Study of a community of small mammals in subalpine spruce woods

Studi Trent. Sci. Nat., Acta Biol., 81 (2004), Suppl. 1: 219-223
219-223
© Museo Tridentino di Scienze Naturali, Trento 2005
ISSN 0392-0542
219
Study of a community of small mammals in subalpine spruce woods at Lavazè Pass
(Trentino, Italy)
Sandro Zanghellini1*, Cristina Salvadori2 & Paolo Ambrosi2
Albatros S.r.l., Via Fiume 20, I-38100 Trento
IASMA Research Center, Natural Resources Department, Via E. Mach 1, I-38010 San Michele all’Adige (TN), Italy
*
Corresponding author e-mail: [email protected]
1
2
SUMMARY - Study of a community of small mammals in subalpine spruce woods at Lavazè Pass (Trentino, Italy)
- In 2003 a community of small mammals was studied in an area of subalpine spruce woods, situated near the Lavazè
Pass (Val di Fiemme, Trentino, Italy), at an altitude of around 1780 m. This study was part of the EFOMI Project
(Ecological Valuation in Alpine Forest Ecosystems by Integrated Monitoring), co-ordinated by the Istituto Agrario di
San Michele all’Adige, which intends to evaluate the health of woods in Trentino using an interdisciplinary approach.
The survey took place through an intensive programme of capture with pitfall traps, lasting around 3 months (capture
programme= 9108 trap-nights). 186 specimens were captured, belonging to 12 different species. The species richness
noted represents the highest recorded within the province. The two species of water shrews, the field vole and the forest dormouse stood out in terms of their importance. The index T of relative density rating of 2.065 was particularly
high. The relationship between insectivores and rodents was 1.818. There are three dominant species: the common
shrew, the pygmy shrew and the bank vole; the other species are minor. The characteristics of the community of small
mammals demonstrate the existence of a forest ecosystem of very high overall quality.
RIASSUNTO - Indagine sulla comunità di micromammiferi in una pecceta subalpina a Passo Lavazè (Trentino, Italia)
- Nel 2003 è stata indagata la comunità di micromammiferi di un’area occupata da pecceta subalpina, situata presso il
Passo Lavazè (Val di Fiemme, Trentino, Italia), a circa 1780 m di altitudine. Tale ricerca rientra nel Progetto EFOMI
“Valutazione ecologica di cenosi forestali sottoposte a monitoraggio integrato”, coordinato dall’Istituto Agrario di San
Michele all’Adige, che intende valutare lo stato di salute dei boschi del Trentino con un approccio interdisciplinare.
L’indagine si è svolta con una campagna intensiva di cattura con trappole a caduta durata circa 3 mesi (sforzo di cattura=
9108 notti-trappola). Sono stati catturati 186 esemplari appartenenti a 12 specie diverse. Il valore della ricchezza specifica è il massimo mai riscontrato nell’ambito del territorio provinciale. Tra le entità censite, spiccano per importanza
le due specie di toporagni d’acqua, l’arvicola agreste e il driomio. L’indice di densità relativa T, pari a 2,065, risulta
particolarmente alto. Il rapporto tra Insettivori e Roditori è pari a 1,818. Ci sono tre entità dominanti: il toporagno
comune, il toporagno nano e l’arvicola rossastra; le altre specie sono recedenti. Le caratteristiche della comunità di
micromammiferi testimoniano l’esistenza di un ecosistema forestale di qualità complessiva molto elevata.
Key words: small mammals, insectivores, rodents, forest ecosystem, Trentino
Parole chiave: micromammiferi, Insettivori, Roditori, ecosistema forestale, Trentino
1. INTRODUCTION
This study, carried out in 2003, constitutes one
of the areas of examination dealt with in the EFOMI
(Ecological Valuation in Alpine Forest Ecosystems by
Integrated Monitoring) project, a three-year scientific
project co-ordinated by the Istituto Agrario di S. Michele
all’Adige. EFOMI aims to evaluate the health of woods
in Trentino using an interdi­sciplinary approach (surveys
on climate, air, water and soil chemistry, flora, vegetation, fauna, etc.). It also intends to identify and describe
the most suitable biological indicators for defining the
health of forest ecosystems (Bonavita et al. 1993; Minerbi et al. 1996). The small mammals were studied in
relation to the relevance of their “ecological weight”
in forest environments (see for example Locatelli &
Paolucci 1998a).
The aim of the survey was the definition of the characteristics of the community of small mammals in the
study area and the verification of whether these can be
used as suitable biological indicators, contributing towards determining the health of the forest ecosystem.
220
Zanghellini et al.
