THE COMMUNITIES

Do u know about community in the living world

That part of an ecosystem that is living, all the animals and plants and other organisms that live together in an area, is called a community. The countless number of species that inhabit a rain forest or the sparse number of species that live in the boiling waters of a hot spring make up a community. Indeed, every inhabited place on earth supports its own particular array of organisms. Over time,
the different species have made many complex adjustments to community living, evolving together and forging relationships that give the community character and stability. Both competition and cooperation have played key roles in molding these communities. The magnificent redwood forest, shown  that extends along the coast of central and northern California and into the southwestern corner of Oregon is an example of a community. Within it, the most obvious organisms are the redwood trees, Sequoia sempervirens. These trees are the sole survivors of a genus that was once distributed through-out much of the Northern Hemisphere. A number of other plants, like the redwood sorrel flower  and the sword fern and animals, like the ground beetle feeding on a slugare regularly associated with redwood trees. Their coexistence is in part made possible by the special conditions the redwood trees themselves create, providing shade, water (dripping from the branches), and relatively cool temperatures. This particular distinctive assemblage of organisms is called the redwood community. The organisms characteristic of this community have each had a complex and unique evolutionary history. They evolved at different times in the past and then came to be associated with the redwoods.

We recognize this community mainly because of the redwood trees, and its boundaries are determined by the redwood's distribution. The distributions of the other organisms in the redwood community may differ a good deal. Some organisms may not be distributed as widely as the redwoods, and some may be distributed over a broader range. In the redwood community or any other community, the ranges of the different organisms overlap; that is why they occur together. Many communities are very similar in species com-position and appearance over wide areas. For example, the open savanna that stretches across much of Africa includes many plant and animal species that coexist over thousands of square kilometers. Interactions between these organisms occur in a similar manner throughout these grassland communities, and some interactions have evolved over millions of years. 

ECOLOGY

How we can clarified about ecology

Darwin's finches teach us an important lesson about evolution, which is that understanding how natural selection occurs is really a matter of understanding how species adapt to particular niches. As we saw on the preceding pages, the diversity of finches Darwin found on the Galapagos Islands arose as a consequence of the availability of a variety of niches on the islands, each fostering the evolution of a new finch species. In a very real sense, the nature of the habitats the finches invaded, and the ways in which different populations of finches came to utilize these habitats, determined the course of the evolutionary radiation that followed. Biologists who study the nature of niches, and how the species that occupy them inter-act, are called ecologists. The word ecology was coined in 1866 by the great Ger-man biologist Ernst Haeckel to describe the study of how organisms interact with each other and with their environment. It comes from the Greek words oikos (house, place where one lives) and logos (study of). Our study of ecology, then, is a study of the house in which we live. Do not forget this simple analogy built into the word ecology—most of our environmental problems could be avoided if we treated the world in which we live the same way we treat our own homes. Would you pollute your own house?

Easy Guide To Know Levels of Ecological Organization

 Ecologists consider groups of organisms at five progressively more encompassing levels of organization.

 1. Populations.Individuals of the same species that live together are members of a population. 'they potentially interbreed with one another, share the same habitat, and use the same pool of resources the habitat provides.

2. Communities. Populations of different species that live together in the same place are called communities. Different species typically use different resources within the habitat they share.

3. Ecosystems. A community and the nonliving factors with which it interacts is called an ecosystem. An ecosystem is affected by the flow of energy, ultimately derived from the sun. and the cycling of the essential elements on which the lives of its constituent organisms depend. The Galapagos Islands pictured in figure 2.13 are an ecosystem, where the giant tortoise and other organisms interact with each other and with their biological and physical surroundings.

4. Biomes. Biomes are major terrestrial assemblages of plants, animals, and microorganisms that occur over wide geographical areas that have distinct physical characteristics. Examples include deserts. tropical forests, and grasslands. Similar groupings occur in marine and freshwater habitats.


5. The biosphere. All the world's biomes. along with its marine and freshwater assemblages, together constitute an interactive system we call the biosphere. Changes in one biome can have profound consequences for others.

Some ecologists, called population ecologists, focus on a particular species and how its populations grow. Other ecologists, called community ecologists, study how the dif-ferent species living in a place interact with one another. Still other ecologists, called systems ecologists. are interested in how biological communities interact with their physical environment.

