- Slides: 24
U 6115: Populations & Land Use Tuesday July 8, 2003 l l l 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? l l 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 l l 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 l l 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 l l l Genetic Diversity Species Diversity Ecosystem Diversity
Genetic Diversity l l 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 l Species Richness: numerical count of species present in an area. Richness tends to increase over area and sampling intensity l Species Diversity: When species are weighted by some measure of importance e. g. abundance, productivity or size. Measures of Diversity include: l – – Shannon-Wiener Index Simpson index
Shannon’s Diversity Index l l l 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 l 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 l l Simpson's diversity index (D) characterizes species diversity in a community. D = 1/(Σpi 2) 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 l l 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 l l l 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 l l l 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 composition across habitats Gamma (γ-) richness: change across large landscape gradients Richness is directly related to physical environment, productivity and structural complexity of communities
Species /Area relations Number of species 100 Cuba Jamaica 10 Monserrat Saba Redonda 10 100000 Area (sq. mi) Relationship between area and number of amphibian species in selected Islands in West Indies- Mac. Arthur & Wilson 1967
Limits of species richness l l 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 l l l 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 l Habitat degradation – – l l Some 93% of coral reefs damaged directly or indirectly by human activities During the 1990 s between 130, 000 and 150, 000 km 2 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 l l l Rare Species Long-lived species Keystone species
Rare species l l 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 l l l 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 l l l 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 Management Conservation vs Preservation? l 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 l l Habitat fragmentation and biological consequences Population dynamics on heterogeneous landscapes
Today’s lab l l 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/Dyna. Page. taf? file=/nature/journal/v 405/n 6783/full/405234 a 0_fs. html&content_filetype=pdf l 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/di 960380/96 p 0004 u/0. pd f? user. ID=a 027019 [email protected] edu/01 cc 9933410050 dc 70 eb&backcontext=tableofcontents&config=jstor&dowhat=Acrobat&0. pdf