IALC Peace Fellowship Report
11 October - 1 November
Ben-Gurion University of the Negev,
Influence of Grass Invasion on Spider Diversity
in an Arid Environment
Influence of grass invasion on spider diversity in an arid environment
B an extension of IALC project: Influence of Savannization and Brush Invasion
on Spider Diversity in an Arid Environment: Implications for conservation
Through a Peace Fellowship project sponsored by the International Arid
Lands Consortium (IALC), I received the opportunity to participate in
part of a two-year research program in Las Cruces, New Mexico, United
States of America. I assisted David Hu, a master student working under
the direction of Dr. David Richman (New Mexico State University, Dept.
of Entomology, Plant Pathology and Weed Science).
The aim of this study is to determine how the invasion of brush and an
exotic grass influences the composition of spider communities. At present
David Hu is collecting data on the effect of the invasion of the exotic
African species Lehmann lovegrass (Eragostis lehmanniana Nees)
on spider populations and diversity.
Spiders were chosen as a model animal since they are both abundant and
diverse in arid environments. In addition they are a crucial part of this
ecosystem because of their role as major arthropod predators in the food
web and as prey for higher vertebrate carnivores such as lizards and birds.
The effects of the introduction of an exotic grass on the spider communities
may include a change in the composition and/or abundance of native spider
species associated with the introduced grass. These changes may be positive,
near zero or negative, depending on whether the grass involved increases,
has minimal effect on, or decreases resources such as prey and/or habitat
for the spiders involved. Other effects, which might have a positive,
near zero or negative influence on the composition or abundance of spiders,
are possible too, such as an increase in competitors or predators.
Research like the present project, dealing with a comparison of natural
ecosystems with ecosystems with possible induced changes in biodiversity,
are important in order to expand existing ecological knowledge and to
refine models used in adaptive management. Such research can provide us
with clues as to how to restore productivity and biodiversity in disturbed
The study sites are located on the College Ranch of New Mexico State
University and the United States Department of Agriculture Jornada Experimental
Range, in New Mexico. The study areas are in Chihuahuan desert grassland,
which has approximately 200 mm annual rainfall.
Thirty 5 m X 5 m plots were selected. Half of them were located in an
upper bajada type grassland near a mountain range, and the others were
approximately 1 km from the mountains in a basin type grassland. The plots
differ in the vegetation composition. There are different levels of lovegrass
dominance (0% to near 80%) in the plots.
Spiders were sampled using several methods. a) Visual search B David
Hu collected spiders beneath, between or on different plants and on ground
surface, using sprayed water to reveal the cryptic species. He collected
all the individuals found within each plot. I helped record the data on
each individual collected; b) Pitfall traps B Five of these were placed
in each plot and trapped specimens were collected daily over three days
during October 2000; and c) Night search B David Hu collected spiders
at night as in method A.
During the time I spent working, I gained knowledge not only about the
project, but about the wildlife in a different desert area as well. In
Israel I live in the Negev, which is a desert zone too, but it is a whole
different world. While the soil in the Negev is yellow and grass is in
most places scarce, the Chihuahuan desert soil is reddish and dense with
grass, cacti and bushes. The animals are, of course, different but I have
found many examples of animals, which are the ecological equivalents of
the animals in Israel. For example, rattlesnakes were found in several
areas at or near the sample sites. These ambushing snakes, feeding as
they do on small vertebrates, have a lot in common with vipers in Israel.
I expanded my knowledge of the biology and taxonomy of spiders, as well.
First I learned how to find and collect them. I also joined Dr. David
Richman's class in Arachnology and learned much on the spider families
found in New Mexico.
During the 13-15 of November I joined the class field trip to the Big
Bend Ranch State Park, Texas. It was a great experience. It is a very
wild and diverse area with very interesting wildlife. The aim of the trip
was to collect specimens of the class Arachnida, but since the other students
were familiar with other groups like reptiles and birds too, we examined
almost every moving creature.
I have learned a lot about the people in this part of the United States,
their manners and view of Israel and had good chance to practice the English
language, which is very important for Israeli citizens.
I want to thank the IALC for providing funding for this fellowship, and
Dr. David Richman and his student David Hu for their guidance. I would
encourage any ecology student to become a Peace Fellow.