The Importance of Body Size in Determining the Ecological Niche of the Black Rat Snake (Elapheobsoleta) Denise M. Roth
So…Why study snakes?? http://www.larry-adams.com/snake-check.jpg http://img114.imageshack.us/img114/8529/snake2tp9.jpg http://www.he-man.org/cartoon/cmotu-pop/snakemen1.jpg
Snake populations are declining! Habitat changes Pet trade Habitat fragmentation Senseless killing “Never wound a snake; kill it.” – Harriet Tubman “If you see a snake, just kill it - don't appoint a committee on snakes.” – Ross Perot http://www.cartoonstock.com/newscartoons/cartoonists/tcr/lowres/tcrn210l.jpg http://magickcanoe.com/snakes/baby-gartersnake-large.jpg
Changes in Habitat Use and Movement Patterns with Body Size in Black Ratsnakes (Elapheobsoleta) Gabriel Blouin-Demers, Laura P. G. Bjorgan and Patrick J. Weatherhead
Question Addressed Do black ratsnakes exhibit an ontogenetic niche shift? In other words: Does body size influence movement patterns and use of habitat in black ratsnakes? Hypothesis: Juvenile black ratsnakes should move more often, move over longer distances and travel further from hibernacula.
Why does body size matter? It influences thermoregulatory requirements Habitat use Susceptibility to predation Diet
Black Ratsnake(Elapheobsoleta) Adult length 3.5-8 ft Hatchlings 11-16 in Live in or near woodlands (near water) Good climbers: competition for tree cavities Diet: Rodents and bird eggs Reproduce in early summer Oviparous- 12-20 eggs Protected in neighboring states Threatened in Canada http://www.michigan.gov/dnr/0,1607,7-153-10370_12145_12201-61209--,00.html
Geographic Distribution http://www.dlia.org/atbi/species/Animalia/Chordata/Reptilia/Squamata/Colubridae/Elaphe_obsoleta.shtml
Queen’s University Biological Station Study area: 30 km² ~36 Snakes/ 1 km² 50 km north of Kingston, Ontario, Canada 100 km south of Ottawa, Ontario, Canada http://www.dlia.org/atbi/species/Animalia/Chordata/Reptilia/Squamata/Colubridae/Elaphe_obsoleta.shtml http://www.queensu.ca/biology/qubs/directions.html
Specimen Capture Funnel traps Measured for Snout-to-vent length (SVL) Weighed Sexed Marked with a passive integrated transponder tag http://icwdm.org/Images/amph-reptile/snake-nonpoison/Nonpoi10.jpg
Distinguishing between adult and juvenile Juvenile Adult < 1050 mm SVL http://animaldiversity.ummz.umich.edu/site/resources/usfws/juvratsnake.jpg/medium.jpg http://www.tamssunshinehouse.com/Snakes/blackrat.jpg
Methods Implanted specimens with radio-transmitters Used movement data of adults from previous study (n = 82) Additional 10 adults tracked 35 juveniles Located snakes on foot and recorded location using GPS Also recorded behavior observed 153 known juvenile locations 153 random locations http://www.sciencedaily.com/releases/2007/07/070721200335.htm
Classification of Variables and Statistical Analysis Analysis of Movement Patterns: Mean distance from hibernacula during active season Total distance travelled during active season Number of times individual moved when relocated Habitat Classification Forest Forest edge Open habitat MANOVA Habitat selection based on the 23 structural variables
Results: Habitat Use Juveniles utilized all available macrohabitats but preferred forest No significant difference in microhabitat use between chosen and random locations Key note: If juveniles are in dispersal stage, they are potentially less selective for previously visited locations n = 306 P = 0.11
Results: Movement PatternsDistance Travelled vs. SVL All individuals followed at least 3 months during active period ANCOVA: Relationship between the total distance travelled and SVL Significant with SVL P = 0.002 No significant relationship with sex P = 0.99
Results: Movement Frequency vs. SVL Do smaller snakes move more often? Relationship between SVL and number of times snake had moved Significant relationship with sex P < 0.001 Significant relationship with size P = 0.04
Conclusion Juveniles and adults differed in habitat use Juveniles visited sites at random Adults seemed to have preferred habitats and locations Movement patterns and behavior varied with body size Larger snakes moved further distances Juveniles moved more often
Discussion Possible explanations for habitat differences Thermoregulation strategies Juveniles escaping predation Juvenile dispersal
Future Research Ontogenetic niche shifts in reptiles Juvenile dispersal stages? Is it related to body size of the individual? Study different land configuration Where do the neonates go? Does habitat fragmentation actually benefit the adults?
What this means for the black ratsnake Ontogenetic shifts in habitat use do not seem to play a major role in species survival at this time and conservation strategies should be focused elsewhere to have an impact in sustaining populations in Ontario, Canada.
References Ohio Department of Natural Resources: Division of Wildlife. Eastern Ratsnake or Black Ratsnake. Accessed from http://www.dnr.state.oh.us/Home/species_a_to_z/SpeciesGuideIndex/blackeasternratsnake/tabid/6556/Default.aspx http://www.washjeff.edu/Chartiers/Chartier/KEY/Reptiles/Snakes/brat.htm http://www.ext.colostate.edu/PUBS/natres/06501.html http://www.statistics.com/resources/glossary/a/ancova.php Blouin-Demers, Gabriel, Bjorgan, Laura P. G. & Weatherhead, Patrick J. (2007). Changes in Habitat Use and Movement Patterns with Body Size in Black Ratsnakes (Elapheobsoleta). Herpetologica, 63(4), 421-429. Arendt, J. D., & Wilson, S. (1997). Optimistic growth: Competition and an ontogenetic niche-shift select for rapid growth in pumpkinseed sunfish (Lepomisgibbosus). Evolution, 51(6), 1946-1954. Harding, James H. (1997). Amphibians and Reptiles of the Great Lakes Region. 308-312. Michigan Department of Natural Resources. Black Rat Snake (Elapheobsoletaobsoleta). Accessed from http://www.michigan.gov/dnr/0,1607,7-153-10370_12145_12201-61209--,00.html http://thinkexist.com/quotes/with/keyword/snake/