Biodiversity

Mass Extinctions

• There have been 5 mass extinctions throughout Earth’s history, the last one believed to be about 65 million years ago when a meteor collided with the planet and wiped out the dinosaurs.

• Scientists now believe that a sixth mass extinction is underway and that this poses a major threat to humans in the next century.

Mass Extinction

• Biologists are currently predicting that one fifth (20%) of all living species could disappear within the next 30 years.

• All of these losses can be attributed mainly to human activities, especially the destruction of plant and animal habitats.

• The explosion of human population, especially in the post-Industrial Revolution years of the past two centuries, coupled with the unequal distribution and consumption of wealth on the planet, is the underlying cause of the Sixth Extinction.

What Is Biodiversity?

• Biodiversity - The variability among living organisms on the earth, including the variability within and between species and within and between ecosystems.

• Biodiversity has 2 main components:

1) Species Richness – the total number of different species within a community.

2) Relative Abundance – the actual number of each type of species in a community.

Biodiversity

• Species richness may be equal, but relative abundance may be different.

• Both forests have 4 species of trees, but the relative abundance of species A is much greater in forest 2.

• Ecologists would say that forest 1 has a greater degree of diversity.

Biodiversity

• Species richness generally declines along an equatorial-polar gradient. Tropical habitats support a much larger number of species than do temperate or polar regions.

• Reasons:1) solar energy 2) water availability3) growing season

All three factors increase the opportunity for speciation events to occur.

• The same thing happens as you increase in altitude on land, or increase in depth in the oceans.

Dominant and Keystone Species

• Dominant Species – those species that have the highest relative abundance.

• Keystone Species – those species that exert a strong control on community structure due to their ecological roles.

• Where sea stars are present, 15 to 20 species of invertebrates and algae occur. Where sea stars are absent, less than 5 species occur because the mussels are unchecked.

• What is a possible advantage to a keystone species of being able to feed mainly on those prey species that are otherwise dominant?

Three Levels Of Biodiversity

• Genetic Diversity – genetic variation within and between populations due to adaptations to local conditions.

• Species Diversity – the variety of species within ecosystems.

• Ecosystem Diversity – the variety of ecosystems in the biosphere.

The Biodiversity Crisis

• To date, scientists have described and formally named about 1.5 million species of organisms.

• We can currently only estimate, but some biologists believe the number of organisms that currently exist is about 10 million.

• Insects, nematodes, fungi, protists and prokaryotes head the list of organisms with great numbers of undiscovered species.

• This means our efforts to understand the structure and function of ecosystems on which our survival depends will remain incomplete.

• Humans evolved in tune with ecosystems, and our incomplete knowledge poses a huge risk to our long term survival.

Why Should Humans Care?

• Biodiversity is a crucial natural resource.• Threatened species could provide crops,

fibers and medicines for human use. 25% of all prescriptions contained substances derived from plants.

• Biodiversity represents the sum of all genomes on Earth. We stand to lose the valuable genetic potential held in the genes of species that become extinct.

Examples• The Rosy Periwinkle

from Madagascar contains alkaloids that inhibit cancer cell growth.

• Enzymes extracted from bacteria that live in hot springs allowed scientists to develop polymerase chain reaction (PCR), a DNA cloning technique.

Ecosystem Services

Ecosystem services encompass all the processes through which natural ecosystems and the species they contain help sustain human life on Earth. These include:

• Purification of air and water• Reduction of severity of draughts and floods• Generation and preservation of soil• Detoxification and decomposition of wastes• Pollination of crops and natural vegetation• Dispersal of seeds• Nutrient cycling• Control of pests by natural enemies• Protection from UV rays• Provision of aesthetic beauty

Biosphere II• A $200 million experiment in

Arizona which attempted to create a system of ecosystems required to sustain human life.

• The experiment was supposed to house 8 humans in isolation for 2 years.

• The artificial biosphere failed after 15 months and the experiment had to be stopped.

• O2 and CO2 concentrations fluctuated wildly, most of the vertebrate species became extinct, all the pollinators died, pest populations exploded and trees toppled.

