 |
|
The distribution and activity of ants (Formicidae) and how they
may affect prey choice of Phrynosoma platyrhinos in the
Alvord Basin
Timm Beeman, Hilary Neveel, Sean Nielsen, & Kim Robertson
Summer Session 2001 Field Biology Course, BIOL 417a Department of Biology
Western Washington University
Bellingham, WA 98225
Introduction
The northern section of the Great Basin Desert is located in the rain shadow of the Steens Mountains. The study site located due east of Alvord Peak is composed of hardpan, sandy flats and dune
mesohabitats. This northern cool desert of the Alvord Basin is home to
at least a dozen species of Formicidae, but even casual observation
reveals that only a few species are common. These common species vary
markedly in size, color, morphology, behavior, distribution and activity. Mound construction techniques are unique to each species and structures are found on all substrates. Phrynosoma species are the
most myrmecophagous (ant predatory specialist) reptiles in North
America. Phrynosoma platyrhinos is found on the field course study site. Our objective was to find the distribution and activity of all ant species found on
the principal study site for the field course, and to correlate this information with P. platyrhinos locations, activity times and prey choice.
Back To Top
Methods
- A survey was conducted over a 100 by 80-meter area to locate and mark Formicidae colonies with numbered flags.
|
| Identifying ant species back at the lab. |
- We designated the numbers 1-5 as operational taxonomic units to classify the five
common species of ants found.
- We identified and mapped seventy-two colonies and recorded substrate type, species and coordinates.
- We randomly selected 36 colonies on which to focus our observations, including nests of all five species. Observations took place at set time intervals for three days, and consisted of taking ground, air and nest-entry temperatures and counting ant activity. Activity
of each colony during an observation bout was measured
with three 30-second counts of all ants entering and leaving the nest with a 30-second interval between each counting period.
- For the final two days, we focused on 17 colonies of the two species of Formicidae which are believed to be the primary prey items of Phrynosoma platyrhinos.
- Standard plot surveys were conducted to capture unmarked and record positions of marked Phrynosoma platyrhinos found in the field. Unmarked P. platyrhinos were marked with paint and permanent toe clips.
- P. platyrhinos fecal matter was collected in the field and expressed from captured lizards. Fecal matter was placed in vials for later dissection in the lab.
Back To Top
Results
- Ant nests were located on the three predetermined substrates in the proportions. These frequencies were used to determine the distribution of each individual species (Figure 4).
- A total of 72 nests were found: 26 of Pogonomyrex californicus; 9 Myrmecocystus
kennedyi; 20 species #3; 4 of species #4; 9 of species
#5.
- There was a significant effect of observation time on the activity of ants across species for observational periods 2 and 3 (Figure 2).
|
| The head of ant species 2 recovered from a fecal pellet. |
- A significant effect of temperature on all ants was found (F = 5.53, p = 0.000). The data
were then split by species to determine which species were temperature dependent.
Using ANOVA, we found significant effects as well for P.californicus, species 3, species 4, and species 5.
- 66 hours were spent dissecting P. platyrhinos feces. A total of 2,962 ant heads were counted; 1,130 P. californicus, 213 M. kennedyi; 15
of sp. #3; 0 sp. #4; 1,085 sp. #5; 239 sp. #6; 261 sp.
#7; 3 sp. #8; 16 sp. #9. The minimum number of heads in a fecal pellet was 15 and the maximum was 312.
- To test if the P. platyrhinos eats ants according to availability we ran a Chi2 analysis. This analysis showed that we were able to reject this null hypothesis that P. platyrhinos eat according to availability (χ2calc = 3,663, χ2crit = 9.448). An ANOVA was run to test for sex differences of lizards who produced the fecal pellet examined, but found no significant effect (P.c.; F = 0.581, p = 0.455: sp. 2; F = 0.522, p = 0.455: sp. 5; F = 0.213, p = 0.649).
Back To Top
Discussion
Our results show that of the three substrate types, sand was the most highly populated by ants (Figure 5). Substrate preferences vary between species and affect nest distribution (Figure 4). Different substrates may accommodate different species because of the types of plants they contain or the types of nests the ants build.
As was expected time of day and temperature have an effect on ant activity. Most of the observed ants showed low above ground activity when the soil temperature reached above 40 °C (Figure 3), and generally ant activity was higher at cooler times of day. Significant differences in activity between species occurred at these temperatures. The significant differences in ant activity came during 0900 - 1100 and 1100 - 1300 hours. P. californicus and species 5 were to some degree active at all observations times. This seemed true no matter the time of day or temperature.
We predicted that the P. platyrhinos would feed on the ants according to their availability. However, this was rejected by the Chi2 test. This may be due to the distribution of the nests of certain species or that P. platyrhinos may be eating whatever is closest to them at the time. Further research is necessary to determine why P. platyrhinos do not eat in accordance to the ant availability.
Back To Top
Figure 2 - Mean Ant Activity per Mound v. Observation Time
Back To Top
Figure 3 - Mean Ant Activity per Mound v. Temperature
Back To Top
Figure 4 - Ant Nest Distribution on FCS
Back To Top
Figure 5 - Substrate Distribution v. Pp Spotting Distribution v. Ant Nest Distribution
Back To Top
Chart 1 - Map of Ant Activity and Mound Locations
Back To Top
Home Course Description Course Application Practical Information Class Projects Photo Gallery
|
|
|
|
