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In Scotland both pine martens and red foxes utilise fragmented habitats of forest and open-grassland. 

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In Scotland both pine martens and red foxes utilise fragmented habitats of forest and open-grassland. 

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Red Foxes are both a competitor and intra-guild predator on the pine martnes, however both have been recorded in several studies to have a preference for field voles due to their high abundance and density in high areas. Pine martens where thought to be strictly forest-dwellers due to the majority of habitat-related studies being in Northern Europe where the landscape has a greater area of forest habitat. However, in Scotland it is observed that pine martens can move around open grasslands to an extent, as long as there is sufficient tree coverage for their protection against predation. Red foxes overlap their niche with pine martens as they are hugely flexible in habitat use, consuming a large variety of species from voles, to amphibians, reptiles, larger mammals like squirrels, deer, lambs, etc. Pine martens are tree-climbers allowing them to easily move around the tree cover, but are also known to hunt on the ground for prey, such as capercaillie, voles, mice, etc.

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Branchiura, commonly called carp lice or fish lices are a group of parasotoc crustaceans of uncertain positions within the Maxillopoda. Although they are thought to be primitive forms, they have no fossil record. Almost all are ectoparasites on fish, a few on amphibians.

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Enter your email address below. If your address has been previously registered, you will receive an email with instructions on how to reset your password. If you don't receive an email, you should register as a new user

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Parasitic tick species in Scotland, consuming blood from various mammals (including HUMANS), birds and reptiles.

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Parasitic tick species in Scotland, consuming blood from various mammals (including HUMANS), birds and reptiles.

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Are known to be deadly spreaders of Lyme disease...

http://php.scripts.psu.edu/users/p/j/pjh18/downloads/165_Kirby_et_al_2004_Sheep_tick_increase_Med_Vet_Entomology.pdf

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1474-919X.2011.01111.x

https://www.researchgate.net/profile/Jolyon_Medlock/publication/274067721_Impact_of_climate_change_on_vector-borne_disease_in_the_UK/links/5a030a3fa6fdcc6b7c9bced8/Impact-of-climate-change-on-vector-borne-disease-in-the-UK.pdf

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Scottish raptors (peregrines, sparrowhawks, Merlins, etc) predate on wintering wader birds.

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Scottish raptors (peregrines, sparrowhawks, Merlins, etc) predate on wintering wader birds.

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Location of a study I researched on the predation of pine martens and foxes on field and bank voles

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Location of a study I researched on the predation of pine martens and foxes on field and bank voles

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Strathspey, Scotland

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Illustrating the pine marten (Martes martes) predation in Scotland, whose main prey item is the field vole (Microtus agrestis).

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Prey - Field Voles

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Abstract

Conceptual models of forest fragmentation that contrast habitat patches with a uniformly unsuitable matrix (i.e., the nonhabitat surrounding habitat patches) ignore the importance of heterogeneity within the matrix ( Kupfer et al. 2006). Although binary fragmentation models may be appropriate for some forest specialists, for many species the matrix forms a continuum of habitats of varying permeability ( Fischer et al. 2004; Haila 2002). Matrix permeability is determined by the structural similarity between matrix habitats and remnant habitats, the perception of which is both species- and context-dependent ( Kupfer et al. 2006). Because ecological processes within remnants (such as dispersal and foraging) vary as a function of their surroundings, the matrix has great potential to mitigate the negative effects of habitat loss and fragmentation ( Dunford and Freemark 2004). Functional connectivity may be maintained even within highly fragmented landscapes depending on how an organism perceives and responds to the intervening matrix between remnants ( Bélisle 2005; Ricketts 2001). In some cases, the matrix may provide alternative or supplementary resources (e.g., food or nest sites) that support greater population densities than would be expected within remnants alone (i.e., habitat complementation [e.g., Andrén 1994]). Ignoring the ecological qualities of the matrix may therefore result in a gross underestimation of its importance to organisms within remnants and its potential to serve as functional habitat. To better understand how wildlife populations persist within fragmented landscapes it is necessary to determine if, how, and why animals utilize matrix habitats.

