Ch 3

3 Ecological and Evolutionary
Principles
Ecological Processes Population Level
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Predation
Competition
Parasitism
Disease
Disturbance
Facilitation
Larval dispersal*
Interactions Between
Individuals
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+- Territoriality
+- Predation
+ - Parasitism
++ Mutualism
+ 0 Commensalism
Predation
POPULATION EFFECTS – reduction of prey, alteration of prey age
and sex distribution, prey population collapse, occasional predator-prey
cycles
Predation effects reduced when
(a) Prey population has rapid recovery rate
(b) Predators limited by other factors (e.g., octopus by den sites)
(c) Escapes from predation: (1) escape behavior, (2) cryptic color,
form, (3) chemical (warning coloration) or mechanical defense (fixed or
inducible), (4) refuge habitat, (5) refuge time (nocturnal, feeding at time
of low tide when predators are away)
Predation Example: Stationary Predator:Anemone
Anthopleura xanthogrammica
20cm
Mobile predators:scale of size and
mobility varies
STRONG SELECTION FOR RESPONSE TO PREDATORS:
CRYPSIS, DEFENSIVE STRUCTURES AND CHEMICALS,
ESCAPE BEHAVIOR, INDUCIBLE DEFENCES (COSTS?)
Peacock flounder Bothus mancus
Peacock flounder Bothus mancus
Thaumoctopus mimicus mimic octopus
Coevolution of anti-predator poison and warning color
15 cm
Pseudoceros bifurcus
(flatworm in
Phillipines) has
tetrodotoxin (blocks
Na channel)
Aposematic (warning
coloration)
Hermodice carunculata
15 cm
Escape Behavior
Scallop Limaria hians
Spisula escaping starfish
Inducible defenses
+predator
bryozoan spines nudibranch.
- predator
Barnacle Chthamalus
anisopoma
Why just a plastic response?
PREDATION – DIRECT AND INDIRECT EFFECTS
DIRECT – KILLING OF PREY
INDIRECT – PREY DETECT ODOR OR VISUALLY
OR MECHANICALLY DETECT PREDATORS, AND
REDUCE ACTIVITY!TRAIT-MEDIATED
INDIRECT EFFECTS
ON POPULATION LEVEL: NON-CONSUMPTIVE
EFFECTS CAN REDUCE ACTIVITY OF PREY
POPULATION CASCADE TO REST OF
COMMUNITY –e.g., reduced feeding and reproduction
Optimal Predator Models
•  Diet breadth - rule: food scarce, increase
breadth
•  Time spent in a patch - rule: greater the
distance between patches, spend more
time in a given patch
•  Size selection - maximize energy intake,
usually leads to selection for intermediate
size
Time in Patch Model
e
m
i
t
t
i
s
Tran
Gain within a patch
Gain within a patch
t1
t2
Gain per unit time: Which is greater? Red or Blue?
Optimal time in patch
•  Increases as distance between patches
increases
•  Increases with more food in patch
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.
Optimal Prey Size:
Maximize intake Function of time
and prey size
Ecological Processes Population Level
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Predation
Competition
Parasitism
Disease
Disturbance
Facilitation
Larval dispersal*
Modes of Population Change
Exponential
Growth
Logistic growth
(resource
limitation)
Random change
Population size – important factors in assessing
change
N
Reproductive rate
Mortality
Immigration-Emigration
Example of population model:
DN
= N 0 + rN - mN + iN - eN
Dt
SPATIAL EFFECTS:MOVEMENT OF SPECIES FROM
PLACE TO PLACE – LEADS TO:
Connectivity – dispersal distance, direction and frequency
of dispersal among subpopulations
Lopez-Duarte, et al. 2012 Integrative and Comparative Biol. 52:511-524
Populations on larger SPATIAL scales….
