Population ecology the study of how natural processes affect the size, composition, and dynamics of populations.

  • Population - a group of interacting individuals of the same species.
  • Community - a group of interacting populations.
  • Ecosystem - a functional environmental unit, consisting of a biotic community and the abiotic (nonliving) factors on which the organisms depend.
  • Biosphere - the total of all ecosystems. In other words, all the area on Earth where life is found.
  • Ecology - the study of relationships between organisms and their environment.
The discovery of laws in ecology has lagged behind those of physics and chemistry. The main reasons seem to be that ecology is a much younger science and that research in all its branches is woefully underfunded and understaffed.


Estuaries and coastal waters are among the most productive ecosystems on Earth.

An ecosystem is a naturally occurring functional unit of organisms—also
referred to as a biotic community. The ecosystem comprises an interacting synergism of living organisms in a particular environment; every plant, insect, aquatic animal, bird, or land species that forms a complex interconnected web of dependency. In an ecosystem, the connections between species are generally related to food and their role in the food chain, but their dependencies also includes all the non-living physical and chemical factors of their environment, which they are linked to through nutrient cycling and energy flow. Therefore, an action taken at any level in the food chain, use of pesticides for example, has a potential domino effect on every other occupant of that system.

Categories of Organisms

The ecosystem is a community of three basic types of organisms - producers, consumers, and decomposers that are linked by energy and nutrient flows, and that interact with each other and with the physical environment.

Types of Biomes

An ecosystem can be as small as a rotting log, pond, field, or forest. In contrast, a biome is a large area with specific types of flora, fauna, and microorganisms, and which may contain many ecosystems. A biome can be thought of as many similar ecosystems throughout the world that share certain similarities. Ecosystems and Biomes are typically identified as a specific type of environment or biotope, possessing characteristic habitats, niches, and species.


Population Size and Density

  1. To begin to study a population, the size of the population (number of individuals) is determined.
  2. For the size of a population to have meaning, the area covered by the population must be known.
  3. Density - the number of individuals per area unit.
    • Density-Dependent Factors - In general, density-dependent factors are biological factors, such as diseases, parasites, competition for resources, predation, and stress.
    • Density-Independent Factors - In general, density-independent factors are physical factors, such as weather factors (severe winter), natural disasters (floods and fires), or the presence of harmful chemicals.
Distribution patterns describe distribution within the area being studied and give a better picture of actual population density. Many animal populations will have different distribution patterns at different times.
  • Random distribution - each individual has an equal chance of being found at any place in a given area. This is a hypothetical condition that might never occur in nature because resources are not randomly distributed.

  • Uniform distribution - animals are evenly spaced throughout the habitat. This can at least be approached in nature.

  • Clumped distribution - animals are found in areas where resources are found. This is by far the most common distribution pattern in nature.

Population age structure can tell more about population dynamics than either density or distribution.

  • Functional age classes: because of the difference in lifespans, the ages of these groups can be very different from one group of animals to another.
    • Prereproductive - too young to reproduce.
    • Reproductive - able to reproduce.
    • Postreproductive - too old to reproduce.
  • Population age profile - an estimation of the number of individuals in each age class.
    • When the number of prereproductive individuals forms a high percentage of the population, the population is likely to be increasing in size.
    • A stable population has a fairly even number of individuals in each age class. When the number of postreproductive individuals is large, the population is declining. There are too few individuals maturing to provide population replacement.
    • A species with a short life span will show all three types of age profiles during one seasonal cycle.
  • Natality - the ratio of the number of births in a given time to the total population.
  • Mortality - the ratio of the number of deaths in a given time to the total population.
Mathematical Models of Population Growth

1. Exponential growth model

  • A population could reach its biotic potential, the maximum growth rate of which a population is physiologically capable, if these conditions are met:
    • environmental conditions are ideal
    • there are no restrictions on reproduction
    • mortality rate is kept extremely low
  • Realized intrinsic rate of growth (r) is measured by the difference between natality (birth rate, n) and mortality (death rate, m).

    r = n − m

    Since environmental conditions are rarely ideal, the maximum growth rate is almost never achieved in nature. The realized intrinsic rate of growth more closely represents the actual growth of organisms in nature than does the biotic potential.