• The experiment taught us that no one yet knows how to engineer a system that can provide humans with all the life support services that natural ecosystems provide.

Causes

There are 3 major threats to biodiversity:

• Habitat destruction

• Introduced species

• Overexploitation

Habitat Destruction

Human alteration of habitat is the single greatest threat to diversity throughout the biosphere. Habitat destruction is due to many factors. These include:

• Agriculture• Forestry• Urban sprawl• Mining• Pollution

Habitat Destruction

• The cumulative area of all tropical rainforests on Earth is about the size of the continental U.S. We lose an area equal to the size of West Virginia each year.

• Along with the oxygen production and air filtering capabilities, we lose the genetic potential of any undiscovered species.

Habitat Destruction

• Open oceans are productive “pastures” of phytoplankton which may help moderate the greenhouse effect by consuming massive quantities of CO2 for photosynthesis. The effects of pollution on these expanses of open ocean is yet unknown.

Habitat Destruction

• In addition to habitat destruction over large regions, many natural landscapes have been fragmented, broken up into small patches.

• In almost all cases, habitat fragmentation leads to species loss.

• Example: Prairie covered most of the mid-west when Europeans first arrived, but now occupies less than 0.1% of its original area. The prairie fragments lost 60-80% of their original plant and animal species.

Introduced Species

Introduced species – those that humans move from the species’ native locations to new geographic regions. The introductions can be intentional or unintentional.

Introduced species rank second behind habitat destruction as a cause for loss of biodiversity. Examples of introduced species include:

• Nile Perch• Brown Tree Snake• Kudzu• Fire Ants• Starlings

Overexploitation

Overexploitation – the human harvesting of wild plants or animals at rates exceeding the ability of those populations to rebound.

Especially vulnerable are large species with low reproductive rates such as elephants, whales, rhinos and other animals considered valuable by humans.

So What Can Be Done?

• Conservation efforts have to occur not only at the species and population levels, but also at the community and ecosystem levels. These include:

• Identification of keystone species• Preservation of natural edges• Corridors• Establishment of protected areas• Captive breeding programs• Restoration ecology• Bioremediation• Ecotourism• More intelligent use of renewable resources

Natural Edges and Corridors

• In contrast to the abrupt edges created by human activity, natural edges are gradual transitions that have been found to be important sites of speciation events.

• Corridors are natural or man-made strips of suitable habitat that connect otherwise isolated patches.

Captive Breeding Programs

• In addition to educating the public about the plight of wildlife and allowing people to see live animals up close, zoos are important in the preservation of species through captive breeding programs.

• Zoos keep genetic libraries of species and regularly exchange animals to promote the genetic diversity.

Restoration Ecology

• Restoration ecology – seeks to reverse population declines by applying ecological principles in an effort to return ecosystems to their natural state.

• The basic assumption is that most environmental damage is reversible. This assumption must be balanced by the realization that ecosystems are not infinitely resilient to damage.

• Biological communities can recover naturally from many types of disturbances. The time frame for recovery is based more on the size of the disturbance than the type of disturbance.

• Areas that have been abandoned such as rainforest after soil has become unproductive and mining sites are prime targets.

• The key to restoration ecology is understanding the specific characteristics of succession for each type of disturbance and each type of ecosystem.

Bioremediation

• Bioremediation – the use of living organisms (usually prokaryotes, fungi or plants) to detoxify polluted ecosystems.

• Some plants adapted to soils with heavy metals can be used to re-establish sites degraded by mining. The plants accumulate high concentrations of metals such as zinc, lead and nickel. The plants are then harvested to recover the metals.

• Certain strains of bacteria have been supplied with growth stimulants and used to clean up oil spills on beaches.

Ecotourism

• Ecotourism - travel to destinations where the flora, fauna, and cultural heritage are the primary attractions.

• Examples include photography safaris in Africa and rainforest tours in Central and South America.

• Many countries are finding that they can make more money through tourism than by exploitation of their natural resources. Ecotourism now comprises a significant percentage of their gross domestic product.

“ We must consider our planet to be on loan from our children rather than a gift from our ancestors” – Chinese Proverb