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Evolutionary Biology
Biodiversity
| Question | Answer |
|---|---|
| What is biodiversity? | The variety of ecosystems, species, populations within species, and genetic diversity within species = ‘genetic’, ‘organismal’ and ‘ecological’ diversity |
| History of biodiversity | General, erratic, rise in overall biodiversity reaching a peak around the end of the Tertiary (2 mya) New groups of organisms appear, diversify and generally persist for very long periods of time |
| Mass extinctions | when > half the multicellular species living became extinct in one go |
| Victims vs survivors | Selective • Entire groups were lost while others survived • Survival greater for species with wider geographical and ecological distributions…. and for species rich groups |
| Victims vs survivors | Random • with respect to many characteristics/adaptations, e.g. mode of feeding • Superb adaptive qualities were lost |
| Third tier of evolution | • Physical & biotic conditions differ before and after mass extinction • Wipe the slate clean - allow new evolutionary radiations |
| Third tier of evolution | 1. Microevolutionary change within populations and species 2. Macroevolution – differential proliferation and extinction of species during normal ecological time 3. Shaping of biota by mass extinctions |
| Background of extinction | Failure to adapt to changes caused by abiotic and biotic factors • Environmental (climate) change • Predation • Disease • Competitive displacement (competition) |
| Background extinction | Resistance to extinction will depend on: • Geographical range / dispersal • Physiological resilience |
| Background of extinction | • Rates of mutation - supplying genetic variation – adaptive potential • Population size – directly - more to survive! indirectly - larger populations create more mutations |
| Rates of origination (of new taxa) | • Highest in early history • Roughly constant thereafter • Peaks in rate of origination • Cambrian explosion due to evolution of photosynthetic bacteria |
| Origination and diversification 1) Release from competition | • Expansion into ecological space or vacant niches • Caused by finding new habitat, or extinction of another group of organisms |
| Origination and diversification 2) Ecological divergence | • Evolution of key adaptations - enables organism to exploit new ecological niche - diversification of the group into new adaptive zones • E.g. flight and sonar in bats |
| Origination and diversification 3) Co-evolution | Species interactions promote the evolution of diversity • Species serve as resources for other species • E.g. Parasites and hosts |
| Origination and diversification 4) Provinciality / Vicariance | • Partitioning of biota among geographical regions into provinces – with distinctive localised taxa • Plate tectonic processes change land mass distribution • Disjunct land masses and ocean systems |
| Origination and diversification 5) Environmental variability | • Ice ages etc. • Range expansion/contraction • ‘Species pump’ |
| Origination and diversification 6) Genome duplications - Polyploidy | • Haploid and diploid gametes are not compatible |
| Overall increase in biodiversity | = rate of origination of taxa – rate of extinction of taxa |
| The future of biodiversity | Human impact: exponential rise, driving many extinction events (and the current sixth mass extinction) |
| But what to conserve? | Genes, species, ecosystems, regions? To decide we have to be able to measure biodiversity |
| Do all species contribute equally to Biodiversity? | - We should quantify the relative values we attach to species - Assign a value to a species’ ‘taxonomic distinctiveness’ or degree of ‘independent evolutionary history’ (IEH) |
| The Tuatara | Iguana-like reptile - sole survivor of a group that flourished in the Triassic More differentiation than between crocodiles and birds = 20% IEH !!! |
| Future evolutionary potential | • Are such species/groups with high IEH evolutionary ‘dead-ends’? • Rare because the group lacks the ability to adapt and diversify? |
| Which areas to focus on to conserve biodiversity? | I. Phylogeny – maximise genetic or character diversity |
| Estimates of the biodiversity value of an area | When dealing with large numbers of species, species richness within families is a reasonable surrogate for gene or character richness |
| Indicator taxa | But how good is species/family richness of one group for predicting the richness of other groups, or of entire biotas? |
| II. Rarity - condition of occurring infrequently | – rarity among areas (range-size rarity) – rarity of individuals within areas (density rarity) Species with restricted ranges do not always have low local abundances (and vice versa) endemism = condition of being restricted to a particular area |
| Conserving genetic diversity | Intra-specific genetic variance - generated through mutation and subject to drift and selection, is the foundation of the evolutionary process by which biodiversity is generated |
| Conserving genetic diversity | Genetic diversity - lowest level of this hierarchy Species are evolving lineages- their ability to evolve requires genetic diversity Hence, preservation of genetic diversity should be high priority in conservation programmes |
| Conserving genetic diversity | In theory we should aim to preserve as much existing genetic diversity as possible for future adaptive potential |
Created by:
reub8n
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