Transcript Marine Ecology 2011, final Lecture 3 Recruitment

Lecture 2 Summary
• Geometric growth model -- used when there is a discrete breeding
season.
• Exponential growth model-- used when populations are growing
continuously
• Intrinsic growth rate--- r = births – deaths
• Because of “Environmental Resistance” population growth
decreases as density reaches a “carrying capacity” (K). The graph
of individuals vs. time yields an S-curved growth curve. This is
logistic growth.
• Density independent growth - changes in physical environmental
factors (generally climatic changes), which lead to dramatic shifts
in populations. Density dependent growth – usually applied to
larger organisms (vertebrates) or sessile organisms (barnacles);
biotic interactions (competition, predation) are important.
Lecture 2 Summary
•
Life Tables are the main tool for demographers, and they have 2
main components. Survivorship schedules – average # of individuals
that survive to any particular age; Fertility schedules (fecundity) –
average # of daughters produced by one female in each life stage
•
Net reproductive rate (Ro) is the average number of daughters
produced by a female in her lifetime. It is the summation of the
products of the fecundity (Lx) and mortality (Mx) values
•
r selection predominates in areas with high density-independent
mortality. r-selected organisms grow rapidly, reproduce early in life
with large numbers of offspring, and then disperse to other habitats.
•
K Selection predominates in stable environments. K-selected
organisms grow amd nature slowly, reproduce repeatedly and
usually produce few offspring at a time.
•
For organisms with modular growth r and K have no meaning
because colonial growth allows them to have incredibly long life
spans. A common theme is that under stressful conditions organisms
with modular growth turn on sexual reproduction for dispersal
REVIEW QUESTIONS
1.
Compare the assumptions of the geometric vs. the exponential growth models.
2.
What is carrying capacity and what factors are thought to be responsible for its
existence?
3.
Compare density independent and density dependent growth graphically.
4.
Explain how cohort and static life tables differ.
5.
Show graphically the three idealized types of survivorship curves.
6.
What is Ro and what does it tell you about the condition of a population?
7.
Describe the differences between r and K selection and give examples of the types
of species associated with each.
8.
Why do the concepts of r and K selection have little meaning for species with
modular growth?
Reproduction and Recruitment
Reproduction
• Sexual
– Hermaphroditism -protandrous, protogynous and
simultaneous (inverts, fish)
– Dioecious (mammals, fish, inverts)
– External fertilization (invertebrates, fish)
– Internal fertilization (mammals, inverts, sharks)
• Asexual
–
–
–
–
Fragmenting (corals)
Rhizomal (Sea grasses)
Budding (hydroids)
Division (anemones)
To have sex or not?
• Asexual reproduction favored in stable
habitats
– Easily propagate, spread, compete, waste no
time or energy on sex, local distribution
• Sexual reproduction favored in unstable
habitats
– Allows for genetic variability, plasticity
Dispersal and Recruitment:
Production of Larvae
• Many marine animals release huge
numbers of eggs.
