The landscape matrix modifies the effect of habitat fragmentation in grassland butterflies

The landscape matrix is suggested to influence the effect of habitat fragmentation on species richness, but the generality of this prediction has not been tested. Here, we used data from 10 independent studies on butterfly species richness, where the matrix surrounding grassland patches was dominated by either forest or arable land to test if matrix land use influenced the response of species richness to patch area and connectivity. To account for the possibility that some of the observed species use the matrix as their main or complementary habitat, we analysed the effects on total species richness and on the richness of grassland specialist and non-specialist (generalists and specialists on other habitat types) butterflies separately. Specialists and non-specialists were defined separately for each dataset. Total species richness and the richness of grassland specialist butterflies were positively related to patch area and forest cover in the matrix, and negatively to patch isolation. The strength of the species-area relationship was modified by matrix land use and had a slope that decreased with increasing forest cover in the matrix. Potential mechanisms for the weaker effect of grassland fragmentation in forest-dominated landscapes are (1) that the forest matrix is more heterogeneous and contains more resources, (2) that small grassland patches in a matrix dominated by arable land suffer more from negative edge effects or (3) that the arable matrix constitutes a stronger barrier to dispersal between populations. Regardless of the mechanisms, our results show that there are general effects of matrix land use across landscapes and regions, and that landscape management that increases matrix quality can be a complement to habitat restoration and re-creation in fragmented landscapes.     

Edge effect and matrix influence on the nest survival of an old forest specialist,the Brown Creeper (<Emphasis Type="Italic">Certhia americana</Emphasis>)

Conservation strategies should be based on a solid understanding of processes underlying species response to landscape change. In forests fragmented by agriculture, elevated nest predation rates have been reported in many forest bird species, especially near edges. In intensively-managed forest landscapes, timber harvesting might also be associated with negative edge effects or broader “context” effects on some species when the matrix provides additional resources to their major nest predators. In this study, we hypothesized that proximity to a forest edge and proportion of cone-producing plantations will increase nest predation risk in fragments of relatively undisturbed forest. We focused on the Brown Creeper (Certhia americana), an indicator species of late-seral forests. We compared habitat configuration and composition at four spatial scales (0.14, 0.5, 1 and 2 km) around 54 nests and related daily nest survival rate to the distance to the nearest forest edge, mean patch size of late-seral forest (r = 141 m), proportion of non-forested lands (r = 141 m), density of maintained roads (r = 1 km), proportion of cone-producing spruce plantations (r = 2 km), and year. The best model included distance to the nearest edge and proportion of cone-producing plantations. Distance of nests to the nearest edge was the best individual predictor of daily nest survival. A larger sample of nests showed a significant threshold in distance to the nearest forest edge; nests located at least 100 m away were more likely to fledge young. These results suggest that even in managed forest landscapes, matrix effects can be important and some bird species may exhibit negative edge effects.     

Independent effects of connectivity predict homing success by northern flying squirrel in a forest mosaic

Landscape composition and configuration, often termed as habitat loss and fragmentation, are predicted to reduce species population viability, partly due to the restriction of movement in the landscape. Unfortunately, measuring the effects of habitat loss and fragmentation on functional connectivity is challenging because these variables are confounded, and often the motivation for movement by target species is unknown. Our objective was to determine the independent effects of landscape connectivity from the perspective of a mature forest specialist—the northern flying squirrel (Glaucomys sabrinus). To standardize movement motivation, we translocated 119 squirrels, at varying distances (0.18–3.8 km) from their home range across landscapes representing gradients in both habitat loss and fragmentation. We measured the physical connectedness of mature forest using an index of connectivity (landscape coincidence probability). Patches were considered connected if they were within the mean gliding distance of a flying squirrel. Homing success increased in landscapes with a higher connectivity index. However, homing time was not strongly predicted by habitat amount, connectivity index, or mean nearest neighbour and was best explained as a simple function of sex and distance translocated. Our study shows support for the independent effects of landscape configuration on animal movement at a spatial scale that encompasses several home ranges. We conclude that connectivity of mature forest should be considered for the conservation of some mature forest specialists, even in forest mosaics where the distinction between habitat and movement corridors are less distinct.     

