Biodiversity Lecture 3

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Biodiversity is
the totality of all genes, species and ecosystems in one location.
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Biodiversity is not distributed evenly
on Earth
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Marine biodiversity tends to be highest
along coasts in the Western Pacific
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There are latitudinal gradients
in species diversity
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Biodiversity generally tends to cluster
in hotspots,
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Biodiversity is the number of species in an ecosystem =
speciation – extinction
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Differences between organisms are caused by differences in their
genetic material (DNA)
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Different forms of a gene =
alleles
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Evolution =
a change in the genetic material (genotype) of a population of organisms from one generation to the next. Thus can change an organism’s appearance (phenotype)
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Genotype
describes the genetic make-up of an organism (the combination of alleles).
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Phenotype
describes the observable, physical characteristics that an organism has. This is often related to a particular gene.
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Genetic drift –
is the change in the frequency of a gene variant (allele) in a population due to random sampling
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Genetic drift may cause gene variants
to disappear completely and thereby reduce genetic variation
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Genetic drift does
not produce adaptation
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When was on hte orgin of the species published
1859
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Natural selection
“A process in which individual organisms that possess favourable traits are more likely to survive and reproduce.”
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Concept of
fitness (Selction of the fitest)
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Peppered moth and the industrial revolution Sulphur pollution killed
white lichens Trees became darker Dark form, which was rare, became common in southern and eastern UK.
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Speciation is the
evolutionary process by which reproductively isolated biological populations evolve to become distinct species.
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Biological species concept:
“species are groups of interbreeding natural populations that are reproductively isolated from other such groups.”
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Biological species concept:
The species problem: Asexual reproduction? Bacteria How to define reproductive isolation? Hybrids
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The species problem is a mixture of difficult related questions that often come up when biologists define the word "species
biological reality means that a definition that works well for some organisms (e.g., birds) will be useless for others (e.g., bacteria).
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Evolutionary species concept:
an entity composed of organisms that maintains its identity from other such entities through time and over space, and has its own independent evolutionary fate and historical tendency
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Problems with evolutionary species concept
gaps in the fossil record impose arbitrary boundaries between species, especially those undergoing gradual size/shape evolution.
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All species of land plant shared a common ancestor which lived
500 million years ago
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Genetic changes are required for
speciation
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Types of non-physical seperation:
Parapatric and Sympatric
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Types of physical sseperation:
Allopatric and Peripatric
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Allopatric
occurs when biological populations of the same species become vicariant, or isolated from each other to an extent that prevents or interferes with genetic interchange.” PHYSICAL SEPERATION
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Peripatric speciation
Jump dispersal Isolated island Small population Genetic drift New environment Natural selection Rapid divergence ( one popultion much smaller than the other)
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. One possible consequence of peripatric speciation is that a geographically widespread ancestral species becomes paraphyletic, thereby becoming a
paraspecies.
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Parapatric speciation
No barrier Environmental gradient Unequal gene flow Evolve differences
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parapatry is the relationship between
organisms whose ranges do not significantly overlap but are immediately adjacent to each other; they only occur together in a narrow contact zone. This geographical distribution is opposed to sympatry (same area) and allopatry or peripatry (two cases
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Sympatric speciation
same population (no geographical barrier) Very rare in animals - Disruptive selection (selection against the average). Chromosomal changes – in plants - different number of chromosomes (polyploid) hybrids
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Vicariance:
The separation of a group of organisms by a geographic barrier, resulting in differentiation of the original group into new varieties or species.
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Examples of vicariance events:
Movement of continents Sea-level change Formation of mountain ranges
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Geographical isolation and vicariance events leads to
ALLOPATRIC SPECIATION
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Mediterranean Sea
Mediterranean is a species-rich area Changes in sea level believed to have separated populations High degree of endemism Timing of speciation in Cyclamen appears linked to timing of major sea-level fluctuations
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Plate tectonics and continental drift
Continents have moved around Massive vicariance events Simultaneous speciation in multiple taxonomic lines
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Mountain building for example in Andes
High biodiversity Many examples of similar species on either side of the range Mountain building considered to have caused allopatric speciation
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Hot spot =
weak point in the mantle were magma is released
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Volcanic activity leads to island formation As the ocean plate passes over the hotspot an island chain forms Repeated
PERIPATRIC speciation
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DARWIN’S FINCHES Classic example of
peripatric speciation Galapagos Islands Also a island archipelago formed over a hotspot
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Is biodiversity important?
Redundancy Diversity – stability hypothesis Diversity – productivity hypothesis
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Redundancy
More than one species performing a similar role within an ecosystem. If a species is removed and the ecosystem remains constant, it was redundant.
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Problems with Redundancy:
Species might be redundant in one community but not in others.
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Diversity and stability: Tilman 2006
Stability = consistency over time 10-year grassland experiment More species = more stable primary productivity
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More on Tilman 2001
Diversity increased productivity More species in grassland more biomass produced
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Other cards in this set

Card 2

Front

Biodiversity is not distributed evenly

Back

on Earth

Card 3

Front

Marine biodiversity tends to be highest

Back

Preview of the front of card 3

Card 4

Front

There are latitudinal gradients

Back

Preview of the front of card 4

Card 5

Front

Biodiversity generally tends to cluster

Back

Preview of the front of card 5
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