Presentation on theme: "Who am I? Mark Ricca, Wildlife Biologist: USGS-WERC. Worked in the Aleutians since 2000 Island caribou research part of Ph.D. dissertation."— Presentation transcript:
Who am I? Mark Ricca, Wildlife Biologist: USGS-WERC. Worked in the Aleutians since 2000 Island caribou research part of Ph.D. dissertation.
Ecological impacts and population dynamics of nonindigenous caribou in the Aleutian Islands of Alaska. Bite Sized Science, Friends of Alaska NWR 21 August 2012
‘The ivory tower esoteric theory’ Non-native caribou can transform island habitat. Non-native caribou can transform island habitat. Change may be difficult to reverse once a threshold is surpassed. Change may be difficult to reverse once a threshold is surpassed. Scheffer et al. 2001
Adak Island: military installations - WWII – Cold WarAdak Island: military installations - WWII – Cold War Caribou introduced in 1958-59Caribou introduced in 1958-59 –Recreational opportunity and emergency food supply –Bottle-reared calves from Nelchina mainland AK herd –No predators, low insect harassment Mixed land ownership and game animal status = management challengesMixed land ownership and game animal status = management challenges –Naval air facility closed in early 1990’s –North side transferred to Aleut Corporation, south side AMNWR Atka: reindeer introduced in 1910’s and largely unmanaged for 100 yearsAtka: reindeer introduced in 1910’s and largely unmanaged for 100 years –also has mixed ownership (native corp / AMNWR) Caribou introduction history
Questions: Are caribou transforming Adak to an alternate ecosystem state, and what is the current population trajectory? Adak caribou irrupted after the base closure
Low-moderate grazing may increase N-cycling by plants…….
H i g h ( A T K A ) H i g h ( S c a b b a r d ) H i g h ( w e s t A d a k ) L o w ( A T K A ) L o w ( N o r t h A d a k ) M o d - H i g h ( m i d A d a k ) N o n e ( I g i t k i n ) N o n e ( K a g a l a s k a ) N-mineralization rate -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 High Density Low Density Nominal Density ….but moderate to high use correlates with soil nitrogen immobilization
No aerial survey since 2005, so ….. Is it the herd still irrupting? Has it crashed? Has it expanded? NOAA 2011
June 2012 aerial survey ….Population growth rate has slowed Why? ….. Classic density dependence, increased hunting pressure?
Most caribou (and the largest groups) were on the south-central side…….
…...and calving was concentrated on the south-central side
Ricca et al. 2012. Biological Invasions Adak caribou now occupy Kagalaska……and reproduce!
Caribou Island Hop Scotch….could it happen? Ricca et al. in 2012. Biological Invasions
Summary Preliminary ecosystem process data suggest shift towards graminoids and altered nitrogen cycling (+/-) –Clearer picture coming soon as data analysis progresses Irruptive population trend apparently halted –Increased harvest rates likely, but habitat feedbacks may also play a role. Adak caribou have become a metapopulation by invading and reproducing on Kagalaska
Project Support USFWS Region 7: Invasive’s with Volunteers Program Alaska Maritime National Wildlife Refuge (J. Williams, L. Spitler, M/V Tiglax) USGS - WERC & UC Davis – GGE (K. Miles, V. Eviner, D. Van Vuren, J. Estes). Friends of Alaska NWR Volunteers (K. Ramey, V. Tutiakoff, A. Duarte, F. Weckerly) 2010 2011 2012