– Even so, rates of fertilizations are thought to
be <20% for a wide range of invertebrates
• Sperm are short-lived (a few hours at most)
• In most cases, sperm concentrations are rapidly
diluted by currents and waves
• Donors are sparse
Dispersal and Recruitment:
Production of Larvae (cont)
• Behavioral modifications can overcome
sperm limitation
– Mollusks can form spawning aggregations
– Barnacles use internal fertilization
Fertilisation
• Internal fertilisation
– Requires males and females to meet
– Rare in sessile organisms (but does occur: for
example barnacles)
• External fertilisation
– Release of eggs and sperm into sea
– Requires eggs and sperm to meet
Most marine invertebrates spawn eggs and sperm into
the sea
Broadcasters vs Brooders
• Broadcast spawning
– shed eggs and sperm into
water column (most fish,
echinoderms)
• Internal fertilization
– females collect sperm from
water column and fertilize
eggs internally (Sponges,
cnidarians mollusks,
ascidians)
– copulation with male
placing sperm inside
female reproductive tract
(gastropods, crust., sharks,
mammals)
Hermaphroditism
• A single individual has gonads that can
produce gametes of both sexes
• A single individual can produce gametes
of either sex at different times in it life
(sequential hermaphrodites)
– protandry male to female
– protogony female to male
Protandry
• Function as Males first
• Found among species in which small
males are able to spawn with large female
Ex. Clown fish
– Males are small, females large and territorial
– Removal of female causes male to switch
– A juvenile then becomes male
Protogyny
• Often Male maintains territory with harem of
females; size of males matters
• If male is removed, one female changes to male
– Behavior (immediately)
– Gonads (a few days)
• Major rearrangement of anatomy, physiology,
hormones, and behavior
(Need not be a pure strategy - gonochoristic males
and females can exist within population)
Synchronous hermaphrodite
• Gonad has sperm and
eggs
• Often a monogamous pair
takes turns playing male
and female role - Ensures
no cheating
• ex. Hamlets (coral reef)
Protogynous
Male
Female
Size
Eggs produced or fertilized
Eggs produced or fertilized
WHY?
Size Advantage Hypothesis
Lifetime fitness and size
Protoandrous
Female
Male
Size
Strange reproductive practices of fish
• Hermaphrodites
Sex change (born one sex, become the other)
Large fish in harems are often sex-change
males (protogyny); large fish in non-harem
species are often sex-change females (protandry)
• Parasitic males
• “Sneaker” males that look like females
• Sex-role reversal (male pregnancy in seahorses)
• Males often provide parental care in fish
Rainbow wrasse
Thalassoma lucasanum
Two types of males
Two types of
reproduction.
1) Females
(yellow/red lateral
stripes)
2) Primary males
(look like females)
3) Terminal males
(blueheads)
- born female, turn
into males
http://www.oceanoasis.org/fieldguide/thal-luc.html
Rainbow wrasse
T. lucasanum
Two types of reproduction
1) Broadcast spawning Many males and females
rush to surface and release
gametes
http://www.oceanoasis.org/fieldguide/thal-luc.html
2) Harems: one terminal male
guards group of females
and mates with them
individually.
Death of secondary malelarge female turns into new
terminal male
Belted sandbass
Gulf of Mexico
(St. Andrews)
Serranus subligarius (belted sand bass)
Simultaneous
hermaphrodite
(can act as male or
female at any time)
-dominant male
in harem mates with
“females”.
Parental care
•
•
•
•
•
Preparation of nests or burrows
Egg guarding
Production of large yolky eggs
Care of young (inside or outside body
Provisioning of young (before or after
birth)
• Care of offspring after independence
Seasonality
• Seasonal Reproduction
– Short reproductive phases where high
percentage of individuals are reproductively
active
– Small eggs, high fecundity and synchronized
gamete development within individuals and
within the population.
Seasonality (cont’d)
• Year-round reproduction
(1) Asynchronous
• Individuals have discrete gamete production
• Not synchronized within the population
(2) Continuous
• Most adults within population contain gametes
year round
Dispersal and Recruitment
• The importance of recruitment has been recognized by marine
ecologists for nearly a century, but only in the past 15-20 yrs
has recruitment become a centerpiece of population and
community models.
– It is a common sense notion that an empty patch of habitat
will be uninhabited by a given species if its propagules are
unable to reach it.
– If true then the intensity of density dependent interactions
will be determined by the degree to which settlement is
successful
Definitions
• Recruitment is the addition of new
individuals to a populations or to successive
life stages within a population
Pre- and Post Settlement
Processes
Immigration
Birth
(Recruitment)
+
+
-
Population
Size
Emigration
Mortality
Dispersal and Recruitment: causes
of variation in recruitment
•
•
•
•
•
Production of varying numbers of larvae
Dispersal of larvae in the plankton
Risk of mortality while dispersing
Larval settlement success
Growth and survival of settlers until they
get counted as new recruits
Many marine species have ‘bipartite’ life histories
1. Planktonic dispersive early
stage
PLANKTONIC
LARVAE
2. Benthic or site attached adult
stage
*Larva:
an independent, often freeliving, developmental stage that
undergoes changes in form and size
to mature into the adult.
