Lecture 22

Biodiversity 1: Basic Principles

Definition of Biodiversity
• Biodiversity = variation among organisms and ecological systems at all levels: populations, species, and biome structure and ecosystem processes
What is Biodiversity?
• Number and variety of species, ecological systems, and the genetic variability they contain.
What determines the number of species?
• In any assemblage
• Latitudinal gradients
What is the value of biodiversity?
• Ecosystem goods and services
• System integrity and function
What are the threats to biodiversity?
• Sinister sextet
• Conservation strategies
How many species exist?
• 1.8 million species are "known to science" — have been classified
• Estimates at 10 to 30 million, but that is very approximate
• New Discoveries are noteworthy - unusual
Phyletic vs species diversity
• Nine of 35 phyla contain over 96% of animal species
• Most species are insects, and so terrestrial
• Most phyla are marine
Biological diversity - patterns
• Few species are common (numerically dominant), many are rare.
• Species richness can vary widely among locations and regions and shows pronounced latitudinal gradients
The geography of life
• The number of species is greatest near the equator,
– Tropical rain forests are especially species-rich
• “Hot spots” harbor an unusually rich local diversity, perhaps because conditions favor evolutionary diversification. (an area that has at least 0.5% or 1500 of the world’s 300,000 species of green plants, and that has lost at least 70% of its primary vegetation)
• Certain areas (islands in particular) contain species unique (“endemic”) to that locale
• Latitudinal gradients are the rule
• Endemic species are limited to a small area – usually remote islands have numerous endemics
Biological diversity - measurement
• Richness, yes; but also recognize variation in relative abundance
– An assemblage with ten species, each represented by ten individuals, is more diverse than one with ten species where nine are represented by only one individual, and the remaining species dominates.
– is the abundance of the ith species
• Species richness increases with area sampled
Species-area equations
• S=cAz
• logS = logc + zlogA
• where S = number of species, A = area, c is a constant, z is the slope of the relationship
• z = 0.20 to 0.35
• S also varies across habitats
Within- and between-habitat diversity
• Local (alpha) diversity is the number of species in a location/habitat
• Regional (gamma) diversity is the total diversity of a region
• Beta diversity is the between-habitat component, maximal if each habitat has a unique list of species (high species turnover)
• Various similarity indices compare the species of two communities (inverse of Beta)
Beta diversity
Local and regional diversity
• Local diversity can be visualized as a sample of the regional species pool
– Species must pass through a series of ‘filters’ to become established at a location
– “”species sorting”
Equilibrium theory of diversity
• First developed to explain S-A relationship on islands
• Steady-state model based on equilibrium of colonization and extinction
• Immigration rate declines as island accumulates species, beginning with good colonizers and ending with last, poor colonizer
• Extinction rate increases as island accumulates species, due to addition of more extinction-prone species and greater crowding
• Higher extinction rates occur on small islands due to smaller population size
• Lower colonization rates occur on far islands due to dispersal limitation
Take-home messages
• Biodiversity can be evaluated across all levels from genes to ecosystems
• Known species approach 2 million, unknown species approximate 10 million or more
• Factors that influence regional and local biodiversity influence the make-up of communities
• Species-rich communities are functionally diverse
• Latitudinal gradients, relative abundance patterns, and species-area relationships are fundamental aspects of biodiversity
What is the value of biodiversity?
• What are the biophysical necessities for human life, that are provided by natural ecosystems?
• How is biodiversity related to nature’s services?
• What types of ecosystem services are there, and what are their roles?
• What is the economic value of nature’s services?
The problem
• Humans have benefited from the conversion of natural ecosystems to human-dominated ones, and from the exploitation of biodiversity
• Degradation of habitats, pollution, overexploitation, climate change and invasive species are resulting in continuing decline in natural systems
• The ability of natural systems to sustainably meet the needs of the world’s population is in question
Provisioning services
• Food: crops, livestock, capture fisheries, aquaculture, wild plants and animals
