What are the Postulates of Darwin’s Theory?

1. What are the Postulates of Darwin’s Theory? • Darwin’s Postulates (theory of natural selection as the major cause of evolution – each postulate can be tested; each potentially falsifiable) 1. Individuals within populations are variable 2. Variations among individuals are, at least in part, passed from parents to offspring (Darwin was not aware of genetic mechanisms) 3. In every generation, some individuals are more successful at surviving and reproducing than others • Most juveniles die before reproducing (note biotic potential) 4. The survival and reproduction of individuals are not random; instead, they are tied to the variation among individuals. The individuals with the most favorable variations, those who are better at surviving and reproducing, are naturally selected • Fitness: measurement of organism’s ability to survive and reproduce

2. What Factors Cause Evolution? • Evolution (population genetics definition): change in gene frequencies in a population (changes in gene pool) • Factors that can change the nature of a gene pool: • Natural selection: a strong force in evolution • Migration: especially strong in island populations • Mutation: a weak force in evolution, but the ultimate source of novelty; mutations are generally mildly deleterious (due to second copy of gene) • Non-random mate choice: sexual selection generally involves female choice (among competing males) • Chance events: environmental changes and catas- trophes; “random” evolution called genetic drift

3. What Evidence Supports the Modern Theory of Evolution? • Direct observations of change through time • Ex., changes in beak morphologies among Darwin’s finches (long-term study at Galapagos Islands) • Ex., change in beak lengths of soapberry bugs after introduction of golden rain trees in Florida • Vestigial traits: functionless or rudimentary version of functional feature in other, closely related species or subspecies • Examples: eye sockets in blind cave fishes; wings in flightless birds; pelvic and leg bones (and spurs) in snakes (similar situation with cetaceans); reduced tailbone (coccyx) and arrector pili muscles in humans ( goosebumps; lift hair in other mammals)

4. What Evidence Supports the Modern Theory of Evolution? • Evidence from the fossil record • Extinction: in 1812, Cuvier provided strong evidence of extinction with analysis of fossils (mammoths, mastodons, and Irish elk) • Law of Succession: general pattern of correspondence between fossil and living forms from the same locale; supported from wide variety of locations and taxonomic groups (ex. marsupials of Australia) • Transitional forms: exhibit various characteristics seen in ancestral species and other characteristics seen in more recent descendents (the latter often including important novel features) • Examples: Archaeopteryx; Basilosaurus; transitional tetrapods

5. What Evidence Supports the Modern Theory of Evolution? • Homology: the study of likeness (modern meaning: similarity due to inheritance of traits from a common ancestor) • Structural and developmental homology • Ex., pattern of limb bones similar in all tetrapods • Ex., vertebrate embryos undergo similar developmental stages before acquiring group-specific features (first noted by Karl Ernst von Baer in 1828) • Molecular homology: shared genetic code for nearly all living organisms; genes for critical enzymes with few differences among groups; shared genetic flaws in related species • Thousands of lab, field, and in silico studies that document the importance of natural selection, sexual selection, mutation, and migration in the evolution of populations

6. What are Adaptations? • Adaptation: a feature used for some function that has become prevalent or is maintained in a population because of natural selection for that function • Multiple functions of single traits: many traits have multiple uses (ex. functions of fish swim bladder include buoyancy, oxygen storage, and sound production) • Trade-offs: single traits may have off-setting benefits and detri- ments (ex. fish swim bladder provides buoyancy, but is a good target for dolphin echolocation) • Key innovations: traits that are associated with large gains in evolutionary success (ex. skeletal fin rays in bony fishes) • Preadaptation: a feature already present in a population that fortuitously serves a new function • Examples: wings in ancestral insects likely selected for surface- skimming performance; bird wings likely enabled uphill running, gliding, and/or thermoregulation before birds obtained flight

7. How Does Speciation Occur? • The Biological Species Concept: species are groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups (Ernst Mayr, 1942); emphasizes reproductive isolation (lack of gene flow); later modified to account for existence of fertile animal hybrids (animal hybrids are rare, and are typically sterile or exhibit low fitness) • Mechanisms of Speciation • Speciation: origin of new species (process vs. event) • Allopatric Mechanisms (physical isolation triggers reproductive isolation) • Via dispersal and colonization (ex., islands, edge of range) • Via physical split of original range (ex., new mountain range or isthmus, change in river’s course) • Sympatric Mechanisms • Genetic mechanisms: polyploidy (ex., wheat), mutations in regulator genes • Behavioral mechanisms: temporal separation, courtship displays

