animal kingdom 2.docx

8/19/2019 animal kingdom 2.docx

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AnimalI INTRODUCTION

Swallowing SnakeAnimal, multicellular organism that obtains energy by eating food. With oer ! million "no#n s$ecies, and many more a#aitingidenti%cation, animals are the most dierse forms of life on earth. They range in si&e from '()m *+(()ft long #hales to microsco$icorganisms only (.(- mm *(.((! in long. They lie in a ast range of habitats, from deserts and Arctic tundra to the dee$)sea oor. Animare the only liing things that hae eoled nerous systems and sense organs that monitor their surroundings. They are also the only

forms of life that sho# e/ible $atterns of behaior that can be sha$ed by $ast e/$erience. The study of animals is "no#n as&oology.Animals are multicellular organisms, a characteristic they share #ith $lants and many fungi. 0ut they di1er from $lants and fungseeral im$ortant #ays. 2oremost among these is the #ay they obtain energy. 3lants obtain energy directly from sunlight through the$rocess of $hotosynthesis, and they use this energy to build u$ organic matter from sim$le ra# materials. Animals, on the other hand, eaother liing things or their dead remains. They then digest this food to release the energy that it contains. 2ungi also ta"e in food, butinstead of digesting it internally as animals do, they digest it before they absorb it.

Fierce Hunter

A ying eagle snatches a %sh from the #ater #ith its long, cured talons. It #ill carry the %sh to a feeding $lace on land before deouring

4agles hunt only during the day5 by night, they $erch safely in their nests or in some other high s$ot.

O/ford 6cienti%c 2ilms

7ost animals start life as a single fertili&ed cell, #hich diides many times to $roduce the thousands or millions of cells needed to form a

functioning body. During this $rocess, grou$s of cells deelo$ di1erent characteristics and arrange themseles in tissues that carry out

s$eciali&ed functions. 4$ithelial tissue coers the body8s inner and outer surfaces, #hile connectie tissue binds it together and $roidessu$$ort. Nerous tissue conducts the signals that coordinate the body *see Nerous 6ystem, and muscle tissue9#hich ma"es u$ oer t#

thirds of the body mass of some animals9contracts to ma"e the body moe. This mobility, cou$led #ith ra$id res$onses to o$$ortunities

and ha&ards, is one feature that distinguishes animals from other forms of life.

6ome "inds of animal moement, such as the slo# $rogress of a lim$et as it cree$s across roc"s, are so slo# that they are almost

im$erce$tible. Others, such as the attac"ing die of a $eregrine falcon or the lea$ of a ea, are so fast that they are di:cult or een

im$ossible to follo#. 7any single)celled organisms can moe, but in absolute terms, animals are by far the fastest)moing liing things o

earth.

Animal life s$ans ary from less than ' #ee"s in some insects to oer a century in giant tortoises. 6ome animals, such as s$onges,

mollus"s, %sh, and sna"es, sho# indeterminate gro#th, #hich means that they continue to gro# throughout life. 7ost, ho#eer, reach a

$re)de%ned si&e at maturity, at #hich $oint their $hysical gro#th sto$s.

II T;346 O2 ANI7A


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Animal Kingdom

=ingdom Animalia includes more than one million liing s$ecies, grou$ed into more than '( $hyla. >ertebrates, members of the $hylum

Chordata, com$rise only one $ercent of these organisms. 3hylum Arthro$oda is more successful in sheer numbers, total mass, and

distribution than all other grou$s of animals combined. The remaining animal $hyla are com$osed of mostly marine)d#elling organisms.

Illustrated here is the eolutionary relationshi$ bet#een all of these grou$s.


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Vertebrate Embryos

>ertebrates that eoled from %sh $ass through similar embryonic stages. As a e/ible notochord deelo$s in the bac", bloc"s o

tissue called somites form along each side of it. These somites #ill become ma@or structures, such as muscle, ertebrae, connectie tissu

and, later, the larger glands of the body. ust aboe the notochord lies a hollo# nere cord. 6uch similarities formed the basis for Berman

biologist 4rnst aec"el8s biogenetic la#, #hich states that an animal8s embryonic deelo$ment reca$itulates its eolution. Althoughscientists no# "no# that this la# does not hold absolutely, aec"el8s idea has remained inuential.

One $hylum of animals, the chordates, has been more intensiely studied than has any other, because it com$rises nearly all the #orld8s

largest and most familiar animals as #ell as humans. This $hylum includes mammals, birds, re$tiles, am$hibians, and %sh together #ith

collection of lesser)"no#n organisms, such as sea suirts and their relaties *see Tunicates. The feature uniting these animals is that at

some stage in their lies, all hae a e/ible su$$orting rod, called a notochord, running the length of their bodies. In the great ma@ority o

chordates, the notochord is re$laced by a series of interloc"ing bones called ertebrae during early deelo$ment. These bones form the

bac"bone, and they gie these animals their nameEthe ertebrates.

>ertebrates total about F(,((( s$ecies. Than"s to their highly deelo$ed nerous systems and internal s"eletons, they hae

become ery successful on land, sea, and air. ;et ertebrates account for only about ! $ercent of animal s$ecies. The remaining G? $erce

collectiely called inertebrates, are far more numerous and dierse and include an immense ariety of animals from s$onges, #orms, a

@elly%sh to mollus"s and insects. The only feature these dierse creatures share in common is the lac" of a bac"bone.

6ome inertebrate $hyla contain relatiely fe# s$ecies. An e/treme e/am$le is the $hylum 3laco&oa, #hich contains @ust one

s$ecies. 7easuring less than (.- mm *(.(! in across, this uniue animal #as %rst discoered in +??' in a salt#ater auarium in Austria.

at body consists of @ust t#o layers of cells, ma"ing it the sim$lest "no#n member of the animal "ingdom, although not the smallest.

