Fractals and search paths in mammals

The fractal index by Katz and George (1985) for thecharacterization of planar curves is applied to wolf search pathsrecorded by radio-telemetry. All the sets of paths studied showspatial patterns whose complexity is between a straight line anda true random walk. Females fractal dimensions show significantchanges throughout the year, depending on the state of their lifecycle (normal, breeding and wandering). There are alsodifferences between males and females, but not between adults andnon-adults. The results are discussed with regard to wolffood-search strategies.     

Analysis of landscape patterns in coastal wetlands of Galveston Bay,Texas (USA)

High productivity and accessibility have made coastal wetlands attractive sites for human settlements. This study analyzed the patterns of wetland landscapes in Galveston Bay, Texas, USA. The first objective of the study was to describe the relationships between the fractal dimension of wetland boundaries and those factors which affect the wetland landscapes (e.g., land use, type of vegetation, size, location, and level of human disturbance). The second objective was to construct a historical database to contrast wetland areas which had experienced different levels of disturbance between 1956 and 1989. The fractal dimension, a measure of how much of the geographical space is filled by boundaries, was measured by the perimeter-area method. The fractal dimension of wetlands was significantly affected by land use, type of vegetation, size, and level of anthropogenic disturbance. In addition, increasing the size of buffers around roads did not significantly affect the fractal dimension of wetlands. Landscape indices, such as fractal dimension, dominance, and diversity, were used to characterize spatial heterogeneity in the historical database. Lake Stephenson, an area of low anthropogenic disturbance, experienced no changes in wetland composition and abundance over time. Anahuac, an area of medium disturbance, experienced changes in both wetland composition and abundance. Texas City, an area of high disturbance, experienced a change in wetland composition. These differences can be associated with the type and level of disturbance present; however, more evidence is needed to determine whether certain landscape patterns have stable, intrinsic properties which allow persistence in the face of disturbance. These results will be informative to resource managers determining how wetlands can be managed as natural resources and nature reserves.     

Quantifying habitat specificity to assess the contribution of a patch to species richness at a landscape scale

Assessing and predicting the species richness of a complex landscape remains a problem because there is no simple scaling function of species richness in a heterogeneous environment. Furthermore, the potential value of an area for biodiversity conservation may depend on which, rather than how many, species the area contains. This paper shows how we can objectively evaluate the contribution of an area, e.g., a habitat patch, to larger-scale plant species richness, e.g., a landscape composed of patches of several habitat types, and how we can test hypotheses that attempt to explain this contribution. We quantified the concept of habitat specificity to assess the proportion of each observed plant population that is concentrated within a given spatial element. A case study of a biodiversity-monitoring program in the Swiss Canton of Aargau showed that the relative contribution of the three main types of land use to the overall species richness differed strongly between higher taxa (vascular plants and molluscs). However, the type of data, i.e., presence-absence or abundance, was not important. Resampling of the plant data suggested that stratification provided an unbiased estimate of relative specificity, whereas unstratified sampling caused bias even for large samples. In a second case study of vascular plants in an agricultural landscape in central Switzerland, we tested whether the type, size or shape of a landscape element can predict its contribution to the species richness of the landscape. Habitat types that were less frequently disturbed contributed more per m² to landscape species richness than more frequently disturbed ones. Contrary to expectation, patch size was negatively correlated to specificity per m² for arable fields, whereas patch shape appeared to be unrelated to the specificity per m² both for arable fields and for meadows. The specificity approach provides a solution to the problem of scaling species richness and is ideally suited for testing hypotheses on the effect of landscape structure on landscape species richness. Specificity scores can easily be combined with measures of other aspects of rarity to assess the contribution of a spatial element to conservation goals formulated at regional, national or global level.     

Influence of landscape structure on local and regional climate

This paper discusses the physical linkage between the surface and the atmosphere, and demonstrates how even slight changes in surface conditions can have a pronounced effect on weather and climate. Observational and modeling evidence are presented to demonstrate the influence of landscape type on the overlying atmospheric conditions. The albedo, and the fractional partitioning of atmospheric turbulent heat flux into sensible and latent fluxes is shown to be particularly important in directly affecting local and regional weather and climate. It is concluded that adequate assessment of global climate and climate change cannot be achieved unless mesoscale landscape characteristics and their changes over time can be accurately determined.     

