ORIGINAL PAPER

Are we conserving peripheral populations? An analysis of rangestructure of longhorn beetles (Coleoptera: Cerambycidae) inFinland

Atte Komonen

Received: 15 June 2006 / Accepted: 8 October 2006 / Published online: 20 December 2006� Springer Science+Business Media B.V. 2006

Abstract This paper characterises range structures of

longhorn beetles (Coleoptera: Cerambycidae) occur-

ring in Finland and classifies species as resource (host

plant), substrate (specific host plant qualities) or cli-

mate limited. This information is then used to evaluate

whether the IUCN red-list classification applied in

Finland is directed towards peripheral European pop-

ulations. Thirty (37%) longhorn beetle species are red-

listed in Finland. Limited host plant distribution is

adequate in explaining the red-list status for 43% of

the red-listed species. All of these species are depen-

dent on hardwood trees. Of the red-listed species that

are dependent on widespread host plants, 30% have a

limited extent of occurrence as well as a small area of

occupancy in Finland. As these species are widespread

outside Fennoscandia, their range in Finland is most

likely limited by climate. Twenty per cent of the red-

listed species have a wide extent of occurrence, albeit a

small area of occupancy in Finland. As these species

are dependent on widespread host plant species, but

require specific substrate qualities (e.g. decaying, large

diameter trunks), it is likely that their range is re-

stricted by anthropogenic activities, mainly forestry

and agriculture. The present study shows that the red-

list classification in Finland is directed towards

peripheral European populations. This study, however,

did not address the conservation value of these popu-

lations.

Keywords Cerambycidae � Coleoptera � Peripheral

populations � Range edge � Red lists

Introduction

The study of species range size, structure and limits has

a long history in ecology, and the recent concern about

global environmental change has increased interest in

large-scale ecological phenomena (Gaston 2003). The

questions about how species respond to climate change

(Davis et al. 1998), what is the best course for main-

taining biodiversity (Gaston 1994), and how to under-

stand the spread of alien invasive species (Williamson

1996) have placed the structure and dynamics of geo-

graphical ranges of species back in the spotlight.

Range size (measured as extent of occurrence or

area of occupancy) of species is also one of the main

criteria used in IUCN red list classification (IUCN

1994), and particularly with invertebrates it is often the

only information available. Accordingly, the Finnish

Red-List of longhorn beetles is largely based on the

range size [criteria B1 (23 spp.) and D2 (1 sp.); criteria

is not applied for near-threatened species (n = 6);

Rassi et al. 2001]. Bunnell et al. (2004), however, crit-

icized the use of range size criteria, because ‘‘...undue

conservation attention is being given to common spe-

cies that are considered rare in jurisdiction because

they are peripheral, or at the edge of their geographic

range.’’ They argued that limited resources should be

focused on species that are endemic to a given region

or for which the nation has global stewardship

responsibility. On the other hand, they also acknowl-

edged that peripheral populations which are geo-

graphically disjunct, rather than continuous, are likely

A. Komonen (&)Faculty of Forest Sciences, University of Joensuu,P.O. Box 111, FI-80101 Joensuu, Finlande-mail: atte.komonen@joensuu.fi

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J Insect Conserv (2007) 11:281–285

DOI 10.1007/s10841-006-9043-8

to exhibit genetic divergence and thus have conserva-

tion value (see also Lesica and Allendorf 1995).

Understanding range patterns of taxonomical

assemblages, as well as their biological correlates, has

theoretical and practical conservation importance

(Gaston et al. 1997; Kunin and Gaston 1997), yet such

studies are scarce with invertebrates in particular. In

this paper, my aim was to characterize range size and

extent of Finnish longhorn beetles (Coleoptera:

Cerambycidae) in the European context. Together

with information on species resource requirements this

information was used to classify red-listed species in

groups reflecting the main factors limiting species

range, i.e. resource distribution, climatic tolerance

and anthropogenic impact. Finally, I evaluate whether

the red-list classification of cerambycid beetles in

Finland is directed towards peripheral European

populations.

Methods

This paper is based on a literature survey. The com-

prehensive recent book about longhorn beetles in

Finland is based on 1,500 scientific articles in Finnish,

Swedish, Norwegian and Danish entomological and

forest science journals and includes 34,000 records of

adult cerambycids obtained from Finnish museums and

private collections (Heliovaara et al. 2004). In Finland,

the area of occupancy for each species is estimated as

the number of 50 km · 50 km grid squares occupied

(n = 170 grid squares). Only species that have been

observed since 1960, and have a permanent population

in Finland, were included (n = 81; two species classi-

fied as regionally extinct were excluded). Species were

considered peripheral in Finland if they occurred in

less than 30 grid squares and their extent of occurrence

was less than 600 km (see below).

