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Appropriate Scales and Bunny Tales: Using Small Herbivores from Archaeological Sites in Ecological R

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1) While Jack Rabbit and Cottontail diets differ, and while their diets are ... The presence of both cottontail and jack rabbit remains in well dated contexts ... – PowerPoint PPT presentation

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Title: Appropriate Scales and Bunny Tales: Using Small Herbivores from Archaeological Sites in Ecological R


1
Appropriate Scales and Bunny Tales Using Small
Herbivores from Archaeological Sites
inEcological Reconstruction.
  • Paper presented at the 111th  Texas Academy of
    Science annual meeting, Corpus Christi, Texas
    (March, 2008).

2
  • Authors
  • Leonard Kemp1, Cynthia Munoz1, Debajyoti Paul2,
  • Grzegorz Skrzypek3 , Robert Hard4 , and Raymond
    Mauldin1.
  • 1 Center for Archaeological Research, University
    of Texas at San Antonio2 Department of
    Geological Sciences, Laboratory of Stable Isotope
    Geochemistry, University of Texas at San
    Antonio3 Laboratory of Isotope Geology and
    Geoecology, Institute of Geological Sciences,
    University of Wroclaw, Poland4 Department of
    Anthropology, University of Texas at San Antonio

3
Abstract Archaeologists commonly reconstruct
paleoecological conditions using proxy data
(e.g., pollen analysis, stable isotopes in
paleosols) that reflect long-term, large scale
climate patterns. Yet, prehistoric
hunter-gatherers adapt to short-term (e.g.,
seasonal, yearly) local conditions, not
multi-century regional trends. Methods that can
monitor local conditions at short temporal scales
are underdeveloped. Stable carbon isotope
analysis of collagen from jack rabbits (Lepus
californicus) and cottontails (Sylvilagus sp.),
both of which are commonly found in many
archaeological sites in Texas, can potentially
help fill this void. Leporids occupy home ranges
that seldom exceed 300 ha in size.  In the wild,
most leporids are dead before the age of three.
The stable carbon isotopic composition present in
their bone collagen should reflect local diet
during this brief lifetime. Preliminary analysis
of collagen extracted from 11 jackrabbits and 6
cottontails from a Central Texas archaeological
site (41MM340) occupied between 3,050 and 2,060
BP, demonstrates that both species consume C3 and
C4 vegetation.  Delta 13C values for jack rabbits
in our samples ranged from -10.7 to -18.9,
while cottontail values ranged from -14.5 to
-21.5. While large numbers of samples will be
required to confidently assess vegetation
structure and changes in that structure, this
study demonstrates that stable carbon isotope
composition extracted from these species can
potentially yield ecological reconstructions at
scales that are informative of local conditions.
Given the distribution of leporids and their near
ubiquity in archaeological sites, this approach
may be widely applicable in paleoenvironmental
studies.
4
This preliminary study shows the following
1) While Jack Rabbit and Cottontail diets
differ, and while their diets are variable, these
herbivores consume both C3 and C4 vegetation
5
This preliminary study shows the following
1) While Jack Rabbit and Cottontail diets
differ, and while their diets are variable, these
herbivores consume both C3 and C4 vegetation
2) With moderate sample sizes, rabbits located
in settings dominated by either C3 or C4
vegetation yield collagen signatures that reflect
the dominate vegetation
6
  • 3) We can isolate these collagen signatures from
    archaeological bone, and potentially use changes
    in those signatures to track ecological shifts
    through time and across space at short temporal
    and limited spatial scales.

7
  • 3) We can isolate these collagen signatures from
    archaeological bone, and potentially use changes
    in those signatures to track ecological shifts
    through time and across space at short temporal
    and limited spatial scales.
  • 4) These short, small, more local scales are
    likely to reflect the scales to which prehistoric
    hunters and gatherers adapted.

8
  • Archaeological Paleoecological
    Reconstructions
  • 1) Commonly Used Climate/Ecological Proxies
    Operate at Long Time Frames (often several
    hundred years) and at Large or Unknown Spatial
    Scales.
  • 2) These Proxy Data Sets (e.g. Pollen,
    Paleosols) are not available
    in many settings,
  • being restricted to specific
  • ecological situations.

