3 Ecological and Evolutionary
Principles
Notes for Marine Biology:
Function, Biodiversity, Ecology
by Jeffrey S. Levinton
©Jeffrey S. Levinton 2001
The Ecological Hierarchy
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Biosphere
Ecosystem
Community
Population
Individual
Ecological Processes
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Competition
Predation
Disturbance
Parasitism
Larval Dispersal
Facilitation
Interactions Between
Individuals
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+- Territoriality
+- Predation
+ - Parasitism
++ Mutualism
+ 0 Commensalism
PREDATION
TYPES:
Stationary:
e.g., anemones
Mobile:
(a) sit and wait and attack
e.g.,
(b) pursuit
e.g., Shark
Effects of Predation
OVEREXPLOITATION - prey population collapse, occasional predatorprey cycles
PREY ESCAPE
(a) rapid recovery rate
(b) defenses
(c) predators limited by other factors (e.g., octopus by den sites)
(d) refuges (space, time)
Predation Example: Stationary Predator Anthopleura
xanthogrammica, anemone living in tide pools of
Pacific coast. Feeds on larger invertebrates that fall
into its tentacles, such as mussels.
Crypsis: A marine flatfish with chromatophores that
allows it to match its sedimentary background (fish
outlined with arrows)
Inducible defenses
A bryozoan makes
spines when placed in
contact with a predatory
nudibranch.
A hydrozoan, Hydractinia,
produces defense stolons
armed with nematocysts
when in contact with
another colony.
Inducible Defense: The conical (right) and bent
(left) forms of the acorn barnacle Chthamalus
anisopoma. The animal develops the bent form if
predatory snails are present.
Inducible Defense 2: Often has a cost. Barnacle
with bent form does not feed as well. Therefore, it
is a good strategy to make the defense optional.
Escape behavior: The bivalve Lima hians can
swim from predators by rapidly clapping its
valves and expelling water in jets through the
hinge. It also has mantle tentacles that secrete a
sticky distasteful material that discourages
predators.
Optimal Predator Models
• Diet breadth - food scarce --> increase
breadth
Optimal Predator Models 2
Time spent in a patch - greater the distance
between patches --> spend more time in a
given patch
Optimal Predator Models 3
Optimal size of prey --> intermediate is usually
preferred, yields the most food per unit time
(larger prey good in reward but takes relatively
long to eat, smaller prey fast to east but food
per prey item is small)
Energy reward
of a mussel as
function of size
Preference of
crab for
different
mussel sizes
Shore crab Carcinus
maenas feeding upon
the mussel Mytilus
edulis.
Parasitism
• Parasites evolve to reduce damage to host
• Commonly involve complex life cycles
with more than one host
• Parasites may invade specific tissues,
such as reproductive tissue of the host
Invasion of the parasitic rhizocephalan
barnacle Sacculina into the body of a crab
Complex life cycle found in a trematode parasite
living in several marine animal hosts
Mutualism: Cleaner wrasse removes ectoparasites from a
number of species of fish that visit localized “cleaning
stations” on a coral reef. Fish (b) is a mimic species that
actually attacks fish that would normally be a “client” of
the cleaner wrasse.
Commensalism
Commensal crab and fish live in this burrow of
Urechis caupo
Construction of a Population
Model
dN/dT = f (N,M,R,I,E)
N = population size
M = mortality
R = reproduction
I = immigration
E = emigration
M is a function of physical environment, competition, predation, etc.
R function of physical environment, resources (e.g., food)
Example of Population Model
Barnacles: What parameters matter the most?
dN/dT = f (N, I, M)
I is larval settlement
M a function of larval-adult interactions, overgrowth, predation
Note R doesn't matter if planktonic larvae mainly go elsewhere
Survivors
Planktonic
larval
stage
Post-settling stage
Mortality pattern expected for a species with a
planktonic larva. Note higher mortality rate of
larval stage.
Modes of Population Change
Exponential
Growth
Logistic growth
Random change
Metapopulation
• Definition: A group of interconnected
subpopulations among which there is
movement of individuals
Metapopulation 2
• Definition: A group of interconnected
subpopulations among which there is movement
of individuals
• Some subpopulations are sources of individuals
that move to other subpopulations
Metapopulation 3
• Definition: A group of interconnected
subpopulations among which there is movement
of individuals
• Some subpopulations are sources of individuals
that move to other subpopulations
• Other subpopulations are sinks, which means
that they may receive individuals from other
subpopulations, but they are not sources
(example, only juveniles disperse, but the
subpopulation in question does not have
individuals that reproduce successfully.
