ORIGINAL PAPER

The impact of hedge-forest connectivity and microhabitatconditions on spider and carabid beetle assemblagesin agricultural landscapes

Christina Fischer • Hella Schlinkert •

Martin Ludwig • Andrea Holzschuh •

Robert Galle • Teja Tscharntke • Peter Batary

Received: 5 April 2013 / Accepted: 29 August 2013 / Published online: 4 September 2013

� Springer Science+Business Media Dordrecht 2013

Abstract Agricultural intensification in terms of decreas-

ing landscape complexity and connectivity has negatively

affected biodiversity. Linear landscape elements composed

of woody vegetation like hedges may counteract this nega-

tive trend by providing habitats and enhancing habitat con-

nectivity for different organisms. Here, we tested the impacts

of habitat type (forest edges vs. hedges) and hedges’ isolation

(connected vs. isolated hedges) from forests as well as

microhabitat conditions (percentage of bare ground and

width) on trait-specific occurrence of ground-dwelling

arthropods, namely spiders and carabids. Arthropods were

grouped by habitat specialisation (forest vs. open-habitat

species vs. generalists), hunting strategy (web-building or

hunting spiders) and dispersal ability (wing morphology of

carabids). Spider and carabid assemblage composition was

strongly influenced by habitat type and isolation, but not by

microhabitat conditions. Activity density of forest species

and brachypterous carabids was higher in forest edges

compared to hedges, whereas open-habitat species and

macropterous carabids showed reverse patterns, with no

effects of isolation. Occurrence of generalist carabids, but

not spiders, was higher in hedges compared to forest edges.

Habitat type and isolation did not affect spiders with dif-

ferent hunting strategy. Microhabitat conditions were less

important for spider and carabid occurrence. Our study

concludes that on a landscape scale, type of linear woody

habitat is more important for arthropod occurrence than

isolation effects and microhabitat conditions, depending on

traits. Hedges provide refuges for species specialised to open

habitats and species with high dispersal ability, such as

macropterous carabids. Forest edges enhance persistence of

species specialised to forests and species with low dispersal

ability, such as brachypterous carabids.

Keywords Dispersal ability � Forest species �Generalists � Habitat isolation � Habitat type �Open-habitat species

Introduction

The intensification of agricultural practices during the last

decades has led to a serious decline of farmland, but also

Electronic supplementary material The online version of thisarticle (doi:10.1007/s10841-013-9586-4) contains supplementarymaterial, which is available to authorized users.

C. Fischer (&)

Restoration Ecology, Department of Ecology and Ecosystem

Management, Technische Universitat Munchen,

Emil-Ramann-Str. 6, 85354 Freising, Germany

e-mail: christina.fischer@tum.de

C. Fischer � H. Schlinkert � T. Tscharntke � P. Batary

Agroecology, Department for Crop Sciences,

Georg-August University Gottingen, Grisebachstr. 6,

37077 Gottingen, Germany

M. Ludwig

Institute of Plant Diseases and Plant Protection,

Leibniz University Hannover, Herrenhauser Straße 2,

30419 Hannover, Germany

A. Holzschuh

Department of Animal Ecology and Tropical Biology,

Biocenter, University of Wurzburg, Am Hubland,

97074 Wurzburg, Germany

R. Galle

Department of Ecology, University of Szeged,

Kozep fasor 52, 6726 Szeged, Hungary

P. Batary

MTA-ELTE-MTM Ecology Research Group,

Pazmany P. s. 1C, 1117 Budapest, Hungary

123

J Insect Conserv (2013) 17:1027–1038

DOI 10.1007/s10841-013-9586-4

woodland biodiversity (Benton et al. 2003; Geiger et al.

2010). One reason for the recent species loss is the

increasing area of arable fields with rapid habitat changes

within a year, accompanied by the destruction of stable

semi-natural habitats like hedgerows (Burel et al. 2004).

Survival and resilience of local populations also depend on

the degree of habitat fragmentation and isolation on a

landscape scale, as well as on trait-specific characteristics

such as niche breadth and dispersal ability (Ewers and

Didham 2006; Bailey 2007). Hedges are linear landscape

elements composed of shrubs and/or trees (Baudry et al.

2000). In agricultural landscape they can increase habitat

connectivity between forest habitats, providing either cor-

ridors and habitat patches (for forest species) or refuges

(for open-habitat species; Michel et al. 2006; Batary et al.

2012b). Furthermore microhabitat conditions of hedges

(e.g. hedge width), which determine local habitat quality,

can also affect species occurrence and assemblage com-

position (Hinsley and Bellamy 2000; Gelling et al. 2007).