9
Hunters and Gatherers Do Not Operate At Extreme
Spatial Scales or in Response to
Climate or Vegetation Shifts that Happen over
100 years.
Adaptation is Local not Global, and
Our Proxies Should Reflect
Local Scales.
10
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11
  • Small Home Range Size- Dietary Collagen Reflects
    Local Vegetation

12
  • Small Home Range Size- Dietary Collagen Reflects
    Local Vegetation
  • Short Life Span- Generally Less Than 3 Years-
    Dietary Collagen Reflects Restricted Period of
    Time

13
  • Small Home Range Size- Dietary Collagen Reflects
    Local Vegetation
  • Short Life Span- Generally Less Than 3 Years-
    Dietary Collagen Reflects Restricted Period of
    Time
  • Consume Both C3 and C4 Vegetation

14
  • Small Home Range Size- Dietary Collagen Reflects
    Local Vegetation
  • Short Life Span- Generally Less Than 3 Years-
    Dietary Collagen Reflects Restricted Period of
    Time
  • Consume Both C3 and C4 Vegetation
  • Wide Geographical Distribution- Especially
    Prevalent in Arid/ Semi-Arid Regions

15
  • Small Home Range Size- Dietary Collagen Reflects
    Local Vegetation
  • Short Life Span- Generally Less Than 3 Years-
    Dietary Collagen Reflects Restricted Period of
    Time
  • Consume Both C3 and C4 Vegetation
  • Wide Geographical Distribution- Especially
    Prevalent in Arid/ Semi-Arid Regions
  • Commonly Recovered in Many Archaeological
    Excavations

16
  • Small Home Range Size- Dietary Collagen Reflects
    Local Vegetation
  • Short Life Span- Generally Less Than 3 Years-
    Dietary Collagen Reflects Restricted Period of
    Time
  • Consume Both C3 and C4 Vegetation
  • Wide Geographical Distribution- Especially
    Prevalent in Arid/ Semi-Arid Regions
  • Commonly Recovered in Many Archaeological
    Excavations

17
  • Previous Research- Analysis of Bone Collagen
    from modern Lepus collected from West Texas,
    Southern New Mexico, and Eastern Arizona suggest
    that the method has potential.
  • Three Upland rabbits from areas with a
    higher occurrence of C3 vegetation produced C3
    collagen signatures.
  • Eight Lowland rabbits from areas with a higher
    occurrence of C4 vegetation produced C4 collagen
    signatures.
  • High variability in the collagen values of the
    lowland rabbits suggests that it will be
    necessary to run large numbers of sample to
    confidently characterize vegetation.

18
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19
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20
  • Site 41MM340
  • Excavated by CAR in 2000 and 2002, the site
    is located in the floodplain of the Little River
    in Milam County.
  • 41MM340 has a diverse fauna that includes
    both jack rabbits and cottontails, and a number
    of radiocarbon dates that span approximately
    1,000 years.
  • The presence of both cottontail and jack
    rabbit remains in well dated contexts makes this
    assemblage ideal for an initial test of the
    paleoecological potential of small herbivore
    fauna.

21
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22
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23
  • Methods
  • At the CAR Laboratory, dry, undeteriorated bone
    is splintered, cleaned, and chemically treated to
    remove contaminates and isolate the collagen
    fraction.
  • Collagen samples are placed into solution, and
    subsequently freeze dried under vacuum at the
    LSG.
  • The dried samples are then measured into tin
    capsules, which are subsequently combusted in a
    Costech EA and analyzed with a ThermoFinnigan
    DeltaPlus XP Stable Isotope Ratio
    Mass-Spectrometer.

24
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25
Assessing Sample Quality C/N Ratio Collagen in
samples can be degraded or contaminated. To
assess the quality of the collagen in our
samples, we considered the carbon to nitrogen
ratio. All modern samples were found to have
the expected C/N ratio (between 2.9 and
3.6). Archaeological collagen samples from
41MM340 jack rabbits had a more variable C/N
ratio, but most samples fell within the expected
range.
26
Expected Range For Unaltered Samples
C/N Atomic Ratio- All Modern Samples Fall In the
Expected Range.
27
Expected Range For Unaltered Samples
Archaeological Samples Are More Variable- With
Two Outliers.
28
  • Results
  • Cottontails and Jack rabbits from 41MM340 have
    carbon isotopic signatures that suggest they
    consumed available vegetation with specimens from
    each species recording an almost exclusive diet
    at either range of the C3 to C4 vegetation
    spectrum.
  • While sample size is smaller than desired,
    preliminary analysis of carbon isotopic
    signatures of jackrabbits suggest that there is a
    trend towards C4 vegetation over time. This
    trend contrasts with long-term paleoenvironment
    sequences that suggest a general move towards C3
    vegetation during this period.

