Q: How do skulls protect horned animals during head butting matches?
A: A special honeycombed bone structure around the base of the horns absorbs the shock of impact during repeated
head-on collisions, allowing the muskox and many other horned animals to survive dominance competitions without
damaging the skull or brain.
Q: Why do some animals have a large sagittal crest?
A: Predators that tackle large prey often develop a sagittal crest, since it provides attachment space for the temporalis
muscle, which is used to snap the jaws shut. Sagittal crests are often larger in males than in females, because they are
associated with larger body size.
Animal skulls have evolved for nearly 500 million years to protect the brain and sensory organs in vertebrate animals.
Each of the skulls feature mechanisms built to support specific functions, including the obtainment of food and
processing, optimal sensory information gathering, and the protection of the brain from trauma. Based on the design
of an animal’s skull, many of its dietary and social patterns can be discerned.
There are four main kinds of teeth in mammals (incisors, canines, premolars and molars).
Carnivores tend to have long canines which are used to rip and tear meat, sometimes in a scissors like action. In
addition, carnivores have sharp molars toward the back of the mouth, used to further rip and shred meat. Carnivores,
tend to have binocular vision, where their eyes are at the front of the head, which results in a smaller field of view, but
allows for depth perception, needed to catch prey.
Herbivores tend to have well-developed flat premolars and molars, often with sharp ridges on the tops. Generally
herbivores do not have canine teeth, and their incisors are usually large and used to snip off foliage from branches.
Because herbivores are often prey for other animals, they generally have their eyes on the side of their head, which
functions to gibe them a wider field of view, so that they can detect their prey earlier, and have a chance to flee.
Omnivores usually have a variety of all kinds of teeth. Humans, bears and raccoons are omnivores, since they eat all
kinds of food (both meat and plant material) they need all kinds of teeth. Generally omnivores have eyes on the front
of their heads like carnivores, in order to best catch their prey.
Species
Species are the different kinds of organisms found on the Earth. A more exact definition of species is a
group of interbreeding organisms that do not ordinarily breed with members of other groups. If a
species interbreeds freely with other species, it would no longer be a distinctive kind of organism. This
definition works well with animals. However, in some plant species fertile crossings can take place
among morphologically and physiologically different kinds of vegetation. In this situation, the definition
of species given here is not appropriate.
Populations
Apopulation comprises all the individuals of a given species in a specific area or region at a certain
time. Its significance is more than that of a number of individuals because not all individuals are
identical. Populations contain genetic variation within themselves and between other populations. Even
fundamental genetic characteristics such as hair color or size may differ slightly from individual to
individual. More importantly, not all members of the population are equal in their ability to survive and
reproduce.
Communities
Community refers to all the populations in a specific area or region at a certain time. Its structure
involves many types of interactions among species. Some of these involve the acquisition and use of
food, space, or other environmental resources. Others involve nutrient cycling through all members of
the community and mutual regulation of population sizes. In all of these cases, the structured interactions
of populations lead to situations in which individuals are thrown into life or death struggles.
In general, ecologists believe that a community that has a high diversity is more complex and stable
than a community that has a low diversity. This theory is founded on the observation that the food webs
of communities of high diversity are more interconnected. Greater interconnectivity causes these systems
to be more resilient to disturbance. If a species is removed, those species that relied on it for food have
the option to switch to many other species that occupy a similar role in that ecosystem. In a low diversity
ecosystem, possible substitutes for food may be non-existent or limited in abundance.
Ecosystems
Ecosystems are dynamic entities composed of the biological community and the abioticenvironment.
An ecosystem's abiotic and biotic composition and structure is determined by the state of a number of
interrelated environmental factors. Changes in any of these factors (for example: nutrient availability,
temperature, light intensity, grazing intensity, and species population density) will result in dynamic
changes to the nature of these systems. For example, a fire in the temperate deciduous forest completely
changes the structure of that system. There are no longer any large trees, most of the mosses, herbs, and
shrubs that occupy the forest floor are gone, and the nutrients that were stored in the biomass are quickly
released into the soil, atmosphere and hydrologic system. After a short time of recovery, the community
that was once large mature trees now becomes a community of grasses, herbaceous species, and tree
seedlings.
Citation:Pidwirny, M. (2006). "Organization of Life: Species, Populations, Communities, and Ecosystems".
Fundamentals of Physical Geography, 2nd Edition. Date Viewed.
http://www.physicalgeography.net/fundamentals/9d.html
WINTER ADAPTATIONS OF ANIMALS
Winter is the most stressful time of year in the north for most forms of life. The key hardships are a lack of
food and cold temperatures. However, don't let a reduction in activity appear as if there is nothing going
on in the woods!
A lack of food occurs for at least two reasons, both related to low temperatures. The first reason has to do
with a reduction in active plant life. Plants, of course, are the sources of nearly all food chains. The
second reason has to do with availability. For many animals, food sources are buried under snow or ice.
Deep snow is not a problem for all creatures. To field mice, it is a protective layer against most predators.
To predators, deep snow means a time of going hungry.
Specialized adaptation to winter involves exploring chemistry, physics, and animal behavior. Managing an
energy budget is the key to survival. There are many ways to manage this budget, primarily through
combinations of physical attributes (morphology, habitat, and behavior) and physiological capabilities (body
chemistry and metabolic controls).
How Do Animals Respond to Cold Winters?
There are three main strategies to surviving inclement conditions, migration, dormancy, and toughing it
out. Each species is suited to a particular variant of one strategy or the other, or a combination of strategic
elements.
