L8 Flashcards
Measuring biodiversity, Taxic approach - examining rate of discovery curves
- Observe rate of new species described each year
- Few new mammal families
- On average 7000+ new species of insect are described each year
Measuring biodiversity, Taxic approach - Extrapolate from intensive local sampling
- Eg beetles exclusive to an individual tree X species of tree
- Estimates of modern biodiversity range from 2-3 million to 30-100 million
- In reality we tend to simply count taxa/ number of individuals (taxic approach) and record richness, density, evenness etc
The three main issues with the fossil record
1 It is incomplete and biased
- Can we recognise in the fossil record?
- species
- ontogenetic stages
- sexual dimorphism
- diseased individuals
- ecophenotypes
3 are linnean hierarchies equivalent for different groups of organisms
Fossil organisms at prescribed intervals of time measure:
1 Morphological diversity (disparity)
- We tend to go for an interval of time and look at all fossils
- how much morphospace is used
Disparity can be calculated:
- Trilobites increase morphospace through time
Fossil organisms at prescribed intervals of time measure:
2 Number of taxa
- We cannot count number of species due to the poor fossil record
- Best to work with groups well known in the extant biota, groups well represented in the fossil record (with good preservation potential) and use higher taxa as proxies
- Species are too variable
- Tend to pick on families/ genera
- Lagerstatten can influence biodiversity curves eg as slugs are preserved and they never usually are heavily influenced biodiversity curve
Estimating the sum total of species that have ever existed
- Average species durations and bifurcating models of evolution
- Extant species represent 2-4% of those that have ever lived
- Fossil record is still quite low
- Proxy at family/ generic level
Biodiversity patterns
- PDB computerised palaeontological data
- Slow start but increased
- Vascular plants go in steps, extinctions has less effect
- Insects show a large pull of the recent
- Different groups give different results, this suggests different patterns
- Sensible to interpret
The three models of biodiversity increase:
Additive/ linear model
Exponential curve
Logistic curve
Additive model
- Straight line
- Speciation usually gives a branching pattern
- Irregular extinction makes it additive otherwise it would be branched
Exponential model
- Bifurcating model
- Starts off slowly and increases
Logistic model
- Slow start, then exponential growth, then flattens down
- Diversity dampening factor
Does theory mirror reality?
- Still increasing biodiversity, should begin to plateau out
- Tetrapod’s evolve slowly then diverse rapidly
- Plants increase then plateau multiple times
- New reproductive strategy sees increases
- Suggests angiosperms are still increasing in diversity
Marine vertebrates
- New taxa replace old taxa after extinctions
Some caveats
- Life is much more diverse on land than in the ocean, this is largely due to insects and soil microbes
- However 95% of described fossils are marine
- Land is more diverse as it is more hetergogenous in terms of environment
- 95 % of described fossils are marine due to lack of exceptional preservation
- Rock record has large influence on marine:
More rock as less time for succession
Explanations for patterns of biodiversity
Equilibrium and Expansion models