SETTLEMENT
REPRODUCTION
BENTHIC
ADULTS
More marine-terrestrial differences:
you don’t see the bipartite lifestyle often on land
Dispersal and Recruitment:
Complex Life Cycles
Dispersal and Recruitment:
Complex Life Cycles
Marine organisms: complex life cycles
Recruitment is a multi-step process
Four major parts of recruitment:
1) Dispersal & survival in water column
2) Settlement in an appropriate site
3) Successful metamorphosis into adult
body form
4) Post-settlement survival and growth
until detected by an observer
1 cm
Three basic modes of larval development
Direct -- essentially no larval stage
Larval stage encapsulated, internally brooded or
bypassed entirely
Lecithotrophic -- “yolk feeding”
Nonfeeding larval stage. Larvae do not require
food to complete development. Planktonic lifespan
is typically short (minutes to days)
Planktotrophic -- “plankton feeding”
Feeding larval stage. Larvae are incapable of
completing development without feeding
Planktonic lifespan typically long (days to months)
Thorson’s rule: a latitudinal cline in pelagic
larvae in gastropods
% Species with Pelagic Development
100
Thorson’s data for
gastropods reveals a
clear latitudinal cline in
the proportion of species
reproducing via a
pelagic larva
80
60
40
20
0
0
30
60
Latitude
90
Red data: northern hemisphere
White data: southern hemisphere
For most marine species, we have NO idea where larvae go
Larval behavior can allow for retention
Tidal Flow – Flood tide
Tidal Flow – Ebb tide
Vertical migration can result in retention of larvae
within estuary: larvae rise on flood tide, and sink on ebb
Typical life cycle of marine organisms
Planktonic dispersal
Pelagic larvae
Roughly 80% of all marine organisms
have a biphasic life cycle and produce
planktonic propagules
Sedentary
Benthic adults
Cue detection &
metamorphosis
Typical life cycle of marine organisms
Planktonic dispersal
Pelagic larvae
Problem with swimming larvae: water
motion often carries them away from
appropriate habitat
Water flow in the ocean is complex -internal waves, longshore drift, winddriven currents and eddies can all affect
where larvae end up
Sedentary
Benthic adults
Cue detection &
metamorphosis
Typical life cycle of marine organisms
Planktonic dispersal
Pelagic larvae
Cues used to assess habitats can
be chemical or physical, and larvae
often respond to some
combination of multiple cues
Cues can be positive or negative
Sedentary
Benthic adults
Cue detection &
metamorphosis
Ecological consequences: egg size, larval
type and dispersal
• Larval type is related to egg size
– Feeding (planktotrophic) larvae hatch from small eggs
– Non-feeding (lecithotrophic) larvae hatch from larger eggs
• Egg size dictates fecundity
– Females produce more small eggs than large ones
(fecundity/egg size trade-off)
• Feeding larvae tend to spend longer in plankton, and hence have
the potential to disperse further
Dispersal scale (km)
Dispersal potential is related to gene flow
and hence speciation
100
10
1
0.1
0.01
0.1
1
10
100
Planktonic larval duration (days)
Data from Siegel et al., MEPS, 260: 83-96 (2003)
How does an aggregation begin?
Someone had to be the first one to settle,
and they didn’t respond to other adults!
Desperate Larva Hypothesis: larvae
search for suitable site until they run out
of energy and then take whatever they
can find rather than die in the water
column
Founders & Aggregators: Some species produce two distinct
types of larvae: one type seeks out adults of their own species,
the other is specifically a ‘pioneer’ larva that seeks new
uninhabited, bare surfaces to colonize.
If the ‘pioneer’ larva survives and grows into an adult, it can
form the nucleus of a new aggregation.
