Lecture 5:
Biodiversity and Conservation of
the Ocean; Ecosystems Ecology,
Productivity, and Trophic Structure
Biodiversity and Conservation of
the Ocean
Marine Biogeography
• Biogeography = the study
of the geographical
distribution and
abundance of species
through out the ocean
• Present distribution of
species is the result of
speciation, dispersal, and
extinction
• Marine biota can be
divided into geographic
provinces
cec.org
Factors in Biodiversity
• Local patterns of species diversity are often
controlled by short-term ecological interactions
• Regional patterns are probably controlled by the
balance of speciation and extinction
• Speciation (formation of new species) usually
requires some degree of isolation of populations
• Extinction can be caused by habitat change or
destruction, widespread diseases, biological
interactions, or random fluctuations of population
size
ALEUTIAN
1. Pt. Barrow
2. Cape Romanzof
3. Nunivak Island
4. Hagemeister Island
5. Prince William Sound
6. Dixon Entrance
7. Vancouver Island
8. Puget Sound
9. Cape Flattery
10. Cape Mendocino
11. Monterey Bay
12. Point Conception
13. Punta Eugenia
14. Cabo San Lucas
70N
ARCTIC
60N
50N
OREGONIAN
40N
CALIFORNIAN
30N
Provinces (named in red) of the Pacific coast of North America
Establishment of Biogeographic
Barriers
• Many coastal provinces are maintained by
barriers to dispersal (ex. currents), combined
with temperature breaks
• Larger scale barriers originate from geological
upheavals, resulting in isolation and speciation
Relating Geography to Evolutionary
History
• The relation of
geography to
speciation can be
accomplished by
relating
evolutionary
trees to patterns
of geographic
occurrence
Relating Geography to Evolutionary
History
– Importance of barriers:
• different groups of evolutionarily related
species found on east and west side of the
Pacific, resulting from long-term geographic
isolation;
• most closely related species found on either
side of Isthmus of Panama, which arose
about 3 million years ago
Relating Geography to Evolutionary
History
• Within-species level - trace genetic markers and
fossils show:
– dispersal 3.5 million years ago from Pacific to Atlantic
– then extinction by glaciers on Atlantic side in New
England-Nova Scotia 18,000 years ago
– then re-colonization of this area from European side of
Atlantic about 4000 years ago
Persistent boundary can isolate
populations of several species
Components of Species Diversity
• Alpha diversity (α) = Within-habitat diversity
• Beta diversity (β) = Between-habitat diversity. A
contrast of diversity in two locales of differing
habitat type.
• Gamma diversity (γ) = Regional diversity
Concepts of Species Diversity
• Diversity and stability – Early discussions of
tropical vs. temperate; polluted vs. nonpolluted areas
• Diversity and productivity – Recent discussions
about a possible relationship
Diversity Gradients
• Latitudinal diversity gradient - one of the
most pervasive gradients; number of
species increases toward the equator
• Gradient tends to apply to many taxonomic
levels (species, genus, etc.)
Latitudinal species richness gradients
Ex. land
birds
Diversity along geographical gradients. Corals from the Great Barrier Reef;
copepods from the Pacific; remaining data from all oceans. After Thorson (1957)
and Fischer (1970).
Factors Hypothesized to Influence
Biodiversity (& Latitudinal Gradients)
Factor
Rationale
History
More time permits more complete colonization and the
evolution of new species
Spatial heterogeneity
Physiologically or biologically complex habitats furnish more
niches
Competition
a. Competition favors reduced niche breadth
b. Competitive exclusion eliminates species
Predation
Predation hampers competitive exclusion
Climate
Climatically favorable conditions permit more species
Climatic variability
Stability permits specialization
Productivity
Richness is limited by the partitioning of production among
species
Disturbance
Moderate disturbance hampers competitive exclusion
Source: Modified after Pianka (1988) and Currie (1991)
Recent Explanations for Latitudinal
Diversity Gradients
• Increased area of the tropics
• Increased effective evolutionary time due to
shorter generation times in the topics
Other Diversity Differences
• Between-ocean differences: Pacific biodiversity
appears to be greater than Atlantic
• 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: estuaries 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
• Area - greater area might result in origin of
more species (b/c of larger diversity of
habitats within a larger area), but also
lower extinction rate of species living over
greater geographic ranges (b/c of higher
population sizes, and presence of more
refuge habitats)
The world’s tropical lands cover about four times the area s the world’s
second largest biome, the tundra. Tropical oceans also cover more
surface than oceans in other climate zones. From Rosenzweig (1992).
