Ecological analyses of carabid communities— potential use in biological classification for nature conservation

Biol Con.~erv.17(1980) 131-141

ECOLOGICAL ANALYSES OF CARABID C O M M U N I T I E S - POTENTIAL USE IN BIOLOGICAL CLASSIFICATION FOR NATURE CONSERVATION

DAGFINN REFSE1-H

Zoological Institute, University of Trondheim, Rosenborg, N-7000 Trondheim, Norway

ABSTRACT

Because insects have an important role in ecosystems, they should be included in any classification regarding the conservation of natural resources. On a basis of pitfalltrap captures, a schemeJor utilising such inJormation about carabid communities in a classification of habitats is proposed. Habitats can, to some extent, be classified according to characteristic species or species groups, but analyses of degrees of similarity and calculations of species diversity values are also necessary to provide a more exact doeumentation of the conservation value of different habitats. The inJbrmation obtained has made a valuable contribution to existing habitat classification systems.

INTRODUCTION

The biological data used for classifying land areas in connection with nature conservation have so far generally been obtained from phytosociological investigations and associated vegetation maps. Recently, a classification system based on the bird communities has been proposed (Bevanger, 1977), but the insect fauna has hitherto not been used in this way. This is probably due to the methodological and taxonomic problems associated with the great diversity of insect types in nature. However, owing to their great importance in almost all ecosystems, the insect fauna should also be considered in relation to the conservation of natural diversity. In the present paper a procedure fotr applying entomological data in ecological classification is proposed. This work forms part of a Norwegian IBP section CT project. Only carabid beetles (Col., Carabidae) are discussed since this group was found to yield the most valuable results with regard to the overall aim of the study. 131 Biol. Conserv. 0006-3207/80/0017-0131/$02.25--~,ty Applied Science Publishers Ltd, England, 1980 Printed in Great Britain

! 32

DAGFINN REFSETH

Because carabids are widely distributed in terrestrial habitats, valid comparison of data from different geographic areas is possible. The group is well-known taxonomically, which facilitates the task of species identification. Most species are restricted to particular kinds of habitat, yet are able to move about in response to the environmental changes. They are therefore well fitted to be used as ecological indicators (Heydemann, 1955). Carabids have in fact already been found to provide good indications of environmental changes due to human activities (Thiele, 1977). Several authors have described the carabid faunas of different habitats (e.g. Thiele & Kolbe, 1962; Greenslade, 1963; Stein, 1965; Obrtel, 1971b; Forsskfihl, 1972), and Thiele (1977) has made a thorough analysis of the factors which affect habitat selection by carabids. However, no attempts have been made to combine such information with other biological data for habitat classification purposes. In fact, such combinations have in the past been impeded by the absence of standardised sampling techniques and treatment of the collected data. The primary aim of the present paper is to put forward such standards.

METHODS The field work on which this paper is based was carried out in the Sjodalen valley, in the Jotunheimen mountains in southern Norway (61 °30'N, 8 °50'E). The vegetation of the area includes pine forest, subalpine birch forest, and low-alpine dwarf-shrub heaths (for details, see Marker, 1972). The samples were collected from six study plots, each situated in one of the main vegetation types (Table l) and within, or close to, the areas chosen for the bird censuses which were carried out at the same time (see Bevanger, 1977). The samples were obtained using pitfall traps, a common method used for sampling carabids and convenient for extensive use in the field. The traps consisted of plastic cups, 6.5cm in diameter and 9.5cm deep, containing 4 % formaldehyde. Twenty traps were used in each study plot, arranged TABLE 1 LOCATION OF THE SIX STUDY PLOTS AND THEIR TYPES OF VEGETATION

Study plot

UTMreference

Altitude (m)

Vegetation type

Fu 1 B1

32VMP9629 32VMP9219

M2 F la

32VMP9119 32VMP9529

F lb

32VMP9529

Sub-alpine birch forest (Betuletum empetro-cladinosum + Betuletum empetro-hylocomiosurn) 955 Lichen heath (Arctostaphyio-Cetrarion nivalis) 1120 Oligotrophic low-alpine dwarf-shrub heath (Mostly Arctostaphylo-Cetrarion nivalis) 1120 Eutrophic low-alpine dwarf-shrub heath (Phyilodoco-