Effects of habitat fragmentation on four rodent species in a Polish farm landscape

Bank vole, striped field mouse, wood mouse, and yellow-necked mouse populations were studied in a mosaic of field and forest habitats. Live-trapping was carried out in 8 woodlots of different sizes (1.5–9.5 ha), situated 5 to 900 m from each other and surrounded by agricultural fields. Near the study area a dense, several hundred hectare forest complex was situated. It was found that the densities of all the studied species' populations in the woodlots were positively correlated with woodlot quality. For local bank vole populations a positive correlation of density with the surface area and circumference of woodlots, as well as with the area/circumference ratio was found. A negative correlation was found for population density and the distance between a given woodlot and the forest complex. For the yellow-necked mouse a positive correlation occurred between the density of local populations and the distance to the nearest neighboring woodlot. For the striped field mouse a positive correlation was found only between the population density in each woodlot and the distance to the forest complex. The wood mouse was insensitive to the variations in woodlot features present except for woodlot quality, and hence was probably responding in density to some other factors. Four rodent species, coexisting in the field-forest habitat mosaic demonstrated different reactions to its spatial characteristics, which were mainly related to different habitat preferences, spatial behavior, and mobility of individuals of the studied species.     

Changes in landscape patterns in Georgia,USA

The objectives of this study were to determine how landscape patterns in Georgia, USA have changed through time and whether the spatial patterns varied by physiographic region. Historical aerial photography was used to analyze spatial patterns of land use from the 1930's to the 1980's. Land use patterns were quantified by: (1) mean number and size of patches; (2) fractal dimension of patches; (3) amount of edge between land uses; and (4) indices of diversity, dominance, and contagion. Forest cover increased in aerial extent and in mean patch size. The mean size of agricultural patches increased in the coastal plain and decreased in the mountains and piedmont. Edges between land uses decreased through time, indicating less dissection of the landscape. Fractal dimensions also decreased, indicating simpler patch shapes. Indices of diversity and dominance differed through time but not among regions; the contagion index differed among regions but not through time. A geographic trend of decreasing diversity and increasing dominance and contagion was observed from the mountains to the lower coastal plain. Landscape patterns exhibited the greatest changes in the piedmont region. Overall, the Georgia landscape has become less fragmented and more connected during the past 50 years. Changing patterns in the landscape may have implications for many ecological processes and resources.     

Using landscape analysis to assess and model tsunami damage in Aceh province,Sumatra

The nearly unprecedented loss of life resulting from the earthquake and tsunami of December 26, 2004, was greatest in the province of Aceh, Sumatra (Indonesia). We evaluated tsunami damage and built empirical vulnerability models of damage/no damage based on elevation, distance from shore, vegetation, and exposure. We found that highly predictive models are possible and that developed areas were far more likely to be damaged than forested zones. Modeling exercises such as this one, conducted in other vulnerable zones across the planet, would enable managers to create better warning and protection defenses, e.g., tree belts, against these destructive forces.     

Using bulked AFLP analysis to assess genetic diversity in Echinacea species

Echinacea is an allogamous genus, thus its cultivars or populations are genetically heterogeneous. Using amplified fragment length polymorphism (AFLP) to estimate the genetic diversity of Echinacea is generally limited by the large number of individual plants and the higher cost that need to be processed. In the present study, effectiveness of several sizes of DNA bulking (10, 15, 20, 25 and 30 individuals) with 20, 36 and 55 primer pairs was compared using AFLP in determining the genetic diversity of Echinacea species. The results indicated that the use of bulked DNA-based AFLP analysis by using the selected eight primer pairs was capable of detecting genetic diversity between the tested Echinacea species, provided that the potential presence of low frequency variants was ignored and a possible bias in the estimates of genetic similarity was accepted. The assessments showed that a bulk of 15 individuals could detect sufficient AFLP variations at most genomic sites. Additionally, 20 primer pairs could generate sufficient polymorphic fragments to achieve high resolving power of AFLP for the tested Echinacea species.     

The role of landscape structure in species richness distribution of birds,amphibians, reptiles and lepidopterans in Mediterranean landscapes

The parameters referring to landscape structure are essential in any evaluation for conservation because of the relationship that exists between the landscape structure and the ecological processes. This paper presents a study of the relationships between landscape structure and species diversity distribution (estimated in terms of richness of birds, amphibians, reptiles and butterflies) in the region of Madrid, Spain. The results show that the response of species richness to landscape heterogeneity varies depending on the group of species considered. For birds and lepidopterans, the most important factor affecting the distribution of richness of species is landscape heterogeneity, while other factors, such as the specific composition of land use, play a secondary role at this scale. On the other hand, richness of amphibians and reptiles is more closely related to the abundance of certain land-use types. The study highlights the importance of heterogeneity in Mediterranean landscapes as a criterion for landscape planning and for definition of management directives in order to maintain biodiversity.     