Metapopulation - interconnected group of
subpopulations
Spatial Distribution of Individuals
Random
Uniform
Aggregated
COMPETITION
LIMITING RESOURCES
(1) Renewable - e.g., copepods exploiting diatom
population
(2) Non-renewable - space on a rock exploited by
long-lived sessile species
Limiting Resources
Space is a limiting resource to these
colonies of colonial ascidians
Outcomes of Competition
COMPETITIVE DISPLACEMENT - one species
outcompetes another for a resource
COEXISTENCE - two species exploit different
resources, some process allows two species to
exploit same resource without
displacement
Interference vs. Exploitation
Competition
Interference - one species overgrows another,
interspecific territoriality, agonistic interaction
Exploitation - one species eats a prey resource more
efficiently than another (also called scramble
competition)
Styles of Competitive
Interaction:
Hierarchy of competitive dominance vs. network
Indirect Effects of Competition
Note: Effectively, B and C beat up on each other, A and B beat up on
each other, interaction between A and C is very weak; B
suffers the most, A and C are not as badly affected.
CONSEQUENCES OF COMPETITION
Extinction: usually local, habitat shift
Coexistence: "niche shift" - character displacement evolution of shift in morphology or behavior
Variable Environment: Unstable, but can permit
coexistence
EVIDENCE FOR INTERSPECIFIC
COMPETITION
1. EXPERIMENTAL MANIPULATIONS remove hypothetical competitor (e.g., barnacles)
2. LABORATORY DEMONSTRATIONS e.g., growth experiments with one and multispecies combinations disadvantage is lack of field conditions
3. DISPLACEMENTS IN NATURE - e.g., increase of resource
exploitation in estuaries. Problem - other factors could be at
work
4. CONTIGUITY OF RESOURCE USE e.g., "adjacent niches" - could arise by evolutionary change
EVIDENCE FOR INTERSPECIFIC
COMPETITION 2
1. EXPERIMENTAL MANIPULATIONS remove hypothetical competitor (e.g., barnacles)
2. LABORATORY DEMONSTRATIONS e.g., growth experiments with one and multispecies combinations disadvantage is lack of field conditions
3. DISPLACEMENTS IN NATURE - e.g., increase of resource
exploitation in estuaries. Problem - other factors could be at
work
4. CONTIGUITY OF RESOURCE USE e.g., "adjacent niches" - could arise by evolutionary change
EVIDENCE FOR INTERSPECIFIC
COMPETITION 3
1. EXPERIMENTAL MANIPULATIONS remove hypothetical competitor (e.g., barnacles)
2. LABORATORY DEMONSTRATIONS e.g., growth experiments with one and multispecies combinations disadvantage is lack of field conditions
3. DISPLACEMENTS IN NATURE - e.g., increase of resource
exploitation in estuaries. Problem - other factors could be at
work
4. CONTIGUITY OF RESOURCE USE e.g., "adjacent niches" - could arise by evolutionary change
EVIDENCE FOR INTERSPECIFIC
COMPETITION 4
1. EXPERIMENTAL MANIPULATIONS remove hypothetical competitor (e.g., barnacles)
2. LABORATORY DEMONSTRATIONS e.g., growth experiments with one and multispecies combinations disadvantage is lack of field conditions
3. DISPLACEMENTS IN NATURE - e.g., increase of resource
exploitation in estuaries. Problem - other factors could be at
work
4. CONTIGUITY OF RESOURCE USE e.g., "adjacent niches" - could arise by evolutionary change
RELATION OF PREDATION TO
COMPETITION Predation suppresses competitive
success of superior species over inferior
species, especially if predator prefers
competitively superior prey
DISTURBANCE
Usually refers to physical change in environment that causes mortality
or affects reproduction (storm, ice scour).
SPATIAL SCALE OF DISTURBANCE
Habitat wide (storms, ice, oil spill)
Localized in patches (horeshoe crabs, logs)
EFFECT CAN BE SIMILAR TO PREDATION
Suppresses effect of competition (Intermediate disturbance-predation
effect)
Intermediate DisturbancePredation Hypothesis
Low levels of disturbance or predation: Competitive dominant
species takes over
Intermediate levels: Promotes coexistence, more species present
High levels: most individuals removed, reduces total number of
species
SUCCESSION
Predictable order of appearance and dominance of species, usually
following a disturbance.
SOME MODES OF SUCCESSION
(1) Early species modify habitat, which facilitates colonization by later
species
(2) Late species exclude colonization of early species
(3) Early species hold space until death, then are replaced by late species,
which do the same
Some Interactions in Succession
Genetic Variation, Species
• Marine species have genetic variation
• Variation found in populations, also
frequency of genes varies over space, within
a species
• Species are identified by presence of
reproductive isolation
Parent-Offspring correlation indicates genetic basis for
variation in trait
Cline: A regular change in gene frequencies over a geographic
space (here, latitude).
Example: latitudinal change in frequency of the A’ allele in the
blenny Anoplarchus purpurescens, in Puget Sound, Washington
Sibling Species in the Sea
Closely related species that are reproductively isolated but
very similar in form, to the point that they cannot be identified
without sophisticated (usually molecular) markers.
Larvae of 5 species of the polychaete sibling species complex
Capitella capitata
Evolutionary Tree: established by
grouping species with shared characters.
Leads to a hierarchy that can be plotted as
a tree.
The End