CH. 4 Biodiversity and evolution

Core case study: why should we protect sharks?

• Sharks have been around for more than 400 million years..• Sharks are a keystone species.• People kill about 1.2 million sharks compared to 1 human killed by sharks. • This amounts to 79-97 million shark deaths a year.

4-1 What is biodiversity and why is it important?

• Biodiversity is a crucial part of the Earths natural capital-• Biological diversity is the variety of the earths species, or varying life-

forms, the genes they contain ecosystems in which they live, and the ecosystem processes of energy flow and the nutrient cycling that sustains all life.

• Every organism is a member of a certain species with certain distinctive traits.

• Humans are a member of the species Homo Sapiens.

• Estimates range from 8-100 million different species on earth.• Biologists have identified about 1.9 million.• Insects make up most of the worlds known species.

Science focus: Have you thanked the insects today?

• Pollination is a natural service that allows flowering plants to reproduce sexually when pollen grains are transferred between plants.

• Insects that eat other insects help control the populations of half the species we consider pests.

• Insects have been around for at least 400 million years.• We and most other land organisms need them.

Individuals matter: Edward O. Wilson

• Before entering college Wilson had decided he would specialize in the study of ants.

• In the 1960s Wilson and other scientists developed the theory of island biogeography which deals with how species diversity on islands is affected by the sizes and locations of the islands.

• Wilson is sometimes credited with coining the term “biodiversity”.• The diversity of life published in 1992 is where he put together the

principles and practical issues of biodiversity more completely than anyone else had at that point.

4-2 How does Earths life change over time?

• Biological evolution by natural selection explains how life changes over time-

• Most of what we know about past life on Earth comes from fossils.• The fossils so far represent probably 1% of all species that have ever lived.• Biological evolution: the process whereby earths life changes over time

through changes in the genetic characteristics of populations.• According to the theory of evolution, all species descend from earlier

ancestral species.

• Darwin and Wallace described a process called natural selection in which individuals with certain traits are more likely to survive and reproduce under a particular set of environmental conditions than are those without the traits.

• Biological evolution through natural selection has become an important scientific theory that generally explains how life has changed over the past 3.5 billion years and why life is so diverse today.

Evolution by natural selection works through mutations and adaptations

• Populations not individuals evolve by becoming genetically different.• The first step of evolution is genetic variability, or variety in the genetic

makeup of individuals in a population.• Mutations: random changes in the DNA molecules of a gene in any cell

that can be inherited by offspring.• Adaptation: any inheritable trait that improves the ability of an individual

organism to survive and to reproduce at a higher rate than other individuals are able to do under prevailing environmental conditions.

Case study: How did humans become such a powerful species?

• Like many other species, humans have survived and thrived because we have certain traits that allow us to adapt to and modify parts of the environment to increase our survival chances.

• Evolutionary biologists attribute our success to 3 adaptations: strong opposable thumbs, ability to walk upright, and a complex brain.

• These adaptations have helped us to develop tools, weapons, protective devices, and technologies that extend our limited sense of sight, hearing, and smell and make up for some of our deficiencies.

• Our brain- may enable us to live more sustainably by understanding and copying the ways in which nature has sustained itself for billions of years despite major changes in environmental conditions.

Adaptation through natural selection has limits

• 2 limitations on adaptation through natural selection.• First, a change in environmental conditions can lead to such an adaptation

only for genetic traits already present in a populations gene pool or for traits resulting from mutations, which occur randomly.

• Second, even if a beneficial heritable trait is present in a population, the populations ability to adapt may be limited by its reproductive capacity.

Three common myths about evolution through natural selection

• “survival of the fittest” means “survival of the strongest”. To biologists fitness is a measure of reproductive success.

• organisms develop certain traits because they need them? It just depends on which gene is passed down through more offspring.

• Evolution by natural selection involves some grand plan of nature in which species become more adapted? From a scientists standpoint, no plan or goal for genetic perfection has been identified in the evolutionary process.

4-3 How do geological processes and climate change affect evolution?

• Geological processes affect natural selection-• Tectonic-plate drifts have had two major important effects on the

evolution and distribution of life.• Latitudes of continents and oceanic basins have greatly influenced the

earths climate and determined where plants and animals can live.• Movement of continents has allowed species to adapt to new

environments, and form new species through natural selection.

Climate change and catastrophes affect natural selection

• Throughout its long history, earths climate has changed drastically.• These long term climate changes have a major effect on biological

evolution by determining where organisms can live.• Species become extinct because the climate changed too rapidly for them

to survive, a catastrophe occurred such as a meteor, or they were killed off by humanity.

Science focus: earth is just right for life to thrive

• The earths orbit is the right distance from the sun to provide conditions for life.

• The earth also spins fast enough to keep the sun from over heating any part of it.

• The size of earth is also just right for life, it has enough gravitational mass to keep the atmosphere from flying off into space.

• In short, this remarkable planet we live on is uniquely suited for life as we know it.

4-4 How do speciation, extinction, and human activities affect biodiversity?

