This study examined modifications made by Pogonomyrmex barbatus, by their
processes of granivory and nest construction, to forb and grass dynamics under large-scale
disturbances of fire, recent drought and long-term, large-mammalian herbivory using
comparative studies, field experimental manipulations, and a simulation model on the
Edwards Plateau, Texas. Ant nests are refugia for grass survival during extreme droughts
as demonstrated during the drought of 1998 to 2002. Significantly greater cover of grasses
and lower abundance and cover of forbs was found beside nests compared with surrounding
habitat throughout the drought and recovery. Grasses near nests may be the seed source for
surrounding habitats during recovery.
Seeds were differentially collected among most forbs and grasses despite seed
abundance. Harvest was significantly reduced in the fall relative to spring. During
preference experiments, harvest differences were found between grazing treatments for two
of four species, but only during the spring. High lipid content seeds were unpreferred in fall
compared to high protein and carbohydrate content seeds.
Granivory influences on seedling establishment were studied by comparing seedling
recruitment among sown and naturally occurring seeds excluded and open to foragers.
Exclosures were placed in three nest densities and two burn treatments. Seeds in exclosures
produced significantly more seedlings than open arenas only during the first year of drought
recovery. Densities of grasses and annual forbs were higher in open arenas the second year due to indirect effects of granivory. By reducing seeds ants release seedlings from
competition. Sown seedling abundance was unaffected by colony density and fire.
Colony density and distribution were influenced by topography, soil types, soil depth
and woody cover, but not by historical grazing treatments. Cleared vegetation on nest disks
impacted less than 1% of total surface area and losses were compensated by greater basal
cover of grasses next to disks compared to surrounding habitats. Foraging areas influenced
17.3-73.6% of surface area and could diminish seed populations for potential seedlings.
Model results agree with experimental observations that communities may be
modified by P. barbatus presence due to differential responses of grass species to interaction
between nests or granivory and rainfall amounts.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/2657 |
| Date | 01 November 2005 |
| Creators | Nicolai, Nancy Carol |
| Contributors | Smeins, Fred E. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 3701627 bytes, electronic, application/pdf, born digital |
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