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Chapter 51 Sections 1, 2, and 4
This chapter deals with animal behavior. There are a lot of terms that describe
different types of behaviors and ways of communicating. That’s really what a lot of
behavior is, is a way of communicating to others of your kind. Most of this is just
common sense. It is only a small fraction of what is covered on the AP exam, so if you
forget some things don’t stress about it. That may cause others in your population to
start stressing too and then we have panic and OMG it never ends!
What is an animal’s behavior?
There are two kinds of explanations for behaviors:
Proximate causation, or “how” explanations, focus on
– Environmental stimuli that trigger a behavior
– Genetic, physiological, and anatomical mechanisms underlying a
These focus on how a behavior actually happens in an organism. Did it see a predator
so it ran type of thing.
Ultimate causation, or “why” explanations, focus on
– Evolutionary significance of a behavior
These would be explanations for why the behavior exists. Well, it saw a predator; it
ran away, so it lived to see another day. I think the answer to why this behavior
occurs is fairly obvious, but all behavior is not so simply explained.
That is why there are people who study this stuff. They work in the field of
behavioral ecology, which is
Behavior is subject to natural selection. Behaviors like the above example that
increase survival would be beneficial and selected for. An antelope that ran toward
the cheetah would probably not live long enough to pass on its genes.
Behavioral responses are grouped into two categories.
1. Fixed action pattern –
What is it triggered by?
Example: male stickleback fish and the red underside of an intruder
2. Oriented movement –
There are several kinds of oriented movement:
Kinesis –
Example – sow bugs more active in dry areas and less active in humid areas
Taxis –
Example – fish swimming upstream is positive taxis (movement toward)
The difference between these two is that taxis is purposeful and kinesis is not. For
example, if it is really hot outside you would purposely go and sit in the shade to be
cooler. That is taxis. If you just wandered around aimlessly in the sun until you
happened to wander under a tree, and then sat down, that would be kinesis.
Migration –
I’m sure you all know what migration is. It is purposeful and therefore it is taxis. It
has been selected for multiple times in various species so it must be advantageous.
Birds going south in the fall is probably the best example. Birds are not the only
animals that migrate. Monarch butterflies go to Mexico during the winter. Different
ones return the following year, but it is still migration. Many ungulates, things with
hooves like bison and pronghorn, also migrate, as do many older Americans with
Winnebagos. Following the same route each time ensures success at arriving at the
correct location. You can Google migration routes and pull up maps that show where
species travel. Conservationists use them all the time to try to keep development at a
minimum so as not to disturb those species. Several have already been disrupted
because we built stuff and fenced off land before we had these maps. This causes
conflict between animals and land owners because those species don’t know any
other route and do not come equipped with bolt cutters for the fence.
Even though animals can’t talk they do communicate with each other. Any type of
organism that lives in groups must have a way of communicating. Even lowly bacteria
and fungi can communicate (remember? Unit 4?). Animals communicate using visual,
chemical, tactile, and auditory signals. They can use some or all of these depending
on the environment.
What is a signal?
So communication is
Some examples of different ways that animals and plants have of communicating are
listed below. Please pick 2 or 3 you like best and have them in your head. Bee
dancing and pheromones are the only examples in the PowerPoint, but all of these
and anything else similar you come up with can be used on a test. Many of these are
not new and should be examples you are familiar with. Notice too, that some of these
examples are showing communication within a species, and others between different
species. Prey has to avoid predators, flowers need to be pollinated, and everything
knows what skunk smell means.
• Fight or flight response – when an individual senses danger the body will ready itself
to fight or run. A running individual may also communicate that there is danger and
thus trigger the same response in other individuals.
• Predator warnings – a call sounded by an individual that sees danger to warn others
to take cover: meerkats, blue jays, monkeys, ground squirrels
• Protection of young – herds of wildebeest or elephants will circle the young
• Avoidance responses – having been sprayed by a skunk once, most animals learn to
avoid them, unless, of course, it is your dog.
• Herbivory responses – plants produce toxins, thorns or spines in response to being
eaten which in turn influences the animals to not eat them.
• Territorial marking in mammals – using urine and/or feces to mark territory for
hunting and breeding tells other individuals to stay away without having to fight and
risk physical harm
• Coloration in flowers – flowers that develop specific patterns in order to attract and
direct pollinators
• Bee dances – tells others where to find food
• Birds songs – used to attract mates as well as define territory
• Pack behavior in animals – can work together to get larger prey and even the
weakest, that might not alone, will get food
• Herd, flock, and schooling behavior in animals – safety in numbers. It is more likely
that someone else will get eaten instead of you.
• Colony and swarming behavior in insects – a united front to protect home. Acting as
one large unit is much more effective than the individual.
• Coloration – can signal readiness to mate; male displays; warning of toxicity
• Pheromones – chemicals emitted in very low quantities by some organisms to
communicate danger (fish) or attract mates (insects)
Remember back in the last unit when we discussed your immune system? There were
two kinds of immune responses, specific and nonspecific, or innate. Innate responses
were the ones you were born with like skin as a barrier and stomach acid. Well, some
behaviors are innate too. Innate behaviors would be those that an organism is born
with, or inherited and is genetic not learned. Most insects show innate behaviors
because there is no parental care. They hatch, go look for food, eat, poop, mate and
die. Such is the life of an insect, but they weren’t taught to do that. They just know!
The red stimulus for the stickleback you saw earlier is another example.
Learning is different. Learning is the modification of behavior based on specific
experiences. It occurs through interactions with the environment and other
organisms. There are many types of learning. We will look at each one and give some
examples, and, hopefully, you will be learning too!!
Habituation is a simple form of learning that involves loss of responsiveness to
stimuli that convey little or no information. This happens when you hear the same
noise or smell the same smell for long periods of time. After a while you “tune it out”you have become habituated to it and don’t notice it anymore. This is also what
happened to Peter when he cried wolf one too many times when there wasn’t one,
and then when there was a wolf nobody came and the wolf ate all his sheep. You can
see from this example how dangerous that could be. If you are habituated to a noise
or a smell that usually indicates danger, but you learn that there is no danger
associated with it, then you may get eaten. Nowadays sheep have border collies.
Imprinting is a behavior that includes learning and innate components and is
generally irreversible.
How can imprinting be distinguished from other learning and what does that mean?
Give an example of imprinting: you should know who Konrad Lorenz is.
Spatial learning involves the spatial relations of environmental cues. This is how
wasps find their nests again, and squirrels and birds can locate food caches. Your
book describes Tinbergen’s experiment with digger wasps in Fig. 51.11 pg. 1127, slide
25. He marked the wasp’s nest with a ring of pinecones before she left to forage. She
had no trouble finding the nest when she came back. The next time Tinbergen moved
the cones and the wasp couldn’t find the nest. She had been using them as an
indicator of where the nest was. You do the same thing when given directions. If you
are told to turn left at the big red house and someone paints it white you probably will
miss the turn.