DIFFERENT NICHES WITHIN ANECOSYSTEM

How species evolve to occupy different niches within anecosystem

Each organism in an ecosystem confronts the challenge of survival in a different way. As we have just discussed, the niche an organism occupies is the sum total of all the ways it uses the resources of its environment, and may be described in terms of space utilization, food consumption, temperature range, appropriate conditions for mating, requirements for moisture, and other factors. Niche is not synonymous with habitat, the place where an organism lives. Habitat is a place, and niche is a pat-tern of living. Many species can share a habitat, but as we shall see, no two species can long occupy exactly the same niche.

Competition is the struggle of two organisms to use the same resource when there is not enough of the resource to satisfy both. When two species compete for the same resource, the species that utilizes the resource more efficiently will eventually out-compete the other in that location and drive it to extinction there. Ecologists call this the principle of competitive exclusion: no two species with the same niche can coexist. Persistent competition between two species is rare in nature. Either one species drives the other to extinction, or natural selection favors changes that reduce the competition between them. In resource partitioning, species that live in the same geographical area avoid competition by living in different portions of the habitat or by using different food or other resources. The rather exotic blue species in the upper left of the figure lives high in the tree, where it doesn't need to compete for food and space with the dark brown species in the upper right that lives on the tree's trunk.











The changes that evolve in two species to reduce niche overlap—that is, to lessen the degree to which they compete for the same resources—arc called character displacements. Character displacement can be seen clearly among Darwin's finches. The two Galapagos finches have beaks of similar size when each is living on an island where the other does not occur. On islands where they am found living together, the two species have evolved beaks of different sizes, one adapted to larger seeds, the other to smaller ones. In essence, the two finches have subdivided the food niche, creating two new smaller niches. By partitioning the available food resourc

es, the two species have avoided direct competition with each other, and so are able to live together in the same habitat.

THE NICHE AND COMPETITION

How to easy learn to study The niche and competition

The niche concept

Within a community, each organism occupies a particular bio-logical role, or niche. The niche an organism occupies is the sum total of all the ways it uses the resources of its environment, including space, food, and many other factors of the environment. A niche is a pattern of living. The zebras you see in the African savanna community  occupy a complex niche featuring open grassland and seasonal migration when food and water become scarce in dry seasons. Sometimes organisms are not able to occupy theirentirc niche because some other organism is using it. We call such situations, when two organisms attempt to use the same resource, competition. Competition is the struggle of two organisms to use the same resource when them is not enough of the resource to satisfy both. However, just because two species occur in the same community and appear to use similar resources does not necessarily mean that they compete. Wildebeests also graze in the savanna alongside zebras, eating the same grass and drinking the same water, but for migrating herds these resources are not scarce. The lives of these two species differ in many other ways important to their survival so that they are not in competition.

 Interspecific Competition

 Interspecific competition refers to the interactions between individuals of different species when both require the same scarce resource. Interspecific competition is often greatest between organisms that obtain their food in similar ways; thus, green plants compete mainly with other green plants, herbivores with other herbivores, and carnivores with other carnivores. In general, competition is more acute between similar organisms than between those that are less similar.   you will learn that interspecific competition can prevent a species from occupying all of its niche—what is possible becomes limited by the realities of sharing a community with other species using the same resources. The white-colored barnacles you see in figure 2.18 would have no trouble covering the entire surface of this ocean rock, but don't in fact do so, because the species of mussel competes with them for space, a very important limiting resource.

Intraspecific Competition 

It is important to distinguish interspecific competition, which occurs between members of different species, from intro-specific competition, which occurs between individuals of a single species. The two seedlings in
re competing for the same resource, sunlight. The taller one, by growing faster, may ultimately shade out the shorter one.