Ground-dwelling arthropods such as spiders and cara-

bids play an important role in agricultural landscapes by

providing ecosystem services and functions. Spiders and

carabids can prevent pest outbreaks in agricultural fields

through their biological control potential (Landis et al.

2000) which reduces densities of pest insects, such as

cereal aphids drastically (Thies et al. 2011). Spiders and

carabids are also important food resource for species of

higher trophic levels like birds and therefore maintain food

chain stability (Traba et al. 2008; Holland et al. 2012).

Additionally these predators respond rapidly to manage-

ment and disturbances, and therefore can serve as an

indicator for human-caused disturbances (Marc et al. 1999;

Kotze et al. 2011).

Environmental factors including landscape structure and

local microhabitat conditions influence species occurrence

and thereby the assemblage composition of ground-dwell-

ing arthropods (Niemela 2001; Prieto-Benıtez and Mendez

2011). If the assemblage composition of spiders and cara-

bids changes, also ecosystem services like the biological

control potential and ecosystem functions like food chain

maintenance may change (Flynn et al. 2009; de Bello et al.

2010). To study effects of habitat fragmentation and iso-

lation of forests on arthropod occurrence at the landscape

scale, many studies were carried out in forests and forest

remnants (Magura et al. 2001; Gurdebeke et al. 2003;

Jennings and Tallamy 2006; Galle 2008). However, few

studies analysed arthropod occurrence in smaller patches

like hedgerows embedded in the agricultural matrix (Petit

and Usher 1998; Millan de la Pena et al. 2003; Buddle et al.

2004).

The response of spider and carabid species to habitat

fragmentation and isolation is often related to their degree

of habitat specialisation (Petit and Usher 1998; Buddle

et al. 2004), hunting strategy in case of spiders (Varet

et al. 2011) as well as dispersal ability in case of carabids

(Wamser et al. 2010). Species specialised to certain hab-

itat conditions and with low dispersal abilities are vul-

nerable to changes in habitat composition and increasing

isolation, whereas habitat generalists and more mobile

species can cope with a variety of habitat changes (Aviron

et al. 2005; Hendrickx et al. 2009). The destruction of

forest patches and hedges reduces the dispersal corridors

of forest species and species with low dispersal ability and

decreases the survival of populations at landscape scale

(Gurdebeke et al. 2003; Millan de la Pena et al. 2003;

Hendrickx et al. 2009). Furthermore web-building spiders

are sensitive to fragmentation because of unsuitable

microhabitat conditions in open habitats for web con-

struction (Pajunen et al. 1995). Increasing patch size and

connectivity can counteract these negative trends (Nie-

mela 2001). By contrast, species specialised to open

habitats, hunting spiders and carabids with high dispersal

ability are less sensitive to increasing isolation of forest

patches and hedges and are thought to dominate arthropod

assemblages of isolated habitats (Pajunen et al. 1995;

Herrmann et al. 2010; Wamser et al. 2010; Taboada et al.

2011). However, open-habitat species can also benefit

from decreasing isolation of forest patches and hedges, as

hedges provide permanent refuges during time after crop

harvest and for hibernation (Thomas et al. 2001; Pywell

et al. 2005). Also microhabitat conditions like increasing

shelter through vegetation and litter at the ground can

enhance arthropod species-specific persistence especially

in overwintering habitats, whereas increasing hedge width

decreases spider and carabid abundances in the soil

(Maudsley et al. 2002).

Because effects of habitat fragmentation and isolation in

agricultural landscapes on arthropod assemblages are very

complex and related to various species-specific traits, it is

important to separate the impacts of habitat type, habitat

isolation and microhabitat conditions on the assemblage

composition, abundance and species richness of species

with different habitat specialisation, hunting strategy and

dispersal ability (Tscharntke et al. 2012). In this study we

investigated the effects of habitat type (forest edges vs.

hedges) and hedges’ isolation from forests (connected vs.

isolated hedges) on assemblage composition, activity

density and species richness of spiders and carabids with

different habitat specialisation as well as on hunting strat-

egy of spiders and dispersal ability of carabids. We com-

pared forest edges, hedges connected to forests and isolated

hedges in agricultural landscapes. Additionally we tested

the potential effect of different microhabitat conditions of

forest edges and hedges, particularly percentage of bare

ground and width of the shrub layer, on spider and carabid

occurrence.

