v. factors affecting recruitment...iii) safety in numbers (e.g., swamping predators) 2) larval...

1. Larval production

2. Larval dispersal

3. Settlement

4. Post-settlement

V. Factors affecting recruitment

III. The evolution of behavioral cues (for settlement)

a) Utility of behavioral cues larval period critical – relocation after settlement is difficult or impossible… life-long fitness consequences consequence of settlement

i) indicates “good” habitat / conditions for the species

ii) facilitates reproduction (particularly) for individuals that are sessile

iii) safety in numbers (e.g., swamping predators)

2) Larval behavior

C) Processes affecting settlement

b) Why not always have cues ? — costs

Reliability of cueHigh Low

Probability of evolving a cue

response

b) Two potential costs (mistakes)

1) cue is in inappropriate…leads to settlement in inappropriate conditions

2) places without cue are in fact appropriate… think about coral heads without blue chromis

b) Why not always have cues ? two kinds of costs… (mistakes)

1) cue is in inappropriate…leads to settlement in inappropriate conditions

Mistakes:

2) places without cue are in fact appropriate… think about coral heads without blue chromis

reliability of cuelow high

low

high

= death

Probabilityof evolving response to

cue low

high

cost of mistake(not using cue)

Can all this behavior at settlement contribute to those patterns that drove ecologists to study intertidal ecology (i.e. patterns of zonation)?

Given…

i) the costs of adapting to inappropriate cues,

ii) how many species exhibit this behavior to so many different kinds of cues

iii) the implied strength of selection for these behavioral responses

iv) the importance of settlement as a life-long consequence for fitness (especially for sessile species)…

…then settlement must be an extremely important stage in the life cycle of a marine organism.

2) Larval behavior

I) types

II) history of larval behavior studies - barnacles

III) conditions for evolution of behavioral cues (settlement)

IV) contribution to vertical zonation

V) Factors affecting recruitment

C) Processes affecting settlement

1) Physical processes (e.g., turbulence, current speed)

IV. Contribution of larval behavior to vertical zonation patterns

A) Processes affecting zonation 4 possibilities

Adult pattern(zonation):

AAA AA A

B BBB

B B

b

b

b

bb

b

bb

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aa

a

a

a

a

a

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aa

a

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b

b

b

1) larvae may (1) be mixed in water column, (2) show no settlement behavior (3) settle randomly and (4) die back to appropriate zonation (post-settlement processes!)




2) Individuals may move after settlement

AAA AA A

B BBB

B B

b

b

b

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bb

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a

a

a

a

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a

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b

b

b

b




AAA AA A

B BBB

B B

b

b

b

bb

b

bb

a

aa

a

a

a

a

a

3) Larvae may (1) be mixed in water column, (2) exhibit settlement behavior (3) settle within appropriate zone

aa

a

aaa

bb

bbb

b



4) Larvae may be stratified in water column (behavior or hydrodynamic effects) and land at different tidal heights


AAA AA A

B BBB

B B b

bb bb

bb

b

a

aa aa

aa

a

aa

a

a

bbbb

b

B) Stratification of larvae in water column

Grosberg 1982, senior thesis!


a) System: Santa Cruz harbor, 2 species of barnacle on pier pilings

b) Pattern:

i) Balanus glandula – upper intertidal barnacle

ii) Balanus crenatus –lower intertidal barnacle

Tide height (m)0

-1.2

1.8

Adult Density (#/100 cm2)

B. glandula

B. crenatus

1000

c) Question: What causes vertical zonation?

d) Hypotheses:

i) HA1: early post-settlement mortality limits species distribution (sensu Connell)

ii) HA2: stratification of larvae limits distribution via behavior

e) Test:

i) HA1 early post-settlement mortality


10 x 10 cm plates

Sampled weekly during a period of high settlement -allows detection of 1–7 day old individuals

Tidalheight2.1

-1.2

f) Results:

Settler density (#/100cm2)

Settler density (#/100cm2)

Question: What causes vertical zonation?