Siberian flying squirrel responses to high- and low-contrast forest edges

We examined responses of Siberian flying squirrels ( Pteromys volans ) to edges between nesting habitat (mature spruce forests), movement habitat (other forests, pine bogs), and open areas within their home ranges in southern Finland in 1996-2000. Radio-tracked squirrels (n=146) were generally associated to edges when they were ac tive at night. Compared to distances expected from the habitat pattern of their home range, squirrels occurred closer to high-contrast edges (of open areas) and low-contrast edges (nesting or movement forest types). Asso ciation with edges of open areas was more pronounced when squirrels were in movement habitat than in nesting habitat, possibly because of stronger channeling of movements in the former habitat. When in nesting habitat, squirrels responded more strongly to field edges than to recent clearcut edges, probably as a result of the pres ence of more deciduous trees on field edges, unlike clearcut edges. Responses to open areas were independent of spatial scale. However, responses to movement habitat from nesting habitat, and vice versa, were more pronounced over hundreds than tens of meters. Nesting cavities and dreys were generally located at random with respect to edges. We conclude that squirrel responses to edges of landscape attributes are diverse and depend both on spatial scale and edge contrast.This revised version was published online in May 2005 with corrections to the Cover Date.     

Landscape context and selection for forest edge by breeding Brown-headed Cowbirds

We evaluated support for four alternate hypotheses explaining the distribution of breeding Brown-headed Cowbirds (Molothrus ater) in forests at varying distances from the forest edge in three Midwestern USA landscapes with varying amounts of forest fragmentation (core forest area ranged from 5 to 70%). We focused on breeding cowbirds’ use of forest because of the risk of nest parasitism to forest-dwelling hosts and to identify factors affecting breeding cowbird habitat selection. We compared distances of cowbird locations in the forest from the forest edge (“edge distances”) to distances of random forest locations in the entire landscape or within individual cowbird home ranges. We analyzed 1322 locations of 84 cowbirds across three landscapes. We found support for the landscape context hypothesis that breeding cowbird preference for forest edge varied with landscape context. Ninety percent of cowbird locations were within 150–350 m of forest edge, despite the overall availability of forest at greater distances from edge (as far as 500–1450 m) both within cowbird home ranges and the entire forested landscape. Cowbird preference for edge varied by landscape context largely due to differences in the availability of forest edge. In a highly fragmented forest cowbirds utilized the entire forest and likely viewed it as “all edge.” In less fragmented forests, cowbirds preferred edge. We consider how variation in cowbird edge preference might relate to patterns in host abundance, host diversity, and host quality because cowbird movements indicate they are capable of using forest farther from edges.     

Edge geometry influences patch-level habitat use by an edge specialist in south-eastern Australia

We investigated patterns in habitat use by the noisy miner (Manorina melanocephala) along farmland-woodland edges of large patches of remnant vegetation (>300 ha) in the highly fragmented box-ironbark woodlands and forests of central Victoria, Australia. Noisy miners exclude small birds from their territories, and are considered a significant threat to woodland bird communities in the study region. Seventeen different characteristics of edge habitat were recorded, together with the detection or non-detection of noisy miners along 129 500-m segments of patch edge. Habitat characteristics ranged from patch-level factors related to patch-edge geometry to site-level floristic factors. Backward (stepwise) logistic regression analyses were used to identify habitat characteristics that were associated with the occupancy of a site by noisy miners. After accounting for the effects of spatial autocorrelation on the occurrence of noisy miners along edges, we identified projections of remnant vegetation from the patch edge into the agricultural matrix (e.g., corners of patches, peninsulas of vegetation) and clumps of trees in the agricultural matrix within 100 m of the edge as significant predictors of the occupancy of edges by noisy miners. This relationship was also confirmed in two other geographically and floristically distinct habitats within Victoria. The use of edges with projections by noisy miners may confer advantages in interspecific territorial defence. In light of these results, we advocate revegetation strategies that attempt to enclose projections within 100 m of the edge, with fencing placed out to this new boundary, to reduce the likelihood of colonisation and domination of an edge by noisy miners. Our study highlights the need for greater consideration to be given to the patterns in habitat use by aggressive edge specialists, particularly in relation to patch-edge geometry and other human-induced components of landscapes.     

