Lecture 13 - Life history, trophic structure, growth rates

Question 1

Growth rate

Answer 1

dN/dt = rN *(K-N)/K

N = # of individuals
K = carrying capacity
t = time
r = growth rate

Question 2

Factors influencing growth rate

Answer 2

Fecundity (# of offspring)
Generation time
Investment per offspring

Question 3

K selected strategy

Answer 3

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

Question 4

r selected strategy

Answer 4

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

Question 5

Iteroparity

Answer 5

Multiple reproductive events over time
Associated with...
   -unstable environments
   -longer lived species
   -longer generation times
Better chance of reproducing when conditions are good

Question 6

Disadvantage of iteroparity

Answer 6

Resources are less efficiently directed to production of offspring

Question 7

Semelparity

Answer 7

Single reproductive event for females
Associated with...
   -stable environments
   -short generation times
   -maximized investment
   -fast growing, short lived "r selected" species

Question 8

Disadvantage of semelparity

Answer 8

only once chance to reproduce

Question 9

Factors favoring larger sizes

Answer 9

1. More resources to reproduce (higher fecundity or I)
2. Aggressive competition
   
   • not in pelagic, unlikely in benthic, certain at vents
3. Escape from predation
4. Greater resource availability (can eat larger prey)
5. Locomotion power increased
   
   • not likely in deep sea, not strong swimmers
   • big fish have low muscle power
6. Surface to volume ratio decreases with larger sizes
   
   • not likely for deep sea since they are all ectotherms

Question 10

Possible factors selecting against larger sizes at all depths

Answer 10

1. Lower time-specific reproduction
2. Increased mortality at larger size
   
   • increased vulnerability
   • starvation due to not getting enough food
   • lack of refuge

Question 11

Larger size at depth due to a combination of…

Answer 11

1. Relaxation of selection for small size near surface (predation)
2. Selection for larger size
   
   • escape predation
   • resource availability
   • reproduction - increased fecundity and investment

Question 12

How do isotope level change from food to consumer?

Answer 12

15N increases relative to 14N in the body of consumer relative to that in the body of the prey item (food)

Question 13

How can growth rates be estimated?

Answer 13

1. Modal size classes
2. Lab studies
3. Banding of hard parts
4. Decay of radioactive isotopic species after incorporation into hard parts
5. Extrapolation from size growth relations in shallow species for comparable temps
6. Added habitats

Question 14

How do modal size classes estimate growth rates?

Answer 14

Discrete size classes progress through the year

Pop dominated by large individuals = long-lived species
Pop dominated by small individuals = short-lived species

Question 15

Growth rate of shallow pelagic species -euphausiids

Answer 15

All show early rapid growth, slowing later
over 1 year, little growth in winter
mostly 1 - 3 years
Thysanophoda spinicauda - 5 to 21 years

Question 16

Growth rate of shallow pelagic species - decapods

Answer 16

12 months - 3 years

Question 17

Growth rate of shallow species - mysids

Answer 17

6 m to 1 yr

Question 18

Growth rate of shallow species - copepods

Answer 18

1 m to 1 yr max

Question 19

Growth rate of shallow species - fishes

Answer 19

varied

Question 20

Growth rate of deep benthic/near bottom - fish

Answer 20

slow growth, asymptotic growth curve
10-100+ yrs
Large numbers of eggs which develop at surface
iteroparous

Question 21

Growth rate of deep benthic/near bottom - clams

Answer 21

populations dominated by smaller sizes

Question 22

Growth rate of deep benthic/near bottom - echinoderms

Answer 22

pops dominated by larger sizes
brittle stars - 5 to 15 years
urchins - up to 30 years

Question 23

Special environments for rapid growth

Answer 23

Whale skeletons

hydrothermal vents

Question 24

Special environments for slow growth

Answer 24

hydrocarbon seeps

sulfidic seeps

Question 25

Seasonality of reproduction - shallow species

Answer 25

typically seasonal

myctophids - winter and spring spawners
crustaceans - spring and summer

Question 26

Seasonality of reproduction - deep sea

Answer 26

Asynchronous or continuous

Some seasonal, cued by disturbances
Some seasonal, when young develop in shallower waters

Question 27

Total investment =

Answer 27

Fecundity and investment per young

Question 28

Number of offspring generally ______ related to Iy and ________ related to total I

Answer 28

inversely

positively

Question 29

Deeper species whose eggs develop at depth tend to have…

Answer 29

lower fecundity

Larger eggs, greater Iy

Question 30

Deeper species whose young develop near the surface tend to have…

Answer 30

higher fecundity

smaller eggs, lower Iy

Question 31

Deeper species of crustaceans tend to have…

Answer 31

larger eggs, greater Iy

sex ratios skewed to females ( 3 to 1 common, as high as 8)

Question 32

Reproduction in angler fishes

Answer 32

Males are parasitic on females
fuse circulatory systems
degenerate to sperm producers