Frammentazione ambientale, connettività, reti ecologiche

164 Connettività
Abstract
Protected areas: Role, design and limitations - As a general rule, protected
areas can preserve the biological diversity of a region only if they comprise a relatively
complete sample of native ecosystems and are large and close to each other.
Indeed, the local extinction of a species may happen more rapidly in small, isolated
reserves. Therefore, although protected areas can constitute the starting focal point
for specific conservation strategies, they do not seem to be sufficient to preserve
populations, communities, and ecological processes in fragmented landscapes,
especially in Europe.
With respect to the last issue, a debate is in progress on natural reserve design,
regarding their location, shape, size, and more appropriate number (SLOSS debate).
Reserves should have a regular shape in order to maximize the core area and
the ratio area/perimeter, so decreasing the edge effect on sensitive species and keeping
some key ecological processes, such as dispersal. Moreover, for a correct design,
the study of the geographic pattern of the sensitive (meta)populations and of
the species-specific requirements may be relevant.
Corridors and connectivity. Role and limitations – In order to minimize the impact
of habitat fragmentation on diversity and ecological processes, the role of corridors
and connectivity has often been emphasized. However, their utility is not
clear due to a lack of experimental success.
The potential advantages may include the increase of movements among fragments
for sensitive species, allowing a gene flow among populations, providing additional
habitats and refuge areas, increasing immigration and recolonization and
decreasing the extinction rates.
Disadvantages are the risk of catastrophes spreading in fragments. Moreover,
sensitive species may perceive corridors of higher perimeter/area ratio as edge/sink
habitat, may compete with generalists or be preyed on during dispersal.
Species-specificity and design – Corridors may have a role as habitat and routes
of dispersal and appear to be species-specific, with intraspecific differences. They
may be classified on the basis of their origin, structure, topographic position, and
shape and their design should take into account those factors which affect the spe-