1028 J Insect Conserv (2013) 17:1027–1038

123

We hypothesised that:

1. forest edges, decreasing isolation and increasing width

will increase occurrence of species specialised to

forests, web-building spiders and carabids with low

dispersal ability, because habitat availability and

accessibility increases in comparison to hedges,

2. hedges and increasing isolation will increase occur-

rence of species specialised to open habitats and

hunting spiders, because hedges are refuges in the

agricultural matrix providing suitable microhabitat

conditions in comparison to forest edges,

3. habitat type, isolation, as well as microhabitat condi-

tions will have no effect on generalists and carabids

with high dispersal ability because they occur in a

variety of different habitats.

Methods

Study area and sampling design

The study was carried out in summer 2009 around the city of

Gottingen, in Germany (51.5�N, 9.9�E, for a detailed map of

all study sites see Batary et al. 2012b). To model effects of

habitat type (forest edges vs. connected and isolated hedges)

and isolation from deciduous forests (connected vs. isolated

hedges), we selected six forest edges, hedges connected to

forests and isolated hedges, respectively. Hedges were

defined as linear landscape elements in the agricultural

landscape with a dense shrub layer, whereas forest edges

were defined as the dense shrub layer of the edge of large

deciduous forest patches. All selected study sites were

composed of blackthorn (Prunus spinosa), hawthorn (Cra-

taegus spp.) and rose (Rosa spp.) interspersed with ash

(Fraxinus excelsior), common dogwood (Cornus sanguinea),

elder (Sambucus nigra), hazel (Corylus avellana), maple

(Acer spp.), and willow (Salix spp.). Green lanes (hedges on

both sides of a road) and forest edges or hedges bordering

water-bearing ditches were not selected as microhabitat

conditions like soil moisture may influence spider and cara-

bid occurrence (Burel 1989; Maudsley et al. 2002; Entling

et al. 2007). All selected study sites had a length of at least

200 m and did not belong to a hedgerow network intersecting

other hedges. Forest edges and hedges were situated in

landscapes mainly composed of arable land, forests and

grasslands, but with different proportions due to edge/hedge

configuration (Batary et al. 2012b). Study sites were directly

bordered by agricultural fields, mainly cereals or oilseed

rape. Connected hedges directly adjoined perpendicular to

the forest. Isolated hedges had a minimum distance of 300 m

to the nearest forest. The distance between study sites was at

least 500 m to reduce spatial autocorrelation.

Percentage of bare ground and width of the shrub layer

of edges/hedges (hereafter referred to as bare ground and

width) were measured in August 2009 at eight locations

spacing 25 m (Fig. 1). Percentage of bare ground was

estimated from both sides of the edge/hedge at each loca-

tion with 10 % precision using a 1 9 1 m plot (n = 16

sampling points per edge/hedge). Width was measured at

the ground level with 0.5 m precision without consider-

ation of the tree layer in case of the forest edges (n = 8

sampling points per edge/hedge), i.e. only the shrub layer

was measured. Mean bare ground and width were calcu-

lated by averaging values per edge/hedge. Bare ground and

width were not correlated (Supplementary Table 1).

Additionally at each sampling point we measured density

of the shrub layer categorized as low ([2/3 of the con-

trasting background visible at a height of 1.5 m through the

hedge/edge), medium (1/3–2/3) and high (\1/3), the height

of the shrub layer of each edge/hedge (without trees) with

0.5 m precision and litter cover with 10 % precision

(Table 1). Habitat types and isolation levels did not differ

in microhabitat conditions (Table 1), as well as in mean

daily temperature within edges/hedges (14.19 ± 0.10 �C,

F2/15 = 1.29, p = 0.31). Shrub layer density and height

determine the shading of the habitat, and litter cover

determines the resource availability. Therefore, these may

also influence arthropod assemblage structure (Taboada

et al. 2004; Entling et al. 2007). However, as bare ground

and/or hedge/edge width were correlated with the density

and height of the shrub layer, and/or litter cover (Supple-

mentary Table 1), we decided to focus just on the first two

parameters, which were proved to be, among others, simple

predictors of arthropod occurrence (Maudsley et al. 2002).

Fig. 1 Study design showing a forest edge, b connected hedge,

c isolated hedge. The arrangement of pitfall traps and sampling points

measuring bare ground and width along the shrub layer of the edge/

hedge are displayed

J Insect Conserv (2013) 17:1027–1038 1029

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Spider and carabid sampling

Spiders (Araneae) and carabids (Coleoptera: Carabidae)

were surveyed once in May and once in July 2009 for three

weeks in each case, during time when spider activity density

is highest all over Europe (Niemela et al. 1994; Cardoso et al.

