| Abstract |
Biogeography studies the distribution patterns of organisms and ecosystems in space
and time and the mechanisms that influence them. Understanding how biological
communities form, why they differ, and identifying the mechanisms that shape them
are key goals of ecology and biogeography. This thesis examines the biogeography of
Aegean terrestrial snails, addressing both patterns and mechanisms influencing
community assembly and biodiversity, as well as applied aspects of biodiversity
conservation. Special emphasis is placed on the impact of human activity, given its
significant effects on ecosystems, climate, and biodiversity globally, with particularly
severe impacts on island biodiversity.
Islands have long attracted biologists’ interest due to their physical isolation, which
theoretically simplifies the assessment of the various processes involved in the
assembly and maintenance of biological communities. Moreover, terrestrial
gastropods are an important component of global biodiversity, representing one of
the most species-rich groups of terrestrial animals, which, although theoretically
having a low dispersal capacity, are found almost everywhere on Earth and occupy
an extremely wide range of habitats.
The Aegean archipelago and snails provide a context that adds particular value to the
study, offering a perspective different from what has been predominantly used to
generate theory and knowledge in island biogeography, namely oceanic islands and
vertebrate or plant organisms. Thus, in-depth study of invertebrates and the
taxonomic and functional diversity of Aegean island biocommunities can refine our
understanding of life composition in island assemblages.
Chapter 2 approached aspects of the assembly of island communities of land snails
on the Aegean islands, using network analysis, nestedness and species cooccurrence. Network analysis is an excellent tool for studying both inter-island
connectivity and network properties such as nestedness and modularity to identify
processes that contribute to the composition and interaction of biocommunities.
Additionally, the study of species co-occurrence on small islands leads to the
identification of species pairs with potential interaction relationships.
Chapter 3 examined whether island communities of terrestrial snails converge
towards similar functional properties and taxonomic composition and assessed
whether island functional diversity is determined by biogeographic features (e.g.,
area, distance from species source) and human influence. It was shown that the
Aegean islands have a significantly high functional diversity of land snails, and
furthermore that land snail communities in the Aegean are shaped by non-random
processes. In this chapter we documented for the first time community convergence
in the functional diversity on continental islands.
Chapter 4 studied the area-species number relationship for six different animal
groups on the Aegean islands, in an initial attempt to determine similarities and
divergences between the different groups using as a tool one of the few 'laws of
ecology'. In this section, it is demonstrated that as different organisms perceive area
and thus the available 'ecological space' differently.
Finally, the thesis addresses gaps in knowledge about species identity and
biodiversity distribution, as biased and unrepresentative data hinder our ability to
describe and understand biodiversity and predict future changes. A complementary
goal of this thesis was to update and improve the quality of data on terrestrial snails
in the Aegean Islands.
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