Download FISH 312: Fisheries Ecology

Physical
factors
Temperature,
pH, oxygen,
light, salinity,
etc.
Fisheries
Ecology
Diversity and
Abundance
Human
factors
Biological
factors
Predation,
competitio
n, disease
Fishing, land
use, dams,
pollution,
introduced
species, etc.
Sub-disciplines of Ecology
Nutrient cycling
Physiological
Behavioral
Evolutionary
Population
Community
Landscape
Primary focus of the class
Physiological and Morphological
Aspects of Ecology
1. Limitation
2. Tolerance
3. Temperature Units
4. Biological rhythms
5. Behavioral regulation
6. Morphological
constraints
Limitation and Tolerance
Law of the Minimum:
“Under steady-state conditions the essential material available
in amounts most closely approaching the critical minimum
needed will tend to be the limiting one.”
For example:
In a lake, primary production may be limited by Phosphorous
rather than by Nitrogen, and addition of Nitrogen may have no
effect on production. At other times of the year light may be
limiting.
From: Odum’s Ecology text
Limitation and Tolerance
Law of Tolerance:
“The presence and success of an organism depend upon the
completeness of a complex of conditions. Absence or failure of
an organism can be controlled by the qualitative or quantitative
deficiency or excess with respect to any one of several factors
which may approach the limits of tolerance for that organism.”
For example:
The ability to exist and thrive may depend on such physical
factors as dissolved oxygen, temperature, salinity, pH, etc.
“Steno” refers to species with narrow tolerances (e.g.,
stenothermal = narrow temperature tolerance); “eury” refers to
those with wide tolerances (e.g., euryhaline = wide salinity
tolerance).
From: Odum’s Ecology text
Time and Temperature
For poikilotherms, physiological processes,
including development of embryos, progress at
a rate determined by temperatures. In many
cases, the stage of development reflects a
rough correspondence between time (number
of days) and temperature (number of ºC > 0).
Thus, for example, coho salmon embryos
develop from fertilization to hatching in about
500 temperature units (TUs). This might occur
after 50 days at 10º or 100 days at 5º.
10º X 50 days = 500 TUs
5º X 100 days = 500 TUs
Effect of temperature on the development
rates of European sea bass
16
6
8
10
fertilization
to hatch
9 10
11 12
13 14
15
Mean temperature (oC)
16
17
Time (days)
12
14
hatch to 50%
mouth opening
4
60 80 100 120 140 160 180 200
Time (hours)
(Jennings and Pawson 1991)
Growth rate
What is the relationship between
feeding, temperature, and growth?
?
low
Temperature
high
1.6
Excess
6%
1.2
1
4.5%
Lethal Temperature
Specific Growth Rate (% weight/day)
1.4
0.8
0.6
3%
0.4
0.2
0
1.5%
-0.2
-0.4
Starved
-0.6
-0.8
0
5
10
15
Temperature Co
20
25
Growth (gain or
loss in weight)
depends on the
interaction
between food
and temperature
Morphological Constraints
Just as some organisms are specialists or
generalists in terms of physiological tolerance,
some are specialists and others are generalists in
terms of morphology (shape). Careful examination
of the mouth parts, fins, and shape indicates the
extent to which the species is adapted for
particular kinds of prey and movement, or is
adapted to prey on a wider range of organisms and
show a wider range of locomotion patterns.
These attributes, along with patterns of physiology,
may determine the range or a species and its
responses to changing conditions.
Biological Rhythms
We are strongly controlled by internal (endogenous) circadian
rhythms affecting temperature, physiology, behavior, etc.
External “zeitgebers” set the clock each day.
Physiology and behavior are strongly controlled by such
rhythms, with periods of a year, a lunar month, a day, or a tidal
cycle. The reproductive biology and feeding patterns are
intimately linked to such rhythms. Examples include vertical
feeding migrations from deep water towards the surface to
feed on plankton, annual migrations from feeding to breeding
grounds, synchrony of breeding on spring high tides, and
movement from the bottom to the middle of the water column
on high and low tides.
Behavioral Regulation
In addition to the physiological capacity to tolerate a
range of conditions (e.g., temperature, salinity,
oxygen, etc.), mobile organisms often move to adjust
their environment, searching for physiologically
optimal conditions. For example, manatees leave
salt water in winter for warm springs, and are
attracted to the heated effluent from power plants.
However, areas that are optimal for some
environmental features may not be optimal for
others, and behavioral regulation may conflict with
other needs such as feeding and reproduction.
