IALC Peace Fellowship Report 11 October - 1 November 2000

Hadas Hawlena 
Undergraduate Student

Ben-Gurion University of the Negev, Israel

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 and management.

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 environments.

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.