B. Density and Distribution of Populations

I. Scope of Ecology

A. Ecology

1. ______is the study of interactions of organisms with their environment.
2. Concept of ecology was first voiced by German zoologist Ernst Haeckel.
3. Ecology studies how environmental factors determine distribution and abundance of populations.
4. Ecology and evolution are related because natural selection has long-term effects.
5. A ______is a group of the same species occupying a certain area.
6. A ______consists of all populations at one locale (e.g., a coral reef population).
7. An ______contains the community organisms and abiotic factors (e.g., energy flow, chemical cycling).
8. Modern ecology is descriptive and predictive with application to wildlife management and agriculture.

B. Density and Distribution of Populations

1. ______of organisms refers to how many live per unit of area or volume.
2. ______of organisms is distribution; varies from uniform to random to clumped.
3. Ecologists study the causes for "patchiness" of organisms across space and through time.
4. Environment includes ______(living) and ______(physical) factors.
5. Physical (abiotic) factors include types of precipitation and amounts, averages, and daily and seasonal
variations in temperature, type of soil or nutrients; moisture or temperature may serve as ______
6. Biotic factors are illustrated by red kangaroos limited to inland Australia by their food source.

II. Characteristics of Populations

A. Population Size

1. ______is number of individuals contributing to gene pool of the population.
2. At any one point in time, populations have a certain size.
3. Future population size depends on natality and mortality (births and deaths), immigration and
emigration (often immigration and emigration are presumed equal).
4. Birthrate and death rate are used to calculate the intrinsic rate of natural increase.
5. ______is used to calculate the growth of a population per unit time.

B. Population Growth Models

1. There are two patterns of population growth.
a. In discrete breeding, organisms reproduce once and cease to grow as adults; they expend energy
in reproduction and die.
b. In continuous breeding, organisms reproduce through their lifetime, which invests energy in future survival.
2. Most organisms do not exactly fit these two patterns.
a. Aphids can switch between sexual and asexual reproduction according to weather.
b. Annual plants can reproduce both by seeds and vegetative extensions.

C. Exponential Growth

1. The ______has two phases.
a. ______(growth is slow because population is small).
b. ______(growth is accelerating).
2. A mathematical equation calculates exponential growth and size for any population that has discrete
generations.
3. ______
a. Exhibited during exponential growth, this is the maximum population growth under ideal circumstances.
b. Includes plenty of room for each member, unlimited resources (e.g., food, water), and no hindrances
(e.g., predators).
4. ______curbs exponential growth; includes all environmental factors that limit population size.

D. Logistic Growth

1. When growth encounters environmental resistance, populations experience an ______or ______.
2. Raymond Pearl (1930) estimated growth in a yeast and arrived at a graph and formula for logistic growth.

3. In addition to the lag phase and exponential growth, there is a deceleration phase where rate of population
growth slows down and a stable equilibrium phase with little if any growth because births equal deaths.
4. Curve is called logistic because exponential portion of curve would plot as a straight line as log of N.
5. A mathematical equation calculates logistics growth.
6. Environmental resistance results in the ______and the ______; population is
at the carrying capacity of the environment.

E. Carrying Capacity

1. ______is the maximum number of individuals of a species that can be supported by environment.
2. When N is small, a large portion of the carrying capacity has not been utilized, but as N approaches K,
population growth slows down because (______is nearing zero.
3. Examples: over-fishing drives a population into the lag phase; it is best to maintain populations in a growth
phase; and reducing crop pests places them in exponential phase again.
4. Farmers can reduce the carrying capacity for a pest by alternating rows of different crops.

F. Mortality Patterns

1. A life table shows how many members of a cohort (group born at one time) are surviving at different ages.
2. ______is the percentage of remaining survivors of a population over time; usually shown graphically.
a. ______: most individuals live out their life span and die of old age (e.g., humans).
b. T______: individuals die at a constant rate (e.g., birds, rodents, and perennial plants).
c. ______: most individuals die early in life (e.g., fishes, invertebrates, and plants).
3. The grass Poa annua is intermediate; most survive till 6-9 months and then chances of surviving diminish.

