Download TOL III: Animals

Introduction to Biodiversity
ASAB – NUST
Fall 2012
The variety of life
is biological diversity.
Use of the term
“biological diversity”
in its current sense began
in 1980.
Biodiversity = biological diversity
Coined in 1985 for a conference, the
proceedings of which were published
as the book “Biodiversity”edited
by E. O. Wilson.
What does it mean?
The variability among living organisms from
all sources including terrestrial and aquatic
systems and the ecological complexes of
which they are a part; diversity within
species, among species, and of ecosystems;
interactions at all levels among organisms.
From Frankel et al., 1995, The conservation of plant biodiversity.
Fundamental levels of
organization
• Genetic
• Organismal
• Ecological
Ecological Diversity
• Communities of species, their
interactions
• Communities + resources (energy,
nutrients, etc.) = ecosystem
• Measured primarily in terms of
vegetation but relative abundance of
species also important
• No unique definition and classification
at the global level
Organismal Diversity
• Individuals, species
• Mostly measured by numbers of
species
• Estimated 1.7 million species
described to date
• Estimated total number ranges from 2
to 50 million (up to 100 million)
species
• Mostly microorganisms and insects
Genetic diversity
• Heritable variation within and between
populations of organisms
• Encoded in the sequence of 4 base-pairs
that make up DNA
• Arises by mutations in genes
and chromosomes
• Very small fraction of genetic
diversity is outwardly expressed
Why care about what we can’t
see?
• Genetic variation enables evolutionary
change and artificial selection
• Estimated 109 different genes across
the Earth’s biota
• Represents a largely untapped genetic
library
Ecosystems
Scale of relationships
Molecules
Genes
Cells
Organisms (individuals)
Populations
Species
Communities
Ecosystems
Biomes
Biosphere
smallest
largest
Ecological Principles
• Everything is connected to everything
else.
• Everything has to go somewhere.
• There is no free lunch in nature.
(Or, you don’t get something for
nothing.)
Communities
Community: all of the organisms in
a given area (habitat) and their
interactions.
Ecosystems
Ecosystem =
biotic community + abiotic environment
e.g., flower +
pollinator
Energy from the sun
Precipitation, etc.
Nutrients such
as carbon, etc.
Ecosystems
The scale can be…
very small
(a leaf)
to
very large
(global)
Ecosystems
Energy flow is one-way
through ecosystems.
Materials (nutrients) are cycled
through ecosystems.
Ecosystems—1) Energy processes
Photosynthesis
Respiration
Ecosystems—1) Energy processes
Photosynthesis transforms radiant (solar)
energy into chemical energy (stored as
chemical bonds in sugars and carbohydrates.
sun
CO2
O2
plant
sugars,
starches
in cells
Ecosystems—1) Energy processes
Respiration is a step-by-step process that
allows organisms to use the energy stored
the chemical bonds manufactured during
photosynthesis.
sugars,
starches
O2
energy for cellular work
+
heat
Ecosystems—2) energy users
There are three main categories of organisms
according to the ecological roles they play:
1) Producers (primary producers, autotrophs)
2) Consumers (heterotrophs)
3) Decomposers (a special type of consumer)
Ecosystems—2) energy users
Producers capture the sun’s energy and transform
it into chemical energy through photosynthesis.
plants
+
algae
+
blue-green algae
Ecosystems—2) energy users
Consumers are organisms that eat other organisms.
Herbivores eat producers directly, carnivores eat
other consumers.
Examples:
panda eating bamboo,
bird eating nectar or flowers
snail grazing on algae
Herbivores (grazers, primary consumers)
Ecosystems—2) energy users
Consumers are organisms that eat other organisms.
Herbivores eat producers directly, carnivores eat
other consumers.
Examples: limpkin eating apple snails
American alligator
amoeba
Carnivores (secondary or tertiary consumers)
Ecosystems—2) energy users
Decomposers (detritivores) are a type of consumer
that feed on dead organic matter—they can obtain
this from any of the other trophic levels.
fungi and many bacteria
but also scavengers such
as vultures
Ecosystems—3) Energy flow
Energy flow is one-way
through ecosystems.