1. Migration and Movement. Many species migrate between seasons. Some, such as the
arctic tern, travel 10,000 miles between winter and summer habitats. It's difficult to ignore the
migration of geese, cranes, and ducks . . . and difficult to believe that monarch butterflies
actually migrate to Mexico. How in the world do tiny hummingbirds fly all the way across the
Gulf of Mexico? The return of the colorful and vociferous warblers becomes obvious in the
Spring, but their departure in the Fall is generally missed. The first Spring bluebird is noted
by many . . . but few can mark their departure date.
Migration is not always a dramatic, long-distance affair. Other species, such as white-tailed deer, move to
areas that are more survivable. Deer pretty much vacate the Lake Superior watershed during the deep
snow season. Biologists have been able to track some of these migration patterns in the U.P. Reptiles
and amphibians move to protected places underground or under water to avoid freezing temperatures.
Fishes will move to different waters. More recently, most of us noted the indoor migration of the Asian
ladybird beetle!
For those people who prefer to be indoors most of the winter, the outdoors may appear to be uniformly cold
and uncomfortable. However, there are many microclimates where winter stress is significantly lower.
Logs, caves, holes, dead trees, spruce and cedar stands, under snow, and human structures are examples
of places that provide shelter from winter extremes. These are critical places for wildlife.
Not all migrators leave Michigan, either. Some actually migrate TOMichigan for the winter or on a cyclical
basis! Chickadees and great gray owls are two good examples. The playful, curious, and nearly fearless
whisky-jack makes its presence well-known at camps and many winter feeders. During lows in the
snowshoe hare population cycles, Canada lynx may roam into the U.P. in search of food. We need to
remember that our winters are not as severe as we sometimes boast about. There is a large land mass to
our north where winters are considerably longer and colder!
2. Dormancy. There are several forms of dormancy as the taxonomic groups are
surveyed. Definitions are difficult due to the many variations of dormancy. There has
been a lot of research into how animals cope with inclement weather, winter in this
case.
Torpidity is a controlled reduction of body metabolism, evidenced by low oxygen
consumption rates and lower body temperatures. A key part of the definition is accurate metabolic control.
It is a phenomenon restricted to warm-blooded animals. Cold-blooded animals experience different
physiology in response to adverse conditions. Some animals will undergo daily states of torpidity as a
response to a lack of food and in combination with other environmental conditions. Other species undergo
seasonal torpidity. In the north, hibernation is the most dramatic form. Torpidity is not restricted to
northern species and can be found in the tropics, too. Estivation is a kind of torpidity in very hot and dry
conditions.
Many northern species undergo metabolic changes that allow them to "sleep" through the winter. Sleep, of
course, is not what they do, but torpor can superficially appear that way. The most advanced form of
torpor is hibernation. Hibernation is quite complex and fascinating. Although definitions are evasive,
hibernation is a controlled significant drop in metabolism to a selected level, although the term hibernation
is sometimes used for cold-blooded animals and any form of winter dormancy. Chipmunks, certain mice,
ground squirrels, and groundhogs are examples of true hibernators. Their body temperatures are
maintained a few degrees above their ambient environment, which is usually in a place protected from
weather extremes. Hibernators are usually small animals because small animals have high rates of
metabolism to begin with. Increases in these already high rates of metabolism in order to maintain body
temperature comes at a metabolic cost that is just too high for some species.
True hibernators cannot be easily "woken up". They are largely unresponsive to external stimuli.
Generally they maintain only a sufficient amount of specialized fat reserves to carry them through the
winter season and arouse them during the late winter or early spring. Arousal is a very expensive
metabolic process that they can usually afford to do only a few times, sometimes only once. Bears do not
hibernate, although this continues to be argued. Their body temperatures drop only a few degrees and
metabolism is reduced to only moderate rates. Female bears give birth during the winter, something that
would not be possible for a true hibernator. Lastly, bears can easily be aroused in the winter and then drop
back into a state of torpidity. Don't be fooled by a "hibernating" bear in its den!
Dormancy in cold-blooded animals is a reduced state of metabolic activity largely controlled by
environmental conditions. Cold-blooded animals must become dormant during the winter because they
lack the internal control over their metabolism. Many seek sheltered places and undergo chemical
changes to prevent their tissues from freezing. Others can tolerate certain levels of ice between cells,
commonly in tandem with chemical changes. Spring peepers, chorus frogs, gray tree frogs, and wood
frogs tolerate and regulate a frozen state. Good snow cover is essential to survival, as they overwinter
under leaf litter on the forest floor. These frogs thaw out in the spring, which is why we hear them sing so
early in the season on those increasingly warm evenings.
Insects overwinter as eggs, pupae, or adults. Dormancy is often coupled with specialized chemical
adaptations to help survive the winter season. Some have the ability to resist freezing, others can tolerate
freezing to certain degrees. There are also insects that can employ either strategy. Chemicals associated
with dormancy are sugars and certain alcohols such as glycerol, sorbitol, mannitol, and ethylene glycol.
Plants also experience dormancy but cannot relocate to sheltered places, other than reverting to seeds on
the ground and roots under the ground. Tree adaptations are covered on another page.
3. Toughing It Out. Winter remains an active time of the year because many species have
adapted to active lifestyles during the winter. Cold-blooded animals (amphibian, reptiles,
and insects) must find sheltered places where they can ride out the winter without freezing
and being eaten by predators. Fish continue to be active (as ice-fishers know!) but often at a
reduced rate. For some species, the winter energy equation is always negative, meaning
they cannot consume or conserve enough energy to survive the winter. While consumption
and conservation are critical, these species must rely on fat reserves and their margin for survival is often
slim. This is part of the reason why long and severe winters can take a heavy toll on wildlife populations
whose northern range occurs in Michigan.
There is a wide array of morphological, physiological, and behavioral adaptations for winter survival. A few
examples are provided below, but investigations into the lives of active winter animals will reveal many
combinations of survival strategies.