Species which have a restricted range size, despite

being dependent on widespread host trees and utilizing

common substrates (e.g. fine woody debris), are likely

to be limited by climatic factors. This is particularly

true in Finland with strong climatic gradients: the

south–north extent of ca. 1,200 km represents highly

variable climatic conditions (mean annual temperature

1971–2000 in Helsinki is +5.6�C and in Sodankyla

–0.8�C; data from Finnish Meteorological Institute).

There is also a SW–NE gradient from marine to con-

tinental conditions. Thus, the diagonal distance be-

tween latitudinal range extent (straight-line distance

between latitudinally most widely separated occupied

grid cells; Kunin and Gaston 1997) and longitudinal

extent (straight-line distance between longitudinally

most widely separated occupied grid cells) approxi-

mates the climatic tolerance of the species and can be

used to indirectly evaluate the role of climate in

restricting species range size.

The European range of the beetles was taken from

maps in Bense (1995), and is expressed as the number

of countries/regions occupied. The maps do not match

the present day political map of Europe and some of

the smaller countries are not visible, thus the maximum

is 26 countries or regions (abbreviations are ISO 3166

country codes): AT, AL, BE, Baltia (EE, LT and LV

combined), BG, CH, Czechoslovakia (CZ and SK

combined), DK, EE, FR, FI, UK, West and East

Germany (DE at present), HU, IT, IE, NO, NL, PO,

PL, GR, RO, RU, SE and former YU. The estimates of

European range sizes based on the number of countries

occupied are robust. Because these data are only used

for general description of species range size in Europe,

the chosen resolution is unlikely to influence conclu-

sions, which are mostly based on detailed data from

Finland. The nomenclature follows Silfverberg (2004).

The host plant distribution data are based on the

national floristic database (Lahti et al. 1995); the

authors kindly provided the numerical data.

Picea abies, Pinus sylvestris and Betula pendula and

B. pubescens are widespread and abundant species

throughout Finland. Large Populus tremula trees are

scattered in the forests. Hardwood trees occur mainly

in the hemiboreal zone in the southernmost Finland.

The area of occupancy for the main host plants of

cerambycid beetles is the number of occupied

10 km · 10 km grid cells: Picea abies (n = 1,872),

Pinus sylvestris (n = 2,128), Betula pubescens

(n = 1,928), B. pendula (n = 1,682), Populus tremula

(n = 1,650), Quercus robur (n = 200), Tilia cordata

(n = 687), Ulmus laevis (n = 52), Corylus avellana

(n = 283) and Anthriscus sylvestris (n = 1,353).

Results

Of the 81 species of longhorn beetles in Finland, 45

(56%) are rare, i.e. their area of occupancy covers <30

grid cells (for all species mean ± SE = 33.4 ± 3.5,

median = 22, min. = 1, max. = 115; Table 1). Seventy-

eight percent (35 spp.) of the species rare in Finland

have a wide European range. Species rare both in

Finland and Europe (n = 11) have their core range in

eastern boreal and temperate zone and are not limited

by the host tree range, as most of the species occupy

plant species that are widespread across Europe.

Globally, there are no cerambycid species endemic to

Finland.

282 J Insect Conserv (2007) 11:281–285

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Thirty (37%) cerambycid species are red-listed in

Finland, of which most occur in hemiboreal and

southern boreal zones (Fig. 1a). Thirteen (43%) red-

listed species utilize hardwood host trees. Species that

are dependent on one or more hardwood tree species

include a significantly higher frequency of red-listed

species than species that are monophagous on common

tree species (v2 = 17.22, df = 1, P < 0.001; Fig. 1b) or

are polyphagous (v2 = 26.48, df = 1, P < 0.001).

There is not a common denominator for the

remaining (n = 17) red-listed species. Five species have

a small extent of occurrence (diagonal distance

<400 km) and small area of occupancy (<6 occupied

grid cells) in Finland. These species are dependent on

host plants that are widespread in Finland, but their

core European range is in temperate zone (Appendix).

Another five species have an eastern boreal or tem-

perate range type, i.e. they are rare both in Finland and

Europe, although they utilize widespread plant species.