Effects of Area and Food Supply
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
• Complex recent historical events - may explain
some current regional differences in species
diversity (e.g., diversity gradient in tropical
American coral reefs may be partially due to
extinctions around periphery of province)
Explanations of Diversity Differences
• Habitat stability - a stable habitat may reduce the
rate of extinction, because species could persist at
smaller population sizes (possible explanation of
deep-sea maximum of species richness)
• 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
Explanations of Diversity Differences
• 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
Is There a Center of Origin?
• Center of Origin Hypothesis: high diversity
centers are places where more species are
produced and retained and also a source of
colonization to peripheral regions where
diversity is lower
Within the Pacific Ocean, species diversity in coral
reefs declines in all directions from an Indo-Pacific
diversity maximum
Example of evidence supporting the center of origin theory:
Number of sea grass species with distance down-current from
Torres Straight
Fossil Record Evidence in Support of
Center of Origin Hypothesis
• Jablonski et al.* looked at first fossil
occurrences of members of a genus in the fossil
record
• First occurrences occur much more frequently
in tropics than at high latitude
• Conclude: Center of Origin hypothesis is
supported
*D. Jablonski et al., Science 314, 102 -106 (2006)
Research in Marine Biodiversity
• Understand patterns, processes, and
consequences of changing diversity in the sea by
focusing on the effects of human activities.
• Increase understanding of how larger-scale
oceanographic processes may impact smallerscale biodiversity patterns and processes.
• Strengthen field of marine taxonomy.
• Encourage new technology, development of
predictive models, and look at things from
historical perspectives.
• Improve predictions concerning human impacts
on the ocean.
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
Shifting Baselines
• Diversity & ecosystem structure today may
be strongly altered relative to a few human
generations ago
• We might mistakenly take today’s situation
as the baseline for conservation
• The baseline for a natural community has
shifted over generations because we have
forgotten the original natural state
Conserving Marine Biodiversity:
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 topdown 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
• More diverse ecosystems may be more resilient,
extinction of one species results in expansion of
ecological function by another species
Conservation Strategies
• Individual species - preserve abundance of target
species, such as large carnivores, marine
mammals
• Conserve total biodiversity of a region - focus on
hotspots of high diversity
Conservation Strategies
• Conserve ecosystem function - concern is focused
on species that are important in ecosystem
processes (such as primary production, nutrient
cycling, decomposition)
– higher biodiversity might enhance some functions,
such as total productivity
• Establish economic value of ecosystem by
evaluating its ecosystem services - ecosystems
have human value that can be quantified in
money (resources, water supply, recreation, etc.)
Conservation Strategies
• Marine Protected Areas (Marine Reserves)
– Set aside a fraction of ecosystem area/volume
to allow populations to thrive and spill over
into remaining unprotected sites
– Population density, body size, biomass,
biodiversity all found to be higher within
marine reserves
Marine Invasions – Threat to
Biodiversity
• Invasion = the arrival of a species to an area
that has not lived there previously
– Increasing in frequency
– Often result in the arrival of species with
strong local ecological effects
– Eventually homogenize the biota world-wide
Properties of Successful Invaders
• 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 suitability of target habitat - 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
Methods of Invasion
• Ship ballast water
• Transport of commercially exploited
mariculture species
• Canals
• Biological control
• Aquarium/Pet industry
Invaders Can Have Significant Effects
• Periwinkle Littorina
littorea
• Shore crab Carcinus
maenas
• Freshwater zebra
mussel, Dreissena
polymorpha
Invasion routes of species of the crab genus Carcinus
maenas from European waters to sites around the world
Ecosystems Ecology, Productivity,
and Trophic Structure
Ecosystem Level
• Ecosystem = An entire habitat, including all
abiotic features of the landscape/seascape
and all the living species within it that interact
• Focus is on:
– Energy flux
– Biological productivity
– Nutrient cycling
Ecological Processes – Ecosystem
Level
• Primary producers – (autotrophs) organisms
that produce organic molecules. Primarily
