Starting in the late summer of 1993, I began observing ants that visited cactus extrafloral nectaries in an area across the street from my apartment complex in Tucson, Arizona. I immediately discovered that there were a number of species visiting these cacti and that the interactions between them were often quite intense. To get a better feel for what was going on, I set up a field site and began to observe the ants and their interactions in a more a systematic fashion. To accomplish this I did the following:
(1) For two years, beginning in September of 1993, I recorded on a near-weekly basis the species of ants using 47 chainfruit chollas and 27 barrel cacti (due to mortality there were 42 chainfruit chollas and 26 barrel cacti at the end of the study). These two species secreted extrafloral nectar throughout the year. There were also other species of cacti on my field site that produced extrafloral nectar seasonally (particularly prickly pears). Unfortunately, including these other species in the study would have greatly increased the time required to do weekly surveys (at least at times of the year when their nectaries were active).Surveys were typically performed in the two hours before sunset. Except for a few strictly nocturnal ants, I could reliably survey most of the prominent species using cactus extrafloral nectaries at this time regardless of season.
(2) In 1994 I not only determined the species of ants using chainfruit cholla and barrel cactus extrafloral nectaries during my weekly surveys but also attempted to count all the Crematogaster opuntiae workers on these plants.
(3) Most of the time, and especially during the warmer months, I made nightly visits to my field site to observe, photograph, and videotape various aspects of extrafloral nectary-visiting ant biology. Also, where possible, I tried to locate nest sites and to determine what ant colony was visiting a particular extrafloral nectary-bearing cactus.
(4) I examined the joint occurrence of different ant species and whether the different species had any size preferences for the plants that they visited. To do this, I did a nocturnal survey of 230 chainfruit chollas (including the 46 on my field site). The survey was done over several nights during September of 1994 (all species of ants at my site that visited cactus extrafloral nectaries were active after dark during this time of year). For each plant I recorded the ant species visiting it and its circumference 10 cm from the ground.
Because I performed no manipulation experiments and am in the process of analyzing a considerable amount of data, most of what I describe in the following web pages is phenomenological and not developed to the depth that I would like. Nevertheless, I still hope some will find it interesting and even take the time to tell me what they think.
Copyright (c) 1998 Barry Sullender
Rice University
All rights reserved