2007), and when carabids are more active in hedges com-

pared to agricultural fields (Varchola and Dunn 2001). Four

pitfall traps (90 mm diameter, filled with 50 % ethylene

glycol) were placed in the middle of the edge/hedge with

50 m in between them (Fig. 1). In case of inaccessibility of

edges/hedges interior traps were placed at least 1 m inside

the edge/hedge. Adult spiders and carabids were identified to

species level. Activity densities and species richness were

calculated as the sum of the four pitfall traps per study site for

each sampling round separately. Spider and carabid species

were classified according to their habitat specialisation

based on expert knowledge and literature into forest species

(associated with forests, forest patches and forest edges),

open-habitat species (associated with open landscapes) and

generalists (with no distinct habitat preferences; following

Koch 1989; Buchar and Ruzicka 2002; Angewandte

Carabidologie Supplement V 2009; Nentwig et al. 2011).

Spiders were separated according to their hunting strategy

into web-building and hunting species (Nentwig et al. 2011;

Batary et al. 2012a), which was not correlated with habitat

specialisation (p = 0.15; Fisher’s exact test for count data).

Carabid species were separated according to their dispersal

ability based on their wing development into brachypterous

(wingless or reduced wings, low dispersal ability), mac-

ropterous (with wings, high dispersal ability) and dimorphic

(wingless and winged, unknown dispersal ability) species

(Cole et al. 2002; Barbaro and van Halder 2009; Hendrickx

et al. 2009). Even though wing development was highly

correlated with habitat specialisation (p \ 0.001; Fisher’s

exact test), with forest species being mainly brachypterous

and open-habitat species being mainly macropterous, we

analysed dispersal ability separately because it can highly

influence carabid occurrence and assemblage composition

(Wamser et al. 2010). We did not separate spider species

according to their dispersal ability, since ballooning activity

and tiptoe behaviour differ with different dispersal levels

between habitats (Entling et al. 2011), between seasons

(Blandenier and Furst 1998) and are correlated with habitat

specialisation (Bonte et al. 2003).

Statistics

Canonical correspondence analysis (CCA) was performed to

give an overview of the effects of habitat type, isolation (forest

edges vs. connected vs. isolated hedges) and microhabitat

conditions (bare ground; width) on spider and carabid

assemblage composition. Partial models were calculated to

analyse the compositional variation of spider and carabid

assemblages using the vegan R package (version 2.0-4, Ok-

sanen et al. 2012) of R version 2.15.0 (R Development Core

Team 2012). Either habitat type/isolation, bare ground or

width were used as constrained variable and the other two

variables as conditioning variables. Assemblage data includ-

ing all species (pooled over both sampling rounds per study

site) were log-transformed. The significance of constrained

variables for the separate partial models was assessed by

performing permutation tests with 999 permutations. Ordi-

nation plots, pseudo-F values and p values are given.

To test the effects of habitat type and isolation, as well

as microhabitat conditions we used linear mixed-effects

models (Pinheiro and Bates 2000) with a maximized log-

likelihood implemented in the nlme R package (version

3.1-103, Pinheiro et al. 2012) of R version 2.15.0 (R

Development Core Team 2012). Activity density and

species richness of the three classes of habitat specialisa-

tion of spiders and carabids (forest species, open-habitat

Table 1 Microhabitat parameters of forest edges, connected hedges and isolated hedges

Forest edge Connected hedge Isolated hedge Habitat type/isolation levels

F/v2 value p value

Bare ground (%) 17.5 ± 4.5 27.4 ± 5.3 22.4 ± 3.2 1.25b 0.32

Density (low = 0, medium = 1, high = 2) 1.2 ± 0.2 1.2 ± 0.2 1.3 ± 0.2 0.60c 0.74

Height (m) 3.5 ± 0.2 3.7 ± 0.2 4.0 ± 0.2 1.42b 0.27

Litter cover (%) 80.2 ± 4.9 66.0 ± 6.1 73.5 ± 4.5 1.85b 0.19

Width (m)a 5.0 ± 0.9 4.4 ± 0.8 5.7 ± 1.1 0.38b 0.69

Mean values and standard errors are given. Differences of microhabitat parameters between habitat types and isolation levels (forest edge,

connected hedge, isolated hedge) are given by calculating F values and p values from a one-way ANOVA (df 2, 15) in case of normal distributed

parameters or v2 values from a Kruskal–Wallis rank sum test (df 2) in case of non-normal distributed parametersa log-transformedb F valuec v2 value

