Download Evolutionary paleoecology

Chapter 8—Stuff to know
• Marine bathymetry zones
– Neritic / bathyal / abyssal / hadal
• Environmental limiting factors (know all)
– Salinity categories
– Stenohaline /euryhaline taxa
• Evolutionary paleoecology
– tiering; escalation;
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Chapter 8—Paleoecology
• Ecology = the study of the interactions between
organisms and their environment
• Paleoecology = ecology applied to the study of fossils and
ancient environments
• Evolutionary paleoecology = study of ecologic phenomena
that operate on the scale of millions of years (and are
invisible to ecologists of the living biota)
• Main applications of paleoecology are in (1)
reconstructing ancient depositional environments and (2)
assessing environmental influences on evolution
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Marine ecosystem
• Modern marine ecosystem is used by
paleontologists as an analogue for ancient marine
ecosystems
• Drawbacks to uniformitarian approach
– Past climates generally have been warmer than today’s
– Past sea levels generally have been higher than today’s
• Few modern epicontinental seas
• No modern tropical epicontinental seas
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Devonian
(360 Ma)
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Marine bathymetry zones
• Neritic = continental shelf (from sea level to ~200 m)
– Intertidal
– Subtidal zone
• Bathyal = continental slope and rise (from ~200 m to
~2000 m)
• Abyssal = deep ocean floor (from ~2000 m to ~ 6000 m)
• Hadal = very deep ocean (> 6000 m)
• Photic zone = depth to which light penetrates
– Highly variable, depending on water clarity
– Photosynthesis usually takes place in upper 100 m of
water column
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Marine environments
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• Ecologic limiting factors = physical,
chemical and biologic properties of the
environment that limit the distribution and
abundance of a particular species
–
–
–
–
–
–
Temperature
Oxygen
Water depth and depth-related variables
Salinity
Substratum
Food
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Limiting factors:
Temperature
• Probably the single most important
limiting factor governing large-scale
distributions (biogeographic provinces)
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15°C
Modern symbiont-bearing corals and foraminifers occur mainly in
water that is warmer than 15°C (winter sea surface temperature)
15°C
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Limiting factors:
Oxygen
• Black Sea: direct relationship between dissolved
oxygen in water and faunal diversity
– As dissolved oxygen decreases with increasing depth,
so too does diversity
– First animals to disappear are large, heavily calcified
invertebrates
– Small, weakly calcified to uncalcified taxa extend to
greater depths (taxa unlikely to be preserved as fossils)
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Limiting factors:
Oxygen
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soft-bodied
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Limiting factors:
Oxygen
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Limiting factors:
Water depth
• Depth, in and of itself, exerts very little influence
over distribution of organisms, but depth-related
factors are very important
–
–
–
–
–
–
Hydrostatic pressure
Light wavelength and intensity
Salinity
Temperature
Nutrients
Dissolved oxygen
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Limiting factors:
Water depth (light)
• Light is attenuated
as it penetrates
through water
– Intensity of light
decreases
– Different
wavelengths of
light are
absorbed at
different rates
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green algae
use red light
red algae
use blue light
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Limiting factors:
Salinity
• Stenohaline species have little tolerance
for salinity fluctuations
• Euryhaline species have greater tolerance
for salinity fluctuations
Term
Freshwater
Brackish
Seawater
Hypersaline
Brine
salinity (‰)
0–0.5
0.5–30
30–40
40–80
> 80
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Limiting factors:
Salinity
• Stenohaline groups include:
– Corals, cephalopods, articulate brachiopods,
and echinoderms
• Euryhaline groups include:
– Inarticulate brachiopods (Lingula), pelecypods,
gastropods, and ostracodes
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Evolutionary paleoecology
• Evolutionary paleoecology = study of
ecologic phenomena that operate on the
scale of millions of years (and are invisible
to ecologists of the living biota)
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Evolutionary paleoecology
• Tiering = degree to which organisms in a
community occupy/exploit different levels above
and below the sea bottom
– Partitioning of space above the seafloor increased in
Ordovician time with advent of tall crinoids, etc.
– No equally tall filter feeders since Jurassic time
– Partitioning of space below the sea bed increased in
Late Paleozoic time (and continues to this day)
– end-Permian extinction caused a temporary reduction in
tiering (throw-back to Precambrian)
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Tiering: infaunal tropical shrimp
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Tiering:
tall crinoid
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Tiering
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Evolutionary paleoecology
• Escalation = “arms race” in the evolution of
predation and defense capabilities
– Triassic increase in kinds of shell-crushing
predators led to decline of lightly protected
shellfish and preferential survival of forms with
robust shells, burrowing, swimming, or other
defense adaptations
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Evolutionary
faunas
weakly skeletonized taxa
(e.g., trilobites) and few predators
increase in calcification of skeletons,
but fauna dominated by sessile
filter-feeders
modern fauna dominated by taxa
with robust shells and/or burrowing,
swimming, or other defense
adaptations
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Predation scars on gastropod shell
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Escalation: increase in “crushers”
through time
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Escalation: decrease in umbilicate and/or
thin-shelled snails through time
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Escalation: increase in heavily fortified
snails through time
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