The European pine marten ( Martes martes) is often described as a forest-dependent specialist of late-successional forests, an association that may be partly due to a large number of habitat studies for martens occurring within the forest-dominated landscapes of Fennoscandia ( Brainerd 1990; Kurki et al. 1998; Lindström 1989; Storch et al. 1990), and to implied similarities with congeneric American martens ( M. americana) within the equally forested regions of North America and Canada (e.g., Buskirk and Powell 1994). By contrast, the landscapes of western Europe are much less forested ( Food and Agriculture Organization of the United Nations 2003). Yet martens are present in western Europe, occurring in landscapes with as little as 4% forest cover ( Balharry 1993). Although their habitat preferences are much less studied, research indicates martens in this region are less dependent on forests than elsewhere in their range (e.g., Pereboom et al. 2008). In Scotland, for instance, where forest covers just 17% of land area ( Malcolm et al. 2001), the primary prey of martens is Microtus agrestis ( Balharry 1993; Caryl 2008; Lockie 1961), a species of vole that is characteristic of open tussock grassland and is absent from forest interiors ( Hansson 1978). This contrasts with dietary preferences of martens within the more forested regions of temperate and boreal Europe, where the most important prey are forest-dwelling Myodes ( Zalewski 2004). Understanding how martens utilize different matrix habitats may facilitate conservation management of this species in regions where forest cover is low. Yet despite this dietary indication that martens are utilizing the nonforested matrix, previous research on habitat use by Scottish martens has focused on their use of forest habitats while treating the matrix as uniformly unsuitable ( Balharry 1993; Halliwell 1997).

In this study we investigated how both forest and matrix habitats are utilized by martens by measuring the structural and trophic components of habitats occupied by martens. predation and winter severity are major limiting factors to European marten populations that directly influence habitat selection ( Helldin 1998; Zalewski and Jędrzejewski 2006). We therefore predicted martens would select structurally complex habitats that provide protective cover from predators and temperature extremes ( Buskirk and Powell 1994), irrespective of whether those habitats occur within forest or the matrix. We also predicted martens would select habitats in which their preferred prey was found (i.e., tussock grassland- Caryl 2008). Matrix permeability is often related to body size; smaller-bodied species tend to be more prone to predation in the matrix, whereas large-bodied species view the matrix as less of a barrier to movement ( Gehring and Swihart 2003). Because there is considerable sexual size dimorphism within Martes species, we predicted smaller-bodied females would be more risk-averse than males and would avoid those habitats that offered the least structural protection from predators.

Habitat loss and fragmentation are landscape-scale processes, yet few studies of their effects on populations of European mammals have been conducted at an appropriate scale (i.e., where individual landscapes are the study units- Mortelliti et al. 2010). To better understand the landscape-level effects of habitat loss and fragmentation on marten populations, we compiled data from previous studies to investigate how the diet and population density of martens varied among landscapes with differing amounts of forest cover and forest edge densities (the latter as a measure of fragmentation). Marten populations are vulnerable to fragmentation ( Bright 2000), yet increased foraging opportunities in forest gaps may allow population densities to increase with low levels of fragmentation, provided forest habitats remain sufficiently connected, although a sharp population decline is expected once fragmentation reaches a threshold level ( Brainerd 1990; Thompson and Harestad 1994).

Materials and Methods

Study area.-The 6,000-ha study area was located around Morangie Forest, a managed coniferous plantation in northeastern Scotland, United Kingdom (57.8°N, 4.1°W). The surrounding landscape has a low human population density (5 people/km ²) and comprises farmland, woodland, and open heath uplands, with elevations ranging from 0 to 400 m above sea level. The region has an oceanic climate with cool, wet summers (July X̄ = 13°C) and mild winters (February X̄ = 0°C- MetOffice 2008). The forest, which covers around 3,000 ha, is dominated by 1st-rotation stands planted on formerly bare ground (61%) with fewer stands on historically wooded land (34%, of which just 4% has been continuously forested since about 1900). Lowland areas are dominated by thinned stands of native Pinus sylvestris that contain dense ground cover by Calluna vulgaris-Vaccinium myrtillus heath. Exposed uplands are dominated by unthinned stands of exotic conifers (e.g., Pinus contorta and Picea sitchensis) managed on a large-scale clear-cut and replant system. Deciduous trees (e.g., Betula pendula and Sorbus aucuparia) are patchily distributed throughout the forest. Shrubby species (e.g., Ulex europaeus, Rhododendron ponticum, and Salix) frequently encroach into open areas. Unplanted areas are dominated by heaths of blanket bogs (e.g., C. vulgaris and Eriophorum vaginatum) and moorland grasses (e.g. Nardus stricta and Molinea caerulae) at higher elevations, and by damp grasslands (e.g., Holcus lanatus and Deschampsia cespitosa [all communities according to Rodwell 1998]) at lower elevations.