G. Age Distribution

1. There are three major age groups in a population: pre-reproductive, reproductive and post-reproductive.
2. An ______is a representation of the number of individuals in each age group in a population.
3. A ______indicates the population has high birthrates; population is undergoing exponential growth.

III. Regulation of Population Size

A. The J-shaped and S-shaped growth curve models do not always predict real populations.

1. In the winter moth (pages 388-389), many eggs did not survive winter and exponential growth did not occur.
2. Growth curve of reindeer herd introduced to St. Paul Island, Alaska, overshot carrying capacity.

B. Populations do not increase in size year after year because environmental resistance, including
both ______and ______, regulates the number of organisms.

1. Some populations were considered to be regulated primarily by density-independent factors.
a. The number of organisms present does not affect the influence of the factor.
b. The damage to a population from an accidental fire does not change with the number of organisms present.
c. Density-independent factors show no correlation with the size of the population.
2. Populations regulated by density-dependent factors are affected by the number of organisms present.
a. Predation, parasitism, competition are considered density-dependent; the more organisms crowd together,
the more damaging are food shortages, parasites, and predators.
b. Density-dependent factors have some effect relative to the size of the population.
3. Weather, food, other animals, pathogens, and habitat are important external factors..
4. Intrinsic factors can also influence population size: territoriality, recruitment, immigration and emigration.
5. Populations may also be inherently unstable and fluctuate from simple models.
6. New theories on chaos help us understand severe fluctuations over time.

IV. Life History Patterns

A. The logistic population model predicts two main life history patterns.

1. ______
a. Species that underwent selection to maximize their rate of natural increase are categorized as r-selected.
b. These populations are often ______, which tend to be colonizers.
c. Strategy for continued existence is based on individuals having the following traits:
1) small size
2) short life span
3) mature fast
4) produce many offspring
5) engage in little care of offspring
d. Thus, they rely on rapid dispersal to new unoccupied environments.
2. ______
a. Species that hold their populations fairly constant near the carrying capacity are K-selected.
b. Such populations are ______, tend to be specialists rather than colonizers, and may
become extinct when their evolved way of life is disrupted (e.g., the grizzly bear, Florida panther, etc.).
c. Overall strategy for continued existence is based on having the following traits:
1) large size
2) long life span
3) slow to mature
4) produce few offspring
5) expend considerable energy in care

B. Most populations cannot be characterized as either r- or K-strategists; they have intermediate characteristics.

V. Human Population Growth

A. The Human Population Is Growing

1. The human population is now in an exponential part of a J-shaped growth curve.
2. World population increases equivalent of one medium-sized city (200,000) per day and 88 million per year.
3. ______is the length of time for population size to double, now 47 years.
4. Zero population growth is when birthrate equals death rate and population size remains steady.
5. World population may level off at 8, 10.5 or 14.2 billion, depending on decline in net reproductive rate.

B. More-Developed versus Less-Developed Countries

1. More developed countries underwent ______1950-1975; their growth rate is now 0.6%.
a. ______were first industrialized (e.g., Europe, North America, Japan, etc.).
b. ______is decline in death rate followed by declining birthrate; results in slower
growth, about 0.1%.
2. ______are now undergoing demographic transition.
a. Less developed countries (LDCs) are fully industrialized (e.g., countries in Africa, Asia, Latin America).
b. LDC growth rate peaked at 2.5% between 1960-1965; it is declining slowly to about 1.8% at year 2000.
3. Most of the explosive growth will occur in Africa, Asia and Latin America unless
a. family planning or birth control are strengthened
b. the desire for more children is reduced
c. the onset of childbearing is delayed

C. Comparing Age Distributions

1. ______will cause population growth to continue due to the age structure of the population.
2. Mere replacement does not produce zero population growth because more women enter reproductive years
than leave them.
3. The LDCs have a higher growth rate because of a youthful age structure and more women entering
reproductive ages than leaving.
4. The MDCs have a low growth rate because of a stabilized age structure.