Another minor $hylum, the loriciferans, #as classi%ed in +G?' #ith the chance discoery of a tiny organism dredged u$ in marine grael.

6eeral other s$ecies of loriciferans hae since been identi%ed, but little is "no#n about ho# they lie.

At the other end of the s$ectrum, some inertebrate $hyla contain immense numbers of s$ecies. These ma@or $hyla include the

annelids *segmented #orms, #ith +!,((( "no#n s$ecies5 the nematodes *round#orms, also #ith +!,((( "no#n s$ecies5 and the mollus

including biales, snails, and octo$uses, #ith at least +((,((( s$ecies. The arthro$ods, #ith about + million "no#n s$ecies, include the

insects, s$iders, and crustaceans. These %gures include only s$ecies that hae been described and named, #hich are only a $ortion of

those that actually e/ist. 6ome biologists estimate that the total number of nematode s$ecies may be as high as a uarter of a million,

#hile the total number of arthro$ods could e/ceed +( million.

Com$ared to ertebrates, most inertebrates are animals of modest dimensions. Biant suids, #hich are the largest inertebrat

can e/ceed +? m *H( ft in length, but the great ma@ority of inertebrate animals are less than !.- cm *+ in long. Their small si&e enables

them to e/$loit food sources and in%ltrate habitats that larger animals cannot use, but it also leaes them e/$osed to changing

enironmental conditions. This is not often a $roblem in the sea, but it can create di:culties on land.


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Penguin Keeping Its oung !arm

3enguins al#ays return to their ancestral nesting sites to lay their eggs and rear their young. The em$eror $enguin, the largest of the

$enguins, lays its single egg during the coldest time of the Antarctic year, #hen tem$eratures dro$ as lo# as )H! degrees C *)?( degrees

The egg is incubated on to$ of the $arent8s feet, $rotected by abdominal folds of s"in. ;oung chic"s remain under these abdominal folds

until they are able to regulate their o#n body tem$erature.

On land, some inertebrates manage to oercome the $roblem of cold by using muscles to #arm themseles. 2or e/am$le, many large

moths and bumblebees use a s$ecial form of shiering to raise their body tem$erature to '-C *G-2 before they ta"e o1, #hich allo#s

them to y in cool #eather. 0ees also maintain #arm conditions in their nests, #hich s$eeds u$ the deelo$ment of their young. 0ut in

inertebrates as a #hole, tem$erature regulation is ery unusual. In ertebrates, on the other hand, it has deelo$ed to a high degree.

>ertebrates are customarily diided into cold)blooded and #arm)blooded animals, but these labels are not ery $recise. 0iologists norma

use the terms ectoderm and endoderm to describe tem$erature regulation more accurately. An ectoderm is an animal #hose tem$eratur

is dictated by its surroundings, #hile an endoderm is one that "ee$s its body at a constant #arm tem$erature by generating internal hea

Re$tiles, am$hibians, and %sh are ectoderms. Although they do not maintain a constant #arm tem$erature, some of these animals do

manage to raise their body tem$erature far aboe that of their surroundings. They do this by behaioral means, such as bas"ing in direc

sunshine #hen the surrounding air is cool. 7ammals and birds are endoderms. These animals generate heat through their metabolic

$rocesses, and they retain it by haing insulating layers of fat, fur, or feathers. 0ecause their bodies are al#ays #arm, they can remain

actie in some of the coldest conditions on earth.III ANI7A< A0ITAT6

2e# $arts of 4arth8s surface are entirely deoid of animal life. Animals cannot surie in $laces #here #ater is unaailable or $ermanentl

fro&en, or #here tem$eratures regularly e/ceed -- C *+'( 2. o#eer, in all habitats that lie bet#een these e/tremes, animal life

abounds.A Auatic abitats

"idal Pool

The uctuation of the tide allo#s for a uniue enironment along shorelines. The current continually circulates and re$lenishes a rich su$

of nutrients along beaches, but organisms liing there must be ada$ted to both bu1eting #aes and freuent shifts from o$en air to

com$lete submersion. 7arine organisms ada$t to the constantly changing surroundings in a ariety of #ays. 6tar%sh use suction)cu$ fee

barnacles %/ $ermanently to large ob@ects li"e roc"s and boats, and sea#eed anchors %rmly to the ocean oor. When the tide goes out,


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$oc"ets of #ater remain tra$$ed in roc"s, de$ressions in the sand, and natural basins called tidal $ools, li"e the one sho#n here during lo

tide.

Animal life %rst arose in #ater. 7illions of years later, marine and fresh#ater habitats continue to su$$ort a large $ro$ortion of t

animal life on earth. Auatic habitatsE$articularly in the seas and oceans9rarely e/$erience abru$t changes in conditions, #hich is a ma@

adantage for liing things.

In the seas and oceans, the greatest diersity of animal life is found in habitats close to shores. The richest of all these habitats

coral reefs, under#ater ridges that form in clear #ater #here the minimum tem$erature is !( C *H? 2 or aboe. Coral reefs are com$o

of an accumulation of the remains of coralEinertebrates #ith stony s"eletonsEcalcareous red algae, and mollus"s. One of the reasons f

the great diersity of animal life in reefs is that liing coral creates a com$le/ three)dimensional landsca$e, #ith many di1erent

microhabitats. The smallest creices $roide hiding $laces for scaengers such as crabs and shrim$s, #hile larger ones conceal $redator

such as octo$uses and moray eels. Oer half the #orld8s %sh s$ecies lie in coral reefs, many hiding a#ay by day and emerging after dar

to feed.

#at$s%The rat%sh is a member of a s$ecies of dee$)#ater %sh related to shar"s. The dee$)#ater habitat of the rat%sh is dar", cold, and ast.