Marten capture and telemetry.-Between January 2006 and July 2007 we set cage traps (Tomahawk Live Trap Co., Tomahawk, Wisconsin) at prebaited locations along forest roads throughout the study area. Captured martens were immobilized with an intramuscular injection of Ketalar and Domitor, antagonized by Antisedan (Pfizer Inc., New York, New York), using dosage rates recommended for similarly sized mustelids ( Fournier-Chambrillon et al. 2003). Captured animals were weighed and aged (juvenile or adult ≥ 1 year) according to body size and tooth wear. Adult martens were fitted with very-high-frequency radiocollars (TW-3; Biotrack Ltd., Dorset, United Kingdom) and uniquely identified with a passive transponder implanted subcutaneously into the neck. Animal capture and handling were consistent with guidelines of the American Society of Mammalogists ( Sikes et al. 2011). All procedures were preapproved by the University of Stirling ethical review committee and adhered to strict Government compliance under the Animals (Scientific Procedures) Act 1986 regarding the welfare of animals in scientific studies (British Home Office License PIL60/10174). All legal requirements of working with a protected species were met (Scottish Natural Heritage Scientific License 6146).

One animal was tracked per night, on foot or by car, for up to 16 h. Locations of martens were estimated at intervals ≥ 20 min with simultaneous biangulations. Preliminary tests showed the mean accuracy of this method was 55 m ( SE = 9 m) and mean bearing error was 12° ( SD = 10°- Zimmerman and Powell 1995). We used Locate III software ( Nams 2006) to estimate animal locations and 95% confidence ellipses from biangulations. Locations with confidence ellipses > 10 ha were excluded from further analysis. Remaining locations had confidence ellipses of 2 ha ± 0 SE, 58% of which were ≤1 ha. We entered marten locations into ArcView GIS (ESRI, Redlands, California) for analysis with the Home Range Extension ( Rodgers and Carr 1998). We used a 95% minimum convex polygon ( Harris et al. 1990) to estimate the home range of each marten. Martens were tracked until plots of home-range size over time reached an asymptote; those that did not were excluded from further analysis.

Habitat mapping.-Delimiting a study area, hence determining the availability of habitats to martens within the landscape, is an arbitrary decision ( Garshelis 2000). We defined the study area as the minimum convex polygon containing the home ranges of all martens buffered by a distance equal to the average length of home ranges belonging to females (1.8 km). We included this additional buffer to make composition of the habitats from which martens could select their home ranges more representative of those within the greater landscape. Within the 5,902-ha study area, land-cover was classified into 7 habitat types based upon ground, shrub, and canopy vegetation using forest inventory maps (Forestry Commission, Edinburgh, United Kingdom), digital land classifications (LCM2000; Land Cover Map 2000; Centre for Ecology and Hydrology, Edinburgh, United Kingdom), and orthorectified aerial photographs (0.5 m ² resolution taken 2005; Forestry Commission, United Kingdom) before being ground-truthed with field visits. We defined 4 matrix habitats where tree canopy was <30% (scrub, tussock, heath, and agriculture), and 3 forest habitats where tree canopy was >30% (closed-canopy forest, mature coniferous forest, and deciduous woodland; Table 1). The selection of 30% canopy cover as a threshold distinguishing between matrix and forest habitats was arbitrary but based on the canopy-cover threshold at which habitat suitability increases for American martens ( Hargis et al. 1999).

Tussock

Ungrazed grassland, typical of low elevations. Contained high-productivity grasses and rushes (e.g., Holcus-Deschampsia- Rodwell 1998).

Present

Absent

Absent

18

Ma, S

Heath

Common on unplanted uplands; dominated by heaths (e.g., Calluna vulgaris)and low-productivity upland grasses (e.g., Nardus-Carex- Rodwell 1998).

