Download Ecology is the study of the interaction between organisms and their

Ecology is the study of the interaction between organisms and their environment.
There are three higher levels of organization:
1. ____________________- groups of individuals belonging to the same species in a given area.
2. ___________________________- units composed of all the populations living in a given area.
3. _____________________- the sum total of the communities and their physical environment considered together.
Ecosystems are linked by biological, chemical, and physical processes.
The entire earth is an ecosystem called ___________________________.
Population organization and growth
Density of a population = ________________________________________________________
Counting populations1. Count the total # of individuals in a given area, easy if the organisms are large and area is not too
large.
2. Divide the area into a # of quadrants and count the number of individuals in several of quadrants and then estimate
the entire area. (extrapolation is an important technique!)
3. Mark-and-recapture technique. A limited number of individual (e.g. 20) are captured at
random and marked then released into the environment. Later a second group of animals
is captured and the percentage of marked individuals determined. If 10% of the animals
in this second group have the tagged, then the original 20 represented 10% of the
population and the population then is 200.
The distribution of individuals within an area may be uniform, random, or clumped but
groups random:
Uniform distribution (rare) intense competition or antagonism between individuals and
uniform environment
Random distribution (rare) no competition, antagonism, or tendency to aggregate and
conditions are uniform.
Clumping but groups random is most common distribution because environmental
conditions are not uniform, reproductive patterns favor clumping, and animal behavior patterns lead to congregation.
- The optimum density for population growth and survival is often an intermediate one; under-crowding can
be as harmful as over-crowding.
How populations are regulated
Organisms with boom-and-bust curves are due to _______________________________________ limitations. The
maximum density occurs before the decline because of organisms' high reproductive rates. Because organisms have
high intrinsic reproductive rates, called high____________________.
Population growth
Organisms have the potential for explosive growth and __________________________ growth.
- Ex. If a pair of house flies begin to reproduce in April and all survived long enough to reproduce a full
complement that by August there would be 2 x 10^20 offspring. Covering all of the land on earth 10 cm.
Elephants would cover the planet in a couple of centuries.
The equation for a population growth is:
N/ t= (b-d) N, where
N= change in population
t= change in time
N= number of individuals in the population
(b-d)=the birth rate minus the death rate called_____________________________________________
Another way to write the above equation is
Nt+1 - Nt= (b-d) N
where t is defining two separate times.
The population grows if (b-d)>0.
The population decreases if (b-d) <0.
There is no growth if b-d=0.
The change in the population is the intrinsic rate of increase or r.
When the birth rate is at its maximum and the death rate is minimum, the population grows fastest and is termed
___________________________________________.
The maximum intrinsic rate of increase (r max) varies with different species.
Growth is not only a function of r-max but also N.
-N becomes larger with each generation and that means that N/ t also becomes larger with
each successive generation.
-The rate of increase is also accelerating.
Exponential growth cannot continue forever. The exponential growth of populations
levels off as the density approaches the carrying capacity(K).
The carrying capacity (K) of a population is the maximum density of a population that
the environment can support over a time period without damage to the environment.
Intrinsic rate (r) of increase is high with lower densities and decreases with larger
population densities until the population levels out reaching a carrying capacity (K).
This growth curve is an S-shaped or logistic growth curve and results from a changing ratio between births and deaths.
In the beginning the rate of increase accelerates but later as the population
increases the rate of increase decreases even though the birth rate is greater
than the death rate.
At some point in time equilibrium is reached or the carrying capacity and the
birth rate equals the death rate.
The population levels out reaching a carrying capacity (K).
After the curve has leveled off, births and deaths are in equilibrium and the population has
_____________________________________________. This occurs because environmental limitations become
increasingly effective in slowing population growth as the population density rises. When the density approaches the
carrying capacity, the limitation becomes severe.
A density dependent limitation, (K-N)/K, is one whose density is determined by the density of the very population it
helps limit.
The equation for the logistic growth curve is
N/ t=rmax ((K-N)/K)N
This inserts the density dependent limiting factor.
At low population densities, population growth is exponential; the rate of increase reaches its maximum at the inflection
point of the curve.
Growth of a population with rmax of 1.0, K = 100, and
N = 4.
It assumes that all individuals in the previous generation survive. In the beginning
and N is small, the density limiting factor is very close to 1.