Bergmann's Rule states that northern species of a particular genus or similar class of birds or
mammals tend to be larger in size, although this is not always true. Larger body size means a
higher body mass-to-surface area ratio. It's easier to retain heat. Polar bears are larger than
tropical bears. White-tailed deer in Michigan dress out at higher weights than their counterparts in
Texas or Florida.











Body appendages tend to get smaller in the north, as a heat conservation measure. Snowshoe
hares have smaller ears that cottontail rabbits. Mammalian legs and snouts are frequently shorter
and stouter.
Specialized fat, called brown fat, is produced during the food-rich seasons and expended during
cold seasons. This is also the kind of fat that most hibernators use for arousal and many migrators
use for fuel.
Various "heat exchange" mechanisms can be found in animal circulatory systems that reduce heat
loss to body extremities.
Certain fish and herptiles produce chemicals within and between cell walls that can lower their
freezing temperature a few degrees. In sheltered environmental niches, these few degrees can
mean the difference between life and death.
Some mammals, such as flying squirrels and small rodents, will occupy collective dens to conserve
body heat, even though some species are non-colonial during the warm season. This is part of the
reason that some species of snakes will do the same thing.
Food preferences change with the season. Some browsers, such as white-tailed deer, have
changes in digestive enzymes to cope with the different food sources. This is one of the reasons
why biologists argue against winter deer feeding. If not done correctly, a deer can starve to death
with a belly full of corn.
Ruffed grouse "snow roost" during periods of extreme cold. Snow provides a very effective barrier
against severe cold. They will rest under the snow until the severe weather passes. Folks who
snowshoe or cross-country ski too close to these snow roosts are often caught off-guard when a
grouse explodes out of the snow. Large piles of grouse droppings are spring-time indicators of how
severe the winter was.
Aquatic mammals, such as otter and mink, grow thick layers of insulating fat and have specialized
fur. Similarly, ducks, geese, and swans have feathers and oil glands that keep water away from the
skin. Some have efficient circulatory heat exchangers between the body and the feet. It's usually
not the cold that causes waterfowl to migrate. It's more a matter of food shortages.
Birds and mammals undergo seasonal changes in feathers and pelage. Trappers know that winter
pelts are the highest quality because they are thicker and have different kinds of hair.
Muskrats and beaver construct shelters, partly for protection from severe weather. A number of
animals dig burrows, such as groundhogs, foxes, chipmunks, and moles.
Many species of birds can adjust their internal body temperature downward to reduce the
temperature gradient with environmental temperatures, thus reducing heat loss. They also tend to
shiver a lot to maintain body temperatures.
developed and created by Michigan State University Extension for the teachers of the State of
Michigan. The website is maintained by the Delta-Schoolcraft Independent School District in support of
the Michigan Forests Forever CD-ROM from the Michigan Forest Resource Alliance.
Three Levels of Biodiversity
Genetic Diversity | Species Diversity | Ecosystem Diversity
Researchers generally accept three levels of biodiversity: 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. The following parts will cover all levels of
diversity, though examples will generally use the species level.
Genetic Diversity
What is it?
Genetic diversity is the variety present at the level of genes. Genes, made of DNA
(right), are the building blocks that determine how an organism will develop and
what its traits and abilities will be. This level of diversity can differ by alleles (different
variants of the same gene, such as blue or brown eyes), by entire genes (which
determine traits, such as the ability to metabolize a particular substance), or by units
larger than genes such as chromosomal structure.
Genetic diversity can be measured at many different levels, including population,
species, community, and biome. Which level is used depends upon what is being
examined and why, but genetic diversity is important at each of these levels.
Why is it important?
The amount of diversity at the genetic level is important because it represents the
raw material for evolution and adaptation. More genetic diversity in a species or
population means a greater ability for some of the individuals in it to adapt to
changes in the environment. Less diversity leads to uniformity, which is a problem in
the long term, as it is unlikely that any individual in the population would be able to
adapt to changing conditions. As an example, modern agricultural practices use monocultures, which are
large cultures of genetically identical plants. This is an advantage when is comes to growing and
harvesting crops, but can be a problem when a disease or parasite attacks the field, as every plant in the
field will be susceptible. Monocultures are also unable to deal well with changing conditions.
What is it related to?
Within species, genetic diversity often increases with environmental variability, which can be expected. If
the environment often changes, different genes will have an advantage at different times or places. In this
situation genetic diversity remains high because many genes are in the population at any given time. If the
environment didn't change, then the small number of genes that had an advantage in that unchanging
environment would spread at the cost of the others, causing a drop in genetic diversity.
In communities, it can increase with the diversity of species. How much it increases depends not only on
the number of species, but also on how closely related the species are. Species that are closely related
(e.g. two species of maple) have similar genetic structures and makeup and therefore do not contribute
much additional genetic diversity. These closely-related species will contribute to genetic diversity in the
community less than more remotely-related species (e.g. a maple and a pine) would.
An increase in species diversity can also affect the genetic diversity, and do so differently at different
levels. If there are many species, the genetic diversity at that level will be larger than when there are fewer
species. On the other hand, genetic diversity within each species can decrease. This can happen if the
large number of species means so much competition that each species must be extremely specialized,
such as only eating a single type of food. If they are so specialized, this specialization will lead to little
genetic diversity within any of the species.
Species Diversity
Biodiversity studies typically focus on species. They do so not because
species diversity is more important than the other two types, but because
species diversity is easier to work with. Species are relatively easy to identify
by eye in the field, whereas genetic diversity (above) requires laboratories,
time and resources to identify and ecosystem diversity (see below) needs many complex measurements to
be taken over a long period of time. Species are also easier to conceptualize and have been the basis of
much of the evolutionary and ecological research that biodiversity draws on.