F2

32VMP8109

1260

920 Pineforest (Barbilophozio-Pinetum) 980

Vaccinium myrtilli+ Kobresieto-Dryadion)

Oligotrophic low-alpine dwarf-shrub heath (LoiseleurietoArctostaphylion + Juncion trifidi scandinavicum)

ECOLOGICAL ANALYSES OF CARABID COMMUNITIES

133

in two rows, the traps being 2-4 m apart. Each trap was sheltered against rain by a plate attached by two metal pins. The sampling took place between 20 June and 15 August 1972 and between 30 May and 17 October 1973. To obtain an expression of the 'ecological similarity' of the species--i.e, how species may be grouped according to their habitat preferences--an 'index of ecological similarity' was calculated (Cody, 1974):

~b = 1 - ½ ~

IP,i - Phil

i=l

in which O~ab the degree of similarity in habitat preference by species a and species b, Pa~ = the relative abundance of species a in habitat i, Pb~ = the relative abundance of species b in habitat i, and n = number of habitats. On the basis of the similarity indices a dendrogram was made by a procedure described by Cody (1974). Species diversity was calculated by means of the Shannon-Wiener formula (Pielou, 1966): =

S

H' = - ~

Pi.lnp~

i=1

where Pi = the relative abundance of species number i, and s = total number of species. RESULTS

The species distribution and numbers of specimens trapped in each of the six study plots are shown in Table 2. Both species composition and the quantitative distribution of species differed from one habitat to another. In addition one or two species constituted the majority of the specimens caught in each habitat, viz. Patrobus septentrionis and Amara alpina in F 2, A. alpina in F la and M 2, Patrobus assimilis and Carabus violaceus in F l b , Amara brunnea and Calathus micropterus in B 1, and P. assimilis and Calathus melanocephalus in Fu 1. Although the only dominant species in F la and M 2 was A. alpina and the other species only occurred in small numbers, the two habitats can be distinguished by the presence of P. septentrionis and C. violaceus in F la and A. brunnea in M 2. The results of the similarity analyses separate the species into three main groups (Fig. 1). The five species in the first group (Miscodera arctica-Nebria gyllenhali) are primarily found in the alpine habitats F 2 and F la. The second group (C. melanocephalus-Notiophilus germinyi) consists of six species which mainly occur in the forested habitats B 1 and Fu 1. Of the species in the third group, Agonum

134

DAGFINN REFSETH

TABLE 2 TOTAL NUMBERS OF SPECIMENS OF EACH SPECIES CAUGHT IN THE SIX STUDY PLOTS, WHICH ARE ARRANGED IN INCREASING ORDER OF STRUCTURAL COMPLEXITY OF THE VEOETATION

Species

F2

Nebria gyllenhali Schn. Patrobus septentrionis Dej. Amara alpina Payk. Agonum consimile Gyll. A. sexpunctatum L. Carabus violaceus L. Notiophilus aquaticus L. Miscodera arctica Payk. Cymindis vaporariorum L. Patrobus assimilis Chaud. Amara brunnea Payk. Calathus melanocephalus L. Carabus glabratus Payk. Cychrus caraboides L. Calathus micropterus Dft. Notiophilus germinyi Faub. Leistus ferrugineus L.

F la

2 227 216

8 119 1 3 9 1

83 2

2

1

4

4

4

-6~

148

40

~

~

- ~ ~

165

E

~ ~ ~, _~ ~ - ~

2

14 44 11 18 40 9 3

17 2 16 4 3 12 5 5

147

70

~ ~

0°908

11

0,6-

o.3' o.2i o.12

1

E

1,0

0,5"

Fu l

4 3 69 9 3 16 4

7

u)

B 1

4 46 11

1 3

1

O

Fib

19

1

536

._

M2

] I

--

-~ ,

I I

Fig. 1. Dendrogram showing the degree of similarity in habitat preference between each of the 17 species.

