Biodiversity
&
Biogeography
N. Adam Smith
Postdoctoral Fellow
National Evolutionary Synthesis Center
Part I: Biodiversity
What is biodiversity?
• “Biodiversity or biological
diversity is the variety of
life in all its forms, levels
and combinations,
including
– ecosystem diversity,
– species diversity, and
– genetic diversity”
(IUCN, UNEP, and WWF
Rio Summit on Biodiversity, 1991)
Copyright (c) 2012 Richard Ling
Genetic Diversity
• The range of genetic
material present in a gene
pool or population of a
species
• High genetic diversity is
thought to make
populations more
resilient to climate
change, environmental
perturbation, and disease
• Low genetic diversity can
cause many problems…
Low Genetic Diversity in Cheetahs
Cheetahs went through a population
bottleneck at the end of the last ice
age which reduced genetic diversity.
Coupled with intense hunting and slow
population growth, genetic diversity
has not recovered.
Problems facing cheetahs
• Habitat loss and human encroachment
• Competition with other predators and predation
by lions and hyenas in protected areas
• Continued trapping and killing of cheetahs on
farmland (sometimes legally!)
• Low genetic variation leads to:
– Abnormal reproductive traits
– Increased disease susceptibility
– Poor reproductive performance
in captivity
Species diversity
• the variety of species per
unit area
– i.e., the number of
species in your study site
Ecosystem diversity
• The range of different habitats in an
ecosystem, community or biome
associated with the variety of niches that
may be exploited by different species.
What factors lead to biodiversity loss?
• Natural hazards (flooding, volcanic activity,
fires)
• Global catastrophe (meteors, climate change)
• Habitat degradation, fragmentation and loss
• Introduction of non-native species, genetically
modified organisms, and monocultures
• pollution
• Hunting, collecting, harvesting
LOSS OF BIODIVERSITY AT A SPECIES LEVEL
LEADS TO EXTINCTION
What makes some species more prone
to extinction?
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Small population
Specialized habitat
Restricted food source
Low reproductive potential (large mammals)
Accumulation of toxins (whales)
A prominent predator so killed by humans
(e.g., cheetahs)
• Migrates long distances
example: Polar Bears
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Large and conspicuous
Population size is shrinking
Food source and warm fur
Huge home range
– Less likely to find mates
• Low reproductive potential
• Top predator
What else makes a species prone to
extinction:
• Living on an island
– High degree of
endemism
– Small populations
– Lower genetic diversity
– Vulnerable to introduced
predators
– EXAMPLE: GALAPAGOS
What else makes a species prone to
extinction:
• Food for thought – does
something have to be
surrounded by water to
be an island?
– Habitat fragmentation
– Micro-niche partitioning
EXAMPLES: AFRICAN
CICHLIDS
Measuring extinction
• Measuring extinction is very difficult
• How can you know when an organism is gone?
• First you had to know it was there, then
somebody needs to count it!
– Charismatic megafauna are more likely to be
missed than cryptic microfauna.
Charismatic Megafauna
• Mammals, birds, reptiles are well
described
• Fish, amphibians, invertebrates,
and even plants are relatively
poorly described
• Extinctions can go unnoticed
– 120 years ago, the Gilbert Islands
(central Pacific) were home to 3
shark species no longer found there
– Evidence from fishing weapons
fashioned from shark’s teeth!
Where is biodiversity the highest?
• Mammal Diversity –
highest in the tropics
• Bat diversity accounts
for a large proportion of
this!
• Latitudinal gradients in
species richness is a
general trend for most
terrestrial plants and
animals
Buckley et al 2010
Biodiversity Hotspots
Species Rich, High Endemism, Threatened
Benefits of Biodiversity
• All of our food comes from other organisms
– Many wild plant species could make important
contributions to human food supplies.
• Rare species provide important medicines
– More than half of all prescription drugs contain
some natural product.
• Biodiversity can support ecosystem stability
• Biodiversity has aesthetic and cultural benefits
• Can generate income through to ecotourism
IUCN Red List
• Attempts to survey and quantify the state of
the planets “at risk” species and governs their
international trade
• Has weaknesses
– probably underestimates the problems
– Some taxa much better surveyed than others
(mammals vs arthropods)
Part II: Biogeography
Subjects Used in Biogeography
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Anatomy
Physiology
Taxonomy
Developmental Biology
Evolution
Geology
Geography
Ecology
Climatology
Paleontology
Persistent Questions in Biogeography
• What enables a species to live where it does,
and what prevents it from colonizing other
areas?
• What are a species closest relatives and
where can they be found? Where did its
ancestors live?
• How have historical events shaped a
species’ distribution?
Persistent Themes in Biogeography
• Classifying geographic regions based on their
biota
• Reconstructing historical development or lineages
and biota, including their origin, spread, and
diversification
• Explaining differences in numbers and types of
species among geographic areas, and along
geographic gradients
Alfred Russel Wallace
“The Man Who Knew Islands”
Malay Archipelago
Figure 9.4
In 1857 Wallace wrote:
“A consideration of the
birds had led us at some
length into this
subject,…how the existing
distribution of species has
arisen, or strictly connect it
with those changes of
surface which all countries
have undergone.”
Cassowaries
on
Aru Islands
What Wallace was trying to say
1. Variation occurs in nature
2. Variation may result in different
reproductive success.
3. Species (populations) with higher
fitness will persist
4. This leads to divergence from
ancestral species.
Islands can serve as a laboratory for the study of
biogeography. The biota of an island is simpler than that of
a continental area, and the interactions are easier to
understand.
Some flying animals,
such as birds and bats,
are capable of reaching
even very distant
islands.
Some plants have developed seeds or
fruits that can be carried in the sea
without being harmed.
Island life is probably more hazardous than that
on the mainland. For one thing, catastrophic
events have more severe effects. There is
typically no place to hide.
Also, when a species is lost by extinction, it is
more difficult to replace it through
immigration than in a mainland situation.
For this reason, islands tend to support fewer
species than mainland areas of similar size
(i.e., lower species diversity).
Rules of Island Biogeography
• Islands closer to a land mass have a higher
probability of colonization
• Older islands are more likely to be colonized
• Larger islands should have more species
• Geographic isolation reduces gene flow
between populations
• Over time, colonial populations diverge due to
selection, mutation, and/or drift
Island Biogeography: Madagascar
• 4th largest island in
the world
• separated from India
~80-90mya
• High endemism due
to isolation
• A biodiversity
hotspot
Island Biogeography: Madagascar
• 4th largest island in the
world
• separated from India
~80-90mya
• High endemism due to
isolation
• A biodiversity hotspot
• Lemurs
– ~100 extant species
– Colonized Madagascar
from Africa 62-65mya
Lemur Distributions – a function of
hydrology or microclimate?
• Pearson & Raxworthy
2009
• Do species
boundaries in lemurs
correspond better
with watershed
boundaries or with
climatic differences?
Lemur Distributions – a function of
hydrology or microclimate?
• Pearson & Raxworthy
2009
• Do species
boundaries in lemurs
correspond better
with watershed
boundaries or with
climatic differences?
• Found BOTH were
important