Species are well known and are distinct units of diversity. Each species can be considered to have a
particular "role" in the ecosystem, so the addition or loss of single species may have consequences for the
system as a whole. Conservation efforts often begin with the recognition that a species is endangered in
some way, and a change in the number of species in an ecosystem is a readily obtainable and easily
comprehensible measure of how healthy the ecosystem is.
For more information on the species level of biodiversity, visit the Redpath Museum's Biodiversity of
Quebec website (link will open in a new browser window).
Ecosystem Diversity
Ecosystem-level theory deals with species distributions and community
patterns, the role and function of key species, and combines species functions
and interactions. The term "ecosystem" here represents all levels greater than
species: associations, communities, ecosystems, and the like. Different names
are used for this level and it is sometimes divided into several different levels,
such as community and ecosystem levels; all these levels are included in this
overview. This is the least-understood level of the three described here due to
the complexity of the interactions. Trying to understand all the species in an
ecosystem and how they affect each other and their surroundings while at the
same time being affected themselves, is extremely complex.
One of the difficulties in examining communities is that the transitions between
them are usually not very sharp. A lake may have a very sharp boundary
between it and the deciduous forest it is in, but the deciduous forest will shift
much more gradually to grasslands or to a coniferous forest. This lack of sharp
boundaries is known as "open communities" (as opposed to "closed
communities," which would have sudden transitions) and makes studying
ecosystems difficult, since even defining and delimiting them can be
problematic.
Some researchers think of communities as simply the sum of their species and
processes, and don't think that any of the properties found in communities are
special to that level. Many others disagree, claiming that many of the characteristics of communities are
unique and cannot be extrapolated from the species level. Examples of these characteristics include the
levels of the food chain and the species at each of those levels, guilds (species in a community that are
functionally similar), and other interactions.
Gaining and Losing Biodiversity
Island biogeograpy | Measuring diversity | Gaining biodiversity | Losing biodiversity
Globally, diversity naturally has increased over time, though the great mass extinctions have decreased it
for a while. The most famous of the mass extinctions is the one that claimed the dinosaurs, but we are
currently in the midst of a human-created mass extinction. Local diversity, on the other hand, is constantly
increasing and decreasing at very short time scales. There are many factors that affect diversity, and the
major natural circumstances are given here. Human-generated impacts on diversity have almost always
been negative, and are covered in the Conservation Issues section.
Island Biogeography
One of the first major theories of biodiversity, the theory of island biogeography, formulated by R.
MacArthur and E.O. Wilson applies to the patterns of diversity found on islands. In it, islands start out
empty of species, who arrive from a large area (referred to as the mainland, though it doesn't have to
actually be a continent) and from neighbouring islands.
The chance that a species will land on the island depends mostly on
the distance that the island is from the mainland; the greater the
distance the less often a species will find its way to the island. In the
figure to the right, island A is closer to the mainland than island B, and
more species find their way to it. Species on smaller islands have
smaller populations, making them more vulnerable to extinction. The
number of species present on the island is a balance between the rate
at which new species arrive and old species go extinct on the island.
This theory is neutral, meaning that all species are considered to be equal. In reality, some species are
better at dispersing than others and are thus more likely to be found on islands. The exact species that are
actually present has been found to be fairly random, though, and the theory does a good job of predicting
the number of species to be found. What the theory calls islands doesn't have to be actual islands; lakes
are effectively islands, as are isolated patches of habitat, and the theory has been extended to deal with
peninsulas, bays, and other only partially isolated areas.
Measuring Diversity
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:
It is possible to measure how many species are found in an area, or how
many alleles (defined above) a species has for a single locus, or how many
functional groups (defined below) 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.
Evenness:
Area 1
If almost every individual in an area is from the same 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. How to represent even these
two components as a single number has been controversial (see Magurran
1988 and Smith and Wilson 1996 for examples of indices and the
controversy), and the number of different abundance indices is large,
although certain ones (the Shannon and Simpson indices, for instance) are
far more commonly used than others.
Area 2
Difference:
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
Three sample areas are given to the above right, each of which is most
diverse in a different way. The top area (area 1) has the greatest number of
species, four in total. But half of the individuals in the sample are from the same species. The middle area
(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. The bottom area (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.
Gaining Biodiversity
Mutation
Mutations increase genetic diversity by altering the genetic material (almost always DNA) of organisms.
Once mutations arise, they are passed on to the mutated organism's offspring, and in time may either
disappear if the line dies out. Depending upon the specific mutation, the result can range from no effect
whatsoever to the creation of an entirely new species. Although this gives rise to differences in organisms,
it is an extremely slow process compared to the other ways in which local diversity increases. Ultimately,
though, this is the only way in which diversity is truly created.
Speciation
The creation of a new species is known as speciation. Species are typically defined as being unable to
successfully breed with other species (the so-called Biological Species Concept), although there are other
ways of defining species. The origin of new species naturally has the largest immediate effect on specieslevel diversity; the immediate changes to genetic and ecosystem diversity are usually minimal, though the
effects will grow in time. Speciation can occur through several different means, including geographical
isolation, competition, and polyploidy. These are described below.
Geographical Isolation: Geographical isolation, such as new mountain chains or a lake whose level
lowers enough that it splits into two separate lakes, can divide a population into two separate populations.
The two isolated populations continue to evolve separately from one another. Eventually they can diverge
to a great enough degree, either through adaptation to their differing environments or through random
mutations, that they are no longer able to interbreed and are considered to be different species.
Competition: If a new resource, such as a new food source, becomes available to a population, some part
of the population may become specialized in obtaining that resource. Being specialized in obtaining either
the new resource or the original resource may be better than trying to obtain both. If so, then the specialists
would be better off mating with the other specialists on the same resource, as mating with someone who
uses the other resources will result in offspring that aren't specialized for either resource and at a
disadvantage. In time, there is a chance that the population will split into two species, each specialized on
one of the two resources. This can happen, but it is probably a fairly rare event.
