Zoology – ANIMAL ECOLOGY

I. Hierarchy of Ecology

A. _________________________ – the study of the relationship of

organisms to their environment.

1. The hierarchy of study includes organisms, populations,

communities, ecosystems and the biosphere.

a. We must first understand the physiological and behavioral

mechanisms of organisms to understand ecology.

2. _________________________ - organisms living together with

others of their species.

a. Populations have group properties and behaviors that

can’t be understood by studying individuals alone.

3. _________________________ - populations of many species

living together.

a. Species diversity - variation and evenness of species

distribution within a community.

b. Many species have relationships such as predator-prey

and parasite-host associations.

c. Competition occurs when food or space becomes

limited.

4. _________________________ – communities interacting with

their physical environment.

5. _________________________ – the part of earth containing

living organisms.

B. Environment and the Niche

1. _________________________ – all conditions that directly

affect an animal’s chances of survival.

a. Physical, or _________________________, factors –

space, energy forms including sunlight, heat, wind and water

currents, and the soil, air, water and chemicals.

b. _________________________ factors – other organisms

as food, or competitors, predators, hosts or parasites.

c. _________________________ - space or food utilized

directly by the animal.

1) _________________________ resources –

resources that must be continually replenished.

a) food, once eaten, is no longer available.

2) _________________________ resources

a) Space is not consumed by being used.

2. _________________________ – the physical space where an

animal lives and is defined by the animal’s normal activity.

3. _________________________ – the role of an organism in an

ecological community; its unique way of life and its relationship to

other biotic and abiotic factors.

a. The life requirements of an organism define its niche.

b. Includes the animal’s limits of temperature, moisture, food

and other factors.

c. _________________________ – animals with wide

niches

1) They can tolerate a wide range of salinity or eat a

wide range of foods.

d. _________________________ have narrow dietary

requirements or limited tolerance to temperature changes,

etc.

1) Benefit – they often escape competition and

predation.

2) Cost – their narrow requirements are often

destroyed by environmental changes and they are

prone to extinction.

C. Populations

1. A _________________________ – a potentially reproductively

interactive group of animals of the same species.

a. _________________________ – local disjunct

populations that do actually interbreed.

1) They share a _________________________.

b. _________________________ among demes provides

some evolutionary cohesion among species.

c. _________________________ – the study of the age

structure, sex ratio, and growth rate of a population.

2. Survivorship defines the age pattern of a population from birth

to death of the last member.

a. Curve I - all individuals die at the same time.

1) This occurs rarely in nature.

b. Curve II - the rate of mortality as a proportion of survivors

is relatively constant across ages.

1) Characteristic of birds that care for their young

2) Humans fall between Curves I and II.

c. Curve III - Species that produce huge numbers of young

but experience rapid and sustained mortality.

1) This explains the need for high reproductive output

of many animals.

2) Characteristic of most invertebrates and fish.

3. Populations that reproduce while their parents are still alive and

reproducing contain multiple cohorts and have an age structure.

4. Population Growth and Intrinsic Regulation

a. Population growth – the difference between rates of birth

and death.

b. Populations can have exponential growth at the intrinsic

rate of increase, symbol r.

1) This is due to their biotic potential in the absence

of environmental resistance.

2) This forms a steeply rising curve.

c. A growing population eventually exhausts food or space.

1) _________________________ – the one

resource, among many, that will be depleted first.

2) _________________________ (K) – the largest

population that can be supported by the limiting

resource.

3) A population slows its growth rate in response to

diminishing resources.

d. The Logistic Growth Curve

1) To calculate population, we use the following

formula…

Δ N = rN K-N

Δ t K

a) The Greek letter Δ is used to indicate

change, and is read as “delta.”

i) It means “change in.”

b) N represents the number of organisms

c) t represents the time

d) r is the intrinsic rate of increase

i) r is measured as the difference

between birth and death rates at any

instant.

e) K is the carrying capacity

2) When the population approaches carrying capacity,

the growth slows down.

a) As the carrying capacity of an environment

changes over time, a population must change

its density to track the limiting resource.

b) Animals experience a lag between the time

that a resource becomes limiting and the

population responds by reducing its rate of

growth.

5. Extrinsic Limits to Growth

a. _________________________ - the number of

individuals of an species within a given area.

b. Density-_________________________ factors - abiotic

factors that reduce population sizes regardless of population

density.

1) Includes floods, fires, storms and severe climate

fluctuations.

2) They cannot truly regulate population growth

because they are unrelated to population size.

c. Density-_________________________ factors - biotic

factors that do respond to the density of the population.

1) These factors become more limiting to population

size as density increases.

2) Includes predators, parasites and diseases.

d. Competition between species for a common limiting

resource lowers the effective carrying capacity for each

species.

II. Community Ecology

A. In a community, populations of different species interact.

1. _________________________ - the number of species that

share a habitat.