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Tro$ical and subtro$ical forests are home to by far the largest number of animal s$ecies on land. These animals include the ma@ority of th

#orld8s insects, most of its $rimates, and a large $ro$ortion of its birds. Tro$ical forests hae e/isted longer than any other forests on ear

and their $lants and animals hae eoled an elaborate #eb of interrelationshi$s.

7uch of the animal life of tro$ical forests is still $oorly "no#n, and ne# s$ecies are constantly being discoered. The ma@ority of these

ne#ly identi%ed animals are inertebrates, but larger animals hae also come to light during the !(th century. 7a@or discoeries hae

included three large but secretie $lant)eating mammalsJ the o"a$i, discoered in Central Africa in +G((5 the "ou$rey, discoered in the

forests of Cambodia in +G'K5 and the sao la, #hich #as identi%ed in forests bordering ietnam in +GG'.

Unli"e tro$ical forests, tem$erate forests $roide animals #ith an abundance of food during s$ring and summer, but a dearth during the

#inter. In this habitat, animals hae eoled seeral di1erent strategies for aoiding staration during the #inter months. 2ood hoarders,

such as suirrels and @ay birds, bury sur$lus food during the fall, and dig it u$ again #hen other food su$$lies run out. Other forest anima

such as the common dormouse, aoid food shortages by hibernation, a $eriod of inactiity #hen body tem$erature is lo#ered. A third gro

of animalsEcom$osed chiey of birds, but also including some bats and insects9migrates to #armer regions before the #inter begins an

returns again in s$ring. In boreal forests, #hich are found in the far north, the seasonal s#ings are more e/treme. ere only a fe# s$ecie

stay and remain actie during the #inter months.

2or land animals, the most testing habitats are ones that e/$erience intense drought or e/treme cold. Desert animals co$e #ith heat and

#ater shortage by behaioral ada$tations, such as remaining belo# ground by day, and also by $hysiological ada$tations. North America

"angaroo rats, for e/am$le, can lie entirely on dry seeds #ithout eer drin"ing liuid #ater. They do this by losing ery little moisture fro

their bodies and using all the Lmetabolic #aterM that is formed #hen food is bro"en do#n to release energy.

In tundra and on $olar ice, #inter air tem$eratures can fall to belo# )F( C *)F( 2, #hich is far colder than the tem$erature of thesurrounding seas. The smallest inhabitants of tundra, #hich include ast numbers of mosuitoes and other biting ies, s$end #inter in a

state of sus$ended animation and are "e$t alie by chemical antifree&e #ithin their tissues. The fe# animals that do remain actie on lan

or ice during #inter, such as seals and male em$eror $enguins, rely on a thic" layer of insulating fat to $reent their body heat lea"ing

a#ay. Without this fat, they #ould die #ithin a matter of minutes.I> 244DINB

Animals all feed on organic matter, but their diets and #ay of obtaining food ary enormously. 6ome animals are omniores, meaning tha

they are ca$able of suriing on a ery #ide range of foods. 7any other animals, from giant $andas to eas, hae e/tremely $recise

reuirements and cannot deiate from their highly s$eciali&ed diet.A erbiores and Carniores

'eat Eaters and Plant Eaters

In carniores *right, the front of the s"ull has a $air of enlarged canine teeth and the lo#er @a# moes only in an u$ and do#n direction,

#hich assists #ith the ca$ture and holding of $rey. In herbiores *left, the canine teeth are absent and the $remolars and molars are #e

deelo$ed. The @a# construction also allo#s for the lateral moement of the lo#er @a# in relation to the u$$er @a#, #hich hel$s to $roide

grinding motion necessary for rendering $lant materials into a state suitable for s#allo#ing and digestion.

Dorling =indersley

In general, animals eat $lants, other animals, or the remains of liing things. 3lant)eaters, or herbiores, often do not hae to search far t

%nd things to eat, and in some casesEfor e/am$le #ood)boring insectsEthey are entirely surrounded by their food. The disadantage of

$lant)based diet is that it can be di:cult to digest and is often lo# in nutrients.


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To oercome the %rst of these $roblems, most herbiores hae tough mouth$arts for che#ing and grinding their food. 7any $lant)eating

animals, from termites to cattle, hae com$le/ digestie systems containing microorganisms that brea" do#n cellulose and other

indigestible $lant substances, turning them into nutrients that the animals can absorb. The second $roblemElac" of nutrients9is harder t

sideste$, $articularly in a diet made u$ largely of leaes. As a result, leaf)eaters often hae to feed for many hours each day to obtain th

nutrients that they need.

Alligator Snapping "urtle

The alligator sna$$ing turtle, the largest of the fresh#ater turtles, has a ridged, camouaged shell and $o#erful @a#s. When a %sh,

mista"ing a small, #riggling $ro@ection on the turtle8s tongue for a #orm, s#ims #ithin reach, the turtle ca$tures it by uic"ly sna$$ing it

@a#s shut.

Dorling =indersley

Carniores lie on esh from other animals that is often nutrient)rich and easy to digest but di:cult to obtain. 2inding and ca$turing this

"ind of food calls for "een senses. 0ut een though a hunter has acute ision or a highly deelo$ed sense of smell, a large $ro$ortion of a

hunter8s ictims manage to esca$e. If this ha$$ens too often, a $redator uic"ly stares.

6ome mammalian $redators, such as the lion and #olf, increase their chances of success by hunting in grou$s. While this strategy enable

them to tac"le larger $rey, a successful "ill has to be shared among members of the grou$. 0ut in the animal #orld as a #hole, many oth

$redators ado$t a less energy)intensie a$$roach to catching their food. Instead of actiely searching out their $rey, they $osition

themseles in a suitable location and #ait for their $rey to come #ithin stri"ing distance.