The inflection point is where the growth changes from accelerating to decelerating.
This point is the maximum sustainable yield.
- If man wanted to harvest an organism, then the population should be kept at the maximum sustainable
yield and not at the carrying capacity
Most populations oscillate around the carrying capacity.
-When a population is above the carrying capacity, the environment cannot sustain it, the
population decreases.
- If it falls below the carrying capacity, then resources are plentiful and population increases.
The populations of many small short-lived animals, or those living in variable environments, go through a period of
exponential growth, followed by a sudden crash (boom and bust curve).
The crash occurs before the populations reach the carrying capacity; it is due to a ________________
________________________ limitation such as weather or other physical environmental factors.
-The operation of such a limitation ________________________________________________.
____________________________________ - is the study of factors that affect birth and death rate.
Age structure and sex ratio
- Populations often have overlapping generations (individuals of different generations coexist). Exceptions are species
where all the adults reproduce at the same time and then die e.g.
annual plants and many insects.
- This phenomenon produces an age structure for the population=relative numbers of individuals of
each age group.
-Every age group has characteristic birth and death rate
a. Birth rate (fecundity) is greatest for those of intermediate age
b. Death rate is often greatest for the very young and very old
c. A population with more older, non-reproductive individuals, grows slower than
a population with a larger percentage of young, reproducing individuals.
Generation time = the average span of time between birth and the birth of their offspring. Characteristics
a. Correlation with body size. ___________________________________________
b. A shorter generation time usually results in faster population growth providing birth rate is greater
than death rate with all other factors being equal.
-_____________________________ is the # males vs. # females.
a. It is not always 50:50.
- If the male mates with more than one female, then he may have a harem of females e.g. elk.
form monogamous pairs, the ratio is more 50:50.
- If the species
Other population determinants include the potential life span, the average life expectancy, and the average age of
reproduction.
Determining the mortality rates for the various age groups in the population gives a
_______________________________ curve.
- type I curve all the organisms live to old age and die quickly;
- type II curve shows a constant mortality rate at all ages;
- type III curve is typical of populations where the mortality among the young is very high, but those who
survive the early stages tend to live for a long time. In nature, high mortality among the young is the rule.
A major factor in the variation of the growth rates among countries is the variation in their age structure.
The human population doubled every 1600 years until the last thousand years.
______________________________________ = An organism's schedule of reproduction and death.
- Factors include trade offs between survival, frequency of reproduction, investment of parental care and
number of offspring per reproductive episode.
Diversity in life history
a. Some animals hatch in one biome, migrate to another to mature and then return to the initial biome to
reproduce. e.g. salmon
b. Animals hatch and mature in a single habitat, then have small reproductive efforts each year for
several years.
e.g. lizards
c. Life histories often vary with environmental factors such latitude. e.g. Tropical birds lay fewer eggs
than those in
higher latitudes because days are longer giving more time to gather food raise more offspring. This pattern is found to
be true in mammals, lizards and insects.
Life histories can be a trade-off between factors like fecundity and mortality. e.g. Albatrosses only average one surviving
offspring every five years but adult birds only have a 5% chance of dying whereas tree sparrows have a 50% chance of
dying between breeding seasons but produce 6 surviving offspring per year.
Delayed maturation and high parental investment in offspring tend to be correlated with low fecundity and low
mortality.
Population Regulation
Populations are regulated by density-dependent factors and density independent factors or both. The importance of
these factors differs among species and their specific circumstances.
I. __________________________________ regulating population are unrelated to population density.
-Density-independent factors affect the same percentage of individuals
regardless of the size of the population
-Weather, climate and natural disasters such as freezes, seasonal changes,
hurricanes and fires are examples. The severity and time of occurrence is the
determining factor on what proportion of the population is affected
-In some populations these effects routinely control population size before
density-dependent factors become important
Ex.Thrips grow during spring in flowers providing food and shelter. Before the population reaches carrying capacity, the
population decreases during the dry Australian summer. A few individuals survive in a few flowers, and these allow the
population to resume when conditions are favorable.
