Evolution and Biodiversity Chapter 4

Chapter Overview Questions How do scientists account for the development of life on earth? What is biological evolution by natural selection, and how can it account for the current diversity of organisms on the earth? How can geologic processes, climate change and catastrophes affect biological evolution?

Chapter Overview Questions (cont’d) What is an ecological niche, and how does it help a population adapt to changing environmental conditions? How do extinction of species and formation of new species affect biodiversity?

Video: Creation vs. Evolution Videos\creation_evolution.flv - From ABC News, Environmental Science in the Headlines, 2005 DVD.

Recorded human history begins about 1/4 second before midnight Modern humans (Homo sapiens sapiens) appear about 2 seconds before midnight Recorded human history begins about 1/4 second before midnight Age of mammals Age of reptiles Insects and amphibians invade the land Origin of life (3.6-3.8 billion years ago) Figure 4.3 Natural capital: greatly simplified overview of the biological evolution by natural selection of life on the earth, which was preceded by about 1 billion years of chemical evolution. Microorganisms (mostly bacteria) that lived in water dominated the early span of biological evolution on the earth, between about 3.7 billion and 1 billion years ago. Plants and animals evolved first in the seas. Fossil and recent DNA evidence suggests that plants began invading the land some 780 million years ago, and animals began living on land about 370 million years ago. Humans arrived on the scene only a very short time ago—equivalent to less than an eye blink of the earth’s roughly 3.7-billion-year history of biological evolution. First fossil record of animals Plants begin invading land Evolution and expansion of life Fig. 4-3, p. 84

How Do We Know Which Organisms Lived in the Past? Our knowledge about past life comes from fossils, chemical analysis, cores drilled out of buried ice, and DNA analysis. Figure 4-4

What is Evolution? Biological Evolution: change in a population’s genetic makeup (gene pool) through successive generations. Populations, NOT individuals, evolve by becoming genetically different Microevolution: small genetic changes that occur in a population Macroevolution: long-term, large-scale evolutionary changes through which new species are formed and other species are lost

Facts about Evolution through Natural Selection Evolution through natural selection is about the most descendants. Organisms do not develop certain traits because they need them. There is no such thing as genetic perfection.

GEOLOGIC PROCESSES, CLIMATE CHANGE, CATASTROPHES, AND EVOLUTION The movement of solid (tectonic) plates making up the earth’s surface, volcanic eruptions, and earthquakes can wipe out existing species and help form new ones. The locations of continents and oceanic basins influence climate. The movement of continents have allowed species to move.

Video: Continental Drift PLAY VIDEO

Climate Change and Natural Selection Changes in climate throughout the earth’s history have shifted where plants and animals can live. Figure 4-6

Catastrophes and Natural Selection Asteroids and meteorites hitting the earth and upheavals of the earth from geologic processes have wiped out large numbers of species and created evolutionary opportunities by natural selection of new species.

Microevolution Gene pool Alleles Mutations Natural selection

What are three types of natural selection? Directional natural selection: changing environmental conditions cause individuals with traits at one end of the normal range become more common than midrange forms. Example: evolution of genetic resistance to pesticides among insects and to antibiotics among disease-carrying bacteria

Second type of natural selection Stabilizing natural selection: tends to eliminate individuals on both ends of the genetic spectrum and favor individuals with an average genetic makeup. Occurs when an environment changes little, and most members of the population are well adapted to that environment

Third type of natural selection Diversifying natural selection: occurs when environmental conditions favor individuals at both extremes of the genetic spectrum and eliminate or sharply reduce number of individuals with normal genetic traits. A population is split into two groups.

Animation: Stabilizing Selection PLAY ANIMATION

Animation: Diversifying Selection PLAY ANIMATION

Animation: Moth Populations PLAY ANIMATION

Animation: Adaptive Trait PLAY ANIMATION

Hybridization and Gene Swapping: Other Ways to Exchange Genes New species can arise through hybridization. Occurs when individuals to two distinct species crossbreed to produce a fertile offspring. Some species (mostly microorganisms) can exchange genes without sexual reproduction. Horizontal gene transfer

What is Coevolution? Coevolution is used to describe cases where two (or more) species reciprocally affect each other’s evolution. So for example, an evolutionary change in the morphology of a plant, might affect the morphology of an herbivore that eats the plant, which in turn might affect the evolution of the plant, which might affect the evolution of the herbivore...and so on.

Ecological Niches and Adaptation Ecological niche: species functional role in an ecosystem. Involves range of tolerance for various physical and chemical conditions (water availability, for example) Types and amounts of resources it uses, such as food or nutrients How it interacts with other living and nonliving components of the ecosystem The role it plays in the energy flow and matter cycling in the ecosystem

How is the niche different from a habitat? The niche is like a species’ occupation, whereas the habitat is like its address The niche represents the adaptations or adaptive traits that its members have acquired through evolution

What is the difference between a species’ fundamental niche and its realized niche? The fundamental niche is the full potential range of conditions and resources it could use if there were no competition from other species The realized niche is the part of the fundamental niche in a community or ecosystem that the species actually occupies

Generalist vs. Specialist Species Generalist species: have broad niches Can live in many different places Eat a variety of foods Tolerate a wide range of environmental conditions Rats, mice, white-tailed deer, cockroaches, flies Specialist species: have narrow niches Live in only one type of habitat Use only one or a few types of food Tolerate only a narrow range of climatic and other environmental conditions Makes them more prone to extinction when conditions change Tiger salamander, red-cockaded woodpeckers, spotted owls

Generalist and Specialist Species: Broad and Narrow Niches Generalist species tolerate a wide range of conditions. Specialist species can only tolerate a narrow range of conditions. Figure 4-7

