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

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

Why is it important for species to evolve? 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)

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

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

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

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

An example: Directional selection

Fig. 5-8

Fig. 5-9

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

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

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

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

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

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

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

Other processes leading to evolution: Genetic drift: Changes in allele frequencies across generations due to chance events: Random disturbances Small populations Founder effects Effect of genetic drift on a population. Because of chance events in the population, allele frequencies in later generations differ significantly from allele frequencies in the initial generation.

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

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

Genetic Variation of Ecotypes An ecotype is a population adapted to its unique (often abrupt) local environmental conditions Yarrow (Achillea millefolium) 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)

Example: Ensatina spp. of California – a ‘ring species‘ 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

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