20th International Congress of Arachnology

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the accuracy of our method. We are now using this
approach to measure the trophic niches of spiders in the
Hawaiian Tetragnatha radiation in order to elucidate the
role of diet in the rapid diversification of this lineage.
Keywords: gut content, metagenomics, trophic niche,
barcoding
Student - poster presentation
Stable isotopes illuminate niche ecology in
an adaptive radiation of Hawaiian spiders
*Susan Kennedy1, Rosemary Gillespie1, Todd Dawson2
1Department of Environmental Science, Policy and
Management, University of California - Berkeley,
130 Mulford Hall #3114 Berkeley, CA 94720-3114,
USA; 2Department of Integrative Biology, University of
California - Berkeley, 3040 Valley Life Sciences Build-
ing #3140 Berkeley, CA 94720-3140, USA
Stable isotopes offer valuable information on organisms’
niche ecology. Used in the context of adaptive radiation,
these data can provide fascinating insights into the
processes by which lineages evolve. Carbon and nitrogen
isotopes have proven especially useful in food web studies,
as they tend to increase incrementally with successive
trophic levels. Isotopes also reflect the chemical stoichi-
ometry of an individual’s habitat, as isotopic signatures
are passed from soil and water to plants, and on to con-
sumers. We used C and N stable isotopes to measure niches
of spiders in the Hawaiian Tetragnatha adaptive radia-
tion. Tetragnatha spiders of both the cursorial (Spiny
Leg) and web-building groups were collected from sites
of different geologic age and were tested for their isotopic
signatures. Ariamnes spiders, which specialize on hunting
other spiders, were also included, and foliar samples were
taken as a baseline. We found a clear stepwise increase in
δ15N from plants to Spiny Leg spiders to web-builders to
Ariamnes for all sites tested; furthermore, as substrate age
increased, δ15N increased in every category. These results
suggest that 1) web-building Tetragnatha may occupy a
higher position in the food web than their Spiny Leg con-
geners, and 2) Tetragnatha and Ariamnes spiders exhibit
high site fidelity, reflected in their site-specific nitrogen
isotopes, which may promote speciation by isolating
nearby populations from each other. Work is now under-
way to test for dietary differences among the spider groups
using gut content metagenomics.
Keywords: niche ecology, trophic ecology, stable isotopes,
adaptive radiation
Student - Poster presentation
Diversity and community structure of
arboreal spiders (Araneae) in grassland-
shrub systems
Eric Knutson
Department of Bioagricultural Sciences and Pest
Management, Colorado State University, 2220 S.
College Ave, Fort Collins, CO, USA
Native grasslands are among the most imperiled ecosys-
tems and with continued habitat alteration, we require
greater understanding on the species potentially affected.
An important component of the invertebrate community
of these grasslands, are spiders. However, relatively little
is known about arboreal species in grassland systems. For
instance, temperature, humidity, and structural complex-
ity of many perennials may allow spiders to segregate in
these systems and be partially determined by these ecore-
gion effects. Thus, without including shrub habitat and its
occupants in modern grassland models, we cannot clearly
determine what ecological drivers within a landscape are
crucial to these spiders survival and its implications for
overall species distribution. The objective is to determine
the responses of arboreal spider populations to habitat
structure and landscape attributes of native grassland
shrubs and how those patterns scale to define habitat
use and niche width. To assess the factors responsible
for diversity variation, I examined data collected for a
multi-year biodiversity study within selected Colorado
National Grassland sites. Preliminary data indicates that
shrub species offer unique structural or temporal factors
to spider communities in grasslands. To measure the
responses to landscape variation, I examined how dif-
ferent spider species respond to broad-scale to fine-scale
ecological gradients (elevation, vegetation density). In this
120 DENVER MUSEUM OF NATURE & SCIENCE REPORTS | No. 3, July 2, 2016
Cushing