1030 J Insect Conserv (2013) 17:1027–1038

123

species and generalists), the two hunting strategies of spi-

ders (web-building, hunting) and the two dispersal ability

classes of carabids (brachypterous, macropterous species;

species with unknown dispersal ability were excluded from

analysis, to make a clear distinction between species with

low and high dispersal ability) were used as response

variables. To model the independence of errors with

respect to temporal autocorrelations (two sampling rounds

nested within each site) study site was included as a ran-

dom factor in each model. Activity density and species

richness were log-transformed to achieve a normal error

distribution and/or to avoid heteroscedasticity. Variance

functions implemented in the nlme library were used to

model a constant variance function structure for habitat

type and isolation. Fitted models with different within-

group variances were compared by choosing the lowest

AIC (Akaike Information Criterion) value from an

ANOVA table (Pinheiro and Bates 2000). Model simpli-

fication was done in a backward stepwise model selection

procedure by AIC implemented in the MASS R package

(version 7.3-17, Venables and Ripley 2002) until minimal

adequate model was obtained using the ‘stepAIC’ function.

Parameter estimates, t-statistics and p values of terms in the

best model were assessed from the summary table. Con-

trasts between habitat type and isolation were investigated

by re-ordering factor levels so that the specified level was

the reference level. In the text and figures non-transformed

means and standard errors are given.

Results

Spiders

In total, 1,659 spiders of 102 species were collected. Forty-

five were categorised as forest species, 22 as open-habitat

species and 35 as generalists (Supplementary Table 2). For

example Pardosa saltans, the most abundant (forest) spe-

cies has mostly been recorded in forest edges, Pardosa

pullata an open-habitat species has been recorded in

hedges and Tenuiphantes tenuis a generalist has been

recorded everywhere.

Compositional variation of spider assemblages was

significantly influenced by habitat type and isolation

(pseudo-F2,13: 1.32, p \ 0.05; differentiated for habitat

specialisation: Fig. 2a and hunting strategy: Fig. 2b), but

not by bare ground (pseudo-F1,13: 0.96, p = 0.62) and

width (pseudo-F1,13: 0.94, p = 0.64). Activity densities

and species richness of forest species were significantly

higher in forest edges than in connected and isolated

Fig. 2 CCA biplot ordination

diagrams for assemblage

composition of a spiders

(n = 102 species) with different

habitat specialisation, b spiders

with different hunting strategy,

c carabids (n = 56 species) with

different habitat specialisation,

and d carabids with different

dispersal ability constrained by

habitat type and isolation level.

Capital letters show centroids

for habitat types and isolation

levels (F forest edge,

C connected hedge, I isolated

hedge)

J Insect Conserv (2013) 17:1027–1038 1031

123

hedges, with no effect of isolation (Table 2: spiders;

Fig. 3a, b). There was a negative impact of increasing bare

ground on activity density of forest species, but not on

species richness. Activity density and species richness of

open-habitat species was lower in forest edges than in

isolated hedges, with no effect of isolation, bare ground

and width. Generalists did not show any response to habitat

type and isolation, bare ground and width.

Concerning hunting strategy, 57 species were catego-

rised as web-building and 45 as hunting spiders (Supple-

mentary Table 2). Activity density and species richness of

web-building and hunting spiders were not associated with

variation in any explanatory variable, except a negative

effect of increasing bare ground on the activity density of

web-building spiders (Table 3; Fig. 3a, b).

Carabids

In total 1,511 carabids of 56 species were collected. Sev-

enteen were categorised as forest species, 10 as open-

habitat species and 29 as generalists (Supplementary

Table 3). For example Abax parallelepipedus, the most

abundant (forest) species has mostly been recorded in

forest edges, Anchomenus dorsalis an open-habitat species

has mostly been recorded in hedges and Pterostichus

melanarius a generalist has been recorded everywhere.

Compositional variation of carabid assemblages was

influenced by habitat type and isolation (pseudo-F2,13:

1.53, p \ 0.01; differentiated for habitat specialisation:

Fig. 2c and dispersal ability: Fig. 2d), but not by bare

ground (pseudo-F1, 13: 0.81, p = 0.74) and width (pseudo-

Table 2 Summary of linear mixed-effects models to analyse effects

of habitat (forest edges vs. hedges), isolation (connected vs. isolated

hedges), bare ground (B. ground) and width on activity density and

species richness of the three classes of habitat specialisation (forest

species, open-habitat species and generalists) of spiders and carabids

Forest species Open-habitat species Generalists

Estimate ± SE t p Estimate ± SE t p Estimate ± SE t p

Spiders

Activity density

C–F -0.90 ± 0.26 -3.42 <0.01 0.38 ± 0.31 1.22 0.24 -0.19 ± 0.18 -1.07 0.30

I–F -0.88 ± 0.25 -3.57 <0.01 0.84 ± 0.31 2.73 <0.05 0.17 ± 0.18 0.99 0.34

I–C 0.01 ± 0.25 0.05 0.96 0.46 ± 0.31 1.51 0.15 0.36 ± 0.18 2.02 0.06

B. ground -0.03 ± 0.01 -3.40 <0.01 – – – – – –

Width – – – – – – -0.05 ± 0.03 -1.50 0.16

Species richness

C–F -0.36 ± 0.14 -2.54 <0.05 0.31 ± 0.23 1.31 0.21 – – –

I–F -0.42 ± 0.13 -3.08 <0.01 0.66 ± 0.23 2.82 <0.05 – – –

I–C -0.05 ± 0.13 -0.39 0.70 0.35 ± 0.23 1.51 0.15 – – –

B. ground -0.01 ± 0.01 -2.13 0.05 – – – – – –

Width – – – – – – – – –

Carabids

Activity density

C–F -1.23 ± 0.58 -2.12 0.05 0.52 ± 0.42 1.25 0.23 1.11 ± 0.44 2.52 <0.05

I–F -1.44 ± 0.55 -2.62 <0.05 1.21 ± 0.42 2.87 <0.05 1.12 ± 0.44 2.53 <0.05

I–C -0.21 ± 0.55 -0.38 0.71 0.69 ± 0.43 1.60 0.13 0.01 ± 0.29 0.04 0.97

B. ground 0.03 ± 0.02 -1.48 0.16 – – – -0.02 ± 0.01 -1.53 0.15

Width – – – -0.20 ± 0.08 -2.42 <0.05 – – –

Species richness

C–F – – – 0.40 ± 0.20 2 0.06 0.63 ± 0.25 2.53 <0.05

I–F – – – 0.41 ± 0.20 2.05 0.06 0.70 ± 0.25 2.78 <0.05

I–C – – – 0.01 ± 0.20 0.05 0.96 0.06 ± 0.25 0.25 0.81

B. ground – – – – – – – – –

Width – – – -0.10 ± 0.04 -2.65 <0.05 – – –

Contrasts between habitat type and isolation were investigated by re-ordering factor levels. The effect size of the fixed effects with standard

errors (Estimate ± SE), t and p values from the summary tables are given. Significant effects are indicated by bold values. Variables indicated by

‘‘–’’ were removed from the minimal adequate model

F forest edge, C connected hedge, I isolated hedge

1032 J Insect Conserv (2013) 17:1027–1038

123

F1, 13: 1.14, p = 0.29). Activity density, but not species

richness of forest species was higher in forest edges than in

isolated hedges, with no effect of isolation levels, bare

ground and width, whereas open-habitat species showed

reverse patterns (Table 2: carabids; Fig. 3c, d). Open-

habitat species decreased with increasing hedge width,

whereas there was no effect of bare ground. Activity den-

sity and species richness of generalists was lower in forest

edges than in connected and isolated hedges, with no effect

of isolation, bare ground and width.

Concerning dispersal ability, 17 species were catego-

rised as brachypterous, 28 as macropterous and 11 as

dimorphic (Supplementary Table 3). Activity density, but

not species richness, of brachypterous species was higher

in forest edges compared to isolated hedges, with no effect

of isolation, bare ground and width (Table 3; Fig. 3c, d).

Fig. 3 The influence of habitat

(forest edges vs. hedges) and

isolation (connected vs. isolated

hedges) on a activity density

and b species richness of

spiders; c activity density and

d species richness of carabids

(mean ? SE, n = 12) for

species-specific traits: habitat

specialisation (forest species,

open-habitat species,

generalists), hunting strategy of

spiders (web-building, hunting)

and dispersal ability of carabids

(brachypterous, macropterous).

Differences between habitat

types and isolation levels are

indicated by *p \ 0.05;

**p \ 0.01 (linear mixed

effects models). For better

visualisation non-transformed

data are presented

J Insect Conserv (2013) 17:1027–1038 1033

123

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1034 J Insect Conserv (2013) 17:1027–1038

123

Activity density and species richness of macropterous

species was higher in isolated hedges than in forest edges,

with no effect of isolation. None of the dispersal traits

showed response to bare ground and width.

Discussion

Our study shows that ground-dwelling arthropod assem-

blages were shaped by habitat type and isolation, but not by

bare ground or width of forest edges/hedges (see also

Niemela 2001; Buddle et al. 2004). Trait-specific activity

densities and species richness of spiders and carabids were

(partly) affected by habitat type (forest edges vs. hedges),

but not by hedges’ isolation from forests (connected vs.

isolated hedges). In contrast to our expectations bare

ground and width were less important for trait-specific

activity densities and species richness of spiders and

carabids.

