“Bipartite” life cycle of benthic marine fishes with pelagic larvae For those species Young produced by adults in a local population

“Closed” Populations “Open” Populations Production Supply Production Supply Little or no exchange among populations Significant exchange among populations Production Supply Supply Production

Population Attributes Life History Traits (individual, heritable, species-wide) reproductive modes longevity, fecundity life cycle Population Attributes distribution structure (size, age, genetic, spatial) dynamics One of the most fascinating aspects of ecology, and a central focus of evolutionary ecology, is understanding the ecological consequences of life history traits. These are heritable traits characteristic of a species, such as longevity… , that can influence the distribution, structure and dynamics of populations… Community Attributes biogeography structure (composition, abundance) dynamics diversity

b) recruitment - broadly, the addition of individuals to a population Definitions: settlement - the permanent transition from the pelagic environment to the benthic environment i.e. from the planktonic dispersive stage to the sessile/sedentary benthic stage b) recruitment - broadly, the addition of individuals to a population theoretically, same as settlement, BUT rarely see/record settlement (brief, unpredictable, involves small propagules, often occurs at night)… operationally, what is recorded as a new addition to a population. (i.e. what you see the first time you see an individual)

b) recruitment (Keough and Downes 1982) subjective, arbitrary as to when and what is measured - daily, weekly, monthly, annually ii) incorporates settlement and post-settlement mortality and movement iii) therefore, estimate and relationship to settlement depends very much on: sampling frequency - patterns of post-settlement mortality (density-independent and density-dependent)

b) recruitment time mortality rate = 0.4 (40%) 20 40 60 80 100 mortality rate = 0.4 (40%) mortality rate = 0.6 (60%) No. of indiv.s time settlement How does sampling frequency influence relationship between settlement and recruitment ? What if rate of mortality varies among sites? How does this influence your conclusions about settlement?

VIII. Settlement and Pre-settlement Processes I) Stability, population regulation and complex life histories A) Post-settlement processes – generally thought to be deterministic i) competition: logistic growth (pop), niche diversification (comm) predation: functional response (pop), switching (pop), keystone (comm) physical environment: resource (space) limitation, carrying capacity, habitat partitioning Species interactions all have predictable effects on populations and communities but recall also, ii) disturbance does not — disrupts patterns, can destabilize systems

N time I) Stability, population regulation and complex life histories B) Populations- can come to an equilibrium, therefore Community- organization can be stabilized because of feedbacks (involve mechanisms of regulation) (e.g., biomedical or thermostat) i) because the effects of ecological processes are manifested in next generation K N time e.g., logistic growth curve remember, dn/dt = rN ((K-N)/K) Which means that the change in a population (what it will be) depends on what the population size is now. As population approaches K, present population size constrains the number of offspring it produces.

Per capita growth rate (r) Limited Growth – caused by changes to birth and death rates that are density-dependent Birth rate Death rate Rate Population (N) Population (N) Per capita growth rate (r)

I) Stability, population regulation and complex life histories ii) So there’s this feedback between generations a) how?  either birth rate decreases, or death rate increases with changes in population size b) either way, assumption is that the feedback occurs locally  local birth rates and local death rates affect size of population in next generation Now… C) Contrast simple life history: (cats, dogs, people) Adult Juvenile survive, grow, mature reproduce Because of limited dispersal, this all occurs in the same local environment. So, life stages interact directly and influence each other’s performance as well as the next generation.

Larvae Pelagic Environment Benthic Environment Adult Juvenile With complex “bipartite” life cycle of benthic marine organisms with pelagic larvae: Larvae survive, grow, develop, disperse Pelagic Environment reproduce settlement Benthic Environment One key life history trait characteristic of many marine fishes is what fish heads refer to as a “bipartite” life cycle, in which Different life stages are adapted for life in either the benthic and pelagic environment. BUT “CLOSED” cycle is misleading… Adult Juvenile survive, grow, mature

Result of complex life history: 1) local supply of larvae (perhaps settlement) is de-coupled from local reproduction  settlers come from elsewhere i.e., no coupling of local reproduction and next generation of settlers therefore… For those species Young produced by adults in a local population 2) no potential for births as a feedback mechanism, theory suggest this could act to destabilize populations — we’ll come back to this we’ve removed the importance of births in population regulation and replaced with variable settlement rates!

II) Open and closed populations (two extremes of a continuum) A) closed population - population where individuals recruit back into (and replenish) population of parents open population - population where individuals recruit to populations different from parents (decoupling of local offspring production from recruitment) “Closed” Populations “Open” Populations Production Supply Production Supply Significant exchange among populations little or no exchange among populations Production Supply Supply Production

C) Reality - populations exist along a continuum of openness depending on… 1) spatial scale – increasing spatial scale of “population”, reduces openness high dispersal potential openness of population low small large spatial scale of population Scale of population = reef Scale of population = bay

Planktonic duration (days) C) Reality - populations exist along a continuum of openness depending on… 2) dispersal potential (relative to adult distribution and movement) e.g., may approximate “openness” by planktonic duration (dispersal potential) high high openness of population dispersal potential (distance) low low short long Planktonic duration (days)

D) if increasing openness of population acts to destabilize populations then there should be a relationship between population variability and planktonic duration: (because no feedback from production) Temporal variability: planktonic duration (days) Temporal variability long short population size (N) time Predict: closed populations should be less variable than open ones

