Evolution and Biodiversity: Origins, Niches, and Adaptation APES Chapter 5 Evolution and Biodiversity: Origins, Niches, and Adaptation

Origins of Life-2 phases: Chemical evolution Biological evolution Evolution of the organic molecules, biopolymers, and systems of chemical reactions needed to from the first protocells Lasted approx. 1 billion years Evolution of single- celled organisms (prokaryotes and then eukaryotes) and then multi-cellular organisms Took approx. 3.7-3.8 billion years.

Chemical evolution 4.6-4.7 billion years ago—cosmic dust cloud condensed to from earth. 4.4 billion years ago—atmosphere was formed— contained NO oxygen. Energy available—lightening, heat from volcanoes, and UV radiation. Stanley Miller and Harold Urey provided experimental support the inorganic molecules could combine to form simple organic molecules under the conditions of the primitive Earth. Organic molecules may have formed membrane – bound protocells.

Biological Evolution Protocells evolved into single-celled prokaryotes 2.3-2.5 billion years ago, evolution of photosynthetic prokaryotes started producing O2 1.2 billion years ago the first eukaryotic cells formed. 400-500 million years: first plants on land, then mammals, then man.

Origins of Life Fig. 5-2 p. 96; Refer to Fig. 5-4 p. 98

How do we know organisms lived in the past? Fossils Relative dating—superposition and index fossils Absolute dating—radioactive decay rate (half life)

Evolution and Adaption Evolution—the change in a population’s genetic makeup through successive generations. Individuals do not evolve, only populations evolve.

Microevolution—describes the small genetic changes that occur in a population. Macroevolution—describes the long-term, large-scale, evolutionary changes among groups of species. 1. speciation (new species formed from ancestral species) 2. species lost through extinction.

How Microevolution Works There must be a change in the Gene Pool (sum total of all genes possessed by the individuals of a population). 1. mutations—only changes in reproductive cells are passed on to offspring Random and unpredictable Most are harmful

Natural Selection Three conditions necessary for evolution by natural selection to occur. 1. natural variability 2. heritable trait 3. differential reproduction-greater chance for one form to reproduce. Three types of natural selection 1. directional 2. stabilizing 3. diversifying

Directional Natural Selection Number of individuals Snail coloration best adapted to conditions Average Coloration of snails New average Previous average Number of individuals Coloration of snails Average shifts Natural selection Proportion of light-colored snails in population increases Figure 5-6 (1) Page 102

Stabilizing Natural Selection Coloration of snails Snails with extreme coloration are eliminated Number of individuals Stabilizing Natural Selection Average remains the same, but the number of individuals with intermediate coloration increases Natural selection Light snails Dark snails Figure 5-6 (2) Page 102

Figure 5-6 (3) Page 102 Diversifying Natural Selection Number of individuals with light and dark coloration increases, and the number with intermediate coloration decreases Coloration of snails Snails with light and dark colors dominate Diversifying Natural Selection Light coloration is favored Dark Intermediate-colored snails are selected against Natural selection Figure 5-6 (3) Page 102

Coevolution Interaction between species that results in microevolution in each of their populations. Ex: flowers and pollinators predators and prey

How Macroevolution Works Evolution that takes place over an extremely long time involving groups of species. Speciation—forming a new species Geographic isolation  reproductive isolation speciation

Macroevolution How do species become extinct? When environmental conditions change, a species may cease to exist if it cannot adapt. Background extinction—disappearance of species’ at a low gradual rate. Mass extinction—abrupt rise in extinction rate above the background level catastrophic and worldwide where large numbers of species are eliminated. We have had five major extinctions with the last being 65 million years ago (at the end of the mesozoic era). A sixth mass extinction is currently happening and caused by humans.

Macroevolution Adaptive radiation—period of recovery, rapid divergent evolution leading to speciation, following mass extinctions. There are two theories about how rapidly macroevolution occurs: 1. gradualist model of evolution 2. punctuated equilibrium hypothesis—gradual evolution interrupted periodically by rapid speciation.

Ecological Niches and Adaptation Ecological Niche—the species’ way of life or role in an ecosystem. Includes: Range of tolerance Type of resources it uses How it interacts with components of the ecosystem Fundamental niche—full potential range of physical, chemical, and biological conditions under with an organism could survive. Realized niche—the actual part of the fundamental niche occupied by the organism.

Species can have broad niches (generalists: roaches, flies, coyotes, humans) while other have narrow niches (specialists: spotted owls, giant pandas) Habitat—the physical location where a species lives.

Common Misconceptions Concerning Evolution

Evolution Misconceptions Misconception: “Survival of the Fittest” means survival of the strongest. Truth: To biologists, Fitness is a measure of reproductive success NOT strength. Misconception: Evolution involves some grand plan of nature in which organisms are becoming more complex/perfect with time. Truth: From a scientific standpoint, no plan or goal exists in the evolutionary process.

Modern humans (Homo sapiens) appear about 2 seconds before midnight Plants begin invading land Evolution and expansion of life First fossil record of animals Plants invade the land Age of reptiles Age of mammals Insects and amphibians invade the land Modern humans (Homo sapiens) appear about 2 seconds before midnight Recorded human history begins 1/4 second Origin of life (3.6–3.8 billion years ago) noon midnight