photosynthetic
• Primary consumers – (herbivores) consume
autotrophs
• Secondary consumers (carnivores) consume
herbivores
– Tertiary productivity
Productivity vs. Biomass
Biomass is the mass of living material
present at any time, expressed as grams
per unit area or volume
Productivity is the rate of production of
living material per unit time per unit area
or volume
Productivity
Primary productivity - productivity due to
photosynthesis
Secondary productivity - productivity by the
consumers of primary producers
Productivity by Ecosystems – per m2
Productivity by Ecosystems – Global
Basis
Measuring Primary Productivity
• Gross primary productivity - total carbon fixed
during photosynthesis
• Net primary productivity - total carbon fixed
during photosynthesis minus that part which
is respired
– Most interesting → gives that part of the
production available to higher trophic levels
Measuring Primary Productivity – Remote
Sensing
• Satellite color scanners can give an estimate of
photosynthetic pigment concentration
• Relationship between chlorophyll
concentration and primary production varies
with region
– Need ground-truthing to determine relationship
Measuring Primary Productivity –
Remote Sensing
Measuring Primary Productivity –
Remote Sensing
Satellite image of estimated chlorophyll
in water column, from SeaWiFS satellite
(Sea-viewing Wide Field-of-view
Sensor)
Coccolithophore bloom from
space - satellite photograph
Geographic Variation of Productivity
• Continental shelf and open-ocean upwelling
areas are most productive
• Coastal areas are nutrient-rich and productive
• Convergences and fronts often are sites of rise
of nutrient rich deep waters
• Central ocean, gyre centers are nutrient poor,
low primary production
Geographic Variation of Productivity
Why are ocean waters more
productive in the higher latitudes than
in the lower latitudes?
In higher latitudes, have
seasonal mixing (in
winter) that occurs when
thermocline breaks down
towards the end of fall.
In lower latitudes, surface
water temps remain
somewhat constant. Do
not have seasonal
breakdown of
thermocline.
Food Chains and Food Webs
Trophic level – a species or group of species that feed
on one or more other species (which can be grouped
into a lower trophic level)
Food chain - linear sequence showing which
organisms consume which other organisms, making a
series of trophic levels
Food web - more complex diagram showing feeding
relationships among organisms, not restricted to a
linear hierarchy
Trophic Levels
• Defines how far an organism is removed from the
producer in obtaining its nourishment
• Producers-always trophic level 1
• Herbivores-always trophic level 2
• Higher order consumers may occupy different
trophic levels depending on what they are feeding on
at any point in time
Trophic Levels
• Primary Producers
– Phytoplankton and
macrophytes
• Consumers: heterotrophic
animals
– Primary consumers:
herbivores
– Secondary and higher-level
consumers: carnivores,
predators
• Decomposers: bacteria and
fungi
Trophic level Name
4
Top carnivore
3
2
1
Carnivore
Herbivore
Autotroph
Food Chains
• The energy flow from one trophic
level to the other is known as a
food chain
• It involves one organism at each
trophic level
– Primary Consumers – eat
autotrophs (producers)
– Secondary Consumers – eat the
primary consumers
– Tertiary Consumers – eat the
secondary consumers
– Decomposers – bacteria and fungi
that break down dead organisms
and recycle the material back into
the environment
Simplified food chain taken from a
food web
Food Chains
The total number of links in a food chain may be
limited by:
1. the structure of the food chain
2. the possible energy that can be
transported through many links
3. possible instability of large food chains
• Unusual to find more than 4-5 trophic levels in
food chains
Food Chains - Structure
• Bottom up control: control of food chain by amount of
primary production
• Top-down control: control of food chain by variation in
top predators
• Three-level food chains: Primary producers will be
abundant because the herbivore population is reduced
by the carnivores
– Remove top level (carnivore) and herbivore increases,
resulting in low population size of primary producer.
• Even-numbered food chains: Primary producers tend
to be rare
Food Chains - Energy Transfer
• Trophic Hypothesis – there is a maximum
number of trophic links through which energy
can travel
– With ecological efficiency of 10%, only 0.01% will
reach a 5th trophic level
– May set a limit to upper trophic levels → bottomup control
Food Chains - Stability
• Food Chain Stability Hypothesis
– Longer food chains are inherently unstable
– Changes at one level will propagate to other levels
– If a population at one trophic level goes extinct, it
will cause species at levels above it to go extinct
• Omnivory – feeding on many food sources (i.e.