Present

Absent

Absent

3.2

Mg

Agriculture

Includes tilled fields but predominantly comprised of grazed pasture.

Present

Absent

Absent

0

-

Habitat selection of martens.-We determined use of habitat by martens at 2 spatial scales; 1st comparing the proportion of habitats found within individual home ranges to their availability within the study area based on the number of hectares of each habitat, referred to herein as home-range-level selection (Design II- Thomas and Taylor 1990); then comparing the proportion of locations in each habitat with their availability within home ranges, referred to herein as location-level selection (Design III- Thomas and Taylor 1990). Locations were differentiated as being active or static depending on the physical state of martens when a location was recorded and separate analyses were conducted for each. To ensure independence of static locations, only 1 static location was recorded per denning event and subsequent locations were disregarded until the animal moved again. Home ranges were defined by the 95% minimum convex polygon buffered by a distance of 55 m (our mean telemetry error). Locations were treated as an ellipse rather than a single point, with the habitat of greatest proportional cover considered used at that location ( Nams 1989). Because female martens are morphologically and energetically more constrained than males, they may be more selective ( Buskirk and Powell 1994). We therefore examined sex-specific habitat selection rather than pooling data across sexes ( Garshelis 2000). Habitat preferences and differences in preferences between sexes were examined with Bonferroni-adjusted 90% confidence limits ( Cherry 1998). To avoid unequal weighting, we randomly selected an equal number of active locations (males: n = 22; females: n = 28) and static locations ( n = 8 for both sexes) from each individual ( Thomas and Taylor 2006). Selection of critical resources is likely to be less variable than others, so we determined variability in individual selection strategies by calculating resource-selection indexes (RSI: % habitat use - % habitat available) from nonpooled data ( Thomas and Taylor 1990). We used t- tests to determine sex-related differences in home-range size and body mass. We also used Mests to evaluate intersexual differences in the distance travelled by individual martens into the matrix after measuring the mean and maximum distance of locations outside forest habitats. A chi-square test was used to compare the frequency with which each sex was located outside forest habitats.

Forest fragmentation, home-range size, and diet of martens across Scotland.-We examined the diet and home-range size of martens in relation to forest cover and forest edge density and extent among Scottish landscapes. We used home-range data from studies that have investigated spatial ecology for martens in Scotland ( Balharry 1993; Bright and Smithson 1997; Halliwell 1997), each of which provided dietary data from scat-content analysis conducted simultaneously with tracking within each landscape. In total, we had home-range and dietary data for martens in 6 landscapes across Scotland (including our data from Morangie, dietary data for which came from Caryl [2008]; Table 2; Fig. 1).

We standardized the dietary importance of small mammals in each landscape as the frequency of small mammal occurrences in scats divided by the number of scats analyzed within that landscape to account for inconsistencies in reporting results. We provide a relative measure of the density of resident adult martens in each landscape using the mean sex-specific home-range size (100% minimum convex polygon). We take this measure to be the approximate inverse of breeding marten population density assuming that martens display intersexual territoriality, that only adult martens defend territories, and that home ranges within each sex abut each other contiguously ( Balharry 1993; Caryl 2008). We recognize that high population density does not necessarily indicate high habitat quality ( Van Home 1983), but by focusing on adult resident martens we effectively ignore the juvenile, dispersing, or transient individuals that often artificially inflate population densities in poor-quality habitat.

Forested extent (%) was calculated within a 9.77-km radius (300-km ² area) from the center of each site. Data on forest cover were obtained from the LCM2000 digital land-use layer ( Fuller et al. 2005). We included land classified as clear-cut to account for changes to forest cover between the year that this data layer was created (2000) and when marten data were collected among studies. We then calculated the density of forest edges per hectare of forest (m/ha) as an index of forest fragmentation within each landscape. General linear models were used to examine relationships between measures of forest cover and fragmentation with small mammal consumption and home-range sizes of martens among landscapes. For each analysis a quadratic function of forest cover or edge density was included in the starting model to assess whether this provided a better fit than a linear function, but was removed if nonsignificant. All statistical tests were conducted in SPSS 17.0 for Windows (SPSS, Armonk, New York) and Microsoft Excel 2007 (Microsoft Corporation, Redmond, Washington).