Six species have a wide extent of occurrence in Finland

(>700 km diagonal distance) despite the small number

of grid cells they occupy. This indicates that these

species have a wide climatic tolerance and together

with information on their specific substrate require-

ments (Appendix) indicates that these species are rare

primarily due to lack of suitable substrates.

Discussion

The present study demonstrates that most of the red-

listed longhorn beetle species in Finland are peripheral

populations of species, which predominantly have an

eastern boreal or southern temperate range type.

Rarity of longhorn beetles and the consequent red-list

status can be explained by three factors, namely the

host plant range, host plant qualities (anthropogenic

impact) and climate. Naturally, these factors are not

mutually exclusive.

Resource distribution (host plant range) determines

the range edge for over 40% (n = 13) of the red-listed

longhorn beetle species in Finland. These species are

confined to the southernmost Finland, following the

core distribution of their hardwood host trees.

According to the principle of parsimony, there does

not need to be any other underlying factors explaining

the limited range of these species. Mesosa myops is the

only species in this group, which clearly calls for an

additional explanation. In addition to the single known

location from Finland, the species is only known from

Latvia and Poland at present and by a historical record

from Sweden (Bense 1995; Heliovaara et al. 2004). This

suggests that the current populations in Europe are

climatic relicts.

Table 1 Range size of longhorn beetles in Finland (number of50 km · 50 km grid cells occupied) and in the entire Europe(number of countries/regions occupied; see Methods for details)

Range sizein Finland

Range size in Europe

Narrow Wide

2–7 8–13 14–19 20–26

Narrow1–29 7 (5) 3 (2) 17 (11) 18 (11)30–58 0 1 2 13 (1)

Wide59–87 0 1 3 1188–115 0 0 1 4

Range sizes are classified in equal intervals (except for the lastinterval), starting from the smallest realized range size. Numbersof species red-listed in Finland are given in parentheses

Fig. 1 Species–range type distribution (A) and species–hostplant distribution (B). Abbreviations: Hembor = hemiborealvegetation zone in south-westernmost Finland, SE = southeast-ern Finland, Norbor = northern boreal vegetation zone, Sou-

bor = southern boreal vegetation zone, S-Mbor = southern-middle boreal zone, and S-Nbor = southern-northern borealvegetation zone; see Ahti et al. (1968) for vegetation zones

J Insect Conserv (2007) 11:281–285 283

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Second major group comprises 30% (n = 10) of the

red-listed species in Finland. These species have a re-

stricted range in Finland, although they are dependent

on widespread host plant species. The simplest and

broadly applicable explanation is that the range edge

of these species is determined by climate. One half of

the species in this group can be considered temperate

species and another half eastern boreal species, as they

are either widespread or rare in Central Europe,

respectively (Bense 1995; Heliovaara et al. 2004).

Third major group includes 20% (n = 6) of the red-

listed species, for which rarity can not be explained by

host plant range or climate. These species have a large

extent of occurrence in Finland, despite their small

area of occupancy, which indicates that the species

have a wide climatic tolerance. These species utilize

common tree species but require specific substrate

qualities, such as large diameter trunks and advanced

decay stages (4 spp.) or burned wood (2 spp.) (Heli-

ovaara et al. 2004). All these suggest that the rarity in

this group is largely determined by anthropogenic

activities, such as forestry and agriculture. Again, the

different groupings applied here are not mutually

exclusive as some species, e.g. Monochamus urussovii,

have an eastern range type.

The present study of range patterns of longhorn

beetles in Finland revealed that the red-list classifi-

cation in Finland according to the IUCN criteria is

directed towards species which are common in Eur-

ope, i.e. towards peripheral European populations

(cf. Bunnell et al. 2004). The Baltic Sea imposes at

least a 100-200 km geographical barrier between

Finland and Estonia or Sweden. Without species-

specific information on long-range dispersal, how-

ever, it is difficult to assess whether these peripheral

populations in southernmost Finland are geographi-

cally disjunct or continuous. If these populations are

disjunct, then they are likely to have significant

conservation importance of genetically distinct pop-

ulations, with the potential for future speciation

events (Soule 1973; Lesica and Allendorf 1995). Even

if the populations are effectively continuous, they are

likely to be important as they will enhance range

expansion northwards if the climate changes. Natu-

rally, only genetic studies will reveal the level of

divergence of such peripheral populations, yet bio-

geographical characterization of range patters is the

necessary first step and should be conducted over a

wider range of taxa.