Population regulated with density-independent factors exhibit with boom-and-bust curves. The population never
reaches the carrying capacity K. The maximum density achieved before the decline is primarily a function of the
organisms' high reproductive rates. Since these organisms have evolved high intrinsic rates, they are called high-rmax
species. (r-strategists)
II. Density-dependent-limiting factors (intraspecific) regulate population growth because increasing population
reduces resource availability and resource limitations ultimately limit population growth.
Intraspecific competition-the reliance of two or more individuals of the same species on the same limited resource.
Competition between individuals of the same species
increases as population size increases and r or (b-d) is reduced
in proportion to the intensity of the competition.
-Population growth declines because death rate increases,
birth rate decreases or both.
- Reduction in food may limit reproductive output
e.g. The number of seeds produced by plantain
decrease with increased sowing density. The average clutch size of a sparrow decreases with increase in population.
- Territoriality is a behavioral mechanism that may reduce intraspecific competition since each individual protects its
own area.
- Health and survivorship decreases as crowding results in smaller less robust individuals.
- Predators - when prey population is high, takes greater percentage of prey.
- The accumulation of toxic metabolic wastes.
Intrinsic factors may also play a role in limiting populations
-High densities may cause stress syndrome resulting in changes hormones that
delay sexual maturation, inhibiting reproduction
-High densities can also suppress the immune system with stress
-High densities can reduce birth rates and increase death rates. e.g. The percentage of flour beetles (Tribolium
confusum)
surviving from egg to adult decrease at moderate to high
populations densities, reducing the
adults in the next
generation.
It is possible for populations to be regulated by both density-dependent and density independent factors. Populations
may display short-term fluctuations due to density-independent factors. The population
Dungeness Crab fluctuates due to density-dependent factors e.g. intra-specific competition
and cannibalism and density-independent factors e.g. changes in water temperature due to
ocean currents.
e.g.Bobwhite quail (southern Wisconsin) survival varies with the depth of snow cover
(density-independent factor), but if the snow depth is shallow then factors like reduction in
fecundity due to limited resources (density-dependent factor) regulate the population.
Together these interact to keep the population stable.
Some populations show regular fluctuations in density in a cyclic way.
Mammals
-Small herbivores (lemmings) 3-5 year
-Large herbivores (snowshoe hares) 9-11 year cycle
Hypotheses for fluctuations
-Stress from high densities may alter hormone balance and reduce fertility or may cause physiological changes
-High density may cause changes in the immune system,
Oscillation in the population of the hare preceded changes in the lynx density.
- Once considered to be inter-related but the hare shows such
oscillations on islands where the lynx is absent. The lynx
population oscillation may be the result of hare population but
not the other way around. (Browse for hares)
The ________________________of a species to reduce populations can be caused by crowding which can cause
physiological changes.
Generalizations-Populations can be K-selected (equilibrium populations) or r-selected (opportunistic populations)
Characteristic
r-selected
populations
Maturation time
short
Lifespan
short
Death rate
high
K-selected
populations
long
long
low
reproductions
per lifetime
Timing of first
reproduction
one
several
early in
life
late in
life
Most insects are r-selected species but honeybees have a low r-max, producing only "one" offspring a year (queen) and
invest in it heavily to assure its success. The progeny is a queen and half of the colony. Each worker gorges itself on
honey to sustain the new colony and make honeycomb.
Interspecific interaction can also act as a density-dependent limitation. Predation and parasitism relationships can
regulate populations.
_____________________________-kills and eats the prey
_____________________________-live on or in they hosts deriving nutrients and energy. If the parasite kills the host,
then it is called a parasitoid.
- Usually the predator and parasite population fluctuates in direct proportion to changes in the
density of the prey.
-The predator population mirrors the population of the
prey with a lag time. As the prey numbers increase, there
is more food available for the predator. So there will be a
corresponding in increase in the predator. This had the
effect of reducing the number of prey available. Thus
with less food available for the predator, there ensued a
corresponding decrease in predator population. This is also true for the population of moose and wolves
found on Isle Royale
Herbivory is also considered a type of predation. The interactions of the herbivore and the plant can be complex.
-e.g. Passion flower vines produce a toxic chemical that help protect leaves from herbivorous insects. A counter
adaptation has evolved in the butterfly, Heliconious: Its larvae can feed on the leaves because they have digestive
enzymes the break down the toxic chemicals. The females of these butterflies avoid laying eggs on passionflowers
leaves that already carry bright yellow egg clusters reducing intraspecific competition. The leaves of the passionflower
have responded by growing yellow nectaries that resemble eggs. The butterflies avoid laying eggs on these leaves.
