Download Lecture 9/24/04 -- Species Concepts and Biological Diversity

Taxonomy
Species Concepts, &
Biological Diversity
EEOB 661
27 September 2004
Hierarchical Indicators of
Biodiversity
• Genetics – (population)
• Population – Species
• Community- Ecosystem
• Landscape –
* Each with: Composition, Structure, &
Function (M&C Fig. E4A)
Levels of Biological Diversity
Genetic
Population
Demographic
Community
Landscape
From Temple 1991, drawing by T. Sayre
Genetic (population)
Composition
• Allelic diversity
• Presence/absence of rare alleles
Structure
• Heterozygosity & genetic structure
• Phenotypic polymorphism
Function
• Inbreeding & outbreeding rate
POPULATION-SPECIES
(demographics)
Composition
• Absolute and relative abundance, density,
Structure
• Sex ratio, age distribution
• Distribution
Function
• Natality, Mortality, Immigration, Emigration
• Population growth and fluctuation
• Behavioral patterns and processes
COMMUNITY-ECOSYSTEM
Composition
• Species richness
• Species diversity (evenness, e.g.,Shannon-Weiner Index)
• Gilds & associations
Structure
• horizontal & vertical foliage profiles
• Range of ages and seral stages
Function
• Frequency & intensity of disturbances
• Flow of energy and Cycling of nutrients
LANDSCAPE
Composition
• Variety and distribution of Communities
Structure
• Patch size frequency distribution
• Edge zone: interior zone ratio
Function
• Rates of nutrient & energy, and biological
transfer between different communities
SYSTEMATICS and TAXONOMY
Systematics: study of phenotypic variation within
& between taxa to reveal phylogenetic relationships
Taxonomy: Naming & ranking of taxa with a goal
of stable, universal nomenclature and a system
for information storage & retrieval.
Several schools but phylogenetics (cladistics) is
most widely practiced and accepted
Taxon: a group of organisms recognized as a formal
unit in a hierarchial system of classification
Central Position of Species in
Biodiversity
• Importance compared to taxa in higher categories,
i.e., genus, family, or class
• Species are real and distinct (?). Real because
they are functional units in nature. Distinct
because of common gene pool and limit gene flow
between species
• Species are also real because many can be
recognized by both laymen professional biologists
• Typological vs. populational views of species
Species: Concepts & Definitions
Biological species concept (traditional)
• Reproductive isolation of sexually reproducing species
• Practical and widely used (basis for nearly all alpha taxonomy)
• Problems & limitations?
Cladistic Species Concept
• The smallest cluster of organisms diagnosable by a
synapomorphy
• Popular among systemitists
• Less so among alpha taxonomists
• Provides valid basis for sup-specific taxa (~ subspecies)
Cladogram of Chordates
Hickman et al Fig.15.3 (2003) - See also, M&C Fig.3.3
Synapomorphies
Wilson 1992 –
Diversity of Life
Patterns in Biodiversity
• Taxonomic Diveristy (richness of higher taxa)
• Species richness of higher taxa
i.e., number species per taxon
• Richness of taxa over geological time
• Patterns of local species richness
• Global patterns in species richness
Hickman et al. 2003
Patterns in Biodiversity
• Taxonomic Diversity (richness of higher taxa)
• Species richness of higher taxa
i.e., number species per taxon
• Richness of taxa over geological time
• Patterns of local species richness:
Point richness = number in single spot (sample plot)
α = total number in a small, homogeneous area
β = rate of change/ turnover across a landscape
Estimates of number of species on
Earth
• Based on the rate at which new species
are being discovered per taxon.
• Projection of a “regression line” based on
body size and species richness
• Terry Erwin’s projection from tropical
rainforest beetle species richness
Estimating number of species from rate of new discoveries
Estimates of number of species on
Earth
• Based on the rate at which new species
are discovered per taxon.
• Projection of a “regression line” based on
body size and species richness
• Terry Erwin’s projection from tropical
rainforest beetle species richness
Dr. Terry Erwin, Entomologist, Smithsonian Institution
*
/ 70 species x 41,389 =
Calculations based on 70 tree species/ha, which projects to about 30 million arthropods worldwide
Erwin, TL 1982. Tropical forests: Their richness in Coleoptera and other arthropod species. Coleopt. Bull. 36:74-75.
Patterns in Biodiversity
• Taxonomic Diversity (richness of higher taxa)
• Species richness of higher taxa
i.e., number species per taxon
• Richness of taxa over geological time
• Patterns of local species richness
• Global patterns in species richness
Patterns in Alpha richness:
Why are there so many species in the tropics?
• High Primary Productivity
• Habitat size (island biogeography)
• Habitat complexity (heterogeneity)