In the checklist, endemics are marked with the letter E. The number of endemic species listed in the Checklist version 1.0 (excluding ‘protozoans’) is 4777 (8.6% of overall species richness). Stoch (2000) postulated that the percentage of Italian endemics may be higher than 10%. This percentage is higher in the invertebrates than in the vertebrates (where it does not exceeds 3%), and is higher in terrestrial and freshwater faunas: the percentage of marine species is less than 2%. Moreover, the percentage is higher in southern Italy and Sardinia. Finally, considering a sample of approximately 6500 terrestrial and freshwater species of invertebrates, STOCH (2003) obtained a value close to 25%.
A first, rough estimation of the distributional pattern of endemics is Italy is given in the following table, where numbers are referred to the endemics of the different regions, not to the number of Italian endemics in that region.
|
|
NtV |
NeV |
NtI |
NeI |
% Ne/Nt |
Area (km2) |
|
N |
629 |
22 |
33414 |
1720 |
5.12 |
97741 |
|
S |
545 |
22 |
24297 |
1825 |
7.60 |
153710 |
|
Si |
399 |
5 |
12988 |
776 |
5.83 |
25708 |
|
Sa |
365 |
6 |
9841 |
676 |
6.68 |
24090 |
|
3 |
455 |
1 |
6529 |
159 |
2.29 |
- |
|
4 |
317 |
2 |
3958 |
79 |
1.89 |
- |
|
5 |
394 |
0 |
3717 |
44 |
1.07 |
- |
Table: Numbers of total (Nsp) and endemic (Ne) species of vertebrates (V) and invertebrates (I), excluding ‘protozoans’, compared with area of: northern Italy, Emilia Romagna excluded (N); central and southern Italy (S); Sicily (Si); Sardinia (Sa); western Thyrrenian sea (3); northern and central Adriatic sea (4); southern Adriatic, Jonic sea and other seas (5)
The percentages, higher in southern Italy and Sardinia, reflect the isolation of these areas and the historical explanations already advocated for species richness patterns (see chapter). On the contrary, the percentage of marine endemic species is very low (< 1.5%).
The number of endemic species reported in the checklist should be taken with caution (Minelli, 1996). In this author’s opinion, several species may be considered endemic just because of our lack of knowledge on their real distribution, and for this reason the real numbers could be overestimated. On the other hand Minelli (1996) correctly stated that this effect may be partially offset by the fact that the word “endemic” was used as “endemic to Italy”; this fact lead to the exclusion of several endemics which are present in restricted areas of neighbour countries as well. For example, most of the troglobiont and stygobiont species of northeastern Italy (Stoch, 1995) are endemic, but excluded from the calculations being distributed also in a small karstic area in Slovenia.
After a thorough analysis of the checklist, I suppose that the total number of endemic species in Italy may be severely underestimated: many endemic species are being discovered at a high rate (Stoch, 1995), are hidden in species-complexes or may be sibling species (Knowlton, 1993).
To test the importance of this hypothesis, an analysis using Steyskal’s curves was performed (STOCH, 1995, for other examples); the curves for invertebrates and vertebrates are illustrated in the following graphs.
Steyskal’s curve of the number of endemic species of invertebrates of the Italian fauna
Steyskal’s curve of the number of endemic species of vertebrates of the Italian fauna
This kind of curves may underestimate the total number of species; they become steeper when new taxonomists begin to work, new taxonomic criteria are used by specialists or new kinds of habitats are explored using novel sampling techniques (STOCH, 1995). Notwithstanding this fact, the cumulative number of Italian endemic invertebrates plotted against the year of description shows that the curve is very steep. This fact suggests that the total number of Italian endemic species will increase in the future: it is reasonable to suppose that the percentage of endemic invertebrates in Italy is higher than 10% of the fauna.