Effects of landscape spatial structure on movement patterns of the hispid cotton rat (Sigmodon hispidus)

A large-scale experimental landscape study was conducted to examine the use of corridors and the forest matrix habitat by the hispid cotton rat (Sigmodon hispidus). The role of micro- habitat selection by S. hispidus in influencing routes of movement was also investigated. The experimental landscape consisted of ten 1.64-ha patches (each 128×128 m) established in a loblolly (Pinus teada) forest. Four of the patches were isolated while the other six were connected in pairs by a 32-m wide corridor. Cotton rats (N=96) were simultaneously released into both an isolated and connected patch, and monitored by radiotelemetry for 10 days. We found that the forest matrix was not a barrier to movements of cotton rats. Fifty percent of the cotton rats moved through the matrix. Corridors had no significant effect on the number of animals leaving connected patches (60%) compared to isolated patches (50%). However, corridors were the preferred route to leave a connected patch. Colonization success for cotton rats leaving connected and isolated patches did not significantly differ. Cotton rats exhibited micro-habitat preferences and these preferences differed within patch/corridor and matrix habitats. In patch/corridor habitats, cotton rats selected sites with tall (>1 m) shrubs and high percent cover. In the forest matrix, cotton rats selected sites with abundant cover by vines and low tree canopy cover. Movement patterns of Sigmodon hispidus are not strongly influenced by large-scale landscape spatial structures. Micro-habitat selection, however, does influence movement patterns. These findings have important implications regarding habitat connectivity for small mammals.     

Land-use changes in Illinois,ASA: The influence of landscape attributes on current and historic land use

The Illinois Geographic Information System was used to compare the soil and landscape attributes of the State with its historic vegetation, current land use, and patterns of land-use change over the past 160 years. Patch structural characteristics among land types in four geographic zones were also compared. The assessment of patch characteristics revealed a highly modified State with most land patches controlled by human influences and relatively few by topographic and hydrologic features. Correlation and regression analyses determined the relationships of land type and abundance within each of 50 general soil associations to properties of the soil associations - typically slope, texture, organic matter, productivity index, and available waterholding capacity. The distribution of the historic vegetation of the State and its current deciduous forests and nonforested wetlands related moderately (r² 0.44) to various landscape attributes. Urban and other highly modified land types were less closely related.     

Modelling the effects of landscape pattern and grazing regimes on the persistence of plant species with high conservation value in grasslands in south-eastern Sweden

Semi-natural grasslands in Sweden are threatened by land-use change and lack of management with attendant risk to their biodiversity. We present a model to explore the effects of grazing frequency and intensity on plant species persistence, and the relative effects of grassland size and pattern. We used a landscape modelling platform, LAMOS (LAndscape MOdelling Shell), to design a landscape model of vegetation dynamics incorporating the effects of local succession, dispersal and grazing disturbance. Five plant functional groups (PFG), representing various combinations of persistence and dispersal character, light requirements and disturbance responses, were defined to model species dynamics. Based on old cadastral maps three different landscapes were designed representing specific time-layers, i.e., a historical (17th to 18th century), a pre-modern (1940s) and a present-day landscape. Simulations showed that a threshold was crossed when grasslands decreased in area to about 10–30% of the modelled area, and as a consequence the biomass of grassland-specific PFGs was strongly reduced. These competition sensitive groups did not persist in the model even with intense grazing in the present-day landscape, where grasslands occupy 11% of the total area. However, all grassland species would have been able to persist in the historical landscape, where grasslands occupied 59% of the total area, even without grazing. Our results suggest that continuous but low-intensity grazing is more positive for grassland PFGs than discontinuous but highly intensive grazing. This effect was particularly strong when the frequency and/or intensity of grazing dropped below a threshold of 20%. Simulations using three landscape maps designed to explore effects of further fragmentation and habitat loss showed that the spatial pattern of remaining grasslands is important for the persistence of grassland-specific PFG. The model presented here is an advance towards more realistic grazing models to explore the effects of prescribed grazing and landscape fragmentation on the persistence species or plant functional groups.This revised version was published online in May 2005 with corrections to the Cover Date.     

