• Variety among living species is called biodiversity

• There are between 1.4 and 1.8 million species described by scientists and many more have not been discovered or described

How Many Species Exist?

Bacteria and Archaea

• Unicellular: each cell is an individual organism

• Prokaryotes (don’t have a nucleus)

• Lack complex organelles

• Microscopic

• Also called microorganisms or microbes– Studied by microbiologists

• Incredibly ubiquitous, chemically complex, and diverse

Domain Bacteria• Many of the currently

identified bacterial species are known because they cause disease in humans, other animals, or crops

• Many other bacteria do not cause disease in humans or other animals – and some have proven tremendously useful to

science…

Domain Archaea• Superficially similar to

bacteria, but are fundamentally different

• Many archaea are well known for living in extreme environments– High salt– High sulfur– High temperature (source

of Taq polymerase)

Eukarya: Protista

• Protista are the simplest eukaryotes

• Most protist are single-celled, but some are multicellular

• The oldest fossil record of eukaryotic cells is 2 billion years old – 1.5 billion later than the first prokaryotic cell

Eukarya: Protista• The appearance of

eukaryotes led to a wide variety of eukaryotic forms

• Protista have wide diversity, although there is no agreement on the exact number of phyla (next level of classification) within the kingdom– Number ranges from 8 to

80

Protista

Fungi• Heterotrophic• DNA sequence analysis

indicates that Fungi and Animalia are more closely related than either is to plants

• Fungi are classified into phyla according to their mode of dispersal of spores

• Convergent evolution has led to the evolution of similar body shapes and lifestyles (“fungal forms”) among the different phyla

• Hyphae are actually functional part of most fungi– Long thin strings that grow to cover a

food source

• Fungi feed by secreting molecules to break down food and then absorb the nutrients

Fungi • Yeast are single-celled fungi• Yeasts can carry out

respiration, but can also carry out fermentation in low oxygen environments– Fermentation produces

some ATP for the yeast, but also produces alcohol, which is toxic

• Mold is also considered fungi

• Fast growing – can quickly spoil food

• Also involved in cheese making

• Have been used to produce antibiotics – including penicillin– Discovered by Alexander

Fleming

Eukarya: Plantae• The kingdom Plantae

consists of multicellular eukaryotes that can make their own food by photosynthesis

• Plants have been present on land for over 400 million years and have evolved to land conditions with increasing effectiveness

• The first land plants were small and lacked means to transport water from the ground to their leaves

• Vascular tissue evolved for transport of water and other substances– Allowed plants to reach

tree-size and to adapt to drier land conditions

• Seeds, structures to protect and provide food to young plants evolved as well

• Just 140 million years ago, the flower, a specialized reproductive organ, appeared– Over 90% of known plant

species are flowering plants

Naturally derived drugs from plantsAspirin – from willow treesDigitalis – from foxgloveVincristine (cancer drug) – from periwinkleMorphine – from poppyCaffeine – from coffee

Animalia• Animals are defined as:

– Multicellular organisms– Heterotrophic– Have the ability to move

during at least one stage of their life cycle

• Humans and all other animals are almost identical in terms of structure and function of cells and common organs

• There is much commonality within the kingdom, but significant diversity exists within it as well

• Invertebrates, animals that don’t have backbones, make up 96% of animal species• Most invertebrates are insects• Invertebrates are of interest to biologists looking for new chemicals to serve human needs (pain killing drugs)

Is the Population Too Large?

• There are 6.3 billion people on Earth

• By 2050, there may be between 10 and 12 billion people

• Growth is being fueled by many factors:– Declining infant mortality

– Increases in life expectancy

– Improvements in medicine

• Historians have used archeological evidence and written records to estimate the size of the human population for the last 10,000 years

• Gives a pattern of growth for the human population• This is an example of an exponential growth pattern – the quantity of new offspring is an ever-growing

number– J-shaped growth curve

• The larger the population, the faster it grows– 77 million people added each year– Three people every second– Quarter of a million every day

Population Growth

The Demographic Transition

• Both birth rates and death rates were high before the Industrial Revolution

• Many deaths due to infectious disease• Many births, but most children did not

survive: high infant mortality• At the same time, modern medicine has

lowered the death rate

• With high birth rates and lower death rates, the population grows

The Demographic Transition• The period of time in a population when

birth rates are dropping toward lowered death rates as the demographic transition

