Download Marine Ecology 2011-final Lecture 2, pop

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.
• 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’ fundamental niche 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
1.
Distinguish between correlation and experimentation in the understanding
of scientific relationships.
2.
Devise a testable hypothesis about something in the marine environment.
How would you test this hypothesis?
3.
Describe the ecological hierarchy.
4.
Distinguish between a population and a community.
5.
Explain the goals of ecosystems ecology.
6.
Why are planktonic species common in marine but not terrestrial
environments?
7.
Describe the changes that took place in the fauna of marine soft sediments
from the Paleozoic to the present.
8.
What is the onshore-offshore hypothesis?
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
• 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 rate of
geometric
growth
=
the ratio of the population
in one year to the
population in the previous
year
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
• 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 rate of
change in
population
size
the contribution the number of
of each
= individual to x individuals in
population
population
growth
Population growth models
exponential
dN/dt = rN
N(t) = No ert
where,
N=number
r = (birth – death)
t=time
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.
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
• 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
• Because of “Environmental Resistance” population
growth decreases as density reaches a “carrying
capacity” or K
• Graph of individuals vs. time yields a sigmoid or Scurved growth curve
• Reproductive time lag causes population to overshoot K
• Population will not be unvarying due to resources (prey)
and predator effects
Population Biology: Logistic growth model
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
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
independent
growth parameter
Population or individual
Density-dependent responses
Density
dependent
Density

http://www.cbs.umn.edu/populus/
r and K selection
r
vs
(intrinsic growth rate)
K
(carrying capacity)
Organisms have three activities that they must allocate
energy to:
1. Growth
2. Reproduction
3. 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 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
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
Notes on length measurements
Age Determination-Otoliths
• Otoliths are composed primarily of aragonite, which is a
form of calcium carbonate
• Readers count bands
5
4
3
2
1
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
Leaf Scars
(plastochrone intervals)
Rhizome
scars
ShortShoot
Stem
Age Structure Diagrams
Positive Growth
Pyramid Shape
Zero Growth
(ZPG)
Vertical Edges
Negative Growth
Inverted Pyramid
Survivorship table
Using these data
, calculate the proportion of
population surviving at the start of each period (lx).
x #barnacles at start (Prop. Surviving (N x/NO)
0
1
2
3
12
6
3
1
100% (12/12)
50% (6/12)
25% (3/12)
8% (1/12)
Survivorship Curves
Humans
Marine inverts
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
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
Survivorship Table ( lx) and Fertility Table ( bx) for Women in
the United States, 1989
Age
Up
Midpoint or
Pivotal Age x
Proportion
Surviving to
Pivotal Age lx
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
----
No. Female
Offspring per
Female Aged
x per 5-Year
Time Unit (bx)
Product of lx
and bx
0.0
0.0020
0.1233
0.2638
0.2772
0.1807
0.0650
0.0125
0.0005
0.0
0.0
0.0020
0.1216
0.2594
0.2717
0.1765
0.0631
0.0121
0.0005
0.0
R0 =
l xbx = 0.9069
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
Ro=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
• 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
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
In area where large 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
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
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
• Semelparity (single reproduction event)
•less energy required for maintenance
•more energy devoted to reproduction
• produces cohorts of similar-aged young
•Iteroparity – 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
• 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
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 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