U6115: Populations & Land UseTuesday July 8, 2003

What is Biodiversity Importance of Biodiversity Levels of Biodiversity Threats to Biodiversity Patterns of Biodiversity

A one-acre patch of elm trees produces oxygen, removes carbon from the atmosphere, and captures at least 16 tons of airborne dirt, which rain then washes back to the ground as productive soil.

Norman Myers 1983

What is Biodiversity?

The variety of different types of organisms present and interacting in an ecosystem.

Often more species equals more diversity, although there are, in fact many more factors beyond a simple count of species that determine whether biodiversity is higher or lower in any given ecosystem.

Biodiversity and global economy

Globally agriculture, which depends on genetic stock from natural ecological systems, is now a $3 trillion global

Recreation and nature tourism generates some $12 billion worldwide in annual revenues

In the United States, the economic benefits from wild plants and animals comprise approximately 4.5% of the Gross Domestic Product.

Global trade in wild plants (timber and others) is estimated at $6 billion annually

Biodiversity and food security

Much of the world's major food crops, including corn, wheat, and soybeans, depend on new genetic material from the wild to remain productive and healthy.

Food production from wild stocks of fish is the single largest source of animal protein for the world's 6 billion inhabitants. In the US alone more than 10 billion pounds of fish, valued at about $4 billion, were caught and sold yearly.

Levels of Biodiversity

Genetic Diversity Species Diversity Ecosystem Diversity

Genetic Diversity

Amount and variety of genetic material within individuals, populations or communities

Source of biodiversity at all levels Knowledge of amount of genetic variability present within local

populations essential in directing conservation programs. Amount of genetic differences among species could help

determine rates of evolutionary change

Species Level

Species Richness: numerical count of species present in an area. Richness tends to increase over area and sampling intensity

Species Diversity: When species are weighted by some measure of importance e.g. abundance, productivity or size.

Measures of Diversity include:– Shannon-Wiener Index– Simpson index

Shannon’s Diversity Index

Assume that there are n possible categories in a data set and that their proportions are pi,.....,pn. Then Shannon’s diversity index for this system is defined to be :

H’ = -Σpiln(pi) accounts for both abundance and evenness of the species

present The proportion of species i relative to the total number of

species (pi) is calculated, and then multiplied by the natural

logarithm of this proportion (lnpi).

Simpson’s Diversity Index, D

Simpson's diversity index (D) characterizes species diversity in a community.

Simpson's diversity index (D) characterizes species diversity in a community.

D = 1/(Σpi2)

The proportion of species i relative to the total number of species (pi) is calculated and squared. The squared proportions for all the species are summed, and the reciprocal is taken.

Ecosystem and Biome diversity

Ecosystems are the collection of all the plants and animals within a particular area

Ecosystems may differ in species composition, physical structure and function as a result of differences in physical structure and composition

Biomes are large ecological units on the basis of dominant vegetation

Preserving a variety of ecosystems and biomes are necessary for preserving species diversity

Temporal Patterns of Species richness

Fossil record indicate variation of species richness over time and space

Largest number of phyla in the Cambrian and pre-Cambrian period

Total number of phyla has since declined but overall richness has increased

Spatial patterns of species richness

Point Richness: number of species that can be found in a single point in space

Alpha (α-) richness: number of species found in a small homogenous area

Beta (β-) richness: rate of change in species in species composition across habitats

Gamma (γ-) richness: change across large landscape gradients

Richness is directly related to physical environment, productivity and structural complexity of communities

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Relationship between area and number of amphibian species in selected Islands in West Indies- MacArthur & Wilson 1967

Species /Area relations

Limits of species richness

Productivity hypothesis: High productivity results in higher number of species

Stability hypothesis- environments that are stable tend to support higher number species

Threats to biodiversity

habitat destruction (slash and burn agric. or felling of old-growth forests)

overexploitation (fishing, hunting) pollution (domestic and industrial emissions) global climate change (the greenhouse effect and

destruction of the ozone layer) invasion by introduced species (displacement of

native species underlying social conditions (increased per-capita

consumption, poverty, rapid population growth, unsound economic and social policies )

Threats to Biodiversity cont’d

Habitat degradation– Some 93% of coral reefs damaged directly or

indirectly by human activities– During the 1990s between 130,000 and 150,000

km2 of forest cover lost each year

Changes in atmospheric composition. siltation, nutrient loading, pollution of air and

water by toxic chemicals

Patterns of species vulnerability

Rare Species Long-lived species Keystone species

Rare species

May be the result of many factors small range, high habitat specificity or small population density

Human-induced rarity may be more damaging

Long-lived species

Well-suited to long-term predictability Often not equipped to adapt to rapid changes

brought by human-induced changes Often population declines may take many

years to recover

Keystone species

A species or group of species that makes and unusual contribution to a community structure or processes

May be predators, food source or species that maintains critical ecosystem processes

A loss of a keystone species may lead to loss of others that depend on it.

Biodiversity ManagementConservation vs Preservation?

All about management of Genetic Variation– Aim is to allow continued evolutionary change in the

populations and species concerned– Since ecological systems are not static- management

should allow for change- Conservation rather than preservation.

– 3 Time scales of concern: extinction avoidance (short-term); ability to adapt or evolve (medium term) and potential for continued speciation (long-term)

– Units of conservation: What are the units of conservation? How do we determine the most appropriate unit?

Next week

Habitat fragmentation and biological consequences

Population dynamics on heterogeneous landscapes

Today’s lab

Review of two short papers. Stuart Chapin III et al 2000. Consequences of changing

biodiversity Nature Vol. 405 pp. 234 http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v405/n6783/full/405234a0_fs.html&content_filetype=pdf

Franklin, J.F. 1993. Preserving Biodiversity: Species,

Ecosystems or Landscapes? Ecological Applications, 3(2), pp. 202 - 205. http://www.jstor.org/cgi-bin/jstor/printpage/10510761/di960380/96p0004u/0.pd f?userID=a027019f@columbia.edu/01cc9933410050dc70eb&backcontext=table-ofcontents&config=jstor&dowhat=Acrobat&0.pdf