to qualify as a category of urban biosphere reserves.

Networks in metapopulation dynamics

The behavior of spatially inhomogeneous populations in networks of habitats provides examples of dynamical systems on random graphs with structure. A particular example is a butterfly species inhabiting the Aland archipelago. A metapopulation description of the patch occupancies is here mapped to a quenched graph, using the empirical ecology-based incidence function description as a starting point. Such graphs are shown to have interesting features that both reflect the probably “self-organized” nature of a metapopulation that can survive and the geographical details of the landscape. Simulations of the Susceptible-Infected-Susceptible model, to mimick the time-dependent population dynamics relate to the graph features: lack of a typical scale, large connectivity per vertex, and the existence of independent subgraphs. Finally, ideas related to the application and extension of scale-free graphs to metapopulations are discussed.

Factors affecting habitat selection by a small spawning charr population, bull trout, Salvelinus confluentus: implications for recovery of an endangered species

AbstractBull trout, Salvelinus confluentus (Suckley), populations are declining in many streams of North America and are listed under the Endangered Species Act in the United States. Many small populations are isolated in fragmented habitats where spawning conditions and success are not well understood. Factors affecting habitats selected for redds by spawning bull trout and redd habitat characteristics within Gold Creek, a headwater stream in the Yakima River within the Columbia River basin, Washington State, USA, were evaluated. Most spawning (>80% of the redds) occurred in upstream habitats after dewatering of downstream channels isolated fish. Habitats were selected or avoided in proportions different to their availability. For example, most bull trout selected pools and glides and avoided riffles despite the latter being more readily available. Although preferences suggest influences of prolonged fish entrapment, site fidelity could be important. A habitat with redds commonly contained abundant cover, gravel substratum and higher stream flows. The major factors influencing habitat selection by spawning fish and their persistence in streams of the Yakima and Columbia River regions include entrapment of fish by dewatering of channels and geographical isolation by dams. The goal of the US Government's recovery plan is ‘to ensure the long‐term persistence of self‐sustaining bull trout populations’. Recovery plans linked to provisions for protecting and conserving bull trout populations and their habitats were recommended. Landscape approaches are needed that provide networks of refuge habitats and greater connectivity between populations. Concurrent recovery efforts are encouraged to focus on protecting small populations and minimizing dangers of hybridization.

Ecologically Differentiated Rules of Thumb for Habitat Network Design – Lessons from a Formula

The present paper addresses the following typical question of metapopulation management: “What habitat distribution is optimal for metapopulation persistence if a habitat network with a given number and configuration of patches is considered?”. By utilizing a generic metapopulation model and performing a special model analysis, rules of thumb for optimum habitat distribution and a general ‘Principle of Optimality’ are derived. The whole study is based on the application of a formula for the mean lifetime of metapopulations derived in a previous study. Finally, some general conclusions are drawn concerning the potential of using PVA techniques for deriving tools for decision support for conservation management.

Two-dimensional gap analysis: a tool for efficient conservation planning and biodiversity policy implementation.

The maintenance of biodiversity by securing representative and well-connected habitat networks in managed landscapes requires a wise combination of protection, management, and restoration of habitats at several scales. We suggest that the integration of natural and social sciences in the form of "Two-dimensional gap analysis" is an efficient tool for the implementation of biodiversity policies. The tool links biologically relevant "horizontal" ecological issues with "vertical" issues related to institutions and other societal issues. Using forest biodiversity as an example, we illustrate how one can combine ecological and institutional aspects of biodiversity conservation, thus facilitating environmentally sustainable regional development. In particular, we use regional gap analysis for identification of focal forest types, habitat modelling for ascertaining the functional connectivity of "green infrastructures", as tools for the horizontal gap analysis. For the vertical dimension we suggest how the social sciences can be used for assessing the success in the implementation of biodiversity policies in real landscapes by identifying institutional obstacles while implementing policies. We argue that this interdisciplinary approach could be applied in a whole range of other environments including other terrestrial biota and aquatic ecosystems where functional habitat connectivity, nonlinear response to habitat loss and a multitude of economic and social interests co-occur in the same landscape.

The relationships between habitat topology, critical scales of connectivity and tick abundanceIxodes ricinusin a heterogeneous landscape in northern Spain

The habitat mosaic was used to quantify connectivity between patches of different tick density of the notorious tick speciesIxodes ricinusin an attempt to determine the cause of variations in tick abundance among apparently homogeneous sites in northern Spain. The analysis revealed that patches with high tick abundance are “stepping‐stone” territories that, when removed from the landscape, cause large changes in connectivity. Sites with medium tick abundance do not cause such a critical transition in connectivity. Patches with low tick abundance, but optimal abiotic conditions for survival, are located within the minimum cost corridors network joining the patches, while those sites where the tick has been intermittently collected are located at variable distances from this network. Sites where the tick is consistently absent, but where the habitat is predicted to be suitable (old, heterogeneous forests ofQuercusspp.) for the tick, are very separated from this main network of connections. These results suggest that tick distribution in a zone is highly affected not only by abiotic variables (vegetation and weather) but also by host movements. Dispersal of the tick is a function of how the hosts perceive the habitat, and the habitat's permeability to host movement. Permanent tick populations seem to be supported by the existence of these critical, high density patches, located at significant places within the habitat network.