Fossils 2

•	What did ancient ecosystems share with modern ecosystems?
>	Producers and consumers
>	Food chains, food web
>	Community processes (succession ex.)
>	The second law of thermodynamics…

•	Like paleoecology, ecology began as a descriptive science
•	It grew from the European tradition of natural history, which mostly consisted of collecting and describing natural objects

•	Once you had collected it, named it, and put it away in a museum, your job was done
•	Great museum collections, cabinets of curiosities, were very popular with Victorians (still buy “curio cabinets” today)

•	A radical young ecologist named Charles Elton brought a new perspective to the field 
•	He published the first modern textbook of ecology - Animal Ecology, in 1927

The large fish eat the small fish; The small fish eat the water insects; The water insects eat plants and mud -  Large fowl cannot eat small grain - One hill cannot shelter two tigers

•	These three ancient Chinese proverbs preface a chapter in Animal Ecology (1927)
•	The author, Charles Elton, was a young British ecologist

•	Elton claimed it was not enough to tally names and numbers
•	To understand a biological community, you had to understand the functional relationships between its organisms

•	What was most important, said Elton, was not who you were, but what you did
•	Niche = functional role of an organism in an ecosystem
•	Ecosystem = all of the biological communities in a given area together with their physical habitat

•	Elton first described the food chain and the food web (what he called the food cycle)
•	Food chain = linear sequence of predator and prey in an ecosystem (who eats who)
•	Food web = interconnection of all the food chains in an ecosystem
•	The large fish eat the small fish; The small fish eat the water insects; The water insects eat plants and mud...

•	Food chains represent the flow of energy through an ecosystem
•	Food chains are a sequence of producers and consumers, prey and predators

•	Elton was struck by the fact that animals came in discrete sizes, much bigger or smaller than others
•	Larger the animals, the scarcer they were
•	Large fowl cannot eat small grain...
•	Life formed a pyramid of numbers

•	Why were big fierce animals rare?
•	Why should life come in discrete sizes?

•	Answer to this dilemma was not proposed until 1942
•	Raymond Lindeman, young aquatic ecologist at the University of Minnesota
•	Lindeman realized that ecosystems were systems that transformed energy

•	Energy flows through ecosystems
•	As energy passes from one trophic level to the next, some energy is lost at each level (trophic level = feeding level)

•	Herbivores eat plants, change the plant’s energy into their own energy
•	Predators eats herbivores, incorporate the energy of the prey into parts of the predator
•	Predator wastage accounts for some of the energy that’s lost going from one trophic level to the next

•	This transformation of energy is always inefficient - simple thermodynamics
•	Most of the energy is lost as heat
•	Therefore, the amount of energy left in the system decreases at each level
•	Elton’s pyramid of numbers is explained by Lindeman’s pyramid of energy

•	Food chains consist of producers and consumers
>	Autotrophs are the producers – green plants, algae, cyanobacteria etc. 
>	Heterotrophs are the consumers – herbivores and carnivores

•	90% of the energy at any trophic level is lost going from one trophic level to the next 
•	By the time you reach the end of the food chain, only ~ 0.03% of the original solar input

•	Inevitable loss of most of the solar energy that enters the ecosystem
•	Only a tiny portion remains when you reach the peak of the pyramid of energy
•	One hill cannot shelter two tigers

•	Many principles of modern ecology can be applied to ancient ecosystems
•	But there are also many problems with this approach
•	One of the most difficult problems is the structure of ancient communities

•	Community structure = the number of species in a community and the number of individuals of each species
•	Communities are structured by the way they feed

•	Most communities have one of two basic food chains
>	Grazing community – centered on plants, algae
>	Detritivore community – centered on dead organic matter
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Ancient food chains and food webs were probably similar to modern ones in many respects
•	But the nature of ancient communities is often hard to determine…

•	The word community may actually be misleading in paleoecology
•	Fossil communities are lacking soft-bodied organisms, incomplete by 40-50%!
•	Many paleontologists prefer to call them associations or assemblages

•	Community processes are important to modern ecologists, but very hard to demonstrate for extinct communities
•	Succession, for example, is the change from one biological community to another, change continues until a relatively stable community is reached