Data were transformed where necessary to achieve normality and equal variance. All averages and coefficients are presented as means with standard errors unless otherwise stated.

Results

We captured and collared 16 adult pine martens (8 males and 8 females), of which sufficient data were collected for 4 males and 7 females to allow home-range estimation. A total of 594 locations were obtained, with 50 ± 4 locations per female and 54 ± 8 locations per male. Home ranges for females reached an asymptote after 29 ± 3 locations and for males after 40 ± 7 locations. Unbuffered home ranges for females (95% minimum convex polygon) were significantly smaller than those of males, measuring 50 ± 1 ha and 353 ± 7 ha, respectively ( = -4.405, P = 0.026). There was considerable body size dimorphism between the sexes; males weighed 1.88 ± 0.7 kg (range = 1.60-2.30 kg), almost 1.4 times heavier than females (1.37 ± 0.4 kg, range = 1.21-1.55 kg: t ₁₄ = 6.195, P < 0.001).

Habitat selection.-Martens clearly selected home ranges from the landscape in a nonrandom pattern ( Table 3; Fig. 2). Both sexes selected the same 3 habitats at the home-range level (mature forest, tussock grassland, and scrub), while avoiding the same 2 habitats (closed-canopy forest and agriculture; Table 3). In addition, females strongly avoided heath moorland at the home-range level, whereas males avoided deciduous woodland. Individual selection strategies suggested female aversions to closed-canopy forest, heath, and agriculture at the home-range scale were universal to all females ( Fig. 2a). Males were more variable in their selection patterns, yet agricultural land was universally avoided ( Fig. 2b). No universal preferences were apparent at the home-range level except that of female selection for tussock grassland.

There were few significant preferences at the location level, suggesting that once habitats were selected from the landscape they were generally used in accordance to their availability ( Table 3). An exception was that stationary females avoided heath within home ranges, whereas stationary males avoided deciduous woodland and active males avoided tussock grassland. Individual selection strategies concur there was much less selection by active martens than at the home-range level, with most resource-selection indexes lying near zero ( Fig. 2a). However, there does appear to be an indication of selection by stationary martens, with females having positive a positive resource-selection index for mature forest and scrub and males having a positive resource-selection index for mature forest and closed-canopy forest ( Fig. 2).

There were intersexual differences in habitat utilization for all habitats at the home-range level except scrub and tussock grassland ( Table 3). Scrub and tussock grassland were equally selected by both sexes despite low availability within the study area. Use of all other habitats appeared to follow a general pattern in which females made greater use of forested habitats than did males (63.5% ± 5.0% of home range forested), whereas males made greater use of matrix habitats than did females (47.2% ± 10.5% of home range forested). For example, females utilized mature forest and deciduous woodland significantly more than males at the home-range level, whereas males used heath and agriculture significantly more than females ( Table 3). Within home ranges, active females utilized tussock grassland more than did males, and active males utilized heath more than did females. There were no significant differences in habitat use at stationary locations.

Greater proclivity for open spaces by males was reflected by significant intersexual differences in both the mean and maximum distance travelled outside forest habitats by individuals ( = −2.601, P < 0.05 and = −2.405, P < 0.05, respectively). Males typically travelled 75.1 ± 18.6 m outside forest habitats, up to an average maximum of 199.6 ± 46.3 m, whereas females typically travelled just 30.4 m into the matrix, up to an average maximum distance of 93.7 ± 21.1 m. Males also travelled outside forested habitats more frequently than females; 46% of male locations occurred outside forests compared with just 33% of female locations ( = 8.786, P < 0.005).

