Ecological interactions form the backbone of an ecosystem. It helps in maintaining the dynamic equilibrium of an ecosystem. All organisms are linked to at least one other species in a variety of critical ways, for example, as predators or prey, or as pollinators or seed dispersers with the result that each species is embedded in a complex network of interactions. Consequently, the extinction of one species can lead to a cascade of secondary extinctions in ecological networks. Moreover, interactions between species can lead to ‘community closure’ after the loss of a species, with the result that a locally extinct species cannot re-establish itself if it is reintroduced. Many ecological interactions involve flagship species and keystone species as in the case of Macaca silenus & Cullenia exarillata. Then some interactions like mycorrhiza help in nitrogen fixation. Strategies like predation reduce the loss of vegetation through grazing. Interaction can be either intraspecific or interspecific. Interactions between individuals of the same species and those between individuals of different species are called intra- & interspecific interactions. respectively. The lichen serves as an example of interspecific interaction and dog fighting. for a common prey for intraspecific interaction.

1. 1. The beauty of an ecosystem lies in its diversity and this diversity is in turn maintained by the
interactions between various organisms at different trophic levels. Ecological interactions depict the
network of influences that the activities of different species have on one another in an ecosystem.
2. Food webs offers an important tool for investigating the ecological interactions that defines energy
flow and prey-predator relationships.
3. The ecological interactions forms the backbone of an ecosystem. It helps in maintaining the
dynamic equilibrium of an ecosystem. All organisms are linked to at least one other species in a
variety of critical ways, for example, as predators or prey, or as pollinators or seed dispersers with the
result that each species is embedded in a complex network of interactions. Consequently, the
extinction of one species can lead to a cascade of secondary extinctions in ecological networks.
Moreover, interactions between species can lead to ‘community closure’ after the loss of a species,
with the result that a locally extinct species cannot re-establish itself if it is reintroduced. Many
ecological interactions involve flagship species and keystone species as in the case with Macaca
silenus & Cullenia exarillata. Then some interactions like myccorhiza helps in nitrogen fixation.
Strategies like predation reduce the loss of vegetation through grazing.
4. Interaction can either intraspecific or interspecific. Interaction between individuals of same species
and those between individuals of different species are called intra- & interspecific interactions
respectively. The lichen which serves as an example for interspecific interaction and dogs fighting
for a common prey for intraspecific interaction.
5. Often with the term ecological or species interaction we do come across the term symbiosis which
means a mutualistically beneficial coexistence of two different groups of organisms.
6. Different researchers are of different views regarding the classification of ecological interactions.
The ecological interactions can be broadly classified into 3 types- positive interactions, where in
either one or both of the species interacting is benefited, negative interactions where either one or
both species are harmed and the last one, neutral interactions where neither species is affected but
live together. Neutral interactions are commonly seen in bacterial cultures. The positive interactions
include facilitation. Negative interactions include predation, herbivory & parasitism & cannibalism.
7. First one facilitation,
Facilitation describes species interactions that are beneficial to at least one of the species involved. It
is commonly seen under environmental stress. Facilitation can be of 2 types- mutualism &
commensalism.
In mutualism, both species benefit from the interaction and in commensalism one member derives a
benefit, while the other neither benefits nor harmed.
Mutualism can again be classified into dispersive, defensive & resource based mutualism.
Commensalism can be classified into inquilinism, phoresy & metabiosis.
8. Mutualism can be either facultative where the interaction is beneficial but not compulsory or
obligate, where in neither species can live without the other. The lichens are example for obligate
mutualism & mutualism between ants and aphids are facultative.
9. The different categories of mutualism. First one, dispersive mutualism. It includes the plant-
pollinator relationships where the pollinator is benefits by nectar & other rewards and pollinators
serve as agents of pollination. Plant-frugivores relationships where on benefited by receiving food
and other by aiding in seed dispersal.