Approaches to studying physiological ecology:
Example: salinity and the distribution of starry flounder
1. Correlate larval catch rate of flounders with average
salinity among years to study recruitment success
Catch per tow of larval flounder
35
30
25
20
15
10
5
0
23.5
24
24.5
25
25.5
26
26.5
Estuarine salinity (ppt)
27
27.5
28
28.5
Approaches to studying physiological ecology:
Example: salinity and the distribution of starry flounder
Catch rate of flounder
2. Conduct surveys and correlate the catch rate of adult
flounder with the salinity of the water to study behavior
20
18
16
14
12
10
8
6
4
2
0
1
6
11
16
21
26
Salinity (parts per thousand)
31
Approaches to studying physiological ecology:
Example: salinity and the distribution of starry flounder
3. Conduct an experiment to determine the ability
of flounder to survive at different salinities
% surviving 24 hours
100
starry
English
80
60
40
20
0
0
5
10
15
20
25
Salinity (parts per thousand)
30
35
Approaches to studying physiological ecology:
Example: salinity and the distribution of starry flounder
4. Conduct a behavioral experiment on the salinity
preferences of individual flounder
35
% of flounder
30
25
20
15
10
5
0
0
5
10
15
20
25
Salinity (parts per thousand)
30
35
Behavioral Ecology
Perspectives on behavior (why animals do what they do)
1. Mechanism: how does it work (e.g., vision, reflex, etc.)?
2. Ontogeny: how does it develop in an individual (learning)?
3. Ecological significance: how does it help an animal survive?
4. Phylogeny: how did it evolve?
Analogy: Why do we stop at red lights?
1. Light of a particular wavelength is perceived by pigments in the
retina, sending a message via the optic nerve, etc.
2. We are taught by our parents that red indicates danger.
3. Stopping at lights increases our odds of surviving to reproduce.
4. Red is the color of fire and of blood, hence we have evolved
instinctive wariness upon seeing the color.
Behavioral Ecology
Natural and sexual selection:
1. Individuals vary in heritable phenotypic traits
2. More individuals are produced than the habitat can support
3. Individuals possessing appropriate traits tend to survive
4. Individuals surviving to maturity vary in reproductive success,
related to competition and mate choice
Fitness of individuals
Fitness of individuals
Natural selection can be balancing, directional or disruptive
25
20
15
10
5
0
1 2 3
4 5 6
7 8 9 10 11 12 13 14 15 16
Some quantitative trait
12
10
8
6
4
2
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Som e quantitative trait
Behavioral Ecology
Spatial distribution:
1. Territory: resources (food, nesting site) actively
defended, within or among species
2. Home range: area routinely used but not actively
defended
3. Migration: movements of individuals between
habitats, coordinated in time and space
4. Schooling: synchronous, polarized movements of
individuals (sometimes distinguished from shoaling)
Behavioral Ecology
Foraging: (we need to eat, but it is not our only need)
1. Organisms differ greatly in activity, metabolic
demand, and food consumption.
2. Energy maximizers: high intake rate, active, often
short lifespan, high risk
3. Time (or risk) minimizers: low intake rate, inactive,
long lifespan, low risk
Tuna: an
energy
maximizer
Rockfish: a time
minimizer
Behavioral Ecology
Reproduction and Parental Investment
1. Sex determination (genetic vs. environmental; determinate vs.
hermaphroditic, protandrous, protogynous, or simultaneous; allfemale species)
2. Mating system (monogamy, polyandry, polygyny, etc.)
3. Mode of reproduction (broadcast spawning, single pair, internal
or external fertilization)
4. Parental investment: anisogamy (females produce a smaller
number of larger gametes than males, and so are generally more
“choosy” regarding mates). Females also typically have a larger
total investment in gametes than males.
5. However, in most animals, everyone has a mother and a father.
Thus the average reproductive success of males and females is
the same but there is usually more variation in males than in
females (e.g., elephant seals and other species with “harems”).
Behavioral Ecology
Life history traits: link behavioral and population ecology
1. Age and size at first reproduction
2. Longevity and maximum size
3. Number of eggs (fecundity, clutch or brood size) and
size of eggs or offspring
4. Frequency of reproduction (iteroparous or
semelparous, annual or otherwise)
5. Parental care
These traits are all related to patterns of
mortality on adults and juveniles
Behavioral Ecology
Fitness: probability of surviving to a given age, multiplied
by the reproductive success (e.g., egg production) at
that age, summed over the individual’s whole life.
W = Σ (lx * bx)
Where l = age-specific survival and b is age-specific
reproductive success, and x is age. This simple
equation allows us to compare the fitness of different
life history patterns.
