179

3. Fruit-eating birds and mammals eat fruits and seeds contained inthem are dropped unharmed with the excrement at various pJaces.Thus, animals derive nourishment from fruits and on the other hand,help fruit in their dispersal. Similarly, bees, moths, butterflies, etc.receive food from the nectar of flower, and in return bring aboutpollination.

4. The classic example of mutualism is furnished by protozoan-termiterelationship. Termites eat wood but are unable to digest, the celluloseof wood. The intestine secretes an enzyme, which help the insect inassimilating wood. The termites die if deprived of flagellates (eachnewly hatched termite licks the anus of an adult termite to obtain theprotoz9an). The flagellates also benefit by this association; they aresupplied with plenty of food and the proper environment; in fact, theycan only survive in the intestine of termites.

, I

5. The bullhorn acacia tree, which grows in Central and SouthernAmerica also, provides an excellent example of mutualism. The treeprovides lodging and boarding facilities for the ants \ of genusPseudomyrmex. The ants live in larger hollow thorns and' eat sugarsecreted by the tree. The ants benefit the host tree by attackingvirtually anything that touches it. They sting other herbivorous insectsand large herbivores if they try to approach it. When ants areremoved, the tree usually die; probably because herbivores damagethem so much that they are unable to compete with surroundingvegetation for light and growing space.

Competition refers to the type of interaction in which two or moreindividuals or species try to gain control of the s,ame resource. The commonfactors for which organisms compete with each other are, food, space, light,nutrients, pollinating or dispersal agents and so on. Competition may occurbetween the individuals of the same species (called Intra-specific Competition) orbetween the members of the different species of a community (called Inter-specific Competition). Competition always harms both participants because eachcompetitor reduces the other's supply of a needed resource.

IX()

The rivalry between species of same' genus (Intra-specific) is usuallymore severe than that between species belonging to different genera, becausethe members of the same species require many of the same resources,Following two types of intra-specific,competition may be recognized.

1. Scramble competition: in which the resource is subdivided in manysmail parts to which all have access. Individuals scramble for theresource, Wllich results in wastage. Each individual obtains such asmall amount of resource that it is unabl,j to survive and as a resultmortality rate increase and birth rate decrease and population growthis curtailed.

2. Contest or interference competition: in which oach c.uccessful orpowerful claims a part of resource and the unsuccessful or weak onesare denied any access 10 it. Contest competition show up in socialdominance, territoriality, etc.

Thus, the maintenance of a social hierarchy with dominaht and'subordinate individuals is another example of Intra-specific competition. Manyanimals have tendency to live together in-groups called shoals, flocks, herds,packs, colonies, etc. Such groups have some form of social organization. Eachindividual occupies a social status and dominanqe in the group with respect toother individual. The social status or dominance is established by a contest .either by actual fighting or by ritual contest or by aggressiveness or by bluffing orthreats in initial stage between any pair of individual or series of individuals. Thedominant animals eat first and may have a chance to mate before lower rankillganimals. The other m.embers of the group may not produce off:-;pring.

Another social interaction that may affect the population size isterritoriality in which successful competitors establish territories. A territory maybe defined as an area within which an animal tends to stay and considers it as itshome and enjoys the maximum possible freedom. The boundaries of territory areactively defended and any trespassers are forcibly driven out. The dimension ofterritory or home range varies in different groups of animals. For example, therange of territory of a bear is 30 - 40 km; porcupine has 1 km; white tailed deerhas 200 - 300 acres; rabbits 1 - 3 hectares; chameleon lizard has 100 meters;wood ants only one meter and so on.

I Ans: Synthetic gaseous or liquid fuel produced from solid coal. I

· IX I

In the breeding season, most fishes, birds and mammals, the male marksout a territory and with the exception 'of female or females, prevents the entry ofother members in the territory.

