X-Sender: jjsulliv@postoffice.sas.upenn.eduMime-Version: 1.0Date: Mon, 1 Dec 1997 10:01:06 -0500To: Daniel Janzen <djanzen@sas.upenn.edu>From: jjsulliv@sas.upenn.edu (Jon Sullivan)Subject: Abstracts of two recent Acacia-ant papersCc: whallwac@sas.upenn.edu, amasis@sas.upenn.edu, ccamarg@ibm.netThe rediscovery begins?Accession Number  099515623Authors  Wagner D.Institution  Dep. Biol. Sci., Stanford Univ., Stanford, CA 94305-5020, USA.Title  The influence of ant nests on Acacia seed production, herbivory and soil  nutrients.Source  Journal of Ecology 85(1). 1997. 83-93.Keywords  RESEARCH ARTICLE.  ACACIA CONSTRICTA.  FORMICA PERPILOSA.  NITROGEN-FIXING  BACTERIA.  SYMBIONT.  HERBIVORE.  SEED PRODUCTION.  TERRESTRIAL ECOLOGY.  SOIL NUTRIENTS.  SOUTHWEST.  USA.  NORTH AMERICA.Concept Codes  *Ecology; Environmental Biology/Plant [07506]  *Ecology; Environmental Biology/Animal [07508]  *Nutrition/General Studies, Nutritional Status and Methods [13202]  *Plant Physiology, Biochemistry and Biophysics/Reproduction [51512]  *Soil Science/Physics and Chemistry (1970- ) [52805]Biosystematic Codes/Super Taxa  Bacteria-General Unspecified (1992- ) [05000]  Leguminosae [26260]  Hymenoptera [75326]  Microorganisms.  Bacteria.  Eubacteria.  Plants.  Vascular Plants.  Spermatophytes.  Angiosperms.  Dicots.  Animals.  Invertebrates.  Arthropods.  Insects.Abstract  1. The ant Formica perpilosa nests underneath the shrub Acacia constricta  in arid regions of south-western United States. The influence of ant nests  on seed production, soil nutrient availability and herbivore protection  was evaluated. 2. Plants with basal ant nests were found to produce 1.9  times as many seeds on average than plants of similar size and location  without ant nests. Seeds from plants with and without ant nests were equal  in fresh mass and were equally likely to germinate. 3. Soil from beneath  plants with ant nests contained significantly higher concentrations of  nitrate, ammonium, phosphorus, and water than soil from beneath plants  without nests. Soil from ant nests also had significantly higher nitrogen  mineralization rates. Seed production was not, however, significantly  correlated with the concentration of any single soil nutrient measured.  Nutrients may interact in ways that benefit plant reproduction. In  addition, the microenvironment of ant nest soils may lead to the  proliferation of soil organisms beneficial to the plant. 4. Because A.  constricta is capable of forming symbioses with nitrogen fixing bacteria,  it was predicted that plants with ant nests, exposed to greater  concentrations and fluxes of available nitrogen, would utilize more soil  nitrogen and less atmospheric nitrogen than plants without basal nests.  Nitrogen isotopic analysis of seed tissue revealed that plants with and  without ant nests obtained nitrogen from the same source or combination of  sources, suggesting that nitrogen may not have limited A. constricta  reproduction. Additional interpretations are also discussed. 5. Ants were  much more abundant on plants with ant nests at the base than on those  without ant nests, but there was little evidence that proximity to ant  nests increased protection against herbivory. Plants with and without  basal ant nests sustained similar levels of damage to leaves and seeds. 6.  If seed production is correlated with reproductive success, then selection  may favor A. constricta plants which harbour Formica perpilosa nests at  the base. Enhancement of soil nutrient concentrations may be of general  importance in understanding how plants benefit from interaction with ants,  especially if ants are more likely to nest near plants bearing extrafloral  nectaries.Authors  Willmer P G.  Stone G N.Institution  Sch. Biological Med. Sci., Univ. St. Andrews, St. Andrews, Fife KY16 9TS,  UK.Title  How aggressive ant-guards assist seed-set in Acacia flowers.Source  Nature (London) 388(6638). 1997. 165-167.Keywords  RESEARCH ARTICLE.  ACACIA ZANZIBARICA.  ACACIA DREPANOLOBIUM.  ANT  GUARDING.  DEFENSE MUTUALISM.  TERRESTRIAL ECOLOGY.  POLLINATION.  RESOURCE ALLOCATION.Concept Codes  *Behavioral Biology/Animal Behavior [07003]  *Ecology; Environmental Biology/Plant [07506]  *Ecology; Environmental Biology/Animal [07508]  *Invertebrata, Comparative and Experimental Morphology, Physiology and  Pathology/Insecta-Physiology [64076]Biosystematic Codes/Super Taxa  Leguminosae [26260]  Plants.  Vascular Plants.  Spermatophytes.  Angiosperms.  Dicots.Abstract  The phenomenon of ant-guarding on Acacia trees is probably the best known  case of a mutualism between plants and animals, the ants conferring biotic  defence against herbivores and perhaps against encroaching vegetation.  However, as with many defence mutualisms, sometimes the interests of the  plant and its defender conflict: for example, when they are in flower the  Acacia trees require the presence and service of other insects to effect  cross-pollination. How is pollinator access achieved in the face of  aggressive ant-guards? Here we report that ants are deterred from young  flowers at the crucial stage of dehiscence, allowing bees and other  pollinators to visit and transfer pollen. This deterrence appears to be a  response to a volatile chemical signal from young flowers, perhaps from  the pollen itself. Ants patrol the young (undehisced) buds, and also  return to the flowers after dehiscence, protecting the fertilized ovules  and developing seeds. The outcome is a directly improved seed-set in the  presence of ants (rather than an indirect extra reproductive resource  allocation due to decreased defoliation).