1. Life History Characteristics and Population Growth in Marine Ecosystems 1 source A. Sharov Population Ecology web course

2. Population Ecology Key questions of population ecology include: A population is a group of individuals of the same species that occupy a specified region at a specified time. What is the size of a population? What is the potential for growth in the population? What form will growth take?

3. Population Growth N(t+1) = N(t) + B(t) + I(t) – D(t)– E(t) where, N=number of individuals, B=births, I=immigrations, D=deaths, and E=emigrations ------BIDE

4. Overview of Ecological Theory Population Growth and regulation biological populations have great potential for increase, however, populations never realize this potential. There appears to be some factors (e.g., food limitation, war) that keep population regulation within some definable limits. Population Growth and regulation biological populations have great potential for increase, however, populations never realize this potential. There appears to be some factors (e.g., food limitation, war) that keep population regulation within some definable limits.

5. Population growth models geometric the rate of geometric growth = the ratio of the population in one year to the population in the previous year

6. Geometric Growth Model Population growth incrementally Geometric Growth rate ( ) –Ratio of the population in one year to that in the preceding year – = N(1)/N(0) – = e r Where r=b-d Population growth incrementally Geometric Growth rate ( ) –Ratio of the population in one year to that in the preceding year – = N(1)/N(0) – = e r Where r=b-d

7. Assumptions of the Geometric Growth Model Population is growing under optimum conditions Population has discrete generations (live and die at the same time) Breeds only one time per year (semelparous-salmon) Focuses only on females (millions of sperm/egg)

8. Population growth models exponential the rate of change in population size = x the contribution of each individual to population growth the number of individuals in population

9. Population growth models exponential dN/dt = rN N(t) = N(o)e rt where, N=number r = (birth – death) t=time

10. Intrinsic Growth Rate r = births - deaths Components of the environment that affect birth or death rate will also affect r. Therefore, each environment a population lives in might produce a different r. And, if r can vary, it can be subject to natural selection and selective pressures can shape the values of r in different situations.

11. Intrinsic Rates of Increase On average, small organisms have higher rates of per capita increase and more variable populations than large organisms.

12. Pops. of pelagic tunicates (Thalia democratica) grow at exponential rates in response to phytoplankton blooms. –Life cycle involves a mixture of sexual and asexual reproduction –Increase pop. size dramatically due to extremely high reproductive rates. Small marine invertebrate : Large marine mammal : Female gray whales (E. robustus) give birth, on average, every other year Reilly et al. (1983) estimated 2.5% growth for California population in 1967-1980

13. Assumptions of the exponential growth model Reproduction is continuous (no seasonality) All organisms are identical (e.g., no age structure) Environment is constant in space and time (resources are unlimited)

14. Logistic Growth Because of “Environmental Resistance” population growth decreases as density reaches a “carrying capacity” or K Graph of individuals vs. time yields a sigmoid or S-curved growth curve Reproductive time lag causes population to overshoot K Population will not be unvarying due to resources (prey) and predator effects

15. Population Biology: Logistic growth model

17. An example with barnacles (Connell 1961): K is determined largely by the amount of space available on rocks for attachment barnacle (Balanus balanoides)

18. Population growth models logistic dN/dt = rN (K-N/K) N(t) = K/1 + e a-rt r = birth – death K=carrying capacity a= integration constant

19. Environmental Resistance Factors that reduce the ability of populations to increase in size –Abiotic Contributing Factors: Unfavorable light Unfavorable Temperatures Unfavorable chemical environment - nutrients –Biotic Contributing Factors: Low reproductive rate Specialized niche Inability to migrate or disperse Inadequate defense mechanisms

20. Two Schools of Thought Density independent school - changes in physical environmental factors (generally climatic changes); which lead to dramatic shifts in populations. Density dependent school - work with larger organisms (vertebrates) or sessile organisms (barnacles); biotic interactions and their importance (competition, predation, or parasitism) Density independent school - changes in physical environmental factors (generally climatic changes); which lead to dramatic shifts in populations. Density dependent school - work with larger organisms (vertebrates) or sessile organisms (barnacles); biotic interactions and their importance (competition, predation, or parasitism) *large controversy over the relative importance of these factors