Forest fragmentation, home-range size, and marten diet across Scotland.-There was considerable variation in the amount of forest cover among landscapes across Scotland, with an order of magnitude between the least (4%) and most (47%) forested, which corresponded to an equally variable degree of fragmentation among landscapes ( Table 2). Similarly, there was an order of magnitude difference between largest (33 km ²) and smallest (3 km ²) home ranges of male martens. The frequency of consumption of small mammals varied from 0.34 to 0.93 occurrences per scat. Small mammal remains were not identified to species at Minnoch and Glen Trool ( Bright and Smithson 1997), but M. agrestis formed an average 80% ( SE = 5%) of small mammals in the diet within the other 4 landscapes. The relationship between small mammal consumption and forest fragmentation demonstrated a strong positive correlation, indicating that as landscapes became more fragmented, small mammals constituted a greater part of the marten's diet (F ₁₄ = 56.77, P = 0.002, β = 0.007 ± 0.001, adj = 91.8%; Fig. 3A). A strong negative correlation existed between the extent of forest cover and forest edge-density within landscapes (Pearson correlation r = −0.83, P = 0.042, n = 6). Henceforth we only present results in reference to the latter, because edge-density had a greater functional significance in relation to the consumption of small mammals. Home ranges of males were logged prior to analysis. As predicted, the relationship between fragmentation and home-range size of female martens was nonlinear (edge density = 25.53, P = 0.015; edge density ² = 26.23, P = 0.014, adj = 82.9%; n = 6; Fig. 3B) as was that of males (edge density F 1,3 = 13.43, P = 0.035; edge density ² = 14.06, P = 0.035, adj = 71.1%, n = 6; Fig. 3C). Home ranges of martens were smallest at intermediate levels of landscape fragmentation (where the forested extent lay between 25% and 30%), and increased in size at higher and lower levels of fragmentation. However, we acknowledge that because of the small sample size these patterns are sensitive to individual points, particularly at the lowest and highest edge densities, and should be viewed with caution.

Discussion

Our results add support to the suggestion that European pine martens, like other marten species (e.g., Hearn et al. 2010), may be less forest-dependent than previously believed ( Mortelliti et al. 2010; Pereboom et al. 2008). Although martens demonstrated a strong preference for mature forest, both sexes showed strong selective preferences for 2 matrix habitats within their home ranges: tussock grassland and scrub. Consistent selection of these habitats suggests the matrix is not only penetrable but utilized by martens. Furthermore, matrix habitats may provide key resources that are unavailable within forest habitats; the most notable of which being Microtus, which are absent from forest interiors ( Caryl 2008), but are the primary prey of martens ( Balharry 1993; Caryl 2008; Halliwell 1997; Lockie 1961).

Matrix habitats that have a high degree of structural contrast with remnant vegetation are less penetrable to species than low-contrast habitats (e.g., Forman 1995). Martens are commonly described as specialists of old-growth forest ( Brainerd 1990; Lindström 1989; Storch et al. 1990), and as such all nonforested habitats have typically been considered to be equally unsuitable. Yet evidence increasingly suggests that it is the structural elements within forests rather than forest composition or age that most influences marten habitat selection ( Brainerd et al. 1994; Hearn et al. 2010; Payer and Harrison 2003; Poole et al. 2004). Many of the structural features associated with old-growth forests (e.g., multilayered tree canopies, large-diameter trees, standing and fallen deadwood, and dense understory vegetation) are required by martens because they help reduce predation threats ( Storch et al. 1990), increase foraging efficiency ( Andruskiw et al. 2008; Thompson and Harestad 1994), and offer thermally insulated resting sites ( Zalewski 1997). However, these structural legacies are often not available in regions of the marten's geographic range in which much of the original forest cover was removed many centuries ago. For instance, the majority (76%) of British forests are secondary, that is, they occupy ground that has not been wooded until recently, and so possess few of the structural features of old-growth forest ( Humphrey 2005). In the absence of suitable structural features it seems that martens in our study area were supplementing the resources required to avoid predation, den, and forage from complementary, low-contrasting habitats within the matrix.