In associative learning, animals associate one feature of their environment with
another. For example, animals learn to associate the coloring of monarch caterpillars
with bad taste so avoid them in the future.
There are two types of associative learning. These are must know terms because
much of psychology is based on these behaviors and how you learn. (And the fact
that whatever problems you have were caused by your mother not properly toilet
training you.) For anyone who is interested, the most famous names associated with
these types of learning are Pavlov and Skinner, respectively. Pavlov worked with dogs,
and Skinner used rats in a box.
Define and give an example of each:
Classical conditioning:
Operant conditioning:
Some parts of behavior are genetic or are affected by genes in some way. You are
programmed genetically to only be able to hear in a certain range of sounds and see
only in the visible light spectrum. You can’t be influenced in any way by something
you can’t see or hear. But what if you could see something others couldn’t? You may
then have more information to base decisions on which may change your behavior.
That would be a good thing if it gave you an advantage in finding food. Then you
might get more mates and pass on more genes and thus be more fit. Or it could work
in the opposite direction, in which case your genes are diminishing in frequency. In
this way genetics can influence behavior which can influence natural selection.
Responses to information and communication of information are also important to
natural selection and evolution. It really doesn’t matter what you see if you don’t act
on it and tell others. So your response or behavior is just as important as the mutant
allele you have that helps you find food. Natural selection favors behaviors that
increase survival and reproductive fitness. Some actual real life examples of how
behavior influences natural selection follow.
Believe it or not, plants have behaviors too. Phototropism, bending toward light, is a
behavioral response that positions the plant so that the maximum amount of light is
shining on the most leaves. Yes, it is triggered by hormones that make the plant bend
that way, but as far as plants go, that is a behavior. Another one is photoperiodism,
their response to the length of night. Plants either get ready for winter or flower
depending on night length. Yes, hormone regulation again, but in response to
changes in the environment and a behavior. When you are literally rooted to the
ground you don’t have a lot of behavioral options. Hormones influence some of your
behaviors too, so it’s not just plants.
Before we continue, what is foraging?
In most of the animal kingdom a great deal of behaviors involve foraging. So if you
are good at foraging, natural selection will select for those behaviors.
What is the optimal foraging model?
What should natural selection favor? (think of this as a trade-off)
Mating and parental care account for most of the rest of the behaviors seen in
animals. Natural selection favors innate and learned behaviors that increase survival
and reproductive fitness so these would be the behaviors that we see most often
exhibited by organisms today. There are several examples here, but not all of them
are in the PowerPoint.
Courtship and mating behaviors – sometimes members of a species will choose mates
based on certain traits (colors, size of appendages, song). In other species there may
be competition between members of the same sex for mates (winner gets the mate).
These behaviors are designed for helping choose the best provider.
Parent and offspring interactions – offspring that can not fend for themselves need
parental care. Usually it is the female because she knows those offspring are hers.
Males may participate if paternity can be established through monogamy or
polygynous harem-like behavior.
There are also several examples of cooperative behaviors. These tend to increase the
fitness of the individual and the survival of the population.
• Pack behavior in animals – can work together to get larger prey and even the
weakest, that might not alone, will get food
• Herd, flock, and schooling behavior in animals – safety in numbers. It is more likely
that someone else will get eaten instead of you.
• Predator warning – a call sounded by an individual that sees danger to warn others
to take cover: meerkats, blue jays, monkeys, ground squirrels
• Colony and swarming behavior in insects – a united front to protect home. Acting as
one large unit is much more effective than the individual.
There are also behaviors in animals which are triggered by environmental cues and
are vital to reproduction, natural selection and survival.
• Hibernation – allows animals to survive winter cold and food scarcity
• Estivation – allows animals to survive long periods of high temperatures and scarce
water supplies (kind of like hibernation but in the summer)
• Migration – a long distance change in location to survive changing environmental
conditions such as winter
• Courtship – provides a way of choosing the best genes
Chapter 52 Sections 2-4
****As we go through the next several chapters that discuss populations,
communities, and ecosystems, there will be a lot of discussion in the notes about
energy or free energy (remember G?). All the energy we have here on Earth comes
from the sun. No organism on Earth operates without a constant supply of energy.
That is also true of biological systems, whether that is one organism and its parts or
an entire rainforest. I’m pointing this out because you need to make the connection
between energy input to a system and the ability of that system to function. Any
change in energy input will have an effect.
All biological systems from cells and organisms to populations, communities
and ecosystems are affected by complex biotic and abiotic interactions
involving exchange of matter and free energy.
Ecology –
Population –
Community –
Ecosystem –
Biosphere –
What important book did Rachel Carson write in 1962?
Interactions between organisms and the environment limit the distribution of species.
Distribution means how they are spread out throughout the environment. Ecologists
look at lots of factors to try to understand why a species lives where it does and not
somewhere else. Fig. 52.6 pg. 1152, slide 51, shows an example of how an ecologist
might think about a particular species, X. In order to help them study these
interactions, scientists have put the factors that determine species distribution into
two categories: biotic and abiotic.
What are biotic factors and give some examples:
Interactions with other species may cause one species to move farther from the area,
especially if it is a prey species trying to live, or a predator species trying to find food.
Competition between individuals of the same species often drives them away from
each other to lessen the competition.
What are abiotic factors and give some examples:
Abiotic factors can influence different species in different ways. It may become too
hot for some species so they move away, but another species that prefers the heat
may move in. There is a lot of this going on now in many places that are experiencing
climate change due to global warming. The adorable American pika (as in Pikachu for
you Pokemon fans) is a rodent that lives at very high altitudes and harvests grass for
a living. It prefers the cooler temperatures and cannot survive in warmer
temperatures. As its mountain habitat warms it must seek out cooler places by going
farther up the mountain. Soon it will have nowhere to go. This is very sad because
they are very cute (you should use Google images now) and could be very useful to
collect grass clippings for composting.
As you can see temperature can have a great effect on species distribution. Pikas live
where they do so they can stay cool. They are very busy little guys. Lizards live in the
desert because they need the heat to help them regulate body temperature. Proteins
will denature at high temperatures so no organisms want to get too hot. Or too cold.
Freezing is not good either. Heat, or lack thereof, affects many animals because it
starts to affect their cellular metabolism.
When you are reading through these chapters and notes remember all the other
things you have learned in this course up to now. Here is where a lot of it will come
The remaining abiotic factors listed in the PowerPoint can all affect species at the
cellular or organism level just as we saw with temperature.
Individuals or populations can move to other habitats if there is not enough. Some
species have adaptations to live with less water like cacti, kangaroo rats, or
tardigrades (pg. 957). Some algae form endospores when water becomes scarce (See
pg. 560).
Usually this only affects aquatic organisms. Some are marine organisms and can
tolerate salt and others are freshwater organisms and can’t. Each type will have
adaptations for osmoregulation that work in that type of environment.