For example, Northern Sea Lions mate only on small islets of rockybeaches. Males that are larger and stronger enough to command the rocky areaenjoy mating privilege with about 10 - 20 females. Those males that are weakand can not secure a territory do not mate at all and hence produce no offspring.

The territorial behaviour helps to avoid both overcrowding and under-crowding. Therefore, territorial behaviour is regulatory in function in populationrelationship.

The competition between two different species in the same habitat (say,two different species of birds in a forestfor nesting site, food, etc.) affects both ofthem)n smaller or larger degree. Eventually, after a certain length of time, there~)Ccurs a complete dominance by one species, the other being completely oustedor eliminated or lead to extinction.

In 1934, G.F. Gause studied the effects of inter-specific competition inlaboratory experiments with two species of paramecia. When two closely relatedspecies of paramecium, P. caudata and P. aurelia were cultured separately on afixed amount of food, both multiplied and finally reached to a constant level. Butwhen both these species were placed on the same limited food, only P. aureliawas left at the end of 16th day. P. aurelia neither attacked nor secreted anyharmful substance, it simply had greater growth rate and out-competed the other.

As a result of Guase's work, ecologists derived a basic ecologicalprinciple that "if two populations compete for the same resource that is necessaryfor the survival of each and is in short supply, one of the population will beeliminated". This principle is known as Competi~ive Exclusion Principle.

One example of competitive exclusion principle involves the day Lily(Hemeroca/lis) a popular cultivated plant. Day lilies often escape garden andbegin multiplying along road-sides and in surrounding community. The result isthat the native plants are displaced or eliminated from their original habitats.

'lI Q. What is wildernJss?

Competition betweeFl organisms is always harmful toboth of the individuals involved because each receives lessthan what it could in the absence of competition. Competitioncould result in the exclusion of one species from a communityor in the specie's "extinction", or it can lead to behavioral andevolutionary changes that reduce harmful interactions.

Predation is an interaction in which one organism (the predator) eatsanother organism (the prey). Since all heterotrophs must eat to survive, predationis an integral part of any ecosystem. Examples include, a lion eating a deer; afrog eating a fly; a mouse eating grains or seeds; a grasshopper eating a leaf,and a cow eating grass. Predatory organisms are almost entirely animals but afew kinds of carnivorous plants (such as, Orosera, Nepenthes, Utricularia whichconsume insects) may also be regarded as predators.

Characteristics of a Predator1. All free living animals that catch, kill anCf consume other

animals or plants are called predators.2. Animals. which prey upon other animals almost always kill

their prey; while the herbivore predators (e.g. rats, insects,deers, sheep,' etc) usually just browse on a portion o~theprey's body (i.e. plants). .

3. Many predators have adaptatJ'ons such as claws, teeths,sharp beaks, fangs, stinger or poison that help catch andsubdue or simply chew the prey. ,

. 4. Predator-prey relationship is usually temporary one, just longenough to consume it or at least a part of it. Although somepredators limit their diets to one type of prey, most rely onmore than one species for nourishment.

5. With few exceptions, predators are always larger in size andstronger than their prey.

6. Predators that pursue their prey have keen eyesight and aregenerally fast and agile, whereas those that lie in ambush areoften camouflaged in their environment.

I Ans: Area where the earth and its community of live has not been disturbed by humans.

lX3

The term predator is not reserved only for carnivorous animals eatingother animal~ but also used for herbivore animals, where the plant is prey. Thus,grazing and browsing animals kill the plants on which they feed by consumingentire plant or part of it, and aquatic herbivores feeding on diatoms, desmids,algae, etc. are also referred to as predators.

If the· prey is a primary producer (i.e. the plant), the interaction is calledherbivory. Plant eating animals are called herbivores; those that eat· other

. animals are called carnivores; and those that eat a mixed diet of animals andplants, like humans, are called omnivores.

