Transcript 17 Biodiversity and Conservation of the Ocean

17 Biodiversity and
Conservation of the Ocean
Notes for Marine Biology:
Function, Biodiversity, Ecology
By Jeffrey S. Levinton
©Jeffrey S. Levinton 2001
Biogeographic Factors
• Geographic isolation + strong environmental
gradients -- isolate groups of species
• Present day world -- mostly north-south trending
coasts, fairly strong latitudinal temperature
gradient, offshore habitat lower in nutrients
• Produces coastal biogeographic provinces
(temperature, current systems, geographic
isolation)
• Provinces can be species boundaries, statistical
construct of different species assemblages
ALEUTIAN
70N
ARCTIC
1. Pt. Barrow
2. Cape Romanzof
60N
3. Nunivak Island
4. Hagemeister Island
5. Prince William Sound
6. Dixon Entrance
7. Vancouver Island
8. Puget Sound
50N
9. Cape Flattery
OREGONIAN
10. Cape Mendocino
11. Monterey Bay
12. Point Conception
40N
13. Punta Eugenia
14. Cabo San Lucas
CALIFORNIAN
30N
Provinces (named in red) of the Pacific coast of North America
Horseshoe
crab
Diamondback
terrapin
American
oyster
Seaside
sparrow
Toadfish
Black sea
bass
Province boundaries: can = species boundaries,
can = genetic boundaries within species
Establishment of Biogeographic
Barriers 1
• Many coastal provinces are maintained by
barriers to dispersal, combined with
temperature breaks (e.g., Point Conception,
California, Cape Hatteras, Massachusetts)
Establishment of Biogeographic
Barriers 2
• Many coastal provinces are maintained by
barriers to dispersal, combined with
temperature breaks (e.g., Point Conception,
California, Cape Hatteras, Massachusetts)
• Larger scale barriers originate from
geological upheavals (e.g., Isthmus of
Panamá, which arose ca. 3 million years
ago), resulting in isolation and speciation (in
Panamá, many paired species on Pacific and
Caribbean sides of Isthmus)
Components of Diversity
• Within-habitat component refers to the number of
species living in the same habitat type
• Between-habitat component refer to the number of
species living in all habitat types
• A within-habitat study might be comparing the
number of species that live in muddy bottoms on
the shelf versus the abyssal bottom
Diversity Gradients
• Latitudinal Diversity Gradient - one of
the most pervasive gradients. Number of
species increases towards the equator
• Gradient tends to apply to many
taxonomic levels (species, genus, etc.)
1,000
Number
Species
Genera
100
Families
10
Latitude
Bivalve diversity versus latitude
Other Diversity Differences
• Between-Ocean differences. Pacific biodiversity
appears to be greater than Atlantic, although
the specifics are complex
• Within-Ocean differences. From a central high
of biodiversity in the SW Pacific, diversity
declines with increasing latitude and less so
with increasing longitude, away from the center
• Inshore-Estuarine habitats tend to be lower in
diversity than open marine habitats
• Deep-sea diversity increases, relative to
comparable shelf habitats, then decreases to
abyssal depths
Explanations of Diversity Differences
• Short-term ecological interactions - presence of
predators might enhance coexistence of more
competing species, competitor might drive
inferior species to a local extinction
Explanations of Diversity Differences 2
• Short-term ecological interactions - presence of
predators might enhance coexistence of more
competing species, competitor might drive inferior
species to a local extinction
• Greater speciation rate - might explain higher
diversity in tropics. Center of origin theory
argues that tropics are source of most new
species; some of which may migrate to higher
latitudes
Explanations of Diversity Differences 3
• Short-term ecological interactions - presence of
predators might enhance coexistence of more
competing species, competitor might drive inferior
species to a local extinction
• Greater speciation rate - might explain higher
diversity in tropics. Center of origin theory argues
that tropics are source of most new species; some
of which may migrate to higher latitudes
• Lower extinction rate - might also explain
major diversity gradients
Explanations of Diversity Differences 4
• Short-term ecological interactions - presence of
predators might enhance coexistence of more
competing species, competitor might drive inferior
species to a local extinction
• Greater speciation rate - might explain higher
diversity in tropics. Center of origin theory argues
that tropics are source of most new species; some
of which may migrate to higher latitudes
• Lower extinction rate - might also explain major
diversity gradients
• Area - Greater area might result in origin of
more species, but also lower extinction rate of
species living over greater geographic ranges
(having higher population sizes)
Explanations of Diversity
Differences
• Habitat stability - A stable habitat may reduce
the rate of extinction, because species could
persist at smaller population sizes
• Sea-level fluctuations - sea level fluctuations,
such as during the Pleistocene, might have
created barriers during low stands of sea level,
leading to isolation and speciation. This
mechanism has been suggested as increasing
the number of species in the SW Pacific in coral
reef areas.
