1. Larval production 4. Post-settlement

Transcription

1 V. Factors affecting recruitment 2. Larval dispersal 3. Settlement 1. Larval production 4. Post-settlement

2 V) Factors affecting recruitment C) Processes affecting settlement 1) Physical processes (e.g., turbulence, current speed) 2) Larval behavior a. Types b. History of larval behavior studies c. Density dependence (facilitative recruitment) d. Conditions for evolution of behavioral cues e. Contribution to vertical zonation 3) Habitat availability

3 C) Interactive effects of vertical distribution of larvae and biogenic structure on the spatial and temporal patterns of recruitment Carr 1994 Ecology 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

4 Hypothesis 1: If giant kelp influences recruitment, there will be a positive relationship between abundance of kelp and kelp bass recruits. Pattern (and test of first hypothesis): Greater density of kelp bass settlers in areas of a reef with giant kelp compared to areas without Density of kelp bass recruits (No. per 60 m 3 ) P < Absent Present Macrocystis

5 Pattern 2: Variation in recruitment among reefs and years kelp bass recruit density (Number per 60 m 3 ) Macrocystis density (Stipes per 30 m 2 ) Density of kelp bass settlers increases with increasing density of giant kelp, but it is not linear!

6 Hypothesis 2: Local kelp bass recruitment should respond to manipulated density of giant kelp kelp bass recruit density 2 (Number / 10 m ) B B A (grams / 10 m ) 1,200 blade biomass B 800 A Macrocystis density (stipes / 30 m 2 ) B

7 Hypothesis 2: Local kelp bass recruitment should respond to manipulated density of giant kelp kelp bass recruit density 2 (Number / 10 m ) 2 (grams / 10 m ) , A B A blade biomass B Macrocystis density (stipes / 30 m 2 ) B B (Number per 10 m 2 ) kelp bass recruit density ,000 1,500 blade biomass (gm per 5 m 3 )

8 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.

9 V. Factors affecting recruitment 2. Larval dispersal 3. Settlement 1. Larval production 4. Post-settlement survival growth movement competition predation

10 V. Factors affecting recruitment 2. Larval dispersal 3. Settlement 1. Larval production 4. Post-settlement survival growth movement competition predation

11 (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 densitydependent mortality?

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

13 Early post-settlement processes Reed 1990 Ecology (2N) SPOROPHYTE - ~~~~EMBRYONIC - SPOROPHYTE SPOROPHYTE SPOROPHYLLS GMTPYE 0 ~~ZOOSPORES FIG. 1. The life history of the brown alga Macrocystis pyrifera, a typical kelp showing a heteromorphic alteration of Kelp undergo an alteration of generations. Most research has focused on 2N juvenile sporophytes, but competition among 1N spores was understudied.

14 Pattern: Macrocystis pyrifera and Pteryogophora california occur in patches across west coast kelp forests and both species recruit heavily after disturbance. April 1990 SETTLEMENT AND RECRUITMENT IN KELPS Hypothesis: Competition among spores could affect recruitment success of both species. and thenreturning themto the l EXPERIMENTAL DESIGN a Macrocystis (spores / mm2) " R E w 50 0 * * 0 0 b & 1987 Test: Seeded tiles with different combinations and densities ofmacrocystis spores of both species. (spores / mm2) slides were transportedwiththe same black plasticbags storedin withseawater.the survivalof g slides was monitoredfor 1 wk of slides that never leftthe labo mortalitywas always negligible indicatingthatthetransportpro outplantedgametophytes.using Deysherand Dean (1986) also fo porton gametophytesofmacrocy ed to the field. Experimentald Experimentswere designedto which variationin spore settlem I also evaluat phyterecruitment.

15 Results 1: Number of viable sporophytes decreased with increasing settlement density = intraspecies competition! Results 2: At high spore density, Macrocystis recruitment density decreased with an increasing proportion of the other species. Macrocystis recruit density a 40- HIGH DENSITY : 30 - ( spores / mm2) /10 1/10 10/10 Seeding ratio (Pterygophora/Macrocystis)

16 V. Factors affecting recruitment 2. Larval dispersal 3. Settlement 1. Larval production 4. Post-settlement survival growth movement competition predation

17 Early post-settlement mortality: predation 1.0 per-capita mortality kelp perch Anderson 2002 Ecology black eyed goby Note! Predators present! Initial density 1.0 Steele 1997 Oecologia kelp rockfish Johnson 2006 Ecology predators present predators absent

18 Conclusions (1) Post-settlement mortality is a source of variation in recruitment! (2) Competition and predation are important sources 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).

