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Understanding the significance and
challenges of juvenile migration in
amphibians
Betsie B. Rothermel The Center of Excellence for Field Biology Austin Peay State University
Background – life history, definitions, migratory events in life cycle
Juvenile emigration – a critical migratory event?
Direct effects on migratory success – habitat alteration and importance of connectivity
Indirect effects on migratory success– carryover effects from one stage to another
Outline
Egg and larval development in aquatic habitats ( Ambystoma, Bufo, Hyla, Rana )
Most of life is spent on land
Juvenile stage often lasts 2-3 years
Some species require specific terrestrial habitats during nonbreeding season
Aquatic-breeding amphibians
Homing – navigation to a familiar home range
Returning to breeding pond every year (or following a displacement)
Definitions
Migration – round-trip, seasonal movements between habitats ( within a population )
Annual breeding migrations of adults
Dispersal – one-way, usually once-in-a-lifetime movements ( between populations )
Permanent movement away from natal pond
Dispersal vs. Migration
- Dispersal vs. migration •True dispersal is a one-way, once-in-a-lifetime event
dispersal
migration
AMPHIBIAN METAPOPULATION
Egg
Larva Metamorph
| ---------------------- AQUATIC ------------------------ | ------- TERRESTRIAL ------- |
Paedomorph
Nonbreeding Adult
Juvenile
Breeding Adult
Dispersers
1
2
3
4
5
AMPHIBIAN LIFE CYCLE
0 10 20 30 40 50 60 Distance to nearest forest (m)
Predicted probability of recapture
at forest edge
Spotted salamanders American toads
Migratory success in fields
Rothermel 2004
NSF Collaborative Study 2003-
University of Maine M. L. Hunter
University of Missouri R. D. Semlitsch, PI
University of Georgia - SREL J. W. Gibbons, B. B. Rothermel
SUNY ESF J. P. Gibbs
Postdoctoral Research: Postdoctoral Research:
Land-use Effects on Amphibian Populations
LEAP Experimental Array
Clearcut CWD Removed
Clearcut CWD Retained
Control
Thinning
acres
Spring 2004
50 m 100 m 150 m
0
0.
0.
0.
Bay 37 Bay 5148 Bay 1000 Bay 119
Forest (^189 21 216) Clearcut 238
Proportion of total captures at site 0
5
10
15
20
25
30
35
Initial One month Two months
Mean number of surviving toads
Forest Clearcut
Habitat choice vs. survival
Captures of juvenile toads in drift fences
Survival of juvenile toads in enclosures
Todd & Rothermel 2006
Photo: J.D. Willson
Direct effects of habitat alteration
Disturbed/open habitats = barriers to movement due to:
- Behavioral avoidance
- Reduced survival and growth
Other potential risks:
- Increased predation risk?
- Exposure to pesticides?
**Connectivity may be constrained more by migratory ability of juveniles than that of adults
Critical habitat and buffers
Maintaining connectivity between aquatic/terrestrial habitats is critical to population viability
Semlitsch & Bodie 2003
More questionsMore questions……
Are short-term studies of migration a good proxy for
what happens during dispersal?
Does most mortality in terrestrial life stages occur
during migratory events?
How important is performance during the first
postmetamorphic migration?
Implications of indirect (carryover) effects for
migratory success
FundingFunding:
ASIH (Gaige Award)
U. S. Forest Service, North Central Research Station
NSF (DEB Award 0242874) and SREL (Financial Assistance Award DE-FC09-96SR18-546 to University of Georgia from the U.S. Department of Energy)
CollaboratorsCollaborators: Ray Semlitsch (Ph.D. advisor), Whit Gibbons (Postdoc advisor), Tracy Green Rittenhouse, Michelle Boone, Brian Todd
Field & Lab AssistanceField & Lab Assistance: B. Bennitt, J. Deters, M. Doyle, C. Mank, N. Mills, L. Murray, A. Nold, S. Rothermel, and Z. Slinker
Acknowledgements