Angler$s%

Angler%sh hae a$$endages that sere as %shing rods or lures to attract $rey, mainly other %sh. They are found in oceans all oer the #o

and generally inhabit dee$ #aters. Certain s$ecies can gro# to lengths of about +.- m *- ft, and hae huge mouths ca$able of s#allo#in

%sh of eual si&e.

ig


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In $redatory animals, teeth or other mouth$arts often $lay a $art in catching and subduing food as #ell as in $re$aring it for digestion.

These mouth$arts include canine teeth in carniorous mammals, enomous fangs in sna"es, and $oisonous Lhar$oonsM in some marine

mollus"s. These har$oons can im$ale and "ill small %sh. 4ach har$oon is used @ust once, and after#ards it is e/$elled and another is form

in its $lace.

0 Other 2eeding 6trategies

(iant Anteater

Anteaters are natie to Central and 6outh America, inhabiting both forest and o$en)$lain regions. The giant anteater, sho#n here, is the

largest of the s$ecies, #eighing u$ to !' "g *-( lb. The animal is #ell)ada$ted to hunt for insects, its sole source of food, because of its

long front cla#s and stic"y tongue, #hich can e/tend to H( cm *!F in.


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Female 'os)uito Sucking Blood

There are a$$ro/imately !,((( s$ecies of mosuitoes ranging from the tro$ics to the Arctic Circle and from sea leel to mountainto$s. Al

mosuitoes belong to the insect order Di$tera, #hich includes all of the ies, or t#o)#inged insects. All s$ecies of Di$terans hae a single

$air of #ings for ying and a second estigial $air called halteres, #hich act as organs of balance. 2emale mosuitoes hae hy$odermic

mouth$arts #hich enable them to $ierce the s"in and suc" the blood of mammals, birds, re$tiles, and other arthro$ods. The males hae

reduced mouth$arts and feed instead on nectar and #ater.

Tim 6he$herdO/ford 6cienti%c 2ilms

In another feeding techniue, $redators see" out sources of food that are much larger than themseles but only eat $art of their $reyE

usually its blood. This #ay of life is has been $ursued #ith great success by seeral grou$s of ying insects, such as mosuitoes and

horseies. 0ut in the animal #orld as a #hole, uid diets are much more common in animals that feed on $lants. A$hids, cicadas, and oth

true bugs use $iercing mouth$arts to suc" sa$ from $lant stems. 7any di1erent animals, including moths, butteries, hummingbirds, and

bats, use $robing bea"s and tongues to reach nectar in o#ers.

*ife +ycle of Human Blood Flukes

2lu"es of the genus 6chistosoma $arasiti&e t#o hosts. The young hatch from their eggs in riers and la"es and enter a s$eci%c "ind of

auatic snail, #here they deelo$ into tad$ole)li"e larae called cercariae. When the cercariae leae the snail, they burro# through the s

of a human host s#imming or #ading in infested #ater. Adult u"es mature in the host8s bloodstream and settle in the eins of the gut.

Their eggs, de$osited in the lining of the human intestine and bladder, $ass bac" into #ater ia the se#age system, and the cycle begins

again. 7ore than !(( million $eo$le #orld#ide su1er from schistosomiasis, a disease characteri&ed by the abscesses and bleeding cause

by the u"es8 infestation.

P 7icrosoft Cor$oration. All Rights Resered.

To aoid the need to trac" do#n food, some animals use a highly s$eciali&ed feeding strategy, called $arasitism *see 3arasite. A $arasite

lies on or inside other animals and sim$ly si$hons o1 some of its host8s food or, more commonly, feeds on the host itself. 4/ternal

$arasites, such as eas, hae #ell)deelo$ed senses and ada$tations that enable them to cling to their hosts. Internal $arasites, such as

ta$e#orms and lier u"es, are highly modi%ed for a life inside their hosts. The sense organs of internal $arasites are rudimentary or

absent because they do not need to %nd food or aoid enemies. Instead, they deote their time entirely to the t#in tas"s of feeding and

re$roduction.> 0R4ATINB


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E,olution of Air-Breat%ing .rganisms

0oth the lung structure of air)breathing organisms and the s#im bladders of most modern %shes eoled from $aired air sacs of $rimitie

bony %shes. In the $rimitie %sh, as in the modern bony %shes, these sacs sered as a buoyancy deice that inated and deated to altethe %sh8s de$th in the #ater. In other %sh, they became $rimitie lung structures, re$eatedly folding in#ard to ma/imi&e o/ygen u$ta"e i

an o/ygen)de$ried enironment. 0oth "inds of %shes im$roed u$on a $ree/isting ada$tation but in so doing eoled into ery di1erent

grou$s of organisms.


Whereer they lie, animals need o/ygen in order to surie. 0y breathing, or res$iring, they e/tract o/ygen from their surroundings and

dis$ose of carbon dio/ide #aste *see Res$iration.

How Fis% Breat%e

A %sh breathes by absorbing o/ygen from the #ater it drin"s. Water o#s into the mouth, through the gills, and out of the body through g

slits. As #ater o#s through the gills, the o/ygen it contains $asses into blood circulating through gill structures called %laments and

lamellae. At the same time, carbon dio/ide in the %sh8s bloodstream $asses into the #ater and is carried out of the body.


>ery small animals do not need any s$ecial ada$tations for obtaining o/ygen. O/ygen sim$ly di1uses in through their body surface, #ith

carbon dio/ide traeling out the same #ay.


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many animals breathe by using gills. A ty$ical gill consists of a stac" of thin a$s connected to the animal8s blood su$$ly. Water moes $

the a$s in a one)#ay o#, either #hen the animal moes, or #hen it $um$s #ater through its body. The a$s e/tract o/ygen from the

#ater and $ass it into the blood, #hich transfers it to needed tissues. The blood releases carbon dio/ide in e/change.

A/olotl S%owing E/ternal (ills

The a/olotl is actually the auatic laral stage of the bro#n salamander. A/olotls are of interest to scientists because not all a/olotls

metamor$hose, or change, into adult salamanders. 7ore interestingly, those a/olotls that do not transform may become se/ually mature

#hile in the laral stage. In ca$tiity, a/olotls can be induced to change into adult salamanders by the addition of thyroid e/tract to the

surrounding #ater.