Predator avoidance is an important determinant of habitat use by martens ( Helldin 1998), and structure near the ground is known to provide protective cover for martens (e.g., Slauson et al. 2007). Female martens are smaller than males and subject to greater predation risk and energetic costs, and are thus likely to be more selective in their habitat choice. We found females were more reluctant to leave forest habitats than males, and typically moved no more than 100 m outside forest edges. Martens have 2 extant predators within Scotland-red foxes ( Vulpes vulpes) and golden eagles ( Aquila chrysaetos- Helldin 1998)-both of which were present within the study area (F. M. Caryl, pers. obs.). One similarity among those habitats strongly avoided by female martens (i.e., closed-canopy forest, heath moorland, and agricultural fields) was that cover near the ground was either absent or greatly reduced in stature. The high shading beneath closed-canopy stands restricts understory vegetation resulting in a ground cover dominated by bryophytes and needle litter ( Hill 1986); exposure and heavy grazing of upland heath often results in compact, low-lying vegetation ( Grant and Hunter 1962), whereas continuous grazing has obvious impacts on agricultural pastures. By contrast, ground vegetation was well established in habitats that were preferred by female martens. Thinning to reduce stem density within mature stands (one of our defining criteria) increases irradiance to the ground resulting in a dense understory similar to that found in seminatural forests ( Ferris et al. 2000; Wallace and Good 1995). Scrub habitats provide essential structural features for many small carnivore species within the agriculturally dominated landscapes of western Europe ( Matos et al. 2009; Pereboom et al. 2008; Rondinini and Boitani 2002; Santos and Santos-Reis 2010; Virgós 2001), and so it is not surprising that this habitat is important for martens within our study area. Although lacking in understory and canopy layers, the Holcus-Deschampsia communities that are typical of ungrazed tussock grassland form characteristic tussocks up to a meter in height ( Rodwell 1998), thus providing some degree of ground cover in addition to foraging resources (see below).

Resource-limited animals may expose themselves to greater risks in order to acquire resources across habitat boundaries ( Bélisle 2005). That martens utilized 2 matrix habitats in addition to mature forest suggests that matrix habitats may provide resources that are unavailable within mature forests alone. The most important prey of Scottish martens are Microtus voles ( Balharry 1993; Caryl 2008), which is unusual given that Myodes are numerically dominant within home ranges of martens ( Balharry 1993; Caryl 2008) and form the bulk of their diet throughout the marten's range ( Zalewski 2004). Microtus are denizens of ungrazed tussock grassland ( Caryl 2008), which undoubtedly accounts for the selection of this habitat by martens within our study area. Interestingly, females made significantly greater use of this habitat while active than did males, which may be indicative of resource partitioning between the sexes. A dietary preference for Microtus may indicate a behavioral trait that has adapted in response to Scotland's highly fragmented past during which forest-dwelling Myodes would have been scarce. Alternatively, low volumes of coarse woody debris within plantations may mean that Myodes remain unavailable to martens despite their abundance, because coarse woody debris is needed to provide sensory cues to martens as to the location of forest rodents ( Andruskiw et al. 2008; Thompson and Harestad 1994). Despite management steps to retain coarse woody debris within plantations, even volumes of coarse woody debris within mature forest stands remain low relative to old-growth forests ( Humphrey 2005; Kirby et al. 1998). It is unclear whether further restoration of coarse woody debris within plantations will change the vole preference of Scottish martens, but at present they are supplementing their prey resources with subsidies from the matrix. Martens in our study area also seemed to be supplementing den sites from the matrix. Plantation forests have few of the arboreal cavities that are commonly used as den sites by martens in old-growth forests to provide protection from foxes ( Birks et al. 2005). Instead, we found that scrub habitat was being used more at female resting locations (23% ± 6%) than at active locations (13% ± 8%), which suggests that it may provide important resting habitat. Ground-level dens are unusual for maternal dens (J. Birks, The Vincent Wildlife Trust, Ledbury, United Kingdom, pers. comm.), yet we observed 4 of the 7 females we tracked (3 of which had young) denning within scrub habitat; specifically 2 beneath dense shrubs ( U. europaeus and R. ponticum) and 2 beneath wind-thrown trees or clear-cut debris, such as piles of branches.

Spatially subsidized predators (i.e., those that gain resources across habitat boundaries) often have abundances that exceed what local resources would otherwise support (e.g., Andrén 1994). The strong positive correlation we found between the consumption of small mammals and forest edge density among Scottish landscapes suggests that foraging opportunities for small mammal prey increase where fragmentation results in increased availability of edge habitat. As predicted, this initially supported higher population densities of martens, as evidenced by smaller home-range sizes. Once forest fragmentation passed a threshold level, however, population densities of martens decreased (i.e., their home ranges expanded). Unfortunately, because of the small sample size of studies used in our synthesis we were not able to investigate the effect of different land uses within the matrix. However, the composition and configuration of the matrix will undoubtedly influence processes within landscapes. Previous studies into the effects of forest fragmentation on population density of martens in Fennoscandia ( Kurki et al. 1998) and North America ( Chapin et al. 1997; Hargis et al. 1999) also have not accounted for variation within the matrix. Yet as our results demonstrate, the nonforested matrix is not homogenous from the perspective of a pine marten. In fact, complementary resources from the matrix may be essential for the completion of their life phases depending on local conditions. Fragmentation effects in landscapes composed of matrix habitats that contrast strongly with remnant vegetation are likely to be worse than those in which the matrix is structurally similar ( Forman 1995). Therefore, to gain greater insight into the landscape requirements of martens (and indeed other forest-dwelling species), we need to account for a more complex perception of habitats than forest versus matrix. This is particularly so where the length of time since habitat loss has impacted faunal life histories, or where remaining forest habitats are secondary.