sexpunctatum, C. violaceus, and Agonum consimile were only found in the alpine habitats F la and F lb, while Carabus glabratus, P. assimilis, and Cymindis vaporariorum are apparently less demanding in their habitat preference, although P. assimilis was most abundant in F 1b (Table 2). Consideration of Fig. 1 and Table 2 shows that the carabid fauna of F 1b shows a

ECOLOGICAL ANALYSES OF CARAB1D COMMUNITIES

135

close resemblance to that found in the forested habitats B 1 and Fu 1, despite the fact that F l b is situated in the alpine region and lies close to F l a . This is also seen in Fig. 2, where the degree of faunal similarity between the two habitats has been calculated on a basis of the same 'index of similarity' values. Habitat type M 2, on the.other hand, has much in common with the oligotrophic alpine habitats F la and F 2, although it lies at the same altitude as the birch forest habitat B 1 and not far away from it.

F1o F2 M2 Flb B1

1.0

Ful

l-

0.9' 0,8 0,7 0.6' 0.5 0,4 0.3 I

0,2~ 0,1 Fig. 2. Dendrogram showing the degree of similarity between the different habitats with regard to the species composition of the carabid fauna.

The diversity indices (H') for all habitats are shown in Fig. 3, together with the curves for species-dominance. The lowest degree of diversity is found in the alpine habitats, with a sparse vegetation cover, and the highest is found in the forested habitats. No information is available about the diversity of the plant communities, but, according to the results of the vegetation survey (Marker, 1972), the carabid results seem to correlate well with the structural complexity of the vegetation. When comparing the carabid results with those obtained from the bird censuses, it appears that the increase in species diversity found for the carabid fauna, in order of habitat F 2-F I-M 2-B 1-Fu 1 closely resembles that found for small passerine birds (see Fig. 4). For habitat type F 1 the mean value of the carabid diversity indices for F la and F lb has been used, since the bird census data for that area cover several vegetation types. A high value was obtained for the passerine diversity index for habitat type M 2 because the bird census area in that area included both the lichen heath and a nearby zone of willow thicket (Salix spp.) along the river banks, which led to an increase in species number and, correspondingly, in the species diversity index. When the diversity index values for the two corresponding sampling periods in 1972 and 1973 were compared, some differences were found, especially a decline in diversity in M 2 from 1972 to 1973 (Table 3), which was probably due to the

136

DAGFINN REFSETH

80' 70. 60-

N=148

40-

H'= 0,84

o~

20

LLI (D Z < Z

10

O O LU

Flo

50-

40"

t

•~.

30" 20" 10-

F2

\

N=536

:22

Flb

40-

N=165

30-

'=

30

,

=1,45

I,,--I

20

20. _J W

10. i

30 20

~

i

,

•

,

,

,

i

N=147 "--

10

30 20

Ful

• N=70 ~=1,88

10

om-.~ •

SPECIES Fig. 3.

,

,

,

,

,

,

,

•

•

SEQUENCE

Species-dominance curves obtained for each type of habitat. H ' = species diversity. N = no. of specimens.

comparatively small number of carabids caught (18 specimens in 1972, 22 in 1973). For the same reason, the differences in trapping frequencies between the two years were most pronounced in M 2 (Table 4). In addition, the greatest variations in trapping frequencies were found for Cychrus caraboides in B 1.

DISCUSSION

Problems concerning the data obtained using pitfall traps According to Greenslade (1964) pitfall traps are quite suitable for studies of

137

ECOLOGICAL ANALYSES OF CARABID COMMUNITIES

2,2

H'

°

2,0-

1,81,61,41,2-

1,0~ !

F2 Fig. 4,

I

i

!

M2

B1

Ful

i

gl

Species diversity index values for carabids (solid) and small passerine birds (dashed) in the five types of habitat; bird data supplied by K. Bevanger (pers. comm.).

TABLE 3 SPECIESDIVERSITYVALUESFOR THE CORRESPONDINGSAMPLINGPERIODS IN 1972 AND 1973

Habitat F 2 M 2 B 1 Fu 1

June-August 1972

1973

1.14 1.59 1.83 1.87

0.92 1.12 1.67 1.99

Habitats F la and F l b are omitted because sampling in these areas took place in one year only.

