Page 3 - Fattorini_etal2015
P. 3
Measuring influence of environmental heterogeneity on island beetles
cates, in practice, a reduction in heterogeneity). Alterna- ta (2012) and Lillig et al. (2012a,b). Species presence/ab-
tively, one could use a specific terminology, such as “envi- sence on individual islands is given in Appendix 1.
ronmental diversity”, “environmental dominance”, or “en-
vironmental evenness”, depending on what is being meas- Environmental categorization
ured (see also Stein & Kreft 2014 for a review of the use For an ecological characterization of island landscapes, we
of various expressions). calculated the extent of island surface occupied by differ-
ent land cover categories according to the European Co-
The case study rine Land Cover classification. Although somewhat crude
To put in practice our observations, we present here a case and of limited value for small regions, Corine land cov-
study in the field of island biogeography dealing, in par- er categories are extensively used to express species-en-
ticular, with the distribution of tenebrionid beetles on the vironment relationships (e.g., Lobo & Martín-Piera 2002,
islands surrounding Sicily. Sicily is the largest Mediterra- Stefanescu et al. 2004, Maes et al. 2005). A total of 24 land
nean island, and it is surrounded by a number of small is- cover categories were found on the circumsicilian islands
lands, collectively known as the “circumsicilian” islands. (Italian Ministry of the Environment and Protection of the
The biogeography of the circumsicilian islands is particu- Territory and Sea 2009, Malta Environment and Planning
larly complex (e.g. Fattorini 2010, 2011a,b, and references Authority 2009). This number of environmental catego-
therein), because they vary greatly in terms of area (Mal- ries is disproportionately large in respect to the small num-
ta, the largest island, has an area of 245.7 km2, but most of ber of islands composing the archipelago. Moreover, some
the islands are below 30 km2), ecological and climatologi- categories are represented by very small patches and can
cal settings, geological origin (volcanic vs. sedimentary), be easily combined into broader categories. Thus, we used
paleogeography (some were connected to Sicily or Africa the following broader land cover categories: Built up ar-
during Pleistocene glaciations, others remained isolated) eas (including Continuous urban fabric, Discontinuous
and distance to two different main sources of colonization urban fabric, Industrial or commercial units, Port area,
(Sicily vs. Africa) showing high degree of biotic diversi- Airports, Mineral extraction sites, Dump Sites, Green ur-
fication. Thus, they represent a good model to explore the ban areas, and Sports and Leisure Facilities), Cultivations
influence of many possible abiotic determinants on animal (including Vineyards, Non-irrigated arable land, Natu-
communities including environmental heterogeneity. In ral grassland [because most often found in areas where
general, the fauna of these islands is also relatively well there is extensive agricultural activity], Annual crops as-
known. Among insects, one of the best investigated groups sociated with permanent crops, Complex cultivation pat-
is the beetle family of Tenebrionidae. Thanks to their low terns, and Land principally occupied by agriculture, with
dispersal ability, tenebrionids represent excellent bioge- significant areas of natural vegetation), Coniferous forest,
ographical markers of historical processes and they have Broad-leaved and Mixed Forests, Sclerophyllous vegeta-
been repeatedly used to investigate the biogeography of tion, Bare rock and Sparsely vegetated areas, and Wet ar-
Mediterranean islands (e.g., Fattorini 2002a,b, 2006a,b,c, eas (including Salt Marshes, Salines, and Water bodies).
2007a,b,c,d, 2009a,b, 2010, 2011a,b, Fattorini & Fowles Even if these broad land cover units are coarse in compari-
2005, Fattorini et al. 1999, Hausdorf & Hennig 2005, Tri- son to the scale at which insects perceive small-scale envi-
chas et al. 2008, Papadopoulou et al. 2008, 2009, 2010), ronmental heterogeneity, they correspond well to distinct
including the circumsicilan ones (Fattorini 2010, 2011a,b). keystone structures (sensu Tews et al. 2004) for tenebrio-
nid species. In particular, each of the seven classes used
Material and methods here corresponded to different microclimate conditions,
food resources, and soil characteristics, which are among
Study area the most important factors shaping tenebrionid communi-
We used data from 25 circumsicilian islands, including: ties in the Mediterranean (Fattorini 2008, 2009c).
the Aeolian Islands (volcanic: Stromboli, Panarea, Vulca-
no, Lipari, Salina, Filicudi, Alicudi, and seven smaller is- Environmental heterogeneity measures
lets), the Egadi Islands (sedimentary: Levanzo, Favignana,
Marettimo), the Pelagie (Linosa, volcanic, and Lampedu- In addition to score the number of land cover categories
sa and Lampione, sedimentary), and the Maltese Islands
(Malta, Gozo, Comino, Cominotto, and Filfla, sedimenta- (N) occurring on each island, we used the land category
ry); Ustica and Pantelleria (both volcanic), are rather iso-
lated. For detailed information on these islands see Maz- information to compute various synthetic indices of envi-
zola et al. (2001), Fattorini (2010, 2011a,b) and Savona
Ventura (2011). Data on tenebrionid distribution in the cir- ronmental heterogeneity (Table 1). For this, we applied in-
cumsicilian islands were extracted from Fattorini (2011b)
and updated with new data reported by Lo Cascio & Pas- dices of diversity, evenness and dominance derived from
those used in community ecology (Legendre & Legendre
1998, Magurann 1988, 2004, Hayek & Buzas 2010):
- Simpson dominance index: 2
C =∑
Ai
A
where Ai is the extent of the land cover category i, and
3