Escape adaptations Effects1 Camouflage

a. Cryptic coloration Hides from predatorsb. Disruptive coloration Distorts shape and confuses predators

2 Individual responsesa. Startle behaviour Confuses predatorb. Playing dead Confuses predatorc. Shedding body parts Escape captured .. Out-distancinQ predators Escape capture

3 Group responses Warn, protect and confuse

Defense adaptation Effects1 Physical defences

a. Armor Deters an attack2 Aposematic Advertises noxious trait3 Mimicry

a. Mullerian mimicry Noxious species avoidedb. Satesian mimiciy Harmless or palatable species avoided

Chemical Defenses Effects1 Poisons Kills predators .2 Hormones Disrupts predator development3 Allelochemicals Repels predators

[Q uctlile upwelling.

IR-l

Predation exerts different affects on different populations of prey. In somesituations, predati,on severely depletes prey's population. In other systems, it hasbeen shown that predatory population improves the health and vitality of preycommunity. i) by eliminating. indivic;iuals weakened by qenot;· disorders, ii) byconsuming sick individuals, and iii) by preying up, ,.: IIldlvlduals which are injuredor susceptible to disease, Predation '!sc; helps in maintaining diversity in acommunity.

Co-evolution between predators and prey over a long per;iod of time hasproduced a number of remarkable and effective adaptations; some improve theskills of predators in capturing the prey, while others improve the prey's chancesof escaping predators,

Adaptations that help survival can be grouped into two generalcategories: i) those that help 'prey escape from being eaten, and ii) those thathelp a prey defend itself against predator attack (Table 7,2).

Following are the examples of devices that help their owners to avoidbeing eaten,

Some prey go undetected because they perfectly l':c:>rl in \ ith theirsurroundings or because they appeJr i, '-.:1lmate or IneiiJ e. ;:)uch aOctf.Jldiiunsare called Camoufl' ge 'f r>rc~2ctive coloration, For example,

1. The white crab, Crypto/fthode perfectly blend with the white pobbleson the beach and hence very difficult to recognize it.

2, The LithopU5 plants. that live among rocks and stones, so perfectlyblend in colour, form and pattern of stones that camouflage theherbivores.

3. The stick caterpillar or moth So/enia (Fig, 7,5 B) resemble a small twigin colour and shape.

wings(mimicingveins of leaf)

4. Indian dead-leaf butterfly Kallima is an excellent example of protectivecoloration (Fig. 7.5 A). Its wings are brilliantly coloured above but theundersurface is dull brown in colour which resemble like a dead dryleaf. When the butterfly rest upon some branch or object, its wings arefolded while the exposed undersurface of t~e body look like a deadleaf and thus escapes predation .

. Camouflage is not reserved exclusively for prey however, predators aJsouse camouflage to help conceal themselves while wailing to ambush prey. Forexample,

1. Polar bears and polar foxes are white in colour and are invisible totheir prey against white snowy background.

2. Stripes and spots of tigers and leopards conceal them in opensavanna fields.

3. The Pastel spiders very much resemble in shape and-colour to theyellow flowers on which they live and hence are not easilydistinguished by the prey.

The protective coloration may again be of two types; Cryptic andDisruptive.

a. Cryptic coloration: The camouflage of some organisms helps theseindividuals resemble their background. This type of adaptation iscalled Cryptic coloration because the camouflage organisms is hiddenfrom view. For example, some flatfishes, crabs, chameleons, etc.change colours and patterns of their bodies to match the seasonal

. changes in its surroundings.

b. Disruptive coloration: Disruptive coloration disguises the shape ofan organism. For example, some butterflies, caterpillars, etc. posses

. black spots on their wings or body (Fig. 7.6 A); these may be simplerounded big spots. Their sudden display by the animal confuses andfrightens away the predators. In some insects, for example, thelantern-fly (Fig. 7.6 B) from Thailand has a false head. Trinidad Iinus(Fig. 7.6 C) affords another example of false head. The "dummy head"mislead the p~edator, which normally attacks towards the head

\ bearing eyes. The victim suddenly darts in the wrong side andescapes.

