Paleoecology
• Question:
• Is it possible to apply modern biological and ecological principles
to fossil assemblages?
• Why or why not?
Paleoecology
• What is paleoecology?
• The study of the relationships between organisms and their environments
• An organisms physical limits and requirements
• Community interactions
• functional morphology is an integral part of paleoecology
Paleoecology
Two Types:
• paleoautecology - study of the life habits of a single fossil species
and how that species related to its environment
• paleosynecology - study of paleocommunities (community = groups of species
that interact within a giving habitat) rather than individual species
- often the distinction between these 2 types is somewhat arbitrary
• Uniforitarianism
Ecological Hierarchy
• Biosphere
• Ecosystem - sum of all physical and biological characteristics
• Communities - local associations of organisms
• Habitat - physical environment in which organism lives
• Niche - sum of all limiting factors
• What is a community?
Classification (ecosystem into subdivisions)
• Environmental factors
• Marine realm - water depth and substrate
• Benthic - epifaunal or infaunal
– Supratidal, intertidal, subtidal, bathyal, abyssal, hadal
• Planktonic or Nektonic
– Neritic, Oceanic
Trophic Levels
• Food Webs - evolve through time
• Trophic Structure - producers and consumers
• Photosynthesis - chemosynthesis
• Suspension feeders
• Grazers
• Scavengers
• Predators
Paleoautecology - single species
• The Questions:
- conditions for the survival and successful reproduction?
- what did the fossil species avoid?
• processes limiting distribution and abundance?
• functional morphology?
• Factors
• 2 types of limiting factors : physical and biological
• physical environment can affect the organism and vice versa
Paleoautecology - limiting factors
• Physical Factors
• What controls temperature?
• temperature - the biological processes affected by temperature
• calcification - decreases at low temperature
• metabolic activity - movement and activity restricted in cold water
– van’t Hoff’s Rule
• photosynthesis - reduced in cold water
• Body size?
• Why is temperature stable in marine environments?
• Closely related to other variables
Physical Factors
• Temperature
• Why is temperature more variable on land?
• More variable and more extreme
• Latitude and elevation
• Ex: plant biomes
Physical Factors
• inferring paleotemperature: - uniformitarianism
• example: hermatypic reef corals (w/i 35º of the equator)
• paleoceanographic patterns
• modern indicator organisms: eurythermic (vs. stenothermic)
• morphologic features: spines and coiling direction
• aragonite / calcite ratios
• Oxygen isotopes - O18/O16 ratios
• Leaf margins
Physical Factors
• oxygen - availability controls distribution
• dissolved O2 in water: aerobic, dysaerobic, anaerobic
• infer paleo-oxygen conditions based on sediment color and minerals present
• oxygen depleted basins - stratified basins common in past epeiric sea
settings
– differences between oceanic basins and epeiric seas (modern analogs:
Baltic, CA Borderland Basins); oceans more thoroughly mixed
Physical Factors
• salinity
• normal salinity = 35 ppt
• hyposalinity - normal salinity - hypersalinity
• stenohaline vs. euryhaline organisms
• indicators:
• physical features: evaporite minerals like gypsum & halite; evidence
for fluvial activity
• presence of stenohaline organisms: echinoderms = great indicators
• Diversity and abundance
• geochemical indicators: trace elements (boron); Sr/Ca ratios
Physical Factors
• water depth
• related to many factors; example, deeper water is usually colder, less
turbulent, and has a finer substrate
• paleoindicators? tough to constrain; often measuring by some other factor
• example of this problem: inferring depth in a basin based on O2 levels
• use relative wavebase and frequency of tempestites
Physical Factors
• Substrate
• A limiting factor for many benthic organisms - space
• Soft - epifaunal versus infaunal
• Mobile - mobile organisms
• Hard - competition - patchy distributions
• A factor that can be preserved
Biological Factors
• Biological factors = recent versus fossil = both difficult
– direct observations in the Recent not possible in the fossil record
– make observations and make inferences from them
• important biological factors:
• competition - important for natural selection
• resource competition - limiting resource, usually food or space
• examples:
• competition for hard substrate space in the rocky intertidal zone
• growth interactions among epibionts
Biological Factors
• interference competition - when the activity of one organism precludes
the presence of another
– example: burrowing clams in Buzzard's Bay, Cape Cod; the fecal pellets
of some species of clam (ones that do not filter feed) turn the substrate to
a fine-grained muck; this prohibits the presence of Mercenaria whose filter-feeding
gill gets fouled
• predation - can have a tremendous influence on marine communities
– example in the fossil record: naticid gastropod borings
• larval recruitment - what organisms get there first can determine community
structure
Paleosynecology
• study of fossil communities
• Communities (a spectrum): an association of species with common physical
needs at one end; and the community as a super-organism at the other; with many
levels of increased integration and interdependence in the middle
• Document community constituency or changes in community structure through
ecological and/or evolutionary time
Paleosynecology
• Community composition
• fossil associations or communities
• fossil associations through time:
• diversity and abundance:
• abundance: number of individuals per species
• taxonomic diversity: number of species
• dominance diversity: Shannon - Weaver Index
• H = - ∑ Pi log Pi where Pi = ni / N
• when all species are equally abundant, H is max
Paleosynecology
• Community succession
– the sequence of communities that replace one another in a particular
area
• autogenic vs. allogenic succession
– pioneer thru climax communities
• Community Replacement