19 VI) Settlement, density dependence and recruitment How would this occur? if post-settlement processes act in a (complete) density-dependent manner Density-independent Density-dependent survivorship: # adults: recruits! % survivorship: # adults: recruits! 50% % 2% #settlers #settlers #settlers #settlers density independence: same probability of surviving regardless of density à direct relationship between settler # and recruit # density dependence: no relationship between settler # and recruit #

20 Pre-settlement / settlement effects on maintenance of species diversity Hypotheses (summarized and reviewed by Connell 78) 1) Equilibrium hypotheses 2) Non-equilibrium hypotheses To determine the possible importance of each hypothesis in a particular community one could test: a) assumptions necessary for each hypothesis b) predicted dynamics and structure of assemblage in response to a perturbation c) test both observationally and /or experimentally

21 Review of hypotheses for maintenance of diversity I. Equilibrium Hypotheses - involve settlement and post-settlement processes - stress biotic interactions - mostly competition based - competitive exclusion principle - community structure and dynamics are predictable - predictable return to pre-perturbation state!

22 Niche Diversification Hypothesis Assumptions: a) competition based (assumes resources are limiting) b) resource partitioning (each species is a superior competitor for particular resources or within particular niche) c) for test, assume perturbation does not alter resource availability, only diminishes species abundances Predictions: a) total number of individuals and total number of species limited by resources, assemblage-wide carrying capacity (K) b) relative abundance of spp. determined by relative niche availability specific carrying capacity for each species c) predictable composition and relative abundance

23 Niche Diversification Hypothesis Proportional abundance Time K Total abundance Species A Species B Species C

24 Niche Diversification Hypothesis Proportional abundance perturbation Time K Total abundance Species A Species B Species C Species composition returns to pre-perturbation state!!!

25 Assumptions: Compensatory Mortality a) Competition based (assumes resources are limiting) b) Disturbance removes most abundant species (mortality is frequency-dependent), thereby freeing resources for competitively inferior, rarer species. c) For test, assume perturbation does not alter resource availability, only diminishes species abundances. Predictions: a) Inverse relationships in species abundances b) Most abundant species at any time suffers disproportionate absolute mortality

26 Compensatory mortality Proportional abundance Time Total abundance K Species A Species B Species C

27 Compensatory mortality Proportional abundance Species B Species A Species C Time Species composition returns to perturbation pre-perturbation state!!! K Total abundance

28 Predation Hypotheses Different equilibrial-based mechanisms: Compensatory mortality (generalist predators consume more of the most abundant species) Predators switch to feed on most abundant species, disproportionately reducing that species Keystone predation where predator prefers competitive dominant, freeing up resources for subordinate competitors Induces competition for refuge from predation (i.e. overall K for assemblage) Predators regulate populations of prey species separately (density dependence)

29 Predation Hypotheses Assumptions: a) predator causes disproportionately higher absolute mortality in most abundant prey species (competitive dominant) b) induces competition or otherwise regulates prey populations c) these allow persistence of rare species or inferior competitors Predictions: a) inverse relationships in species abundances b) most abundant species at any time suffers disproportionate absolute mortality

30 Predation Hypothesis (compensatory, switching or keystone) Proportional abundance Time Total abundance Species A Species B Species C Note similarity of predicted pattern with compensatory mortality

31 Predation Hypothesis (compensatory, switching or keystone) Proportional abundance perturbation Time Total abundance Species B Species A Species C Note similarity of predicted pattern with compensatory mortality

32 Predation Hypotheses Predictions for recruitment patterns: Compensatory mortality, switching differences in recruitment diminish over time as numbers converge Induced competition for refuge pattern similar to niche diversification Proportional abundance Regulation of prey populations separately (density dependence) leads to predictable relative abundance of recruits Recruitment pulse Time Species A Species B Species C