TABLE 4 DOMINANCE VALUES (PER CENT) FOR THE THREE MOST ABUNDANT CARABID SPECIES CAUGHT IN EACH HABITAT IN 1972, 1973, AND THE MEAN VALUE FOR BOTH YEARS TOGETHER

Habitat F2

M 2

B 1

Fu 1

Species P. septentrionis A. alpina N. aquaticus A. alpina A. brunnea P. assirailis A. brunnea C. micropterus C. caraboides C. melanocephalus P, assimilis C. micropterus

1972

1973

Mean

44.9 42.5 11.0 25-0 31.3 18.8 31.0 14.3 23-8 31.6 10.5 10.5

60.0 32.7 6.4 66-7 11.1 -51.9 14-8 3-7 19.2 23.1 23.1

52.5 37.6 8.7 45.9 21.2 9.4 41.5 14.6 13.8 25.4 16.8 16-8

Habitats F la and F l b - - s e e comments in Table 3.

138

DAGFINN REFSETH

reproduction and of the activity patterns of carabids, while there are several objections attached to the method when quantitative interpretations of the data collected are made. The size of the catch may be influenced by the size and number of traps, the preservative fluid used, differences in the behaviour of individual species, weather changes during the survey period, and variations in the density of the vegetation cover. Estimation of the true population densities is therefore difficult. However, in zoo-sociological studies of the present kind, in which the results from several localities are to be compared, it is actually not necessary to have exact estimates of population densities. Bombosch (1962) stated that when the sizes and numbers of traps and the duration of the sampling periods are all approximately equivalent, the catches made will be an expression of the relative abundances of the different species and hence yield comparable data. It therefore seems very important to ensure that standard sampling techniques are used in making systematic studies of carabid communities. Estimates of the number of traps necessary for providing a valid population sample at a study site have varied from 5 (Stein, 1965) to 70 (Bombosch, 1962), but usually 10-20 traps are sufficient for quantitative analyses (Stein, 1965, Obrtel, 1971a). Luff (1975) compared the trapping efficiency of traps of different size. He concluded that 6--10 cm was a suitable diameter to use. The most commonly used preservatives are formaldehyde and ethylene glycol. The former has the advantage of being both cheaper and better suited both for killing and preserving (Heydemann, 1956). Formaldehyde may exert some attractive effect on beetles, although there seems to be little or no difference in the reactions of the different species (Luff, 1968). The seasonal pattern of activity of carabids is related to their breeding biology, since different species breed at different times of the year. The sampling period used, therefore, must cover the breeding seasons of all the species in question at any particular locality. In this way the influence of changing weather conditions will also be reduced. The effects of the vegetation cover and the behaviour of each species have been considered by some authors, but are difficult to quantify. According to Greenslade (1964), habitats with an open field layer permit greater speed of movement, resulting in higher trapping frequencies than those obtained in habitats with a dense vegetation cover. This applies in particular to the larger carabid species, which move faster than the smaller ones, are more easily trapped, and hence may be overrepresented in the samples. On the other hand, Luff(1975) found that small species were in fact more easily trapped than large ones. However, most habitats contain some vegetation, and because this obstructs the movement of the larger species more than that of the smaller ones, the effect of the faster speed of movement of larger species should thereby be diminished. Since the number of beetles caught in pitfall traps depends on both the

ECOLOGICAL ANALYSES OF CARABID COMMUNITIES

139

abundance and the activity of each species, the trapping results are commonly expressed by the term 'activity density', introduced by Tretzel (1955) and Heydemann (1956). This is thought to yield a good estimate of the role of a species in an ecosystem (Thiele, 1977), and data obtained from pitfall traps ought therefore to yield valuable information about both the numerical and ecological status of each carabid species.

