Lec 15, 17, 18 Flashcards
Biodiversity
AKA Biological diversity
Refers to the number of species (or families, phyla, etc.) within a community, as well as the relative abundance of each species (family, phylum, etc.)
2 components of Biodiversity
1) Richness: the number of species within the community
2) Evenness: The relative abundance of each species within the community (the distribution of individuals among species)
Biodiversity Example
Consider 2 communities (A and B) with four species each
Species richness (# species) is EQUAL
Both communities consist of 20 total individuals
Is species diversity equal?
It depends on evenness (the distribution of individuals among the species)
Community B has greater evenness and therefore greater diversity
Estimating Species Richness
2 common methods employed:
1) Species accumulation curves (graphical approach)
2) Jackknife Estimates (equation approach)
Measuring Species Diversity
2 common methods employed:
1) Rank abundance curves (graphical approach)
2) Diversity indices (equation approach)
Species Accumulation Curves
Plotting the number of species observed on y-axis, against sampling inteknsity on x-axis
These curves ALWAYS start at the origin (0)
Very accurate approach to determine species richness; not always practical, though
Jackknife Estimates
Estimates of species richness based on number of rare species observes
Sactual = Ssampled + (n-1/n)K
Where K = number of rare species
n = number of plots
Rank Abundance Curves
Abundance of each species on the y-axis ranked in order from most abundant to least abundant on the x-axis
Y-axis is LOG-TRANSFORMED
We will usually see the CURVE, not the bars
Forms 3 types of curves:
1) Broken stick: High richness + High evenness = High diversity; present in TROPICAL (rainforests, coral reefs)
2) Log Normal: High richness + Moderate Evenness = Intermediate diversity; present in TEMPERATE (grasslands, shrubs)
3) Geometric Series: Low richness + low evenness = Low Diversity; present in HIGH ALTITUDE/LATITUDE (Alpine, tundra)
Diversity Indices (Index singular)
Equations that combine richness AND evenness into one single value
2 common types:
1) Simpson’s Index (SDI)
- -SDI = 1 - Epi^2
- -Emphasize richness
- -pi = proportional abundance of each species
- -More common method now
2) Shannon’s Index (H’)
- -H’ = -Epi lnpi
- -Emphasize Evenness
- -Note: E is actually supposed to be “summation”
Patterns of Biodiversity: Latitude
Biodiversity is GREATEST near the equator and DECREASES with increasing latitude (toward the poles)
Related to this is the DECREASE in diversity seen with increasing elevation or depth (deep ocean has LOWER diversity than shallow/surface)
I) The peninsula effect demonstrates that diversity at similar latitudes is LOWER in peninsulas than in landmasses with larger areas
II) The equilibrium theory of island biogeography (Robert MacArthur and E.O. WIlson, 1967) states that species richness on islands depends on the size of the island, as well as the distance from the mainland
–Emphasize species richness
The number of species on an island reflects a balance between extinction and immigration (colonization) rates
Extinction rates should be GREATER on SMALLER islands
Immigration rates should be greater on islands nearer the mainland
The equilibrium theory of island biogeography applies to the biodiversity of isolated areas on land (such as mountain tops and lakes) in addition to isolated oceanic islands
Patterns of Biodiversity: Latitude - Possible Explanations
a) Productivity: HIGHER at equator, GREATER diversity associated with HIGH productivity
b) Long-term climatic stability: The tropics provide a refuge fro species when conditions are unfavorable elsewhere
- -During Ice Ages, glaciers covered all but the equatorial regions
- –Drove a lot of species to the tropics
c) Available Land Area: A GREATER amount of land near the equator provides MORE habitat and therefore supports GREATER diversity
Patterns of Biodiversity: Habitat Heterogeneity
A complex topography and patchy vegetation structure provide different kinds of habitat and therefore increase diversity
Exemplified by the bird species diversity versus foliage height diversity studies conducted by Robert MacArthur (1961)
Heterogeneous habitat has GREATER diversity than homogeneous (multiple plants and life forms vs single type of plant)
Patterns of Biodiversity: Interactions among species
a) Mutualism and commensalism: INCREASE biodiversity by allowing species to survive where they otherwise would not
- -Example: Mycorrhizal fungi (+,+), ecosystem engineers (0,+)
b) Competition and amensalism: Can DECREASE biodiversity if competitive exclusion results
- -Can INCREASE biodiversity if resource partitioning and niche differentiation result
c) Predation, herbivory, and parasitism: Can DECREASE diversity if the predator feeds on many different species
- -Can INCREASE the diversity if the predator feeds on the dominant competitor in the community = Evenness increases, thus diversity increases
- -This allows the competitively inferior species to survive
Patterns of Biodiversity: Disturbance
Disturbances can also slow competitive exclusion by decreasing the dominant competitor’s population size, thereby increasing diversity
-Smaller disturbance
Too much disturbance will decrease diversity by destroying the entire community
-Big disturbance
The INTERMEDIATE DISTURBANCE HYPOTHESIS states that an intermediate frequency and intensity of disturbance is best for maximizing biodiversity