THE BIOLOGICAL THEMES

How living world is organized by major  Biological themes

Just as every house is organized into thematic areas suet as bedroom, kitchen, and bathroom, so the living world is organized by major themes, such as how energy flows within the living world from one part to another. As you study biology in this text, five general themes will emerge repeatedly, themes that serve to both unify and explain biology as a science

1. Evolution;
2. The flow of energy;
3. Cooperation;
4. Structure determines function;
5. Homeostasis.

Evolution

 Evolution is genetic change in a species over time. Charles Darwin was an English naturalist who, in 1859, proposed the idea that this change is a result of a process called natural selection. Simply stated, those organisms whose characteristics make them better able to survive the challenges of their environment live to reproduce, passing their favorable characteristics on to their offspring. Darwin was thoroughly familiar with variation in domesticated animals (in addition to many non domesticated organisms), and he knew that varieties of pigeons could be selected by breeders to exhibit exaggerated characteristics, a process called artificial selection. You can see some of these extreme-looking pigeons pictured in table under the heading "evolution." We now know that the characteristics selected are passed on through generations because DNA is transmitted from parent to offspring. Darwin visualized how selection in nature could be similar to that which had produced the different varieties of pigeons. Thus, the many forms of life we see about us on earth today, and the way we ourselves are constructed and function, reflect a • long history of natural selection. Evolution will be explored in

 The Flow of Energy

 All organisms require energy to carry out the activities of 1 living—to build bodies and do work and think thoughts. All of the energy used by most organisms comes from the sun and is passed in one direction through ecosystems. The simplest way to understand the flow of energy through the living world is to look at who uses it. The first stage of energy's a journey is its capture by green plants, algae, and some bacteria by the process of photosynthesis. This process uses energy from the sun to synthesize sugars that photosynthetic organisms like plants store in their bodies. Plants then serve as a source of life-driving energy for animals that eat them. a Other animals, like the eagle in table 1.1, may then eat the plant eaters. At each stage, some energy is used for the processes of living, some is transferred, and much is lost, primarily as heat. The flow of energy is a key factor in shaping ecosystems, affecting how many and what kinds of animals live in a community.

Cooperation

 The ants cooperating in the upper right photo in table 1.1 protect the plant on which they live from predators and shading by other plants, while this plant returns the favor by providing the ants with nutrients (the yellow structures at the tips of the leaves). This type of cooperation between different kinds of organisms has played a critical role in the evolution of life on earth. For example, organisms of two different species that live in direct contact, like the ants and the plant on which they live, form a type of relationship called symbiosis. Animal cells possess organelles that are the descendants of symbiotic bacteria. and symbiotic fungi helped plants first invade land from the sea. The co evolution of flowering plants and insects—where changes in flowers influenced insect evolution and in turn, changes in insects influenced flower evolution—has been responsible for much of life's great diversity.

Structure Determines Function 

One of the most obvious lessons of biology is that biological structures are very well suited to their functions. You will see this at every level of organization: within cells, the shape of the proteins called enzymes that cells use to carry out chemical reactions are precisely suited to match the chemicals the enzymes must manipulate. Within the many kinds of organisms in the living world, body structures seem carefully designed to carry out their functions—the long tongue with which a moth sucks nectar from a deep flower is one example. The superb fit of structure to function in the living world is no accident. Life has existed on earth for over 2 billion years. a long time for evolution to favor changes that better suit organisms to meet the challenges of living. It should come as no surprise to you that after all this honing and adjustment, biological structures carry out their functions well.

Homeostasis

 The high degree of specialization we see among complex organisms is only possible because these organisms act to maintain a relatively stable internal environment, a process introduced earlier called homeostasis. Without this constancy. many of the complex interactions that need to take place within organisms would be impossible. just as a city cannot function without rules to maintain order. Maintaining homeostasis in a body as complex as yours requires a great deal of signaling back-and-forth between cells. As already stated, you will encounter these biological themes repeatedly in this text. But just as a budding architect must learn more than the parts of buildings, so your study of biology should teach you more than a list of themes, concepts, and parts of organisms. Biology is a dynamic science that will affect your life in many ways. and that lesson is one of the most important you will learn. It is also an awful lot of fun.

