What Is a Keystone Species?

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Transcript What Is a Keystone Species?

What is biodiversity?
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Simply put, it's the variety of life. More broadly, biodiversity is our
collective life support system.
“Biodiversity is the variability among living organisms from all
sources, including inter alia [among other things], terrestrial,
marine and other aquatic ecosystems and the ecological
complexes of which they are a part; this includes diversity within
species, between species and of ecosystems.”
The key points of the above definition are:
 biodiversity is scalable — that is it exists on many levels, e.g.
the genes within populations, the populations within species, the
species within ecosystems, the ecosystems within landscapes,
the landscapes within bioregions, and so on.
 biodiversity is a key element of ecosystems — without the
connections biodiversity creates, ecosystems fall apart.
The first challenge to protecting biodiversity is understanding
what it means and then, why you should care about it.
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Why you should care about biodiversity?
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You are a part of biodiversity. The same things that affect bugs, trees and
fish have an impact on you too — the quantity of clean, fresh water, or the
quality of the air we breathe.
Everything is connected. The health of biodiversity affects you. And what
you do affects biodiversity. Everything we do either uses natural resources or
returns them as waste. The amount of land and resources that a population
or a person uses is called an ecological footprint. We all can do things to
make our personal footprints smaller.
Natural systems based on healthy biodiversity provide all kinds of
services for you…for free! Things like cooling and filtering air, controlling
floods, pollinating plants, controlling pests, aerating soil, and filtering and
storing water. These ecosystem services would cost a lot if we had to (or
even could) use technology to provide them. These services are called
ecosystem services.
You have to live with what's left. A wise saying states “We don't inherit the
earth from our parents, we borrow it from our children.” If you're a parent,
what kind of environment will you be leaving your children? If you're one of
the children, you might want to know what you'll be getting in the future. What
we do or don't do now, matters greatly to our future quality of life.
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Did you know? Wetlands provide us with ecosystem services valued at more
than $20,000 per hectare each year. (Costanza, R., et al., 1997)
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Three Levels of Biodiversity
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Researchers generally accept
three levels of biodiversity:
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genetic,
species, and
ecosystem.
These levels are all interrelated
yet distinct enough that they can
be studied as three separate
components. Some researchers
believe that there are fewer or
more levels than these, but the
consensus is that three levels is a
good number to work with. Most
studies, either theoretical or
experimental, focus on the
species level, as it is the easiest
to work on both conceptually and
in practice.
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Different levels of biodiversity
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Genetic diversity is:
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a building block of life
responsible for the variability among individuals within any species,
based on variations in genes
Genetic variability increases the chance that a species will adapt
to changing environmental conditions or impacts, since some
individuals will be able to handle the change better than others.
The more individuals there are, the greater the chance of genetic
variation. Species with a small population of individuals have
limited variability and therefore have limited ability to respond to
change. This is why populations of “species at risk” can be so
difficult to recover. Once you get below a certain number of
individuals, it is virtually impossible based on reproductive
potential. Genetic variation is the cornerstone of all
biodiversity.
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Different levels of biodiversity
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Population diversity. While we often hear about species, what we generally see and
interact with are populations - distinct groups of members of a particular species that have a
limited exchange of genetic material among the groups. They can reproduce together but
they don't often do so.
As a result, the genetic differences between populations tend to increase, even though the
variability within any one population may be less than across the species as a whole. Also,
because of the isolation, local impacts on one population may not be felt by another. A
conservative first estimate indicates that about 220 populations per species puts the total
number of populations world-wide into at least the low billions (Hughes, et. al, 1997).
Extreme population variability can be a double-edged sword. For example, lake trout in
Ontario's Great Lakes were once very diverse. There were at least 15 to 20 different forms of
lake trout recognized by commercial fishermen before the sea lamprey appeared. The lake
trout differed in where they were found, when they spawned, and in their appearance. They
were given such names as blacks, redfins, yellowfins, paper bellies, fats, humpers and sand
trout. Undoubtedly, the number of genetically distinct populations was much higher.
However, even all this diversity could not withstand over-harvest, sea lamprey predation and
loss of habitat, particularly inshore rubble shoals required for spawning. The catches of lake
trout plunged to 10% of the original yield in Lake Superior and down to almost nothing in the
other Great Lakes. When conditions improved and it came time to try and reintroduce lake
trout, the results were disappointing in all but Lake Superior where enough wild populations
survived to make a decent comeback.
