20th International Congress of Arachnology

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DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
organisms, and on the interactions with their physical
environment. Elevational gradients offer one powerful tool
to disentangle the relative effects of these processes because
the zones or bands along a gradient represent different con-
ditions across which species composition and abundances
vary. In our talk we will present a novel framework to
investigate community assembly using spider communi-
ties as a model. By combining habitat-related physical and
(functional and phylogenetic) community structure data
we are looking into the way climate and geography, habitat
use and dispersal all interact to determine how species are
filtered into communities. We will show our first findings
on the spatial changes in communities while introducing
our model system: the Udzungwa Mountains, part of the
Eastern Arc Mountains (EAM), Tanzania. The elevational
range (300–2500 m) in the Udzungwa Mountains creates
gradients in temperature and humidity, allowing for a
variety of habitat types. From evolutionary and conserva-
tion points of view, the EAM are particularly exciting as they
form an inland archipelago with a history at least as fasci-
nating as that of the Galápagos Islands, and they contain
some of the oldest and most stable forests of Africa and
some of the most endemism-rich forests in the world.
Keywords: beta diversity, community assembly, Eastern
Arc Mountains, functional structure, habitat, Udzungwa
Student - oral presentation
The ecological niche of subterranean spiders
*Stefano Mammola, Elenia Lazzaro, John Dejanaz,
Marco Isaia
Department of Life Sciences and System Biology,
University of Torino, via Accademia Albertina 13
10123 Torino, Italy
The geometry of the Hutchinson’s hypervolume derives
from multiple selective pressures defined, on one side by
the physiological tolerance of the species, and on the other,
by intra- and interspecific competition. The quantification
of these evolutionary forces is essential for the understand-
ing of the coexistence of top predators. We address this
topic by investigating the ecological niche of three spider
species showing different adaptations to subterranean
life (Meta menardi, Pimoa . and Troglohyphantes
vignai), occurring syntopically in different hypogean sites
of the Western Italian Alps. We surveyed different popula-
tions of our model organisms over one year, monitoring
monthly their spatial and temporal dynamics in the caves
and the associated physical and ecological variables. We
quantified the ecological niche of the three species through
multi regression techniques (GLMMs) and assessed inter-
specific competition by evaluating the overlap between
their n-dimensional niche hypervolumes. We detected a
remarkable overlap between the microclimatic and trophic
niche of M. menardi and Pimoa . However, the former
—being larger in size—resulted the best competitor in
the vicinity of the surface, causing the latter to readjust its
spatial niche slightly towards the internal part of the cave,
where prey availability was scarcer. On the other hand,
lacking true competitors in the inner sections of the cave,
T. vignai realized its niche as a trade-off between optimal
microclimatic conditions and trophic availability. With this
work, we aim at providing new insights about the complex
relationships among subterranean species, demonstrating
that energy-poor environments such as caves maintain
the potential for diversification of top predators via niches
differentiation.
Keywords: autoecology, cave, Hutchinsonian hypervolume,
interspecific competition, niche overlap
Student - Poster presentation
Ecology of Argyroneta aquaticain a small
resurgence
Stefano Mammola, Riccardo Cavalcante, Marco Isaia
Department of Life Sciences and System Biology,
University of Torino, via Accademia Albertina 13
10123 Torino, Italy
The water spider Argyroneta aquatica is the only known
spider to conduct a wholly aquatic life. For this reason, it
has been the object of an array of studies concerning dif-
ferent aspects of its peculiar biology such as reproductive
behavior and sexual dimorphism, physiology, genetic and
silk. On the other hand, besides some empirical observa-
tions, the autoecology of this spider is widely understudied.
20th International Congress of Arachnology