WHY?
Ecosystems—3) Energy flow
In any energy transformation (e.g., from
one trophic level* to another) there is a net
loss of usable energy.
*Trophic level: feeding relationships, who is
eating whom.
Ecosystems—3) Energy flow
Lost as heat
decomposer
sun
plant
decomposer
cow
Lost as heat
decomposer
jaguar
Ecosystems—3) Energy flow
Lost as heat
decomposer
decomposer
decomposer
90%
90%
90%
10%
10%
10%
sun
1-5%
plant
10%
cow
10%
jaguar
captured
90%
90%
Lost as heat
Ecosystems—3) Energy flow
Carnivores, especially
secondary or tertiary
ones, are rare.
carnivores
herbivores
producers
Ecosystems—Materials
Water and elements (e.g., carbon, nitrogen) and
other materials are cycled through ecosystems.
They move between organic and inorganic phases
by both biotic and abiotic processes.
The diversity of microorganisms (especially
bacteria) controls key steps in various cycles
(see textbook examples of the nitrogen cycle,
the carbon cycle, etc.)
Ecosystem Services
• Services provided by biodiversity that
keep ecosystems functioning.
• Often thought of in terms of human
wellbeing.
• Indirect-use value of biodiversity
(these services are not factored into
the marketplace).
Ecosystem Services—examples
• Photosynthesis
• Nutrient cycling
• Decomposition
Tree of Life III: Eukaryotes
(Fungi and Animals)
ASAB - NUST
Fall 2012
TOL III: Fungi and Animals
• Fungi and animals probably share a
common ancestor with
choanoflagellates (collar-flagellates)
based on genetic data
• Cell wall components and other
complex biosynthetic pathways are
similar between fungi and animals
TOL III: Fungi and Animals
fungi
single-celled
protistan
ancestor
choanoflagellates
animals
TOL III: Fungi
• Primarily terrestrial
• No motile cells except in reproductive
cells of chytrids
• Chitin in cell walls
• Unique features of chromosomes and
nuclear division
• Dominant part of life cycle has only
one set of chromosomes per nucleus
TOL III: Fungi
• Most are filamentous, multicellular; a
few are unicellular (chytrids, yeasts)
• Oldest fossils 450-500 million years
ago
• About 70,000 species described;
estimated to be up to 1.5 million
• 4 lineages: chytrids, zygomycetes,
ascomycetes, basidiomycetes
TOL III: Fungi
chytrids
zygos
ascos
basidios
TOL III: Fungi
• Consumers by absorption
• In addition to natural sources of organic
matter, can obtain nutrition from a wide
variety of man-made substrates (cloth,
paint, leather, waxes, jet fuel,
photographic film, etc.)
