Ants & Soil Foodwebs

  Ants on Islands

  Spiders on Islands

  Monkeys on Islands

  Curriculum Vitae

  Works in Progress

  Related Links

  Fun Pictures
 
 

ANTS & SOIL FOODWEBS

Coring soil from ant nests at McLaughlin Reserve in northern California

I am examining the effect of harvester ants on soil foodwebs in northern California serpentine.  Specifically, I am studying how these ants structure belowground foodwebs by transporting massive amounts of aboveground productivity below the soil’s surface.  Soil foodwebs are central to the processing of organic matter and control much of the spatio-temporal distribution of water and nutrients.  Thus, any organism affecting the diversity and abundance of soil biota will play an integral role in ecosystem integrity.  In one study, I compared soil biota and chemistry between harvester ant (Messor andrei) nests and adjacent, non-ant soil from a semi-arid, serpentine grassland.  The major soil groups were examined, namely bacteria, fungi, nematodes, miscellaneous eukaryotes, and microarthropods (e.g., mites and collembolans).  Bacteria, fungi, and other eukaryotes were identified using the culture-independent method, phospholipid fatty acid analysis (PLFA).  All soil groups were more abundant and diverse in ant nests than in non-ant soil, and all soil nutrients were similarly enriched inside nests.  A principal component analysis indicated that the enrichment of bacteria and fungi inside ant nests explains the majority of variation in the other response variables.  Thus, it appears that M. andrei performs some activity and/or enriches one or more nutrients (e.g., phosphorous), which heavily impacts the base of the soil foodweb (bacteria and fungi).  This suggests that these ant nests effect a form of bottom-up control in the resident soil biota.  

In the next study, I examined the mechanism behind this "ant effect" using a field experiment.  I replaced local soil cores inside M. andrei nests and in four adjacent cores (N nests = 10).  The four cores outside the ant nest were treated with one of four conditions (i.e., 2 X 2 factorial design with water and food additions as the two independent variables).  The results were complex, but the two treatments with food additions most closely resembled ant nest soils for soil biota and chemistry.  Thus, I have initial evidence suggesting that the "ant effect" is produced largely via ant deposition of organic matter into their nest and surrounding soil.
 

Baiting with peanut butter in order to attract ants

I conducted a classical island biogeographic study of the ant fauna in the Sea of Cortez (with a lot of ID-help from Dr. Phil Ward).  This work will soon appear in Case and Cody's second edition of their well received book, "Island Biogeography in the Sea of Cortez."  In short, I have found that ant species number varies as a function of island area (not isolation, sea depth or any other abiotic factor measured).  In addition, ant species number is negatively associated with seabird presence, and plant cover does not affect ant richness.

Boulton, A. M.  & Ward, P. S. In press for 2003.  Island biogeography of ants in the Sea of Cortez.  In Case & Cody, eds. Island Biogeography of the Sea of Cortez,  2nd ed. University of California Press:  Berkeley & Los Angeles
 

     Formed some 8,000 years ago, inlets, sea-level rise, and human activities have fragmented most of the linear Long Island barrier islands making them ideal areas for testing the stepping-stone population model in a sedentary spider, Geolycosa pikei. Ten isolated populations collected from the barriers were analyzed via allozyme electrophoresis to estimate gene frequencies at 12 loci. Only four loci were polymorphic (i.e., AAT, APK, GPI, IDH-1), and populations showed little differentiation (mean FST = 0.020). Contrary to stepping-stone model predictions, the matrix of genetic distances among sites was not significantly associated with the physical distance matrix, which suggests that G. pikei on Long Island barriers does not adhere to a stepping-stone model. Geolycosa pikei may be better dispersers than previously estimated and/or the ephemeral quality of the inlets may not allow for the development of significant inter-populational genetic differences. In addition, geologic evidence suggests that these barriers became relatively stable only 8,000 B. P. Therefore, these habitats have been only recently colonized, which may result in low genetic variability and inter-populational differentiation possibly due to genetic drift from repeated and prolonged bottlenecks during recolonization (i.e., founder events).

Boulton, A. M., Ramirez, M. G. & Blair, C. 1997. Genetic structure of a coastal dune spider (Geolycosa pikei ) on Long Island, New York barrier islands.  Biological Journal of the Linnean Society 60: 69-82.  
  

Long Island, New York	Barrier Islands off Long Island, NY resemble a stepping-stone model

Dune collection site on Long Island barriers	Geolycosa pikei burrow entrance

Excavating G. pikei's burrow	Loading starch gels for allozyme electrophoresis

 This paper investigates changes in population size and crop damage for the vervet monkey (Cercopithecus aethiops sabaeus) in Barbados over the period 1980-1994.  In both 1980 and 1994 data were obtained primarily through a survey of farmers islandwide to obtain estimates of troop size and number of troops on agricultural land.  The farmers' estimates were independently assessed for reliability by conducting counts
of numbers of troops and troop size on a sub-sample of farms.  Approximately 20% of the total land area in Barbados was surveyed and the results extrapolate to the whole island.  The results suggest that, despite the removal of over 10,000 vervets through trapping and hunting over the 14-year period, population abundance has increased marginally by about 4.5% from a population size of about 14,190 in 1980 to a current
size of about 14,835.  Over the same time period, the % of crops damaged by vervets is estimated to have increased by almost 30%.  The increase in crop damage relative to the increase in vervet abundance may best be explained by a decrease in the availability of crops to vervets, since substantial amounts of agricultural land have been taken out of crop production between 1980 and 1994.

Boulton, A. M., Horrocks, J. A., & Baulu, J. 1996. The Barbados vervet monkey (Cercopithecus aethiops sabaeus ):  Changes in population size and crop damage 1980-1994. International Journal of Primatology 17: 831-844.
 
 
 

Map of Barbados showing sampling locations	African Green Monkey (Cercopithecus aethiops saebeus )

Boulton AM, Jaffee BA, & Scow KM. Submitted to Applied Soil Ecology.  Effects of a harvester ant (Messor andrei ) on the diversity and abundance of soil biota.

Boulton AM & Amberman KD. To be submitted to Ecology.  A mechanistic approach to the effects of a harvester ant (Messor andrei ) on the diversity and abundance of soil biota: A field experiment.

Boulton AM & Stapp PT. To be submitted to Journal of Arid Environments.  A comparison of ant and rodent feeding guilds on desert islands in the Sea of Cortez using stable isotope analysis.

Lontoh DN, Boulton AM & Amberman KD. To be submitted to Journal of Arid Environments. Seed bank analysis on desert islands in the Sea of Cortez.

Boulton AM. To be submitted to Ecography.  Species richness and abundance of ants on desert islands in the Sea of Cortez.
 
 

• Graduate Group In Ecology (GGE)
• U.C. Davis Home Page
• My Advisors: Susan Harrison and Phil Ward