29
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30
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31
  • Summary
  • 1) Both Jack Rabbits and Cottontails consume
    both C3 and C4 vegetation. Their dietary choices
    seem to track available vegetation, and those
    choices are reflected in their bone collagen.
  • 2) Given a short life span and small home
    range, carbon isotopic measurements on collagen
    from rabbit bone can potentially track short
    term, local shifts in vegetation dominance. These
    short term shifts have increased significance for
    hunter-gatherer adaptive decisions.
  • While problems of chronology and sample size
    remain, we have demonstrated the potential of
    these small herbivores by focusing on samples
    from a well-dated Late Archaic site, 41MM340.
    While sample sizes for some periods are certainly
    inadequate, the carbon isotopic values of jack
    rabbit bone seem to suggest a shift towards a C4
    vegetation structure between 3000 and 2000 BP.
  • With additional sites investigated from other
    portions of Texas, as well as other time periods,
    researchers may be able to piece together a high
    resolution picture of past environments, as well
    as document shifts in those environments.

32
  • Summary
  • 1) Both Jack Rabbits and Cottontails consume
    both C3 and C4 vegetation. Their dietary choices
    seem to track available vegetation, and those
    choices are reflected in their bone collagen.
  • 2) Given a short life span and small home
    range, carbon isotopic measurements on collagen
    from rabbit bone can potentially track short
    term, local shifts in vegetation dominance. These
    short term shifts have increased significance for
    hunter-gatherer adaptive decisions.
  • While problems of chronology and sample size
    remain, we have demonstrated the potential of
    these small herbivores by focusing on samples
    from a well-dated Late Archaic site, 41MM340.
    While sample sizes for some periods are certainly
    inadequate, the carbon isotopic values of jack
    rabbit bone seem to suggest a shift towards a C4
    vegetation structure between 3000 and 2000 BP.
  • With additional sites investigated from other
    portions of Texas, as well as other time periods,
    researchers may be able to piece together a high
    resolution picture of past environments, as well
    as document shifts in those environments.

33
  • Summary
  • 1) Both Jack Rabbits and Cottontails consume
    both C3 and C4 vegetation. Their dietary choices
    seem to track available vegetation, and those
    choices are reflected in their bone collagen.
  • 2) Given a short life span and small home
    range, carbon isotopic measurements on collagen
    from rabbit bone can potentially track short
    term, local shifts in vegetation dominance. These
    short term shifts have increased significance for
    hunter-gatherer adaptive decisions.
  • While problems of chronology and sample size
    remain, we have demonstrated the potential of
    these small herbivores by focusing on samples
    from a well-dated Late Archaic site, 41MM340.
    While sample sizes for some periods are certainly
    inadequate, the carbon isotopic values of jack
    rabbit bone seem to suggest a shift towards a C4
    vegetation structure between 3000 and 2000 BP.
  • With additional sites investigated from other
    portions of Texas, as well as other time periods,
    researchers may be able to piece together a high
    resolution picture of past environments, as well
    as document shifts in those environments.

34
  • Summary
  • 1) Both Jack Rabbits and Cottontails consume
    both C3 and C4 vegetation. Their dietary choices
    seem to track available vegetation, and those
    choices are reflected in their bone collagen.
  • 2) Given a short life span and small home
    range, carbon isotopic measurements on collagen
    from rabbit bone can potentially track short
    term, local shifts in vegetation dominance. These
    short term shifts have increased significance for
    hunter-gatherer adaptive decisions.
  • While problems of chronology and sample size
    remain, we have demonstrated the potential of
    these small herbivores by focusing on samples
    from a well-dated Late Archaic site, 41MM340.
    While sample sizes for some periods are certainly
    inadequate, the carbon isotopic values of jack
    rabbit bone seem to suggest a shift towards a C4
    vegetation structure between 3000 and 2000 BP.
  • With additional sites investigated from other
    portions of Texas, as well as other time periods,
    researchers may be able to piece together a high
    resolution picture of past environments, as well
    as document shifts in those environments, at
    small, meaningful scales.
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