Movement behaviour of a forest songbird in an urbanized landscape: the relative importance of patch-level effects and body condition during migratory stopover

With expansion of urban areas worldwide, migrating songbirds increasingly encounter fragmented landscapes where habitat patches are embedded in an urban matrix, yet how migrating birds respond to urbanization is poorly understood. Our research evaluated the relative importance of patch-level effects and body condition to movement behaviour of songbirds during migratory stopover within an urban landscape. We experimentally relocated 91 migrant Swainson’s thrushes (Catharus ustulatus) fitted with 0.66 g radio-transmitters to seven forest patches that differed in area (0.7–38.4 ha) and degree of urbanization within central Ohio, USA, May 2004–2007. Fine-scale movement rate of thrushes (n = 55) did not differ among urban forest sites, but birds in low energetic condition moved at higher rates, indicating an energetically mediated influence on movement behaviour. In larger sites, Swainson’s thrushes (n = 59) had greater coarse-level movement during the first 3 days and utilized areas farther from forest edge, indicating stronger influence by patch-level factors. Thrushes exhibited strong site tenacity, with only five individuals (7%) leaving release patches prior to migratory departure. Movement outside the release patch only occurred at the smallest forest patches (0.7 and 4.5 ha), suggesting that these sites were too small to meet needs of some individuals. Swainson’s thrushes exhibited edge avoidance and apparent area sensitivity within urban forest patches during stopover, implying that conservation of larger patches within urban and other fragmented landscapes may benefit this species and other migrant forest birds.     

A comparison of satellite data and landscape variables in predicting bird species occurrences in the Greater Yellowstone Ecosystem,USA

We compare the accuracy of predicting the occurrence of 11 bird species in montane meadows of the Greater Yellowstone National Park ecosystem, in the states of Montana and Wyoming, USA. We used remotely sensed, landscape, and habitat data. The meadow type, as determined from the remotely sensed data, was highly correlated with abundances of six of the 11 bird species. Landscape variables significant in predicting occurrence were selected using a stepwise multiple regression for each bird species. These variables were then used in a multiple regression with the variable meadow type. As expected, the abundances of the generalist species (American Robin, Dark-eyed Junco, White-crowned Sparrow, Brewer's Blackbird, and Chipping Sparrow) were not strongly correlated with landscape variables or meadow type. Conversely, abundances of the Common Snipe, Common Yellowthroat, Lincoln's Sparrow, Savannah Sparrow, Vesper Sparrow, and Yellow Warbler were highly correlated with meadow type and landscape variables such as percent cover of willow (Salix spp.), graminoid, woody vegetation, sagebrush (Artemisia spp.), and graminoid and shrub biomass. The results from our study indicate that remotely sensed data are applicable for estimating potential habitats for bird species in the different types of montane meadows. However, to improve predictions about species in specific sites or areas, we recommend the use of additional landscape metrics and habitat data collected in the field.     

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.     

Landscape-scale Edge Effect in Predation Risk in Forest-farmland Mosaics of Central Europe

Avian nest predation is known to increase with the degree of forest fragmentation. A common explanation is that farmland allows for high densities of generalist predators, and predators penetrating into the forest cause higher nest losses at forest-farmland edges than in forest interiors. In contrast to numerous patch-level studies of forest edge effects conducted earlier, we broadened the spatial extent to the landscape. We tested the hypothesis of increased predation near farmland over distances of >4 km from forest–farmland edges into forest interiors in five mountain ranges in Germany, using artificial ground nests. We considered two landscape settings: (1) Transitions between a forest matrix and a farmland matrix, and (2) farmland patches within a forest matrix. Nest losses were not significantly higher in vicinity to a farmland matrix, but proximity to a pasture within the forest matrix strongly increased predation risk. We speculate that these differences resulted from landscape geometry. Farmland patches and matrix alike are highly attractive to generalist predators, and are regularly visited by red foxes from the forest. Predators that traverse the forest and take prey along the way, will cause a concentration of predation risk towards a patch (pasture), but not towards an adjacent matrix (farming lowlands), of feeding habitat. Contrary to previous evidence that edge effects in nest predation level off after 50 m, nest fate was related to distance to pastures across the entire study extent of 4.1 km. Our results suggest that landscape context and predator mobility may greatly affect spatial predation patterns.     

Contemporary spatial and environmental factors determine vascular plant species richness on highly fragmented meadows in Central Finland

Context

Habitat loss is a major threat to biodiversity. It can create temporal lags in decline of species in relation to destruction of habitat coverage. Plant species specialized in semi-natural grasslands, especially meadows, often express such extinction debt.

Objectives

We studied habitat loss and fragmentation of meadows and examined whether the changes in meadow coverage had caused an extinction debt on vascular plants. We also studied whether historical or present landscape patterns or contemporary environmental factors were more important determinants of species occurrence.

Methods

We surveyed the plant species assemblages of 12 grazed and 12 mown meadows in Central Finland and detected the meadow coverages from their surroundings on two spatial scales and on three time steps. We modelled the effects of functional connectivity, habitat amount, and isolation on species richness and community composition.