D. A Sustainable World

1. The decision is not between preservation of ecosystems or human survival.
2. Both the growing populations of LDCs and the high consumption of MDCs stress the environment.
3. An average American family, in terms of consumption and waste production, is equal to thirty people in India.
(Fig. 23.16)
4. ______is used to describe how cities borrow resources from the rural areas and the
entire society borrows from the past and future.
5. Overpopulation and over-consumption contribute to pollution and extinction of species.
6. Sustainable practices include selective cutting, traditional logging, etc.

VI. Structure of the Community

A. Interaction Between Populations is Complex

1. Interactions include: competition for resources, predator-prey interaction, parasite-host interaction.
2. Competition for limited resources negatively affects population size of both species.
3. Predation and parasitism increase the predator population at expense of prey and host populations.
4. In ______, one species is benefitted, the other is harmed.
5. In ______, one species is benefitted, the other is neither benefitted nor harmed.
6. In ______, both species benefit.

B. Habitat and Ecological Niche

1. A ______is where an organism lives and reproduces in the environment.
2. An ______is a role an organism plays in its community, including its habitat and its
interactions with other organisms.
a. The ______is the range of conditions under which it can survive and reproduce.
b. The ______is the set of conditions under which it exists in nature.

C. Competition Between Populations

1. ______occurs when different species utilize a resource that is in limited supply.
2. If the resource is not in limited supply, there is no competition.
3. Lotka and Volterra (1920s) developed a formula: competition favors one species, eliminates the other.
4. Gause grew two species of paramecia in one test tube; only one survived if they were grown together.
5. ______: no two species can occupy the same niche at the same time.
6. Over time, either one population replaces the other or the two species evolve to occupy different niches.
7. If it appears two species occupy the same niche, there must be slight differences; Gause found two species
of paramecium coexisted if one fed on bacteria at the bottom of the tube, the other fed at top.
8. ______occurs when species shift niches; they no longer directly compete.
a. Three species of island finches have three sizes of beaks for small, medium, and large seeds.
b. When species live on separate islands, beak sizes are intermediate; this is ______
c. Five species of warblers in same tree spent time in different tree zones to avoid competition.
d. Swallows, swifts, and martins fly in mixed flocks eating aerial insects but have different nesting sites, etc.
e. Above examples are deduced from already completed partitioning.
f. Joseph Connell studied competition occurring in barnacles that consistently shift to match shoreline tidal zones.
1) By removing large Balanus barnacles from the lower zone, the smaller barnacles easily moved in.
2) The smaller barnacle is more resistant to drying out; the larger one overgrows it.

D. Predator-Prey Interactions

1. ______occurs when one organism (______) feeds on another (______).
2. In a broad sense, it includes not only single predator-prey kills, but also filter feeding whales that strain krill, parasitic ticks that suck blood, and herbivorous deer that eat leaves.
3. Predator-Prey Population Dynamics
a. Some predators reduce the densities of their prey.
1) When Gause reared the protozoans Paramecium caudatum and Didinium nasutum together in culture,
Didinium ate all the Paramecium and then died of starvation.

2) When cactus was introduced to Australia, it spread wildly without competition on the desert; a natural
predator moth was introduced and the cactus populations plummeted dramatically.
b. Natural predator-prey relationships allow persistent populations of both predator and prey populations,
though both may fluctuate over time.
1) Often a graph of predator-prey population densities shows regular peaks and valleys with the predator
population lagging slightly behind the prey; two reasons are possible.
2) The biotic potential of the predator may be great enough to overconsume the prey; the prey population
declines and so does the predator.
3) Or the biotic potential of the prey is unable to keep pace and the prey population overshoots the
carrying capacity and suffers a crash.
4. Classic Case of the Snowshoe Hare and Canadian Lynx
a. Careful records of pelts of both animals for over a century demonstrated regular fluctuations.
b. To test whether the lynx or hare food supply was causing the cycling, three experiments were done.
1) A hare population was given a constant supply of food and predators were excluded; the cycling ceased.
2) Hare populations were given constant food supply but predators were not excluded; cycling continued.
3) Predators were excluded but no food was added; the cycling continued.
c. The interpretation of these results is that both a hare-food cycle and a predator-hare cycle combine
to produce the overall effect.
d. Grouse population also cycle, perhaps because the lynx switches to grouse when the hare populations
decline; thus predators and prey do not normally exist as simple two-species systems.