Polyploidy: Speciation through polyploidy happens far more often in plants than in animals, as animals are
much more sensitive to large changes in their genetic structure. Most species are diploid, meaning they
have two ("di" meaning two) copies of each chromosome (large packages of DNA), one from each of their
parents. An individual in a normally diploid species may have more copies of these chromosomes, being
polyploid ("poly" meaning many), through errors at the cellular level. The additional copies of the
chromosomes render them unable to produce functional offspring with normal members of their species.
Plants often fertilize themselves to at least some extent, so polyploid species can arise from a single
individual. This method of speciation is almost instantaneous, happening in a single generation, and is
more common in plants than animals.
Immigration
Immigration increases diversity as new individuals and perhaps even new
species enter an area, increasing its diversity. The rate at which immigration
happens depends on the size of the area in question, how many species are
there already, and how close the area in question is to the source of
immigration. Even if a species is unable to survive in an area, a constant flow
of immigrants to the area can keep the species present indefinitely. Island
biogeography is the classic theory on the topic of how these factors affect
immigration and more, and is explained above.
Most species that immigrate to a new ecosystem have only minor effects on
their new system, though some drastically change it. Zebra mussels, native to
the Caspian Sea and Ural river, were first recognized in the Great Lakes in
1988. It is most likely that they were brought over in ballast water. Since then
they have spread throughout the Great Lakes and beyond, killing native
mussel populations and fouling all manner of pipes and intakes.
Succession
Succession is the process through which an area gains species as successive communities of organisms
replace one another until an endpoint is reached. This endpoint, or climax community, is commonly a forest
in southern Canada. Succession may begin on bare rock, an abandoned field, the burned remnants of a
forest, or any stage before the endpoint. A hypothetical bare field isn't bare for long before annual plants
appear. They are replaced within a few years by perennial plants and shrubs, who in turn are replaced by
pine trees. Eventually, hardwood trees invade and replace the pines, forming the hardwood climax
community.
Different regions have varying climax communities; the tundra of the north is extremely different from the
grasslands of the prairies or the west coast rainforests, though they are all the local endpoints of
succession. One usually refers to the different stages of succession in terms of the plants rather than the
animals because the plants precede the animals and provide the structure and environment that the
animals live in. One exception to this is aquatic communities, where sponges, corals, bivalves and other
animals are responsible for much of the three-dimensional structure of the community. The climax
community is typically the most diverse stage of succession, and each stage of succession is more diverse
than the one preceding it. This pattern depends on the group being looked at; plant diversity actually
decreases at the final stage, while animal diversity increases to the end. Species that were common in the
early stages of succession will not be common in the later stages, but may still be found if small
disturbances in the area effectively set the disturbed area back to an earlier successional stage (see the
page on Abundance and Composition for more details).
Losing Diversity
Extinction
Extinction is more an outcome than a process. Once a species goes extinct, all the
diversity that it represented is lost forever. The vast majority of species that have
ever existed are now extinct through natural processes, whether by mass extinction
or by the more common individual extinction. Genes also go extinct if they fail to get
passed on to the next generation, though it's not necessary for the entire species to
go extinct as well. Ecosystems may be destroyed by severe disturbances, but they
don't really go extinct unless the species that make them up are lost.
Species can also go locally extinct; in this case, they are said to be extirpated.
Although the local loss of diversity is the same, the species still exists elsewhere
and may be able to return in the future through immigration. Much the same thing
can happen to genetic diversity, as particular alleles are lost in a population.
Competition
If one species outcompetes others to a dramatic extent, the result may be extirpation or perhaps even
extinction of the other species and a reduction of diversity. Diversity, in the sense of evenness, will also be
lowered if other species have their populations greatly reduced by a competitor or predator, even if the
species aren't extirpated. As species that have been eliminated simply aren't around, it's rare to see this
process happening unless a species has recently invaded or conditions have recently changed.
Disturbances
Disturbances can maintain diversity (see Abundance and Composition, below), but extremes can reduce
diversity. Constant large-scale disturbance can eliminate many populations and keeps an area at the early
levels of succession, which have lower diversity (see above). An area with no disturbances at all would end
up completely at the final stage of succession. This would prevent the presence of the species that would
normally be found at intermediate stages of succession, living in the disturbed areas.
Bottlenecks
Genetic bottlenecks happen when many
individuals in a population die. In the example to
the right, the population initially has many
different types of shapes and colours,
representing genetic diversity (A). The few
individuals that are left after most die (B) have a
small amount of the genetic diversity that
originally existed, as much of the genetic diversity was lost with the rest of the population. Although the
population's numbers quickly recover (C), the genetic diversity is much slower to respond, which can cause
problems if conditions change in the future, as the reserves of diversity that would be useful won't be there.
Abundance and Composition
Why do we have so many species? | Variable Environments | Niches | Keystone Species |
Catastrophes | Chance
In addition to diversity increasing and decreasing, it can also change by alterations in the relative numbers
of individuals in species or by the particular species that are present. Understanding how the specific
species and numbers present got there and interact is the focus of this section. In addition to two
theoretical techniques that are used to work out how diversity takes shape, some of the known ways in
which abundance and composition are affected are covered.
Why do we have so many species?
One question that comes up when dealing with biodiversity is why there are so many species in the first
place. Why doesn't a single species outcompete and eliminate the rest? The answer is that no species can
be perfect at everything; it must instead make trade-offs between different abilities, and the species that we
see around us are the results of these different trade-offs. Characteristics that are traded off include the
ability to compete vs. the ability to disperse offspring; being able to thrive in average conditions vs. being
able to take advantage of sudden pulses of resources; and being able to compete for different resources in
a varying landscape. So many species exist because they all have different niches.