This has an obvious effect on plants. All green plants need some light for
photosynthesis. Some kinds of plants like more sun than others. There is also a
correlation here with temperature so plants will need appropriate adaptations. The
types of plants that grow in an area will be determined by the amount of light, and in
turn, these types of plants will influence what kinds of animals will also live there. It
will also determine human population to some extent. There are a lot fewer people
living in the Arctic than there are in the Caribbean and it is not because of the rum
and reggae.
Rocks and soil
These also will determine what types of plants are in an area which in turn, influences
the kinds of animals.
If we take some of the above abiotic factors, namely temperature, water, and
sunlight, and add some wind we have climate. Climate is the long-term prevailing
weather conditions in an area. In other words, it is what the weather is going to be
like in that place year after year, always the same or cycling with the seasons.
Define each type of climate:
Macroclimate consists of
Microclimate consists of
What plays a big part in determining global climate patterns?
Let’s put all this together for a minute. Climate is basically the weather in a place, and
it is determined largely on how much sunlight there is and how intense it is. This,
along with soil, also determines what kinds of plants there will be, and this determines
what types of animals. So, if I understand this right, a particular area can be
described by its characteristic weather, plants, and animals. That would describe a
biome. Actually land, or terrestrial, biomes since aquatic ones are not described by
weather but salinity. I think this will make more sense to you than whatever it says in
the PowerPoint that I read three times and still don’t like. To me it just means they
are big.
Aquatic biomes come in two flavors: salt (marine) or no salt (freshwater).
Oceans are marine biomes and cover 75% of the Earth. Freshwater biomes are lakes,
ponds, rivers and streams, bogs, and swamps. Basically any water that is inland and
not in the ocean. Your drinking water comes from a freshwater source. These are all
smaller in size than an ocean and are therefore subject to changes in weather, like
freezing in the winter. Living in these environments will require different adaptations
than living in an ocean that doesn’t have such temperature fluctuations. Why doesn’t
it, you ask? I recall discussing something called specific heat in Unit 1 and that water’s
is very high. Review. I told you that here is where it all comes together. There are
different levels within the ocean that have different types of organisms living in them,
but it is not necessary that you know what they are, but feel free to read anything
you wish in the book. Most things that live in the ocean live near the top because that
is where the sunlight is that provides the energy for photosynthesis that the
phytoplankton does which is at the bottom of any marine food chain. Maybe that is
why Plankton wants the Crusty Crab so bad, so he can move up the food chain.
Terrestrial biomes are characterized by their climate, plants, and animals. The map
in Fig. 52.19 pg. 1166, slide 66, shows you how the many different biomes are
distributed throughout the world. And, yes, there is a definite correlation to latitude.
Biomes are affected not just by average temperature and precipitation, but also by
the pattern of temperature and precipitation through the year. I am sure that you are
all aware that there are different kinds of plants and animals here than there are in
South America. That’s because here we have cold and snow in the winter and there
they don’t. The tropical rainforest is pretty much the same all the time. Again, you do
not need to learn all the different terrestrial biomes and their characteristics, but feel
free to read the book. What you should know is that there are different types of
climates and environments which do affect the types of organisms that live there and
that natural selection will produce organisms with the best adaptations to live there.
Chapter 53 Sections 1- 6
In the last chapter we spent a lot of time talking about the interactions of organisms
with each other, other species, and abiotic factors in their environment. Many of these
interactions will determine where members of a population live with in their habitat,
how many of them can live there, and how closely they live to each other. Some
words you need to know are:
Density –
Dispersion –
There are several ways scientists can estimate the size of populations. Which one is
used usually depends on what the species is. The mark-recapture method is used
quite frequently. Populations are estimated because organisms we want to count are
either hard to find, extremely small, spread out over large areas, and don’t line up
and count off like you do in PE class.
Another reason population size is estimated is because the size is always changing.
This would be due to births, deaths, immigration (moving into), and emigration
(moving out of). This will affect the density of the population as well. Dispersion, on
the other hand, is affected by things other than how many individuals there are.
There could be things in the environment that force all the individuals to be in one
part of the habitat like only one area of trees in which they can sleep. Social factors
also will play a part in how they are dispersed. Bees live together in a hive for a
number of reasons. They work together to find food, stay warm, and defend their
There are three patterns of dispersal shown in Fig. 53.4 pg. 1176, slide 75. On the top
of the next page, draw a picture of what each pattern looks like and label it.
Demography is the study of the vital statistics of a population and how they change
over time. This information includes birth and death rates, causes of death, number of
offspring, illnesses, etc. Much of this is not known for animal populations, but is useful
for human populations. This information would be kept in a table called a life table
which would be used to make a survivorship curve like those in Fig. 53.6 pg. 1178,
slide 77. Much of this type of data is collected by following a cohort throughout their
What is a cohort?
The vital statistics that are used to make a life table are the traits that comprise an
organism’s life history which affects its schedule of reproduction and survival. There
are different types of life histories, and each which would be effective in a different
type of environment. What works best would, of course, be selected for by natural
selection. For example, the agave plant uses semelaprity, or big-bang
production. It reproduces only once in its lifetime when conditions are favorable and
produces hundreds of seeds. This type of reproductive strategy works well when
environmental conditions are unpredictable. By contrast, organisms that live in more
stable environments usually follow iteroparity, or repeated reproduction. They
will have fewer offspring at one time, but more times, like once or twice a year.
Other factors besides environmental conditions also contribute to what type of
reproduction an organism uses. There are many intermediate versions between the
two above examples. Nutrient availability and parental care will affect the survival of
the offspring so organisms may have more/less, larger/smaller offspring to account
for that. Review the examples in Figs. 53.8 and 53.9 pgs. 1180-1181, slides 81-87.
Back in Unit 7 we learned about the Hardy-Weinberg equation which could be used to
determine if populations were evolving or to find out how many individuals were
carries of a particular allele. We also made a dynamic model of this on the computer
so we could model change to a population. Scientists use mathematical models all the
time. That way, predictions can be made as to what may happen to the population if
there is a change in some biotic or abiotic factor. I’m sure you are aware of the
climate change models being used today to predict sea level rise as the planet warms.
This is supposed to be alerting us to what will happen so we can change our ways
and reduce carbon emissions in time to lessen the impact. If I were you I would not
plan on retiring to Miami.
Scientists also use mathematical models to show population growth patterns and
interactions. We will discuss the two in your book covered in sections 53.3 and 53.4.
The exponential model describes population growth in an idealized,
unlimited environment.