E. Prey Defenses and Other Interactions

1. Prey have evolved a variety of ______defenses.
2. Plant adaptations for discouraging predation include:
a. sharp spines,
b. tough leathery leaves,
c. poisonous chemicals in their tissues,
d. chemicals that act as hormone analogues to interfere with insect larval development.
3. Animals have defenses that include:
a. ______for concealment; this also requires behavior (stillness),
b. fright of the predator
c. warning coloration , and
d. vigilance and association with other prey for better warning.

F. Mimicry

1. ______occurs if one species (the mimic) resembles another species (the model) possessing an
antipredator defense.
2. ______, named for Henry Bates, is a form of mimicry in which one species that lacks defense
mimics another that has successful defenses .
3. ______, named for Fritz Muller, is where several different species with the protective defenses
mimic one another (e.g., stinging insects all share same black and yellow color bands).

G. Symbiotic Relationships

1. Symbiosis is a close relationship between members of two populations.
2. Parasitism
a. ______is similar to predation; the parasite derives nourishment from the host.
b. Viruses are always parasitic; parasites occur in all kingdoms of life.
c. Endoparasites are small and live inside the host.
d. Ectoparasites are larger and remain attached to the body of hosts by specialized organs or appendages.
e. Many parasites have several hosts.
1) The primary host is the main source of nutrition.
2) The secondary host may serve to transport (vector) the parasite to other hosts.
f. Parasites are specific and require certain species as hosts.
g. Lyme Disease
1) The bacterium causes arthritis-like symptoms in humans.
2) The bacterium primarily lives in white-tailed deer mice.
3) The larval deer ticks feed on deer mice and can transfer the bacterium to humans.
3. Commensalism
a. In ______one species benefits and the other is neither harmed nor benefitted.
b. It is difficult to determine true commensalism because it is difficult to ensure host is not harmed.
c. Barnacles that attach themselves to the backs of whales and the shells of horseshoe crabs.
d. Remora fish attach themselves to the bellies of sharks.
e. Epiphytic plants grow in branches of trees to receive light but take no nourishment from the tree.
f. Clownfishes live within the tentacles of sea anemones for protection.
g. Some relationships are so loose that it is difficult to know if they are true commensalism.
1) Cattle egrets feed near cattle because the egrets flush insects as they graze.
2) Baboons and antelopes forage together for added protection.
4. Mutualism
a. In ______both species benefit.
b. Mutualism can be found among organisms in all kingdoms of life.
c. Examples include the following:
1) Bacteria in the human intestinal tract are provided with food but provide us with vitamins.
2) Termites can only feed on wood because their gut contains protozoa that digest cellulose.
3) Mycorrhizae are symbiotic associations between roots of fungal hyphae and plants.
4) Flowers and insect pollinators represent a shift from insects eating pollen to eating nectar.
5) Lichens are made of algae (produce food) and fungi (preserve water), although the algae can survive alone.
d. Classic Example of the Ant and the Acacia Tree
1) In tropical America, the bullhorn acacia provides a home for ants in its hollow thorns.
2) The acacia also provides ants food from nectaries, and protein nodules called Beltian bodies.
3) In return, the ant protects the plant from herbivores and other plants that might shade it.
4) When ants on an experimental tree were killed with insecticide, the tree also died.
e. Tree-Ant-Caterpillar Complex
1) Trees in the genus Croton have nectaries that feed ants.
2) Ants have a mutualistic relationship with Thisbe caterpillars that feed on Croton saplings.
3) Thisbe caterpillars offer nourishment to ants, keeping them nearby.
4) The caterpillar releases the same chemical that causes ants to defend an ant colony.
5) The result is that caterpillars are protected while feeding on the trees.
f. Cleaning Symbiosis
1) Crustacea, fish, and birds act as cleaners to a variety of vertebrate clients.
2) Large fish in coral reefs line up at cleaning stations and wait their turn to be cleaned by small fish.
3) The possibility of feeding on host tissues as well as on ectoparasites complicates this case of mutualism.