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Material Type: Notes; Professor: Blumer; Class: Ecology; Subject: Biology; University: Morehouse College; Term: Unknown 1989;
Typology: Study notes
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Section I Outline
Introduction to Course
Ecological Limiting Factors
The Meaning of Adaptation
Ecology and Evolution
Introduction to the study of ecology
Scope of the course
Levels of organization of life
Atoms
Molecules
Compounds
Cells
Tissues
Organs
Organisms (Individuals)
Populations
Species
Communities
Ecosystems
Biosphere
“Ecology” = from the Greek “Oikos” meaning “house”, the immediate environment
Term coined by Ernst Haeckel (1869)
(best known for his biogenetic law, “ontogeny recapitulates phylogeny”).
Present meaning:
Study of interactions between organisms and environment
The economy of nature, the total relations of an organism to both
its organic and inorganic environment
Biotic and abiotic interactions
Levels of interest in modern Ecology
Individual (organism or cell)
interactions with environment
interactions between living things
Populations (a group of individuals of one species)
presence or absence of a species at a given site
abundance (census)
change over time
Communities (groups of populations)
structure
diversity
change over time
Ecosystems (groups of communities)
flux in energy and matter
Modern Ecology is interdisciplinary, a synthetic science that draws from and builds
upon the study of genetics, physiology, biochemistry, evolution, and behavior.
Organisms do not evolve for the present or the future, change is a consequence of
the past.
Fitness is the relative success of an individual in a given population, and selection is
between better and worse. Perfection need not occur.
Yet, there is often a striking match between form and function.
Causes for selection
Darwin’s Hostile Forces of Nature (factors that cause selection)
weather
climate
predators
parasites and diseases
resources shortages (including mates)
These hostile forces can also described as
Ecological Limiting Factors
Limiting Conditions
Limiting Resources
Conditions
not consumed or used-up by other organisms
not made unavailable or less available by other organisms
climate and weather, physical environment, abiotic environmental factors
temperature
relative humidity (RH)
hydrogen ion concentration (pH)
salinity
wind speed
stream water flow velocity
pollutant concentration
Resources
something consumed, used, or incorporated or transformed
something eaten, incorporated in biomass
using it makes it unavailable or unusable for other organisms
reuse may occur after a period of use by another organism
water
nutrients (C, N, S, K, P)
minerals
food
mates
shelter
solar radiation
Major nutrients required by organisms (Ricklefs, 1996, p 41, Table 2.1)
Solar radiation: a critical resource
arriving energy varies with latitude
highest at the equator (see Ricklefs, 1996, pp 80 and 81, Fig. 4.1 and 4.2)
varies with degree of atmospheric scattering and reflection
at leaf surface light can be
reflected
filtered and transmitted
absorbed
eukaryotic chloroplasts absorb light between 380nm and 710nm
visible light spectrum
56% of incident radiation is outside visible range
photosynthetically active radiation (PAR) (~400nm - 700nm)
prokaryotic chlorophylls: absorption peaks at 800nm, 850nm, and 870-890nm
Photosynthesis rate as a function of light intensity. The compensation point is the light
intensity at which the rate of photosynthesis just compensates for the maintenance needs of
the organism (cell respiration rate) (Ricklefs, 1996, p 46, Fig. 2.15).
Water absorbs light energy and scatters light
In sea water: At 10m, the energy of visible light decreases 50%
At 100m, the energy of visible light decreases to <7%
Red is absorbed first
Blue and violet scatter easily
Green penetrates water best
Euphotic zone: Depth to which photosynthesis exceeds respiration in water.
Rarely the compensation point, the bottom of the euphotic zone, is as
deep as 100m.
Examples, very clear ocean or lakes near equator.
In highly turbid waters, the compensation point may be reached at 1m.
Major Essential Elements
Calcium (Ca), Iron (Fe), Nitrogen (N), Magnesium (Mg), Potassium (K), Phosphorus (P),
Sodium (Na), Sulfur (S)
Limiting Nutrient Elements
In aquatic (freshwater) environments: nitrogen and phosphorus
In marine (saltwater) environments: iron
In terrestrial environments: nitrogen and phosphorus (calcium)
Other Essential Resources
Carbon Dioxide: Not limiting
Oxygen: Can be limiting in water
Water: Often limiting in terrestrial environments
Limitations for one essential resources can influence the availability of other essential
resources. This is the case among terrestrial plants for the relationships between
photosynthetic rates, water loss, and gas exchange.
Photosynthetic Capacity and Water Conservation
Photosynthesis rate varies widely among species (100x) even with light saturation
and all other resources in abundance. This variation is due in part to differences between
plant species in the biochemistry of carbon fixation in photosynthesis (Calvin Cycle).