• Fiber: timber, cotton, fuel
• Genetic resources (for plant breeding)
• Medicines and pharmaceuticals
• Fresh water
Regulating services
• Pollination
• Pest regulation and invasion resistance
• Climate regulation
– Water cycle
– Carbon sequestration
• Water purification, flood control
• Erosion regulation
• Natural hazard regulation
Pollinator Diversity Declining in Europe
• Over one million records, 10km x 10km cells, pre-and post-1980
• Statistically significant declines on bee diversity in over half of UK cells, two-thirds of Netherlands
• Wild plants requiring bee pollination have shrinking distributions
Cultural services
• Spiritual and religious values
• Aesthetic Values
• Social relations
• Sense of place
• Cultural heritage
• Recreation and ecotourism
Supporting services
• Soil formation
• Plant productivity
• Nutrient cycling
• Water cycling
• Healthy ecosystems depend on more species
– Biodiversity ®Productivity
• Diversity (the more species) keeps an ecosystem stable
– Biodiversity ®Ecosystem Stability
The rationale for BEF*
• Complementarity
– When species have complementary roles, the rate and efficiency of a process should increase when multiple species are present
• Redundancy
– When species have redundant roles, the presence of multiple species serves as insurance against the loss of any one
• Uniqueness
– When species have unique roles (such as denitrifying bacteria), their loss can be particularly serious
– In that case, species identity matters
Do Individual Species Matter?
• A migratory, detritus-feeding fish modulates ecosystem function in a hyperdiverse neotropical stream.
• The Unique Role of the Flannel-mouth Characin
• more organic-rich sediment on the stream bed
• Less downstream transport of POC due to reduced bioturbation and consumption
• Increased respiration by microbes on the stream bed
• Doubling of primary production
Economic Costs and Benefits ?
• What are the ‘hidden’ costs of not protecting biodiversity?
• How do economic subsidies promote unsustainable practices?
• How might market evaluation of ecosystem functions be accomplished?
Costs of failing to protect biodiversity and services
• Control of invasive species costs hundreds of millions
• Flood damage due to loss of wetlands
• Storm damage due to loss of mangroves
• Emergence of infectious diseases
• Loss of ‘opportunity value’ ( new medicines, genes, products)
Subsidies can lead to unsustainable practices
• Annual agricultural subsidies to OECD countries 2001-2003 equaled one-third the annual global value of agricultural products
• Fisheries subsidies to OECD countries in 2002 of $6.2 billion equaled 20% of gross value received
• These subsidies encourage agricultural and fish harvest practices that are not justified on their economics and may not be sustainable in terms of resource use
Market mechanisms can work
• Protection of New York City water supply by purchasing riparian lands and easements
• Costa Rica has paid $30 million to land owners to protect land for watershed services
• Carbon markets value carbon sequestration in trees
Towards more inclusive valuation
• Include explicit monetary values for regulating, cultural and supporting services
• Recognize option and existence values
• The potential value of the resource for future use
• the intrinsic value of some asset, normally natural /environmental, derived from the asset's existence alone.
• Find creative ways to deal with differences between:
• Public values versus private values
• Immediate versus sustainable or long-term return
Economic benefits under alternative management
• When the economic value of sustainable management has been compared to the value of converting the ecosystem or unsustainable practices, managing the system more sustainably had the greatest long-term benefits.
• However, immediate monetary benefits favor unsustainable management
• Thus, market failure to value ecosystem services
What are the additional values?
• Tropical forest, Cameroon:
• Sediment and flood control, carbon sequestration, option values
• Mangrove forest vs shrimp farm:
• Timber, charcoal, fisheries, storm protection
• Freshwater marshes to agriculture:
• Cost of drainage subsidies, loss of fishing, hunting, trapping
• Timber harvest, Cambodia
• Swidden agriculture, non-wood products, watershed protection, carbon storage
Take-home messages
• Biodiversity supports ecosystem services
• Provisioning, regulating, cultural, supporting
• Both diversity and redundancy have value
• Current valuation typically excludes services, option and intrinsic values
• Unsustainable practices often are enabled by subsidies, private ownership, immediate benefits
• A fuller valuation can show benefits of sustainable practices

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