47.1 The Biodiversity Crisis

A number of levels of organization of living organisms can be estimated.

When the main concern of biologists is the loss of biodiversity, the estimation indices are less useful than they should be.
Measures of biodiversity, in terms of species diversity, may help focus efforts to preserve biologically or technologically important elements of biodiversity.

The Lake Victoria cichlids are an example of what we can learn from this.

In the 1980s, biologists discovered hundreds of species representing a variety of specializations to specialized habitat types and specific feeding strategies, such as eating plankton floating in the water.
Lake Victoria's cichlids are the product of an adaptive radiation.
The speciesradiates into different habitats.
The 15 species of finches on the Galapagos Island are an example of modest adaptive radiation.
The cichlids of Lake Victoria are an example of a spectacular adaptive radiation that used to include 500 species.

Some species quickly disappeared when biologists made this discovery.

The Nile perch, a large predatory fish, was introduced to Lake Victoria by the fisheries to feed the people living around the lake.
The Nile perch was introduced in 1963, but its populations did not begin to increase until the 1980s.
The Nile perch, declining lake water quality due to agriculture and land clearing on the shores of Lake Victoria, and increased fishing pressure were some of the factors that played a role in the extinction of 200 cichlid species in Lake Victoria.
Many of the species that were lost were never named.
The diversity is not what it used to be.

Contemporary rapid species loss that occurs all over Earth is caused primarily by human activity and is depicted in the cichlids of Lake Victoria.

At the rate of one out of 1 million species becoming extinct per year, extinction is a natural process of macroevolution.
There is a major difference between the previous mass extinctions and the current extinction.
There are three human activities that have a major impact: destruction of habitat, introduction of exotic species, and over-harvesting.
In the history of the planet, there have only been five extinctions on this scale, which were caused by catastrophic events that changed the course of the history of life.

The term "biodiversity" describes the number of species and their abundance on the planet.

Most biologists feel comfortable with the concept of species and are able to identify and count them in most contexts.

One of those concepts is genetic diversity.

The future potential of a species depends on the genetic diversity in the populations that make up the species.
The same is true for higher categories.
A group with different types of species will have more genetic diversity than a group with the same types of species.
The most genetically diverse of the genera is the one that has the greatest potential for evolution.

metabolic processes that keep organisms alive and reproducing are carried out by many genes.

One way to measure diversity that is important to human health and welfare is by using chemical diversity as a source of pharmaceuticals.

Humans have created a variety of organisms.

This diversity is also suffering losses because of migration, market forces, and increasing globalism in agriculture, especially in densely populated regions such as China, India, and Japan.
The human population depends on diversity as a stable food source, and its decline is troubling biologists and agricultural scientists.

Even if some of the species survive, whole ecosystems can disappear.

The loss of an ecosystems means the loss of interactions between species, the loss of unique features, and the loss of biological productivity.
The prairie ecosystem is an example of a largely extinct one.
Prairies once stretched from northern Canada down into Mexico.
Crop fields, pasture lands, and suburban sprawl replaced them.

The most productive agricultural soils in the United States are no longer created by the hugely productive ecosystem.

Native soils are disappearing or must be maintained at great expense.

There is a great diversity of species on Earth.

The knowledge of the species that live on the planet is limited because of a lack of financial resources and political will.

According to a recent estimate, less than 20% of the total number of species on the planet are known by science.
Estimates of the number of prokaryotic species are largely guesses, but biologists agree that science has only begun to catalog their diversity.
There is no way to be sure that the 1.5 million descriptions are accurate because there is no central repository of names or samples.
It is a guess based on the opinions of experts.
Science is very much in the same place as it was with the Lake Victoria cichlids, knowing little about what is being lost.

The internet is facilitating the effort to catalog accessible species.

According to the State of Observed Species Report, it will take close to 500 years to describe life on this planet.

The pursuit of naming and counting species may seem unimportant, but it's not just an accounting of species.

Biologists determine the unique characteristics of an organisms and whether or not it belongs to any other described species.
After the initial discovery, it allows biologists to follow up on questions about the biology of the species.
The unique characteristics of each species make it potentially valuable to humans or other species on which humans depend.

It's not evenly distributed on Earth.

Lake Victoria had almost 500 species of cichlids, ignoring the other fish families present in the lake.
The 500 species of cichlids were endemic because they were all found in Lake Victoria.
Highly restricted distributions are vulnerable to extinction.
The genera and families can be endemic.
Many of the fish found in Lake Michigan are found in other lakes in North America.
Lake Michigan is a recently formed lake while Lake Victoria is an ancient tropical lake.

