1. What is your opinion on culling? Is there a time that it is appropriate? Culling is the process of segregating organisms from a group according to desired or undesired characteristics. Humans usually cull by killing individuals of a species population.Please be original and no references per the professor. Must be in your own words__________________________________________________________________________________________2. Please respond to my peer response belowCulling is a very intriguing subject. I think it comes down to each person ethics and morales. For me I think culling is ethical if it benefits the majority to keep them safe. The example of the badgers in the U.K. is a prime example that culling is needed. The spread of disease to cattle and other live stock that can be spread to humans. In this situation the badger is an heavily protected animal by the government. Culling should only be used in situations where it can be control or we end up it a problem where the species can be threaten. Farmers do this practice to protect their investment and the rest of their animals. Culling is done with fruits and vegtables, due to not being desirable to sell or carrying diseases
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Community Ecology: Biodiversity, Keystone
Species, and Food Webs
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Unit IV, Community Ecology: Biodiversity, Keystone Species, and Food Webs
Course Learning Outcome
4. Summarize the importance of biodiversity within the environment.
Unit Learning Outcomes
4.1 Discuss what community ecology is and how the level of biodiversity relates to interactions among organisms and the
4.2 Explain how food webs shape species diversity and how keystone species play a vital role in the environment that
shapes habitats and impacts biodiversity.
4.3 Describe how ecology and biodiversity benefit human life and how human life negatively impacts the environment.
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Unit IV Introduction
Life is all around us; even in habitats we think have no life, organisms are plentiful. From the smallest bacteria to the largest predators,
each organism plays a vital role in maintaining the health of the ecosystem. In this unit, we will discover the diversity of life that exists
around us and how this diversity plays an important role in our everyday lives. We will start by understanding the foundations of population
ecology and use that knowledge to understand what is happening in our ecosystems today.
Food Chains and Food Webs
Where do you get energy from every day? If you think your energy comes from the food you eat, you are right. Let’s take your breakfast as
an example; assume you had some delicious pancakes, eggs, and bacon this morning. Have you thought about where the energy for
these foods comes from? Eggs obviously came from chickens, but where did the chickens get their energy to make the eggs? We know
that the bacon came from pigs, but where did the pigs get their energy? What was the pancake made from?
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The chicken and pig are fed a diet of grains (i.e., wheat, corn, soy) that provides them with the energy needed to grow and survive.
Pancakes are primarily made from flour, a product derived from wheat. Now, where does the wheat, corn, and soy get the energy to grow?
The answer is the sun!
The sun provides for all life on Earth. Although we often do not relate our bacon to the sun, we can trace the steps back to the sun’s
energy. We ate the bacon, which provided us with energy; the bacon came from the pig; the pig ate grains made from plants (i.e., wheat,
corn, soy); and those plants originally got the energy to grow from the sun. The process of this energy flow, which passes from one
organism to the next, is called a food chain. Energy travels in one direction from the sun and up through the food chain. Each level or link
in the food chain is a trophic level. The trophic level is based on the number of energy steps it takes to get to that level. Let’s see what this
looks like using wildlife in an ecological environment.
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The plants are the first trophic level. Kangaroo rats eat seeds from plants at the second trophic level, a Western diamondback rattlesnake
can eat a kangaroo rat at the third trophic level, and the red-tailed hawk
is at the fourth trophic level eating the rattlesnake. However, at every trophic level, you do not pass up the full amount of energy from the
level below. The energy acquired at each trophic level is used and lost to the environment as heat before it can enter the next trophic level;
therefore, at every step up the food chain, there is only 10% of the previous trophic level’s energy available for the next. This explains why
there are more organisms on lower trophic levels and less at higher trophic levels. There is more energy to support lower levels than
We are missing one part in this food chain above. Food chains do have an end however. The red-tailed hawk in our example does not live
forever. When the red-tailed hawk dies, scavengers eat as much of the organism as possible, and then decomposers, such as bacteria
and fungi, break down the bones, feathers, and leftovers—returning all of the nutrients into the soil. When new plants grow in that location,
nutrients provided by decomposers are available for new growth.
See the following example: deer / grass / field.
What is more efficient—being an herbivore or carnivore?
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Are there other animals that would eat a kangaroo rat, or is there something besides a red-tailed hawk that would eat a Western
diamondback rattlesnake? Yes! This makes the food chain a bit more complicated, and we, therefore, use a food web to describe what is
actually happening in our world. A food web is a number of interconnected food chains in an ecosystem. It is a more realistic version of the
energy flowing through an ecosystem. Check out this graphic of an Arctic food web. Notice how in real ecological systems the options
increase, but all the organisms are connected. What if one of the species in the food web goes extinct? How will that affect other members
in the food chain?
