Lecture 1 Summary

1. Lecture 1 Summary • The ecological hierarchy consists of the individual, population, community, ecosystem, and biosphere. • Ecology is the study of biotic and abiotic interactions betweenorganisms and their environment as they affect distribution and abundance. • Autecology concerns the relationships between individual organisms and their environment. • Population ecology concerns individuals of the same species, and the factors that determine their size and structure. • Community ecology concerns multispecies assemblages that inhabit the same place at they same time and their interactions. • Ecosystems ecology is concerned with fluxes of energy and materials between organisms and their environments.

2. A species’ fundamentalniche includes the entire range of conditions and habitats it can inhabit. Its realized niche is a reduced range of conditions and habitats owing to interactions such as competition, predation, commensalism, mutualism, and parasitism. • Marine ecologists use the scientific method—or observation, hypothesis formation and experiment—to frame and test hypotheses. • There are good reasons for replicating and using control sites, as there is for randomly allocating sample effort. • Ecological experiments can be natural, mensurative or manipulative. Manipulative experiments can be either press or pulse types, but any experiment has potential artifacts that must be guarded against. Terrestrial vs Marine Ecosystems • Seawater is much denser than air (thus, organisms float in it readily) • Seawater strongly absorbs light (most light is gone below 100m). • Gravity–because bouyancy is provided by the seawater, organisms do not invest as much energy in skeletal material • Oxygen can be limiting in marine environments • Microscopic plants dominate the sea, and herbivores are usually small

3. The marine fauna is relatively long-lived and large animals are often carnivores Plant production in the sea is lower than on land, but transfer of energy is more efficient; thus, there are usually more trophic levels Factors Influencing the Distribution of Marine Organisms Salinity, Light, Temperature, Oxygen, Waves and Tides, Sediment Type, Nutrients, Dispersal, Biological Interactions, and Habitat Selection Important Discoveries in the Past Several Decades Hydrothermal Vents-Chemosynthesis Enormous Biodiversity Tiny Phytoplankton very Abundant and Productive Indirect Effects (e.g., trophic cascades) are Common and Important Humans Have Affected all Ecosystems-Shifting Baselines

4. REVIEW QUESTIONS • Distinguish between correlation and experimentation in the understanding of scientific relationships. • Devise a testable hypothesis about something in the marine environment. How would you test this hypothesis? • Describe the ecological hierarchy. • Distinguish between a population and a community. • Explain the goals of ecosystems ecology. • Why are planktonic species common in marine but not terrestrial environments? • Describe the changes that took place in the fauna of marine soft sediments from the Paleozoic to the present. • What is the onshore-offshore hypothesis?

5. Population Growth in Marine Species 1 source A. Sharov Population Ecology web course

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

7. 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

8. 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.

9. Population growth models Geometric -- used when there is a discrete breeding season Exponential-- used when populations are growing continuously

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

11. Geometric Growth Model • Population growth is incremental • Geometric Growth rate () • Ratio of the population in one year to that in the preceding year •  = N(1)/N(0)

12. 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 (e.g., semelparous salmon) • Focuses only on females (millions of sperm/egg)

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

14. Population growth models exponential dN/dt = rN N(t) = Noert where, N=number r = (birth – death) t=time

15. 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. Intrinsic Growth Rate

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

17. Small marine invertebrate: • Pops. of pelagic tunicates (Thalia democratica) grow at exponential rates in response to phytoplankton blooms. -Increase pop. size dramatically due to extremely high reproductive rates. 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

18. 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)

19. 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

20. Population Biology: Logistic growth model

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

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

24. 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

25. Two Schools of Thought Density independent school - changes in physical environmental factors (generally climatic changes) lead to dramatic shifts in populations. Mostly works with inverts. Density dependent school – applies mostly to 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

26. Density-dependent responses Density independent Population or individual growth parameter Density dependent Density

27. http://www.cbs.umn.edu/populus/

28. r and K selection r vs K (intrinsic growth rate) (carrying capacity) Organisms have three activities that they must allocate energy to: • Growth • Reproduction • Maintenance (basal metabolic activity; and building of bone and supporting structures)

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

30. Metapopulations Hypothetical metapopulation dynamics. Closed circles are habitat patches, dots are individual plants or animals. Arrows indicate dispersal between patches. Over time the regional metapopulation changes less than each local population. Also, some patches can be sources while others are sinks

31. Demography • Demography is the study of the vital statistics of a population

32. 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 Population size = double the # of daughters born to each female (assumes the same # of sons as # of daughters)

33. Types of Life Tables • 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

34. Notes on length measurements

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

36. 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

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

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

39. 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 /N ) x O 0 12 100% (12/12) 1 6 50% (6/12) 2 3 25% (3/12) 3 1 8% (1/1 2)

40. Survivorship Curves Humans Marine inverts

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

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

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

44. A highly significant way of reducing fecundity is increase the age of first reproduction Population 1 Population 2 X(age) lx bx X(age) lx bx 0 1.0 0 0 1.0 0 1 0.5 1.0 1 0.5 0 2 0.4 3.0 2 0.4 1 3 0.2 0 3 0.2 3 R o=E lxbx=1.7 Ro=1.0 lx=proportion of population surviving bx=average number of offspring born to a female of age x

45. 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

46. Life History Strategies • Assumptions: • Natural selection will produce a life history strategy that maximizes the individual fitness of an organism 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 theory of life history strategies: to predict the characteristics of any organism that you should expect to find under any given set of conditions

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

48. Stable Environments 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) organisms should do well here when they allocate energy to slow development, delayed reproduction, usually large offspring and may have frequent reproductive events throughout life.

49. 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 effort, larger litters, and shorter lifespan

50. Reproductive Strategies • Semelparity(single reproduction event) • less energy required for maintenance • more energy devoted to reproduction • produces cohorts of similar-aged young