An idealized unlimited environment does not exist. This describes a hypothetical
environment where there is plenty of food, water, space, everything. No predators, no
disease, everyone lives out their intended life span. Utopia. If this does not exist then
why are we studying it? Here’s why: if you know what the growth curve would look
like under the best possible conditions, then when you look at an actual growth curve
of a population and compare them, you will be able to tell whether the population is
doing well or is in trouble by how closely it resembles the “perfect” curve. Since this is
a model conditions can be changed to see what effect that has on the population as
A population’s per capita (per individual) growth rate equals how many additions
there are to the population minus how many left. If one ignores immigration and
emigration, then the growth rate equals the birth rate minus the death rate.
When would you have zero population growth?
• Zero population growth occurs when the birth
rate equals the death rate
• Most ecologists use differential calculus to
express population growth as growth rate at a
particular instant in time:
N 
where N = population size, t = time, and r = per
capita rate of increase = birth – death
Don’t be afraid of the calculus. You aren’t really going to be doing any. It is just here
to get the equation. As you can see, the amount of change in the population, ΔN, is
dependent upon the size, N, of the population. What I mean is, if the rate, r, is
constant, let’s say 0.5, but we change N from say 5 to 10 (increase the population),
then the left side of the equation will increase from 2.5 to 5. If Δt, the time interval
remains the same, then the increase is entirely in ΔN. This means that as the
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
population gets bigger, it will increase faster. This makes perfect sense. The more
individuals there are in a population the more offspring there will be. With no famine,
predation, or disease to decrease the population prematurely, this will be the
maximum rate of reproduction called the intrinsic rate of increase.
The equation you will see and use in problems is the equation of exponential
population growth:
What kind of curve do you get?
These types of curves are seen in rebounding populations and colonizing populations.
A graph of the entire human population over time is also J-shaped.
Can this exponential growth go on forever? Of course not. At some point food, water,
space, something is going to be maxed out, or limited. This is what’s called a limiting
factor. At this time competition will be tough and exponential growth will no longer
continue. Population growth will have to be limited. Only those who get enough of the
limiting factor will be able to reproduce. The limiting factor(s) will, basically,
determine the size of the population.
The maximum population size the environment can support is called what?
Since this is a more realistic way of looking at population growth, scientists developed
another, ‘more logical’, model called the logistic population growth model. The
logistic model describes how a population grows more slowly as it nears its carrying
The formula for the logistic model starts with the exponential model and adds an
expression that reduces per capita rate of increase as N approaches K:
Look at Table 53.3 pg. 1184, slide 99, and notice what happens to the population
growth rate as the population increases. Initially it goes up, but when it reaches a
certain point the growth rate slows and drops. This is what real populations do when
they approach their carrying capacity.
What type of curve does this produce?
Fig. 53.13 pg. 1185, slides 102-106, show examples of real populations and their
growth curves. The Daphnia curve show that some populations will overshoot their
carrying capacity before declining back below and kind of fluctuating at or just below
carrying capacity. It is common for populations of many organisms to do that.
Different environmental conditions that may limit population growth and population
density could both contribute to which life history traits will be selected for. There are
two types of selection that can be modeled with the logistic equation. Describe each
K-selection –
r-selection –
Many factors that regulate population growth are density dependent. In other words,
when there are more individuals in the population certain things are going to start
limiting the growth of the population. Some populations are density-independent.
Their birth and death rates do not change with density so these populations would be
unaffected by such things. However, most populations are density-dependent and
their birth and death rates would change. When there are more individuals the death
rate would increase and the birth rate would decrease to lessen the rate of growth.
THIS IS REGULATED BY NEGATIVE FEEDBACK. When the population density becomes
less, birth rate could again increase and death rate decrease.
What are some factors that regulate a density-dependent population?
All of these factors are explained in slides 111-117 and should be fairly simple
common sense explanations. Please feel free to write down the explanations too if
that helps you.
What is the study of population dynamics?
Many things can affect the size of a population over time. Predation, disease, or even
the weather is some examples. Slides 119-128, pgs. 1188-1189 in your book explain
some of these. The hare and the lynx is a very common example of how fluctuation in
one population (prey) is followed by fluctuation in another (predator). Again it is
common sense. If there are a lot of you and you eat most of the prey species their
numbers go down so there aren’t as many to have babies. With less prey you can’t
have as many babies so your numbers will go down. Now there are fewer predators
so the prey species can rebound. More prey means more food so now there can be
more predators. It is a vicious cycle.
What type of growth curve do you see in Fig. 53.22 pg. 1191, slide 131?
One important demographic factor in present and future growth trends is a country’s
age structure. It is a graph like the ones in Fig. 53.25 pg. 1192, slide 134, which
shows the distribution of a human population by age. It is also separated into male
and female, which, as you would expect is roughly the same until you get over 70.
These diagrams can be useful by showing growth trends and helping to predict when
there may be a larger group of older people on the way. Countries will then have to
plan for increased services and health care.
Growth began to slow a little in the 1960s, but we are still currently off that graph you
saw earlier and on our way to 8 billion. We will at some point hit carrying capacity.
What do you think will be our limiting factor?
Chapter 54 Sections 1- 3
A community is a group of populations that live in the same area and, thus, interact.
In this chapter we will look at only how species interact with each other. Please
remember that plants are living things, so this includes them too.
Interactions between populations can affect the distribution and abundance of these
populations. Interactions between species are called
(Don’t confuse this term with intraspecific interactions. This refers to interactions
between members of the same species, or within a population not between
populations of different species.)
There are many examples of different types of interspecific interactions. You are
not required to know any specific ones. Those talked about here are for clarity in
describing the concept. If you asked to describe any interactions on an exam you can
explain the interaction or give a brief description and an example of your choosing.
On an exam the most important thing is being able to use and describe, if necessary,
the correct terminology. They like the big words.
Throughout this discussion we will uses the standard notation used by scientists to
describe species interactions: (+) means positive or good, (-) means negative or bad,
and (0) means there is no effect either way. This generally refers to the effect on a
species reproduction and survival. As you have already seen with predator-prey
relationships, many of these interactions can be modeled mathematically.
Let’s look at some specific examples. Interspecific competition (–/– interaction.
The two minus signs mean that it is bad for both species involved.) occurs when
species compete for a resource in short supply. If it is in short supply then it is a
limiting factor. This can lead to a condition called competitive exclusion. What
does that mean?
There is always going to be interspecific competition. Chipmunks and squirrels eat the
same food. I know because I feed them, and there is plenty of competition. Blue jays
will get into the act too, if they notice what is going on. They also live in the same
areas. So how is it that they can all live there and one species is not excluded? It has
to do with their ecological niches. What is a species niche?