2. STUDY AREA
The study area was chosen on the basis of results
from a previous survey carried out in 2000 in two
forest sites in the province of Trento: Lavazè, in Val
di Fiemme, and Pomarolo, in Vallagarina. Of these,
only the first was shown to be potentially suitable for
achieving the objectives, as the Pomarolo area was
shown to lack variety in terms of species and above
all the necessary number of individuals. The Lavazè
site is situated at the pass of the same name (eastern
Trentino), at an altitude of 1780 m a.s.l. It covers a
surface area of 2 hectares within subalpine spruce
woods.
3. MATERIALS AND METHODS
3.1.
Data collection
The capture programme, which provided for the
suppression of the small mammals captured, was carried out using pitfall traps without bait, partially filled
with water.
The 99 traps were laid out over a rectangular grid of
9x11 traps, around 10 metres apart from one another.
Each trap was numbered in order to define the exact
point of capture for each small mammal.
The traps were active from 4 July to 4 October 2003,
thus for 92 consecutive nights, and they were checked
weekly to recover the samples.
The capture programme (sensu Jones et al. 1996)
was thus particularly extensive, involving 9108 trapnights.
3.2. Indices adopted
- Index of relative density (Cagnin et al. 1998):
(1) T = N x 100 / (t x n)
where: N= number of animals captured; t= number
of active traps; n= number of trapping nights (as the
animals are mainly active at night we prefer to talk
about trap/nights).
- Relationship between insectivores and rodents:
(2) I/R = n° insectivores / n° of rodents
- Index of dominance of the different species:
(3) C = ∑ (Ni/N)2
where: Ni= number of individuals of each species;
N= total number of individuals (the classes are:
C > 0.05= dominant species; 0.05 > C > 0.02= subdominant species; C < 0.01= minor species).
Small mammals in subalpine forests
- Shannon-Wiener index of diversity (biotic diversity)
(Krebs 1989)
(4) H1 = (pi)(Logn pi)
where pi indicates the relative abundance of each
species, expressed as the relationship between the
number of individuals of the same species and the
number of individuals making up the whole sample.
4. RESULTS AND DISCUSSION
A synoptic outline of the mammals captured is
presented in the table 1.
186 individuals belonging to 12 different species
were captured. In the table the capture of 3 Microtus
sp. is recorded, although these are not counted among
the species present as it was not possible to classify the
samples accurately.
The course of the growth curve for the number of
species captured probably indicates that the number of
individuals captured corresponds very closely to that
of the species actually present (Fig. 1).
The sequence of captures is displayed in the graph
of figure 2.
The captures did not show a significant tendency to decrease, as often occurs in the event of the
progressive impoverishment of the community as a
result of capture. The sequence would not appear to
be significantly influenced by the substitution of the
individuals captured with others coming from outside
the area of study. Indeed, application of the chi-square
test to compare the frequency of capture at the 64
traps situated on the two most external concentric
rectangles and those of the 35 “internal” traps did
not highlight significant differences. The most likely
explanation for the lack of a progressive decrease in
captures should thus be sought for in the abundance
of the mammal population rather than in the entrance
of new individuals to the sample area.
Lastly, the very clear concurrence of minimum capture levels with the full moon is worth noting (nights
with full moon: 13/07, 12/08/, 10/09). To a certain
extent this is surprising, as the reduction of activities
such as elusive behaviour with regard to predators is
known to occur for species living in open areas but has
not been unambiguously demonstrated for those living
in a forest habitat (Kaufman & Kaufman 1982; Price
et al. 1984; Bowers 1988; Wolfe & Summerlin 1989;
Jensen & Honess 1995).
At 2.065 the T index of relative density is particularly high in relation to the high number of individuals
captured.
The most important result of the study is the species
variety, representing the highest level of theriological
biodiversity ever noted in stations in the province of
Studi Trent. Sci. Nat., Acta Biol., 81 (2004), Suppl. 1: 219-223
Tab. 1 - Captures made at the site
(the explanation of the indices is in
the text).
Tab. 1 - Catture effettuate nel sito
(la spiegazione degli indici è nel
testo).
Species
No. individuals
Common shrew Sorex araneus
58
Pygmy shrew Sorex minutus
57
Miller’s water shrew Neomys anomalus
1
Water shrew Neomys fodiens
4
Snow vole Chionomys nivalis
1
Bank vole Clethrionomys glareolus
50
Field vole Microtus (M.) agrestis
4
Common vole Microtus arvalis 3
Common pine vole Microtus (T.) subterraneus
1
Vole sp. Microtus sp.
3
Yellow necked mouse Apodemus (S.) flavicollis
1
Wood mouse Apodemus sylvaticus
1
Forest dormouse Dryomys nitedula
2
Number of collected individuals 186
Number of species
12
Total T
I/R
1.818
H1 1.566
No. of species
12
10
8
6
4
2
0
1
2
3
4 5
221
6
7 8
9 10
Collection week
11 12 13
Fig. 1 - Growth curve in the number of species captured in
the course of thirteen weeks trapping.
