Lecture 22 Notes

Biological diversity defined

  • Biodiversity refers to variation among organisms and ecological systems at all levels
    • genetic diversity
    • ecological diversity
    • phylogenic diversity
    • ecosystem and biome diversity

What is biodiversity?

  • The variety and variability among living organisms and the ecological complexes in which they occur
  • Number and variety of species, ecological systems, and the genetic variability they contain
  • In its narrowest sense, biodiversity refers to the number of species on the planet

How many species exist?

  • ~1.8 million species are "known to science" (ie. classified by a specialist)
  • Experts estimate that there are 10 to 30 million species on Earth
  • Except for land vertebrates and flowering plants, there are many more species that have yet to be identified than those that have
  • New discoveries of large mammals are noteworthy
    • Not entirely unusual to discover that one species is actually two
  • Plant diversity of the world primarily consists of flowering plants, which are mainly on land
  • The vast majority of known animal species are insects

Phyletic v. Species Diversity

  • Approx 35 phyla
  • Only nine phyla contain over 96% of animal species
  • Most species (mostly insects) are terrestrial, but mos phyla are marine

Biological Diversity Patterns

  • Rank abundance plots display from commonest to rarest
    • Reveals that a few species are common, but many are rare
  • Species richness can vary widely among locations and regions
  • Pronounced latitudinal gradients in species richness

The Geography of Life

  • Number of species typically greater near equator and declines with movement toward the poles
  • Certain areas are home to an unusually rich local diversity ("hotspots" idea)
  • Certain areas (especially islands) contain species unique to that locale (endemism)
  • Most accepted theory for latitudinal gradient is that higher productivity leads to higher biodiversity
    • More species, more interactions, smaller niches (more specialization)

Species diversity and functional diversity

  • Upstream/downstream example
  • Species diversity incrases as stream becomes larger and has more habitat and food diversity
  • Upstream has fewer functional feeding groups
  • More species diversity -> more functional diversity

Biological diversity - measurement

  • Often focuses just on species richness, but also should recognize variation in relative abundance
  • Species richness increases with area sampled

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 turnover)
  • Various similarity indices compare the species of two communities (inverse of Beta)
    • As distance increases, similarity decreases

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

Value of Biodiversity

  • Provide provisioning services
    • Food
    • Fiber
    • Genetic resources
    • Medicines and pharmaceuticals
    • Fresh water
  • Regulating services
    • Pollination
    • Pest regulation and invasion resistance
    • Climate regulation
    • Water purification and flood control
    • Erosion regulation
    • Natural hazard regulation
  • Supporting services
    • Soil formation
    • Plant productivity
    • Nutrient cycling
    • Water cycling


  • 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

Hypothesis that healthy ecosystems depend on more species

  • Biodiversity —> Productivity
  • Diversity keeps an ecosystem stable
  • Rationale
    • Complementary - When species have more 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, their loss can be particularly serious

Costs of failign to protect biodiversity and services

  • Control of invasive species costs hundreds of millions of dollars
  • Flood damage costs from loss of wetlands
  • Storm damage from mangrove loss
  • Emergence of infectious disease
  • Loss of "opportunity value"

Subsidies can lead to unsustainable practices

  • Encourage agricultural and fish harvest practices that are not justified on their economics and ma not be sustainable in terms of resource use

More inclusive valuation can show benefits of sustainable practices

  • Include explicit monetary values for regulating, cultural and supporting services
  • Recognize option and existance values
    • Potential value of resource for future use
    • Intrinsic value of some asset derived from existance alone
  • Find creative ways to deal with differences between public values vs. private values and immediate vs. sustainable or long-term return
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