These nectaries attract ants and other insects that prey on butterfly eggs.
There are times when the relationship can be mutualistic (mutualism).
-e.g. Ants live in acacia trees. The ants harvest the trees' nectar and leaves, and they also burrow into the thorns and
stems to make their nests. The acacia trees benefit by fact that the ants keep the trees relatively free from plant-eating
insects and attack any mammals that are eat the tree. The ants also prevent vines from growing on the trees. The acacia
provides hollow thorns for the ants to live in and Beltian bodies found at the tips of the leaves. These Beltian bodies
provide a source of protein for the ants.
Interspecific competition can be a density-dependent limitation. The more two species go
for the same limited resource, the greater the competition.
_______________-refers to the functional role and position of an organism in an
ecosystem.
- Every aspect of an organism's existence helps define that organism’s niche. A
niche, theoretically, can be quantified by graphing two or more resources. For
instance with a bird, the density of the branches for nesting, versus temperature
tolerance, versus food size. Where these intersect would define the
hypervolume of the niche. Many more factors could be added to the graph, giving more multidimensional
enclosed space for the species.
When 2 species are competing for the same limited resource their niche's overlap.
- The more similar two niches are, the more likely that both species will compete for at least one
limited resource.
There is a limit on the amount of niche overlap compatible with coexistence.
Competition for one most limited resource therefore usually leads to one or two of four possible outcomes:
1. One species will become extinct.
2. One species may superior in some regions and the second in other regions. Sympatry will
disappear.
3. One species may be superior under normal conditions but at a strong disadvantage under periodic
crises, which
will reduce the population size of the superior species. Competition will then begin
anew as long as generations
overlap and the periodic crises are frequent enough to prevent the
extinction of the inferior species.
4. Given enough time and slight differences in niche, selection
may act to produce character displacement, which reduces
competition.
e.g. Paramecium cultures of 2 different species demonstrate
#1. The graphs show the population growth of P. aurelia and
P. caudatum by themselves in a culture. They both exhibit
typical logistics curves, but when both are put together in a
culture, P. aurelia out competes P. caudatum. The growth of
P. caudatum actually decreases.
e.g.#2 Joseph Connell carried out studies using barnacles. He cleared a rocky
area and observed repopulation patterns of 2 species. Semibalanus by itself
lived in the lower regions of the tidal zone. It can not survive the periodic drying
out in the upper part of the tidal zone. When Chthamalus lived by itself it could
exploit both the upper and lower tidal zones however when both species were
living together, whenever the Chthamalus ventured in the lower tidal zone of
the Semibalanus, it was crushed by the Chthamalus. So that being the case the
Chthamalus restricted itself to the upper tidal zone and the Semibalanus was
found in the lower tidal zone.
This leads to the concept of a fundamental niche vs. a realized niche. A
fundamental niche is the full environmental range that a species can occupy if there is no direct competition. A
realized niche is a niche that is narrowed from the fundamental niche due to competition.
___________________________________________ - No two species can occupy exactly the same niche at the same
time
Communities where competition occurs between species are
characterized by resource partitioning, meaning that every
species uses a different aspect of the resource.
-e.g.Three different species of warbler occupies the same spruce
tree but they are found in different areas of the tree. The Cape
May warbler feed on the tips of the highest branches; the
yellow-rumped warbler feeds among the lower branches; and
the bay-breasted warbler feed in the middle part of the tree. Species with narrow niches (they can only use
one or a few types of food or growth sites) are termed specialist and those species adapted to a wide range
of conditions are termed generalist. These warblers are specialists and the common crow is a generalist
living from the farms to urban areas.
Social organization often plays an important role in limiting the size of populations.
-Sociality carries the cost of increased competition and the benefit of increase food supply through cooperative hunting,
cooperative defense of food territory against predators and sharing of information about food availability. By hunting
together, these African wild dogs can capture a much larger prey (wildebeest) than an individual could take on its own.
-Dominance pays an important role in access to resources, particularly resources critical to breeding. --Male-contest
sexual selection has a profound effect on gene frequency, since a certain phenotype is more likely to succeed than
others.