Fig. 1 - Curva di crescita del numero di specie catturate nel
corso delle tredici settimane di cattura con le trappole.
Trento1. This should be considered particularly high if
we bear in mind the limited extent of the studied area
and the presence of a single macro-environment, but
also the relatively high altitude at which the area is
situated. This level of biodiversity indicates the high
overall quality of the forest ecosystem, as it demon­
strates the existence of a wide richness of ecological
niches and of particularly complex trophic networks.
As regards the species captured, in terms of ecological
significance certain species of small mammals stand
out: the two water shrews, the field vole and the forest
dormouse. The water shrew is an insectivore typically
T
0.644
0.633
0.011
0.044
0.011
0.555
0.044
0.033
0.011
0.033
0.011
0.011
0.022
2.065
linked to wetland sites (banks of streams, marshes). It
appears to be relatively widespread in Trentino but is
never common, whereas the Miller’s water shrew, which
usually lives in marshes and peat bogs on the valley floor,
is much less widespread. Distribution of both the field
vole and the forest dormouse, whose ecology is closely
linked to humid conifer forests, glades and peat bogs, is
limited to a geographical area to the east of the Adige
and there are also few known stations in the rest of Italy
(Lapini et al. 1993; Locatelli & Paolucci 1998a).
The relationship between insectivores and rodents, another indication of the community structure, is
heavily weighted in favour of the first, corresponding
to 1.818. Given that insectivores are predators and occupy a high trophic level, this result demonstrates the
existence of an abundant and diversified coenosis of
soil invertebrates, and thus of high productivity, which
is also an indication of the high overall quality of the
forest ecosystem.
As regards the “weight” of the various species in
the context of the community, there are three dominant
species, two insectivores and one rodent: the common
shrew (C= 0.097), the pygmy shrew (C= 0.094) and
the bank vole (C= 0.072). All the other nine species are
minor. As far as the dominant species are concerned, the
picture is only partly comparable with the data obtained
from similar mountain habitats in Trentino, although
with different capture methods, both in the Adamello
Brenta Nature Park (Locatelli & Paolucci 1998a) and in
the Cadino Forest (Locatelli & Paolucci 1998b), where
the pygmy shrew appeared as a minor species.
In the sampling test carried out in 2000 an alpine shrew (Sorex alpinus) was also captured at the same site; thus in total there were 13
species identified in the census at the site.
1
222
Zanghellini et al.
Small mammals in subalpine forests
32
Insectivores
28
Rodents
Total
No. of individuals
24
20
16
12
8
Fig. 2 - Capture sequen­
ce.
Fig. 2 - Andamento delle
catture.
4
3
3
t-0
ot
se
t-0
3
t-0
se
3
3
t-0
se
t-0
se
03
oag
03
oag
03
oag
03
o-
oag
ag
03
03
glu
03
glu
lu
g-
03
0
Biotic diversity, calculated using the ShannonWiener function which takes into consideration both
the number of species and the relative abundance of
each, is an important parameter in estimating the value
of the forest ecosystem, also because it represents a
measure of the stability of the communities (Begon et
al. 1989). At the Lavazè site it is 1.566, thus relatively
high (Washington 1984), once again indicating the very
good health of the ecosystem.
as regards the overall quality of the forest ecosystem
studied;
- the methods adopted allow the comparison of data
for different years and different stations; with a relatively limited effort they are capable of contributing to the determination of the health of the forest
ecosystem.
5. The present work was carried out in the framework
of the project EFOMI (Ecological Valuation in Alpine
Forest Ecosystems by Integrated Monitoring) funded
by the Autonomous Province of Trento.
Our thanks go to Lucia Corrà for her assistance
in the field work, Eva Ladurner and Luca Lapini for
their help in defining the material gathered and Paolo
Paolucci for his advice.
CONCLUSIONS
The results which emerge from examination of the
community of small mammals in the study area demonstrate the existence of a forest ecosystem of very high
overall quality, meaning that it is very “healthy”.
In general, as regards the possibility of using small
mammals within the context of the ecological evaluation of forest coenosis, the following conside­rations
can be made:
- the most effective descriptive factors have been
identified as follows: species present in the study
area, with relative naturalistic importance; species
richness; insectivores/rodents relationship; relative
density; dominance; biotic diversity;
- a considerable amount of data on populations is necessary in order to carry out statistical correlations
with the environmental variables;
- the demographic fluctuations typical of many species
of small mammals may complicate the identification
of correlation between community parameters and
environmental variables;
- certain community parameters which it is straight­
forward to obtain (species richness and diversity first
of all) undoubtedly supply trustworthy indications
AKNOWLEDGEMENTS
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