A. South American butterfly showing eye spotsB. Lantern-fly C. Trinidad linus

When faced with a predator, some prey rely on sudden escaperesponses. Generally, the predator is momentarily stopped by the unexpectedresponse, especially if the escape response seems dangerous. This moment'shesitation may give a chance to escape. Examples of such responses include:

1. An owl fluffs its feathers and spreads out its wings, a last minutebluff that usually startles an attacking predator.

2. Mosquito fish frantically splashes on the surface of a pond whenapproached by some. predatory fish, making it difficult for thepredator to launch a pinpoint attack

1. American opossum, Didelphis becomes unconscious, rolls overand simulates ·.asdead when, confronted with a predator.

2. Hard bodies beetles fall downlike pebbles when they findthemselves in danger.

A few organisms may escape a predator by detaching the seized partof their body. For example, a lizard quickly detaches its tail whenapproached by sO,me predator. The tail continues to move for severalminutes and thereby keeping the predator busy sometime. The lizard,in the meantime runs away to safety.

Some animals escape becoming prey simply by out-running thepredator. For example, a healthy antelope or deer, for instance, canusually outdistance a lion.

1,0 Define over-grazing.

Schools, packs, colonies, herds, and shoals typically defend themselvesmore effectively than can a single organism. For exal...,le, the first smelt fishwhich notices the approach of any predator, immediately releases some kind ofchemicals into the water, which immediately alerts the other members of theshoal and they flee in various directions. The confused predator does not knowwhich way to turn.

Many species of plants and animals possess protective armor thatprotects it from predators. For example,

1. A number of plant species have thorns, spikes Or prickles that playimportant role in discouraging browsers. Some have hooks on theirleaves, which make feeding difficult even for small insects. Thedefense role is of plant hairs, particularly those having glandular tips isalso important. For example, glandular sticky hairs of wild potato aredefenses against aphids.

2. Among animals, for example, molluscs and turtles have shells;porcupines have quills; sea rchins possess needle like spines;anteaters have thick scales and so on.

Animals equipped with effective chemical defenses or a stingingmechanism or obnoxious taste qre often brightly coloured, a warning to predatorsknown as Aposematic coloration ("apo" - meaning "away" and "sematic"meaning "signal"). In general, yellow-black and bright red tend to be commoncolour patterns of these animals. The aposematic or warning coloration is. tIleopposite of camouflage; it makes an organism stand out from its surroundin~s.These ..animals make no effort to conceal themselves but sometimes evendeliberately flash colour with the uplift of th~ body o~ wings.

'" .IDestruction of vegetation when too many animals fe~d and exceed the carrying capacity of a range'lnd area. \ .

IX9

For example, a species of European toad has a bright scarlet belly. Thetoad has certain chemicals secreted by its skin glands, which make it extremelyunpalatable, and whenever a predatory bird, such as stork, swoops over acongregation of toads, they flop on their backs exposing their scarlet red belliesas warning. The stork and other predatory birds apparently become conditionedby the association of red colour and the bad taste and avoid toads assiduously.Similarly, the distinctive coloured strips of skunk advertise to potential predatorsthat this animal can yield an a very bad smelly counter attack.

The term mimicry is derived from Latin word "mimicus" which means toimitate closely or to simulate. Mimicry may.be defined as a superficial but closeresemblance of one organism to another or to natural objects (such as twigs,stone, etc.). The organism, which mimics is called "Mimic" and the organism or.object which is imitated or copied is called "Model".

The type of mimicry in which a palatable or harmless species mimics anLjnpalatable or harmful model, is called Batesian Mimicry (after HW. Bates whofirst advocated the theory of mimicry). However, if two unpalatable species thatinhabit the same community mimic each other, it is called Mullerian Mimicry (afterFritz Muller who named the phenomenon).