10. Invasive mutualism,

2. Alstroemeria aurea is a keystone mutualist in South Andean forests relies principally on the giant
bumble bee, Bombus dalhomii for its pollination. Introduced Europen bumble bee, Bombus ruderatus
invaded South America and replaced the native keystone mutualist Bombus dahlbomii. In this article
by Aisen et. al, they suggest that less- efiicient poinator Bombus ruderatus would in long term may
select for smaller flowers.
In this article by Hanna et al, they examined the restoration of plant-pollinator mutualisms following
the large scale removal of an invasive nectar thief & arthropod predator, Vespula pensylvanica.
Metrosideros polymorpha a functionally important tree endemic to Hawaii. The reduction of V.
pensylvanica in the managed sites resulted in a significant increase in the visitation rates of effective
bee pollinators.
11. Mutualism disruption hypothesis
Muutualism disruption hypothesis suggest that inhibition of native mutualists can provide invaders
with a competitive advantage over mutualism-dependent native species. In this article by Hale et al,
they demonstrate that Alliaria petiolata produce allelochemicals like glucosinolates which in soil are
hydrolysed to isothiocyanates, a class of compounds toxic to AMF thus inhibiting the growth of AMF
dependent forest understorey native, Maianthemum racemosum commonly called false Solomon’s
seal.
12. Plant-frugivores relationship
Some fishes, birds, bats & other animals serve as agents of seed dispersal and establish a mutualistic
relationship with plants.
13. Mistletoes are obligate stem parasites whose seeds are dispersed by passerine birds. The seeds
contain a sticky substance called viscin which causes the seeds to clump together even after passage
through bird’s gut. They often stick to the branches or the birds and are directly wiped onto the branch
by the bird. Seeds defecated onto the ground die.
14. Defensive mutualism involves an animal defending a plant or a herbivore.
The red carpenter ant, Camponotus pennsylvanicus tends aphids feeding on a twig. The ants
receive honeydew produced by the aphids and in return protect the aphids from predators.
Next, Pseudomyrmex ferruginea ants make nests inside the large, hornlike thorns of the bull’s horn
acacia, Acacia corrigera and defend the plant against insects and mammals. In return, the acacia
provide protein rich granules, Beltian bodies and nectar from extrafloral nectaries.
This is Festuca rubra the main fodder of the Soay sheep, Ovis aries. Festuca rubra harbors an
endophytic fungus, Acremonium sp. Which lives inside the blades. The fungi syntheize toxic
chemicals that function as anti herbivory defense. In return, the fungi gains access to a food source
within the plant leaves. As the sheep number increase and the pasture height decreases through
grazing the sheep encounter higher concentrations of chemicals which reduce the sheep numbers.
When herbivory is reduced, grass grows longer and concentration of toxins at the tips of the grass is
less, permitting sheep population density to increase.
15. Resource based mutualism. It involves the increased acquisition of resources for both species.
Examples include mycorrhiza, where the fungi require soluble carbohydrates from their host as
carbon source and they supply minerals and water which they are able to extract more efficiently from
the soil than the host.
Next one involves corals and dinoflagellates. Dinoflagellates live within the corals, photosynthesise
and provide oxygen and nutrients to their hosts as well as give the corals their colouration. In return,
the corals provide carbon dioxide and waste products used by the dinoflagellates.
Leaf cutting ants exhibit resource based mutualistic relationship with a fungus. Ants cut & chew the
leaves into a pulp which they store underground as a substrate on which the fungus grows. The ants
shelter and tend the fungus, protecting it from competing fungi, helping it reproduce and grow. In

3. return, the fungi produces gongylidia which serve as food for the ants. In this way the ants circuimvent
the chemical defenses of the leaves which are digested by the fungus and the fungi exists as a healthy
colony underground.
16. Other examples include lichen.
Then the honey badger and honey guides. Honeyguides like Prodotiscus are unable to open bees’nest
for themselves. They attract the attention of honey badgers like Mellivora capensis by a distinctive
call and by flying from perch to perch with tail feathers fanned out. The honeybadgers follow the
honeyguides to the bees’ nest and rip it open and consume the contents, leaving the scraps for the
honeyguides to feed on.
