Understanding Biodiversity: Calculating, Causes, and Evolution

1. Chapter 5 Evolution of Biodiversity

2. What is biodiversity? Three different scales – all three contribute to the overall biodiversity of Earth • Ecosystem diversity – the variety of ecosystems within an area • Species diversity – the variety of species within a particular ecosystem • Genetic diversity – the variety of genes within a particular species

3. Calculating biodiversity • Species – a group of organisms that is distinct from other groups in terms of size, shape, behavior, and biochemical properties, and that can interbreed and produce viable offspring • The number of species on Earth is difficult to estimate • Species are not evenly distributed on Earth

4. Calculating biodiversity… For local or regional ecosystems we use two measures: • Species richness – the number of species in a given area • Species evenness – the relative proportions of individuals within the different species Species richness and evenness often decline after a human disturbance – it is helpful to know the baseline Higher numbers mean more diversity In most cases higher diversity = greater stability

5. Calculating biodiversity… A simple biodiversity index works this way: number of species in the area (numerator) = index total number of individuals in the area ( denominator) Examples: • A 4x4 meter square area in a carrot patch has 300 carrot plants, all the same species. Biodiversity index = ? • A 4x4 meter square area in the forest has 1 pine tree, 1 fern, 1 oak tree, 1 moss, and 1 lichen, for a total of 5 different species and 5 individuals. Biodiversity index = ?

6. What causes biodiversity? Evolution • A change in the genetic composition of a population over time Levels of evolution: • Microevolution – below the species level – example: different breeds of dogs • Macroevolution – at the species level (speciation) – example: domestic dogs versus African wild dogs

7. Why does evolution happen? Genetic diversity leads to evolution Genes (genotype) control physical traits (phenotype) There is genetic diversity within a population. This is due to two factors working together: • Mutations • Genetic recombination

8. Mutation • Mistakes in copying of a gene • Can be caused by environmental factors (example: UV light, some environmental chemicals - carcinogens) • If it occurs in a body cell, it will only affect that organism; only mutations that occur in a sperm or egg cell can be passed on to offspring • Most mutations are harmful – they may cause sever illness or death. Even if they do not cause direct death they may make the organism less likely to survive (ex: color change that makes them stand out to predators) • A mutation that increases the organism’s chances of survival may lead to evolution (‘survival of the fittest’)

9. Genetic recombination • During meiosis, chromosomes ‘trade’ sections in a process called crossing over. This creates new combinations of genes. • During sexual reproduction, new combinations of chromosomes passed to the offspring from the parents

10. So how does evolution happen? Three ways: • Artificial selection • Natural selection • Random processes

11. Artificial Selection • Humans determine which individuals breed, typically with a preconceived set of traits in mind • Examples: • Breeds of dogs, horses, cattle • Unintended consequences: • Antibiotic resistant bacteria • Pesticide resistant insects • Modern science: • Genetic engineering techniques • We now have the ability to take DNA from totally different species and create GMOs – genetically modified organisms • Inserting a bacterial gene that is a natural insecticide into crop plants

12. Natural Selection • Charles Darwin: On the Origin of Species by Means of Natural Selection (1859) • Key ideas: • Individuals produce an excess of offspring (overproduction) • Not all offspring can survive (competition) • Individuals differ in their traits (genetic diversity) • Differences in traits can be passed on from parents to offspring • Differences in traits are associated with differences in the ability to survive and reproduce • Natural selection does NOT select for specific traits that tend toward a predetermined goal • Natural selection favors any combination of traits that improves an individual’s fitness – the traits are adaptations

13. Nonadaptive (random) evolution • Genetic composition changes over time, but it is not related to differences in fitness • Mutation – random changes can lead to different composition over time • Genetic drift – in small populations, random mating and mutation can cause the composition to shift in one direction, making it different from the original population. • Bottleneck effect – a drastic reduction in the size of a population can cause following generations to reflect a different genetic makeup than the original population. • Founder effect – a small subset of an original population becomes isolated and the subsequent population is more like those founders and less like the original, more diverse, population.

14. Speciation • Once ‘enough’ genetic variation exists, a population becomes a different species – this is macroevolution • Geographic isolation – two populations become separated by some sort of physical barrier. Over time, genetic drift combined with the founder effect can lead to … • Reproductive isolation – two populations can no longer interbreed, which means they are now two different species

15. The pace of evolution • A species can adapt better to an environmental change if: • The rate of the environmental change is relatively slow • The population has high genetic variation for new traits to be selected • The population is relatively small so that a beneficial mutation can spread quickly • The population’s generation time is short

16. Evolve or die • Species that cannot adapt to changing environmental conditions will eventually go extinct • 99% of all species that have ever lived on Earth are now extinct • 5 global mass extinctions have occurred in Earth’s history, mainly caused by drastic changes in the environment • Currently we are in the middle of the 6th global mass extinction – this one caused by human activity