Habitat type and isolation

In general spider and carabid assemblages seem to be

sensitive to habitat changes, e.g. Varet et al. (2011) found

distinct differences in spider assemblage composition of

hedges situated in urban and rural areas. For carabid

assemblage composition Fournier and Loreau (1999) and

Millan de la Pena et al. (2003) showed that carabids

respond to increasing distances from hedges into crop fields

(habitat) and to different hedge densities within a certain

landscape (isolation). Thereby assemblage composition of

spiders and carabids is often related to species-specific

habitat preferences, with forest species inhabiting mainly

dense and well-connected woody habitats, whereas open-

habitat species mainly occur in more isolated habitat pat-

ches within the agricultural landscape (for spiders see

Varet et al. 2011; for carabids see Aviron et al. 2005).

In our study the activity density and species richness of

spiders specialised to forests and activity density of forest

carabids, were higher in forest edges compared to hedges.

There are two possible explanations for the distinct habitat

preferences of forest species occurrence: (1) forest species

decrease with decreasing habitat area (Galle 2008) and/or

(2) the competition between forest species and open-habitat

species increases in hedges, which decreases the occur-

rence of forest species (Wise 2006). Activity density and

species richness of open-habitat spiders as well as activity

density of open-habitat carabids were highest in isolated

hedges, suggesting that hedges are important landscape

elements not only for species specialised to forests and

woody habitats, but also for species specialised to perma-

nent open habitats or partly to cereal fields (Fournier and

Loreau 1999; Toft and Lovei 2002). Gurdebeke et al.

(2003) showed that in forest patches 50 % of the spider

species were non-forest species immigrating from the

surrounding habitats. For open-habitat arthropod species

hedges function as refuges and as recolonisation habitats

after disturbances due to agricultural practice and for

overwintering (Pywell et al. 2005). Generalist spiders did

not respond to habitat type occurring in forest edges, as

well as in hedges, which may increase the overall spider

species richness in habitat edges compared to managed

sites (Prieto-Benıtez and Mendez 2011). By contrast,

generalist carabid occurrence was higher in hedges com-

pared to forest edges. However, it seems that for carabids

occurrence their dispersal ability is more important than

their habitat specialisation. Brachypterous species were

more abundant in forest edges compared to hedges and

macropterous species showed reverse patterns (c.f. Jen-

nings and Tallamy 2006; Jelaska and Durbesic 2009).

Similar patterns could also be shown for grasslands with

higher species richness of brachypterous species in con-

tinuous and connected grasslands within the arable matrix

and macropterous species being mainly associated with

isolated grasslands (Wamser et al. 2010). Good dispersers,

such as macropterous species have the potential to (re-

)colonise isolated habitats in the agricultural landscape

faster than poor dispersers, such as brachypterous species.

This indicates the importance of hedges for the mainte-

nance of good disperses in the agricultural landscape,

which may enhance the biological pest control for adjacent

agricultural crops via carabids’ colonisation potential

(Niemela 2001). By contrast we could not show any

response to habitat type for the different hunting strategies

of spiders. One possible explanation could be that edge

habitats such as the studied forest edges and hedges pro-

vide suitable conditions for web-building spiders, finding

enough branches to attach their webs, but also for hunting

spiders, which colonize hedges from the surroundings

(Pajunen et al. 1995). Therefore the availability of these

edge habitats seems to be more important for spiders with

different hunting strategies than the particular habitat type.

In contrast to our expectations, we could not show an

isolation effect (connected vs. isolated hedges) on the

occurrence of spiders as well as carabids. Herrmann et al.

(2010), who sampled spiders in orchards with different

isolation from woody habitats, found only two out of 13

forest species that decreased in their abundance with

increasing isolation, whereas for open-habitat species local

plant diversity was the most influential factor. Magura et al.

(2001), who sampled carabids in small forest patches with

different isolation from a large forest, found only non-

significant results of the species richness of forest species

and generalists in relation to increasing distance from the

large forest. Studies showing negative effects of fragmen-

tation on spiders and carabids exclusively focused on

J Insect Conserv (2013) 17:1027–1038 1035

123

forests with different sizes and not on forest edges/hedges

(e.g. Jennings and Tallamy 2006; Galle 2008; Jelaska and

Durbesic 2009; Prieto-Benıtez and Mendez 2011; but see

Petit and Usher 1998; Buddle et al. 2004). Therefore it

might be possible that these studies only showed a habitat

effect with forest size as a function of habitat availability,

rather than an isolation effect with e.g. forest patches with

similar size but different degrees of isolation from a forest

mainland. In contrast to forest fragments, which are either

habitat patches (for forest species) or matrix (for open-

habitat species), hedges are linear landscape elements

consisting of shrubs and/or trees that can act as a corridor

for forest species but also as refuges for open-habitat

species (Baudry et al. 2000). Hedges might provide both

edges, which are probably mainly inhabited by open-hab-

itat species invading from the agricultural area, and inte-

riors (if hedges are wide enough), which might be mainly

inhabited by forest species (Fournier and Loreau 1999;