0

-1.2

1.8B. glandula

800

Tidalheight

Adult Density (#/100 cm2)0

0

-1.2

1.8B. glandula

B. crenatus

100

Adult pattern…

Settlement pattern…

0

-1.2

1.8

B. crenatus

1000

2) not post-settlement processes causing adult distribution

g) Conclusions:

1) settlement was same distribution as adults



d) Test — clever

i) plankton pulls on 3 days: new, full, half moon

ii) sampled hourly for 24 hour periods on each day

iii) sampled from a floating dock at 4 depths:




Time of day

Tidal rangesampled

-4.0

1.8surface

3m 3m depth

surface, 0.5 m, 1.5 m, and 3 m

sampling range: -4 m to 1.8 m

e) Results — differ between species: 1) 94% of glandula larvae taken in surface waters (irrespective of tidal

sequence) 2) 98% of crenatus larvae were collected < 0 m mllw, (meaning their

distribution in water column changed as a function of tide)


Time of day

Tidal rangesampled

-4.0

1.8surfaceB. glandula

B. crenatus

Larvalabundance

B. glandula B. crenatus

-4.0 1.80 -4.0 1.80

f) Conclusions-

1) Distribution of adults determined by position of larvae in water column

2) Larval distribution set by two different behaviors:

a) B. glandula stays in surface water, which over tidal sequences travels from about -1.2 to 1.8 m(abundances correspond to time at tidal height)

b) B. crenatus stays below a particular tidal level orients to bottom?


Example: Carr 1994 Ecology

C) Interactive effects of vertical distribution of larvae and biogenic structure on the spatial and temporal patterns of recruitment

Question: Does kelp provide settlement habitat for reef fishes, and if so, does the temporal and spatial variability of kelp influence patterns of fish recruitment?

System: Forests of giant kelp, Macrocystis pyrifera and the kelp bass, Paralabrax clathratus at Santa Catalina Island, CA

0

10

20

30

MacrocystisAbsent Present

P < 0.0001

Den

sity

of k

elp

bass

recr

uits

(No.

per

60

m3

)

d) Pattern:

Greater density of kelp bass settlers in areas of a reef with giant kelp compared to areas without

and test of first hypothesis:

c) Hypothesis 1: If giant kelp influences recruitment, there will be a positive relationship between abundance of kelp and kelp bass recruits.

10

2030

0 100 200 300 4001

23

5

Macrocystis density (Stipes per 30 m2)

kelp

bas

s re

crui

t de

nsity

(Num

ber

per

60 m

)3

Pattern 2: Variation in recruitment among reefs and years

Density of kelp bass settlers increases with increasing density of giant kelp, but it is not linear!

Macrocystis density (stipes / 30 m2 )

0

A

BB

400

800

1,200

(gra

ms

/ 10

m )2

0 40 80 120

blade biomass per reef area:

Hypothesis 2: Local kelp bass recruitment should respond to manipulated density of giant kelp

(Num

ber

/ 10

m )2

0 40 80 120 160012345

A

BB


0

A

BB

400

800

1,200

(gra

ms

/ 10

m )2

0 40 80 120


kelp bass recruit density:



blade biomass(gm per 5 m3 )

0 500 1,000 1,5000

2

4

6

(Num

ber

per

10 m

2 )(Num

ber

/ 10

m )2

0 40 80 120 160012345

A

BB


0

A

BB

400

800

1,200

(gra

ms

/ 10

m )2

0 40 80 120




Conclusions:

i) Local and “regional” patterns of kelp bass recruitment are influenced by dynamics of giant kelp abundance.

ii) The relationship is not based strictly on plant density, but on biomass (shelter!). Because kelp biomass changes with plant density, recruitment relationship is asymptotic.

iii) Giant kelp facilitates recruitment of kelp bass by providing habitat that they encounter as they pass over reefs.

e.g., Carr 1994, Ecology

Settlement (post-settlement): habitat structure(1) Macrocystis (kelp bass in southern California)

- manipulated kelp density and monitored recruitment

(2) Macrocystis (kelp surfperch in so. California)e.g., Anderson 1994, MEPS

- manipulated presence of giant kelp canopy andmonitored recruitment

(3) Sea urchins (blue-banded goby and red abalone)