VOLUNTARY AND AUTOMATIC NERVOUS SYSTEM

explain the voluntary and automatic nervous system

the nervous system is divided into two main parts: the central nervous system which include the brain and spinal cord) and the peripheral nervous system (the blue boxes, which include the motor and sensory pathways). The motor pathways of the peripheral nervous system of a vertebrate can be further subdivided into the somatic (voluntary) nervous system, which relays commands to skeletal muscles, and the autonomic (involuntary) nervous system, which stimulates glands and relays commands to the smooth muscles of the body and to cardiac muscle. The voluntary nervous system can be controlled by conscious thought. You can, for ex-ample, command your hand to move. The autonomic nervous system, by contrast, cannot be controlled by conscious thought. You cannot, for example. tell the smooth muscles in your digestive tract to speed up their action. The central nervous system issues commands over both voluntary and autonomic systems, but you are conscious of only the voluntary commands.

  Voluntary Nervous System

 Motor neurons of the voluntary nervous system stimulate skeletal muscles to contract in two ways. First, motor neurons may stimulate the skeletal muscles of the body to contract in response to conscious commands. For example, if you want to bounce a basketball, your CNS sends messages through mo-tor neurons to the muscles in your arms and hands. However

The divisions of the vertebrate nervous system 

The motor pathways of the peripheral nervous system are the somatic (voluntary) and autonomic nervous systems.skeletal muscle can also be stimulated as part of reflexes that do not require conscious control. Reflexes Enable Quick Action. The motor neurons of the body have been wired to enable the body to act particularly quickly in time of danger—even before the animal is consciously aware of the threat. These sudden. involuntary movements are called reflexes. A reflex produces a rapid motor response to a stimulus because the sensory neuron bringing information about the threat passes the information directly to a motor neuron. The escape reaction of a fly about to be swatted is a reflex. One of the moat frequently used reflexes in your body is blinking, a reflex that protects your eyes. If anything. such as an insect or a cloud of dust, approaches your eye. the eyelid blinks closed even belay you realize what has happened. The reflex occurs before the cerebrum is aware the eye is in danger.

 Because they involve passing information between few neurons, reflexes are very fast. Many reflexes never reach the brain. The "danger" nerve impulse travels only as far as the The most famous involuntary response, the knee jerk, is produced by activating stretch receptors in the quadriceps muscle. When a rubber mallet taps the patellar tendon, the muscle and stretch receptors in the muscle are stretched. A signal travels up a sensory neuron to the spinal cord, where the sensory neuron stimulates a motor neuron, which sends a signal to the quadriceps muscle to contract.

 spinal cord and then comes right back as a motor response. Most reflexes involve a single connecting inter neuron be-tween the sensory neuron and the motor neuron. A few, like the knee-jerk reflex in are mono synaptic reflex arcs. You see in the figure that the sensory neuron, a stretch receptor embedded in a muscle, "senses" the stretching of the muscle when the tendon is tapped. This stretching could harm the muscle and so a nerve impulse is sent to the spinal cord where it synapses directly with a motor neuron—there is no interferon intermediary between them. If you step on some-thing sharp, your leg jerks away from the danger: in the same way, the prick causes nerve impulses in sensory neurons, which pass to the spinal cord directly to motor neurons, which cause your leg muscles to contract, jerking your leg up.

Automatic nervous system

Some motor neurons are active all the time, even during sleep. These neurons carry messages from the CNS that keep the body going even when it is not active. These neurons are called the autonomic nervous system. The word autonomic means involuntary. The autonomic nervous system carries messages to muscles and glands that work without the animal noticing.

CNS uses to maintain the body's homeostasis. Using it, the CNS regulates heartbeat and controls muscle contractions in the walls of the blood vessels. It directs the muscles that control blood pressure, breathing, and the movement of food through the digestive system. It also carries messages that help stimulate glands to secrete tears, mucus, and digestive enzymes. The autonomic nervous system is composed of two elements that act in opposition to one another. One division, the sympathetic nervous system, dominates in times of stress. It controls the "fight-or-flight" reaction, increasing blood pressure, heart rate, breathing rate, and blood flow to the muscles. The sympathetic nervous system is colored pink and consists of a network of short motor axons extending out from the spinal cord to clusters of neuron cell bodies, called ganglia, indicated by the darker-colored band, located just to the right of the spinal cord in the figure. You can also see this chain of ganglia Long motor neurons extend from the ganglia directly to each target organ. Another division, the parasympathetic nervous system, has the opposite effect It conserves energy by slowing the heart-beat and breathing rate and by promoting digestion and elimination. The parasympathetic nervous system is colored in blue and consists of a network of long axons extending out from motor neurons within the spinal cord; these axons extend to ganglia in the im


mediate vicinity of an organ. It also consists of short motor neurons extending from the ganglia to the nearby organ. Most glands, smooth muscles, and cardiac muscles get constant input from both the sympathetic and parasympathetic systems. The CNS controls activity by varying the ratio of the two signals to either stimulate or inhibit the organ.