33 Review of Hypotheses for maintenance of diversity (summarized and reviewed by Connell 78) II. Non-equilibrium Hypotheses Various processes can be involved: competition, predation, disturbance, recruitment limitation Relative and total abundance fluctuates unpredictably Species composition is unpredictable Species composition and abundance does NOT return to preperturbation state

34 Intermediate Disturbance Discussed at length previously Competition based mediated by physical or biological disturbance Involves mostly post-settlement interactions but also attributes of pre-settlement stages (recall both r vs K species characters and Sousa s work). Life History Early Successional Late Successional Character ( r-selected ) ( K-selected ) Reproduction semelparous (once) iteroparous (multiple) Fecundity high low Dispersal ability good-long poor-short Growth rate fast slow Life span short long Competitive ability POOR GOOD

35 Recruitment Limitation Hypothesis Assumptions: Peter Doherty 1983, Ben Victor 1986 Assumes high mortality of pelagic larvae limits number of recruits to benthic populations Larval supply limits recruitment below that which is required to saturate resources No competition so mortality is density-independent Predictions: total numbers and relative abundance fluctuates with variable larval supply

36 Review: Density-independent mortality K Density- independent Density- dependent No. Adults (t+1) Settlement rate (t) (number per time)

37 Recruitment Limitation Hypothesis Proportional abundance Time K Total abundance Species A Species B Species C

38 Lottery Hypothesis (Connell s Equal Chance Hypothesis) Assumptions: Peter Sale 1977 competition based (resource limitation) larval pool saturates resource (space) no resource partitioning (all species equal competitors) likelihood of creating and acquiring resource (space) due to random chance (deaths and larval settlement unpredictable) likelihood of settlement = relative abundance in larval pool but, requires some mechanism in plankton to maintain the relative abundance of species in larval pool! Assumes species compositions on different reefs out of sync!

39 Lottery Hypothesis (Connell s Equal Chance Hypothesis) Predictions: Peter Sale 1977 unpredictable as to what species will recruit to any location or at any time maximum total abundance across all species (K) relative abundance of species fluctuates unpredictably including after perturbation

40 Lottery Hypothesis Proportional abundance Time K Total abundance Species A Species B Species C

41 Lottery Hypothesis Proportional abundance perturbation Time K Total abundance Species A Species B Species C

42 Lottery Model Storage Effect (Huthchinson s Gradual Change Hypothesis) Assumptions: Bob Warner and Peter Chesson 1985 competition based (resource limitation) same assumptions as lottery hypothesis, but relative recruitment success of species changes through time (akin to gradual change hypothesis) variable success due to variation in larval production, planktonic conditions, settlement conditions species persist through bad recruitment periods and store recruitment events in extended lifetime (age classes) of adults Predictions: same as Lottery Hypothesis but different mechanism

43 Gradual change hypothesis i) Competitive rank varies with changing environmental conditions: A B C D ii) Hutchinson s paradox of the plankton iii) Species must not decline to extinction before environment changes to favor it again Abundance / competitive rank TIME

44 Lottery Model Storage Effect Proportional abundance Time K Total abundance Species A Species B Species C

45 Proportional abundance Lottery Model Time K Total abundance Species A Species B Species C perturbation NOTE: pattern and response similar to Lottery Hypothesis, but mechanism cannot be distinguished!

46 Assumptions: Pluralistic Approach Geoff Jones (in Sale s book) 1991 probably a combination of several of the above varying in importance over scales of space and time because several of these competing hypotheses create similar patterns of variability in relative and combined numbers, helps to distinguish them experimentally involves orthogonal manipulations of competition, predation and disturbance Predictions: Relative importance of any model is determined by whether recruitment is modified by post-recruitment processes

47 Pluralistic Approach Jones 1991 Post-recruitment (PR) Competition Intense Weak Recruitment modified by (PR) processes Recruitment NOT modified by (PR) processes

48 Pluralistic Approach Jones 1991 Post-recruitment (PR) Competition Intense Weak Recruitment modified by (PR) processes Competition Model (Niche Diversification) Predation Disturbance Models Recruitment NOT modified by (PR) processes