• Food-obtaining strategies: decomposers,
parasitic, predaceous, symbiotic
TOL III: Fungi
1) Decomposers: use dead organic matter
through excretion of digestive enzymes
2) Parasitic: obtain organic matter from
living cells; many cause disease this way
(pathogens)
3) Predaceous: trap and kill small organisms
(nematodes, protozoans)
4) Symbiotic: form mutualistic relationships
with other organisms (lichens,
mycorrhizae)
TOL III: Fungi
Structure, Growth and Reproduction
-usually consist of hyphae (threadlike filaments)
-mass of hyphae = mycelium
-grow under a wide range of
conditions
-reproduction mostly sexual by
spores; but asexual reproduction is
common
TOL III: Fungi
fungal mycelium on wood
TOL III: Fungal Diversity
(chytrids)
• Mostly aquatic
• Reproductive cells with a
characteristic flagellum
• Unicellular or multicellular with a
mycelium
• About 750 species
• One cause of frog die-offs
TOL III: Fungal Diversity
(zygomycetes)
•
•
•
•
•
Mostly decomposers, a few parasitic
Multicellular, filamentous
About 600 species known
Best known as the bread molds
About 100 species form mycorrhizae
with plant roots (now thought to
include many more undescribed
species)
TOL III: Fungal Diversity
(ascomycetes)
• Filamentous except for yeasts (unicellular)
• Mostly decomposers or parasitic, some
predaceous or symbiotic
• Over 30,000 described
• Includes most Fungi Imperfecti (e.g.,
penicillium)
• Economic importance: yeasts (bread, beer,
wine); Dutch elm disease, chestnut blight,
ergots; edible fungi (truffles, morels);
antibiotics
TOL III: Fungal Diversity
scarlet cups
ergot on rye
Cordyceps
ascomycetes
TOL III: Fungal diversity
yeast (ascomycete)
bread
wine
beer
TOL III: Fungal Diversity
morels
truffles
edible ascomycetes
TOL III: Fungal Diversity
(basidiomycetes)
• Mainly decomposers and pathogens
• About 25,000 species described
• Ca. 5,000 species involved in
mycorrhizal associations
• Economic importance: edible
(mushrooms, corn smut); poisonous;
pathogens (rusts, smuts); decomposers
(woodrotters)
TOL III: Fungal Symbionts
• Lichen = symbiosis with a green alga
or blue-green alga (cyanobacteria)
• Fungal partner usually an ascomycete,
usually about 90% of the lichen
biomass
• Have a unique biology
• Close to 17,000 species
TOL III: Fungal Symbionts
• Mycorrhiza = symbiosis between a fungus
and a plant root
• Important in evolution of plants and fungi;
allowed exploitation of many more habitats
for both partners
• At least 85% of plants form mycorrhizae
• Involves zygomycetes (endomycorrhizae)
and basidiomycetes (ectomycorrhizae)
TOL III: Mycorrhizal diversity
endomycorrhizae
(zygomycetes)
ectomycorrhizae
(basidiomycetes)
TOL III: Fungi and Animals
fungi
single-celled
protistan
ancestor
choanoflagellates
animals
Tempeh and tofu
Tempeh is made by a natural culturing and controlled fermentation process
that binds soybeans into a cake form, similar to a very firm vegetarian burger
patty
Tofu is made by coagulating soy milk and
pressing the resulting curds. Although premade soy milk may be used, most tofu
producers begin by making their own soy
milk, which is produced by soaking, grinding,
boiling and straining dried (or, less
commonly, fresh) soybeans.
Characteristics features
The original Animal Kingdom proposed by Linnaeus included the protozoans,
sponges, jelly fishes, worms, crabs, insects, spiders, snails, starfishes, sharks, bony
fishes, frogs, lizards, birds and mammals. In general, animals exhibit the following
distinguishing characters.
•The animal body generally exhibits a definite symmetry, form and shape.
•Animals have the capacity to move from place to place in search of their
necessities.
•Growth in animals is determined and occurs proportionately in all parts of the body.
•Animals are generally heterotrophic, obtaining their food from plants and other
animals.
•Animals have the property of irritability - the capacity to respond to a stimulus.
•The cells, which form an animal's body do not have a cell wall.
•Plastids and vacuoles are generally absent and centrioles & lysosomes are
present..
•Animal cells cannot synthesize all the necessary amino acids, vitamins and
coenzymes and as such will have to obtain them from external sources.
•Reserve food is glycogen.
