Paleoecology

• What is paleoecology?
– study of the relationships between organisms and their environments, and how organisms functioned in physical and biological interactions, in the geologic past

Paleoecology
• Two Types:

(1) paleoautecology - study of the life habits of a single fossil species and how that species related to its environment

(2) paleosynecology - study of paleocommunities (community = groups of species that interact within a giving habitat) rather than individual species

• distinction between these 2 types is somewhat arbitrary

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?

Paleoautecology - single species
• Factors
- 2 types of limiting factors : physical and biological
- physical environment can affect the organism and vice versa
• Physical Factors
(1) temperature - biological processes affected by temperature
a. calcification - decreases at low temperature
b. metabolic activity - movement and activity restricted in cold water
c. photosynthesis - reduced in cold water

Paleoautecology - single species
• Temperature
example: hermatypic reef corals
- inferring paleotemperature:
1. paleoceanographic patterns
2. modern indicator organisms
3. morphologic features: spines and coiling direction
4. aragonite / calcite ratios
5. O18/O16 ratios

Paleoautecology - single species
• oxygen - availability controls distribution

a. dissolved O2 in water: aerobic, dysaerobic, anaerobic
b. infer paleo-oxygen conditions - sediment color, minerals, bioturbation
c. oxygen depleted basins
Paleoautecology - single species
• 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

Paleoautecology - single species
• turbulence - water turbulence can affect the distribution of in many ways:
a. suspension of sediment - by wave action
b. unattached organisms
c. burrowing organisms
d. attached organisms
e. infer by using taphonomic data

Paleoautecology - single species
• salinity
- normal salinity: 35 parts per thousand
- hyposalinity (brackish water) - fresh water influx
- normal salinity; hypersalinity - evaporation
- stenohaline vs. euryhaline organisms
- indicators:
1. physical features: evaporite minerals (gypsum & halite); fluvial activity
2. presence of stenohaline organisms: echinoderms = great indicators
3. stunted growth
4. geochemical indicators: trace elements (boron); Sr/Ca ratios

Paleoautecology - single species
• substrate - organisms require specific substrates
a. hard vs. firm vs. soft substrates
b. grain size important in soft substrates
- grain size important in burrowing: sculpture in clams
- infer this from sedimentology of the containing rock:

Paleoautecology - single species
• Biological Factors
- biological factors = difficult to prove in the modern world, and even harder in fossil situations;
- can only make observations and make inferences from them
• most important biological factors:
– competition - inherent in Darwin's concept of natural selection
– resource competition - when there's a limiting resource, usually food or space
example:
- competition for hard substrate space in the rocky intertidal zone
- growth interactions among epibionts

Paleoautecology - single species
• 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 integration and interdependence
• Document community constituency or changes in community structure through ecological and/or evolutionary time.

Paleosynecology- study of fossil communities
• Community composition
- fossil associations or communities
- fossil associations through time:
- diversity and abundance:
1. abundance: number of individuals per species
2. taxonomic diversity: number of species
3. dominance diversity: Shannon - Weaver Index
H = - ∑ Pi log Pi where Pi = ni / N
- when all species are equally abundant, H is max