  • Zero population growth is reached when r = 0, natality equals mortality, and population size remains constant.
2. Logistic Growth Model
  • Environmental resistance - the combination of many factors that tend to prevent exponential growth.
  • Exponential growth begins to slow because of a combination of declining birthrate and increasing death rate. Eventually, the population stops growing as it fluctuates around zero population growth at the habitat's carrying capacity - the maximum population density that the environment can support for an extended time.
  • Restricted or logistic population growth can be expressed by the following equation:

    d N / d t = r N x (K − N) / K

    • d - means an instantaneous change in
    • N - the number of individuals already in a population
    • t - a unit of time
    • r - realized intrinsic rate of population growth
    • K - carrying capacity

Population Changes Based On Carrying Capacity

r-selected species

Unstable environment, density independent
K-selected species

Stable environment, density dependent interactions
Organism size Small Large
Energy used to make each individual Low High
# Offspring produced Many Few
Timing of maturation Early Late
(with much parental care)
Life expectancy Short Long
Lifetime reproductive events One More than one
Survivorship curve Type III Type I or II

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Noah's ark

Noah's Arkwas the immense vessel that God told Noah to build. The account is recorded in the book of Genesis beginning in chapter 6. The Ark's purpose was to save Noah and his family from the coming global flood and to preserve mating pairs of every kind of terrestrial animal.



Popular conceptions of the Ark have varied with the culture. In the early days of Western shipbuilding, artists depicted the Ark to resemble contemporary ships, though such portraits were inconsistent with either the size or the proportions of the Ark. The most accurate portrait in the era of the Renaissance was that made in 1675 by Athanasius Kircher, who thought the Ark to be rectilinear.

Sadly, in the nineteenth century, scholars who were under the influence of secular scientists like Charles Lyell and Charles Darwin began to take the Flood story less than seriously. Artists then began to depict the Ark in a manner befitting an illustrated children's book. A typical portrait of the Ark, even in church windows, gave it the shape of a claw-footed bathtub surmounted by an over-sized pilothouse with a gabled roof.

In 1961, John Whitcomb and Henry Morris published The Genesis Flood, their landmark work that incited the modern creation science movement. In that work, Whitcomb and Morris discussed the Ark and emphasized its carrying capacity and hypothetical seaworthiness.

Shortly after this, a number of witnesses came forward claiming to have climbed Mount Ararat in modern Turkey and actually seen the Ark, or spoken to those who had. All the putative witnesses described an immense rectilinear structure, though they provided few details of its size and proportions. Artists now began to depict the Ark as a simple rectilinear solid. The most famous such painting was by Elfred Lee, who in 1985 painted the Ark as a long barge surmounted by a ventilatory superstructure running the entire length of its roof. The artist alleged that he based his illustration on the testimony of one George Hagopian, who died in 1972 after granting multiple interviews in which he described to Mr. Lee what he had seen.

Design considerations

The Ark was not designed as a ship. It would not have required a propulsion or navigation system, nor even anchors. Its purpose was to keep its passengers safe, while leaving their course and ultimate destination completely in the hands of God.


The book of Genesis describes Noah's Ark as a wooden vessel 300 cubits long, 50 cubits wide, and 30 cubits high. Based on the shortest estimated length of the cubit, this means it was at least 450 feet (135 meters) long, 75 feet (22.5 meters) wide, and 45 feet (13.5 meters) high. (If long cubits are assumed, these dimensions increase to 516 ft by 86.0 ft by 51.6 ft, or 157 m by 26.2 m by 15.7 m.) These proportions are ideal to balance the demands of sea-kindliness, hull strength and stability. The Ark's size is equivalent to an average cargo vessel by today's standards, which is in line with the limits of timber construction. The account in Genesis 6-8 is workable. Even simple requirements such as the height between decks make good sense.

The Ark had lower, middle, and upper decks and an additional clearance of one cubit at the roof. This last might refer to an elaborate ventilation system.