Again, how is it that they can all live there and one species is not excluded? The
answer is resource partitioning. There must be something that is different in each
species niche to allow them to all live and thrive in my woods together. Each species
lives in a different part of the woods. Chipmunks live in holes in the ground, squirrels
live in holes or nests in trees, and blue jays make nests in other trees. They all eat
peanuts, seeds, and insects. Since they all have varied diets, they are not competing
for an exclusive resource. There are lots of kinds of seeds to choose from. Chipmunks
usually search for seeds on the ground while squirrels harvest pine cones from the
trees. Squirrels will also steal peanuts from the chipmunks. They don’t get too many
because I hand feed the chipmunks and try to watch out for squirrels. Squirrels could
be hand fed too and get their own nuts, but for some reason they are not as easily
trainable. They won’t come to people as willingly as the chipmunks. But don’t feel bad
for the chipmunks. They get plenty of nuts and half of those they steal from the
chipmunks are stolen from the squirrels by the blue jays. (Peanuts in the shell are
wonderful for feeding critters like this. Just be sure to get the unsalted ones. Excess
salt is harmful to them because water is usually scarce.)
Your book’s example of resource partitioning is the Dominican Republican lizards.
They perch in different locations so there is not competition for sunny spots. I like my
example better. You can go outside and watch mine in action.
As a result of competition, a species’ fundamental niche may differ from its
realized niche. The difference here between realized and fundamental is this.
Squirrels live in trees mainly because chipmunks inhabit the ground. In some areas
where there are no chipmunks, red squirrels do live in the ground also. Their
fundamental niche is above and below ground, but due to competition with
chipmunks, their realized niche is smaller and they only inhabit the trees. You can see
the same thing in Fig. 54.3 pg. 1200, slide 150 with barnacles.
Predation is a +/- interaction- good for the predator, bad for the prey. Predators are
noted for their fangs, claws, sharp beaks, poison, etc. Prey can usually run very fast,
hide, or have display behaviors that warn others of impending doom. When none of
these are possible, like in the ocean, prey often join together and form schools or
herds. This is the safety in numbers principle. If there are a hundred of you all
together in the same place, chances are that the predator will choose someone other
than you to eat. Of course, someone is always chosen.
Another defense mechanism some organisms have is camouflage or cryptic
coloration. Why would they want that?
Some species, however, go for the opposite effect. Instead of blending in they display
very bright colors such as reds, yellows, and oranges. Why?
This is called aposematic coloration. DO NOT EAT RED MUSHROOMS!
Some species take advantage of another species poisonous announcement by
mimicking their coloration. There are two types of mimicry: Batesian and
Mullerian, both named for the men who first described each. There are tons of
examples of each out there. You can use the two in the book and PowerPoint, or find
others that might be easier to remember or more significant for you. Either way, write
down what each type of mimicry is and give an example of each.
Batesian –
Mullerian –
Another type of +/- interaction is herbivory. It is just like predation only with plants.
They get eaten. If an herbivore were to eat all the plants of a particular species in one
area, then that plant may go extinct if it does not get the opportunity to reproduce.
Therefore, plants have developed mechanisms to fight back. This is why some plants
have hairs, thorns, or toxins. In return, some animals have developed defenses
against the plants defenses, such as toxin resistance. Now the plants will have to
come up with something else. This could go on indefinitely.
Symbiosis is a relationship where two or more species live in direct and intimate
contact with one another. One species may actually live INSIDE the other like the E.
coli living in your intestines. There are three types of symbiotic relationships. Define
each one and give an example. (This would make a good test essay question. Hint.
Parasitism (+/-) –
Mutualism (+/+) –
Commensalism (+/0) –
The structure of a community will be strongly influenced by just a few species. For
example, predator species keep their prey species from overpopulating, which in turn
influences how many lower species there are, as well as plant species. Without
predators herbivores may become so numerous that all vegetation is stripped and the
ecosystem collapses. That is an extreme case. It is not likely that all vegetation would
be stripped because the community probably consists of more than one type of
vegetation as well as multiple types of herbivores. This is an example of the two
fundamental features of community structure: species diversity and feeding
What is species diversity?
Species diversity has two components: species richness and relative abundance.
These, respectively, are how many different kinds of species there are and how many
of each there are. This has a big impact on a community. Look at Fig. 54.9 pg. 1204,
slide 170. Which forest is more diverse? Both have four different kinds of trees (equal
species richness), but Community 2 is made up of mostly one kind of tree (low
relative abundance for 3 trees). This makes Community 1 more diverse.
Altogether the feeding relationships between organisms in a community are called
trophic structure. Energy from the autotrophs, or primary producers, is transferred
to herbivores then to carnivores and finally decomposers. This is called a food chain.
There are two examples in Fig. 54.11 pg. 1205, slide 172. A food web, which is more
complex and has many interconnecting food chains, is shown in Fig. 54.12 pg. 1206
slide 174.
Just to refresh everyone’s memory:
An autotroph is something that makes its own food. It could be a plant, algae, or
some chemosynthetic organism. They are at the bottom of every food chain. Primary
consumers are herbivores. They eat plants only. Carnivores eat herbivores or other
carnivores. Those that eat herbivores are secondary consumers; those that eat
secondary consumers are tertiary consumers. Decomposers get wastes and dead
organisms. They recycle nutrients back into the soil or water for the autotrophs.
Decomposers are bacteria and fungi.
Certain species have a very large impact on community structure, either because
there are so many of them or they play some very important role within the
community. Dominant species are those that are most abundant or have the
highest biomass. (Biomass is the total mass of all individuals in a population.)
Dominant species exert powerful control over the occurrence and distribution of other
species. Why they become dominant no one is sure, but some have suggested that
dominant specie are more competitive or are more successful at escaping predators
than other species. Either of these also explains invasive species, which are species
that are introduced to an area where they have not been living before and seem to
just take over. Since they have not been there before there are no predators to eat
them and they are often immune to diseases. This also makes them hard to get rid of.
Examples of invasive species locally are purple loosestrife, Asian ladybugs, giant
hogweed, emerald ash borer, and zebra and quagga mussels.
Keystone species fill an important niche and exert strong control on their
community. Unlike dominant species, they are not necessarily the most numerous.
The effects of keystone species on the ecosystem are disproportionate relative to their
abundance in the ecosystem, and when they are removed from the ecosystem, the
ecosystem often collapses. The example in the book is the sea star Pisaster
ochraceus. When it is removed from the ecosystem the number of other species
present declines. This demonstrates the importance of a keystone species.
Another example not in your book is the gray wolf, Canis lupus. Ranchers and farmers
in Colorado, Wyoming, and other surrounding states have complained for decades
about losses to wolves. Hunters complained that wolves were killing all the elk so they
had nothing to hunt. Most of the wolves were killed. Their numbers became extremely
low. Elk thrived. There were elk everywhere. There were so many elk in Yellowstone
National Park that the environment began to change. Elk are vegetarian. They eat A
LOT. They kept eating the trees before they had a chance to grow so all that was left
were really old, big trees and shrubs. In 1972, President Nixon signed into law the
Endangered Species Act. Since we had killed most of the wolves they were eventually
listed as endangered. Wolf numbers increased and wolves were introduced back into
Yellowstone. In the last ten years the park, too, has made a comeback. The elk
population has been somewhat controlled and the trees are beginning to grow again.