8. What are Some Patterns of Macroevolution? • Adaptive Radiation: ancestral species evolves into multiple descendent species, with each exploiting a different available lifestyle in their respective environment • Darwin’s finches on Galapagos Islands • African cichlids (very diverse family of fishes in African Great Lakes) • Convergence: independent evolution of superficially similar traits (in response to similar selection pressures) • Streamlining in dolphins, penguins, tunas (reduces drag in water) • Echolocation in bats and dolphins (swarmed, patchy food sources) • Coevolution: reciprocal changes in two or more species in close association with each other • “Arms races” between predators and their prey • Adaptations for pollination (insects/hummingbirds/bats and flowering plants) • Gradualism: slow emergence of new species (Darwin emphasized) • Punctuated Equilibrium: long periods of stasis interrupted by sudden emergence of new species (Stephen J. Gould and Niles Eldridge, 1972)

9. What do Ecologists Study? • Ecosystem: all interactions between living things (community) and physical factors in a given area • Biotic (living) vs. abiotic (non-living) factors (ex., floods, droughts) • Habitat: place where organism lives; can be general or specific (biomes are major climatic zones) • Niche: organism’s way of life; multi-dimensional; in theory, only one species can occupy a niche (ecological speciesconcept) • Energy Flow: producers, autotrophs, phytoplankton; consumers, heterotrophs, zooplankton, herbivores, carnivores, omnivores, detritivores, decomposers • Food Chains: ~90% energy loss each trophic step • Food Webs: more realistic; note importance of krill in Southern Ocean food web (shared resource, not necessarily limited) • Food Pyramids: less biomass (and abundance) at higher levels; decomposers act on all trophic levels • Biogeochemical Cycles: hydrologic, carbon, nitrogen cycles • Carbon cycle: related to global warming theory

10. Figures 4-20 and 4-21

11. What Relationships Exist Between Organisms in Ecosystems? • Predation and Anti-predation • Diet Specialists/Generalists: specialists can have morphological, behavioral, and physiological adaptations for capturing/assimilating prey; scarcity of prey can lead to extinction of diet specialists • Anti-predation: cryptic and warning colorations, mobbing, displays • Competition: assumes a limited (not just shared) resource; removal experiments used to test for effects on fitness • Intraspecific: between members of same species; most intense is between males for access to females • Interspecific: between separate species; can lead to competitive exclusion • Scramble: rare in nature; all may get less than needed • Contest: mechanisms; ex. harems vs. sneakers (ex., wrasse, marine iguana) • Symbiosis: evolved life-relationship between two or more species • Mutualism: both species benefit (ex. anemone and clownfish) • Parasitism: one benefits, other is harmed; endo- and ectoparasites • Commensalism: one benefits, other with no effect; least common, examples often debated (exs. whale shark with pilotfish; reef shark with remora? – debatable, since remora may cause hydrodynamic drag) • Facilitation: organism indirectly benefits others (ex., earthworms aerate soil, nightly excretion of ammonium by blacksmith benefits algae)

12. Why is Biodiversity Important? • Biodiversity: variation among living organisms • Species diversity: number of species in an ecosystem; increases with stability/uninterrupted evolution (ex., deep sea, tropical rain forests), and available niches; decreases with isolation • Genetic diversity: variation within a species • If low, more vulnerable to catastrophic changes/extinction • Importance of Biodiversity • Ecosystem stability: keystone species are those with influence disproportionate to their abundance (ex. sea otter in Alaska) • Genetic reserves; esp. regarding agriculture; endemic species are unique to particular habitat (ex. marine iguana in Galapagos Is.) • Practical uses (ex. medicine, future foods) • Aesthetic and ethical value: biophilia, Gaia Hypothesis • Largest Threats to Biodiversity 1. Habitat loss and fragmentation: conservation incl. wildlife corridors 2. Introduced species (especially on islands) 3. Hunting/poaching; illegal trade  international treaty (CITES)