In contrast, the Epic of Gilgamesh suggests that the Ark was cuboidal, rather than rectilinear. Such a design would have been neither seakindly nor stable.

Structural elements

A model of Noah's Ark, showing its proportions, its scale, and hypothetical design elements; suggested by Tim Lovett's work

A rectilinear structure would be vulnerable to the shock of wave impacts. A curvilinear structure would be able to deflect the waves safely. Furthermore, any ship designed to stay afloat in the rough seas of the Flood would have a keel.

Examination of the ancient war vessels of the Greeks and Romans reveals many common elements that would enhance seaworthiness. They include a tapered bow with a projection below the water line, and a large sail-like projection on the stern. These features would have caused the Ark to head into the wind and fall back before it.

The door of the Ark need not have been on the upper level. In fact, the terms used to describe the decks as lower, middle, and upper, rather than first, second, and third, suggest that the door was at the middle level. The door was probably in the stern of the Ark to avoid compromising the strength of its hull. The word usually translated "window" in Genesis 6:16 actually meant "midday" and thus would indicate a series of hatches in its roof.


The Ark was made of "gopher wood," an unidentified hardwood, and was coated inside and out with a covering that is translated as "pitch." The term gopher wood appears only in the Flood account (thereby making it a hapax legomenon), and thus the Bible gives few clues to its actual meaning.


Skeptics have often doubted whether the technology of shipbuilding in antediluvian times was sufficiently advanced to enable Noah, or any other shipwright, to build a ship more than 500 feet (150 m) long. In fact, modern man cannot know the level of antediluvian technology, because all evidence of that technology lies buried under one or more miles of sedimentary rock. In addition, the recent finds of out-of-place artifacts suggest that antediluvian civilization might have commanded a far higher level of technology than modern archaeologists or even Biblical scholars generally suppose.

Tim Lovett suggests that the minimum technology that Noah would have had available to him was that of the ancient Egyptians, which would have been capable of building a wooden vessel as large as the Ark, and certainly within the 120 years probably allotted to the task.

One persistent objection is that a wooden vessel 450 feet or more in length would not be able to stay watertight. Lovett answers this objection with his description of the mortise-and-tenon-planking technique that Greek shipwrights used often and to excellent effect as early as four centuries before Christ. In addition, reports persist of a forty-oar Greek galley built in the fourteenth century BC, though neither ruin nor wreck of such a ship has ever been found.


The Bible does not definitely fix the date on which construction of the Ark began. Yet the Bible says that God delivered a message in advance of the Flood:
"And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years." - Genesis 6:3

While many creationists purport that the reference to 120 years in the above verse was a proclamation that human life expectancy would be reduced following he flood, others believe it refers to the date when the flood would occur - providing a period of warning, during which Noah preached repentance to a world that, sadly, did not listen. (1_Peter 3:20 , 2_Peter 2:5 ) Lovett suggests that Noah began to build the Ark at the same time that he began to preach to his world. Given that the Flood occurred on 17 Bul 1656 AM, Noah probably received God's instruction to build the Ark in the fall of 1536 AM and laid the keel of the Ark in the next spring.

The Bible further states that God instructed Noah to board the Ark, together with his family and all the animals, seven days before the Flood broke out. (Genesis 7:1-10 ) The Bible then gives the date of the Flood as the seventeenth day of the second month of the six hundredth year of Noah's life, which would be 17 Bul 1656 AM. (Genesis 7:11-13 )

The above statements suggest this tentative schedule of the career of the Ark:

  1. Construction authorized: Ethanim 1536 AM
  2. Keel laid: Abib 1536 AM
  3. Commissioned: 10 Bul 1656 AM
  4. Launched: 17 Bul 1656 AM
  5. Grounded: 17 Abib 1656 AM(Genesis 8:3-4 )
  6. Decommissioned: 27 Bul 1657 AM (Genesis 8:14 )


Noah's Ark has not been found. According to Scripture, the Ark came to rest in the mountains of Ararat, which are in Turkey. There have been numerous reports of sightings throughout history, but the region remains largely unexplored. Although the Ark has probably decomposed since the flood, it remains a dream of Biblical archaeologists worldwide that the Ark will be found. The Ark's discovery would substantiate the Biblical account of a recent global flood and God's judgment. Discovering a vessel of that size in Turkey would lend credence to the Bible's account of the Earth's early history and the catastrophic interpretation of the fossil record.

