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Lecture 1 Summary. The ecological hierarchy consists of the individual, population, community, ecosystem, and biosphere. Ecology is the study of biotic and abiotic interactions between organisms and their environment as they affect distribution and abundance.

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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.


  • 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


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


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?


Population growth in marine species
Population Growth in Marine Species

1 source A. Sharov Population Ecology web course


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?


Population growth
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


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 models

Geometric -- used when there is a discrete breeding season

Exponential-- used when populations are growing continuously


Population growth models

Geometric

the ratio of the population in one year to the population in the previous year

the rate of geometric growth

=


Geometric growth model
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)


Assumptions of the geometric growth model
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)


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


Population growth models

exponential

dN/dt = rN

N(t) = Noert

where,

N=number

r = (birth – death)

t=time


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


Intrinsic rates of increase
Intrinsic Rates of Increase

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


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


Assumptions of the exponential growth model
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)


Logistic growth
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



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)


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


Environmental resistance
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


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


Density dependent responses
Density-dependent responses

Density independent

Population or individual

growth parameter

Density dependent

Density



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)


  • 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


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


Demography
Demography

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


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)


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



Age determination otoliths
Age Determination-Otoliths

5

  • Otoliths are composed primarily of aragonite, which is a form of calcium carbonate

  • Readers count bands

4

3

2

1


Coral growth rings
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


Seagrass Demography

Leaves

Short-

Shoot

Stem

Leaf Scars

(plastochrone intervals)

Rhizome

scars


Age structure diagrams
Age Structure Diagrams

Positive Growth Zero Growth Negative Growth

(ZPG)

Pyramid Shape Vertical Edges Inverted Pyramid


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)


Survivorship Curves

Humans

Marine inverts


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


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


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


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


Life history components
Life History Components the

  • 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


Life History Strategies the

  • 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


Stressful Environments the

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


Stable Environments the

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.


Bet hedging the

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


Reproductive Strategies the

  • Semelparity(single reproduction event)

    • less energy required for maintenance

    • more energy devoted to reproduction

    • produces cohorts of similar-aged young


  • Iteroparity the– offspring are produced multiple times during an organisms lifetime; found in most marine organisms

  • Favored by unstable, non-predictable environments

    • - 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


Egg size and number in fish
Egg Size and Number in Fish the

  • 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 (Mola mola)


Life history variation among fish species
Life History Variation Among Fish Species the

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


Modular growth
Modular growth the

  • 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


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