Treatment of collected data Classification of biological communities is usually based on species lists and characteristic species. These may include either the most numerous species, or those which are specific to the habitat in question. Knowledge of whether a species is present in a particular habitat or not may therefore suffice, but when the bulk of a sample consists of a single, or only a few, species, this is probably a result of a high population density and consequently represents expression of a preference for that particular habitat. In the present case most of the species do seem to prefer certain habitats, and their occurrence, for the most part, accords with the information given in the literature. For example, A. alpina, which was most numerous in the oligotrophic low-alpine habitats F la and F 2, is reported to be a characteristic insect for the Siberian tundra (Lindroth, 1945). A comparison with the data of Forssk~hi (1972), who studied the carabid fauna of Kilpisj~irvi in northern Finland, reveals a great deal of faunal similarity between corresponding habitats in Sjodalen and Kilpisj~irvi. The two, and in some cases three, dominant species in each habitat were the same in both areas. However, in many cases the dominant species may be euryoecious and widespread, whereas stenoecious species are usually best suited for use as characteristic species, since they are more specific in their selection of habitat. A similarity analysis helps to pinpoint such species. A good example is Miscodera arctica, which, although found in both the pine forest and in the two sub-alpine habitats, was found to be grouped together with the alpine species (Fig. 1), a relationship which is consistent with its known distribution and ecology (Lindroth, 1945). It is also noteworthy that the carabid fauna of the pine forest consists of species, e.g.P, assimilis, A. brunnea, and C. glabratus, which were also encountered at several other localities. These species may be undemanding in their choice of habitat, but the possibility still exists that the pine forest is a somewhat more differentiated habitat than the results of the vegetational analyses would suggest. The catches made in the two adjacent habitats, F la and F l b , also show the degree of variation which may exist in the carabid fauna present within quite a restricted area. It is thus possible that information about carabid distribution may prove to be useful for making a more detailed classification of habitats, according to vegetational analyses, since habitats which are apparently similar may differ in some hitherto unrevealed manner.

140

DAGFINN REFSETH

A primary aim in nature conservation is the preservation of areas of great productivity and environmental variability. The concept of species diversity has turned out to be useful in assessing such qualities. In the present case the results of the calculations of species diversity did not add much more information to that already obtained from the plant and bird surveys, except for the above-mentioned difference which was found between F I b and the other two low-alpine habitats, F I a and F 2 (Fig. 3). The relatively high value found in F l b is nevertheless consistent with the greater richness in plant species and the more complex structure of the vegetation in this habitat (Marker, 1972). However, interpretations of diversity indices depend on a background knowledge to which the results can be related. Such knowledge can only be obtained by investigating a whole range of different habitats to provide a basis for comparison. This is particularly advantageous in zoological classification when the geographical factor has to be considered. Because of the restricted geographical distributions of many carabid species, similar habitats in widely-separated areas may yet contain characteristic different species. For instance, subalpine birch forest in the Budalen valley, Sfr-Tr6ndelag province, does contain different dominant species from those in the birch forest in Sjodalen (B 1), yet the species diversity index was as high as 2.15 (compared with 1.73 in B 1, see Fig. 3) (Refseth, unpublished information). The Budal value is the same as the diversity index value calculated from pitfall-trap data for a Danish beech forest (J6rum, 1976). For comparative purposes, therefore, the inclusion of information about species diversity seems necessary in any biological classifications. A further factor also needs to be taken into consideration. Both species abundance and species diversity values may vary from year to year. Trapping therefore needs to be carried out during a period of at least two years, in order to get reliable results. CONCLUSION

Although a separation of various habitats by using their characteristic carabid species or species groups seems possible, a separate classification system for carabid communities is scarcely appropriate. The results obtained should preferably contribute to providing a more detailed knowledge of habitats previously classified in other ways, in particular the results of similarity analyses and species diversity indices. Such a method of quantifying the biological data will aid a more exact documentation of the sort of qualities worth conserving, especially when the information obtained from insect and bird surveys and from vegetation mapping is considered in combination. ACKNOWLEDGEMENTS

I would like to thank Olav Hogstad for valuable criticism of the manuscript, and

ECOLOGICAL ANALYSES OF CARABID COMMUNITIES

141

P h i l i p A . T a l l a n t i r e for i m p r o v i n g the E n g l i s h . T h e field w o r k h a s b e e n s u p p o r t e d b y g r a n t s f r o m t h e N o r w e g i a n R e s e a r c h C o u n c i l for Science a n d the H u m a n i t i e s (NAVF), and from the Norwegian IBP. REFERENCES

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