Some believe that they have found the Ark in northern Iran. A Christian archeological expedition has found a rock formation that seems to have the same dimensions as the Ark spoken of in the Bible. The formation was discovered in the Elburz mountain range on Mt. Suleiman. Scientists from the expedition have taken slices from the rocks and run tests on them. They figured out that there are wood cell structures within these samples. It is impossible for the expeditioners to ever know for sure whether or not it really was Noah's Ark, but they do know that it was a place of great importance to ancient peoples. Explorers have discovered an ancient shrine near the supposed Ark.

Recent satellite image from Digital Globe's Quickbird examined by NASA as possible Noah's Ark location on Mt. Ararat.
There have been many supposed "sightings" of Noah's Ark on or around Mt. Ararat.

George Hagopian

One of the most famous is that of George Hagopian.

He was eight years old, Hagopian said, and it was in the year 1908 [note: another account says the year was 1905 and Hagopian was 10 years old] when his uncle took him up Ararat, past Ahora Gorge, passing the grave of St. Jacob on the way. As the mountain grew more precipitous his uncle carried him on his shoulders until they came to something that looked like a great ship located on a rock ledge over a cliff and partially covered by snow. It had flat openings like windows along the top and a hole in the roof. Hagopian had first thought it was a house made of stone but when his uncle showed him the outline of planks and told him it was made of wood he realized it was the Ark, just like the other people had described it to him. His uncle boosted him up from a rock pile to reach the Ark roof telling him not to be afraid, "because it is a holy ship ..." (and) "the animals and people are not here now. They have all gone away." It is also said that Hagopian's uncle tried to shoot the Ark, but the bullets bounced off as if it were metal.[12]

Ararat anomaly

Declassified Central Intelligence Agency (CIA) Keyhole-9 satellite image of Mt. Ararat and the Ararat Anomaly taken on Dec. 20, 1973

The Ararat Anomaly is basically an object appearing in pictures on the snowfields at the peak of the Mt. Ararat. This object is often considered to be the remains of Noah's Ark.


The Durupınar site is the location of boat-shaped formation, which was named after its discoverer. Its size, unusual shape, and location were immediately recognized as a close parallel to Noah's Ark. The size of the formation matches the description from the Bible almost exactly. Although the shape of the Durupınar site formation is very compelling, it is not unique to the region. There are other similar formations nearby, which are apparently the result of solidified mudflows.


Stories of a global flood, and of a favored family that survived it, abound in ancient folklore. John D. Morris collected two hundred such stories and found a surprising number of common elements. Most of the stories collected speak of a global catastrophe, consisting solely of a flood that a god or gods sent to punish the wickedness of mankind. Most stories also tell of a family, forewarned of the flood, who built a ship to save themselves and all the different kinds of animals. More than half the stories say that this ship ran aground on a mountaintop.

The Animals

Genesis does not tell us that every kind of animal came to the Ark to be saved from the flood. God only brought animals "with the breath of life", a phrase that most modern creation apologists associate with land vertebrates (Genesis 7:15 ). One pair of each unclean animal, and seven pairs of each clean animal came on board (Genesis 6:20 ). The majority of the fossil record was laid down during the flood, so there were many more kinds of animals alive in Noah's time. These would include dinosaurs, pterosaurs, marsupial lions, and others; mammoths were almost certainly part of the elephant kind. Noah did not have to round up the animals, because God sent them to him (Genesis 7:2 ).

The capacity of the Ark matches estimates of the number of animals kept by Noah that have since diversified into an apparently much larger number of species. For example, the variety of modern dogs are believed to have descended from a single ancestral pair.