• How do species evolve-• Under certain circumstances, natural selection can lead to an entirely new

species.• Speciation- one species splits into two or more different species.• Geographic isolation- occurs when different groups of the same

population of a species become physically isolated from one another for a long period.

• Reproductive isolation- mutation and change by natural selection operate independently in the gene pools of geographically isolated populations.

Extinction is forever

• Extinction is the process in which an entire species ceases to exist.• Species that are found in only one area are called endemic species, all

species eventually become extinct.• Background extinction rate has been 1-5 species every million species on

earth.• Mass extinction is a significant rise in extinction rates above the

background level.

Science focus: changing genetic traits of populations

• We have used artificial selection to change the genetic characteristics of populations with similar genes.

• Artificial selection has given us food crops with higher yields, cows that give more milk, trees that grow faster, and different cats and dogs.

• Scientists using genetic engineering to speed up our ability to manipulate genes.

• Genetic engineering is the alteration of an organisms genetic material by adding, deleting, or changing DNA.

4-5 What is species diversity and why is it important?

• Species diversity includes the variety and abundance of species in a particular place-

• Species diversity: the number and variety of species in a community or ecosystem.

• species evenness is the comparative numbers of individuals of each species present.

• The species diversity of communities varies with their geographical location.

• An important component of species diversity is species richness, the number of different species present.

Species-rich ecosystems tend to be productive and sustainable

• The more diverse an ecosystem is, the more productive it will be.• A complex system has more ways to respond to most environmental

stresses because it does not have “all its eggs in one basket”.• Ecologist David Tilman and his colleagues found that communities with

high plant species richness produced a certain amount of biomass more consistently than one with fewer species.

• Ecologists hypothesize that in a species-rich ecosystem, each species can exploit a different portion of resources available.

Science focus: species richness on islands

• In the 1960s, Robert MacArthur and Edward O. Wilson began studying communities on islands to discover why large islands have more species.

• To explain these differences MacArthur and Wilson carried out research and created the species equilibrium model.

• According to this widely accepted scientific theory, the number of different species found on an island is determined by the rate at which new species immigrate to the island and the rate at which species become locally extinct or cease to exist on the island.

4-6 What roles do species play in an ecosystem?

• Each species plays a role in its ecosystem-• Scientists describe the role that a species plays in its ecosystem as its

ecological niche.• It is a species way of life in a community and includes everything that

affects its survival and reproduction.• Scientists use the niches of species to classify them broadly as generalists

or socialists.• Generalist species have broad niches, specialist species occupy narrow

niches.

Case study: Cockroaches- natures ultimate survivors

• they have existed for around 350 million years outliving the dinosaurs.• They are generalist species.• The earths 3,500 cockroach species can eat almost anything including

algae, dead insects, fingernail clippings, electrical cords, glue, paper, and soap.

• They can live and breed almost everywhere except in polar regions, some cockroach species can survive without food or water for a month, and withstand massive doses of radiation.

Species can play 5 major roles within ecosystems

• Native , nonnative, indicator, keystone, and foundation species.• Any given species may play one or more of these five roles in a particular

ecosystem.• Native species are those species that normally live and thrive in a

particular ecosystem.• Nonnative species are animals that migrate into, or are deliberately or

accidentally introduced.

Indicator species serve as biological smoke alarms

• Birds are excellent biological indicators because they are found almost everywhere and are affected quickly by environmental changes such as the loss or fragmentation of their habitats and the introduction of chemical pesticides.

• Butterflies are also good indicator species because their association with various plant species makes them vulnerable to habitat-loss and fragmentation.

Case study: Why are amphibians vanishing?

• Many amphibian species are having difficulty adapting to some or the rapid environmental changes that have taken place in the air and water.

• Changes due to human activity.• Since 1980s populations have been decreasing but no single cause has

been identified.• Habitat loss, prolonged drought, increase in U.V. radiation, parasites, viral

and fungal diseases, pollutions are some causes.

Keystone species play critical roles in their ecosystems

• Keystone species are species whose roles have a large effect on the types and abundance of other species in an ecosystem.

• Keystone species often exist in relatively limited numbers in their ecosystem.

• The loss of keystone species can lead to population crashes and extinctions of other species in a community.

• Keystone species can play several critical roles in helping sustain ecosystems.

Case study: The American alligator- a keystone species that almost went extinct

• This species has outlived the dinosaurs.• In the 1930s, hunters killed them for their exotic meat and their supple

belly skin.• Alligators dig deep depressions, these depressions hold freshwater during

dry spells, serve as refuges for aquatic life, and supply freshwater and food for fishes, insects, snakes, turtles, birds, and other animals.

• 1976, the us government placed the American alligator on the endangered species list, today however today there are well over a million alligators in Florida.

Foundation species help to form the bases of ecosystems

• Foundation species play a major role in shaping their communities by creating and enhancing their habitats in ways that benefit their species.

• Elephants push over, or uproot trees creating openings in the grassland and woodlands of Africa, this promotes the growth of grasses and other forage plants that benefit small grazing species such as antelopes.

• Beavers build dams in streams to create ponds and wetlands that they and other species use.