21. Density-dependent responses Population or individual parameter Density Density independent Density dependent

22. r and K selection r vs K (intrinsic growth rate)(carrying capacity) r vs K (intrinsic growth rate)(carrying capacity) Any organism has three categories that it needs to allocate energy to: 1.Growth 2.Reproduction 3.Maintenance (basal metabolic activity; building of bone and supporting structures) 1.Growth 2.Reproduction 3.Maintenance (basal metabolic activity; building of bone and supporting structures)

23. r selected traits - rapid development - small body - early reproduction - semelparity (single reproduction) r selected traits - rapid development - small body - early reproduction - semelparity (single reproduction) K selected traits - slow development - large body - delayed reproduction - iteroparity (repeated reproduction) K selected traits - slow development - large body - delayed reproduction - iteroparity (repeated reproduction) Thought to divide invertebrates from vertebrates; many exceptions; all are relative (barnacle to whales) Overgeneralization, but it does seem to have some usefulness in organizing thinking Thought to divide invertebrates from vertebrates; many exceptions; all are relative (barnacle to whales) Overgeneralization, but it does seem to have some usefulness in organizing thinking

24. Hypothetical metapopulation dynamics. Closed circles represent habitat patches, dots represent individual plants or animals. Arrows indicate dispersal between patches. Over time the regional metapopulation changes less than each local population.

25. Demography Demography is the study of the vital statistics of a population

26. Demography Life Tables are the main tool for demographers, and they have 2 main components Survivorship schedule – average # of individuals that survive to any particular age Fertility schedule (fecundity) – average # of daughters produced by one female on each life stage Life Tables are the main tool for demographers, and they have 2 main components Survivorship schedule – average # of individuals that survive to any particular age Fertility schedule (fecundity) – average # of daughters produced by one female on each life stage Population size = double the # of daughters born to each female (assumes the same # of sons as # of daughters) Population size = double the # of daughters born to each female (assumes the same # of sons as # of daughters)

27. Types of Life Tables 1.Static life table – calculated on a cross section of the population at a specific time. Estimate # of individuals from each age group and look at # of deaths for each age group 2. Cohort life table – follow a cohort through out their life and record the # of individuals surviving to each stage. Both will give the same results if birth rate and death rate remain constant 1.Static life table – calculated on a cross section of the population at a specific time. Estimate # of individuals from each age group and look at # of deaths for each age group 2. Cohort life table – follow a cohort through out their life and record the # of individuals surviving to each stage. Both will give the same results if birth rate and death rate remain constant

28. Notes on length measurements

29. 1 2 3 4 5 Age Determination-Otoliths Otoliths are composed primarily of aragonite, which is a form of calcium carbonate Readers count bands

30. Coral growth rings Each of the light/dark bands in this x-ray of a cross-section of a coral core formed during a year of growth

31. Seagrass Demography Leaf Scars (plastochrone intervals) Rhizome scars Short- Shoot Stem Leaves

32. Age Structure Diagrams Positive Growth Zero Growth Negative Growth (ZPG) Pyramid Shape Vertical Edges Inverted Pyramid

33. Survivorship table Using these data, calculate the proportion of population surviving at the start of each period (l x ). X #barnacles at start (Prop. Surviving (N x /N O ) 0 12 100% (12/12) 1 6 50% (6/12) 2 3 25% (3/12) 3 1 8% (1/12)

34. Survivorship Curves

35. Type III Curve High juvenile mortality Little chance of surviving to adulthood Oysters, clams

36. Fertility Schedule  Provides the average number of daughters produced by one female at each particular age  Customarily, only females are tracked, since it is virtually impossible to measure the fecundity of males  It is assumed that the male population will grow the same way the female population grow

37. Net Reproductive Rate (Ro)  Is the average number of offspring produced by each female during her entire lifetime  Can be calculated by summing the products of the survivorship and fecundity schedules from birth to death  When Ro<1, the population declines; when Ro=1, the population is stable; and when Ro> 1, the population increases

39. Life History Components The important components include: –the age and size at which reproduction occurs –the relative apportionment of energy to reproduction, growth, survivorship, and predator avoidance –production of many small or a few large offspring –the age of first reproduction –age of death

40. Life History Strategies Assumptions: Natural selection will produce a life history tactic (strategy) that will maximize the individual fitness of the organism under study by optimizing the allocation of energy between these function. Fixed amounts of energy (investing energy in one will take it from another) Assumptions: Natural selection will produce a life history tactic (strategy) that will maximize the individual fitness of the organism under study by optimizing the allocation of energy between these function. Fixed amounts of energy (investing energy in one will take it from another) The goal of life history strategy: to predict the characteristics of any organism that you might expect to find under any given set of conditions