Plants can be categorized as having C 3
or CAM metabolism.
Photosynthetic Rate, Water Loss and Gas Exchange
Specializations and Compromises Among Plants
(seed stage) (desert annuals)
or dry season) (deciduous woody plants)
capacity (woody evergreens, evergreen desert shrubs)
4
photosynthesis: increased efficiency of carbon dioxide use per unit of water
loss, but inefficient at low light intensity (not shade tolerant), high temperature optima,
adaptation for water conservation and efficient nutrient capture (arid, tropical, and saline
environments) (see figures on next page)
limiting atmospheric carbon dioxide capture to night hours when water transpiration rates
are at a minimum, stomata are open at night and are closed during the day, good water
conservation but there are limits on photosynthetic capacity (arid, high elevation, windy
environments)
4
Photosynthesis
Comparison between C 3
and C 4
plants showing the differences in the physical distribution
of chloroplasts in the leaves, and differences in first steps of atmospheric carbon dioxide
capture for photosynthesis. Abbreviation key: RuBP = ribulose bisphosphate (a 5C compound), PGA
= phosphoglycerate (two molecules of a 3C compound), PEP = phosphoenolpyruvate (a 3C compound),
OAA = oxaloacetate (a 4C compound), Pyr = pyruvate (a 3C compound). Water loss is better
controlled in C 4
plants by physically separating carbon dioxide capture from the
atmosphere and the addition of one carbon to RuBP in the first step of the Calvin Cycle.
Water loss is minimized in this system because the atmospheric carbon dioxide capture step
is catalyzed by the enzyme PEP carboxylase which has a higher affinity for carbon dioxide
than does the enzyme RuBP carboxylase (Ricklefs, 1996, pp 68 and 69, Fig. 3.7 and 3.8).
3
Plants C 4
Plants
Ecological Niche (Hutchinson, 1957)
The set of conditions and resources minimum and maximum values that are limiting
to a population of a given species. This is an n -dimensional hyperspace.
The fundamental niche is the niche defined by abiotic factors alone.
The realized niche is the fundamental niche with biotic factor limitations
superimposed. The realized niche is typically smaller than the fundamental niche.
Two or three-dimensions are typical in niche descriptions (see Ricklefs, 1996, p 107, Fig 5.4)
Limiting Conditions and Resources
Generalizations
occasionally.
lethal) leading to reductions in growth, reproduction, or increased predation.
condition is critical can be difficult).
conditions in the center of that species range.
Ecology and Evolution
What is changing as a result of evolution? Phenotypes
Changes in phenotypes is reflected in qualitative and quantitative aspects of
interactions between organisms and their environment.
What is the phenotype? Any aspect of an organism except the information encoded in the
genetic materials (genotype).
Genotype + Environment >>>> yields>>>>>>>Phenotype
Given another population with two alleles, A and a , in equal frequency and given
random mating within that population, there should be three genotypes produced in ratios of
1:2:1 as given below (so population is polygenic, has more than one genotype):
Alleles for plant height: A tall information a short information
Genotypes: AA Aa aa
tallest information shortest information
Allele frequencies: f( A ) = 0.5 f( a ) = 0.
Genotype frequencies: f( AA ) = (0.5)(0.5) = 0.
f( Aa ) = 2(0.5)(0.5) = 0.
f( aa ) = (0.5)(0.5) = 0.
Frequency histograms for plant height in isogenic and polygenic populations with strong
environmental influences on phenotypic expression.
Note that both populations exhibit very similar phenotypic variation, frequencies of
specific heights, indicated by the darker outline curve.
Selection can and will occur in both isogenic and polygenic populations.
No phenotypic change can occur in the isogenic population as a result of selection. No
evolution can occur in the isogenic population.
Only selection on traits whose variation has a genetic basis (polygenic population, heritable
variation) can result in phenotypic change = evolutionary change.
Forms of selection and resulting forms of evolution. The frequency distributions show how
populations respond to selection assuming that the observed phenotypic variation results, in
part, from genotypic variation (polygenic populations). The shaded area of each distribution
indicates the negative action of selection, for example predation on the tallest individuals in a
population.
The causes for natural selection, the causes for differential survival and reproduction, are the
hostile forces of nature (limiting resources and conditions).
During this same time, pollution from coal burning (industrial revolution) was killing
lichens on tree and covering tree trunks with soot.
1937 E.B. Ford proposed that differential predation on dimorphic moths depends
on the color of the perches.
1950 H.B.D. Kettlewell performed experiments to test the hypothesis that the
change in moth color morphs was due to natural selection (differential
predation).
Hypothesis: Cryptic (camouflaged) moths will be at lower predation risk than non-cryptic
moths.