different trophic levels)
• Reduces effects of fluctuations of a species in
a given level of a food chain
Food Webs
• Community food web
is a description of
feeding habits of a set
of organisms based on
taxonomy, location or
other criteria
• Rule: The more intricate
the food web the more
stable the ecosystem
Food Webs
• Food webs portray flows of matter and energy
within the community
• If community is like a city, then Food Web is
like a street map of a city
• Web omits some information about
community properties
– e.g., minor energy flows, constraints on predation,
population dynamics
Descriptive Food Webs
Interaction or functional food webs depict the most
influential link or dynamic in the community
Food Webs: Methods of Study
1. Identify component species
2. Sample to determine who is eating whom
3. Sampling and gut analysis to quantify
frequency of encounters
4. Exclosures and removals of species to
determine net effects
5. Stable isotopes
6. Mathematical models
Food Web Analysis
• Modern Approaches to Food Web Analysis
– Connectivity relationships
– Importance of predators and interaction strength in
altering community composition and dynamics
– Identification of trophic pathways via isotope analysis.
• Weakness of above: no quantitative measure of food
web linkages.
Food Webs: Complexity meets Reality
• Fallacy of linear food chains as a adequate
description of natural food webs
– Food webs are reticulate
– Discrete homogeneous trophic levels an abstraction or an
idealism
– omnivory is rampant
– ontogenetic diet shifts (sometimes called life history
omnivory)
– environmental diet shifts
– spatial & temporal heterogeneity in diet
Energy Flow Through Ecosystems
• Energy transfer between trophic levels is not
100% efficient, and energy is lost as it passes up a
food chain.
• Herbivores eat a small proportion of total plant
biomass
• They use a small proportion of plant material
consumed for their growth. The rest is lost in
feces or respiration
• Less energy is available at the next trophic level.
Trophic Basis of Production
• Assimilation efficiency varies with resource
–
–
–
–
–
–
10% for vascular plant detritus
30% for diatoms and filamentous algae
50% for fungi
70% for animals
50% for microbes (bacteria and protozoans)
27% for amorphous detritus
• Net Production Efficiency
production/assimilation ~ 40%
Food Webs & Efficiency
• Ecological efficiency is defined as the energy supply
available to trophic level N + 1, divided by the energy
consumed by trophic level N. You might think of it as
the efficiency of copepods at converting plants into
fish food.
• In general, only about 10% of the energy consumed
by one level is available to the next.
• Difficult to measure so food web scientists focus on
measures of transfer efficiency for selected groups of
animals.
Food Web Transfer Efficiency
• Et = Pt/ Pt-1
• Where:
– Pt = The annual production at trophic level t
– Pt-1 = The annual production at the lower trophic
level
Transfer Between Trophic Levels
Budget for ingested food (use energy units):
I=E+R+G
I → amount ingested
E → amount egested
R → amount respired
G → growth (partitioned between somatic
growth and reproduction)
**usually constructed in terms of energy units (e.g. calories)
Transfer Between Trophic Levels
Use food chain efficiency to calculate
Potential production at highest trophic level:
P = BEn
B = primary production
P = production at highest level
E = food chain efficiency
n = number of links between trophic levels
Food Webs and Energy
• Pyramid of biomass
represents the amount of
energy, fixed in biomass, at
different trophic levels for
a given point in time
Food Webs in the Ocean
• Pyramid of biomass for the
oceans can appear inverted
• Pyramid of energy shows
rates of production rather
than biomass.
Marine Food Webs
• Food webs in the oceans vary systematically in
food chain efficiency, number of trophic levels,
and primary production
– Oceanic system
– Coastal/Shelf system
– Upwelling
Marine Food Webs
Food Chain
Primary
Trophic
Food
Potential
Type
Productivity Levels
Chain
Fish
Efficiency Production
gCm-2y-1
mgCm-2y-1
Oceanic
50
5
10
0.5
Coastal/Shelf
100
3
15
340
Upwelling
300
1.2
20
36,000
After Ryther, 1969 Science 166: 72-76.
Variation in Planktonic Food Webs
Oceanic
Coastal/Shelf
Upwelling
Marine Food Webs
• Great potential of upwelling areas due to
combination of:
• High primary production (have high and
continuous nutrient supply)
• Higher food chain efficiency (related to ease of
ingestion and assimilation of large diatoms by
planktivorous fish)
• Lower number of trophic levels (less overall
loss of energy)
Are trophic levels useful?
• Even if organisms are not strict herbivores,
primary carnivores, etc., as long as they are
mostly feeding at one trophic level, the
concept can have value (e.g., trophic cascade
concept).