The mutualistic relationship between crops and humans. The population size of humans is increased
by the presence of the introduced or hybrid crop varieties and domesticated animals and similarly
populations of crops and domesticated animals are increased in the presence of humans.
17. Next the second type of facilitation i.e., commensalism where one member derives benefit while
the other neither benefits nor is harmed. Different types of commensalism are inquilinism, phoresy
and metabiosis.
Inquilinism occurs when one species uses a second species for housing. Example epiphytes
like orchids.
Phoresy occurs when one organism uses a second organism for transportation. Example, flower
inhabiting mites travel between flowers in the nostrils of humming birds.
In metabiosis, an organism uses something produced by the first, usually after its death. For example,
hermit crabs use snail shells for protection.
18. Some more examples for commensalism. First one, the pitcher plant providing habitat for
mosquitoes. Next the cattle providing insect food for cattle egrets. Then certain algae inhabiting the
sloth body.
19. Whales’ body serving as the habitat for barnacles. Anemones providing protection to the
clownfish. Sea cucumber providing habitat to the pearlfish.
20. Negative interactions. First one competition. Competition is a biological interaction between two
or more organisms of the same or different species where the species compete with each other for a
common resource, when the resources are not sufficient to fill the needs of all the organisms.
Competition can be either harmful to both the species i.e. equal or unequal, harmful to one and does
not affect the other.
Competition can also be characterized as exploitation competition or as interference competition. In
exploitation competition, organisms compete indirectly through the consumption of a limited
resource, with each obtaining as much as it can as in the case with plants competing for light, nutrients
& water in a forest. In interference competition, individuals interact directly with one another by
physical force or intimidation. Often this force is ritualized into aggressive behaviour associated with
territoriality. In these cases, strong individuals survive and take the best territory, and weaker ones
perish or at best survive under suboptimal conditions. Interference competition occurs most
commonly in animals. Both intraspecific and interspecific competition may be caused by exploitation
competition, interference competition, or both.
21. Some interactions involving competition are unequal, i.e. a –/0 relationship, called amensalism
or antibiosis. Examples for amensalism include allelopathy. Roots of Juglans nigra produces the
allelochemical, juglone which kill the roots of neighbouring plants. This phenomenon is called
allelopathy.
Next, South African bitou bush, Chrysanthemoides monilifera, which has invaded Australia
following its introduction to stabilize dunes produced by mining, secretes low-molecular-weight

4. volatile compounds into the soil that inhibit growth of native Australian plants, including the normally
dominant acacia, Acacia longifolia.
22. In apparent competition, two species do not compete for the same resource but they do share at
least one natural enemy. This often leads to the exclusion of the more susceptible of the species.
In North America, the usual host of the meningeal worm, Parelaphostrongylus tenuis, is the white-
tailed deer, Odocoileus virginanus, which is tolerant to the infection. Moose, Alces alces, however,
are potential hosts and in them the worms can cause severe neurological damage leading to reduced
resistance to other disease and direct mortality. This differential pathogenicity of P. tenuis makes the
white-tailed deer a potential competitor with moose.
23. The associational susceptibility. Associational susceptibility, occurs in plants where herbivores
spill over from one species onto another. In northern Utah, the caterpillars of the moth Alsophila
pometaria, commonly known as fall cankerworms, prefer to feed on box elder trees and are rarely
found on isolated cottonwood trees. However, when cottonwoods occur under box elder, the
cankerworms spill over and cause increased defoliation of the cottonwoods, though without actually
killing them.
24. Competitive exclusion principle was proposed by Garett Hardin in 1960 which means that
complete competitors cannot co-eixst. It is hypothesized that one species excludes other from its niche
as a result of interspecific competition. This he demonstrated by an experiment where each of three
species, Paramecium aurelia, Paramecium bursaria, and Paramecium caudatum, grows according
to the logistic model when grown alone. When P. aurelia is grown with P. caudatum, the density of
P. aurelia is lowered compared to when grown alone, but P. caudatum goes extinct. When P. caudatum
is grown with P. bursaria, the population densities of both are lowered but they coexist. Species may
avoid competitive exclusion by partitioning resources or being of different sizes, which permits them
to feed on different sized resources.