Environment (Perch Color)
Polluted (Dark Perch) Non-Polluted (Light Perch)
Dark Morph More Cryptic
Lower Predation Risk
Less Cryptic
Higher Predation Risk
Light Morph Less Cryptic
Higher Predation Risk
More Cryptic
Lower Predation Risk
Prediction: Birds take non-cryptic morphs more frequently than the cryptic morphs.
Predation on Moths by Birds
Light Morph Dark Morph
Polluted Forest 43 (74%) 15 (26%)
Non-Polluted Forest 26 (14%) 164 (86%)
Hypothesis: Cryptic (camouflaged) moths will survive longer in nature than non-cryptic
moths.
Prediction: When both moth morphs are marked and released in nature, the more cryptic
morph will be more readily recaptured than will the less cryptic morph.
Polluted Forest Non-Polluted Forest
Light
Morph
Dark
Morph
Light
Morph
Dark
Morph
Moths marked and released 201 601 496 473
Moths recaptured 34 205 62 30
Percentage recaptured 16% 34% 12.5% 6.3%
A given trait may be an adaptation in one environment and not in another.
Mutation keeps reintroducing the rare color morph in all populations.
Natural Selection does not have a goal.
Differential survival and reproduction simply occurs among the individuals in a given
population. The outcome of selection depends on the specific environment at a given place
and time, and the phenotypes present in a given population.
Natural selection is not the only means by which evolution can occur.
Potential causes for evolutionary change are:
Natural selection is the principal guiding force in evolution.
Mutation does not guide change.
Mutations do not respond to need.
What is the purpose of life?
Is there a singular goal? No
Is there a singular consequence? Yes
If evolution by natural selection is the major force molding phenotypes then:
All organisms must be striving to do one thing, maximize their genetic representation in
future generations.
There is no single best means of achieving this, but in general, organisms are selfish.
Natural Selection and Selfish Phenotypes
“Natural Selection cannot possibly produce any modification in a species
exclusively for the good of another species; though throughout nature one species
incessantly takes advantage of, and profits by, the structures of others... If it could be
proved that any part of the structure of any one species had been formed for the exclusive
good of another species, it would annihilate my theory, for such could not have been
produced through natural selection.” (Darwin’s Challenge)
Charles Darwin, 1859, The Origin of Species
How do individuals reproduce?
An individual may influence allele frequencies in future generations by:
descent (indirect reproduction). These influences are called Inclusive Fitness Effects (W.D.
Hamilton, 1964) or Kin Selection.
Examples of Inclusive Fitness Effects:
Parental care
Helpers at the nest, cooperative breeding (birds and mammals)
Eusocial insects (Hymenoptera, Isoptera)
Aposematic coloration
Inclusive Fitness Effects
Individuals carrying genes identical by descent are relatives (family members).
Genetic relationships can be expressed as the coefficient of relationship ( r ), the proportion
of genes identical by descent.
Inclusive Fitness Effects
Given sexually reproducing, diploid organisms:
Relationship Type Coefficient of Relationship( r )
Parent - Offspring 0.
Full Siblings 0.5 on average (range 0 - 1.0)
Grandparent - Grandchild 0.
Uncle (Aunt) -Nephew (Niece) 0.
First Cousins 0.
Altruism: Behavior benefiting another individual while being detrimental to the individual
providing the benefits. Benefits and detriments are defined in terms of survival and
reproduction.
“Altruism” is defined in much the same way that Darwin’s Challenge is framed. This is
behavior that we predict cannot be produced by natural selection.
Aiding relatives is an alternative means of individual reproduction, which depends on:
Natural selection molds phenotypes. Behavioral traits may appear selfish or altruistic, but
all are ultimately selfish in an evolutionary sense.
Can altruism evolve by means of natural selection?
Imagine a cleaner fish species in which individuals get no benefits from cleaning
parasites from other fish species, but cleaners did sustain some costs. If there were
variation in the cleaner fish population so some individuals were cleaners and others were
non-cleaners, and the variation was heritable, which behavioral trait would be most
successful in leaving descendents?
If the process of evolution by natural selection applies to all organisms, then it must apply to
human too. A vulgar theory? Does it apply to humans?
Does altruism occur in human behavior?
adoption, life saving, anonymous gifts
Behaviors that appear to make no sense today may have clearly been biologically selfish in
their original context. Humans are not living in the environments in which we evolved,
physical or social. Context (environment) is essential for understanding the evolution and
maintenance of phenotypic traits.
An evolutionary view of life provides a framework for interpreting ultimate function, the
origin of phenotypes, structure and function. The theory of evolution by natural selection
enables us to interpret how phenotypes were molded to their present state, but this theory
does not indicate what should be.