Variable Environments
If the environment varies in some way, then species that are
specialized to those variations should be found there, allowing
more species to exist in an area as the variation increases.
Variation provides the new niches for species. For variations in
space, such as bare rock or marshy areas, specialized species
will be found in those areas. Three-dimensional structures, such
as trees or kelp beds, also provide more variation and let more
species coexist. If the variation is in time, such as seasons,
diversity will be different at different times. For example, spring
ephemerals (plants that grow in the short period in spring before
trees produce leaves and reduce the light) will only be found in
early spring, and only if they can obtain enough light in the early spring.
Niches
A niche is the "role" of a species in a community, and can be defined as the conditions in which the species
can survive or the way of life that it follows. An example of a simple niche description could be "large
grazing herbivore." Based on the diversity-production patterns that have been observed, niche
differentiation is the rule, meaning that species tend to find niches in which they can avoid competition
rather than engaging in direct competition with other species for resources. When two species share the
same niche, one will eliminate the other by outcompeting it.
Niche Packing
One approach to understanding the number of species and their relative abundance is called "niche
packing". Any ecosystem has a limited amount of resources, and it is assumed that there are rules about
how the resources can be used. The rules deciding how the resources are allocated to species and the
species fit into their niches (i.e. how the niches are packed) determines how many species can exist in the
system and how abundant each species is. Each species is added to the system one by one, with each
species following the same rules. Rules include whether new species invade already occupied niches or
only unused niches, or whether the size of the niche makes a difference to its chance of being invaded.
In the illustration to the right, each bar represents the total resources available to the community. Each
colour represents a different species, with the amount of colour reflecting the
number of individuals of the species. The two bars have been filled with the
same number of species, but by using different rules, and the species reside in niches of various sizes.
One species, represented by the red, dominates the bottom system, while in the top one it is only slightly
more abundant than the species represented by yellow and orange.
Niche packing is studied in two ways. The first is by examining how species are packed in nature and
trying to come up with the rules that most closely match reality. The second is by deciding how the niches
are packed by various theories and them comparing the results to reality. Both approaches have the
problem that the rules that generate the patterns may create the same patterns found in nature without
being the actual rules followed by species.
Assembly Rules
Assembly rules look at why certain types of species are found together in a community by beginning with a
theoretical community with no species and adding species one by one according to certain rules. This
approach differs from niche packing by focusing on the niches that have already been filled rather than
only the sizes of the niches that species occupy. Diffuse competition, the competition faced by a species by
several other, usually closely related, species is very important in this approach, as every new species is
treated as an invader and has to be able to fit into an already crowded community.
Which type of species is added next depends upon what type of species are already present and which
rules are being followed. One common rule in these models says that the niches of new species added to
the community should be as different as possible from those of the species already present. Similar areas
will not necessarily have the same species, as the order that they appear in will affect which other species
may successfully invade. By comparing the results from the models to the patterns seen in nature, insights
into how communities form can be gained.
Keystone Species
Keystone species are species that are more important to an ecosystem than one would expect based on
their abundance. This importance comes from their niches and interactions affecting the system as a
whole, rather than only affecting the species that they directly interact with. Removing or adding keystone
species to a community can result in enormous changes to the rest of the community through the effects
they have on other species. The resulting cascade of interactions can have drastic effects on the
ecosystem.
One of the better-known keystone species is the sea otter,
Enhydralutris. They are found in the waters off the west
coast, where one of their main prey species are sea urchins.
Sea urchins, in turn, eat algae such as kelp. By keeping the
population of sea urchins low, the otters indirectly let kelp
flourish. An increase in kelp coincides with a decrease in
barnacles, mussels, and chitons. Fish species that can use
the kelp for cover increase, and other species also take
advantage of the structured environment. Rock greenlings, harbour seals and bald eagles are more
common in areas with sea otters. When sea otters were removed from some areas, the sea urchins and
other herbivores quickly managed to severely reduce the kelp, allowing barnacles and mussels to flourish
at the cost of other species.
An example of a keystone species found throughout Canada is the beaver. Beavers modify large amounts
of land through the flooding caused by their dams. While the dams are being actively used by the beavers
ponds and lakes are formed, allowing many aquatic species to thrive. Once the pond fills with sediment,
succession (see Gaining and Losing Diversity in this section) begins. If beavers are removed from an area,
many species that live in the ponds caused by beavers would drop in numbers or go locally extinct.
Catastrophes
Disturbances and catastrophes change which species are found in an ecosystem and their relative
abundance. By disturbing the system, the catastrophe mostly effects the current stage of succession and
effectively sets the disturbed section into an earlier successional stage. This reduces the uniformity of
succession and allows plants and animals who would not be present in the final stage of succession to
persist in the system.
When species from earlier stages are present, diversity increases. They also allow succession to occur at
a faster rate, as the species that are needed for a given stage are relatively nearby in other recently
disturbed areas.
Chance
Lastly, random chance can play a very important role in determining composition and abundance in an
ecosystem. The order in which species show up can determine which one makes the dominant tree
species in the forest, for example (see Assembly Rules, above). An insect species that is specialized on a
particular host plant will usually go extinct if the host species does, no matter how well-adapted and
otherwise successful it is. If the insect had lived on another plant species, it would not have gone
extinct.
Poor conditions can make the difference for a species that is not very abundant, whether it is an
invader or a struggling species that has been in the area for a long time. A particularly wet year is good for
mushrooms, while a dry year is bad for them. What kind of first year it experiences in a new territory can
make the difference between an invading species of mushroom flourishing or failing.