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MAJOR FUNCTIONAL REGIONS OF HUMAN BRAIN

What are the major function of human brain

Specific areas of the cerebral cortex are associated with different regions and functions of the body.the brain called the corpus callosum (the blue-colored band in , each half of the brain controls muscles and glands on the opposite side of the body. In general, the left brain is associated with language, speech, and mathematical abilities, whereas the right brain is associated with intuitive, musical, and artistic abilities. Researchers have found that the two sides of the cerebrum can operate as two different brains. For instance, in some people the tract between the two hemispheres has been cut by accident or surgery. In laboratory experiments, one eye of an individual with such a "split brain" is covered and a stranger is introduced. If the other eye is then covered instead, the person does not recognize the stranger who was just introduced! Sometimes blood vessels in the brain are blocked by blood clots, causing a disorder called a stroke. During a stroke, circulation to an area in the brain is blocked and the brain tissue dies. A severe stroke in one side of the cerebrum may cause paralysis of the other side of the body.

How related thalamus and hypothalamus process information in the brain

Beneath the cerebrum are the thalamus and hypothalamus, important centers for information processing. The thalamus is the major site of sensory processing in the brain. Auditory (sound), visual, and other information from sensory receptors enter the thalamus and then are passed to the sensory areas of the cerebral cortex. The thalamus also controls balance. Information about posture, derived from the muscles, and information about orientation, derived from sensors within the ear, combine with information from the cerebellum and pass to the thalamus. The thalamus processes the information and channels it to the appropriate motor center on the cerebral cortex

. The hypothalamus integrates all the internal activities. It controls centers in the brain stem that in turn regulate body temperature, blood pressure, respiration, and heartbeat. It also directs the secretions of the brain's major hormone-producing gland, the pituitary gland. The hypothalamus is linked by an extensive network of neurons to some areas of the cerebral cortex. This network, along with parts of the hypothalamus and areas of the brain called the Hippocratic. pus and Alameda, make up the limb system. The areas highlighted in green in  indicate the components of the limb system. The operations of the limb system are responsible for many of the most deep-seated drives and emotions of vertebrates, including pain, anger, sex, hunger, thirst, and pleasure, centered in the Alameda.  that the limb system is the area of the brain affected by cocaine. It is also involved in memory, centered in the hippo campus.

 

The cerebellum coordinates muscle movements

Extending back from the base of the brain is a structure known as the cerebellum. The cerebellum controls balance, Posture, and muscular coordination. This small, cauliflower-shaped structure, while well developed in humans and other mammals, is even better developed in birds. Birds perform more complicated feats of balance than we do, because they move through the air in three dimensions. Imagine the kind of balance and coordination needed for a bird to land on a branch, stopping at precisely the right moment without crashing into it.

 

HOW THE BRAIN WORKS

Whould you like to know the Cerebrum Is the Control Center of the Brain

 Although vertebrate brains differ in the relative importance of different components. the human brain is a good model of how Vertebrate brains function. About 85% of the weight of the human brain is made up of the cerebrum, the tan convoluted area in . The cerebrum is a large rounded area of the brain divided by a groove into right and left halves called cerebral hemispheres. The sectioned brain in
is cut along the center groove, with the left hemisphere removed, showing the right hemisphere. The cerebrum functions in language, conscious thought, memory, personality development. vision, and a host of other activities we call "thinking and feeling."  shows general areas of the brain color-coded for easy identification (yellow for the frontal lobe, orange for the parietal lobe, light green for the occidental
lobe, and light purple for temporal lobe) and the functions they control. The cerebrum, which looks like a wrinkled mushroom. is positioned over and surrounding the rest of the brain. like a hand holding a fist. Much of the neural activity of the cerebrum occurs within a thin. gray outer layer only a few millimeters thick called the cerebral cortex (cortex is Latin for "bark of a tree"). This layer is gay because it is densely packed with neuron cell bodies. The human cerebral cortex contains the cell bodies of more than II) billion nerve cells, roughly 10% of all the neurons in the brain. The wrinkles in the surface of the cerebral cortex increase its surface area (and number of cell bodies) threefold. Underneath the cortex is a solid white region of eliminated nerve fibers that shuttle information between the cortex and the rest of the brain.