-Kin selection has a profound effect on gene frequency, since a certain phenotype is more likely to succeed than others.
Eg. Honeybees cooperate to regulate the internal temperature of the hive. They fan air out of the hive entrance,
drawing cooler air in else-where. When the internal temperature is even higher, bee collect water and spread it on the
comb then fan it to cool the hive evaporatively.
Forming communities from populationsThe species of a community interacts with each other and with the physical environment. The biotic community they
form can be considered a unit of life, with its own characteristic structure and functional interrelationships.
- Species diversity (biodiversity) and complexity of interaction influence community stability. A simple
community may respond more violently to a disturbance but often recovers quickly. The complex
community may sometimes respond less dramatically but may continue to show effects over a longer
period. A diverse physical environment seems to favor community stability. The number of species in a
particular area varies. The rule of thumb, the closer the environment is to the equator, there is an increase
in species diversity.
Type Locality
Seed plants # of species
size
Costa Rica
8,000
18,400 sq. mi.
Coastal California
3,050
24,520 sq. mi.
Baja California
1,500
24,100 sq. mi.
British Isles
1,600
___________________ is the sequence
showing the energy flow.
producers (autotrophs), ->primary
consumers (herbivores),-> secondary
consumer, (herbivore eating
carnivores),-> tertiary consumers
(carnivore eating carnivores), and
decomposers,
The levels are called
_____________________________.
A more complete picture of the flow of energy is ______________.
The arrows shows movement of energy and material.
Less than 10 % of the energy can make it from level to the next. There are reasons why only 10% of the energy can
move from one level to the next.
1. Lack of complete consumer harvest of available biomass.
2. The inability to assimilate all that is consumed.
3. Energy used for growth and reproduction.
4. Loss of energy due to dissipation of heat energy.
The pyramid of productivity is
the basis on which a pyramid of
biomass exists. In general the
decrease of energy at each
successive trophic level means
that less biomass can be
supported at each level. Hence
the total mass of carnivores in
a given community is almost
always less than the total mass
of herbivores. However the
size, growth rate, and longevity of the species at various trophic levels are important determining factors.
The pyramid of productivity and the pyramid of biomass support the
pyramid of numbers. This is because in general, carnivores are larger
than the herbivorous prey. Since total biomass tends to decline at
successive trophic levels, it follows the number of individuals must
decline at each level (except decomposer which outnumber all other
groups combined).
Gross primary productivity is the ability of producers to “fix” or convert carbon dioxide into organic material.
- Consumers reduce gross primary productivity by consuming the producers.
- Producers also reduce gross primary productivity because they also engage in cellular respiration.
Net primary productivity is the amount of organic material that is produced beyond what is needed by the living
organisms in an ecosystem.
A __________________________ is the species which are present in the greatest numbers or greatest biomass.
A __________________________ is one that exerts an effect on regulating others in a community.
Sea otters are considered to be a keystone predator species. Sea otters
prey on sea urchins. Sea urchins eat kelp. Where sea otters are plentiful,
sea urchins are rare and kelp beds are plentiful. Where sea otters are
population is low, sea urchins are plentiful and kelp beds are almost
absent.
________________________species are species that exert their effect by
changing their environment profoundly.
Ex. Beavers can profoundly change the environment by damming a creek
or river.
While both of these ecosystems have the same number of species of trees,
the first community is more stable because of the relative number of
individual trees is almost equal unlike the second community where one
species dominates. This first community is described as having species
richness
_______________________: is the process of change in which one
community of organisms replaces another.
-This happens after some sort of change- volcano, fire, tornado, etc has
disturbed the environment.
-As each community is established, the environment is modified and change
making it possible for another community to become established.
__________________________________: begins with bare rock or sand and
involves first the building of soil.
-Once organisms colonize an area, they change it so that other organisms may follow. Examples include
what happens after a volcano erupts or glacier retreats.
e.g.The first organisms to colonize the area may be mosses and lichens. These plants may produce acids
as a waste produce to break down rocks in the formation of soil. Once soil formation is begun, ferns may come in and
colonize the area. Its rhizoids help to form more soil, and as they die
and decompose, the soil may become more rich and suitable for
different types of organisms. It is easy to see that organisms can
change the environment they interact with.
_________________________________- Soil is present and occurs at a
much more rapid rate. Can be the result of fire, tornados, floods and
other like events.