The present form of Lake Michigan is about 7,000 years old, while the present form of Lake Victoria is about 15,000 years old.

Two factors, latitude and age, have been suggested as possible explanations for the diversity of the planet's flora and fauna.

In May, 20, 2012

The work of biogeographers is important to understanding our physical environment, how the environment affects species, and how environmental changes impact the distribution of a species.

Both ecology and biology need to be understood by biogeographers.

They need to know about evolutionary studies, soil science, and climatology.

There are three main fields of study under the heading of biogeography.

One of the oldest patterns in ecology is that species increase as latitude decreases.

The number of amphibian species across the globe is shown on the map.

The pattern is the same for most groups.
There is a lack of data in the study.

Scientists don't know why there is an increase in biodiversity closer to the equator.

The tropics have a greater age of the ecosystems than the temperate regions, which were largely devoid of life during the last glaciation.
The idea is that older people have more time for speciation.
It is possible that the tropics receive more direct energy from the sun than the polar regions.
More opportunities for coevolution, specialization, and perhaps greater selection pressures are provided by the greater heterogeneity.

The tropics have been seen as being more stable than the other parts of the world.

The tropics are assumed to be more stable than other environments and this might promote speciation into highly specialized niches.

Regardless of the mechanisms, it's true that the tropics have the greatest levels of biodiversity.

Knowledge of species is very low and there is a high potential for extinction because of the richness of diversity.

The idea of identifying areas rich in species and at significant risk for species loss was developed in 1988 by British environmentalist Norman Myers.

The purpose of the concept was to identify important locations on the planet.
Governments are able to protect a larger number of species.
The original criteria for a hotspot included the presence of 1500 or more endemic plant species and 70 percent of the area disturbed by human activity.
Half of Earth's endemic plants are included in the 34 biodiversity hotspots.

Only 2.3 percent of the Earth's surface is covered by the 34 biodiversity hotspots, which are endemic to 42 percent of the species and 50 percent of the plants.

The number of species on the planet is the result of an equilibrium of two evolutionary processes.

Both are natural processes of macroevolution.

The number of species will increase and decrease when extinction rates surpass speciation rates.

The percentage of extinction occurrences reflected in the fossil record has fluctuated throughout Earth's history.

Mass extinctions have occurred five times.

More than half of all species in the fossil record have disappeared, and Paleontologists have identified five different types of extinctions in the fossil record.

The five mass extinctions have attracted the most research.
The five mass extinctions are the most extreme events in a continuous series of large extinction events.
The most recent mass extinction event seems to be clear in most cases.

The mass extinctions were the basis for defining periods of geological history and they occur at the transition point between geological periods.

The gradual origin of new species is reflected in the transition in fossils from one period to another.
The transitions can be seen in the rock.
There are five mass extinctions.

There are five mass extinctions in Earth's history.

Only a small percentage of marine species lived outside the oceans.

The main hypothesis is a period of warming.
There are two extinction events separated by 1 million years.
The first and second events were caused by cooling and warming.
Sea levels were affected by the climate changes.
Some researchers think that a nearby supernova may have caused the extinction of the Silurian.
The Earth's protective ozone layer would have been stripped away by the gamma-ray burst, allowing intense ultraviolet radiation from the sun to reach the surface of the earth.
extraterrestrial influences on Earth's history are an active line of research, and the hypothesis is very speculative.
After the mass extinction, the recovery of biodiversity took 20 million years.

It seems to have mostly affected marine species and not much of the plants or animals in the land.

The causes of extinction are not understood.

An argument could be made that Earth was nearly devoid of life during the extinction event.

Estimates show that most of the marine and terrestrial species were lost.
The trilobites, a group that survived the extinction, became extinct at this time.
The leading suspect is extended and widespread volcanic activity that led to a runaway global-warming event.
The oceans became suffocating.
The end-Permian extinction took 30 million years to recover.
The extinction of the dinosaurs changed the makeup of Earth's flora and fauna.

The extinctions may have occurred more slowly throughout the Triassic, according to recent scholarship.

The causes of the extinction event are best understood.

About 65 million years ago, the majority of the dinosaurs disappeared from the planet, with the exception of the theropod clade that gave rise to birds.

The cause of extinction is thought to be the result of a large meteorite hitting the coast of the Yucatan Peninsula.