TOL III: Animals (Metazoa)
• Multicellular consumers by
ingestion
• Storage product is animal starch
(glycogen)
• Most have nervous tissue and
muscle tissue (which are unique to
animals)
• Most are mobile
TOL III: Animals
• Gas exchange through aqueous medium
surrounding the organism or through
specialized gas exchange structures
(e.g., gills or lungs)
• Some kind of internal circulation
system present (food, gases,
maintenance of proper water and
mineral concentrations, waste
elimination)
TOL III: Animals
• Animals arose in the oceans from
single-celled protistan ancestors
• The earliest animals appeared at least
1 billion years ago
• Most modern groups of animals
appeared around 600 million years ago
(the Cambrian explosion) in the oceans
TOL III: Animals
• About 35 major modern lineages
(phyla) and several fossil lineages of
animals are known
• In contrast, protists have at least 16
major lineages, plants have 12 modern
and 5 fossil lineages, and fungi have 4
modern lineages
• Over 1 million species of animals are
known; >75% of these are insects
TOL III: Animals
• Of the 35 modern lineages of animals, most
remain aquatic (marine)
• About half of the lineages are exclusively
marine
• Only 5 lineages have adapted to land
(nematodes, annelids, mollusks, arthropods
and chordates represented by vertebrates)
• Only the nematodes, arthropods and
vertebrates have diversified extensively on
land
Fig. 1a. Phylogenetic Tree for Major Phyla of Animal Kingdom
64
Fig.1b. Changes in body plan added (-------)
65
9 Phyla of the Animal kingdom
1)Porifera
6) Mollusca
2)Coelenterata
7) Echinoderm
3)Flatworms
8) Arthropoda
4)Roundworms
9) Chordata
5)Segmented worms
sponges
radiates
annelids
mollusks
& others
arthropods
nematodes
& others
chordates
echinoderms
simplified
evolutionary tree
for the animal kingdom
TOL III: Animals (major
lineages)
• Earliest lineage of animals is the
sponges
• Least specialized of all animals
• Lack any kind of tissues
• Tissue = an integrated group of cells
with a common structure and function
(e.g., muscles, nerves)
sponges
radiates
annelids
mollusks
& others
arthropods
nematodes
& others
presence of tissues
chordates
echinoderms
TOL III: Animals (major
lineages)
• The next major adaptation, after the
evolution of tissues, was the split between
radial vs. bilateral body symmetry
• Radial = parts radiate from the center, any
plane through the animal creates two equal
halves
• Bilateral = has two sides, left and right,
such that a plane through the animal can be
placed only one way to get two equal halves
TOL III: Animals (radiates)
• Radial symmetry an adaptation to a
more sedentary lifestyle in which the
organism stays in one place and meets
the environment equally from all sides
• Radiates (or cnidarians) have stinging
tentacles
• Include the jellyfish, sea anemones,
and corals
sponges
radiates
annelids
mollusks
& others
arthropods
nematodes
& others
chordates
echinoderms
bilateral symmetry
presence of tissues
TOL III: Animals (major
lineages)
• Bilateral symmetry is an adaptation to a
more active lifestyle in which the organism
moves around to obtain food and must
detect and respond to stimuli
• Associated with the concentration of
sensory function into the head
• The three major groups of bilateral animals
exhibit various specializations in the
formation of the body cavity
TOL III: Animals (annelids &
friends)
earthworms (annelids)
leeches on a turtle
banana slug (mollusks)
Phylum Mollusca
(mollusks)*
• Second largest animal phylum
• 93,000 living species (35,000 fossil species)
• Mostly are marine, some freshwater and
terrestrial
• Incredible morphological diversity
*Material thanks to Dr. Jeanne Serb
Class Gastropoda
snails, slugs, sea slugs
Class Cephalopoda
squids, octopus, cuttlefish, nautilus
Adaptations to predatory life style
• Active and very mobile
– Closed circulatory systems
• Camouflage
– Chromatophores in skin
– http://www.youtube.com/watch?
v=SCgtYWUybIE
• Exceptional vision
• Beak to tear prey
• Arms (tentacles) to grip
prey
Class Bivalvia
clams, cockles, mussels, oysters, scallops
TOL III: Animals (arthropods &
friends)
TOL: Arthropods
(current diversity)*
 regardless of how one measures diversity,
the arthropods are among the most
successful lineages
 nearly a million described, w/ estimates of
undescribed species reaching 40 million
 have colonized all major habitats on earth:
nearly all marine, freshwater, and
terrestrial habitats
*material thanks to Dr. Greg Courtney
TOL: Arthropods
Platnick (1992): “Speaking of biodiversity is essentially
equivalent to speaking about arthropods. In terms of
numbers of species, other animal and plant groups are just a
gloss on the arthropod scheme.”