Results

We observed drastic and dynamic meadow loss in landscapes surrounding our study sites during the last 150 years. However, we did not find explicit evidence for an extinction debt in meadow plants. The observed species richness correlated with contemporary factors, whereas both contemporary factors and habitat availability during the 1960s affected community composition.

Conclusions

Effective conservation management of meadow biodiversity builds on accurate understanding of the relative importance of past and present factors on species assemblages. Both mown and grazed meadows with high species richness need to be managed in the future. The management effort should preferably be targeted to sites located near to each other.

     

Butterfly dispersal in inhospitable matrix: rare,risky, but long-distance

Metapopulation models typically assume that suitable habitats occupied by local populations and unsuitable matrix separating them form a ‘black-and-white’ landscape mosaic, in which dispersal is primarily determined by the spatial configuration of habitat patches. In reality, however, the matrix composition is also likely to influence dispersal. Using intensive mark-recapture surveys we investigated inter-patch movements in Maculinea (Phengaris) nausithous and M. teleius occurring sympatrically in six metapopulations. Three of these metapopulations had the matrix dominated by forest, an inhospitable environment for grassland butterflies, whereas in the remaining three the matrix was mostly composed of open environments. Dispersal parameters derived with the Virtual Migration model revealed significant differences between both groups of metapopulations. Both species had a lower propensity to emigrate from their natal habitat patches, and they suffered substantially higher dispersal mortality in the metapopulations with forest matrix. On the other hand, mean dispersal distances were roughly an order of magnitude longer in forest matrix as compared with open landscapes (ca. 500–1,500 vs. 100–200 m). Our results suggest that inhospitable forest matrix induces strong selection against dispersal, leading to a reduced emigration rate. At the same time, the selection may promote emigrants with good dispersal abilities, which are able to perform long-distance movements. Thus, while it is generally believed that a matrix structurally similar to the habitat of a species should improve the functional connectivity of habitat patches, our findings imply that this may not necessarily be the case.     

Maintenance of flying squirrel habitat and timber harvest: a site-specific spatial model in forest planning calculations

Spatial and temporal continuity of resources often benefits both ecological and economic goals in landscape management. Consideration of multiple and conflicting goals is also needed to view the future production possibilities of forests in successful forest management. Our aim was to estimate the production potential of a planning area in Finland by examining different forest management strategies from ecological and economic perspectives using long-term forest planning calculations. Economic objectives referred to timber production, whereas ecological objectives were based on suitable habitats for arboreal Siberian flying squirrel (Pteromys volans). Suitable habitats were defined using an empirical site-specific model, which includes a spatial variable reflecting the availability of habitat within an individual’s activity area. Five alternative forest plans were worked out with different objectives for flying squirrel habitat and timber production. The alternative plans were compared with respect to values of objective variables at the end of the planning period of 60 years and against a production possibility frontier among net present value and flying squirrel habitat. Varying objective values in our analyses resulted from different utilization of production possibilities, and the changes were in line with the objectives used. The formation of flying squirrel habitat clusters in the landscape was enhanced, and it did not always incur severe reductions in harvestable timber volume. Possibilities to combine ecological and economic goals, both spatial and aspatial, in the planning process seems to be an encouraging alternative for the long-term forest management in the future.     

Matrix Matters: Effects of Surrounding Land Uses on Forest Birds Near Ottawa,Canada

Matrix quality affects probability of persistence in habitat patches in landscape simulation models while empirical studies show that both urban and agricultural land uses affect forest birds. However, due to the fact that forest bird abundance and species richness can be strongly influenced by local habitat factors, it is difficult to analyze matrix effects without confounding effects from such factors. Given this, our objectives were to (1) relate human-dominated land uses to forest bird abundance and species richness without confounding effects from other factors; (2) determine the scale at which forest birds respond to the matrix; and (3) identify whether certain bird migratory strategies or habitat associations vary in richness or abundance as a function of urban and agriculture land uses. Birds were surveyed at a single point count site 100 m from the edge of 23 deciduous forest patches near Ottawa, Ontario. Land uses surrounding each patch were measured within increasingly large circles from 200 to 5000 m radius around the bird survey site. Regression results suggest that effects of urban and agricultural land uses on forest birds (1) are not uniformly positive or negative, (2) can occur at different spatial scales, and (3) differentially affect certain groups of species. In general, agriculture appeared to affect species at a broad spatial scale (within 5 km), while urban land use had an impact at both a narrower spatial scale (within 1.8 km) and at the broad scale. Neotropical and short distance migrant birds seemed to be the most sensitive to land use intensification within the matrix. Limiting urban land use within approximately 200–1800 m of forest patches would be beneficial for Neotropical migrant birds, which are species of growing conservation concern in temperate North America.     