Arctic marine food web (Hassol, 2004)
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Are some species more valuable in a food web than others are? Keystone species are crucial to the maintenance and composition of an
ecosystem. Keystone species are influential to the stability of the environment due to their role in some ecosystem functions such as
nutrient cycling or production of plant biomass. Keystone species are often not the most numerous, they do not have to be the largest, and
they can be the smallest in an ecosystem. For example, the elephant can change an entire vegetation structure by bulldozing larger trees,
grazing on taller plant species, and promoting a prairie ecosystem. Bison in the Americas promote the same prairie system by grazing
grasses, which prevents larger trees and shrubbery from coming in, and wallowing in the dirt, which creates microhabitats for species such
as frogs and other amphibians. Starfish found along coastlines of North America feed on mussels, and if they are removed, mussel
populations will increase sharply, which crowd out algae and, therefore, decrease the number of herbivore species.
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Now that we understand what a food web looks like in an environment, let’s talk about how each species interacts with one another and
their environment. A community is a group of organisms of different species occurring together in the same area and interacting with each
other. When referring to community ecology, that also assumes the interactions of organisms with their environment—living (biotic) and
non-living (abiotic). An ecologic community is usually termed by the habitat it occurs in (e.g., a wetland community or a forest community).
In looking around your home, have you noticed that you are not overrun with one species of bird or one species of mammal, and you have
different species around your residence? Also, what you have around your home is much different than someone across the country. How
do these species maintain their populations?
In past units, you have learned about the hierarchy of communities and symbiosis—how species can interact with each other and either
help others, hurt others, or neither. This interconnectedness is the foundation for forming a functioning ecosystem that maintains diversity.
Every species in a particular area has a carrying capacity. A carrying capacity is the maximum number of individuals of a species that the
natural habitat can sustain over an indefinite period of time without deterioration of the natural habitat. In other words, how many animals
can live in an area without having too many? How would too large of a population affect the environment they live in?
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Let’s look at this crazy example. In 1944, 29 reindeer (yes, there are real reindeer; they just cannot fly) were introduced onto St. Matthew
Island in the Bering Sea (a part of the northern Pacific Ocean where snow crabs are fished). Reindeer previously had never inhabited the
island so the vegetation was lush and full of nutrients. The reindeer thrived, and their birth rates shot up quickly, increasing the population
of reindeer to 6,000 in the early 1960s. Because the population was so large, the reindeer ate their entire food source (lichens), and in the
winter of 1963-1964, virtually the entire population of reindeer starved to death. Only 42 female reindeer survived (Klein, 1968).
Without any males, the
population was destined
to go extinct.
If there are too many of a species in an area, what do you think would happen to the surrounding habitat?
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In the reindeer example, you can see that without a carrying capacity or without achieving the optimal number of individuals in an area, it
can be a detriment to the species and the habitat. To achieve a carrying capacity, organisms have limiting factors. Limiting factors prevent
unlimited population growth. Limiting factors can be extrinsic (come from outside the population) and intrinsic (come from within the
population). An extrinsic factor could be a lack of food source, competition from another species, a natural disaster (e.g., tornado,
hurricane), or a lack of sunlight. An example of an intrinsic factor is a change of behavior when a population gets too big; there is
overcrowding, and individuals will breed less, reducing the population numbers.
The carrying capacity is a stable amount of individuals in a population. Many species will fluctuate around the carrying capacity line but will
maintain an average stable population number.
Watch the quick video on the next slide for an understanding of carrying capacity. You will need to use your myCSU login and password to
access the video. Understand that when the narrator says “on this reserve,” he is referring to a nature reserve, but this idea of carrying
capacity can be extended beyond a reserve to anywhere, including your own backyard.
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Do you know how many people there are in the world? As of August 2016, the human population is at 7.4 billion people. We have not
leveled off to a carrying capacity and are still growing our numbers exponentially.
Watch the video segment on the next slide to get an idea of what might limit our human population in the future.
How does this carrying capacity relate to our human population?
Earth (Mary1826, 2017)
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The same way that limiting resources in an area can decrease the carrying capacity of a population, increasing resources can increase the
carrying capacity of a population. When weather patterns provide an area with optimal conditions, which creates a good environment for
plants, food will be plentiful for many animals. In these conditions, communities will thrive, and populations will do well. This can also be
the case for man-made intervention. If food is provided to wildlife, the resources available to them increases, and that can increase their
populations. Wildlife should not be fed for other reasons, as well, such as dietary and behavior alterations.
Let’s look at how feeding feral cats can affect the community ecology of an area. Feral, or free ranging, simply means any domestic animal
that now lives under wild conditions (not in the comfort of a home). Feral cats are house cats that are outdoor cats and spend their time in
the “wild.” Feral cats are often fed by humans, or when feral cats occupy urban areas around schools, stores, or neighborhoods, many
people feel the urge to provide food for the feral cats. Providing food increases the resources available for cats, and the cat population can
increase. This would not be so bad to have more cats in an area, but feral cats greatly affect the community ecology.
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Cats hunt for sport, and they like to kill more than they consume. A recent study estimated that free-ranging domestic cats kill 1.4–3.7
billion birds and 6.9–20.7 billion mammals annually (Loss, Will, & Marra, 2013). Feral cats are likely to be the single greatest source of
human-caused mortality of birds and mammals in the United States, which ranks above car collisions, habitat destruction, poisoning, and
more. The effect feral cats have on bird populations has been well documented. Furthermore, what effect does the decline in bird
populations (from feral cats) have on insect populations, seed populations, and larger birds of a prey species?