Hypothesis: closed populations (species with shorter larval durations) should be less variable than open ones Russell Schmitt tested the relationship predicted by this hypothesis using fish species in So. Cal. Bight planktonic duration (days) Temporal variability long short predicted observed closed pop.s (surfperches): intermediate variability driven by local habitat variability over time fully open (long larval duration): highest variability driven by vagaries in the plankton intermediate openness (limited larval duration): lowest variability Conclusion: perhaps some population openness dampens variability by reducing both of these other sources of variability. i.e., some dispersal increases (homogenizes) scale at which population responds to habitat variability

III) Settlement and density dependence A) The theoretical complications arising from open systems and no local feedbacks assume what? 1) That the number of adults is in large part determined by larval supply and the number of settlers: Adults (t+1) Settlers (t) (1) e.g., Adults  (settlers): (2) 2) if instead adult density is unrelated to larval supply / settlement, this means: a) most influential processes occur post-settlement and, therefore, b) decoupling between local reproduction and subsequent local settlement is unimportant to regulation and stability

III) Settlement and density dependence B) How would this occur? if post-settlement processes act in a (complete) density-dependent manner 1) example: Post-settlement survivorship Density-independent Density-dependent settlers survive adults 2 50% 1 10 5 100 50 settlers survive adults 2 100% 10 20% 100 2%

III) Settlement and density dependence B) How would this occur? if post-settlement processes act in a (complete) density-dependent manner Density-independent Density-dependent survivorship: 50% 2 10 survivorship: # adults: 100 2 10 # adults: 5 1 100 2 10 50 30% 2% 100% 100 2 10 100 #settlers #settlers #settlers #settlers density independence: same probability of surviving regardless of density  direct relationship between settler # and adult # density dependence: no relationship between adult # and settler #

simple case, assume single pulse of recruits (settlers): brings us to another major paradigm in marine ecology, IV) Recruitment limitation: [definition], occurs when number/rate of settlers (“recruits”) is sufficiently low (i.e. limited) because of low production or high mortality in the plankton such that adult density remains below carrying capacity, thereby precluding competition: simple case, assume single pulse of recruits (settlers): No. settlers time K Therefore, occurs… A) when there is no density- dependence or it doesn’t fully eliminate the relationship between # of adults and # settlers B) evidence for recruitment limitation: most is from coral reef fish literature e.g., Victor 1983, Doherty 1983, Doherty and Fowler 1994 (in readings)

(number of settlers per unit time and area) IV) Recruitment limitation Now, a more unified perspective typified by… Classic invertebrate example is Connell 1985 JEMBE: Density- independent dependent K No. Adults (t+1) Settlement rate (t) (number of settlers per unit time and area)

IV) Recruitment limitation No. Adults (t+1) Settlement rate (t) (number per time) K Density- independent dependent C) So as predicted, (d-i) settlement is important and limiting but only to a certain point, where (d-d) post-settlement processes eventually overwhelm variability in settlement (i.e. increasing settlers has no affect on population size)

IV) Recruitment limitation No. Adults (t+1) Settlement rate (t) (number per time) K Density- independent dependent D) Up to a certain level, settlement could affect stability [population size] because: i) settlement affects local abundance, and ii) settlement is unrelated to local production no linkage among generations and therefore more likely to be de-stabilizing!

IV) Recruitment limitation No. Adults (t+1) Settlement rate (t) (number per time) K Density- independent dependent E) After a certain level, settlement unimportant to stability or regulation (equilibrium set by carrying capacity) at which point: i) settlement variability has no effect on local abundance (beyond some level of settlement always get same #of adults) ii) only local processes affect local abundance

WANTED Whitey The Goat Brownie The Goat

Pattern: The good professor Carr incurs physical damage when he accesses the goat behavior research facility. Whitey The Goat expresses shock and despair, while Brownie The Goat runs around the research facility jubilantly. Question(s): Is Brownie The Goat (BTG), and only BTG, responsible for professor Carr’s physical injuries? Is Whitey The Goat (WTG) a possible accomplice? General Hypothesis (1): Brownie The Goat, on her own, is responsible for professor Carr’s physical injuries. General Hypothesis (2): Whitey The Goat is an accomplice.

General Hypothesis (1): Brownie The Goat, on her own, is responsible for professor Carr’s physical injuries. Specific Hypothesis (1): If professor Carr repeatedly visits BTG and WTG separately, then the likelihood of incurring physical injury (proportion of visits he is injured), will be greater (and only) when he visits BTG than WTG. General Hypothesis (2): Whitey The Goat is an accomplice. Specific Hypothesis (2): If professor Carr repeatedly visits BTG and WTG separately and together, then the likelihood of incurring physical injury (proportion of visits he is injured), will be greater when he visits both BTG and WTG than when he visits either goat separately.

Predicted Results BG and WG multiplicative synergistic together BG only WG only B&W both 0.5 1.0 BG only WG only B&W both 0.5 1.0 BG only WG only B&W both 0.5 1.0 BG only WG only B&W both 0.5 1.0 Proportion of visits resulting in injury BG and WG additive together BG and WG multiplicative synergistic together Brownie only Whitie is accomplice