41. Examples of life history considerations If environmental conditions change, what effect might this that have on growth or reproduction? Should most energy be allocated to growth in year 1 or should more energy be put into factors that protect you from predators or to reproduction? How many young should be produced? How many reproductive events would best take place during an organism’s life to maximize fitness? Should organisms allocate energy to care for young? If environmental conditions change, what effect might this that have on growth or reproduction? Should most energy be allocated to growth in year 1 or should more energy be put into factors that protect you from predators or to reproduction? How many young should be produced? How many reproductive events would best take place during an organism’s life to maximize fitness? Should organisms allocate energy to care for young?

42. In area where large amounts of density independent mortality occurs (catastrophic events that cause high mortality; weather or climatic) r selection dominates: organisms should survive here when they allocate a lot of energy to early reproduction, rapid growth, and dispersal to new habitats Stressful Environments

43. When K selection dominates: populations will increase until they approach K where competition will increase. In this situation good competitors will be selectively favored (density dependent mortality) Stable Environments organisms should survive when they allocate energy to slow development, delayed reproduction, usually large and may have frequent reproductive events throughout life.

44. Bet hedging Occurs where environmental conditions vary greatly and juveniles or adults are subject to high density independent mortality If high juvenile mortality: smaller reproductive output, smaller litters at any given time, and longer lived organisms If high adult mortality: increased reproductive effect, larger litters, and shorter lifespan

45. Egg Size and Number in Fish Fish show more variation in life-history than any other group of animals. –clutch size (# of offspring per brood): ranges from 1-2 live births produced by mako shark (Isurus oxyrinchus) to 600,000,000 eggs produced by ocean sunfish (Mako mako)

46. Life History Variation Among Fish Species Gunderson (1997) studied adult survival and reproductive effort of several fish spp. –Reproductive effort measured as gonadosomatic index (GSI) = (ovary weight / body weight) x (# of batches of offspring produced per year) –Species with higher rates of mortality show higher relative reproductive effort

47. Modular growth Modular growth occurs when organisms reproduce asexually by increasing the # of modules they possess (e.g., corals, bryozoans, and cnidarians). r and K have no meaning for these organisms; 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.

48. Frequency & Timing of Reproduction Semelparous – Spawn only once and die, synchronized and massive gonad, usually seasonal Iteroparous – Spawn multiple times a) Daily b) Seasonal c) Opportunistic d) Variations of the above

49. Semelparity Favored by stable, predictable environments less energy required for maintenance more energy devoted to reproduction produces cohorts of similar-aged young Reproductive Strategies

50. Iteroparity – offspring are produced multiple times during an organisms lifetime; found in most marine organisms Favored by unstable, non-predictable environments - likened to “bet-hedging” - survival of juveniles is low and unpredictable, thus selection favors repeated reproduction and long reproductive life - tends to produce young of different ages - much variation in # of clutches and size of clutch

53. INSERT POPULATION DYNAMICS

54. Comparing models of population dynamics Malthusian Unstructured per-capita instantaneous rate of increase r is independent of density N grows exponentially when r is positive. dN/dt increases linearly with N Populations growing in this manner are Not Regulated: they are predominantly affected by DI factors. Pearl-Verhulst Unstructured per-capita instantaneous rate r of increase (r actual ) is negatively density dependent N maxes out at K - sigmoid (S shaped) curve dN/dt maxes out at K/2 and tends towards 0 when N approaches 0 as well as K Population is regulated.

55. Logistic Model Is it real? –In the laboratory - sometimes Paramecium Daphnia Often overshoot carrying capacity Usually fluctuate around carrying capacity However, most organisms are limited by factors other than density.

56. Biotic Potential Ability of populations of a given species to increase in size –Abiotic Contributing Factors: Favorable light Favorable Temperatures Favorable chemical environment - nutrients –Biotic Contributing Factors: Reproductive rate Generalized niche Ability to migrate or disperse Adequate defense mechanisms Ability to cope with adverse conditions

57. ? human activities 140 biological fixation 200 denitrification SOIL ATMOSPHERE OCEANS 15 biological fixation 140 denitrification 1200 internal cycling 8000 internal cycling ? burial ? river flow <3 fixation in lightening groundwater Nitrogen Cycle Without Microbes All processes slow. Would life be possible?