Life history comparison of anadromous and non-anadromous sockeye
Age
form
1st spring
1st fall
2nd spring
2nd fall
3rd fall
4th fall
length
survival
number
fecundity
fitness
kokanee
28
0.1
50
sockeye
28
0.1
300
kokanee
60
0.4
20
3
0.12
sockeye
60
0.4
120
3
0.12
kokanee
80
0.5
10
sockeye
80
0.5
60
kokanee
120
0.8
8
24
0.38
sockeye
180
0.3
18
85
0.51
kokanee
180
0.6
4.8
85
0.82
sockeye
360
0.4
7.2
700
1.68
kokanee
300
0.8
3.84
500
3.84
sockeye
560
0.8
5.76
3000
5.76
Population Ecology
Abundance (number of organisms)
Biomass (weight)
Density (number or biomass per unit of distance,
area or volume)
Production (number or biomass per area or
volume per time)
Population Ecology
Survivorship patterns:
Species with high rates of juvenile mortality and low
rates of adult mortality will tend to be long-lived,
iteroparous, fecund and slow-growing (e.g., rockfish)
Species with high rates of adult mortality and low
rates of juvenile mortality will tend to be short-lived,
semelparous and fast growing (e.g., salmon)
Species with low rates of adult and juvenile mortality
and large offspring will tend to reproduce late in life,
and reproduce at a low rate (e.g., sharks, whales)
Population Ecology
Density-dependent mortality:
“Compensatory mortality” increases as the density of
organisms increases. This means that at low densities,
populations tend to increase but at high densities,
fewer offspring are produced per capita, and the
population levels off or even declines. Competition for
food, limited breeding sites, and disease are common
causes of compensatory mortality.
Spawner-recruit relationships
Adult offspring
25,000
1:1 replacement
20,000
Beverton-Holt
15,000
10,000
Ricker
5,000
0
0
5,000
10,000 15,000 20,000 25,000
Spawning adults
Spawner-recruit relationships:
Iliamna Lake sockeye salmon
Adult ofspring
60,000
45,000
30,000
15,000
0
0
5,000
10,000
15,000
Spawning adults
20,000
25,000
Population Ecology
Density-dependent mortality:
“Depensatory mortality” increases as the density of
organisms decreases. This means that at low densities
there are higher per capita mortality rates, and the
population can fluctuate widely. This kind of mortality
can result from predators that take a fixed number
rather than a fixed percentage of the population.
The number of salmon killed by bears each year on
Hansen Creek rises to an asymptote and then levels
off; the proportion killed decreases with density.
5000
# killed
4000
~ 60%
~ 25%
3000
2000
1000
0
0
5000
10000
Number of adult salmon
15000
Population Ecology
Density-independent mortality:
Some forms of mortality do not vary with density but
result from physical factors that operate without regard
to density. However, even some of these factors
(freezing, flooding, high temperatures) may interact with
density. For example, at high densities, some
organisms may be forced to breed in marginal habitats,
where they are more vulnerable to adverse physical
conditions.
Population Ecology
“Strong year class” Phenomenon:
In long-lived organisms that breed many times over
their lives, most seasons of reproduction produce no
offspring at all. However, when environmental
conditions are good, high survival results. In such
cases, the “year class” spawned in that year dominates
the population for (and often sustains the fisheries) for
years to come.
Data from Hjort (1914),
diagram from
Jennings et al. Marine
Fisheries Ecology
Percentage of sample
Age composition of
herring caught in the
North Sea.
Age of herring (years)
Community Ecology
Characterization of communities:
1. Abundance (number or density of organisms)
2. Diversity (number of species)
3. Evenness or dominance (extent to which the species
are equally abundant)
4. Resistance (the ability or tendency of a community to
remain the same in the face of environmental change)
5. Resilience (the speed with which a community returns
to its former state after it has been perturbed)
Community Ecology
Perspectives on the controls over communities:
1. Non-equilibrium perspective
2. Equilibrium perspective
3. Biotic factors:
a) predation
b) competition
c) disease
4. Abiotic factors:
a) habitat age
b) opportunities for colonization
c) stability
Community Ecology
Why do the Hawaiian islands have fewer species of
fishes and corals than are found in the Philippines?
Why are many species in Hawaii endemic?
What factors controls the extent and diversity of fish and
coral species among the different Hawaiian islands?
Community Ecology
Mature vs.
Pioneer communities:
# of species
large
small
Dominance?
no
yes
Life span
long
short
Diet
specialized
generalized
Growth
slow
fast