Wolves are a keystone species. The park is doing better and wolves are too.
Unfortunately, the hunters, ranchers, and farmers are still complaining and after
spending all that time and money on saving the wolves, they have been taken off the
endangered species list and are once again fair game for killing in most places. Just
for doing what they were meant to do.
A hundred years ago scientists thought that communities were in a state of
equilibrium, they were stable. Recently, say over the last century, there has been
evidence of change, that communities are not stable but constantly changing due to
disturbances. A disturbance is an event that changes a community, removes
organisms from it, and alters resource availability. In the above example the removal
of wolves from Yellowstone was a disturbance. Any natural disaster such as forest
fire, flood, volcano or hurricane is a disturbance. To us these things are bad, but
some types of communities need these disturbances once in a while to remain
healthy. There is a type of ecosystem called a pine bush that requires a fire every now
and then in order for some of the species to be able to reproduce. Burning opens up
new areas for species and fosters diversity. It also dries out and opens some types of
cones so the seeds can get out and grow. The Albany Pine Bush Preserve in Albany,
NY is about two hours from here. They have controlled burns every so often for the
reasons I just explained so all of the preserve is not always available for hiking. It
resembles a sparse pine forest with short scrubby trees and lots of bushes and
When an ecosystem has a disturbance it has to start over, to regrow. Human
communities rebuild after natural disasters, so do natural communities. The sequence
of changes that occur after a disturbance is called ecological succession.
Describe both types of ecological succession:
Primary –
Secondary –
These two processes are essentially the same with the exception of having to produce
soil for primary succession. Weathering of rock into enough soil to allow pioneer
species to grow is the most time consuming part of the whole process. Soil
accumulates very slowly, so secondary succession is much faster than primary.
Pioneer species are lichens, those hard, crusty, scaly-looking things that grow on
rocks and some trees. These help to further break down the rocks and create more
soil for mosses and grasses. Eventually there will be bushes and shrubs, then these
will make way for small trees, usually evergreens first, and then if the climate is right,
the hardwood trees, the ones with leaves, will grow. Succession will only proceed as
far as the climate will allow. It won’t matter how much time passes, as long as it stays
cold with little rain and even less sunshine up in the Arctic, you will not get trees.
Ecological succession is usually only talked about using plant species. As plant species
change through the process, so will the animal species. Animals that live in the forest
will not come to an area until there is a forest. Animals and insects that depend on
grass, like grasshoppers, will leave the area once the grass become scarce and the
trees begin to grow.
Chapter 55 Sections 1-5
This chapter focuses on ecosystems which includes all biotic and abiotic factors in a
particular area. The area can be very small such as a puddle, (yes, some organisms
live in a puddle) or as large as the Amazon rainforest. Size doesn’t matter. All
ecosystems have the same dynamics, that’s how they work. In every ecosystem
energy flows through (one way) but chemicals, like nutrients, are cycled
around within the ecosystem. Ecologists study how energy flows through a
particular ecosystem by changing forms and the chemical changes in nutrient cycles.
Think back to Chapter 8 in Unit 3 when we studied the laws of thermodynamics. The
first law, conservation of energy, states that energy can not be created or destroyed,
but can change form. In an ecosystem, energy comes in (usually) in the form of light,
or sunlight. The process of photosynthesis changes that solar energy into chemical
energy in the bonds of glucose, much of which is stored as starch in plants. Plants are
eaten by herbivores, which are eaten by carnivores, etc. At each level of the food
chain energy is transformed from chemical bond energy into mechanical energy of
motion of the organism and heat energy. The heat energy is mostly lost to the
environment which satisfies the second law of thermodynamics which states that
every energy transfer must increase the entropy (disorder) of the universe.
Another law, the law of conservation of mass, states that, like energy, matter can
neither be created nor destroyed, but it can change form. If you think of organisms as
big piles of chemicals, (which really, you are; the chemicals are just organized in a
particular way.) how is the law of conservation of mass satisfied?
Because of the second law of thermodynamics and that connection to the universe,
ecosystems are open systems. Energy flows in (as light), through, and out (as heat)
and chemicals also are brought in through rain, wind, or migration, cycle around, and
leave through migration, or as wastes in water. Thus, ecosystems are open systems.
Some ecosystems, such as a terrarium, that are completely closed as far as nutrients
go (they are just recycled) are still open systems because they will not function
without the constant supply if light energy.
A food chain shows the flow of energy (and most, but not all chemicals) through an
ecosystem. Since matter is recycled all the chemicals organisms are made of will need
to be used again. What is it that connects all trophic levels so this can happen?
Decomposers are nature’s recyclers. Without them chemical flow would also be in one
direction and once all the chemicals were used, life would cease to exist and we
would not be here. Decomposers are bacteria (prokaryotes) and fungi.
Scavengers like vultures and hyenas, eat dead organisms. The difference is that
decomposers get rid of remains, things like bones and fur, which other things don’t
eat. Scavengers eat the meat and organs just like other carnivores do, they just don’t
kill. They are either smart enough to let someone else do the work for them or lazy.
I’m not sure which.
Just like households have budgets, so do ecosystems. You can’t spend more than you
make, unless you are the US government. So for an ecosystem, the amount of energy
(sunlight) available to that ecosystem will determine how much it can use (convert to
chemical bond energy). This is known as primary production. Primary production is
measured in two ways. Define each:
Gross primary production (GPP) –
Net primary production (NPP) –
Since in most ecosystems energy is put into the system by sunlight, the amount of
sunlight an ecosystem receives will affect its productivity. Other factors, such as
availability of nutrients, also have an effect on productivity so the amount of sunlight
alone is not a measure of productivity. Tropical rainforests and coral reefs are the
most productive per unit area. Deserts are very sunny, but not very productive.
Marine ecosystems are also not very productive. Their photosynthetic organisms are
extremely small so they don’t produce much. However, due to the volume of
organisms in these ecosystems they contribute the most to global net productivity as
you can see in Fig. 55.6 pg. 1226, slide 202.
As previously mentioned, two things affect productivity: the amount of sunlight
received and the availability of nutrients. In aquatic ecosystems the amount of light is
not as big a factor because there is nothing to block the sun. As long as the sun
shines it will be available. Photosynthetic organisms live in the upper layer of the
oceans where the light is and pretty much cover it. So the biggest limiting factor in an
aquatic ecosystem will be the limiting nutrient.
What is a limiting nutrient?
What are two examples?
Please keep in mind that adding a nutrient can help an ecosystem, but it can also
hurt. Too much can cause eutrophication, a condition where there has been an
overgrowth of vegetation and its decay has used up all the oxygen in the water
leaving none for any kind of aquatic life.
What affects primary production in a terrestrial (land) ecosystem?
Actual evapotranspiration can represent the contrast between wet and dry climates.
What is actual evapotranspiration?
