Lecture 2 Evolution and Ecology

1. Lecture 2 Evolution and Ecology ‘Nothing in biology makes sense, except in the light of evolution.’ Dobzhansky

2. Ecosystem Structure and Evolution • Niche: functional role an organism plays in an ecosystem…. • ‘the sum total of all activities and relationships in which individuals of a species engage as they secure resources necessary to survive and reproduce’… job or role in an ecosystem • Adaptation: ‘a genetically determined characteristic that … improves fitness • Fitness: the ability to leave reproductively viable offspring

3. What is evolution? • Why is it important for species to evolve? • ‘Evolution is a population thing’: • Individuals do not evolve • occurs over generations in populations. • ‘descent with modification’ (see page 645)

4. Evolutionary thought: Charles Darwin/Alfred Russell Wallace Thomas Malthus: social philosopher - Charles Lyell: geologist/natural philosopher

5. Natural selection: Selection in a genetically variable population for those with traits which favor survival and reproduction: 1. Over reproduction 2. Struggle for existence – competition for resources 3. Differential survival and reproduction Fitness: ‘the ability to survive and leave reproductively viable offspring 4. Genetic variation Adaptation: a trait that is possessed by an individual enables an enhanced ability to survive and reproduce

6. Evolution has a genetic basis: Genes are heritable units that determine traits Variation in genes occurs naturally: due to mutation  Alleles Gene Pool: the total collection of gene/alleles within a population Changes in the gene pool  changes in a population

7. Shaping of Populations • Selection for one extreme • Selection for the ‘average’ • Selection for two extremes (bimodal)

8. An example: Directional selection

9. Fig. 5-8

10. Fig. 5-9

11. Stabilizing Selection: average is favored • Goldenrod gall size – formed by fly • Small: attacked by wasp • Large: attacked by birds

12. Species have become specialists feeding on seed providing optimal energy efficiency • Disruptive Selection: Specialist forms develop

13. Adaptive Radiation: Single ancestral from give rise to multiple ‘specialist’ forms

14. Sexual selection: an aspect of natural selection • A process in which (usually) females select amongst potential mates • Example - Peacocks: female selects males with large, bright, colorful tails- why? • Handicap hypothesis • Operates in plants too – competition for pollinators  various mechanisms to lure pollen transferring animals

15. Sexual selection – an aspect of natural selection: includes two aspects • Intrasexual: males compete - selection leads to evolution of structures used in combat with other males • Deer’s antlers or ram’s horns, bright colors, etc. • selective pressure is for ability to compete successfully with members of same sex • Intersexual selection- Females select amongst winners • agents of selection • Selection based on various cues – appearance and behavior • goal (evolutionary sense) select mate with best fitness

16. Female peahens prefer to mate with males with greater number of eyespots in their tail feathers

17. Evolution without natural selection - Genetic drift: • Genetic drift refers to fluctuations in allele frequencies in a population arising from chance events. • Most pronounced in small populations resulting from • Founding events • Natural disasters • High levels of predation - bottlenecks • Random: population not selected based on adaptations

18. Other processes leading to evolution: • Genetic drift: • Changes in allele frequencies across generations due to chance events: • Random disturbances • Small populations • Founder effects

19. Natural Selection Can Result in Genetic Differentiation • The geographic range of a species can result in phenotypic variation of neighboring populations • A wider geographic range includes a broader range of environmental conditions • In general, the greater the distance between populations, the more pronounced the phenotypic differences

20. Geographic Variation in Species • Ecotype: Subpopulation of a species adapted to a specific environment • Cline: measurable change in a species characteristics over an environmental gradient Variation in white tailed deer – larger animals at higher latitudes in NA

21. Genetic Variation of Ecotypes • An ecotype is a population adapted to its unique (often abrupt) local environmental conditions • Yarrow (Achilleamillefolium) response to altitude • How much variation observable in the field is due to genetic variation and how much is due to impact of environment (phenotypic plasticity)? • Common Garden Experiment • Seed collected from plants of same species growing in different environments grow in same location(s) (p 85)

22. Geographic isolates result when gene flow among subpopulations is prevented • The isolation is rarely complete, and so these isolated subpopulations are often classified as subspecies because of a set of unique characteristics • Example: Ensatina spp. of California – a ‘ring species‘ http://evolution.berkeley.edu/evolibrary/article/0_0_0/devitt_02

23. Summary: • Evolution involves heritable differences amongst individuals in a population which ultimately impact fitness • Organisms become ‘tailor made’ for their niche within an environment by processes of evolution • Characteristics of individuals making up current populations are a product of natural selection in ancestral populations