B.I. 0ernardO/ford 6cienti%c 2ilms

Bills do not #or" on land because their a$s colla$se and stic" together. Instead, land animals hae eoled t#o di1erent "inds of

res$iratory organsJ tracheal systems and lungs. Tracheal systems are found in insects and many other arthro$ods. They consist of slendehollo# tubes, called tracheae, that reach dee$ into the body, deliering o/ygen from outside.


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form of cree$ing moement, seen in earth#orms, inoles changes in body sha$e. The #orm8s segments e/tend and contract in a set

seuence, allo#ing it to force its #ay through the surrounding soil.

6ome of the earth#orm8s relaties hae a$s called $ara$odia that hel$ them to moe, but een #ith these, their s$eed is fairly modest.

With a fe# notable e/ce$tionsEsuch as suid and octo$uses, #hich can moe by a form of @et $ro$ulsionEthe fastest animals by far are

ones that hae s"eletons and @ointed limbs.A ointed


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7any animals can glide, but only insects, birds, and bats are ca$able of $o#ered ight. The fastest ying insects are dragonies, #hich c

reach s$eeds of about !G "mh *about +? m$h in short bursts. o#eer, in terms of s$eed and endurance, birds are by far the most

successful animal aiators. 6#ans and geese can cruise at HF "mh *F( m$h for many hours at a time, #hile $eregrine falcons can brie

reach +F- "mh *G( m$h #hen they s#oo$ do#n on their $rey.

0 3atterns of 7oement

'igrating !ildebeest

The blue #ildebeest, or brindled gnu, migrates annually from =enya to northern 6outh Africa. Along their migratory route the #ildebeests

sto$ at #atering holes on the Brameti Rier, #here they become the chief source of food for Nile crocodiles. 6cientists s$eculate that the

crocodiles of the Brameti Rier may feed only once a year, #hen blue #ildebeests arrie during their annual migration.

ohn Do#nerO/ford 6cienti%c 2ilms

0eing able to moe gies animals many adantages, but it also generates its o#n demands. 2or any animal, random moement can be

unhel$ful or een dangerous. To be useful, moement has to be carefully guided.

Animals are guided by their senses, #hich $roide feedbac" about their changing surroundings. In animals that hae radial symmetry

*symmetry around a central $oint, such as @elly%shes, sensory neres are arranged more or less eenly around the body. This arrangeme

ma"es the animal eually sensitie to stimuli from any direction. In bilaterally symmetrical animals *animals made of eual hales, sens

neres are concentrated in the head. They coney signals to the brain from organs such as ears and eyes, telling an animal about the

surroundings that it is about to encounter.

'onarc% 'igration


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The monarch buttery, Danaus $le/i$$us, is "no#n for its e/traordinarily long migrations. During the summer months, monarchs can be

found throughout the continental United 6tates and $arts of Canada, and they migrate to the California coast and central 7e/ico for the

#inter. The longest recorded ight for a tagged adult is !,G(( "m *+,?(( mi. A large number of monarchs s$end their #inters in the

mountains #est of 7e/ico City. 6cientists s$eculate that the mountainous climate $roides a faorable mi/ of moist air and cool, but not

free&ing, tem$eratures. These conditions "ee$ the buttery from drying out and "ee$ its metabolism lo# enough to consere fat stores b

high enough to maintain life.

B. B. Dimi@ian3hoto Researchers, Inc.

These sensory systems hel$ animals to moe to#ard food and a#ay from $ossible danger. On a longer time s$an, they also guide them

through much more com$le/ $atterns of moement that are essential for their surial. These moements include s$ecial "inds of beha

needed to locate a $artner, and also seasonal moements or migrations.

6ome of the shortest migrations are carried out by microsco$ic at#orms that lie on sandy shores. These #orms migrate u$ to the surfa

of the sand at lo# tide and bac" into it at high tideEa total distance of about !( cm *about ? in roughly t#ice a day. In the o$en ocean,

many $lan"tonic animals carry out larger daily migrations, rising to the surface at dus" and then sin"ing at sunrise. 0y doing this, they

reduce the chances of being eaten.

The longest migrations are annual ones, underta"en by animals in res$onse to the changing seasons. 0y carrying out these @ourneys,

animals can breed in $laces #here food is abundant for @ust a fe# months each year.


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'odes of Frog #eproduction

00C World#ide Americas, Inc.

Ase/ual re$roduction is relatiely easy to achiee because it inoles only a single animal. 6e/ual re$roduction is much more com$le/

because the $artners often hae to %nd each other and $recisely coordinate their re$roductie behaior. In most cases, each $artner is

either male or female, but in some animalsEsuch as earth#orms, slugs, and snails9each one is a herma$hrodite, an animal that has both

male and female organs. erma$hrodites usually fertili&e each other, #ith both $artners $roducing young *see erma$hroditism.

!estern (rebe +ourts%ip

During the s$ring, #estern grebes $erform s$ectacular courtshi$ dances. In the LrushingM dis$lay, the mating $air s#im side)by)side #ith

their #ings held bac", their long nec"s arched, and their yello# bea"s angled u$#ard. They s#im so uic"ly that their bodies are $ushed

out of the #ater and they a$$ear to run across the surface. After courtshi$ the male and female build a oating nest out of $lant materia

00C World#ide Americas, Inc.

7ost auatic animals shed their eggs and s$erm into the #ater, #here e/ternal fertili&ation ta"es $lace. In corals and many other sessile

s$ecies, the moment of s$a#ning is often triggered by the tides, ma/imi&ing the chances that the egg and s$erm #ill meet. In a minority

marine animals, fertili&ation is internal, meaning that the male mates #ith the female, inserting his s$erm into her body. 2or this to #or",

the male needs s$ecial ada$tations to ma"e the transfer. 7ale shar"s and rays use s$ecial clas$ers that are attached to their $elic %ns,

#hile barnacles, #hich are often herma$hrodites, use a threadli"e $enis that can be almost as long as their bodies.