25. Ian Kaplan & Robert Denno put forth some predictions based on competition theory. These are
Intraspecific competition should be severe than interspecific competition since resource overlap is
greater. The strength of interspecific competition is greater between more closely related species or
in similar guild. The strength of interspecific competition increases with decreased resources.
26. Second type of negative interaction is predation. In predation, predators feed on other living
organisms known as prey, either killing their prey before they eat them or during the act of eating.
Often the predators occupy the higher trophic levels. Predation plays an important role in maintaining
the population size in different communities.
27. A predator that is more efficient at catching prey exerts a strong selective force on its prey. Over
time, adaptations that reduce the probability of being captured may evolve in the prey species. These
anti predator adaptations, in turn, exert a strong selective force on the predator. This type of
interdependent evolution of two interacting species is known as co-evolution. Some of the anti-
predator adaptations are listed here.
28. First one chemical defenses. Example involves the bombardier beetle, Stenaptinus insignis. When
threatened they eject the chemicals into an explosion chamber where the subsequent release of oxygen
causes the whole mixture to be violently ejected as a hot spray that can be directed at the beetle’s
attackers.
29. Next the aposematic colouration or warning colouration, which advertises an organism’s
unpalatable taste. Ladybird beetles’ bright red colours warn of the toxic defensive chemicals they
exude when threatened. Monarch butterfly caterpillars, Danaus plexippus, accumulate emetic

5. chemicals called cardiac glycosides from milkweed plants. Emetic chemicals cause predators to vomit
or throw up. The caterpillars advertise their emetic compounds with bold colours. The chemicals are
also present in the adult butterflies, which advertise their distastefulness with bright orange and black
colours.
30. Third one the Cryptic colouration. Cryptic colouration is an aspect of camouflage, the blending
of an organism with the background of its habitat. Cryptic colouration is a common method of
avoiding detection by predators. Many grasshoppers are green and blend in with the foliage on which
they feed. Stick insects mimic branches and twigs with their long, slender bodies. Many sea horses
adopt a body shape and colour pattern that mimics the habitats in which they are found. Leaf wing
butterflies also mimic leaves. Even the veins of leaves can be mimicked on the butterfly’s wings.
31. Fourth one mimicry. Mimicry, the resemblance of a species (the mimic) to another species (the
model) secures protection from predators. There are two major types of mimicry. Batesian mimicry,
named after the English naturalist Henry Bates, is the mimicry of an unpalatable species (the model)
by a palatable one (the mimic). The non-venomous scarlet king snake, Lampropeltis triangulum,
mimics the venomous coral snake, Micrurus nigrocinctus, thereby gaining protection from the
predators. In Müllerian mimicry, named after the German biologist Fritz Müller, many noxious
species converge to look the same, thus reinforcing the basic distasteful design. Monarchs and
viceroys may be an example of Müllerian mimicry, in which two or more different species that are
distasteful or poisonous have come to resemble each other during the course of evolution. This
likeness provides an adaptive advantage because predators learn quickly to avoid all butterflies with
the colouration and markings of monarchs and viceroys. As a result, fewer butterflies of either species
die, and more individuals survive to reproduce.
32. Fifth one, physical defense. This includes the shells of tortoise & freshwater turtles, tough
exoskeleton of beetles, venomous stingers of scorpions, powerful jumping ability of grasshoppers
and the giliding of flying fish.
33. Sixth one, intimidation. A toad swallows air to make itself appear larger, frilled lizards extend
their collars when frightened to deceive potential predators about the ease with which they can be
eaten. In a display of intimidation, this porcupine fish, Diodon holocanthus, puffs itself up to look
threatening to its predators.
34. Seventh one, predator satiation. Predator satiation is the synchronous production of many progeny
by all individuals in a population to satiate predators and thereby allow some progeny to survive.
Thirteen- and 17-year periodical cicadas, Magicicada sp., are so termed because the emergence of
adults is highly synchronized to occur once every 13 or 17 years.