In other words, a place that has lots of vegetation that transpires a lot but where
there is not much evaporation will have a moister climate.
What type of terrestrial ecosystem is the most productive?
Energy transfer between trophic levels is typically only 10% efficient.
Biomass refers to the amount of organic matter in an organism, species, or trophic
level. This does not include water. Your total biomass would be the dry pile that was
left after all the water was taken out. Define each:
Secondary production –
Production efficiency –
To figure the caterpillar’s production efficiency find the percentage of energy actually
used for growth:
Production efficiency = energy assimilated – used for respiration X 100
energy assimilated
= 100J – 67J X 100 = 33J X 100 = 33%
Note that the amount of energy lost in feces does not count toward energy
assimilated, or energy actually taken into the organism. Remember from Unit 8 that
undigested, unabsorbed food (feces) just passes through and is never really ‘in’ the
body. Since the leaves had 200J worth of energy half of it was wasted from the start.
Of the half that the caterpillar actually took in, only one third (one sixth of the total)
was used for growth. That’s actually pretty good compared to birds and mammals
that typically only use 1-3% of what they take in. Most of their energy is used to
maintain body temperature. Insects and microorganisms are the most efficient, with
average production efficiencies around 40%.
So what happens to the 100J in the feces? Most of it is lost as heat when it is
consumed by the decomposers after they take out what they need for respiration and
This can be calculated for an entire food chain by finding the trophic efficiency of
each level. Trophic efficiency is the percentage of production transferred from one
trophic level to the next. Only about ten percent of energy is transferred to
each level. If we look back at the caterpillar, he may be 33% efficient in using the
energy he took in, but he only took in half of the energy that was available in the
leaves. So out of the total energy available (200J) he only used 16.5% of it for
biomass production (growth). Energy is transferred to the next trophic level by
organisms being eaten. Energy stored in the biomass of one organism that is eaten
can then be used by the eater. On average this is only about 10% of the total energy
available at each level. This is why food chains can also be represented by food (or
biomass) pyramids. Since only 10% of the energy is transferred to the next level,
each successive trophic level has less area in the pyramid. This represents the lower
energy availability and the lower total biomass of each level. See Fig. 55.10 pg. 1229,
slide 216.
This is how it normally works. What happens if there is a disruption? What if a disease
wipes out most of the vegetation in an area? How does that affect the rest of the food
chain? What if the sun was blocked by something, say volcanic ash, for a lengthy
period? There would be a ripple effect through the entire ecosystem.
Enough about energy. That is only half of what keeps an ecosystem going. The other
half is nutrients in the form of chemicals that cycle between biotic parts of an
ecosystem and abiotic. Some cycle on a global scale (gases such as oxygen, nitrogen,
and carbon in the form of CO2) and some are more localized. Be familiar with all these
cycles and learn at least one. You may be asked to explain one on a test. I have
provided the key parts of each here and some simple diagrams. You may also use
slides 222-230.
Water moves by the processes of evaporation, transpiration, condensation,
precipitation, and movement through surface and groundwater. This may also be
referred to as the hydrologic cycle.
CO2 is taken up through photosynthesis and released through respiration; additionally,
volcanoes and the burning of fossil fuels contribute CO2 to the atmosphere.
The main reservoir of nitrogen is the atmosphere (N2), though this nitrogen must be
converted to NH4+ (ammonium) or NO3– (nitrate) for uptake by plants, via nitrogen
fixation by bacteria.
Phosphate (PO43–) is the most important inorganic form of phosphorus. The largest
reservoirs are sedimentary rocks of marine origin, the oceans, and organisms.
Phosphate binds with soil particles, and movement is often localized.
Decomposition is how most nutrients become available again to living things. The
nutrients are freed from dead organisms by decomposers. What controls the rate of
Rapid decomposition results in relatively low levels of nutrients in the soil. This is what
happens in the tropical rainforest. It is very hot and moist. This accelerates the rate of
decomposition and nutrients are rapidly made available. They are also rapidly used
again, so soil does not have a chance to build up. Much of what makes topsoil rich
and dark is decaying organic matter. In the tropical rainforest growth is so fast that
when something dies there are many things ready to take up all the nutrients
immediately, so little or nothing is left to add to the soil. When the forest is cut down
to grow crops, it is only a few years before the ground is depleted of nutrients and
nothing grows. The people move on to another patch of forest, remove trees and
start farming again only to get the same result. This is one reason the rainforest is
disappearing so fast and becoming dry, arid desert land.
The Case Study of nutrient cycling in the Hubbard Brook Experimental Forest shows
the importance of vegetation on an ecosystem and the impact humans can have on
an ecosystem. As you look at what happened here try to understand the role the trees
played in keeping the nutrients within the ecosystem. The area that was clear cut lost
a tremendous amount of nutrients due to the lack of vegetation. Yes, trees use
nutrients, but they also store and replenish them. Remember your nutrient cycles you
just learned. Plants are a big part of those. They also hold soil in place. No plants and
the soil can just wash away. Trees also lose leaves on a regular basis which adds
nutrients back into the soil. Even evergreen trees lose approximately a quarter of their
needles every year.
Human activities now dominate most chemical cycles on Earth.
Humans have disrupted most ecosystems in some way. We have added chemicals,
some of which are toxic, added or removed species, and removed habitats altogether.
Species that are able to adapt survive, those that do not become extinct. In the case
study above, removing the trees removed the nutrients. When people farm crops they
remove the crops to eat and remove the nutrients. Now those nutrients need to be
replaced or the soil will become depleted, dry up, nothing will grow, and the soil will
blow away. So we add artificially produced chemical fertilizers so crops can continue
to grow. That’s good- to a point. What is critical load?
What happens to the ‘extra’ nutrients?
Eutrophication is caused by excess nutrients, mainly nitrogen and phosphorus,
finding their way into a freshwater source such as a lake or pond. This is the reason
phosphates were taken out of detergents in the 1980s. These nutrients are harmful to
lakes and ponds for the same reason they are good for crop fields- they encourage
plant growth. Excessive plant growth in a lake, mainly algae, can cover the entire lake
surface. This prevents underwater plants from growing because their light source is
cut off. Less plant growth means less oxygen in the water for aquatic animals. When
the algae die they are decomposed by bacteria which need oxygen for the
decomposition process. This uses up what oxygen there is in the lake. The lake is now
considered dead because nothing can live in it due to the lack of oxygen. More is not
always better.
What causes acid rain?
Which acids are in acid rain?
Biological magnification concentrates toxins at higher trophic levels, where
biomass is lower. This means that as you move up the food chain, organisms at the
higher trophic levels, like humans, eagles, and lions, will have higher amounts of
toxins per organism because each one eats many of the lower level organisms and
gets a dose from each one. Common chemicals found in higher organisms are PCBs,
mercury, and DDT. None of these are commonly used today in this country, but are
still in use in others. They are also persistent molecules that don’t readily leave the
environment so it will take a very long time before they are gone, hence the
continued warning for pregnant women and small children not to eat a lot of tuna.