Wilson (1999): “Entomologists often are asked whether
insects will take over if the human race extinguishes
itself. This is an example of a wrong question inviting and
irrelevant answer: insects have already taken over… Today
about a billion billion insects are alive at any given time…
Their species, most of which lack a scientific name,
number in to the millions… The human race is a newcomer
dwelling among the masses… with a tenuous grip on the
planet. Insects can thrive without us, but we and most
other land organisms would perish without them.”
Arthropoda:
Makes up 75% of the animal kingdom
Basic Characteristics:
hard external skeleton
segmented body
jointed legs
Ex: beetle, milli & centipede, spider, crab
TOL: Arthropods
(major groups)
• 1) Chelicerates – includes spiders,
mites, scorpions
• 2) Crustaceans – includes crabs,
shrimp, copepods, barnacles, etc.
• 3) Uniramia – includes millipedes,
centipedes, insects
• 4) Trilobites – extinct, known only
from fossils
TOL: Arthropods
(major features)
• 1) Body segmented internally and
externally
• 2) Tagmosis (regional body
specialization of groups of segments:
e.g., head, thorax, abdomen)
• 3) Chitinous exoskeleton (with thin
areas between segments)
• 4) Segmented (jointed) appendages
• 5) Cephalization well developed
Arthropods
Reasons for success
1) Small size
Advantages:
a) assists escape, movement in confined
spaces
b) need smaller bits of resources
Disadvantages:
a) small surface : volume ratio, which leads to
increased heat and water loss
Arthropods
Reasons for success
2) Exoskeleton
Advantages:
a) protection - much stronger than internal skeleton
b) greater surface area for muscle attachment
c) helps prevent desiccation
Disadvantages:
a) constrained movement
b) problems re. growth… needs to be shed
c) respiratory, sensory, & excretory issues
(impervious layer)
Arthropods
Reasons for success
3) Arthropodization (presence of jointed appendages)
Includes legs, antennae, mouthparts, etc.
Permits fine-tuned movements, manipulation of
food & other objects, locomotion, etc.
Regional specialization of body (tagmosis); e.g.,
insect w/
(a) head: feeding, nerve & sensory center
(b) thorax: locomotory center… legs, sometimes
wing
(c) abdomen: specialized for reproduction &
contains much of digestive system
Arthropods
Reasons for success
4) Short life cycles - allows use of food resources
that may be available for only short period of
time
5) High fecundity - typically several hundred to
several thousand eggs (but is high mortality)
Arthropods: Insects
Reasons for success
6) Wings (re. most insects)
Advantages:
a) allow dispersal to food resources
b) increased potential for finding mates
c) assist escape from predators
d) miscellaneous: sexual displays, signaling
Disadvantages:
a) require lots of energy to produce
b) can be awkward / bulky
c) windy, exposed habitats?
Arthropods: Insects
Reasons for success
7) Metamorphosis
Advantages:
a) different life stages adapted for different habitats
& food
… immature stages adapted for feeding & growth
… adults adapted for reproduction & dispersal
b) minimizes competition between various life stages
Disadvantages:
a) require lots of energy for drastic changes
b) molting difficult, potentially damaging / dangerous
sponges
radiates
annelids
mollusks
& others
arthropods
nematodes
& others
chordates
echinoderms
body cavity
lining from the
digestive tube
bilateral symmetry
presence of tissues
TOL III: Animals (chordates
and echinoderms)
echinoderms
reversion to radial
symmetry
chordates
dorsal nerve chord
body cavity lining
from the digestive tube
TOL III: Animals (echinoderms)
starfish
sea urchins
TOL III: Animals (chordates)
• Chordates include all animals with a
dorsal nerve cord
• About 50,000 species total
–
–
–
–
Tunicates
Hagfishes
Amphioxus
Vertebrates:
fishes, amphibians, reptiles, birds and
dinosaurs, mammals
TOL III: Animals (chordates)
tunicates or
sea squirts
TOL III: Animals (vertebrates)
reptiles and amphibians
fishes
birds and dinosaurs
mammals
TOL: Summary
1) Close to 2 million species of organisms
have been described.