Metapopulation
•  Definition: A group of interconnected
subpopulations
•  Sources and Sinks
•  Sink is a location where a local population can only
persist if immigrants come from elsewhere
•  Source is a site that has conditions suitable for
population growth
Metapopulation - interconnected group of
subpopulations
sink
source
Littoraria filosa
McKillup and
McKillup 2000
Oecologia
Interactions Between Species
Understand population responses of individual species
Understand interactions among species:
Community: set of interacting species
Community Structure - important
factors to consider
•  Species that determine structure to a major
degree - foundation species, interacting
species
•  Interacting Species - Processes:
Competition, predation, disturbance,
disease, parasitism, facilitation
•  Environmental influences: temperature,
salinity, light, water energy, depth, nutrient
regime
Foundation species (Ecosystem Engineers)
SALT MARSH
GRASS
REEF CORAL
SEA GRASS
MUSSEL
Keystone species – have
disproportionate effects on
community structure as predators
(or structure or competitors)
Example: top predators in food webs
EXPERIMENT: REMOVE A HYPOTHETICAL
KEYSTONE SPECIES
Keystone species –
disproportionate effects on
community structure
Example: top predators in food webs
Sea otter Enhydra lutris – eats urchins that eat kelp
Predation and Food Webs
Sea otter Trophic cascades: Predator at top of food web controls levels
beneath (
)
Removal of top predators cause major reorganizations of
Urchin communities
Some communities also strongly affected by bottom-up
processes – algal food supply
Seaweed
COMPETITION
LIMITING RESOURCES – FOOD, SPACE
Two species exploit same limiting resource: one
will displace the other, unless some process reduces
direct competition between species
Limiting Resources
Limiting Resources
Interference vs. Exploitation
Competition
Interference - one species overgrows another,
interspecific territoriality, agonistic interaction
Exploitation (scramble) - one species eats a prey
resource more efficiently than another
Outcomes of Competition
COMPETITIVE DISPLACEMENT - one species
outcompetes another for a resource (local
extinction)
COEXISTENCE - two species exploit different
resources, some process allows two species to
exploit same resource without
displacement- evolutionary process
COEXISTENCE (shifting) – shifting environment
favors different species at different times, locations
RELATION OF PREDATION TO
COMPETITION Predation suppresses competitive
success of superior species over inferior
species, especially if predator prefers
competitively superior prey
Pisaster ochraceus
Normal circumstances: mussel wins in competition
Predator removal expt. – remove starfish, mussel wins; leave starfish,
other sessile species can persist
Predator on top reduces competition for space?
Nucella
*
Pollicipes
See Paine, R. T. 1966, American Naturalist
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
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
•  Parasites can strongly affect host
populations
•  Parasites can alter host to become more
vulnerable to parasite invasion
FIG. 3.11 Marine parasitic trematodes have complex life cycles
with several intermediate hosts. (From Sousa, 1993)
San Francisco Bay
Killifish
Heron
(adult
worm)
eggs
.3 mm
trematode cercaria
trematode
miracidia
Horn snail
Ulva sp.
Trematode complex life cycle
FIG. 3.10 Diagram of the extent of invasion of a rhizocephalan
barnacle into the body of a crab. Swimming larvae (left, not to
scale) invade a crab host and inject cells that reproduce and
propagate a nutrient-absorbing tissue within the crab’s body
(right). (After Nicol, 1967)
Invasion of the body snatcher Sacculina carcini
Effects of Disease
•  Destruction of important species, e.g.,
shellfish disease attacks
•  Removal of ecologically important species
(example: removal of key grazer, Caribbean
urchin Diadema antillarum)
•  Often rapid spread, perhaps in ocean
currents
•  Interaction with other factors such as
climate change
Diadema antillarum –loss of an ecologically important species
Sea urchin
seaweed
coral
Seastar Wasting Disease – several episodes over
past 40 years
1.  Affects several species of seastars on west coast of
North America.
2.  Carried by some starfish (experiment)
3.  Infectious agent: virus (verified through extraction
of virus and culture and reinfection of seastars
Pisaster ochraceus on three successive days
Hewson et al. 2014. Proc. Nat. Acad. Sci. 111:17278–17283
Haplosporidium nelsoni, MSX in
oyster tissue (protistan) –
interspecies transfer
Perkinsus marinus,
dermo in oyster tissue
(related to
dinoflagellates)
Diseases of eastern oyster Crassostrea virginica
Disease can take out species that have major effects
On communities:
1. Seastars major predators
2. Urchins major grazers
3. Oysters create major habitat for other species
SUCCESSION
Predictable order of appearance and dominance of species, usually
following a disturbance.
Examples of disturbances:
volcanism--> coral colonization
Deposition of sand --> colonization by burrowers
IMPORTANT QUESTIONS:
IS THERE A PREDICTABLE OUTCOME – EVENTUAL DOMINANT?
DOES THE SEQUENCE OF DOMINANCE IMPLY ALTERATION OF
THE ENVIRONMENT, PAVING THE WAY FOR NEW SPECIES?
IS THE ORDER OF COLONIZATION JUST THE SUM OF RATES OF
POPULATION GROWTH/COLONIZATION RATE OF SPECIES?
Quiz
1.  Using a +-0 system, what would be the two
digit code for commensalism?
2.  Under what circumstances might a prey
species have a very bright color pattern, easily
visible to a predator species?
3.  Given a consumer that is exploiting food in a
patchy environment: As the distance between
patches increases, how should the consumer
change its behavior with regard to feeding
within a patch?
Quiz
1.  Using a +-0 system, what would be the two
digit code for commensalism?
0+
2.  Under what circumstances might a prey
species have a very bright color pattern, easily
visible to a predator species? Associated with
a poison to deter predator
3.  Given a consumer that is exploiting food in a
patchy environment: As the distance between
patches increases, how should the consumer
change its behavior with regard to feeding
within a patch? Stay longer in the patch
The End