Explain the greenhouse effect and what gases are involved.
This, like the fertilizer, is another example of too much of a good thing.
Why is the ozone layer important?
What is responsible for its destruction?
CHAPTER 56.1,3, and 4
We have been very successful as a population with almost 8 billion of us and climbing.
This has put a great strain on natural resources, not just for us, but all creatures.
Habitats have been disconnected, disturbed, or destroyed. Our wastes have polluted
land, water and air. We have produced chemicals that can change the environment,
sometimes in ways unknown until many years later. This chapter in the book, untitled
“Conservation Biology and Restoration Biology”, takes a look at how we can mitigate,
lessen, or correct, some of the effects we have had on the environment of our world.
We have banned the use of many chemicals that are destructive or harmful to the
environment. Many laws have been passed to insure we have clean air and water.
There are also laws to protect endangered species to hopefully prevent their
But out biggest challenge is yet to come. Our dependence on fossil fuels that
contribute to global warming will probably lead to the biggest environmental changes
our species has yet seen. Scientists have confirmed it and we have been warned as a
global community that we must cut back, but the quest for more sources of fossil
fuels goes on. The mining, drilling, and wastes associated with fossil fuels destroys
the environment and displaces species, but the burning of those fuels releases carbon
into the atmosphere. Global warming is controlled by positive feedback, the warmer it
gets the more carbon is released, which makes it warmer, etc., etc. Add to this the
mountains of plastics made from petroleum that are non-biodegradable and found
now throughout the environment and inside almost every living creature, and you can
see why our dependence on fossil fuels may lead to our own destruction.
Economically it is a tough choice, especially for developing nations, but in the end
natural selection will decide, not us.
I’m sure you remember from Living Environment that the tropical rainforests have the
greatest biodiversity, the most different kinds of species, of any biome or ecosystem.
Diversity is very important. The more different kinds of organisms there are in an
ecosystem the more stable that environment is. When there is a disturbance or
change, there are bound to be some organisms that can withstand that change and
adapt quickly or carry on. Ecosystems with few types of organisms may not be able to
and are, therefore, less stable. Since humans have changed many habitats greatly
and quickly diversity is key. This is also what makes global warming such a threat.
The rate of change in Earth’s temperature is rapid and many species may not be able
to evolve fast enough to adapt to the changing climate. Each population in an
ecosystem needs diversity among individuals (genetic) as well. The more variety there
is among individuals the greater the chances are that some of the individuals will have
the ability to survive change.
What are the three levels of biodiversity?
There are benefits to humans in preserving biodiversity. Many prescription drugs
come from plants. What happens if they become extinct? Animals provide us with
food, companionship, and some chemicals. We can not live on this planet by
ourselves without other species. Conservation of ecosystems, habitats, and species
will help us as well.
Ecosystems also perform many services for people that we don’t often think about.
List some:
What are the three major threats to biodiversity?
Habitat loss is the greatest threat to biodiversity.
Logging, slash and burn agriculture, urbanization, monocropping, infrastructure
development (dams, transmission lines, roads), and global climate change threaten
ecosystems and life on Earth. All of these result in habitat destruction or
fragmentation. Fragmentation doesn’t allow members of a species to move from one
part of their habitat to another to find food or mates because there is a road or
housing development splitting there home range. This is part of the reason we have
bears and mountain lions in people’s backyards.
What is an introduced species?
An introduced species can exploit a new niche free of predators or competitors, thus
exploiting new resources. Give some examples:
Introduction of new diseases can devastate native species. Some examples are:
• Dutch elm disease
• Potato blight
• Small pox [historic example for Native Americans]
What is overexploitation and how does that affect species? List some examples.
All these species you have just written down are only a few examples. Unfortunately
there are many more. Over time we have learned that saving a species is not as
effective as saving whole ecosystems. Protecting and preserving a wetland, for
example, protects all the species that live in and use that environment. Today most
communities make use of land-use planning before any major development
projects can be done. This involves looking at the current landscape and planning
around natural features and species that inhabit the area. This can get quite
complicated if there are protected lands or species involved. The use of movement
corridors to join areas of habitat, especially for larger organisms that maintain large
territories, is now common. Several communities are installing artificial corridors such
as tunnels or elevated crossings so that species can move between areas without
having to cross the road and risk being hit. You can see an example in Fig. 56.16 pg.
1257, slide 282. Notice the overhead walkway does not have a sidewalk but grass and
weeds as it continues the natural landscape found on both sides of the road.
Other examples of land-use planning are providing proper drainage to contain runoff,
building new wetlands near an area that may be filled in, and building fences,
roadways, or railways to accommodate migrating animals. Sometimes areas are so
important to the survival of species that the area is protected from any kind of
development. Our national parks and nature preserves are examples. Some, like the
Great Barrier Reef in Australia are not even on land. Many protected areas are
biodiversity hot spots. A biodiversity hot spot is a relatively small area with a great
concentration of endemic (native) species and many endangered and threatened
We are more aware today of how important it is to protect species and unique
ecosystems from damage, but that was not always the case. Some environments have
already been damaged, but not always by us. Natural disasters like forest fires, floods,
and volcanoes show us that ecosystems can recover if given enough time. In some
instances, though, we try to help it along and speed things up. Much environmental
damage has been done in places where strip mining, mountain top removal, oil
drilling, cattle ranching, or toxic spills have occurred. There are two strategies most
often used to artificially restore natural habitats: bioremediation and augmentation.
Fig. 56.21 pg. 1260, slide 286 shows you what a tremendous difference this can
Bioremediation is the use of living organisms to detoxify ecosystems. Most of the
time, these organisms are plants, bacteria, or fungi which can take up toxic material
and metabolize it so that it is no longer harmful. This removes the toxin from the
environment making it safe for other organisms to live there. Oil eating bacteria were
used to help clean up spilled oil from the Exxon Valdez tanker spill in Alaska in 1989,
and the BP Deepwater Horizon spill in the Gulf of Mexico in 2010.
Biological augmentation uses organisms to add essential materials, like nutrients,
to a degraded ecosystem. Nitrogen-fixing plants such as legumes can add nitrogen to
soil to help other plants to grow. This is the basis for the practice of crop rotation in
farming. It also cuts down on the need for artificial fertilizers.
I hope you have learned many things from this course. I know much of it was difficult
and detailed, probably beyond what you expected (or wanted), but you made it
through. I have, at times, given you things to think about that you may come across
later in life. If you have learned nothing else in this course, please take with you the
knowledge that you can think, reason, and make choices. Some of those choices will
affect only you, others may change the world. Think big! And do great things because
you can.
“Think left and think right and think low and think high.
Oh, the things you can think up if only you try.”
- Dr. Seuss