TaxonomySpecies 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)

Population

Community

Landscape

Levels of Biological Diversity

Genetic

Demographic

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 & associationsStructure • 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 relationshipsTaxonomy: 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 ChordatesHickman 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

*

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.

/ 70 species x 41,389 =

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)