Surface metrics: an alternative to patch metrics for the quantification of landscape structure

Modern landscape ecology is based on the patch mosaic paradigm, in which landscapes are conceptualized and analyzed as mosaics of discrete patches. While this model has been widely successful, there are many situations where it is more meaningful to model landscape structure based on continuous rather than discrete spatial heterogeneity. The growing field of surface metrology offers a variety of surface metrics for quantifying landscape gradients, yet these metrics are largely unknown and/or unused by landscape ecologists. In this paper, we describe a suite of surface metrics with potential for landscape ecological application. We assessed the redundancy among metrics and sought to find groups of similarly behaved metrics by examining metric performance across 264 sample landscapes in western Turkey. For comparative purposes and to evaluate the robustness of the observed patterns, we examined 16 different patch mosaic models and 18 different landscape gradient models of landscape structure. Surface metrics were highly redundant, but less so than patch metrics, and consistently aggregated into four cohesive clusters of similarly behaved metrics representing surface roughness, shape of the surface height distribution, and angular and radial surface texture. While the surface roughness metrics have strong analogs among the patch metrics, the other surface components are largely unique to landscape gradients. We contend that the surface properties we identified are nearly universal and have potential to offer new insights into landscape pattern–process relationships. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Response of generalist and specialist insect herbivores to landscape spatial structure

The purpose of this study was to investigate the effect ofchanges in landscape pattern on generalist and specialistinsects. We did this by comparing the species richness andabundance of generalist and specialist herbivorous insects inalfalfa (Medicago sativa, L.) fields on 26 agriculturallandscapes that differed in spatial structure. The insects werefrom the families Curculionidae (Coleoptera), weevils, andCicadellidae (Auchennorhyncha), leafhoppers.We hypothesized that: (1) generalist richness and abundancewould be highest in landscapes with high diversity(Shannon-Wiener); (2) specialist richness and abundance would behighest in landscapes with (i) high percent cover alfalfa and(ii) low mean inter-patch distance. We tested for these effectsafter controlling for the patch-level effects of field size,field age, frequency of disturbance and vegetation texture.The important findings of the study are: (1) generalist richness andabundance increased with increasing landscape diversity and (2)isolation (percent cover alfalfa in the landscape and/or meaninter-patch distance) does not affect specialist insects. Theseresults are significant because they indicate that bothgeneralist and specialist insects may move over much largerdistances than previously thought. This is one of the firststudies to demonstrate a large scale effect of spatial structureon insects across a broad range of landscapes.     

Pattern of Kirtland's warbler occurrence in relation to the landscape structure of its summer habitat in northern Lower Michigan

Studies of the endangered Kirtland's warbler in relation to landscape ecosystems were conducted from 1986–1988 on a large wildfire-burn surrounding Mack Lake in southeastern Oscoda County, Michigan. A landscape ecosystem approach was used to distinguish low- and high-elevation segments of the landscape, as well as 11 local ecosystem types. The ecosystems were distinguished by physiography, microclimate, soil, and vegetation. The early occurrence of the warblers was strongly related to landscape structure, i.e., to the broad low- and high-elevation areas and the local ecosystem types within them. Territories of male warblers were observed in 5 of the 11 ecosystems. The five ecosystem types where warblers were observed were characterized by (1) a physiography of level or rolling terrain; (2) soil series of Grayling, Graycalm, Montcalm, or Rubicon; (3) uplands with relatively warm temperature during the breeding season; (4) vegetation dominated by low sweet blueberry, bearberry, wintergreen, northern pin oak, blue stem grasses, and hair cap moss; and (5) canopy of relatively tall, dense, and patchy jack pine and oak. Landscape structure appears to be an important factor affecting the occurrence of the warbler in its summer habitat in northern Lower Michigan.     

Effects of landscape structure on nest predation in roadsides of a midwestern agroecosystem: a multiscale analysis

Nest predation is an important cause of mortality for many bird species, especially in grassland ecosystems where generalist predators have responded positively to human disturbance and landscape fragmentation. Our study evaluated the influence of the composition and configuration of the surrounding landscape on nest predation. Transects consisting of 10 artificial ground nests each were set up in 136 roadsides in six watersheds in south-central Iowa. Nest predation on individual roadside transects ranged from 0 to 100% and averaged 23%. The relationship of landscape structure within spatially-nested landscapes surrounding each roadside transect (within 200, 400, 800, 1200, and 1600 m of the transect line) to nest predation was evaluated by using multiple regression and canonical correlation analyses. The results of this multiscale landscape analysis demonstrated that predation on ground nests was affected by the surrounding landscape mosaic and that nest predators with different-sized home ranges and habitat affinities responded to landscapes in different ways. In general, wooded habitats were associated with greater nest predation, whereas herbaceous habitats (except alfalfa/pasture) either were associated with less nest predation or were not important. Different landscape variables were important at different spatial scales. Whereas some block-cover habitats such as woodland were important at all scales, others such as rowcrops and alfalfa/pasture were important at large scales. Some strip-cover habitats such as gravel roads and paved roads were important at small scales, but others such as wooded roadsides were important at all all scales. Most landscape metrics (e.g., mean patch size and edge density) were important at large scales. Our study demonstrated that the relationships between landscape structure and predator assemblages are complex, thus making efforts to enhance avian productivity in agricultural landscapes a difficult management goal.     