A meta-analysis on the impact of different matrix structures on species movement rates

Many biodiversity conservation strategies aim to increase species movement by changing the landscape between suitable areas of habitat. We applied systematic review and meta-analytical methods to robustly assess evidence on the impact of matrix structure on movement rates, with the hypothesis that movement will be greater through matrix of a more similar structure (vegetation height and cover) to the home habitat. Twenty studies of movement through two or more different matrix types provided 107 effect sizes, expressing the difference between the relative movement rates in different matrix types. The studies were all on animals, including relatively mobile taxa such as birds and butterflies but also rodents and amphibians. We were able to detect that on average, movement was greater through matrix of a more similar structure to the species?? habitat despite the variation in studies in terms of matrix types, species and methods. The effect size was larger when there was a greater difference in the structure of the two matrix types being compared (e.g. comparing grassland to forest rather than short grass to long grass). However, there was a high degree of covariation between matrix contrast and studies and other significant subgroupings such as taxonomic group and matrix openness. The biological significance of the increase in movement is not clear; however, ecological theory predicts dispersing individuals are important for population dynamics. Changes to the structure of landscapes intended to improve permeability to movement are supported by the findings of this study, particularly for relatively mobile species. However, research over longer timescales, greater distances and range of taxonomic groups is necessary.     

Living on the edge: quantifying the structure of a fragmented forest landscape in England

Forest ecosystems have been widely fragmented by human land use, inducing significant microclimatic and biological changes at the forest edge. If we are to rigorously assess the ecological impacts of habitat fragmentation, there is a need to effectively quantify the amount of edge habitat within a landscape, and to allow this to be modelled for individual species and processes. Edge effect may extend only a few metres or as far as several kilometres, depending on the species or process in question. Therefore, rather than attempting to quantify the amount of edge habitat by using a fixed, case-specific distance to distinguish between edge and core, the area of habitat within continuously-varying distances from the forest edge is of greater utility. We quantified the degree of fragmentation of forests in England, where forests cover 10 % of the land area. We calculated the distance from within the forest patches to the nearest edge (forest vs. non-forest) and other landscape indices, such as mean patch size, edge density and distance to the nearest neighbour. Of the total forest area, 37 % was within 30 m and 74 % within 100 m of the nearest edge. This highlights that, in fragmented landscapes, the habitats close to the edge form a considerable proportion of the total habitat area. We then show how these edge estimates can be combined with ecological response functions, to allow us to generate biologically meaningful estimates of the impacts of fragmentation at a landscape scale.     

Landscape-level movements of North American elk (<Emphasis Type="Italic">Cervus elaphus</Emphasis>): effects of habitat patch structure and topography

We examined movements of North American elk (Cervus elaphus) in northeastern Oregon, USA. Movement vectors at 449 locations over a 7762 ha area were calculated based on 16,724 sequential observations of 94 female elk-year combinations during spring (15 April–14 May) 1993, 1995, 1996. We calculated movement vectors at the start of morning and evening feeding bouts (0500, 1900 h) and during periods of least activity (0100, 1500 h). Here, we measured characteristics of habitat patches (habitat type, mean patch size, coefficient of variation in patch size, edge density, mean shape index, and mean nearest neighbor) at two levels of habitat grain (eight habitat types, two habitat types) and at three spatial scales (250, 500, and 1000 m) around each movement vector. We also measured topographic features around each vector including distance to nearest stream, direction of drainage, elevation, slope, and convexity (a measure of ridge top vs. valley bottom land form). We used mixed models adjusted for positive spatial correlation among vectors to examine the relationship between vector length, or speed of movement, and habitat patch characteristics, and between vector direction and topographic features. Speed of movements by elk were not related to characteristics of habitat patches that we measured. The direction of movement, however, was dependent on topography. Elk were more likely to move parallel to major drainages than perpendicular to them. Furthermore, elk were less likely to move perpendicular to drainages when close to the nearest stream, in valley bottoms vs. ridge tops, and on steep slopes. The dendritic nature of movements by elk with respect to topography may help elucidate ecosystem processes such as nutrient flows, nutrient cycling, and successional trajectories of plant communities.     

