BEETLES: study of late Quaternary beetle faunas began with G.R. Coope's (1977) study
of British deposits, J.V. Matthews (1975) North American, S.A. Elias (1985) western U.S.
BEETLE (INVERTEBRATE) ASSEMBLAGE = f(P,D,R,I)
- PRODUCTION: More species of beetles than of all other animals.
J.B.S. Haldane (1892-1964). Theologian asked him what one could conclude as to
the nature of the Creator from a study of creation, Haldane replied,
"An inordinate fondness for beetles." (S.J.Gould, 1993)
- DISPERSAL: taphonomy poorly studied, but fossils are
interpreted as local, however, many beetles can fly and
their remains are present in streams.
- PRESERVATION: beetle carapaces are the most resistant of
all insect fossils. Their elytrae (chitinous wing covers)
are particularly abundant, heads and legs also common.
- IDENTIFICATION: beetles are probably the best studied
insect group (taxonomically), and their preserved remains useful in
identification (after adaption by paleoecologist)
- splitting along bedding plains and hand-picking fossils from surface
- kerosene flotation
- in macrofossil (lake sediment, packrat middens) after screening, produces few articulated remains
INTERPRETATION: (indicator approach)
- temperature sensitivity: stenotherms, eurytherms
- edaphic preferences: soil texture, organic matter content, salinity, pH
- water chemistry (aquatic beetles): trophic level (eutrophic, nutrient rich) oligotrophic
Beetles provide an example of DISAGREEMENT OF FOSSIL INDICATORS:
Disharmonious-Assemblage, Disharmonious-Association, No-Analog Environment
- During the "Windermere Interstadial" 13,500 - 13,000 yr B.P., beetle faunas indicate
summer temp. equal to today. Of 248 species in the deposits, only 1 has
distribution limits north of the area today.
- Pollen analysis of these sediments shows treeless vegetation.
- Coope (1977) concludes that beetles responded more rapidly than vegetation
(i.e. trees), which had to migrate into the area. =LAG
TYPES OF LAG IN QUATERNARY PALEOECOLOGY (two types)
- LAGS DUE TO SLOW POPULATION CHANGE (diversity effects)
- Migrational Lag (centuries, millenia):
- If migration keeps pace with climatic change, the arrival or departure of
a species can be given a climatic interpretation.
- Species arrive after a (fatal, extirpating) climatic change; e.g., species diversity
DECREASES before immigrants established. (Cole, 1985)
- Vegetation Inertia Lag (centuries, millenia): Long-lived resident species may be able to exclude
immigrating plants temporarily; e.g., species diversity INCREASES
before natives extirpated. (Cole, 1985)
- Soil-Development Lag (centuries, millenia): immigrants unable to establish on "raw soils" with
low organic matter or low nutrient (e.g., nitrogen) content. Diversity LOW before soil
- Commensial Lag (years, decades): Commensal organisms such as pollination or seed-dispersal
vectors, or parasitic hosts (e.g., mistletoes and oaks) must immigrate first.
Diversity LOW before commensal organisms arrive
- LAGS DUE TO FACTORS OTHER THAN POPULATION CHANGE
- Biotic Response (decades): Organisms respond to climate change before population increases
(e.g., plants produce more pollen, plant macrofossils, marker pigments).
~ 50 years (Williams et al., 2002).
- Forcing Function Lag (years - decades):
Thermohaline circulation = Upwelling <
Vegetation (50 yr)
- Proxy Lag
- Climate System Lag:
Climate < vegetation (50 yr) <
; glaciers (1000 yr)
- Mixing of paleoclimatic indicators referred to as "Disharmonious" assemblage
- associations may have resulted from climates that are unusual today.
The sagebrush, pika (Ochotona princeps),
bristlecone association may indicate more
"equable climate" (mild winters) (Mead and Grady, 1996).
Small rodent biogeographic range
- False "disharmony" may result from imperfect knowledge of modern associations.
EXAMPLE: In lower Grand Canyon a "no-analog" plant association was later found
to be common a few km away (Cole, 1981 p.11)
- A major assumption of the indicator approach is that ancient organisms
had the same ecological requirements as the modern organisms i.e.,
- PHYLETIC GRADUALISM: gradual morphological and/or ecological adjustment
to evolutionary selective pressures.
- PUNCTUATED EQUILIBRIUM: organisms exist for long periods of time with
relative static morphology and ecology. Evolution occurs by sudden speciation
events interspersed over periods of quiescence.
- THE INDICATOR APPROACH assume stasis (inconsequential ecological change)
SINCE THE SPECIES ORIGINATED. Decreasingly plausible with time if gradualism operative.
Late Quaternary operating assumption: past environment duplicated today
somewhere within the organism's current range = "REPRESENTATION".
Morphologic Methods Avoid the Assumption of Stasis: based on modern biogeographic theory.
- example: Bergman's rule and Kurten's Cave Bears.average size larger during glacial periods
- example: Bergman's rule and packrat size (Smith et al., 1995)
- example: Wolf's leaf margin index. Margins entire in modern tropical rain forests,
divided farther north. So calculate relative abundance of entire leafs in fossil floras.