Download Defining biodiversity

Conservation Ecology – Defining Biodiversity
Timothy Bonebrake – January 24 2014
I. What is Biodiversity?
The Diversity of Life – Edward O. Wilson
Convention on Biological Diversity - “Biological diversity’ means the variability among
living organisms from all sources including… terrestrial, marine and other aquatic
ecosystems and the ecological complexes of which they are part; this includes diversity
within species, between species and of ecosystems.”
1. Biodiversity is hierarchical and makes up all levels of biological organization
including genetic, species and ecosystems (among many others, e.g.
molecular, populations, communities, landscapes).
2. Though we tend to focus on genetic, species and ecosystem diversity, the
world is very diverse at all levels including individuals (1030 prokaryotes)
and populations (109 pops).
II. Genetic Diversity
Gaston – “the components of genetic coding that structures organisms (nucleotides,
genes, chromosomes) and variation in the genetic make-up within a population and
between populations.”
Definitions from Mark Ridley’s Evolution
1. Chromosomes – structures in the cell nucleus that carry the DNA.
2. DNA - (deoxyribose nucleic acid) provides the physical mechanism of
heredity in all living creatures. The DNA molecule consists of a sequence of
units; each unit, called a nucleotide, consists of a phosphate and a sugar
group with a base attached. There are four different bases: adenosine,
cytosine, thymine and guanine. Triplets of bases, called codons, code for
amino acids. (coding – exons, non-coding – introns)
3. Gene - a sequence of nucleotides coding for a protein (or, in some cases, part
of a protein). A gene may exist in alternative forms, called alleles.
4. Locus (Loci) - the location at some point on a chromosome in the DNA
occupied by a particular gene.
5. Genotype -> Phenotype
6. Variation in genetic diversity ultimately comes from mutation, e.g. single
nucleotide substitution.
7. Genetic drift, population size/ structure and natural selection can change
genetic diversity in addition to mutation.
III. Species Diversity
1. What is a species? There are over 20 species definitions!
a. Biological Species Concept - species can interbreed with one another developed by Ernst Mayr (1942) in Systematics and the Origin of
Species -a widespread definition -what about asexual species? -what
about individuals separated by space or time?
b. Evolutionary Significant Units - -substantially reproductively isolated
(thus allowing for evolutionary distinctiveness) -evolutionary legacy
for a species -reciprocally monophyletic (e.g. reptiles are paraphyletic
unless you include birds)
i.
“A monophyletic group is a group which contains all the
descendants of a common ancestor: the group has a
common ancestor unique to itself.”
ii.
“A paraphyletic group contains some, but not all, of the
descendants from a common ancestor.”
http://www.conservationmagazine.org/2008/07/what-really-is-an-evolutionarilysignificant-unit/
2. 8.7 million species estimated globally – 1.2 million described
a. 350,000 species of beetles described (a huge proportion!)
b. Difficulties in estimating species diversity include:
i. understudied species (prokaryotes, parasites) and
understudied habitats (deep sea, forest canopy)
j. cryptic species (i.e. one species is actually many species, e.g.
the moth species Astraptes fulgerator which is ten species in
one!).
k. “Lumpers” vs. “Splitters”
3. The number of species (genera, families etc.) have changed markedly
through time with major “mass extinction events”.
4. Species/ biodiversity is not distributed evenly across the earth and species
are especially concentrated in the tropics/ low latitudes.
5. Are the tropics a cradle (high origination, many species born), a museum
(extinction rates low) or both? Some data suggest both (Jablonski et al. 2006)
and further suggest that species migrate out of the tropics and supply
diversity to the rest of the world (“out of the tropics”).
http://www.conservationmagazine.org/2008/07/tropics-are-the-cradle-ofbiodiversity/
IV. Ecosystem Diversity
1. Ecosystem diversity -variety of habitats, biomes, ecoregions within a space or
landscape -hard to define - only really relevant at larger spatial scales
2. WWF defines 867 terrestrial and 232 marine ecoregions and a recent
phylogenetic study of birds, amphibians and mammals defines 20 new
zoogeographic regions.