All those discrete lake trout stocks had evolved for a reason: reproductive success of lake
trout in each area. The fish were in effect "tailor-made" for the area. Now many of those
stocks have disappeared forever. It will take a lot of time and effort to find stocks that might
be reasonable replacements.
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Different levels of biodiversity
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Species diversity is all of the different kinds of living things found in a certain habitat or ecosystem.
World-wide more than 1.4 million species have been identified (Wilson, 1992) but estimates of the
actual number vary from 5 million up to 100 million. 14 million appears to be an estimate that is
commonly quoted in the literature (Global Biodiversity Assessment, 2001 Summary).
Globally the estimated numbers of identified species are (KY Afield, 1997; CFM, 1997):
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35,000 micro-organisms
70,000 fungi
273,000 plants
875,000 invertebrates (insects, spiders, etc.)
19,000 fish
10,500 reptiles and amphibians
9,000 birds
4,000 mammals
105,000 other animals
Species diversity, however, is more than just the number of species in a given area, habitat or
ecosystem. Some species' importance can be out of line with their numbers, for example keystone
species. There can also be great differences in species composition over time. Species diversity can
also be greatly affected by physical conditions in the ecosystems where they live, such as
differences in temperature, light, structure and chemical composition.
The point is, biodiversity cannot be reduced to a single number. There are dimensions to
diversity, many of them.
Ecosystem diversity is the variety of ecosystems within a landscape or region including wetlands,
prairies or savannahs, lakes and rivers, forests and agricultural landscapes. The basic principles of
biodiversity apply here as well but the scope is much larger. It is at this level that the interactions
and links among species and the consequences of those links are evident. Less diverse
ecosystems, such as coldwater streams or small lake trout lakes, contribute to the functioning and
productivity of larger areas such as bioregions.
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Keystone Species
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What Is a Keystone Species?
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Black-Tailed Prairie Dogs Are a Keystone Species of the Prairie Ecosystem.
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A keystone species is a species whose very presence contributes to a diversity of life and whose
extinction would consequently lead to the extinction of other forms of life. Keystone species help to
support the ecosystem (entire community of life) of which they are a part.
More than 200 other wildlife species have been observed on or near prairie dog colonies. Some of
these animals depend on prairie dogs as a food source or for their habitat. Among those animals
associated with prairie dogs and their colonies are bald and golden eagles, swift foxes, coyotes,
ferruginous hawks, burrowing owls, badgers and black-footed ferrets. Countless insects and some
plants are also associated with prairie dog towns. Countless plants and invertebrate species also
rely heavily on prairie dogs and their activities. As a keystone species, black-tailed prairie dogs
impact the prairie ecosystem in multiple ways:
Their burrows act as homes to other creatures, including burrowing owls, badgers, rabbits, blackfooted ferrets, snakes, salamanders, and insects.
Their burrowing activity works to loosen and churn up the soil, increasing its ability to sustain plant
life.
Their foraging and feeding practices enable a more nutritious, diverse and nitrogen-rich mixture of
grasses and forbs (broad-leafed vegetation) to grow.
The enriched vegetation attracts an amazing array of wildlife who graze in their colonies.
Black-tailed prairie dogs play an integral role in the prairie food chain; they are a critical food source
for such animals as the endangered black-footed ferret, swift fox, coyotes, hawks, eagles and
badgers.
The extinction of the black-tailed prairie dog would be catastrophic for the entire Great
Plains ecosystem.
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The importance of connections
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Connections, everyone has them. Being “well-connected” means a lot in our society. It
means everything in nature — it's a Web of Life. All species and populations in isolation
accomplish little. It's only when they are linked that things begin to happen and ecosystems
begin to work. Generally the more diverse things are, the more links there are and the
better things function. (Tilman, 2000)
Biodiversity is in some ways very new science, although it's supported by years of study in
related fields. In fact, the term “biodiversity” (a short form of the term biological diversity)
wasn't used until 1985. There are still lots of uncertainties, and the complex, interactive,
chaotic nature of the subject makes it hard to study, but some generalities are emerging
from a developing body of scientific literature:
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greater biodiversity leads to greater productivity in plant communities;
greater biodiversity reduces the relative size of productivity fluctuations brought on by seasonal
change;
greater biodiversity leads to greater nutrient retention in ecosystems;
greater biodiversity leads to greater ecosystem stability (i.e. returns quickly to an equilibrium);
ecosystem processes are less stable or reliable at lower diversity levels;
greater biodiversity leads to greater resistance to invasive species;
greater biodiversity leads to greater resistance to disease.
removal or addition of any species can lead to big changes in community composition and structure.