1. Certain non-poisonous snakes of family Colubridae exhibit colourpattern of poisonous coral snakes. They have alternate bright red andblack stripes. .

2. The palatable Viceroy's butterfly (Fig. 7.7) which can easily be preyeJupon, mimics the unpalatable monarch butterfly of the genus Dan(jisand thus escapes predation.

3. Similarly, a moth of genus Sesia carboniformes, mimics a dangerouswasp of yellow colour (Fig. 7.8).

I Q. What are game species?

(B)Fig. 7.4: Viceroy's (A) and Monarch (B)butterfly showing close resemblance

191

As described above, in Mullerian mimicry, two or more unparatablespecies resemble each other. Presumably each species gains an additionaladvantage, because the pooling of numbers causes predator to learn morequickly to avoid any prey with a· particular appearance. For example, a type ofwasp called Yellow-jacket wasp, and a species of bee, the Cuckoo bee, bothhave stingers that release strong toxic chemicals. Presumably both gainadvantage beyond their own defenses because predator will le.arn quickly toavoid any prey with this appearance ...

Predators also use mimicry in a variety of ways to capture prey. Forexample, some snapping turtles have tongues that resemble a wriggling worm,thus luring small fish; any small fish that tries to eat the "bait" is itself quicklyconsumed. Another interesting example is afforded by Anglerfish, Lophius. Thisfish lives in deep sea and camouflage itself with the surrounding. The first ray ofits dorsal fin is located on the dorsal edge of upper lip. This ray is known as"licium". It can be rotated freely. The anglerfish moves it in such a way that itappears as if #some worm is moving. If another fish tries to snap this dummyworm, the anglerfish swallows it immediately.

a. Poisons: Some tropical toads, frogs, newts: and puffer fish secreteextremely poisonous chemicals that kill the predators.

b. Hormones: Some chemicals act as hormone analogues and interferewith the development of larval stages.

c. Allelo-chemicals: Some animals and plants release Allelo-chemicals...... chemicals that deter, kill, or in some other ways discourage \predators.

Many plants produce chemicals that function in defense by making thevegetation distasteful or harmful to a herbivore. Estimates suggest that 50,000 to100,000 different secondary plant compounds may exist.

I Q. What is indicator species?

Secondary compounds, chemicals that are notinvolved in primary metabolism, play the dominant rolein protecting plant from being eaten by herbivores orpredators.

Because plants can not run away from herbivores, chemical toxins aretheir main weapons against being eaten. For example. Strychnine is produced bya plant strychnos; morphine from opium poppy; nicotine from tobacco; masculinefrom cactus~ digitoxin from foxglove, and so on.

Animals also manufacture a variety of chemicals that they use in theirdefense. Venomous snakes, lizards, fishes are well known; in addition, bees,wasps, predatory bugs, scorpions, spiders and many other arthropods havechemicals that they use to defend themselves as well as to capture or kill theirprey.

\7.8PARASITISM '

",It is, the rel~tion between two individuals where'ir::l one individual called

parasite receives benefit at the expense of another individual called host. Aparasite usually parasitizes a host, which is larger in body size than it. Furthpr i1

parasite never kills its h Jst immediate y in it. 1)'.'::1 ;nterest.

parasite is an organism, w.hich resides on or in the bodyof a larger living organism and obtains its nourishment from itstissues, and causes harm to it.

Although parasitism is sometimes regarded a form ofpredation, the victim of parasitism usually survives the interaction,whereas the victim of-predation is almost killed always.\ .

Apparently no organism i-s free from parasites. Even parasites can haveparasites,. a condition called hyp.erparasitism. Most organisms are host to anumber of different kinds of parasites. For example, a single bird may have,asmany as 20 - 40 different kinds of parasites in its skin, feathers, gut, blood, etc.