Much of the forest cover in Scotland today comprises afforested plantations in the closed-canopy stage ( Malcolm et al. 2001; Mason 2007), which make poor-quality habitat for martens. In addition, a large proportion of the Scottish landscape is dominated by inhospitable matrix habitats (i.e., moorland and agriculture). The reluctance of martens to cross large areas without cover means that even relatively nearby forest remnants may not be used if they are isolated by unsuitable intervening habitats ( Ricketts 2001), and as slow-breeding mammals, martens are particularly vulnerable to local extinctions should functional connectivity be lost ( Bright 2000). Strategies for conserving martens in these highly fragmented landscapes should seek to restore old-growth conditions within existing forest stands while managing the surrounding matrix to ensure that complementary (i.e., low-contrast) habitats are available. As our results have shown, the matrix has enormous potential to mitigate some of the negative effects of habitat loss and fragmentation that should not be overlooked.

Acknowledgments

We thank Scottish Natural Heritage, Forest Research, and the University of Stirling for providing funding for this work; Forest Enterprise Scotland for logistical support; numerous volunteers who assisted with fieldwork; A. Peace for statistical advice; and R. Raynor, R. Coope, and D. Balharry for invaluable advice and discussion. The manuscript was greatly improved by suggestions from 2 anonymous reviewers.

Literature Cited

# data[].attributes.attachment_link.title
Martens in the matrix: the importance of nonforested habitats for forest carnivores in fragmented landscapes

# data[].attributes.attachment_link.description
Conceptual models of forest fragmentation that contrast habitat patches with a uniformly unsuitable matrix (i.e., the nonhabitat surrounding habitat patches) ignore the importance of heterogeneity within the matrix ( Kupfer et al. 2006). Although binary fragmentation models may be appropriate for some forest specialists, for many species the matrix forms a continuum of habitats of varying permeability ( Fischer et al.

# data[].attributes.headline
"We found that aspen overstory recruitment ceased during the same years that wolves, a significant source of elk predation, wereremoved from Yellowstone National Park. Wolves may positively influence aspen overstory recruitment through a trophic cascades effect by reducing elkpopulations, modifying elk movement, and changing elk browsing patterns on aspen."

# data[].attributes.subject
"We found that aspen overstory recruitment ceased during the same years that wolves, a significant source of elk predation, wereremoved from Yellowstone National Park. Wolves may positively influence aspen overstory recruitment through a trophic cascades effect by reducing elkpopulations, modifying elk movement, and changing elk browsing patterns on aspen."

# data[].attributes.headline
Re-introduction of wolves showed behavioural change in elk...

# data[].attributes.subject
Re-introduction of wolves showed behavioural change in elk...

# data[].attributes.body
In summary:
Male elks during the study showed no change in vigilance, whereas female adults and young showed an overall increase in vigilance over the study period.

# data[].attributes.headline
"Elk  respond  to  wolves  on  their  winter range by a shift in habitat selection, which leads to local reductions in the use of aspen by elk."

# data[].attributes.subject
"Elk  respond  to  wolves  on  their  winter range by a shift in habitat selection, which leads to local reductions in the use of aspen by elk."

# data[].attributes.body
In summary:
This paper concluded that where wolves are distributed, elk are observed to consume (and therefore cause damage) to aspen trees. Where wolves were absent, aspen forest were observed to be grazed at higher rates.

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Enter your email address below. If your address has been previously registered, you will receive an email with instructions on how to reset your password. If you don't receive an email, you should register as a new user

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The wolves were brought in because the increased elk population was overgrazing the deciduous, woody species such as aspen and cottonwood.