- Examples abandoned crop lands, unused rail roads etc.
Ecological succession may lead to a stable community of plants and animals called the
_______________________________________
- Catastrophic events (hurricanes, volcanoes, fires, etc.) may disturb a climax community, causing the process
of succession to occur again.
A ___________________ is an environment that has a characteristic climax community.
The earth has two main types of biomes, land biomes and aquatic biomes.
Most land biomes are named for their climax community or dominant type of plant life.
The major types of biomes are the tundra, taiga, temperate deciduous forest, grassland, tropical rain forest, and desert.
TUNDRA
Where Found: northern North America, Europe, Asia
Plants: mosses, lichens, grasses, a few stunted trees
Animals: caribou, reindeer, wolves
Other Characteristics: permafrost – creates freezing and thawing cycle
TAIGA
Where Found: most of Canada and Asia
Plants: pine trees
Animals: bears, wolves, moose, elk, voles, wolverines,
Characteristics: long and cold winter, summers completely thaw the soil.
TEMPERATE DECIDUOUS FOREST
Where Found: southern Canada, eastern U.S., Europe, and Japan
Plants: trees that lose their leaves (oak, maple, birch)
Animals: huge variety, including fox, deer, moose, etc.
Characteristics: lands cleared by hunting and farmingGRASSLANDS
Where Found: interior of many continents
Plants: grasses and small leafy plants
Animals: grazers and browsers
Characteristics: Large variation in temperature and seasonal changes. Grazing and prairie fires halts succession.
TROPICAL RAIN FORESTS
Where Found: South America, S.E. Asia, Central Africa, Central America
Plants: rich vegetation in canopy and undergrowth
Animals: colorful insects, lizards, amphibians, reptiles, small mammals
Characteristics: 200 – 400 cm rain, constant (25o C)
DESERTS
Where Found: northern Africa, southern Asia, central Australia
Plants: cactus and other non-leafy plants
Animals: lizards, small rodents
Other Characteristics: very little rainfall, although some deserts have seasonal rain
Nutrients are recycled into the ecosystem unlike energy. The major nutrient cycles are water, carbon, nitrogen and
phosphorus.
In the carbon cycle, carbon is recycled mainly through the process of
photosynthesis, cellular respiration and burning of fossil fuels. In the
carbon cycle, carbon is recycled mainly through the process of
photosynthesis, cellular respiration and burning of fossil fuels. Carbon
dioxide (CO2) and carbon monoxide emissions have been increasing and
increasing in the atmosphere. It allows light energy in but traps the
reflected heat energy
in atmosphere so that
it does not go back
into space. It causes global warming.
Nitrogen used for proteins and nucleic acids. The air is over 75%
N2, but this nitrogen can not be used because of its triple bond. N2
is broken down by bacteria into NH4 (ammonia), then NO2 (nitrite)
and finally NO3 (nitrate). Plant roots absorb this NH4, NO2 or NO3
and then make amino acids and then proteins. Animals get their nitrogen from eating plants or other animals. Nitrogen
also gets into the soil when man uses fertilizers made from factories. Nitrification is the process of putting N2 into the
ecosystem. Another way to get nitrogen into the ecosystem is through decaying organisms and wastes.
Plants absorb water through their roots. Land animals absorb water
from their food or drink it. Aquatic animals are bathed in it. Water
gets into the atmosphere from cellular respiration, transpiration and
evaporation from the oceans. Water vapor condensing will result in
precipitation (rain or snow). The excess nitrogen and sulfur in the air
(pollution) combines with the water. This results in acid rain. These
leech minerals from the soil killing plants.
The phosphate cycle is the one nutrient that does not have an
atmospheric component. It cycles through the soil and water. The
main source of phosphorous is the weathering of rocks.
There are times when unwanted chemicals
accumulate in organisms through the food chain.
In the 1960's, cities sprayed with DDT, a chemical
to get rid mosquitoes. This chemical
accumulated in the lakes. It found its way into
the aquatic plants. Fish ate the plants and DDT
accumulated in the fish. Eagles ate the fish. DDT
accumulated in the eagles. It affected their eggs
as the shells were not hard. The chicks would not
hatch. As a result, eagles became endangered.
This process is called biological magnification.