If we break the word biodiversity down, bio means life, and diversity means a range of different things or having variety. Therefore,
biodiversity is a variety of different living organisms in our environment. Biodiversity occurs at all levels of biological organization from a
population to an entire ecosystem. At a population level, it is important to have high genetic diversity—a wide range of genetic variation
within a population of one species. At an ecosystem level, it is important to have ecosystem diversity—a wide variety of ecosystems on the
planet. In addition, within each ecosystem, it is important to have a high diversity of species. At every level, diversity serves the ecosystem
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Let’s look at a far-fetched example to make it relatable. Imagine there is such a thing as a zombie apocalypse, and a zombie virus has
infected some of the human population, turning them into zombies. The only humans that survive are the humans who carry a genetic
code that makes them immune to the virus—they will not become zombies. The human population will live on because the humans with
the zombie immunity will reproduce and pass on their genetic material to the next generation. But, what if we didn’t have a wide variety of
genetic variation in our human population? Less diverse genes means there is a lower chance that we would have individuals who carry
the right genetic makeup that makes them immune to the zombie virus.
Low genetic diversity means all of the individuals who make up the population are similar in reducing the chances that a population would
have a variation for survival. Several things influence genetic diversity of a population: mutations, sexual reproduction, population size,
selective breeding, and migration.
Influencers on Genetic Diversity of a Population
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Mutations are changes in the genetic information of an organism. We usually think of a mutation in our genetic material as a bad thing or
as a cancerous development, but a mutation can also be of benefit to an organism. A mutation could introduce new genetic material to a
population that makes them resistant to an environmental factor that would harm them or give them an advantage at survival.
Mating does not introduce new genes, but it does create new possibilities of combinations of genes. If the new combination provides an
advantage for that individual to survive and reproduce, this will influence the next generation’s genetic diversity.
The bigger the population size, the more genetic diversity there is. If a population is low in numbers, there are simply not as many
individuals to carry a variety of genetic makeup. Chance events that decrease population size can greatly impact diversity if small diverse
subsets of a population are impacted.
Domestic animals are a great example for this. We have selected animals to breed based on desirable characteristics. This selective
breeding decreases the genetic diversity by eliminating undesirable characteristics in the populations. In the wild, if selective breeding
occurs and natural selection does not, certain genetic variations will be lost, and some could be important for that species’ survival In the
In order for individuals to continue to share genetic material throughout their species, they must mate with individuals outside of their
populations. Genes need to enter and leave a population to maintain high genetic diversity.
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Take a look at this example of natural selection in action. The peppered moth was once an ivory color to camouflage itself against the bark
of trees that it lived on. The adaptation of camouflage gave it an advantage against the moth’s predators, which are birds. As the Industrial
Revolution took place in the United States, and our air became polluted and black soot was found on tree bark, the ivory-colored moths
began to stick out against their background. Birds were now able to see the moths, and ivory-colored moths were eaten. In the population
of moths, there was genetic diversity that produced some moths of a darker color variation (similar to the way that many humans have a
variety of hair colors). The darker-colored moths survived because they were now camouflaged against the soot-colored bark. Since they
survived, the dark-colored moths were the ones able to reproduce and pass on their genetic material to the next generation. After the
reduction in air pollution because of the Clean Air Act, there was less black soot in the air and on trees. The genetic diversity in the moth
population gave the moths the ability to shift their physical genetic traits back to the ivory color to avoid becoming extinct. Without a large
population of genetically diverse individuals, the moths would not have survived these drastic environmental changes. It is important to be
diverse within a species.
Biodiversity and Humans
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How does biodiversity in our ecosystem affect us? To answer this question, let’s look at the oceans. You may not eat seafood, but the
health of our oceans is vital to your survival. If we continue to take out the top predators in our oceans (e.g., tuna), there are less predators
to feed on the mid-sized fish, making the populations of mid-sized fish increase. Since they have increased numbers, they eat more of the
small-sized fish, reducing the numbers of small-sized fish that eat plants and algae. Without fish to eat the plants and algae, the plants
increase without anything to limit their growth. They overcrowd the space and die. As the bacteria decomposes the dead plants, they use
up oxygen to break down the material. The water loses oxygen, and there are no plants to go through photosynthesis to create the oxygen
we breathe. Roughly, 70% of the oxygen in our atmosphere is created by marine plants. Maintaining the diversity of species in our oceans
keeps the ecological system in check and maintains the air that we breathe. Every inhale and exhale is connected to our oceans. Go
ahead, and take a deep breath.
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Photosynthesis is the process plants go through to make their own food. During the process, plants take in carbon dioxide and release
oxygen. This is an ecosystem service. Ecosystem services are the benefits that our ecosystems provide our human societies; many times,
we are unaware of these benefits. Ecosystem services are difficult to put an economic value on. Trees in urban environments filter out air
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