Diversity and Ecosystem Functions
There are many theories about how the number of species affects ecosystem
functions. One of these is the redundancy hypothesis, shown to the right, which
assumes that the rate of ecosystem functions increases as more species are
present, but only up to a point. After this point, more species are redundant and
do not have any additional effect on ecosystem functions. In this theory the loss
of species has no initial effect, but after a certain point functions begin to suffer.
In the figure to the right, three possible patterns of increasing function as related
to diversity are shown.
Another theory, the rivet hypothesis, shown to the right, claims that each species
added to an ecosystem increases ecosystem functions, although the increase in
function may increase more slowly as more species are included. In this model
any loss of diversity should be noticeable.
Opposed to theories that assume a definite relationship between diversity and
ecosystem functions is the idea that there is no fixed relationship, and that the
functions of an ecosystem are the result of what the interactions between species
are. In this case what is important is not how many species are present but which
species are present together and what environment they are in. The figure to the
right shows just one of the possible relationships between ecosystem function and diversity according to
this hypothesis.
Which of these theories is most accurate is not certain, given the problems of scale and the complexity of
the measurements. The Rivet Hypothesis looks like a small scale (on the figures above, the leftmost part)
of the Redundancy Hypothesis, so it may be difficult to tell the two apart at the relatively small scale that
most studies are done.
Species Extinction and Endangered Species
Georgia is home to more than 4,000 species of native or naturalized vascular plants and vertebrate
animals. At least 10 percent of these species are in danger of extinction. The chief factor in the loss of
biodiversity in Georgia is loss or deterioration of habitat.
Extinction and Extermination
Conservation biologists indicate that as many
as half of the earth's plants and animals may be in danger of becoming extinct by
the twenty-second century. They estimate that for every new species that emerges
from the process of evolution, thousands become extinct. This rate of extinction
is thought to be even greater than that of 65 million years ago, during the period
in which dinosaurs disappeared from the planet.
The exact number of organisms on the earth is unknown, and estimates range
from 5 million to more than 50 million. Only about 1.4 million organisms have
been classified and named by taxonomists. But species are not distributed evenly on our planet. Indeed,
more than half of the world's known biodiversity (biological diversity) can be found in less than 2
percent of the world's land surface. In the United States roughly one-third of our flora and fauna is
considered to be of conservation concern.
Pigeon Mountain Salamander
Species extinction is a naturally occurring event, the inevitable outcome of changing environments and
evolutionary processes.
However, the current episode of accelerated species extinction is notable for the
fact that it is driven primarily by human activities. Plants and animals are being
hastened to extinction by direct or indirect effects of mineral extraction, road
construction, residential and industrial development, and intensive agricultural,
forestry, and fishery practices. Other human activities that accelerate species
extinction include introduction of nonnative species, poaching, and illegal trade
Etowah Darter
in rare species.
Extermination usually refers to the deliberate destruction of populations of a given species. Examples
from the southeastern United States include the complete elimination of the Carolina parakeet and
passenger pigeon as a result of unregulated hunting, and the loss of nearly all Florida panther and red
wolf populations, which is partly attributed to predator-control programs. These and many other
examples of catastrophic species decline have demonstrated that the continued destruction of local
populations leads to species extinction.
Biodiversity Trends
Of Georgia's more than 4,000 species of native or naturalized vascular plants and
vertebrate animals,
32 species are known to be endemic to the state (i.e., restricted in their range of
distribution to Georgia alone). Examples of species endemic to Georgia include:
(1) the Etowah darter (Etheostomaetowahae), a fish restricted to the upper
reaches of the Etowah River (Coosa River basin) in Georgia; (2) hairy
rattleweed (Baptisiaarachnifera), a plant in the legume family found in pine
flatwoods habitats in scattered locations in Wayne and Brantley counties; and
(3) the Pigeon Mountain salamander (Plethodonpetraeus), found only on the
eastern slopes of Pigeon Mountain in northwestern Georgia.
Hairy Rattleweed
Approximately 440 species of vascular plants and vertebrate animals in Georgia are considered to be of
critical conservation concern. In addition, 60 species of invertebrate animals and 12 species of
nonvascular plants tracked by the Georgia Natural Heritage Program (a program of the Georgia
Department of Natural Resources) are considered imperiled. Many other species of invertebrates and
nonvascular plants may be in danger of extinction but have not yet received sufficient attention from
field biologists or taxonomists for a clear determination to be made.
Species previously found in Georgia and known to be extinct today include the Carolina parakeet and the
passenger pigeon. Species considered close to extinction or possibly extinct include two birds (the
ivory-billed woodpecker and Bachman's warbler), several freshwater mussels (the upland combshell,
Ochlockoneearcmussel, fine-lined pocketbook, winged spike, and southern acornshell), and a number of
plants (the roundleaf leafy liverwort, Porter's goldenrod, and Georgia beaksedge). Many more species
are presumed extirpated from the state.
Land Use Change and Habitat Loss
The most significant factor contributing to the loss of biological diversity is the destruction or
degradation of natural habitats. The rapid loss of native species populations is correlated with a
burgeoning human population, rising per capita consumption of natural resources, and technological
advances that increase the rate of habitat destruction.
Urban and suburban development has contributed greatly to habitat loss in Georgia. From 1992 to 1997
approximately 1,053,200 acres in Georgia were converted from open space to developed land;
Mat-forming Quillwort
this represents the third largest loss of undeveloped acreage in the nation. From
1990 to 2000 Georgia's human population increased by 26 percent, the sixth
fastest rate of growth in the nation. In the metropolitan Atlanta area 350,000
acres of forestland were lost to development from 1973 to 1998. This trend can
be seen in many other states in the Southeast. In fact, five of the ten major U.S.
cities with the worst suburban sprawl problems are in the South: Nashville and
Memphis, Tennessee; Charlotte and Greensboro, North Carolina; and Atlanta.