•	Succession is difficult to infer from fossils
•	Thin layer of rock can encompass several hundred thousand years or more
•	A few good examples, such as ancient reef communities (start with stromatolites end with stable, complex reef communities)

•	Other studies of fossil succession are not so clear cut
•	Long-term patterns of community replacement in the fossil record probably reflect long-term changes in the environment, rather than succession in a stable environment

•	Paleoecology is more successful at tracking large-scale long-term changes in community structure
•	Evolutionary faunas – groups of organisms that dominate the fauna for extended periods of time

•	Jack Sepkoski charted three major evolutionary faunas:
>	Cambrian fauna – fades away early in Paleozoic
>	Paleozoic fauna – dominates early Paleozoic to end Paleozoic
>	Modern fauna – arises in the Paleozoic, dominates the Mesozoic and Cenozoic

•	Great example of applying evolutionary paleoecology
•	Big picture reveals patterns that finer focus might miss
•	Shows, for example, that the world was once much simpler than it is today

•	Cambrian marine ecology had much simpler food webs
>	Very few swimming organisms, mostly primitive trilobites (Agnostids)
>	Swimming predators were mostly ammonites and nautiloids
>	No fish with jaws, no large predators except Anomalocaris

•	Cambrian marine ecology had much simpler food webs
>	No mobile sea floor predators or carnivores
>	No complex reef communities
>	Few burrowing organisms in bottom sediments

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Modern food web is a relatively recent innovation
•	Didn’t become truly “modern” until well into the Mesozoic

•	Evolution of large predators was a significant escalation of the evolutionary arms race
•	Can see their influence in what Vermej calls the “Mesozoic marine revolution”

•	Many new predators appeared in the early Mesozoic – bony fish, crabs etc. – that were better at crushing shells
•	Survivors were species that could swim away, burrow deeper and faster, or were better protected with spines, armor etc.
•	Fundamental change in Mesozoic fauna

•	Careful analysis of fossil data can be very revealing
•	Can reveal aspects of the life history strategies of extinct organisms

•	All organisms have a finite amount of lifetime energy, must allocate that energy to survival or reproduction - must find a balance between the two
•	Life history strategies represent a balance between two conflicting forces, survival and reproduction

•	Life history strategies include:
>	Number of offspring (many or few)
>	Size of offspring (big or little)
>	Development rate (age to reproduce - early, late)
>	Dispersal ability (good, bad)
>	Amount of parental care (intensive, little or none)

•	Colonizers must disperse quickly, rapidly develop to reproductive age, and generate lots of small offspring very quickly
•	This is the strategy of a dandelion or a crawfish

•	Larger, more settled organisms have fewer (and larger) young, mature slowly with intensive parental care
•	This is the strategy of an oak tree, or a bear

•	Analysis of the brachiopod Dielasma shows few large shells, many small shells in the fossil  record
•	Reveals a pattern of high juvenile mortality
•	Same life history strategy followed by many modern invertebrates, like bivalves

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Must take great care interpreting fossil data
•	Many sources of bias
>	Preservation Bias
>	Environmental Bias
>	Collection Bias
>	Sampling Bias
>	Interest Bias

•	Preservation bias – hard parts are much more likely to be preserved than soft parts
•	Environmental bias – preservation more likely in or near lowlands, rivers, and deltas
•	Collection bias – we tend to collect the things that most interest us – ex. large carnivore skeletons vs. herbivore skeletons

•	J.W. Valentine plotted species richness since the Cambrian
•	Data seem to show rapid increase in biodiversity in the Cretaceous, continuing into the Cenozoic
•	But is this trend real?

•	One source of bias is the relative amount of easily accessible rock strata
•	More recent the period, more areas to find those fossils

•	Even rocks don’t last forever – erosion wears them away
•	Greater volume of rocks available from more recent time periods
•	Big built in sampling bias

•	Paleontologists themselves might be a source of bias
•	Species are “invisible” until they are recognized, described, and named

•	This process often occurs in big chunks – major books, articles etc.
•	Apparent increases in diversity might simply reflect paleontologists’ interest in certain groups of organisms

•	Fungi are a great example
•	Fossil record is very poor for fungi
>	Soft bodies (preservation bias)
>	Most primitive forms were probably tiny
>	Not many people looking for them (interest bias)