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Internal Fertili1ation

Terrestrial ertebrates clas$ each other tightly during co$ulation, the act by #hich the male de$osits his s$erm into the female8s

re$roductie tract. In the giant BalQ$agos tortoises $ictured here, mating may ta"e hours.Tui De RoyO/ford 6cienti%c 2ilms

On land, e/ternal fertili&ation is rare because egg and s$erm cells cannot surie for long in the o$en. As a result, almost all land animals

must mate to trigger internal fertili&ation in order to re$roduce. Di1erent grou$s of animals hae eoled a #ide ariety of mechanisms t

ma"e sure that males and females manage to locate suitable $artners. 6ome female insects emit chemicals called $heromones, #hich

guide males to#ards them, #hile others use sound signals or biochemically $roduced light *see 0ioluminescence. In birds, elaborate

$lumage and courtshi$ dis$lays hel$ to attract females to#ards the males *see Animal Courtshi$ and 7ating.

Honey Bee From Egg to Adult

The ueen honey bee may lay +-(( eggs in a single day. Wor"er bees feed the #ormli"e lara constantlyEas many as +'(( times a dayE

after it hatches, sealing the cell #hen the grub has gro#n to %ll it. The lara $u$ates in about +! days, and the adult bee che#s through t

#a/ ca$ of its cell a$$ro/imately three #ee"s after the eggs #ere %rst laid. Ne#ly emerged adults $erform arious maintenance tas"s un

they are ready to begin foraging outside the hie.



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The males of many insects and irtually all mammals use a $enis to transfer s$erm to the female, #ho harbors the eggs, in a $rocess

"no#n as co$ulation. The $enis ensures that s$erm is transferred successfully #ithout being carried a#ay by #ind, #ater, or other

enironmental elements. 7ost birds and re$tiles mate using a cloaca, a single o$ening located on the lo#er abdomen. During mating, the

animals align their cloacas for transfer of s$erm. 6ome birds, such as bald eagles, can $erform this feat in mid)air.

Once a female has mated, egg deelo$ment can $roceed in t#o di1erent #ays. In oi$arous s$ecies, #hich include the ma@ority of

ertebrates e/ce$t mammals, and also most insects, the fertili&ed eggs are laid and deelo$ outside the mother8s body. In ii$arous

animals, #hich include nearly all mammals together #ith some re$tiles and shar"s, the young deelo$ inside the mother and are born li

7ost animals that are born lie loo" similar to their $arents, although they are not fully deelo$ed. 0y contrast, many egg)laying

inertebrates loo" com$letely di1erent from their $arents #hen they hatch and often lie in a com$letely di1erent #ay. =no#n as larae,

these young change sha$es as they gro# u$, during a $rocess called metamor$hosis.


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Killer !%ale Family

6ho#ing the characteristic contrasting #hite $atches aboe the eyes and under the @a#s, a male and female "iller #hale, Orcinus orca,

s#im $rotectiely on either side of their baby. =iller #hales maintain close ties to the social structure of their natal $ods, or grou$s, for lif

To $reent inbreeding, ho#eer, the #hales ty$ically see" mates outside of their original $od.

Betty ImagesDaid 4 7yers Tony 6tone Images

With the e/ce$tion of birds, the ma@ority of egg)laying animals $lay no $art in hel$ing their young to surie. A large $ro$ortion of their

young die, and to o1set this, they often $roduce a huge number of eggs. A housey, for e/am$le, can lay oer a thousand eggs in the

course of its life, #hile a female cod can lay ' million.

7ost am$hibians and re$tiles lay smaller clutches of eggs, and some of them remain #ith their eggs and guard them until they hatch. 0i

lay smaller clutches still, and the $arents incubate the eggs, or "ee$ them #arm until they hatch, and continue to care for their young onthey hae hatched. 7ost ground)nesting s$ecies $rotect their young and lead them to food, but ty$ical tree)nesting birds $roide their

young #ith both food and shelter until they are able to fend for themseles. Without this $arental care, the young birds #ould hae no ho

of surial.

American #edstart Feeding oungA female American redstart turns to#ard her o1s$ring, #hich begs for food #ith its ga$ing mouth.

Ral$h A. ReinholdAnimals Animals

3arental care is eually im$ortant in mammals, #hich $roide food for their young in the form of mil". Raising a family in this #ay create

close lin" bet#een the mother and her young. This method also allo#s the young to learn im$ortant $atterns of behaior by #atching the

mother at #or". In small rodents, this learning $eriod lasts for @ust a fe# days, but in larger mammals, it can last for more than a year.>III 6TRAT4BI46 2OR 6UR>I>A<

In the liing #orld, resources such as food and s$ace are limited. As a result, surial is a constant struggle. Through eolution, animals

hae deelo$ed a range of ada$tations that gie them the best chances of success.

The most obious of these ada$tations are $hysical ones that a1ect the sha$e or structure of an animal8s body. 4ually im$ortant, althou

often less cons$icuous, are ada$tations that a1ect behaior and body $rocesses. Together, these di1erent ada$tations allo# each s$ecie

to $ursue a distinctie #ay of life.A 3hysical Ada$tations


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"ulip-"ree Beauty

The tuli$)tree beauty is a large moth that feeds on the foliage of the tuli$ tree as a cater$illar. 2ound from southern Canada to 2lorida, th

moths often hae banded coloration that camouages them against tree bar".ohn R. 7acBregor3eter Arnold, Inc.