Number of seagrass species
15
10
5
0
2000 4000
6000 8000
Km
10,000
Example of evidence supporting the center of origin theory. Number
0f seagrass species with distance downcurrent from Torres Straight
Number of species
Eutrophic
Oligotrophic
Area (hectares)
Species-area effect: Danish ponds and lakes.
After Hughes, 2001, Science
Within-ocean coral reef diversity gradients. Pacific coral reefs
Conserving Marine Biodiversity
• In many habitats the number of species
present is poorly known and severely
underestimated
• Need methods of recognizing species.
Morphology has limited use, but
molecular markers are being used
commonly to distinguish among species
Conserving Marine Biodiversity 2
Value of biodiversity
• Aesthetic value of diverse ecosystems
• Many species play crucial roles in elemental
cycling
• Loss of species at apex of food chains has
drastic top-down effects on marine systems
• Loss of species that are structural elements in
communities (e.g., corals, seaweeds, seagrasses)
might cause loss of many more species
Marine Invasions
• Invasion is the arrival of a species to an
area that has not lived there previously
• Invasions are increasing in frequency
• Invasions often result in the arrival of
species with strong local ecological effects
• Invasions eventually homogenize the
biota world-wide
Properties of Successful Invaders 1
• Vector - a means of transport must be
available, e.g., ballast water of ships, ability to
disperse (e.g., planktotrophic larvae)
Properties of Successful Invaders 2
• Vector - a means of transport must be available,
e.g., ballast water of ships, ability to disperse (e.g.,
planktotrophic larvae)
• Invasion frequency - because most arrivals do
not result in invasion success, frequency of
arrival is important
Properties of Successful Invaders 3
• Vector - a means of transport must be available,
e.g., ballast water of ships, ability to disperse (e.g.,
planktotrophic larvae)
• Invasion frequency - because most arrivals do not
result in invasion success, frequency of arrival is
important
• Ecological compatibility - invading species need
an appropriate habitat in which to colonize and
propagate
Properties of Successful Invaders 4
• Vector - a means of transport must be available,
e.g., ballast water of ships, ability to disperse (e.g.,
planktotrophic larvae)
• Invasion frequency - because most arrivals do not
result in invasion success, frequency of arrival is
important
• Ecological compatibility - invading species need
an appropriate habitat in which to colonize and
propagate
• Survival of initial population variation - initial
fluctuations of small population size results in
extinction of invading species
Invasions are Common
• Ship ballast water has many potentially
invading species
• Transport of commercially exploited
mariculture species resulted in transport
of other species as well
• Canals are important routes for invaders.
Suez Canal facilitated invasions, mainly
from Red Sea to Mediterranean Sea
Invaders can have significant effects
• Periwinkle Littorina littorea invaded New
England, USA from Europe. Now most
common rocky shore snail and has significant
effects on seaweed communities
• Shore crab Carcinus maenas invaded from
northern Europe to become common all over
the world
• Freshwater zebra mussel, Dreissena
polymorpha invaded from eastern Europe to
North America, has exerted strong effects on
water column, and on native mussels
Invasion routes of species of the crab genus Carcinus maenas
from European waters to sites around the world
Conservation Genetics
• Genetic markers (e.g., DNA sequences, length
fragment polymorphisms in mitochondrial
DNA) allow identification of populations
• This allows species identification, identification
of different migrating stocks of fishes, turtles,
and marine mammals
• Examples: Green turtle females shown to home
to the same nesting beaches, after migrations of
thousands of km to feeding grounds; fishing of
Loggerhead turtles in eastern Atlantic shown to
deplete nesting turtles in Florida; stocks of
migrating humpback whales have been
identified
The End