2) Estimates of total diversity range from
10 to 50 (in one case, up to 100) million
species (with very conservative estimates
as low as 5 million)
3) Species diversity in several groups,
primarily micoorganisms, is grossly
understudied and underestimated; among
multicellular eukaryotes, fungi and
nematodes are also relatively unknown
TOL: Summary
4) Prokaryotes ruled the world long
before eukaryotes evolved;
prokaryotes exhibit a wide array of
metabolic diversity and so control key
steps in many nutrient cycles.
5) Evolutionary trees of major groups
provide frameworks for understanding
the evolutionary history and major
adaptive changes in those groups.
TOL: Summary
6) The ecological function of diversity
can be subdivided by roles:
a) primary producers: some bacteria
(e.g., cyanobacteria; aquatic), some
archaens (aquatic), algae (aquatic),
plants (aquatic and terrestrial)
b) consumers: some bacteria and
archeans, protozoans, fungi, animals;
includes pathogens and predators
TOL: Summary
6) cont’d.
c) decomposers: primarily bacteria
and fungi, also some fungus-like
protists, as well as some animals such
as nematodes; a few vertebrate
carrion-eaters could also be
considered as decomposers
d) nutrient cyclers: many bacteria
TOL: Summary
6) cont’d.
e) symbionts: diverse, many kinds of
organisms are involved; includes
mycorrhizae (plant root + fungus),
endosymbionts (e.g., corals,
dinoflagellates), lichens (cyanobacteria
or green alga + fungus)
Arthropods rule!
Value and Maintenance of
Biodiversity
ASAB – NUST
Fall 2012
Value and Maintenance
• Benefits to humans, direct or indirect
• Intrinsic value
• What kind of a world do we want to
live in?
• Redundancy in ecosystems (how much
is enough?)
Benefits to humans
• Direct use value = marketable
commodities
–
–
–
–
–
Food
Medicine
Raw materials
Recreational harvesting
Ecotourism
Benefits to humans: food
• About 3,000 species (ca. 1% of
300,000 total) of flowering plants
have been used for food
• About 200 species have been
domesticated
• Wild relatives source of genes for
crop improvement in both plants and
animals
Benefits to humans: medicine
• Organisms as chemists
• About 25% of all medical prescriptions
in the U.S. are based on plant or
microbial products or on derivatives or
on synthetic versions
• Some medicinal products from animals
(e.g., anticoagulant from leeches)
Benefits to humans: raw
materials
• Industrial materials:
–
–
–
–
–
–
–
–
Timber
Fibers
Resins, gums
Perfumes
Adhesives
Dyes
Oils, waxes, rubber
Agricultural chemicals
Benefits to humans:
recreational harvesting
• Recreational harvesting:
–
–
–
–
Hunting
Fishing
Pets
Ornamental
plants
Benefits to humans: ecotourism
• By definition based on biodiversity
• Growing portion of the tourism
industry
Indirect Use Value
• Indirect use value = services provided
by biodiversity that are not normally
given a market value (often regarded
as free)
• Include primarily ecosystem services:
atmospheric, climatic and hydrological
regulation; photosynthesis; nutrient
cycling; pollination; pest control; soil
formation and maintenance, etc.
Indirect Use Value
• Biosphere 2 was an attempt to
artificially create an ecosystem that
would sustain human life
• Ca. US$200 million invested in design
and construction plus millions more in
operating costs
• Could not sustain 8 humans for two
years
Intrinsic value
• Simply because it exists
• Moral imperative to be good stewards,
the preservation of other life for its
own sake
• Supported in many different religious
or cultural traditions
• Recognized in the Convention on
Biodiversity
Intrinsic Value
• Biophilia = the connection that human
beings subconsciously seek with the
rest of life (nature) or the innate
connection of humans to biodiversity
Intrinsic Value
• Biophilia = the connection that human
beings subconsciously seek with the
rest of life (nature) or the innate
connection of humans to biodiversity
• Should we put a monetary value on
everything?