FUNDAMENTAL PROPERTIES OF LIFE

What are the fundamental properties of life?

As we discussed in chapter 1, all known organisms share certain general properties. To a large degree, these proper-ties define what we mean by life. The following fundamental properties are shared by all organisms on earth.

Cellular organization. All organisms consist of one or more cells—complex, organized assemblages of molecules enclosed within membranes.

Sensitivity. All organisms respond to stimuli—though not always to the same stimuli in the same ways.  

Growth.  All living things assimilate energy and use it to maintain order and grow, a process called metabolism. Plants, algae, and some bacteria use sunlight to create covalent carbon-carbon bonds from CO2 and H2O through photosynthesis. This transfer of the energy in covalent bonds is essential to all life on earth. 

Development. Both unicellular and multicellular organisms undergo systematic, gene-directed changes as they grow and mature.
  
Reproduction. All living things reproduce, passing on individuals from one generation to the next.  

Regulation. All organisms have regulatory mechanisms that coordinate internal processes. 

Homeostasis. All living things maintain relatively constant internal conditions, different from their environment.

HOW BIOLOGISTS DO THEIR WORK?

   What do biologists do their work?

The Consent

 Late in November, on a single night Not even near to freezing, the ginkgo trees That stand along the walk drop all their leaves In one consent, and neither to rain nor to wind But as though to time alone: the golden and green Leaves litter the lawn today, that yesterday Had spread aloft their fluttering fins of light. What signal from the stair? What senses took it in? What in those wooden motives so decided To strike their leaves, to down their leaves, Rebellion or surrender? And if this Can happen thus, what race shall be exempt? What use to learn the lessons taught by time, If a star at any time may tell us: Now.

                                                                                                                                     Howard Nemerov

What is bothering the poet Howard Nemerov is that life is influenced by forces he cannot control or even identify. It is the job of biologists to solve puzzles such as the one he poses, to identify and try to understand those things that influence life.

 Nemerov asks why ginkgo trees (figure 1.A) drop all their leaves at once. To find an answer to questions such as this, biologists and other scientists pose possible answers and then try to determine which answers are false. Tests of alternative possibilities are called experiments. To learn why the ginkgo trees drop all their leaves simultaneously, a scientist would first formulate several possible answers, called hypotheses:

called experiments. To learn why the ginkgo trees drop all their leaves simultaneously, a scientist would first formulate several possible answers, called hypotheses:

Hypothesis 1:

 Ginkgo trees possess an internal clock that times the release of leaves to match the season. On the day Nemerov describes, this dock sends a "drop" signal (perhaps a chemical) to all the leaves at the same time. 

 Hypothesis 2:

 The individual leaves of ginkgo trees are each able to sense day length, and when the days get short enough in the fall, each leaf responds independently by falling.

  Hypothesis 3:

 A strong wind arose the night before Nemerov made his observation, blowing all the leaves off the ginkgo trees. 

Next, the scientist attempts to eliminate one or more of the hypotheses by conducting an experiment. In this case, one might cover some of the leaves so that they cannot use light to sense day length. If hypothesis 2 is true, then the covered leaves should not fall when the others do, because they are not receiving the same information. Suppose, however, that despite the covering of some of the leaves, all the leaves still fall together. This result would eliminate hypothesis 2 as a possibility. Either of the other hypotheses, and many others, remain possible.

This simple experiment with ginkgoes points out the essence of scientific progress: Science does not prove that certain explanations are true; rather, it proves that others are not. Hypotheses that are inconsistent with experimental results are rejected, while hypotheses that are not proven false by an experiment are provisionally accepted. However, hypotheses may be rejected in the future when more information becomes available, if they are inconsistent with the new information. Just as you can find the correct path through a maze by trying and eliminating false paths, scientists work to find the correct explanations of natural phenomena by eliminating false possibilities.