The hypothesis was first proposed in 1980 and was based on a spike in the levels of iridium in the rock that marks the boundary between the Cretaceous and Pboundary.
The researchers who discovered the iridium spike thought it was a rapid influx of iridium from space to the atmosphere rather than a slowing of the deposition of sediments.
The report of an appropriately aged and sized impact crater in 1991 made the hypothesis more believable.
The theory is supported by an abundance of geological evidence.
The recovery times for biodiversity after the end-Cretaceous extinction are shorter than for the endPermian extinction.

It is possible that extensive volcanism began forming about 66 million years ago at the same time as the impact of the Yucatan asteroid.

Over 50 percent of India is covered by lava flows.
Climate change may have been caused by the release of volcanic gases during the formation of traps.

A group of people discovered a spike in the concentration of iridium at the K-Pg boundary in 1980.

The K-Pg mass extinction was caused by an asteroid impact.
The light band is the iridium layer.

There was an abundance of fern spores below the K-Pg boundary.

There was an abundance of fern spores above the K-Pg boundary, but they were not found below.

The large animals disappeared at the end of the last glaciation period.

The extinction appears to have happened in a very short period of time.
The losses in North America were dramatic and included the woolly mammoths, mastodons, giant beavers, saber-toothed cats, and the North American camel.
The rapid extinction of large animals was thought to be caused by over-hunting.
Today's research continues into this hypothesis.

The arrival of paleo-humans, perhaps as long as 40,000 years ago, was correlated with the timing of the extinctions.

The extinctions began in Australia about 40,000 to 50,000 years ago, after the arrival of humans in the area.
The extinctions of large mammals in North America occurred 10,000-12,000 years ago.
Smaller mammals such as bears and moose are the only ones left.

The extinctions of many species occurred due to human arrivals.

When there were large animals on the islands, they were often forced into extinction.
The large mammals that lived there became extinct as a result of colonization.
Africa did not experience a recent arrival of hunter-gatherer humans.
Humans arrived in the area hundreds of thousands of years ago.
This topic is still being researched and hypothesized.
Most cases of extinctions were caused by human hunting, even if climate played a role.

There have been many extinctions of individual species recorded in human writings.

The European colonies have been expanding since the 1500s.

The dodo bird is one of the earliest examples.

The forest of Mauritius, an island in the Indian Ocean, was once home to the odd pigeon-like bird.
The dodo was an easy prey because it approached people without fear.
Dodo young and eggs were killed by animals brought to the island.

Steller's sea cow became extinct in the 18th century, it was related to the manatee and used to live along the northwest coast of North America.

Europeans discovered Steller's sea cow in 1741 and over hunted it for meat and oil.
The last sea cow was killed in 1768.

A number of species have gone extinct since 1900.

The species was over hunted and suffered from habitat loss due to the clearing of forests for farmland.

The Carolina parakeet died out in 1918.

It was hunted to prevent it from eating fruit.

The Japanese sea lion, which inhabited a broad area around Japan and the coast of Korea, became extinct in the 1950s due to fishermen.

The Caribbean monk seal was hunted to extinction by 1952.

There have been many extinctions in the past 500 years.

The list does not include all of the extinct species after 1500 AD.

Humans are likely to notice the extinction of a bird or mammal if it has been hunted or used in other ways.

There are organisms that are less interested in humans than others.

The expectation is that ten species will become extinct each year, representing ten million species per year.

The extinctions in the written record have been used in one contemporary extinction rate estimate.

The method yields an estimate of 26 E/MSY for birds alone.
There are three reasons why this value may be underestimated.
Many species wouldn't have been described until later in the time period, so their loss wouldn't have been noticed.
The number of recently extinct species is increasing because they are being described from bones.
Even though they are reluctant to call them extinct, some species are already gone.

The extinction rate is closer to 100 E/MSY if taken into account.

The rate will be 1500 E/MSY by the end of the century.

A second approach to estimating present-time extinction rates is to correlate species loss with habitat loss.

As the size of the island increases, the number of species increases.
This phenomenon can be seen in other island-like habitats, such as the mountain-top tepuis of Venezuela, which are surrounded by tropical forest.
The number of species living there will decline if the habitat area is reduced.
Estimates of extinction rates based on habitat loss and species-area relationships suggest that 50 percent of species will become extinct if 90 percent of habitat is lost.

The extinction rate calculations are 1000 E/MSY and higher.

There are suggestions that there is a delay in extinction because actual observations do not show this amount of loss.
The applicability of the species-area relationship when estimating the loss of species has been called into question by recent work.