Increasing human population combined with sprawling development patterns has lead to rapid loss of
both terrestrial and aquatic habitats. In addition to direct mortality associated with destruction or
degradation of habitats, the long-term effects of habitat fragmentation on populations can include higher
levels of parasitism or predation, increased competition from "weedy" species, reduced genetic diversity,
and greater vulnerability to natural catastrophes. In other words, those populations not wiped out directly
by habitat destruction are often left weakened and vulnerable from habitat fragmentation.
What Can Be Done?
Many scientists believe that the first half of the twenty-first century will be a critical period in the fight
to protect our remaining biological resources. Projections indicate that the earth's human population may
eventually level off at between 8 to 9 billion. (The world population in 2003 was more than 6 billion.) If
humans can curb their excessive consumption of natural resources and place greater emphasis on
protection, restoration, and maintenance of the earth's remaining natural habitats, they may be able to
salvage much of the earth's remaining biological diversity. However, the most optimistic predictions
indicate a loss of hundreds of thousands of species by that time. The following initiatives are critical to
protection of the world's natural heritage: (1) increased emphasis on biological inventories, focusing on
the identification and description of species, biotic communities, and ecosystems; (2) greater
commitment of human, financial, and technological resources to identify and protect those natural
habitats that contribute most significantly to global biodiversity; (3) further development and funding of
conservation programs that emphasize public-private partnerships for broad-scale conservation of
"working landscapes"; (4) greater emphasis on land-use planning to minimize impacts of future
developments on natural habitats; (5) increased collaboration between researchers and educators to
heighten public awareness of the magnitude and significance of global biodiversity decline; and (6)
recognition of biodiversity protection as a global priority, and incorporation of this goal as a key
component in international treaties and trade agreements.
Suggested Reading
Linda G. Chafin, A Field Guide to the Rare Plants of Georgia (Athens: University of Georgia Press,
2007).
Whit Gibbons, Keeping All the Pieces: Perspectives on Natural History and the Environment
(Washington, D.C.: Smithsonian Institution Press, 1993).
Bruce A. Stein, Lynn S. Kutner, and Jonathan S. Adams, eds., Precious Heritage: The Status of
Biodiversity in the United States (New York: Oxford University Press, 2000).
U.S. Geological Survey, Status and Trends of the Nation's Biological Resources (Washington, D.C.:
U.S. Government Printing Office, 1998).
Edward O. Wilson, ed., Biodiversity (Washington, D.C.: National Academy Press, 1988).
Jonathan Ambrose, Georgia Department of Natural Resources
Hunter Education Requirements
Residents and non-residents born on or after January 1, 1961 must successfully complete a hunter education course prior to purchasing
a season hunting license. However, a hunter education course is not required to purchase an Apprentice License or a three (3) day
Combo Hunting/Fishing License. Hunter education courses certified or mandated by any state wildlife agency or Canadian province are
accepted. Hunter Education is not required to hunt on one's own land or land of a parent or guardian. Course options include a FREE
classroom course, a FREE CD-ROM course or three online courses (with varying fees). Students may request a copy of the FREE CDROM from any Game Management or Law Enforcement office.
Hunters Under Age 12
Hunters under age 12 are not required to complete a hunter education course. However, no one under age 12 may hunt unless under direct
supervision, i.e. within sight or hearing of licensed adult (at least 18 years old) hunter. It is unlawful for an adult to permit their child or ward
under age 12 to hunt unsupervised. Special restrictions apply to Wildlife Management Areas (WMA's) &National Wildlife Refuges (NWR's).
Hunters Age 12 - 15
Must complete a hunter education course prior to hunting unless under direct supervision of a licensed adult hunter. It is unlawful for an adult
to permit their child or ward (12-15) to hunt without adult supervision unless the child possesses a hunter education certificate while hunting.
See other special rules for WMA's.
Hunters Age 16 - 25
Must present a hunter education certificate when purchasing a season hunting license and must possess the certificate while hunting.
Hunters Over Age 25
Hunters over age 25 and born after January 1, 1961 must meet hunter education course requirements but need not present their hunter
education certificate when buying a season hunting license or possess it while hunting.
Resource: http://georgiawildlife.com/node/659?cat=1
HIPPO
Many different factors contribute to the destruction of biodiversity on Earth. Scientists have come up with a list of factors that can
be summarized by the acronym "HIPPO":
H=
Habitat Destruction
I=
Introduced Species
P=
Pollution
P=
Population Growth
O=
Over-consumption
Habitat Destruction
From clear cutting ancient forests in the Pacific Northwest to the pollution that runs into our streams,
human activity has had devastating effects on many habitats around the world. Habitat destruction along with introduced species - pose the most threats to biodiversity.
Introduced Species
Due to the delicate balance of nature, when a new plant or animal is taken from its natural environment
and introduced into a new ecosystem, the effects can be drastic. Some native plants and animals are
decimated while others may flourish to higher-than-average levels due to the new introduced species.
Humans sometimes introduce new species into an environment by accident. For instance, the European zebra mussels hitched
rides on cargo and cruise ships and now pose a great threat to the health of the Great Lakes and other northeastern United
States lakes. Native mussels have been nearly eliminated from the western basin of Lake Erie by the zebra mussels.
In Washington state, there are currently over 200 species of "exotic" plants and trees that threaten the plants and animals native
to the state.
Pollution
Pesticides, oils, heavy metals and common household chemicals run off into our waterways and affect the salmon and other
wildlife in Washington state.
Population Growth
With the world's population estimated to double within the next 12 years, more people means increased use of natural
resources, possible increase in habitat destruction and more waste generated.
Over-consumption
Although the United States accounts for less than 5% of the world's population, Americans consume over 25% of the world's
resources. We use more natural resources and produce more waste per capita than any other nation.