Specialized Feeding Niches Resource partitioning reduces competition and allows sharing of limited resources. Figure 4-8

Insect and nectar eaters Fruit and seed eaters Insect and nectar eaters Greater Koa-finch Kuai Akialaoa Amakihi Kona Grosbeak Crested Honeycreeper Akiapolaau Figure 4.9 Natural capital: evolutionary divergence of honeycreepers into specialized ecological niches. Each species has a beak specialized to take advantage of certain types of food resources. Maui Parrotbill Apapane Unknown finch ancestor Fig. 4-9, p. 91

What limits adaptation? A change in environmental conditions Reproductive capacity. Quickly reproducing populations adapt in a short time Slowly reproducing populations take a long time to adapt through natural selection Most of the population has to die or become sterile so individuals with the desirable trait could predominate and pass the trait on.

Different species of bowerbird construct elaborate bowers and decorate them with different colors in order to woo females. The Satin bowerbird (left) builds a channel between upright sticks, and decorates with bright blue objects, while the MacGregor’s Bowerbird (right) builds a tall tower of sticks and decorates with bits of charcoal. Evolutionary changes in mating rituals, such as bower construction, can contribute to speciation. http://evolution.berkeley.edu/evolibrary/article/_0_0/evo_44

Speciation, Extinction, and Biodiversity Speciation: when two species arise from one. Geographic isolation: groups of the same population of a species become physically separate for long periods Part of the population migrates Population separated by a physical barrier Population separated by volcanic eruption or earthquake A few individuals are carried to a new location by wind or water

Speciation Reproductive isolation: mutation and natural selection operate independently in two geographically isolated populations and change the gene pools in different ways (called divergent evolution).

matches snow for camouflage. Adapted to cold through heavier fur,short ears, short legs,short nose. White fur matches snow for camouflage. Arctic Fox Northern population Early fox Population Spreads northward and southward and separates Different environmental conditions lead to different selective pressures and evolution into two different species. Adapted to heat through lightweight fur and long ears, legs, and nose, which give off more heat. Southern Population Figure 4.10 Geographic isolation can lead to reproductive isolation, divergence of gene pools, and speciation. Gray Fox Fig. 4-10, p. 92

Extinction: Lights Out Extinction occurs when the population cannot adapt to changing environmental conditions. The golden toad of Costa Rica’s Monteverde cloud forest has become extinct. Reason? Figure 4-11

How do species become extinct? Extinction is the second process affecting the number and types of species on the earth When environmental conditions change, a species must Evolve, or become better adapted Move to a more favorable environment, if possible Cease to exist (become extinct)

Species and families experiencing mass extinction Bar width represents relative number of living species Millions of years ago Era Period Extinction Current extinction crisis caused by human activities. Many species are expected to become extinct within the next 50–100 years. Quaternary Today Cenozoic Tertiary Extinction 65 Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including many foraminiferans and mollusks. Cretaceous Mesozoic Jurassic Extinction Triassic: 35% of animal families, including many reptiles and marine mollusks. 180 Triassic Extinction Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites. 250 Permian Carboniferous Extinction 345 Figure 4.12 Fossils and radioactive dating indicate that five major mass extinctions (indicated by arrows) have taken place over the past 500 million years. Mass extinctions leave many organism roles (niches) unoccupied and create new niches. Each mass extinction has been followed by periods of recovery (represented by the wedge shapes) called adaptive radiations. During these periods, which last 10 million years or longer, new species evolve to fill new or vacated niches. Many scientists say that we are now in the midst of a sixth mass extinction, caused primarily by human activities. Devonian: 30% of animal families, including agnathan and placoderm fishes and many trilobites. Devonian Paleozoic Silurian Ordovician Extinction 500 Ordovician: 50% of animal families, including many trilobites. Cambrian Fig. 4-12, p. 93

Earth’s long-term patterns of speciation and extinction Affected by: Large-scale movements of the continents Gradual climate changes caused by continental drift and slight shifts in the earth’s orbit around the sun Rapid climate change caused by catastrophic events (such as large volcanic eruptions, huge meteorites and asteroids crashing into earth)

Types of Extinction Background extinction Mass extinction Mass depletion Adaptive radiations

Effects of Humans on Biodiversity The scientific consensus is that human activities are decreasing the earth’s biodiversity. Figure 4-13

How do speciation and extinction affect biodiversity Speciation minus extinction equals biodiversity Mass extinction and mass depletions temporarily reduce biodiversity Also create evolutionary opportunities Much evidence indicates that humans have become a major force in premature extinction of species During the 20th century, extinction rates increased by 100-1000 times the natural background rate

GENETIC ENGINEERING AND THE FUTURE OF EVOLUTION We have used artificial selection to change the genetic characteristics of populations with similar genes through selective breeding. We have used genetic engineering to transfer genes from one species to another. Figure 4-15

Genetic Engineering: Genetically Modified Organisms (GMO) GMOs use recombinant DNA genes or portions of genes from different organisms. Figure 4-14

Animation: Transgenic Plants PLAY ANIMATION From ABC News, Biology in the Headlines, 2005 DVD.

THE FUTURE OF EVOLUTION Biologists are learning to rebuild organisms from their cell components and to clone organisms. Cloning has lead to high miscarriage rates, rapid aging, organ defects. Genetic engineering can help improve human condition, but results are not always predictable. Do not know where the new gene will be located in the DNA molecule’s structure and how that will affect the organism.

Controversy Over Genetic Engineering There are a number of privacy, ethical, legal and environmental issues. Should genetic engineering and development be regulated? What are the long-term environmental consequences?