Niemela 2001; but see Taboada et al. 2004). Therefore,

other factors like species turnover from or into the agri-

cultural fields, or edge effects may have a great importance

for arthropod occurrence in hedges, buffering negative

effects of isolation. Furthermore, arable spiders, which can

be also classified as open-habitat species, mainly respond

to the percentage of non-crop habitats in the landscape at a

larger spatial scale (mainly [500 m radius; Schmidt et al.

2005). Thus, it is likely that the spatial scale of our study to

measure isolation (300 m to the nearest forest) was too

small to detect effects of isolation on spiders. For carabid

occurrence the spatial scale used in our study seems to be

appropriate to study isolation effects. Aviron et al. (2005)

showed that especially large species respond to a scale of

250 m, but also habitat types like woodlands and field

boundaries in the agricultural landscape strongly shape

carabid occurrence.

Finally, carabids seem to be generally less sensitive to

habitat type and isolation effects compared to spiders.

Varet et al. (2011), who observed carabid and spider

activity densities and species richness in hedges along an

urban–rural gradient and Pywell et al. (2005), who com-

pared species richness of overwintering spiders and cara-

bids between hedges and field margins, showed effects

only on spider occurrence, but not on carabids.

Microhabitat conditions

Spider and carabid occurrence may not only be determined

by habitat type and isolation, but also by microhabitat

conditions (Maudsley et al. 2002). Here we could not find

an impact of microhabitat conditions (bare ground and

width) on spider and carabid assemblage composition.

Furthermore there was only little impact of microhabitat

conditions on activity density and species richness of spi-

ders and carabids with different degrees of habitat spe-

cialisation and with different hunting strategy of spiders.

Activity density of forest and web-building spiders

decreased with increasing bare ground, which was nega-

tively correlated with litter cover, which provides habitat

and structural heterogeneity for forest species, and hunting

places for web-building spiders (Pajunen et al. 1995;

Gurdebeke et al. 2003). However, other factors such as the

geographic orientation of hedges (Maudsley et al. 2002),

local plant diversity (Herrmann et al. 2010) and spiders’

dispersal mode and mobility (Bonte et al. 2003; Bucher

et al. 2010) could be more important for local spider

occurrence. For carabid occurrence also, various internal

factors such as flight muscle development, body size and

feeding behaviour (Kotze et al. 2011), as well as external

environmental factors such as vegetation composition, lit-

ter depth, topography and landscape history are important

(Gongalsky and Cividanes 2008). In our project forest

edges and hedges were selected according to habitat type

and isolation, keeping structural and microhabitat param-

eters as constant as possible, therefore variations in per-

centage of bare ground and hegde width may be too low to

detect effects on arthropod occurrence.

Conclusion

In conclusion, spiders and carabids specialised to open

habitats and with high dispersal ability benefit from hedges.

This could lead to a spill over of these species into agri-

cultural fields thereby enhancing biological pest control

(Landis et al. 2000). For spiders and carabids specialised to

forests and carabids with low dispersal ability, forest edges

in comparison to hedges are important habitats increasing

their activity density and species richness. Effects of linear

woody habitat type are more important than effects of

isolation and microhabitat conditions for the occurrence of

ground-dwelling arthropods. The strength of the effect

depends on species-specific habitat specialisation and dis-

persal ability but not on spiders’ hunting strategy. In order

to draw general conclusions for persistence of arthropods in

agricultural landscapes a high variety of internal (e.g. body

size, feeding behaviour) and external factors (e.g. ground

vegetation composition, landscape history) with appropri-

ate gradient lengths have to be studied simultaneously.

Acknowledgments We thank A. Kovacs-Hostyanszki and B. Jauker

for help with the selection of study sites, G. Lovei and two anony-

mous reviewers for valuable comments, and V. Kodobocz for iden-

tification of carabids. P.B. was supported by the Alexander von

Humboldt Foundation and the Bolyai Research Fellowship of the

Hungarian Academy of Sciences.

1036 J Insect Conserv (2013) 17:1027–1038

123

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