Study Guide for Principles of Ecology | HBIO 320, Study notes of Ecology and Environment

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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

, C

4 ,^

or CAM metabolism.

Photosynthetic Rate, Water Loss and Gas Exchange

Specializations and Compromises Among Plants

1. Short life, high photosynthetic rate when water abundant, dormant at other times

(seed stage) (desert annuals)

2. Long life, leaves produced when water abundant, leaf drop during droughts (winter

or dry season) (deciduous woody plants)

3. Leaves long lived, transpire slowly, tolerate water deficit but have low photosynthetic

capacity (woody evergreens, evergreen desert shrubs)

4. C

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)

5. CAM photosynthesis (Crassulacean Acid Metabolism): control of water loss by

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)

C

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).

C

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

1. Lethal conditions may limit distributions but such conditions need only occur

occasionally.

2. Distributions are more often limited by regularly suboptimal conditions (rather than

lethal) leading to reductions in growth, reproduction, or increased predation.

3. Sub-optimal conditions act by altering outcomes of biological interactions.
4. Sub-optimal conditions often interact with other factors (determining which single

condition is critical can be difficult).

5. At the edge of a species distribution, individuals occupy patches most like the

conditions in the center of that species range.

6. Evolutionary responses tend to modulate effects of suboptimal conditions.

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:

1. Natural Selection
2. Mutation (random process, but the source of all variation)
3. Drift (random process)
4. Migration (random process)

Natural selection is the principal guiding force in evolution.

1. Altering the direction of selection alters the direction of change.
2. Causes of mutation are independent of the causes for selection.

Mutation does not guide change.

Mutations do not respond to need.

3. Only the causes for selection remain consistently directional for long time periods.

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:

1. Production of offspring by that individual (direct reproduction).
2. Influencing the survival and reproduction of individuals carrying genes identical 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:

1. The magnitude of r. The greater the value of r , the more likely
2. Magnitude of benefit to aid receiver (includes reciprocity).
3. Magnitude of cost to aid giver (depends on alternative activities).
4. Magnitude of benefit to aid giver from sources other than the aid receiver.

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.