49 Pluralistic Approach Jones 1991 Post-recruitment (PR) Competition Intense Weak Recruitment modified by (PR) processes Competition Model (Niche Diversification) Predation Disturbance Models Recruitment NOT modified by (PR) processes Lottery Hypothesis (Model) Recruitment Limitation

50 Biodiversity and ecosystem function Why study? 1. Ongoing loss of biodiversity and conservation implications 2. Experimental approachs to these questions address fundamental questions about the maintenance of diversity! What is diversity? Definition: The number of species (species richness) and their relative abundance. What is ecosystem function? Definition (Chapin et al. 1998): Aggregate or community or ecosystem-level processes and properties, such as production, standing biomass, invasion resistance, element cycling and trophic transfer.

51 Biodiversity and ecosystem function Expectation: Biodiversity increases ecosystem function. Function Species richness Sampling effect: As species richness increases, it becomes more likely that a community will have a species with a particular functional attribute. Functional redundancy: As species richness increases, the number of species that play functionally similar roles in the community increases.

52 Biodiversity and ecosystem function Expectation: Biodiversity increases ecosystem function. Stability Species richness Sampling effect: As species richness increases, it becomes more likely that a community will have a species with a particular functional attribute. Functional redundancy: As species richness increases, the number of species that play functionally similar roles in the community increases.

53 Biodiversity and invasion resistance Stachowicz et al Pattern: Invasive species are common in areas frequented by humans and boats (harbors). Some communities have lots of invasives, while others don t. Hypothesis: Species diversity could limit invasion with more diverse communities utilizing the resources more completely.

54 Biodiversity and invasion resistance Stachowicz et al Methods: deployed settlement tiles with different species richness but same Invasive Conclusions: More efficient space utilization in species rich communities!

55 Biodiversity and invasion resistance Stachowicz and Byrnes 2006 But the relationship between native diversity and invasibility depends on the identity of the native species! Facilitators present Facilitators rare or absent Invader richness Low free space High free space Invader richness Low free space High free space Native richness Native richness Figure 3

56 Biodiversity and coral reefs Rasher et al Ecology Pattern: Higher diversity of fish in coral reef reserves, as well as lower overall algal biomass. Not all fish eat all algae some fish avoid specific algae with chemical defenses.

57 Biodiversity and coral reefs Rasher et al Ecology Amount consumed Pattern: Higher diversity of fish in coral reef reserves, as well as lower overall algal biomass. Not all fish eat all algae some fish PREY DIVERSITY INTERACT 1353 avoidconsumer specificand algae with chemical defenses. Species of algae FIG 3.dominant Rate of macroalgal consumption (bites per hour; mean 6 SE) by macroalgal consumption perofhour; mean 6consumption SE) by (A, C, E,. G) dominant browsers on seven macroalgae FIG. 3.(bites Rate macroalgal (bites per hour; mean 6 SE) by (A, C, G)dominant dominant browsers oneps common to degraded reef on habitats or (B, D,Data F,E,H) grazers on the d reef habitats or (B, D, F, H) dominant grazers on the epilithic algal matrix (EAM) the substrata. for common to degraded reef habitats or (B, D, F,consumer H) dominant grazers on the epilithic algal matrix (EAM) onhoc the co su each weredifferent analyzed separately by a Friedman s test and post analyzed separately by a Friedman s test and post hoc comparison. Bars with letters above them were each consumer were analyzed separately by a Friedman s test and post hoc comparison. Bars with letters significantly different at the Py-axes;, 0.05 level. Scarids were all different initial phase (IP nt at the P, 0.05 level. Scarids were all initial phase (IP). Note the different scales for n ¼ 9. significantly different at the P, 0.05 level. Scarids were all initial phase (IP). Note the different scales for y-ax Hypothesis: Higher diversity of consumers is necessary to control algal overgrowth on coral reefs.

58 Rasher et al Ecology Test: Surveyed fish and algal diversity and biomass inside and outside of marine protected areas, which had varying levels of both. Conclusion: Consumer diversity interacts with prey defenses to influence ecosystem function, but a few critical species drive this relationship (sampling effect)!