35. Additional prey defenses include camouflague by chameleon, decorating crabs covering their
body with debris for camouflage, evisceration by sea cucumbers etc.
36. Predators have evolved adaptations to help them catch prey. Prominent among these is aggressive
mimicry, where predators mimic a harmless model, allowing them to get close to prey. crab spiders
sometimes mimic the colour of flowers and sit in the flower’s center, waiting to catch a passing
pollinator such as a bee. Praying mantises also mimic flowers and leaves to get close to their prey.
The humpback anglerfish, Melanocetus johnsonii, uses a modified dorsal spine as a bioluminescent
fishing rod to attract prey close to their mouth. The alligator snapping turtle, Macrochelys temminckii,
wriggles its tongue, which resembles a little pink worm, to attract small fish.
37. Female bolas spiders of the genus Mastophora attract male moths by producing analogues of the
female’s pheromones. Female fireflies of the genus Photuris mimic the light-flashing patterns of

6. females of the genus Photinus to attract—and then consume—Photinus males. The saber-toothed
blenny, Aspidontus taeniatus, mimics the blue streak cleaner wrasse, Labroides dimidiatus. The saber-
tooth mimics the cleaner’s dance and is allowed to approach close to its prey, whereupon it bites off
a piece of fin and flees. In flight, the zonetailed hawk, Buteo albonotatus, resembles the turkey vulture,
Cathartes aura, and flies among them. It peels off from the flock to ambush its prey.
38. Predation by brown tree snakes, Boiga irregularis devastated the avifauna of Guam in the Mariana
Islands during the last half of the twentieth century, On Guam, the snake has no natural predators to
control it. The birds on Guam did not evolve with the snake, they had no defenses against it causing
the extirpation or serious reduction of most of the island’s 25 resident bird species. Here you can see
the population trends for Guam birds.
39. Third type of negative interaction is herbivory. Herbivory involves the predation of plants or algae.
Monophagous herbivores feed on one plant species or just a few closely related species. Polyphagous
species, which are mainly mammals, feed on many different host species, often from more than one
family. Panda which feed only on bamboo serve as an example for monophagous species whereas
grasshoppers serve as an example for polyphagous species.
40. Herbivory can be classified into different types based on what they eat. Folivores specialize in
leaf feeding, while frugivores, such as parrots, eat mainly fruit. Nectarivores feed only on nectar and
granivores only on seeds. Leaf miners lay eggs on leaves and the larvae feed between the leaf surfaces,
creating blister-like mines on leaves. Some herbivore species even live deep underground, feeding on
roots. Bark beetles feed just under the bark, while other beetles feed deep within the heart wood. Gall
insects like flies, aphids, or wasps, lay their eggs on stems or leaf buds, and induce a tumor-like
growth. The larvae feed safely inside the developing gall.
41. The defense mechanisms evolved by plants to resist herbivory. The sea of green is armed with
defensive spines, tough cuticles, and noxious chemicals. Constitutive defenses are always present in
the plant. These are called phytoanticipins. Induced defenses are only switched on when herbivores
attack. These are called phytoalexins. Some of the strategies employed by plants to defend herbivory
are listed here which includes mechanical defense, chemical defenses, mutualisms with defensive
agents, associational resistance & mimic semiochemicals.
42. First one, mechanical defenses. A plant’s first line of defense is mechanical. This includes thorns
and spines that deter vertebrate herbivores, trichomes on the leaves that trap and kill small insects,
sticky resins produced by plants that gum up the mouthparts of insects when they puncture the leaf
veins, tough fibers which are common in plant bark, seed coats and the outside of nuts discourage
herbivore feeding. Similarly, grasses and palms sequester silica, which makes them difficult to chew.
43. Next one, the Chemical defenses. This includes an array of unusual and powerful secondary
metabolites that provide a second line of defense against herbivores. Most of these chemicals smell
bad or are bitter tasting or toxic, and they deter herbivores from feeding and plant pathogens from
colonizing and establishing. These secondary metabolites can be categorized as alkaloids, phenolics
& terpenoids.