Gregarious settlement
Gregarious settlement
• Larvae settle on (or very near)
adults of the same species
•Identifying settlement cues is
difficult and not many larval
inducers have been conclusively
identified
•Many species cannot move after
settlement & even those that can
need to feed soon
•Larvae settling with adults can
obviously tell that site will be
able to support them after they
settle
Settlement choice
• Bacteria probably play an important role, but exact effects
are unknown for all but a couple of species
• Physical cues associated with flow conditions at site of
settlement are frequently important
• Chemical cues (e.g., from food source or conspecifics) also
frequently play a role very near the substrate
Do numbers of settlers reflect number that
eventually recruit to the assemblage?
• Barnacles (Bertness et al., 1996)
– Yearly differences in number and
distribution of larval settlers, reflecting
wind effect on larval populations
• Scallops (Peterson & Summerson, 1992)
– Variability in spat explained 71%
variability in recruitment in 1988, but
only 4% in 1989
• Lobsters (Hernkind & Butler, 1994)
– No relation between settlers and
subsequent recruits over 3 years in
Florida
So, the answer is… sometimes
Post-settlement mortality
Organisms only recruit to population (establish) if they survive after
settlement
Taxon
Weekly
Annual
Polar
survival % mortality % survival %
Ascidians
Barnacles
Bryozoans
Bivalves
Gastropods
Decapods
Echinoids
Octocorals
Polychaetes
~71
~88
~94
~86
~91
~93
~86
~92
~93
75-100
92-100
99-100
90-99
10-100
~99
90-99
75-95
90-99
ND
95-100
89-100
90-100
ND
ND
ND
ND
90-100
Little suggestion that mortality higher in polar regions
Causes of post-settlement mortality
•
•
•
•
•
•
Delay of metamorphosis
Biological disturbance
Physical disturbance
Physiological stress
Predation
Competition for space or food
Physical and chemical defenses of larvae
Physical -- spines & bristles
make it difficult for small fish &
invertebrate predators to swallow them
Chemical -- chemical defenses make larvae
distasteful
• some chemical defenses just taste bad
• others have more dramatic effects –
some coral and tunicate larvae make fish
vomit immediately after ingesting a larva
Other -- larvae may have behavioral or
physical adaptations to avoid detection
• larvae may be transparent, or only active
at night when it is difficult to see them
So Why Disperse?
•
High probability of local extinction
–
•
Therefore, best to export juveniles
Spread your young over a variety of habitats
–
•
evens out the probability of mortality
Maybe it has nothing to do with dispersal at all
–
•
just a feeding ground in the plankton for larvae?
Life history theory predicts species in marine
environments do best when they ‘hedge their bets’
–
some larvae recruit to adult habitats and others disperse to
try new habitats
Dispersal: Metapopulations
Sources and Sinks
How do we Design an
What is
the
optimal
network
design?
Effective Network?
We need a much better understanding of larval dispersal
Migratory patterns
• Anadromous - breed in freshwater and
living in seawater
– salmon, shad, sea lamprey
• Catadromous - Adults live in in freshwater
then migrate to seawater to spawn
– eels Anguilla
• Oceanodromous- live totally in seawater
– herring cod and plaice
Catadromous - breed at sea, migrate into rivers to grow
(16 spp freshwater eels), adults spawn and die in Sargasso Sea
larvae in plankton 1 yr+/ metamorphose into juveniles / grow and
mature in rivers
Salmon (Anadromous)
Figure 8.22
Spend lives at
sea feeding, return
to rivers to breed:
Magnetic field and smell
of home rivers
Skipjack tuna
(Oceanodromous)
Tropical species that travels
to temperate water to feed.
Halfway across globe each
year.
• http://www.youtube.com/watch?v=mFC96vg
WNC4 first spawn of the season
Coral spawning (Lindsey et al.)
http://www.flickr.com/photos/usfwspacific/5764
239282/
http://web.me.com/russellkelley/rk/The_Spawni
ng.html
Sponge spawning
http://www.youtube.com/watch?v=Zfwd687DHQ
Fish spawning http://www.arkive.org/brownsurgeonfish/acanthurus-nigrofuscus/video11a.html