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Stable Isotopes and Animal Migration

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Stable Isotopes and Animal Migration February 24, 2010 During periods of low (~20%) C4 intake the family unit was usually within ~2 km of the riparian corridor of the ... – PowerPoint PPT presentation

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Title: Stable Isotopes and Animal Migration


1
Stable Isotopes and Animal Migration
  • February 24, 2010

2
Outline
  • Using isoscapes to track animal migration a
    quick review.
  • Examples
  • African elephants - Cerling et al., 2009, PNAS
  • Sockeye Salmon Finney et al., 2002, Nature
  • American Redstarts Norris et al., 2004, Science
  • Bats in the eastern US Britzke et al., 2009,
    Journal of Mammalogy

3
Three Principles of isotopic tracking
  • The isoscape terrain through which the animal
    of interest moves must be known.
  • Isotopic values in animals can be offset from
    base- line isoscape values due to isotopic
    discrimination and such discrimination factors
    need to be known for the tissue of interest .
  • The time period of spatial integration
    corresponding to a particular animal tissue needs
    to be known.

Hobson et al., 2010
4
C3/C4/CAM (d13C, dD)
Red-winged Blackbird Example Study showed strong
segregation between two groups of Red-winged
Blackbirds clearly related to corn consumption in
agricultural areas. Authors further associated
those corn areas with more northern latitudes in
the USA using feather dD values.
Wassenaar and Hobson, 2000
5
d13C, dD
1999, Oecologia
Stable hydrogen and carbon isotopic compositions
of adult monarch butterflies closely resemble
those of their natal (larval) diets. dD provides
a good indicator of latitude. Stable carbon
isotope values in milkweed and butterfly wings
across eastern N. America showed a distinct
pattern of enrichment along a SW to NE gradient
bisecting the Great Lakes- they provided further
resolution in the determination of monarch natal
origin.
6
Deuterium and 18O in Precipitation and Surface
Waters
2008, PNAS
Ehleringer et al. (2008) showed excellent
agreement between drinking water dD and d18O
measurements and those in human hair across the
United States.
7
Strontium Isotopes (87Sr/86Sr)
  • For some freshwater vertebrates, such as fish,
    dissolved Sr in water is the primary source of Sr
    in tissues-
  • it therefore has great potential for tracking
    where fish travel (but requires that geology is
    different).

Hobson et al., 2010
8
Isotopic turnover
Important to identify whether or not multiple
nutrient pools are involved in tissue synthesis,
but absolute half lives are less important. Note
that the one-pool model (2) does the worst job
of predicting the environment particularly for
the region where the elephant spends the least
amount of time. Illustrates the apparent
enrichment b/twn diet and tissue is different in
different environments and is a result of a
non-equilibrium condition.
Hobson et al., 2010
9
Case Studies
  • Birds and Insects
  • Feathers, wing chitin both inert following
    formation and provide info about origin.
  • Mammals
  • Claws, hair, hooves, bone collagen.
  • Sequential sampling holds great promise.
  • Fish
  • Otoliths

10
Example 1 African elephants
2009, PNAS
11
Example 1 African elephants
MOTIVATION
  • In the face of climate change, it is of interest
    to trace the relationship between elephant diet
    and vegetation change over a long time period,
    particularly because elephants play such a key
    role in savanna ecosystems.
  • Previous studies of African savanna elephants
    show that they prefer grass during the wet season
    but rely on browse during the dry season.