The need to eat e/$oses animals to the danger of being attac"ed and eaten themseles. To aoid this fate, all animals hae $hysical

ada$tations that enable them to esca$e being attac"ed or to surie an attac" once it is under#ay.

"urtle SkeletonThe turtle or tortoise body is encased in a shell made u$ of a series of bony $lates coered #ith a horny shield. The ertebrae and ribs ar

fused to the inside of this shell, #hich gies it additional su$$ort and strength. It is im$ossible for turtles or tortoises to cra#l out of their

shells. Turtles hae a relatiely attened shell and are auatic, #hile tortoises hae a dome)sha$ed shell and are terrestrial.

Dorling =indersley

The sim$lest form of defense is a ra$id esca$e, #hich calls for "een senses and #ell)deelo$ed systems for moement. 7any $lant)eatin

mammals de$end on this strategy for surial and must maintain a constant loo"out for danger. A less)demanding surial strategy, foun

in many small animals such as insects, inoles dece$tion. These animals use camouage to blend in #ith their bac"grounds, or they mi

inedible ob@ects such as t#igs or bird dro$$ings. If a $redator does come too close, they still hae the o$tion of ma"ing a dash for safety.


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#egal Horned *i1ard

The #ell)camouaged regal horned li&ard, 3hrynosoma solare, reuires so many ants a day to sustain it that it almost al#ays is found ne

an anthill. Regal horned li&ards usually fare $oorly in ca$tiity, #here uantities of ants are often insu:cient. It remains motionless if

a$$roached, but if $ic"ed u$, it may attem$t to disconcert its attac"er by $u:ng u$ its body and suirting blood, sometimes as far as a f

feet, from a resere behind its eyes. The regal horned li&ard is the largest of the American s$ecies of horned li&ards and can be recogni&e

by the four large horns on the bac" of its head.

7.3.


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Egyptian Vulture

This 4gy$tian ulture holds a stone in its bea" in $re$aration for smashing an ostrich egg. 4gy$tian ultures are unusual among birds

because they use stones as tools for obtaining food.

Roy ToftTom 6tac" and Associates

In sim$le animals, behaior is goerned almost entirely by instinct, meaning that it is $re)$rogrammed by an animal8s genes. In more

com$le/ animals, instinctie behaior is often modi%ed by learning, $roducing more)e/ible res$onses to the outside #orld.

7any forms of behaior hel$ animals to surie seere enironmental conditions. T#o e/am$les are hibernation, #hich enables animals t

surie cold and food shortages in #inter5 and estiation, #hich allo#s animals to surie drought and heat in summer. True hibernators,

such as bats and some rodents, become com$letely inactie during #inter, and their body tem$erature falls close to free&ing. While in th

state, they surie entirely on food reseres stored in their bodies. 4stiating animals, #hich include land snails and some am$hibians, se

themseles u$ #hen conditions become dry and only become actie again #hen it rains. 0et#een these t#o e/tremes, many other anim

sho# less drastic $atterns of behaior that are triggered by cold or heat. Winter #rens, for e/am$le, often cro#d together for slee$ #hen

tem$eratures fall belo# free&ing. On #armer nights, they slee$ on their o#n.

6$ecial forms of behaior also hel$ animals to %nd food, to aoid being eaten, and to $rotect their young. One of the most adanced form

of this behaior is the use of tools. 6eeral "inds of animals, $articularly $rimates and birds, $ic" u$ im$lements such as t#igs and stone

and use them to get at food. 7ore rarely, some tool)using animals see" out a $articular ob@ect and then sha$e it so that it can be used.

Wood$ec"er %nches $robe for insect grubs by ma"ing tools from cactus s$ines, and chim$an&ees sometimes dig for termites using s$eci

$re$ared t#igs.

Defensie behaior is e/hibited by indiidual animals and also by animal grou$s. Brou$ defense is common in herding mammals,

$articularly in s$ecies such as the mus")o/, #hich form a $rotectie ring around their cales #hen threatened by #oles. It can also be

seen in s#allo#s, starlings, and other songbirds, #hich instinctiely mob ha#"s and other birds of $rey. 0y grou$ing together to harass th

enemies, they reduce the chances that they or their young #ill be singled out and attac"ed.

Indiidual defensie behaior is often based on threatening gestures that ma"e an animal loo" larger or more dangerous than it actually

6ometimes it inoles some highly s$eciali&ed forms of dece$tion. One of the most remar"able is $laying dead. 6een in animals such as

>irginia o$ossum and some sna"es, this last)ditch defense is e1ectie against $redators that habitually hunt moing $rey but leae dead

animals alone. After the $redator has ins$ected the LdeadM animal and moed on, the $rey comes bac" to life and ma"es its esca$e.I ORIBIN6 O2 ANI7A


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7ost biologists agree that animals eoled from sim$ler single)celled organisms. 4/actly ho# this ha$$ened is unclear, because fe# foss

hae been left to record the seuence of eents. 2aced #ith this lac" of fossil eidence, researchers hae attem$ted to $iece together

animal origins by e/amining the single)celled organisms alie today.

7odern single)celled organisms are classi%ed into t#o "ingdomsJ the $ro"aryotes and $rotists. 3ro"aryotes, #hich include bacteria, are

sim$le organisms, and lac" many of the features seen in animal cells. 3rotists, on the other hand, are more com$le/, and their cells cont

all the s$eciali&ed structures, or organelles, found in the cells of animals. One $rotist grou$, the choanoagellates or collar agellates,

contains organisms that bear a stri"ing resemblance to cells that are found in s$onges. 7ost choanoagellates lie on their o#n, but

signi%cantly, some form $ermanent grou$s or colonies.

This tendency to form colonies is #idely belieed to hae been an im$ortant ste$$ing stone on the $ath to animal life. The ne/t ste$ in

eolution #ould hae inoled a transition from colonies of inde$endent cells to colonies containing s$eciali&ed cells that #ere de$enden

on each other for surial. Once this deelo$ment had occurred, such colonies #ould hae e1ectiely become single organisms. Increasi

s$eciali&ation among grou$s of cells could then hae created tissues, triggering the long and com$le/ eolution of animal bodies.

