Lecture 13 - Life history, trophic structure, growth rates Flashcards
Growth rate
dN/dt = rN *(K-N)/K
N = # of individuals K = carrying capacity t = time r = growth rate
Factors influencing growth rate
Fecundity (# of offspring)
Generation time
Investment per offspring
K selected strategy
For pops close to carrying capacity, high r values not selected for.
Favor improving the survival of one’s offspring (investment)
-longer generation times
-lower fecundity
- higher investment per offspring
r selected strategy
Pop often below K, able to deal with variable environment and/or competition
Focus on maximizing the number of offspring
-increased fecundity
-lower investment per young
-shorter generation times
Iteroparity
Multiple reproductive events over time Associated with... -unstable environments -longer lived species -longer generation times Better chance of reproducing when conditions are good
Disadvantage of iteroparity
Resources are less efficiently directed to production of offspring
Semelparity
Single reproductive event for females Associated with... -stable environments -short generation times -maximized investment -fast growing, short lived "r selected" species
Disadvantage of semelparity
only once chance to reproduce
Factors favoring larger sizes
- More resources to reproduce (higher fecundity or I)
- Aggressive competition
- not in pelagic, unlikely in benthic, certain at vents
- Escape from predation
- Greater resource availability (can eat larger prey)
- Locomotion power increased
- not likely in deep sea, not strong swimmers
- big fish have low muscle power
- Surface to volume ratio decreases with larger sizes
- not likely for deep sea since they are all ectotherms
Possible factors selecting against larger sizes at all depths
- Lower time-specific reproduction
- Increased mortality at larger size
- increased vulnerability
- starvation due to not getting enough food
- lack of refuge
Larger size at depth due to a combination of…
- Relaxation of selection for small size near surface (predation)
- Selection for larger size
- escape predation
- resource availability
- reproduction - increased fecundity and investment
How do isotope level change from food to consumer?
15N increases relative to 14N in the body of consumer relative to that in the body of the prey item (food)
How can growth rates be estimated?
- Modal size classes
- Lab studies
- Banding of hard parts
- Decay of radioactive isotopic species after incorporation into hard parts
- Extrapolation from size growth relations in shallow species for comparable temps
- Added habitats
How do modal size classes estimate growth rates?
Discrete size classes progress through the year
Pop dominated by large individuals = long-lived species
Pop dominated by small individuals = short-lived species
Growth rate of shallow pelagic species -euphausiids
All show early rapid growth, slowing later
over 1 year, little growth in winter
mostly 1 - 3 years
Thysanophoda spinicauda - 5 to 21 years
Growth rate of shallow pelagic species - decapods
12 months - 3 years
Growth rate of shallow species - mysids
6 m to 1 yr
Growth rate of shallow species - copepods
1 m to 1 yr max
Growth rate of shallow species - fishes
varied
Growth rate of deep benthic/near bottom - fish
slow growth, asymptotic growth curve
10-100+ yrs
Large numbers of eggs which develop at surface
iteroparous
Growth rate of deep benthic/near bottom - clams
populations dominated by smaller sizes
Growth rate of deep benthic/near bottom - echinoderms
pops dominated by larger sizes
brittle stars - 5 to 15 years
urchins - up to 30 years
Special environments for rapid growth
Whale skeletons
hydrothermal vents
Special environments for slow growth
hydrocarbon seeps
sulfidic seeps
Seasonality of reproduction - shallow species
typically seasonal
myctophids - winter and spring spawners
crustaceans - spring and summer
Seasonality of reproduction - deep sea
Asynchronous or continuous
Some seasonal, cued by disturbances
Some seasonal, when young develop in shallower waters
Total investment =
Fecundity and investment per young
Number of offspring generally ______ related to Iy and ________ related to total I
inversely
positively
Deeper species whose eggs develop at depth tend to have…
lower fecundity
Larger eggs, greater Iy
Deeper species whose young develop near the surface tend to have…
higher fecundity
smaller eggs, lower Iy
Deeper species of crustaceans tend to have…
larger eggs, greater Iy
sex ratios skewed to females ( 3 to 1 common, as high as 8)
Reproduction in angler fishes
Males are parasitic on females
fuse circulatory systems
degenerate to sperm producers