Spatial pattern analysis of pre- and post-hurricane forest canopy structure in North Carolina,USA

Existing spatial patterns of a forest are in part a product of its disturbance history. Using laser altimetry and field measures of canopy top height to represent pre- and post-hurricane canopy topography, respectively, we measured changes in spatial patterns of stand structure of a United States southern mixed coniferous-deciduous for est. Autocorrelative and fractal properties were measured in this opportunistic study to quantify changes in canopy architecture along twelve, 190-250 m transects that were subjected to moderate to high levels of wind disturbance. Prior to the hurricane, canopy heights were autocorrelated at scales <40 m with an average fractal dimension of 1.71. After the disturbance, autocorrelation disappeared; the average fractal dimension rose to 1.94. This shift towards spatial randomness illustrates part of the cyclical nature of ecosystem development. It shows how a catastrophic collapse of biomass accumulation corresponds to a decrease in ecosystem organization across a landscape. This revised version was published online in July 2006 with corrections to the Cover Date.     

Using landscape metrics to model source habitat for Neotropical migrants in the midwestern U.S.

Size of a forest patch is a useful predictor of density and reproductive success of Neotropical migratory birds in much of eastern North America. Within these forested landscapes, large forest tracts appear to be sources – fragments in which surpluses of offspring are produced and can potentially colonize new fragments including woodlot sinks where reproduction fails to balance adult mortality. Within agricultural landscapes of the midwestern U.S., where forests are severely fragmented, high levels of brood parasitism by brown-headed cowbirds (Molothrus ater) and intense predation on nests generally result in low reproductive success for Neotropical migrants regardless of forest size. In some midwestern U.S. landscapes, however, the variation in reproductive success among forest fragments suggests that `source' habitat could still exist for Neotropical migrants. We used vegetation, fragment and landscape metrics to develop multivariate models that attempt to explain the variation in abundance and reproductive success of Neotropical migrants nesting in an agricultural landscape in northern Indiana, USA. We produced models that reasonably described the pattern of species richness of Neotropical migrants and the abundance of wood thrushes (Hylocichla mustelina) and several other Neotropical migrant species within 14 forest fragments. In contrast, we were unable to produce useful models of the reproductive success of wood thrushes breeding in the same forest fragments. Our results suggest that (1) abundance patterns of Neotropical migrants are probably influenced by both landscape- and fragment-scale factors; (2) multivariate analyses of Neotropical migrant abundance are not useful in modeling the corresponding patterns of reproductive success; and (3) the location of any remaining `source' habitat for Neotropical migrants breeding within agricultural landscapes in North America will be difficult to predict with indirect measures such as vegetation composition or landscape context. As a result, the potential for developing conservation strategies for Neotropical migrants will be limited without labor-intensive, direct measurements of demographic parameters.     

Patterns of abundance and movement in relation to landscape structure: a study of a common scarab (Canthon cyanellus cyanellus) in Southern Mexico

Few relevant data are available to analyze how landscape features affect the abundance and movement patterns of tropical insects. We used mark-release-recapture techniques to study the effects of landscape structure and composition on habitat preferences and movements of Canthon cyanellus cyanellus individuals, within a complex tropical deciduous forest landscape in South Mexico during 2004 and 2005. In total, 2,460 individuals of C. c. cyanellus were captured, including 1,225 females and 1,235 males, out of which 124 individuals (65 females and 59 males) were recaptured once, and 9 individuals (seven females and two males) were recaptured twice. The abundance of individuals was equally high in large forest fragments, small forest fragments and hedgerows, but the abundance in pastures was less than half of the abundance in the other habitat types. To disentangle the movement behaviour of the species from the spatially and temporally varying sampling effort, we applied a Bayesian state-space modelling framework with a diffusion based movement model. Males showed generally faster movement rate than females, and they moved faster within forests and hedgerows than within pastures. Contrary to the assumption of the diffusion model, individuals did not move in a continuous fashion, indicated by the large fraction of individuals that were recaptured in the site of release. However, the posterior predictive data did not deviate substantially from the real data in terms of the mean and maximum movement distances recorded, and in terms of the dependence of movement distance on time between captures. Our results suggest that an important component of the biota in Mexican agro-pasture landscapes can utilize contemporary landscape elements such as hedgerows or small forest fragments in addition to large fragments of remnant habitat. These habitats are still locally common in semi-natural ecosystems and require less intensive conservation management.