193

The parasites exhibit a great diversity of adaptations. The parasites maybe Viral (e.g. all kinds of viruses on plants and animals are regarded asparasites), Microbial (that infect bacteria, protozoans, fungi, etc.), Phytoparasites(e.g. species of Cascuta is found on the same stem of other plants on Wllich theydepend for food), and Zoo parasites (e.g. animal parasites such as,platyheminthes, nematodes, cestodes, crustaceans, protozoans, etc).

The parasites may occur on the outside of the host (called ecto-parasite). or may live within the body of the host (called endo-parasile). The parasite maybe full-time (permanent) or part-time (temporary). Mosquitoes, bed-bugs, fleas,etc., which are usually in contacts with their hosts for only short periods arereferred to as temporary parasites. Permanent parasites, however, spend theirlife completely on other organisms. The parasites also vary in their hostspecifically; they may depend only on one kind of host or may choose any host.Most parasites are host specific i.e. they live in one particular species only. Forexample, Taenia solium and Taenia saginata (tapeworms) are so. specificallyadapted to live in human intestine that they can not live in intestine of monkey,dog, cat, sheep, rabbit, etc.

In contrast to parasites, some insect's larvae are parasitoids, which killtheir host by completely consuming its soft tissues. For example, a giant wasp,Pepsis marhinata when ready to lay eggs, she sometimes sit on a giant spiderTarantula. Although the spider can easily kill the wasp, but it does not do so andmakes little effort to escape. Female wasp stings the spider and lays a single eggwhich attaches to the abdomen of paralysed spider. When the larva hatches outfrom the egg, it obtains its entire food from the tissues of paralysed spider andhence the helpless spider is literally eaten alive.

Some parasites exploit the behaviour of their host, an interaction calledSocial Parasitism. European cuckoos, American cowbirds, African honey guides,etc provide examples of social parasitism. For example, the American cowbirdnever builds its own nest or care for it eggs and offsprings. Instead, it removesone egg from the nest of a bird of another species and lays one of its own eggs,a "replacement". The egg is usually so similar in shape, size, and colour that thehost bird fails to recognize it as an alien egg and incubates the parasite's egg asits own. Since the newly hatched young cowbird is larger, stronger andaggressive than the host's babies, it pushes them out of the nest or takes most ofthe food and leaving them to starve to death.

I Q. What is demography? =oJ

An interaction in which one population definitely inhibits the other whileremaining unaffected itself. Here none of the population derives any benefit.Amensalism involves some type of chemical interaction, by which the organismsof one species affect the well· being or growth of individuals or the populationbiology of the. other.

i. Pond blooms of green algae, eSP.8cially of the genus Microcystis, areknown to produce toxins, such as hydroxylamine, which causes U18death of fish and even of cattle that drink the water.

ii. Certain land plants are harmful to animals. For example, a semi-de~ert plant, Halgeton glomeratus, found in Nevada, kills the sheeptha't eat it.

iii. Production of chemicals that are antagonistic to microbes "'tileantibiotics" .are well known. Bacteria, actinomycetes, and fungiproduce a number of anti-microbial substances, which are widespreadin nature. The action of penicillin, streptomycin, aureomycin and otherantibiotics produced by fungus in destroying various pathogenicbacteria is familiar.

Chapter8

POPULATION ECOLOGY

The word "Population" may be defined as a group of individuals belongingone and the same species and living in the same geographical area. The

embers of a population generally interbreed with one another except fewHth.ogenic species .

. A some what less rigid definitionconsiders a population to be a group ofindividuals of a species that use commonresources and are regulated by the samenatural phenomenon such as, temperature,water, food supply, predation, etc.

Population ecology, therefore, is the study of individuals of same speciesIccupying a particular area at a given time. For example, a tropical deciduous::lrest not only contains a population of Acacia trees, but also populations of-::assia trees, Ficus trees, barking deers, wild cats, pheasants, partridges, etc.

The aim of population ecology is to understand and to explain theluctuations in population which takes place under natural conditions. a~.v..,t' c.l:-;

rvhen these are exploited by man.