- manipulated presence of urchins and monitored recruitmente.g., Hartney and Grorud 2002, Oecologia

e.g., Rogers-Bennet and Pearse 2001, Conserv. Biology- compared abalone recruitment in and out of MPAs with

more or fewer red urchins

- greater kelp bass recruitment with increase in kelp

- greater kelp perch recruitment in presence of canopy

(Early) post-settlement processes as sources of variation in recruitment

Remember: recruitment estimates occur at some point after settlement…

1. Do post-settlement processes (competition or predation) alter recruitment patterns?

2. Can post-settlement processes de-couple settlement and recruitment through density-dependent mortality?

3. How important are competition and predation as sources of variation in recruitment AND density-dependent mortality?


2. Larval dispersal

3. Settlement

4. Post-settlement


growthmovementcompetitionpredation

survival

General approach:

i) To test for predator or competitor effects, manipulate presence and absence of competitors or predators

ii) To test for density-dependence, manipulate density of settlers

iii) To test for density dependence caused by predation, manipulate BOTH orthogonally

(Early) post-settlement processes as sources of variation in recruitment

Kelp undergo an alteration of generations.Most research has focused on 2N juvenile sporophytes,but competition among 1N spores was understudied.

Early post-settlement processesReed 1990 Ecology

Pattern: Macrocystis pyrifera and Pterygophora californica occur in patches across west coast kelp forests and both species recruit heavily after disturbance.

Hypothesis: Competition among spores could affect recruitment success of both species.

Test: “Seeded” tiles with different combinations and densities of spores of both species.

Hypothesis: Competition among spores could affect recruitment success of both species.

Test: “Seeded” tiles with different combinations and densities of spores of both species.

Design:Tested for and compared strength of intraspecific and interspecific competition

Result 1: Number of viable sporophytes decreased with increasing settlement density= intraspecific competition!

Result 2: At high spore density, Macrocystisrecruitment density decreased with an increasing proportion of Pteryogophora.

Mac

rocy

stis

recr

uit d

ensi

ty

Seeding ratio (Pterygophora/Macrocystis)

Steele 1997a, Ecology

Conspecific and interspecific resident effects

- black-eyed and blue-banded gobies in So. CA- manipulated presence of adults of both

- adult black-eyed reduced settlement of black-eyed young

- adult blue-banded had no effect on settlement of blue-banded

- adult blue-banded increased settlement of blue-banded

- adult black-eyed had no effect on settlement of blue-banded

Early post-settlement: competition


2. Larval dispersal

3. Settlement

4. Post-settlement


- growth- movement

competitionpredation

- survival

V. (Early) post-settlement processes as sources of variation in recruitment

General approach:

i) To test for predator effects, manipulate presence and absence of predators

ii) To test for density-dependence, manipulate density of settlers

iii) To test for density dependence caused by predation, manipulate BOTH orthogonally

0 20 40 60 80 100

kelp rockfish

Early post-settlement mortality: predation

1.01.0

0 40Initial density

0.00.20.40.60.8

0 5 10 15

black eyed goby

Initial density

per-capitamortality

Steele 1997 Oecologia

1.0

Note! Predators present!

0 20 40 60 80 100

kelp rockfish


Kelp perch

Johnson 2006 Ecology

predators present

1.01.0

0 20 40 60

Anderson 2002 Ecology

Initial density Initial density

mor

talit

y

mor

talit

y

0 20 40 60 80 100

kelp rockfish


Kelp perch

Johnson 2006 Ecology

predators present

predators absent

1.01.0

0 20 40 60

Anderson 2002 Ecology

Initial density Initial density

mor

talit

y

mor

talit

y

Conclusions

(1) Post-settlement mortality is a source of variation in recruitment

(2) Predation is an important source of post-settlement mortality

(3) Predation is also a source of density-dependent mortality, which can decouple estimates of settlement and recruitment (think about this with respect to testing for recruitment limitation)

Density-independent Density-dependent

survivorship:

#settlers #settlers #settlers #settlers

How would this occur? if post-settlement processes act in a (complete) density-dependent manner

VI) Settlement, density dependence and recruitment

50

100

survivorship:

50%

2 10

30%2%

100%

1002 10

density dependence: no relationship between settler # and recruit #

1002 102

density independence: same probability of surviving regardless of density direct relationship between settler # and recruit #

51

1002 10

# adults: recruits!# adults: recruits!

v. factors affecting recruitment...iii) safety in numbers (e.g., swamping predators) 2) larval...

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