Download Chapter 3b - Department of Ecology and Evolution

Aggregations on larger scales….
Metapopulation
• Definition: A group of interconnected
subpopulations
• Sources and Sinks
Metapopulation - interconnected group
of subpopulations
sink
source
McKillup and
McKillup 2000
Oecologia
Predictable
recruitment
gradients - bluehead
wrasse Thalassoma
bifasciatum
St. Croix
www.reef.org
Hamilton et al. 2006. Marine Ecology Progress Series 306: 247-256
Population Level
1. Population size
2. Spatial aspects - metapopulation connectivity - sources, sinks (larval
dispersal
Community Structure - Important
Factors to Consider
• Species that determine structure foundation species, interacting species
• Processes: Competition, predation,
disturbance, disease, parasitism, facilitation
• Environmental influences: temperature,
salinity, light, water energy, depth, nutrient
regime
Foundation species
coral
seagrass
salt marsh grass
mussels
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
Limiting Resources
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 (scramble) - one species eats a prey
resource more efficiently than another
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 (“Paradox of the plankton” - coexistence of
many phytoplankton species, despite nutrient limitation)
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., invasive species, increase
of resource exploitation in estuaries. Problem - other factors could
be atwork
4. CONTIGUITY OF RESOURCE USE e.g., "adjacent niches" - could arise by evolutionary change
Predation
SPATIAL SCALE
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.
Examples of disturbance and colonization:
volcanism--> coral colonization; deep-sea invertebrate
colonization
Deposition of sand --> colonization by burrowers
SOME MODES OF SUCCESSION
(1) Early species modify unoccupied habitat, which
facilitates colonization by later species (bioturbation) primary succession
SOME MODES OF SUCCESSION
(2) Inevitable colonization of successively competitively
superior species, following some initial community secondary succession. Later species tolerate competition,
lower resources.
Factors in succession
1. Initial colonists - properties: not specialized, high
reproductive rate, dispersal-oriented
2. Later colonists - better competitors that displace
earlier species?
3. Prevention of invasion - good competitor? Good at
resisting predation? Environment altered, which
prevents further colonists from invading?
4. Is there a climax community? Assemblage of
competitively superior species? Resistant to
predators? Evidence for such communities?
Dominance?
SOME MODES OF SUCCESSION
(3) When patterns exist, they are an accidental result of a variety of
interactions, including priority effects, seasonal colonization, random change
Membranipora
sp.
Direct versus Indirect Effects
Direct effects: Predator consumes prey, prey population
decreases
Indirect effects: Sea otter consumes urchins; as a
consequence, seaweed prey of urchins increases in
population size
Density mediated indirect effect: Density at one feeding
level increases, which reduces prey of another species, and,
in turn results in an increase of the prey of the second
species
Trait-mediated indirect effect: Presence of a predator, causes
prey to be active less and feed less on their own prey, so
prey of second species increase in abundance, even though
the second species did not decline (their feeding activity
declined).
Ecosystem level
• Ecosystem: group of interdependent biological
communities and abiotic factors in a single
geographic area that are strongly interactive.
• Nearly all ecosystems have primary producers
(mainly photosynthetic), secondary producers
(herbivores), and carnivores. Material escaping
this cycle is material to be decomposed in the
saprophytic cycle.
• Food webs may be controlled by top-down
processes where top predators have strong effects
or bottom-up processes where changes in primary
production drive changes in food web.
• Strong top-down linkages or bottom-up linkages
generate a tropic cascade through the food web.
The End