k. yoganand & n. owen-smith · k. yoganand & n. owen-smith centre for african ecology...
TRANSCRIPT
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K. Yoganand & N. Owen-Smith
Centre for African EcologySchool of Animal Plant & Environmental SciencesUniversity of the Witwatersrand
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� Round trip travel between distinct areas
� Highly variable (which makes it most interesting!)
� Various spatial scales – from 30 m (tree frog) to 70,000 km (Arctic tern)
� Time scales - daily (zooplankton) to annual to multiple-year movements (sea turtles)
� Sizes - tiny copepods to huge grey whales
� Mass, synchronized movements (e.g., 1.2 million wildebeest in Serengeti or 65 million red crabs in Christmas Island)
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� Often to feed or breed; sometimes to escape
predation
� To exploit spatially discrete resources
� Along a resource gradient (e.g., rain-driven,
altitudinal)
� Mammalian examples include: wildebeest,
saiga, caribou, white-eared kob, springbok
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� Affects ecosystem processes:
� Competition and facilitation effects on large
herbivore communities
� Effects on predation pressure
� Nutrient cycling and transport
� Primary productivity
� Grazing effects on fire frequency and tree cover
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� Migration may promote and sustain high
abundance
� Migration collapse may lead to population
crash
� E.g., Nairobi National Park, Central Kalahari
Reserve
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� Collapses ?
� Lingers on?
� Re-establishes?
� Influences of:
� Regional-scale resource gradient
� Landscape-scale heterogeneity
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West-central
(western boundary)
subpopulation
Map from
Joubert (2009)
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� Seasonal migratory movements in 1950s, moving southwards from Orpen gate region
� Access to water in Sand river
� Congregations in Ripape seepline grasslands
� Western boundary fencing in early 1960s
Ref: Smuts (1974), Whyte (1985), Whyte & Joubert (1988), Joubert (2009)
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� Population crash – >85% decline in this subpopulation by late-1970s, due to:� Loss of access to habitat across the fence
� Exclusion of herds from key wet season grazing on gabbro by a second fence
� Culling and other management interventions
� Combined with a wet decade in 1970s
� Similar interventions on Manyaleti side and similar crash!
� Crash due to combination of post-fencing factors
� Not clear if there was a migration collapse directly linked to fencing, but eventual collapse due to the population crash
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� The removal of the boundary fence in mid-
1990s has not brought about population
recovery
� Migration has not been restored to former
levels (at least not visible)
� It has been thought of as a resident sub-
population of wildebeest
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� Study period: 2009-2012
� GPS/GSM collars on 10 wildebeest herds
� Hourly locations
� Up to three years of movement data for some
herds
� Habitat maps from satellite imageries
� Intensive field sampling of forage and cover
features
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� Classified movements into migratory travel, exploratory visit
and seasonal ranging
� Differences in net displacement (Euclidean distance from
initial location) between successive locations indicated long
and speedy movements and spatial shifts
� Locations within each time segment was used to map
seasonal ranges, using KDE method
� Classified movement strategy of herds into migration,
dispersal, nomadic, etc.
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Herd 1 – 2009
Green – wet season range
Orange – dry season range
Lines with arrow –
migratory travel routes
and directions
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Herd 2 - 2009
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Herd 2 - 2010
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Herd 3 - 2009
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Herd 3 - 2010
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Herd 4 - 2009
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Herd 4 - 2010
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Herd 4 - 2011
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Herd 5 – 2009-10
Wet season
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Herd 5 – 2009-10
Dry season
No migration by
this herd, but
showed expansion
of home range
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Data from only
6 herds
Pink shaded –
gabbro areas
White –
granite/gneiss
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• Onward to dry season ranges – highly variable; return – more synchronous
• Data from only six herds given here (analysis ongoing)
0
1
2
3
4
5
6
7
Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
No
. o
f h
erd
-ye
ar Onward Return
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0
1
2
3
4
5
6
7
8
4-8 km 8-12 km 12-16 km 16-20 km 20-30 km
No
. o
f h
erd
-ye
ar
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herd_id year movement strategy35 2009 migration
145 2009 migration
145 2010 migration
145 2011 migration
196 2009-10 no migration
196 2010-11 no migration
148 2009 migration
148 2010 Migration
149 2009 Migration
149
…2010
…Migration
…
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• Lengthy use of small ranges
0
1
2
3
4
5
6
7
0 100 200 300 400
sea
son
al r
an
ge
siz
e (
km
2)
Duration of stay (days)
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� Migratory shifts by many herds from grazing lawns on gabbro and sodic sites to seep-zone (midslope) grasslands on granite or recently burned areas
� The timing of range shifts, length of use of seasonal ranges and distance between seasonal ranges were variable among herds that showed such migration
� Herds that did not show migratory shifts expanded their home ranges in the dry season to encompass seep-zone grasslands
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� Most (7 of 9) herds showed migratory behaviour
� Migratory pattern repeated every year
� Distances up to 30 km
� Directional, linear, back-and-forth movements
� No synchronous, mass movements
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� Landscape-scale heterogeneity
� No large-scale resource gradient (e. g.,
rainfall-driven)
� Larger population probably meant quicker
resource depletion of small patches and thus
farther movements (in 1950s)
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� Facultative migration
� Lengthy use of small, often exclusive habitat
patches by herds
� The current abundance and herd distribution
is inadequate to force resumption of more
extensive migration by this subpopulation
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� Augusto Mabunda – for field assistance
� Sanparks Veterinary Services and Helicopter team
� for collaring operations (Peter Buss, Markus Hofmeyr, Johan, Grant
Knight, CharlesThompson)
� Sanparks Protection Services – Richard Sowry and KFI field rangers
� Manyaleti Nature Reserve – Jimmy Thanyani, Mark Bourn and
Dr. Ferreira (Mpumalanga Veterinarian)
� Timbavati Private Nature Reserve – Jacques Britts & Almero Bosch
� Sanparks Scientific Services
� GIS data and support (Sandra MacFadyen and Izak Smit)
� Thembi Khoza, Patricia Khoza and Adolf Manganyi – for liaisoning and
administrative support
� Africa Wildlife Telemetry – for the collars and data downloads
� NRF and University of the Witwatersrand for funding support