• The length of time that a human population remains in transition has a huge effect on the population’s size– The longer a population takes to

pass through the transition, the higher their population growth

• Developed countries have passed through demographic transition and have low population growth rates

• Developing countries are still in demographic transition – and still have high growth rates

• Infant mortality rates have dropped drastically

Limits to Population Growth

• Even though populations can theoretically grow exponentially, there growth is limited by physical factors

Carrying Capacity and Logistical Growth

• Carrying capacity – the maximum population that can be supported by a given environment

• Even though a population may start out with exponential growth, the growth rate tends to slow down

• The population growth graph of this type is called an S-shaped growth curve

• The growth rate approaches zero as the population size reaches the carrying capacity– There, birth rate = death rate– Population size is stable

Carrying Capacity and Logistical Growth

• The growth rate slows as it reaches the carrying capacity because of density dependent factors– Food supply– Increased risk of

infectious diseases– Increased risk due to

waste accumulation

Carrying Capacity and Logistical Growth

• There are also density independent factors that limit growth– Severe weather, such as drought or very high or

low temperatures

Earth’s Carrying Capacity for Humans

• If, and how rapidly, the growth rate is declining is a way of figuring out if we are reaching Earth’s carrying capacity

• The growth rate has slowed– From high of 2.1% in

1960 to 1.2% now• The UN has offered

three projected tracks for future growth to 2050

The amount of resources:• The Net Primary Production

(NPP) is the amount of food energy available on the planet – measured by plant growth

• Estimates suggest that we are only using 1/3 of the total land NPP– Suggests that the carrying

capacity is three times the current population (or 19 billion people)

• But this human population size would consume all the resources and leave nothing for other species

Signs That the Population IsNear Carrying Capacity

• U.S. residents comprise 5% of Earth’s population, but use 24% of its energy

• U.S. residents consume 815 billion food calories every day – 200 billion more than are necessary (this could feed 80 million more people)

• 1 person U.S. uses as many resources as:– 2 Japanese– 2 Spaniards– 3 Italians– 6 Mexicans– 13 Chinese– 31 Indians– 128 Bangladeshians– 301 Tanzanians– 370 Ethiopians

13.3 The Future of the Human Population

• Unlike other species, the human population is not completely at the mercy of the environment

• Through ingenuity humans have the ability to transform environmental conditions – at least the hypothetical ability

A Possible Population Crash?

• A population crash is a steep decline in number as death rates soar and birth rates drop after a too large population competes for too few resources– Even if birth and growth rates continue to

grow for awhile

A Possible Population Crash?• Some populations crash over and over again as a

result of a tendency to grow beyond carrying capacity– “Booms” and “busts” continual indefinitely

• This is called a population cycle

A Possible Population Crash?

• Ecologists notice a lag between the time humans reduce birth rates and when the population size responds and call this lag demographic momentum

• The demographic momentum can be estimated by looking at a population pyramid, a summary of numbers of individuals at each age group

A Possible Population Crash?• Stable population pyramids are actually shaped more

like a column– The proportion that is young is not significantly larger than

the middle aged

• Populations with high demographic momentum have a large proportion of young people

Avoiding Disaster• Humans have one distinct advantage in that – unlike any other

known species – they can actively choose to limit birth rates

• Evidence of this is seen in the birth rates of countries

14.1 The Sixth Extinction• The Endangered Species

Act (ESA) was passed in 1973 to protect and encourage population growth of threatened or endangered species– Ultimately, to avoid species

extinction – the complete loss of a species

– Threatened: Whooping cranes, bald eagles, peregrine falcons, gray wolves, elephant seals

The Sixth Extinction

• Critics of the ESA:– Unrealistic to try to save all 10 million species

– Extinction is a natural process

– Steps taken to stave off extinctions can be detrimental to humans

•The fossil record shows 5 mass extinction events in Earth’s history•A mass extinction is a species loss that is global, affects large numbers of species, and are dramatic in impact

•50-90% of all living species are lost•Takes a few thousand to a few hundred thousand years

• Mass extinctions were probably caused by global changes such as:

– Changes in sea levels

– Climate fluctuations

– Shifts in ocean and land forms from continental drift

– Asteroid impact • Normal extinctions occur when a

species lacks the ability to adapt to environmental changes

When a species goes extinct, usually a new species arises to fill the gap

Measuring Extinction Rates

• Malaysia: looked for evidence of 266 known species of fish – only found 122

• Lake Victoria, Africa – 200 of 300 native fish species haven’t been seen in years

• Oahu, Hawaii – half of the 41 native tree snail species have not been found

• Tennessee River – 44 of 68 shallow-water mussel species are missing

• Since 1600– 113 (out of about 9000) identified bird species are

extinct– 83 (out of about 4500) identified mammal species

are extinct

• Severe threats to species fall into 4 categories:– Loss or degradation of habitat– Introduction of nonnative (exotic)

species– Over-harvesting– Effects of pollution

• Habitat destruction is the greatest threat

• Instead of completely destroying a habitat, human activity can often fragment a habitat

– Subdividing one large habitat into several smaller sections (habitat fragmentation)

Habitat Loss and Food Chains

Habitat Fragmentation

• Especially threatens large predators, that require large, intact hunting areas

• Energy flows in one direction within an ecological system along a food chain

Energy flows from:• Producers (photosynthetic

organisms) • to primary consumers that

feed on them • to secondary consumers

(predators feeding on primary consumers)

Habitat Fragmentation• Each trophic level (level of

the food chain) only gets about 10% of energy available from previous level

• The biomass (total weight) of the low trophic levels is larger than high levels

• This is necessary to support the chain as part of the principle of the trophic pyramid

• Habitat fragmentation causes low levels of the trophic pyramid to shrink, so the higher levels also shrink

Habitat Fragmentation

• Species that remain in fragmented habitats are susceptible to extinction because they are very isolated

• It is difficult to leave the area and find a more desirable habitat • Asian elephants face almost certain

extinction in almost every place they exist in the modern world. Only about 30,000 Asian elephants remain in the wild, scattered across fragmented habitats in 13 Asian countries

Other Human Causes of Extinction:Introduced Species

• Introduced species are species that are brought in by humans to an area they have never been found before

• This can be very dangerous to existing species

Overexploitation

• Human also engage in the overexploitation of species

• Certain organisms are highly prized and therefore are endangered

• Overexploitation can occur in plants as well as animals

15,000 of 50,000 medicinal plants are under threat of extinction

Pollution• Pollution – the release

of poisons, excess nutrients, and other wastes into the environment –also threatens biodiversity

• For instance, the herbicide atrazine can harm frogs and salamanders

Disruption of Ecological Communities• Most endangered species won’t affect survival of humans, but

the effect on the biological community can be disastrous• A biological community consists of all the organisms of

different species living together in a particular area• These organisms are connected by a food web – the complex

linkage among organisms within a community

Mutualism: How Bees Feed the World

• Bees are the primary pollinators of flowering plants

• Plant benefits by getting fertilized

• Bee benefits by getting pollen and nectar for food

• Wild bees pollinate at least 80% of all agricultural crops in the U.S.

• But bees have suffered dramatic declines in recent years, dramatically threatening humans in the process

– Threats to bees include parasites, competition from invading species, and habitat destruction

Predation: How Songbirds May Save Forests

• Predator: a species that survives by eating another species

• Warblers collectively remove tons of tree-damaging insects from forest trees every summer

• Warbler populations are declining; this will affect the growth rate of trees– Warblers decline due to habitat

destruction and increased attacks by human-associated predators (i.e. cats, raccoons)

Keystone Species

• As seen in a food web, most organisms have multiple connections

• Some single species indirectly affect more than one other species to the extent that – if it is removed – the community collapses (analogous to a keystone in an archway) keystone species

• Ex. grave wolves in Yellowstone National Park

Their extermination within the park by the mid-1920s and subsequent reintroduction in 2003 both had profound effects on organisms as diverse as willow trees, elk, and beaver

Changed Ecosystems

• Ecosystem: all the organisms in a given area along with their non-biological environment

• Energy flows through an ecosystem

• Nutrients are recycled within an ecosystem

• Nutrient cycling– Nitrogen – Carbon– Other nutrients