Intrinsic Value
• Biophilia = the connection that human
beings subconsciously seek with the
rest of life (nature) or the innate
connection of humans to biodiversity
• Should we put a monetary value on
everything?
• If something can be valued, it can be
devalued.
What kind of a world do we
want to live in?
• Human co-opt about 40% of the
net primary productivity on an
annual basis
• Human population at over 6 billion
and growing at about 80 million
per year
• Loss of some biodiversity is
inevitable
What kind of a world do we
want to live in?
• Current extinction rate much higher than
background; also commitment to extinction
• Extinction is forever; species may have
unforeseen uses or values (e.g., keystone
species, medicinal value, etc.)
• Biodiversity has recovered after previous
mass extinctions, but are we also
eliminating that possibility by severely
restricting conditions conducive to
evolution?
What kind of a world do we
want to live in?
If 6 billion people consume 40% of
the annual net primary productivity,
what is the theoretical limit (=
carrying capacity) for humans under
current conditions?
2.5 x 6 billion = 15 billion
What kind of a world do we
want to live in?
But this number does not factor in the
costs of dealing with wastes or nonrenewable resources.
Nor does it leave room for other
biodiversity, upon which we depend
for ecosystem services (such as waste
removal/recycling).
Human population is expected to reach
ca. 12 billion by 2050.
What kind of a world do we
want to live in?
• This is why many now argue that we
have to find a way to put biodiversity
into the economic equation
• Previously no monetary values were
associated with natural resources
except the actual ones generated by
extraction (the world is there for us
to use)
What kind of a world do we
want to live in?
• Extraction costs (e.g., labor, energy)
usually computed
• But cost of replacement not included,
nor costs of the loss of the services
provided by that resource or its
ecosystem (e.g., cutting forest for
timber)
• Because costs are undervalued,
benefits of extraction are overvalued
What kind of a world do we
want to live in?
• Green accounting proposed as part of
the solution
• But requires that environmental assets
have proper prices (p. 171,
Chichilnisky essay in text)
• Tie in to property rights for natural
resources
Redundancy in Ecosystems
• Or, how much biodiversity is
enough?
• How much redundancy is built into
ecological processes/communities?
• To what extent do patterns of
diversity determine the behavior
of ecological systems?
Redundancy in Ecosystems
Two opposing views: rivet
hypothesis vs. redundancy
hypothesis
rivet
redundancy
Redundancy in Ecosystems
• Rivet hypothesis: most if not all
species contribute to the integrity of
the biosphere in some way
• Analogy to rivets in an aircraft—there
is a limit to how many can be removed
before the structure collapses
• Progressive loss of species steadily
damages ecosystem function
Redundancy in Ecosystems
• Redundancy hypothesis: species
richness is irrelevant; only the
biomass of primary producers,
consumers and decomposers is
important
• Life support systems of the planet
and ecological processes will generally
work fine with relatively few species
Redundancy in Ecosystems
• In the past (from fossils), most
ecological systems have been
conspicuously less species rich
• But no evidence that they operated
any differently
Redundancy in Ecosystems
• Major patterns of energy flow and
distribution of biomass in existing ecological
systems may be broadly insensitive to
species numbers
• But systems with higher diversity and more
kinds of interactions may be more buffered
from fluctuations
• Lack of data regarding the link between
species-richness and ecosystem function
Redundancy in Ecosystems
• Middle ground: ecosystem processes
often but not always have
considerable redundancy built into
them
– Not all species are equal (e.g., functional
groups, keystone species)
– The loss of some species is more
important than the loss of others
– Species loss may be tolerated up to some
critical threshold