Noah's Ark in fiction

Many novels have been written having Noah as a character, and often as the central character. They include:

  1. Noah by Ellen Gunderson Traylor. It speculates rather heavily on whether antediluvian civilization might have included prominent figures having names that prefigured the classical Greek pantheon, but otherwise tells a story faithful to the Bible about the Ark, its shape, its construction, how long the project took, and its voyage.
  2. Ice by Shane Johnson. Noah figures here, too, though not as the central character. Johnson speculates that humans might have stood on average one-third again as tall as they stand today, and therefore the cubit might have been twenty-four inches long, not merely eighteen. The Ark would therefore have been 600 feet long, not merely 450, and hence quite large enough by any standard to hold two of every created kind of land animal and bird (and seven of every kind of clean bird). Johnson also suggests that the "gopher wood" might have been an advanced composite, and the "pitch" likewise an advanced blend of natural resins. Both of these would have been the products of a civilization that, Johnson suggests, was far more advanced than is usually supposed and even more advanced than human society today.

Noah's Ark Gallery

Survivorship Curves
  • Type I curves are typical of populations in which most mortality occurs among the elderly (humans in developed countries).
  • Type II curves occur when mortality is not dependent on age (many species of large birds and fish).
  • Type III curves occur when juvenile mortality is extremely high (plant and animal species producing many offspring of which few survive). In type III populations, life expectancy increases for individuals who survive their risky juvenile period.

The following two mathematical models help us understand, but not necessarily precisely describe, how populations actually grow. Both models make important simplifying assumptions that do not actually relate to nature.

  • The exponential model assumes that populations grow without being influenced by environmental resistance.
  • While the logistic model may seem more realistic, it makes several assumptions:
    • Assume the carrying capacity is constant.
    • Assume each individual affects the growth of the entire population by increasing environmental resistance as soon as it is born.
    • Assume the number of offspring produced by an individual relates directly to the resources available at the time of birth.
Species Characteristics Related To Population Growth
  • r-selected species - capable of very rapid population growth, approximating an exponential growth pattern followed by a crash in the adult population .
  • K-selected species - have more or less stable populations adapted to exist at or near carrying capacity in relatively stable habitats.
  • euryoecious species - widely distributed with a high tolerance for many environmental factors.
  • stenoecious species - narrow distribution with a low tolerance for changes in environmental factors.
Two things can be said about populations
  1. Population density varies from habitat to habitat.
  2. No population increases indefinitely.
Law Of Minimums - essential material available in amounts most closely approaching the minimum needed by an organism will tend to limit the organism's growth and development.

Limits Of Tolerance - organisms can only tolerate certain extremes in environmental factors. Populations cannot exist outside the tolerance limits of its individuals.

Competitive Exclusion Principle - competition between populations of two species for the same limiting resource eventually leads to the elimination of one of the species populations.

An animal's niche is determined by all the ways the animal interacts with its environment, including what it eats, how it obtains its food, what physical and chemical conditions it will tolerate, what conditions are optimal for its well-being, and how it interacts with its predators and parasites.

Predation - the feeding of free-living organisms on other organisms.

  • Predator-prey relationships
    • Optimal foraging brings a predator the maximum net food energy gain. Predators do not normally spend great effort pursuing rare, energy-poor, or hard to handle prey.
    • Prey availablility is a key factor in the foraging behavior of predators. Increasing numbers of prey elicit two types of responses from predators:
      1. Functional response - There is a relationship between prey density and the number of prey consumed per predator per unit of time. The predator seems to focus its attention on the shape and general appearance of the abundant prey, filtering out other potentially distracting stimuli. The abundant prey makes up an increasing percentage of the predator's diet.
      2. Numerical response - There is a relationship between prey density and predator density. Predator numbers increase as a prey population increases.

Some species are linked, with population numbers fluctuating together.

But do the predators control prey populations, or do prey populations control predators?


49791126 d67ced4793.jpg

Predation in nature is the act of killing a creature with the intent to eat it. It is often associated with such animals as lions, wolves, and sharks. Many of these predators have specialized features like claws. Other creatures that form the prey are in many cases equipped to hide from or defend against predators. Predation is an easily seen form of natural selection.