This con@ectural seuence of eents $robably occurred along seeral $arallel $aths. One $ath led to the s$onges, #hich retain a collectio

of $rimitie features that sets them a$art from all animals. Another $ath led to t#o ma@or subdiisions of the animal "ingdomJ the

$rotostomes, #hich include arthro$ods, annelid #orms, mollus"s, and cnidarians5 and the deuterostomes, #hich include echinoderms an

chordates. 3rotostomes and deuterostomes di1er fundamentally in the #ay they deelo$ as embryos, strongly suggesting that they s$lit

from each other a long time ago.

Animal life %rst a$$eared $erha$s a billion years ago, but for a long time after this, the fossil record remains almost blan". 2ossils e/ist th

seem to sho# burro#s and other indirect eidence for animal life, but the %rst direct eidence of animals themseles a$$ears about H-(million years ago, to#ard the end of the 3recambrian $eriod. At this time, the animal "ingdom stood on the threshold of a great e/$losion

diersity *see 0iodiersity. 0y the end of the Cambrian 3eriod, +-( million years later, all of the main ty$es of animal life e/isting today

had become established.

A 7oing onto


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(al2pagos Finc%es

The fourteen s$ecies of %nch that inhabit the BalQ$agos Islands are belieed to hae eoled from a single s$ecies resembling the blue)

blac" grassuit, >olatinia @acarina, abundant in


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7any habitats are directly inuenced by the #ay animals lie. Brasslands, for e/am$le, e/ist $artly because grasses and gra&ing animals

hae eoled a close $artnershi$, #hich $reents other $lants from ta"ing hold. Tro$ical forests also o#e their e/istence to animals,

because most of their trees rely on animals to distribute their $ollen and seeds. 6oil is $artly the result of animal actiity, because

earth#orms and other inertebrates hel$ to brea" do#n dead remains and recycle the nutrients that they contain. Without its animal life

the soil #ould soon become com$acted and infertile.

0y $reying on each other, animals also hel$ to "ee$ their o#n numbers in chec". This $reents abru$t $o$ulation $ea"s and crashes and

hel$s to gie liing systems a built)in stability. On a global scale, animals also inuence some of the nutrient cycles on #hich almost all li

de$ends. They distribute essential mineral elements in their #aste, and they hel$ to re$lenish the atmos$here8s carbon dio/ide #hen the

breathe. This carbon dio/ide is then used by $lants as they gro#.A Animals and 3eo$le

African Elep%ant Killed by Poac%ers

4le$hant $o$ulations are on the brin" of e/tinction due to $oachers #ho "ill ele$hants for their iory tus"s. An international ban on iory

trade, instituted in +G?G by the Conention on International Trade in 4ndangered 6$ecies of Wild 2auna and 2lora *CIT46, has diminished

the illicit iory trade and reduced the "illing. Oer +!( countries su$$ort the ban.

Wolfgang 0ayer0ruce Coleman, Inc.

Until relatiely recently in human history, $eo$le e/isted as nomadic hunter)gatherers. They used animals $rimarily as a source of food a

also for ra# materials that could be used for ma"ing tools and clothes. 0y today8s standards, hunter)gatherers #ere eui$$ed #ith

rudimentary #ea$ons, but they still had a ma@or im$act on the numbers of some s$ecies. 7any scientists beliee, for e/am$le, that

humans #ere inoled in a cluster of e/tinctions that occurred about +!,((( years ago in North America. In less than a millennium, t#o)

thirds of the continent8s large mammal s$ecies disa$$eared.

This sim$le relationshi$ bet#een $eo$le and animals changed #ith domestication, #hich also began about +!,((( years ago. Instead of

being actiely hunted, domesticated animals #ere slo#ly brought under human control. 6ome #ere "e$t for food or for clothing, others fo

muscle $o#er, and some sim$ly for com$anionshi$.

The %rst animal to be domesticated #as almost certainly the dog, #hich #as bred from #oles. It #as follo#ed by s$ecies such as the ca

horse, camel, llama, and aurochs *a s$ecies of #ild cattle, and also by the Asian @ungle fo#l, #hich is the ancestor of today8s chic"ens.

Through selectie breeding, each of these animals has been turned into forms that are $articularly suitable for human use. Today, many

domesticated animals, including chic"ens, astly outnumber their #ild counter$arts. In some cases, such as the horse, the original #ild

s$ecies has died out altogether.

Oer the centuries, many domesticated animals hae been introduced into di1erent $arts of the #orld only to esca$e and establish

themseles in the #ild. Together #ith sto#a#ay $ests such as rats, these feral animals hae often had a highly damaging e1ect on nati

#ildlife. Cats, for e/am$le, hae inicted great damage on Australia8s smaller marsu$ials, and feral $igs and goats continue to be serious

$roblems for the natie #ildlife of the BalQ$agos Islands.

Des$ite the gro#th of domestication, humans continue to hunt some #ild animals. 6ome forms of hunting are carried out mainly for s$or

but others $roide food or animal $roducts. Until recently, one of the most signi%cant of these forms of hunting #as #haling, #hich reduc


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many #hale stoc"s to the brin" of e/tinction. Today, highly e:cient sea %shing threatens some s$ecies of %sh #ith the same fate *see

2isheries.

Endangered 34n4 (oose

Rats and mongooses introduced in the a#aiian Islands hae found an easy meal in the nSnS goose, one of the many bird s$ecies natie

only to a#aii. Through ca$tie breeding $rograms, the $o$ulation of this endangered bird had rebounded to more than +,((( by the ea

!(((s, but today the birds are all genetically similar, creating inbreeding that harms their chances of surial.

ames


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