Habitat attributes of landscape mosaics along a gradient of matrix development intensity: matrix management matters

The matrix is an important element of landscape mosaics that influences wildlife indirectly through its influence on habitat, and directly, if they live in or move through it. Therefore, to quantify and manage habitat quality for wildlife in modified landscapes, it is necessary to consider the characteristics of both patch and matrix elements of the whole landscape mosaic. To isolate matrix effects from the often simultaneous and confounding influence of patch and landscape characteristics, we identified nineteen 500 m radius landscapes in southeast Queensland, Australia with similar remnant forest patch attributes, habitat loss, and fragmentation, but exhibiting a marked gradient from rural through high-density suburban development of the matrix, quantified by a weighted road-length metric. We measured habitat disturbance, structure, and floristics in patch core, patch edge and matrix landscape elements to characterise how landscape habitat quality changes for small mammals. Correlation analyses identified that with increased matrix development intensity, human disturbance of core sites increased, predators and exotic plant species richness in matrix sites increased, and structural complexity (e.g. logs and stumps) in the matrix decreased. Ordination analyses showed landscape elements were most similar in habitat structure and floristics at low to moderate levels of matrix development, suggesting enhanced landscape habitat quality. Matrix development intensity was not, however, the greatest source of overall variation of habitat throughout landscapes. Many variables, such as landholder behaviour, complicate the relationship. For enhanced conservation outcomes the matrix needs to be managed to control disturbances and strategically plan for matrix habitat retention and restoration.     

Response of snails and slugs to fragmentation of lowland forests in NW Germany

Habitat fragmentation is a major cause for species loss, but its effect on invertebrates with low active dispersal power, like terrestrial gastropods, has rarely been studied. Such species can not cross a hostile habitat matrix, for which the predictions of island theory, such as positive relations between species richness and patch size, should apply. In order to test this prediction, we studied gastropod species diversity by assessing gastropod assemblage characteristics from 35 sites in 19 fragments of deciduous old-growth forests in the Lower Rhine Embayment, Germany. Assemblages differed between larger (≥700 ha) and smaller forests (<400 ha), those of large forests held a higher percentage of forest species. Although α-diversity was similar between the two forest size classes, small forests often comprised matrix species, resulting in a higher β-diversity. Edge effects on the species richness of matrix species were noticeable up to 250 m into the forest. Hierarchical partitioning revealed that distance to disturbances (external edge, internal edges like roads) explained most assemblage variables, whereas forest size and woodland cover within a 1 km radius from the sites explained only a few assemblage variables. Densities of two forest-associated species, Discus rotundatus and Arion fuscus, decreased with forest size. Yet, forest size was positively correlated with richness of typical forest species and densities of Limax cinereoniger. The latter species seems to need forests of >1,000 ha, i.e., well above the size of most fragments. In conclusion, the prediction is valid only for forest species. The response to fragmentation is species specific and seems to depend on habitat specialization and macroclimatic conditions. Jean-Pierre Maelfait: Deceased.     

Short perceptual range and yet successful invasion of a fragmented landscape: the case of the red-bellied tree squirrel (<Emphasis Type="Italic">Callosciurus erythraeus</Emphasis>) in Argentina

Dispersal is a key element of the invasion process for introduced species, and is influenced by landscape connectivity. The red-bellied squirrel (Callosciurus erythraeus) was introduced to Argentina in 1970. Suitable forest habitat for this arboreal species is highly fragmented in a rural–urban matrix, but despite this, the squirrel population has spread. Squirrels disperse into new habitat patches using connective features such as forest corridors. They may also cross gaps but up to what extent is not known. Gap crossing success is influenced by perceptual range, which is the distance from which animals can perceive suitable habitat. Perceptual range has been previously estimated for vulnerable species, but not for introduced species. We used a model relating perceptual range to body mass to predict the perceptual range of the red-bellied tree squirrel in Argentina. We then tested our prediction of 202–221 m by releasing squirrels in an unfamiliar arable field at different distances (300, 200, 100 and 20 m) from woodland habitat. We assumed that if woodland could be perceived, squirrels would orientate toward it. We estimated perceptual range to be between 20 and 100 m, considerably lower than predicted. Our results indicate that squirrels can potentially cross small habitat gaps, but dispersal over greater distances lacking connectivity is less likely. Incorporating this information when modelling the spread of exotic squirrels in the Pampas Region can yield more accurate prediction of the invasion process and guide management practices to minimise their expansion.