Argument against creation

Predation often arises in origins debates as an argument against the God of the Bible in general and creationists in particular. Young Earth Creationists point to the descriptive words of "good" and "very good" in Genesis 1, as well as God’s giving plants for food to everything with the "breath of life." The term "very good" would seem to imply that there was no death at this point, and hence no predation. This is in contrast to what is observed today, where many kinds of animals depend upon the meat of other animals in order to survive. Moreover, many types of animals exhibit traits which appear specifically suited for killing and consuming meat. It is claimed that there is no instance in scripture that indicates any such shift.

Creationist arguments

There are several hypotheses given as to the origin of carnivory and predation. Note that not all of these are mutually exclusive.

Fall and alteration


Some creationists point to Genesis 3:18, where an aspect of nature was redesigned to be hostile towards man:

It [the ground] will produce thorns and thistles for you, and you will eat the plants of the field. Genesis 3:18

This instance may have encompassed more than just plants and covered animals as well. It is earlier mentioned that at least the serpent was changed:

So the Lord God said to the serpent, "Because you have done this, "Cursed are you above all the livestock and all the wild animals! You will crawl on your belly and you will eat dust all the days of your life." Genesis 3:14

Fall and activation

A related line of thought is that certain offensive and defensive features were already preprogrammed into the animal’s DNA, but laid dormant until they were "switched on" by the Creator at the Fall of man. God would have known that man would give in to sin and set up a sort of "safety feature" wherein animals would be able to survive in a fallen world.

Flood and shift

Perhaps a very pertinent verse regarding animal predation is Genesis 9:1-6:

Then God blessed Noah and his sons, saying to them, "Be fruitful and increase in number and fill the earth. The fear and dread of you will fall upon all the beasts of the earth and all the birds of the air, upon every creature that moves along the ground, and upon all the fish of the sea; they are given into your hands. Everything that lives and moves will be food for you. Just as I gave you the green plants, I now give you everything. But you must not eat meat that has its lifeblood still in it. And for your lifeblood I will surely demand an accounting. I will demand an accounting from every animal. And from each man, too, I will demand an accounting for the life of his fellow man. Whoever sheds the blood of man, by man shall his blood be shed; for in the image of God has God made man." Genesis 9:1-6

After the Flood, man was given permission to eat the meat of other creatures, but there is also mention of a behavioral change in animals. They were made to fear man. But another interesting note is that any animal that killed a man was to be held accountable. This may infer that animals would be allowed to kill other animals, but just not man.

Degenerate mutations

Another idea is that predatory features and behavior arose as a result of degenerate mutations. These mutations would have corrupted the original animal designs, distorting such features as teeth and claws to be more suited for killing. Mutations could also have resulted in certain animals losing the ability to digest their original plant foods, or having that ability lessened. This may be evident in animals for which certain species eat meat, but for which the animal's kind in general does not exhibit such characteristics.

Definition of life

It is stated that life is in the blood of a creature:

For the life of a creature is in the blood, and I have given it to you to make atonement for yourselves on the altar; it is the blood that makes atonement for one's life. Leviticus 17:11

Therefore, any creature that does not have blood may be considered as not living in the Biblical sense. This would mean that plants and insects are not technically alive, and their "deaths" would not be an act of "killing."

Change in environment

Tied in with a switch of diet after the Flood is the likelihood that nutrient values of plants would have been much different before and after the cataclysmic environment change. Certain protein levels in plants can be quite high. Antediluvian ecosystems may have been able to support plants with even higher amounts.

Herbivorous carnivores

Animals that are usually considered meat eaters, such as dogs and even lions, in reality consume a significant level of grain and fruit. Domestic dog meal is comprised largely of cereal, and coyotes are actually fond of fruit. There is a case of the lion that could not stomach even the smell of a bone, but was raised by humans on a diet of grain, eggs, and milk. Mosquitoes are not all blood suckers either--the males survive on nectar. Furthermore, features that are commonly associated with carnivory are in many cases used for purposes other than killing. For example, reptiles with sharp teeth and bats with fangs eat fruit. In at least one instance, an evolutionist has even presented the possibility that dinosaurs used their claws to open coconuts (although this was meant to mock creationists).

You have come to the end of the lesson. Please go to the review.

Last modified: Thursday, 5 January 2012, 06:59 PM