Community Structure

1
Community Structure
Dover sole (Microstomus pacificus)

• Large numbers of species
• High abundance of most species
• High specialization of species
• High reproductive output
• planktonic larvae
• High variation of assemblage
• across reefs (space)
• across surveys (time)
• Four hypotheses

Pacific hake (Merluccius productus) unknown
Sebastes or Sebastomus
eelpout (Lycodes cortezianus)
2
Competition Hypothesis
Dover sole (Microstomus pacificus)

• Competition determines community structure
• Adults are adundant
• Food and space are limiting
• Resources are finely partitioned
• Community is stable and predictable
• But assemblage varies across space and time

Pacific hake (Merluccius productus) unknown
Sebastes or Sebastomus
eelpout (Lycodes cortezianus)
3
Lottery Hypothesis
Dover sole (Microstomus pacificus)

• Random events create vacant space on reef
• Unlimited larvae available as recruits (assumed)
• Random recruitment of larval individuals
• lottery winner
• Assemblage varies over space and time
• Biological interactions are not considered

Pacific hake (Merluccius productus) unknown
Sebastes or Sebastomus
eelpout (Lycodes cortezianus)
4
Recruitment Limitation Hypothesis
Dover sole (Microstomus pacificus)

• Larval recruits are limited
• Adult population never reaches carrying capacity
• Adult density determines larval density
• more adults more larvae
• Assemblage changes over space and time
• Biological interactions are not considered

Pacific hake (Merluccius productus) unknown
Sebastes or Sebastomus
eelpout (Lycodes cortezianus)
5
Predation Hypothesis
Dover sole (Microstomus pacificus)

• Predation maintains low population size
• space not limiting for recruits
• resources not limiting for adults
• Predators account for up to 50 of reef species
• Most species have defenses against predators
• Assemblage varies across space and time
• Resource partitioning not explained

eelpout (Lycodes cortezianus)
6
So, which hypothesis is it?
Dover sole (Microstomus pacificus)
7
Epipelagic Region
Dover sole (Microstomus pacificus)

• Euphotic zone 1-200m
• Fewer than 2 of all species
• few permanent residents
• Structure is scarce
• Nutrients are scarce
• Why?
• Environmental factors
• structure
• upwellings
• temperature and light

Pacific hake (Merluccius productus) unknown
Sebastes or Sebastomus
eelpout (Lycodes cortezianus)
8
Structure
Dover sole (Microstomus pacificus)

• Oceanic islands, seamounts, and shallow banks
• Sargassum and other weeds
• ca. 50 species in community
• Cnidarians
• Anthropogenic
• trash
• old fishing nets

Pacific hake (Merluccius productus) unknown
Sebastes or Sebastomus
eelpout (Lycodes cortezianus)
9
Upwellings and Currents
Dover sole (Microstomus pacificus)

• Upwellings bring nutrient-rich waters to surface
• coastal
• equatorial
• Currents form boundaries between oceanic regions
• Warm-core rings transport fishes long distances

Pacific hake (Merluccius productus) unknown
Sebastes or Sebastomus
eelpout (Lycodes cortezianus)
10
Temperature and Light
Dover sole (Microstomus pacificus)

• Species prefer specific temperature ranges
• salmon lt 8-10C
• tuna gt 8-10C
• Visual predators in nutrient-poor waters
• Filter-feeders in nutrient-rich waters

Pacific hake (Merluccius productus) unknown
Sebastes or Sebastomus
eelpout (Lycodes cortezianus)