2. Species interactions may benefit or harm the species involved.

a. In a predator-prey interaction, the predator is benefited

and the prey is harmed.

b. _________________________ benefits the animal and

harms the plant.

c. Parasitism benefits the parasite and harms the host.

d. In _________________________, one species is

benefited and the other is neither benefited nor harmed.

1) About 70% of humans have microscopic mites

living in their eyebrows.

e. Commensalism may grade into _____________________

where both species are benefited.

1) E.g. Escherichia coli is a floral bacteria of our large

intestine.

a) We feed and water it with food we can’t

digest (and therefore can’t use) anyway.

b) Our guests return the favor by synthesizing

vitamin K and B-complex vitamins for us.

2) Some mutualistic relationships become obligate;

where neither can survive without the other.

g. Competition between two species for a limiting resource

reduces the fitness of both.

1) Asymmetric competition affects one species

less than the other species.

B. _________________________ – when two or more species share a

limiting resource.

1. If the resource is not in short supply, the species sharing the

resource are not negatively impacted.

2. _________________________ – the portion of the niche’s

resources that are shared by two or more species.

3. _________________________ – the principle that no two

species will occupy the same niche for a long time.

a. Eventually one will exclude the other.

4. To coexist, two species can specialize by partitioning a shared

resource and using different portions.

a. _________________________ - the morphology or

behavior of a species shifts so that they no longer compete

with each other directly.

b. _________________________ - two or more species

reduce niche overlap to share the same general resources.

C. Predators and Parasites

1. The predator-prey relationship is an example of co-evolution.

a. The species are in an “arms race” with each other.

b. If a predator relies primarily on a single prey species, the

populations cycle with each other.

c. _________________________ - where a harmless

species mimics a model that has toxins or stings – has

developed due to the predator-prey relationship.

2. _________________________ – a population whose influence

on the community is so critical that its loss drastically changes the

community.

a. E.g. In coastal regions, the sea otter is a keystone

species.

1) Sea otters are a major predator of sea urchins.

2) Sea urchins, in turn, feed upon kelp.

3) When the sea otters were removed, the sea

urchins overpopulated, almost wiping out the kelp that had

previously supported 25 other species.

a) This severely reduced species diversity in this

community.

b. Keystone species reduce competition and allow more

species to coexist on the same resource.

3. Parasites live in or on a host, benefiting at the expense of a host.

a. _________________________ – external parasites

1) They secure nutrition from their host but are also

dispersed by the host.

2) E.g. ticks and lice

b. _________________________ – internal parasites

1) They have lost the ability to choose habitats and

must have tremendous reproductive output to ensure

that some offspring will reach another host.

2) E.g. roundworms and pinworms

c. Generally, the parasite and host co-evolve toward a less

virulent relationship because the death of the host also ends

or shortens a parasite’s life.

1) Exceptions occur when alternative hosts are

available.

III. Ecosystems

A. Trophic Levels

1. Energy flows through organisms and is used to construct and

maintain organisms at several levels.

a. The diagram below depicts a generalized diagram of

energy flow through trophic levels. In the diagram,

decomposers are referred to as “detritivores.” The

decomposers recycle nutrients from all trophic levels and

return them to the soil for use by producers (plants).

b. This diagram, below, depicts how much energy is lost

c. from trophic level transfer.

2. Primary producers, usually green plants, fix and store energy,

usually from sunlight.

3. Herbivores are the first level of consumers that eat plants.

4. Carnivores eat herbivores (forming a second level of consumer)

or eat carnivores forming higher trophic levels.

5. The most important consumers are decomposers, mainly

bacteria and fungi.

a. They break dead organic matter into mineral components

at all trophic levels.

b. This frees the minerals for reuse by plants, starting the

cycle over again.

6. Chemicals cycle endless through the system.

7. Energy, however, is lost as heat and must constantly be

replenished, usually by the sun.

a. Ecosystems are open systems.

B. Energy Flow

1. Much energy is lost when it is transferred between trophic levels

in food webs.

2. More than _________________________ of the energy in an

animal’s food is lost as heat; less than ______________________

is stored as biomass.

3. Each succeeding trophic level contains only 10% of the energy of

the next lower trophic level.

4. This 90% loss of energy between tropic levels produces

ecological pyramids.

C. Life Without the Sun

1. From 1977 to 1979, dense communities were first discovered on

sea floor thermal vents.

2. The producers in these vent communities are chemoautotrophic

bacteria that oxidize hydrogen sulfide.

3. The tubeworms and bivalve molluscs form trophic communities

that rely on this nonphotosynthetic source of nutrients

D. Nutrient Cycles

1. Decomposers feed on the remains of animals and plants and

return substances to the ecosystem.

2. Biogeochemical cycles involve exchanges between living

organisms, rocks, air and water.

3. The continuous input of energy from the sun keeps nutrients

flowing and the ecosystem functioning.