Download - Black Ratsnake Class Presentation
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The Importance of Body Size in Determining the Ecological Niche of the Black Rat Snake (Elaphe obsoleta)
Denise M. Roth
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So…Why study snakes??
http://www.he-man.org/cartoon/cmotu-pop/snakemen1.jpg
http://img114.imageshack.us/img114/8529/snake2tp9.jpg
http://www.larry-adams.com/snake-check.jpg
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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
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Changes in Habitat Use and Movement Patterns with Body Size in Black Ratsnakes (Elaphe obsoleta)
Gabriel Blouin-Demers, Laura P. G. Bjorgan and Patrick J. Weatherhead
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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.
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Why does body size matter?
It influences thermoregulatory requirements
Habitat use
Susceptibility to predation
Diet
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Black Ratsnake(Elaphe obsoleta)
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
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Geographic Distribution
http://www.dlia.org/atbi/species/Animalia/Chordata/Reptilia/Squamata/Colubridae/Elaphe_obsoleta.shtml
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Queen’s University Biological Station
50 km north of Kingston, Ontario, Canada
100 km south of Ottawa, Ontario, Canada
http://www.queensu.ca/biology/qubs/directions.html
http://www.dlia.org/atbi/species/Animalia/Chordata/Reptilia/Squamata/Colubridae/Elaphe_obsoleta.shtml
Study area: 30 km² ~36 Snakes/ 1 km²
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Specimen Capture
Funnel traps Measured for Snout-to-vent length (SVL)
Weighed
Sexed
Marked with a passive integrated transponder taghttp://icwdm.org/Images/amph-reptile/snake-nonpoison/Nonpoi10.jpg
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Distinguishing between adult and juvenile
JuvenileAdult
http://animaldiversity.ummz.umich.edu/site/resources/usfws/juvratsnake.jpg/medium.jpg
http://www.tamssunshinehouse.com/Snakes/blackrat.jpg
< 1050 mm SVL
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MethodsImplanted 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 locationshttp://www.sciencedaily.com/releases/2007/07/070721200335.htm
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Classification of Variables and Statistical Analysis
Habitat Classification
Forest
Forest edge
Open habitat
MANOVA
Habitat selection based on the 23 structural variables
Analysis of Movement Patterns:
Mean distance from hibernacula during active season
Total distance travelled during active season
Number of times individual moved when relocated
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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
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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
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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
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Conclusion
Movement patterns and behavior varied with body size
Larger snakes moved further distances
Juveniles moved more often
Juveniles and adults differed in habitat use
Juveniles visited sites at random
Adults seemed to have preferred habitats and locations
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Discussion
Possible explanations for habitat differences
Thermoregulation strategies
Juveniles escaping predation
Juvenile dispersal
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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?
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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.
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ReferencesBlouin-Demers, Gabriel, Bjorgan, Laura P. G. & Weatherhead, Patrick J. (2007). Changes in Habitat Use and Movement Patterns with Body Size in Black Ratsnakes (Elaphe obsoleta). 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 (Lepomis gibbosus). 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 (Elaphe obsoleta obsoleta). Accessed from http://www.michigan.gov/dnr/0,1607,7-153-10370_12145_12201-61209--,00.html
http://thinkexist.com/quotes/with/keyword/snake/
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
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Questions
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Description of Microhabitats
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Distance from
Hibernacula vs.
Snout-to-Vent
Length
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Area of Home Range vs. SVL
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1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 19980
20
40
60
80
100
120
Average Number of Black Ratsnakes Found in Queen's Biological Station over a Period of 17 Years
Average ~ 65 snakes/ 1.8 km² (Blouin-Demers et. al 2002) This study (Blouin-Demers et. al 2007) was 30 km²
Based on previous data: Average in this study~1087 snakes/ 30 km ² or 36 snakes/1 km²