58. Density Independent Growth Rate of increase at any particular instant of time Two principles - exponential growth rate (r) expresses the population increase on a per individual basis - rate of increase (dN/dt) varies in direct proportion to the size of the population (N) Rate of increase at any particular instant of time Two principles - exponential growth rate (r) expresses the population increase on a per individual basis - rate of increase (dN/dt) varies in direct proportion to the size of the population (N) r = intrinsic rate of population increase (birth rate – death rate) N = # of individuals in population r = intrinsic rate of population increase (birth rate – death rate) N = # of individuals in population Exponential growth equation

59. r vs. K Selection Pianka (1970, 1972): r and K are ends of a continuum. Most spp. fall somewhere in between. r- vs. K-selection correlated with env. and pop. attributes: –r-selection: Variable, unpredictable envs Type III survivorship –K-selection: Constant, predictable envs. Type I or II survivorship

60. Uniform dispersion is when individuals are evenly spaced. Clumped dispersion is when individuals aggregate in patches. Random dispersion is the position of each individual is independent of the others. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

61. How many bacterial species are there? Wilson 1988 Total number species: ~ 1.4 million Bacteria: ~3,500 Hammond 1995 Total number species: ~ 11 million Bacteria: ~10 million

62. 100 human activities 140 biological fixation 200 denitrification SOIL ATMOSPHERE OCEANS 15 biological fixation 140 denitrification 1200 internal cycling 8000 internal cycling 10 burial 36 river flow <3 fixation in lightening groundwater Example: The Nitrogen Cycle

63. IV. Logistic growth Biologists beginning with Thomas Malthus & Charles Darwin understood that populations cannot grow exponentially for very long Increasing population size gives rise to … … shortages in food and other limiting resources … greater intraspecific aggression … increased attention from predators … greater risk of disease outbreaks These factors can act to lower birth rates and elevate death rates

64. Antarctic sponges and asteroids Work by Paul Dayton at McMurdo Sound in 1960s showed strong interannual variability in recruitment of a dominant hexactinellid sponge, linked to predation by a sea-star and oceanographic variability (El Niño) Acanthaster (crown-of-thorns starfish) and coral recruitment Acanthaster outbreaks kill coral but allow for new recruitment

65. Population Growth and regulation Darwin incorporated many of Malthus’ idea’s and proposed that diversification of species was the direct result of intraspecific competition driven by food/resource limitation

66. 66 CS Fig. 4.7 Competition for resources causes evolution

67. Population growth models geometric -- used when there is a discrete breeding season exponential -- used when populations are growing continuously

70. The fundamental processes of sexual reproduction Adult Embryo/LarvaZygote Juvenile Fertilisation Development Metamorphosis Growth & Maturation Life Cycle

71. Definitions: Life Tables Cohort is a group of individuals within a population that are born at the same time. A population is a collection of cohorts

73. Life Table Construction Steps Determine the age distribution and # of intervals you want Standardize l x to 1,000 (some do it to 1.0 or 100%) Calculate d x Q x = d x/ l x Lx= (l x +l x +1)/2 T x = Sum L x ex = Tx/lx

74. Life Table Terminology

75. How to calculate a life table: an example Agenxnx lxlx dxdx QxQx LxLx TxTx exex 0-1 1-2 2-3 3-4 4-5 5-6 6-7 93 74 32 14 5 1 0 1000 796 344 151 54 11 0 204 452 193 97 43 11 0.204.568.561.642.796 1.0 0 898 570 248 103 33 6 0 1858 960 390 142 39 6 0 1.858 1.21 1.134.94.72.55

76. Survivorship Table ( l x ) and Fertility Table ( b x ) for Women in the United States, 1989 Age Up Midpoint or Pivotal Agex Proportion Surviving to Pivotal Agel x No. Female Offspring per Female Aged x per 5-Year Time Unit (b x ) Product ofl x andb x 0-9 10-14 15-19 20-24 25-29 30-34 35-39 40-44 45-49 and above 5.0 12.5 17.5 22.5 27.5 32.5 37.5 42.5 47.5 ---- 0.9895 0.9879 0.9861 0.9834 0.9802 0.9765 0.9712 0.9643 0.9528 ---- 0.0 0.0020 0.1233 0.2638 0.2772 0.1807 0.0650 0.0125 0.0005 0.0 0.0020 0.1216 0.2594 0.2717 0.1765 0.0631 0.0121 0.0005 0.0 R 0 = l x b x = 0.9069