6-year, temporally fine-scale chronology of diet
change in an elephant family group using isotopes
in tail hair.
Cerling et al., 2009
12
Example 1 African elephants
C4 in diet matches fluctuations in rainfall and
NDVI in the Samburu region.
NDVI Normalized Differential Vegetation Index
High d15N values correspond with high d13C
values- C4 plants tend to have a higher d15N
value in this ecosystem.
Cerling et al., 2009
13
Example 1 African elephants
Changes in diet d13C track the chronology of NDVI
values, but lag by several weeks peak in
protein content is likely influential to timing
in dietary switching. Changes in dD are more
closely synchronized with NDVI demonstrates
importance of seasonal rains. Peak in births
will occur 22 months later, at the beginning of
the rainy season and just prior to peak grass
consumption.
Cerling et al., 2009
14
Example 1 African elephants
Cerling et al., 2009
15
Example 1 African elephants
CONCLUSIONS
  • Seasonal diet changes are well correlated with
    changes in NDVI.
  • Dry season d13C values have a baseline value that
    indicates a diet composed of 5 20 C4 biomass.
  • The peak in grass consumption occurs 2 weeks
    after the peak in NDVI.
  • Long-term NDVI changes will likely be accompanied
    by changes in the amount of grass available to
    elephants during the wet season.
  • Changes in the dD of hair are well correlated
    with the isotopic composition of local drinking
    water.
  • The minimum value for dD occurs at essentially
    the same time as the peak NDVI.
  • Tail hair of wild animals represents an archive
    of dietary behavior that provides an opportunity
    to quantify diet and the environmental conditions
    experienced by those animals.

16
Example 2 Sockeye Salmon
Nature, 2002
Photo Credit Thomas Quinn
17
Oligo-meso taxa
Example 2 Sockeye Salmon
Oligotrophic taxa
Eutrophic indicator
18
Example 2 Sockeye Salmon
The abrupt reduction in d15N at 100 BC roughly
coincides with a major cultural change associated
with transition from Early to Late Kachemak.
The increase in d15N from 800 - 1200 AD matches
the change from late Kachemak to Koniag period
a time when human populations rose and began to
utilize more salmon.
Frazer Lake serves as a reference lake
obstructed by a steep waterfall, it had no salmon
before the 1950s.
19
Example 2 Sockeye Salmon
From AD 300 AD 1200, sardines and anchovies
were more abundant when Alaskan sockeye stocks
were much weaker than average this trend is
reversed for the past 800 years.
Long-term trends reported here are distinct from
the pattern seen in historical records sardines
covary with salmon but are out of phase with
anchovies. Suggests that multiple modes of
variability in ocean-atmosphere circulation and
ecosystem dynamics operate in the N. Pacific.
20
Example 3 American Redstarts
Photo Credit Arthur Morris
Science, 2004
21
Example 3 American Redstarts
  • Important points
  • Warbler
  • Breeds in Ontario
  • Migrates to the Caribbean
  • Only grow tail feathers
  • once a year (in the fall)

2 Year Study Year 1) Color band male birds
measure parental care males that lost nests
to predators didnt have to work as hard (no
chicks to feed) track their fall migration
departure time. Year 2) Recapture all returning
banded males pluck tail feathers measure dD
to determine at what latitude the feather was
grown measure the feather color how orange?
22
Example 3 American Redstarts
RESULTS
Birds that did not work as hard the previous year
molted before migration (dD values were very
negative) and were also very vibrantly colored.
Birds that worked hard (i.e. raised chicks)
molted during migration (dD values were less
negative) and were less vibrantly colored. Why
would color be less vibrant? Maybe poor food
quality? Tired?
23
Example 4 Bats
  • Goal To examine dD values of hair in four bat
    species in the eastern US and test the assumption
    of a clear relationship between modeled dDprecip
    or latitude (LAT) and dDhair.
  • Two questions
  • Is there significant intraspecific variation in
    the relationship between dDh and LAT or dDp based
    on age or sex?
  • Is there significant interspecific variation?
  • 4 bat species 1 long-distance migrant, 3
    regional migrants.

Photo Smithsonian
Myotis sodalis
Photo Merlin D. Tuttle
Lasiurus borealis
24
Example 4 Bats
Found strong relationship between dDh and LAT for
two species M sodalis and M. septentrionalis. Ho
wever, dDp and LAT explain very little of the
variance in the two other species M. lucifugus
and L. borealis. -expect to see the relationship
between dDp and dDh break down if precipitation
is not the primary source of hydrogen to the food
web used by bats (e.g. lake environment) M.
lucifugus.
-expect timing and duration of molt to also be
responsible for blurring the relationship between
dDh and dDp.
25
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