(Tilman, 2000; McCann, 2000)
So biodiversity is often a reasonable measure of how well an ecosystem functions and
biodiversity is integral to the ecosystem.
One way to visualize the stability of diverse systems is to picture a diverse meadow and a
manicured lawn containing nothing but one variety of grass. Imagine the relative impact of
removing one important species from each system.
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The importance of connections
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One way to visualize the stability of diverse systems is to
picture a diverse meadow and a manicured lawn containing
nothing but one variety of grass. Imagine the relative impact
of removing one important species from each system.
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Measuring Diversity
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To detect changes in biodiversity there has to be a way to measure it.
Although at first glance biological diversity seems to be an obvious
idea, quantifying it is much more difficult. Making an attempt to express
it as a single number is futile, as a single number cannot hope to
convey the different components. There are three common ways to
measure diversity:
Numbers:
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It is possible to measure how many species are found in an area, or how
many alleles a species has for a single locus, or how many functional groups
or taxonomic groups higher than species are present in an ecosystem. This
is considered a reasonable if incomplete way of measuring diversity, and can
be expressed as the number of species found per unit area, per unit mass,
or per number of individuals identified. What controversy exists about this
component is mainly about how to standardize measures that are taken at
different scales.
Area 1
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Measuring Diversity
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Evenness:
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If almost every individual in an area is from the
same type of species, the diversity would not
seem high, even if there are many species
present. Evenness measures to what extent
individuals are evenly distributed among species
(if one is looking at the species level). The most
common values that are used are species number
and species evenness.
Area 2
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Measuring Diversity
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Difference:
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A site with many species is considered to have high
diversity, but what if those species are all very closely
related? If another site had fewer species, but those
species were more distantly related, would that second site
have a lower or higher diversity? Measuring the
evolutionary distance between the different units is
important, as it is on a different level than something like
species number, which doesn't measure how different the
species are. Measurements of difference include disparity
and character diversity.
Area 3
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Measuring Diversity
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Three sample areas are given to the above, each of
which is most diverse in a different way. Area 1 has the
greatest number of species, four in total. But half of
the individuals in the sample are from the same
species. Area 2 has fewer species, only three, but it
has a greater evenness; there is an equal chance of
getting an individual from each of the three species.
Area 3 has even fewer species, just two, but it has the
greatest difference. While the other samples contain
only insect species, this one contains both insects and
a mammal, which is very distantly related to insects.
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How ecosystems function?
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At least 40 per cent of the world's economy and 80 per cent of the
needs of the poor are derived from biological resources." — The
Convention About Life on Earth (UN Convention on Biodiversity)
Ecosystem functions are a good thing. They keep our air and water
clean, help regulate our climate, and provide us with sources of food,
shelter, clothing and medicine. They do these things for us, and for all
life, if they are healthy. Sometimes the ecosystem functions for free.
More often to keep them functioning and healthy, we have to give up
competing uses of that ecosystem, such as resource extraction, waste
disposal or land development (residential, recreational, transport,
industrial). While we often can put a value on these competing uses of
the land (for housing, industry etc.) in terms of economic benefits or
jobs, we don't know how to assign a value to the ecosystem services
that nature provides. This makes it difficult to compare and choose
among various uses of the land.
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Ecosystem goods and services & natural
capital
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To deal with this challenge, we now have two concepts:
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ecosystem goods and services (most often shortened to ecosystem services)
natural capital
Ecosystem services are “services that humans derive from ecological functions
such as photosynthesis, oxygen production, water purification and so on.”
Natural capital is the ecosystem that produces the goods and services.
The average value of all these goods and services, estimated world-wide, is 33
trillion US dollars per year. To put that into perspective, the global gross national
product (GNP), a measure of the productivity of all of the world's economies, is
around 18 trillion US dollars per year . Some of the values are determined directly,
e.g. sport fishing; and others are determined by what it would cost to artificially
replace the natural service, e.g. water storage and flood control. For example,
when New York City's drinking water fell below standards, the estimated cost to
install a filtration plant was $6-8 billion, with annual operating costs of $300 million.
Not surprisingly, the city opted to restore the “natural capital” in its watershed at a
cost of “only” $660 million.
Freshwater wetlands, considered by some as “wastelands”, are actually the
second most valuable ecosystem (behind coastal estuaries), with a value of well
over 20,000 Canadian dollars per hectare per year .
The net benefits of protecting biodiversity and ecosystem services are significant.
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