When Desert, Chaparral And Forest Collide - Insect Natural history Of The Devils River Of Texas

1 Pages·1994·0.35 MB·English

by  C R Nelson

Vol. 105, No. 5, November&December, 1994 303
SOCIETY MEETING OF APRIL 27, 1994
WHENDESERT,CHAPARRALANDFORESTCOLLIDE:
INSECTNATURALHISTORYOFTHEDEVILSRIVEROFTEXAS
C.RileyNelson
DivisionofBiologyand BrackenridgeField Laboratory
UniversityofTexas, Austin
ThefinalmeetingofTheAmericanEntomological Society's 1993-1994schedulewasoneof
the moreexciting ofrecent years, featuring ajoint gathering with the Entomological Society of
Pennsylvania,presentationoftheannual CalvertAwardforthebestlocalstudentprojectinento-
mologyand aspectacularly illustrated andpresentedtalk by Dr. C. Riley Nelson, ofthe Univer-
sityofTexas. Dr. Nelson,wellknownforhisworkonthesystematicsandecologyoftwodiverse
insect groups, stoneflies (Plecoptera) and robber flies (Diptera: Asilidae), combined his wide
knowledgeofaquaticandterrestrial insects, otheranimals and plants, andgeology ingiving the
PhiladelphiaaudienceaninsightintoauniqueripariansystemsetinthearidlandsofwestTexas.
At the same time, he clearly conveyed his great enthusiasm for this inventory work which he
calleda"systematist'sdream."
The Devils Riveris an exceedingly interesting tributary ofthe Rio Grande riversystem in
NorthAmerica,lyingclosetotheborderofMexicoand flowingthroughthejunctionofecotones
of the Edward's Plateau woodland, South Texas Plains chaparral and the Chihuahuan Desert
desertscrub. This intersecting ofdifferent biotypes explains much ofthe high diversity ofboth
plants and animals, including many ofthe rarest plants in Texas. Unlike other systems, like the
nearby Pecos River, which have been greatly affected by intensive farming and oil drilling, the
low human population surrounding the Devils Riverand theirhistorical reliance on low impact
grazing has allowed this areato serve as arefuge forthe native faunaofthis part ofTexas. To
insure that this area remains unimpacted and its beauty unspoiled, the State ofTexas and the
NatureConservancy have purchased40,000acres surroundingthe Devils River. It is from fund-
ingbythe NatureConservancy and throughcooperation by the State Parksagencythat Dr. Nel-
sonhasbeenabletoconductanon-goingstudyoftheaquaticinsectsoftheDevils River.
Working with specialists in various groups. Dr. Nelson has enumerated more than 200
speciesofaquaticinsects,andthisdoesnotincludethechironomids,whichmightbeexpectedto
makeupathirdofthefaunaofanystream!Thespeciesofthisriveraredominatedbycaddisflies,
and, becauseoftheopennatureoftheriparianregion,theseareprimarilygrazersandfilter-feed-
ers(hydroptilids,hydropsychidsandleptocerids),reachingdensitiesofthousandspersquarefoot.
Othergroupswellrepresentedintheflowingsectionsoftheriverincludebaetidmayflies,aquatic
pyralidmothsanddobsonfiies. Deeppools, includinganenormousonebelowawaterfall (Dolan
Falls),arehavensformorethan25speciesoffish,includinggarandtheonlyU.S.speciesofcich-
lids and tetras. Interesting aquatic life is not restricted to the river itself, though. Other habitats
withtheirownparticularfaunaincludeashorttributaryoftherivercalledDolan'sCreek,numer-
ous springs flowing out along the base of high cliffs running along the creek and river, and
ephemeral pools forming in the exposed limestone bedrock beside the creek. The springs are
apparently wheremostofthespeciesofcrane fliesoccur,andtheseinterestingsitesalsoinclude
cave dwelling organisms like isopods and amphipods. Ephemeral pools possess characteristic
pupfishand fairyshrimp.
ENT. NEWS 105(4): 303-304, September&October 1994