Acknowledgements Esko Hyvarinen & Mats Jonsell gaveuseful comments on the earlier version of the manuscript. RainoLampinen & Arto Kurtto kindly provided data on the plantdistribution.

Appendix

Classification of Finnish red-listed longhorn beetles

(n = 30) in ecological groups based on their range size,

range extent and resource use. Range size in Finland is

the number of 50 km · 50 km grid cells occupied

(max. 170) and in Europe the number of countries

occupied (max. 26, incl. Finland; see Methods for the

countries included). Range extent is the diagonal dis-

tance (rounded to the nearest integer; max. 1,390 km)

between latitudinal and longitudinal extent. Host plant

column gives the documented main host plants in

Finland, and if not known, the most likely host plants

based on observations in northern Europe. Species can

occasionally use other host plants than the ones listed.

Species groups Range size Extent Finland IUCN status Host plants

Finland Europe

HardwoodRhamnusium bicolor 1 18 71 CR Ulmus laevisAnoplodera sexguttata 1 23 71 EN Quercus roburStrangalia attenuata 1 21 71 CR Quercus roburPhymatodes testaceus 2 24 180 EN Quercus roburClytus arietis 1 21 71 VU Quercus roburPlagionotus arcuatus 2 23 141 CR Quercus roburChlorophorus herbstii 2 14 316 EN Tilia cordataMesosa myops 1 3 71 CR Quercus robur, Tilia cordataOplosia cinerea 4 16 283 VU Tilia cordataPogonocherus hispidus 4 24 224 VU Tilia cordata, Ulmus laevisLeiopus nebulosus 4 23 180 NT Quercus robur, Corylus avellanaExocentrus lusitanus 9 18 354 NT Tilia cordataStenostola dubia 10 19 292 NT Tilia cordata, other deciduous

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IUCN (1994) IUCN Red list categories. IUCN-The WorldConservation Union, Gland

Kunin WE, Gaston KJ (1997) The biology of rarity. Causes andconsequences of rare–common differences. Chapman Hall,London

Lahti T, Lampinen R, Kurtto A (1995) Atlas of the distributionof vascular plants in Finland. Computer Version 2.0.University of Helsinki, Finnish Museum of Natural History,Botanical Museum, Helsinki

Lesica P, Allendorf FW (1995) When are peripheral populationsvaluable for conservation? Conserv Biol 9:753–760

Rassi P, Alanen A, Kanerva T, Mannerkoski I (2001) The 2000Red List of Finnish species. Ministry of the Environment,Edita, Helsinki. [In Finnish with English summary)

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Soule M (1973) The epistasis cycle: a theory of marginalpopulations. Annu Rev Ecol Syst 4:165–187

Williamson M (1996) Biological invasions. Chapman Hall,London

Species groups Range size Extent Finland IUCN status Host plants

Finland Europe

TemperatePrionus coriarius 5 25 364 NT Pinus sylvestrisLeptura pubescens 4 19 354 EN Pinus sylvestrisLeptura maculata 2 25 112 VU Betula spp., other deciduousPhytoecia cylindrica 4 23 292 VU Anthriscus sylvestrisStenocorus meridianusa 5 22 430 VU Hardwoods, other deciduous

EasternTetropium aquilonium 1 2 71 NT Picea abiesAcmaeops smaragdula 4 6 474 VU ConiferousNivellia sanguinosa 2 9 474 EN DeciduousLeptura nigripes 6 9 583 VU Betula spp.Leptura thoracica 1 7 71 CR Populus tremula

Substrate limitedTragosoma depsarium 9 16 763 VU Pinus sylvestrisAcmaeops septentrionis 17 14 962 VU Picea abiesAcmaeops marginata 6 16 636 VU Pinus sylvestrisXylotrechus rusticus 39 22 1,141 NT Populus tremulaMonochamus urussovii 22 6 1,012 VU Picea abiesSaperda perforata 20 16 890 NT Populus tremula

MiscellaneousObrium canthariumb 27 19 763 VU Populus tremula

a The primary host plants of the species are hardwoods, but the species must be able to use other host trees in Finland as it has beendocumented from locations without hardwoods.b Obrium cantharium is not included in the group ‘Substrate limited’ based on the information on its specific substrate requirements(e.g. branches of Populus tremula); the species may simply be difficult to find and thus artificially rare.

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