44. Some powerful alkaloids against herbivory include Scopolamine produced by Brugmansia
suaveolens, Swainsonine produced by Swainsona canescens, Nicotine produced by Nicotiana
tabaccum & Caffeine produced by Coffea arabica.
45. Phenolics include quercetin, a flavonoid present in Levisticum officinale & Camellia sinensis. In
Citrus medica & other species of citrus, many flavonoids and tannins are present which act against
herbivory.

7. 46. Terpenoids include menthol produced by mint, camphor produced by Cinnamomum camphora,
Cannabinoids produced by Cannabis, and those produced in Syzygium aromaticum, Zingiber
officinale.
47. A plant’s chemical defenses are often induced, produced in reaction to damage caused by
herbivores. In some plants, herbivore damage induces defense hormones, systemin and jasmonic acid,
to be produced. These volatile compounds travel through the air and induce neighboring plants to
increase the levels of their own chemical defenses, leading to the idea of “talking plants.”
48. Plant chemical defenses can be classified as quantitative or as qualitative, depending on the
volume of defense present in the plant. Quantitative defenses are substances that are ingested in large
amounts by the herbivore as it eats and that prevent energy gain from the digestion of food. Examples
are tannins in Vitis vinifera & Castanea sp.. Qualitative defenses are toxic substances that are effective
in very small doses. These compounds are present in leaves at low concentrations, usually less than
1% of dry weight. Example atropine produced by Atropa belladonna & Cerberin in Cerbera odollam.
49. Next the apparency. Qualitative and quantitative defense strategies are correlated with plant
apparency. Apparent plants are long-lived, large, and always apparent to the herbivores. Their
defenses are thought to be mainly quantitative, effective against both monophagous and polyphagous
herbivores whereas unapparent plants are small, ephemeral, difficult to find, and unavailable to
herbivores for long periods. Their defenses are thought to be mainly qualitative, guarding against
polyphagous enemies like deer or other vertebrates, which would find them only by chance. Oak trees
are example for apparent plants & weeds are example for unapparent plants are weeds.
50.Plants may sometimes enter into a mutualistic relationship with insects that defend them, as in the
case of bull’s horn acacia and ants. Second, they can grow next to unpalatable plants that tend to deter
herbivores, a phenomenon known as associational resistance. Third, they may selectively abscise
leaves, heavily infested by sessile insects such as leaf miners or aphids causing the leaves to fall to
the ground and preventing the insect from completing its life cycle. Fourth, some specialized species-
specific plant defenses exist. For example, Passiflora produce physical structures that mimic eggs of
the Heliconius butterflies, whose larvae feed on them. Since the females are less likely to lay eggs
where other eggs are present, oviposition is discouraged. Finally, the behaviour of many insect
herbivores is altered semiochemicals. In some cases these are pheromones, which act as sex
attractants between males and females. In others they are allelochemicals that affect behaviour
between different species. In many cases, plants produce analogues of these chemicals, which serve
to disrupt herbivore behaviour. Disruptions to behaviour ultimately reduce reproductive success and
hence future population densities.
51. Herbivores can overcome plant defenses in five different ways. These are mechanical adaptations
like flat grinding teeth, behavioural adaptations like feeding when toxin concentration is lowest,
digestive adaptations which include the presence of mixed function oxidases which catalyses the
oxidation of secondary metabolites to a corresponding alcohol, microbial symbionts present in
digestive tract of herbivores and the host manipulation such as by inducing tumour like growths by
wasps.
52. Certain chemicals that are toxic to polyphagous herbivores actually increase the growth rates of
adapted monophagous species, which can circumvent the defense or put the chemicals to good use in
their own metabolic pathways. The memebers of Brassicaceae like cabbage contain acrid smelling
glucosinolates like sinigrin. Large white butterflies, Pieris brassicae, preferentially feed on cabbage.
If newly hatched larvae are fed an artificial diet, they perform much better when sinigrin is added to
it. When larvae are fed cabbage leaves on hatching from eggs and are later switched to an artificial

8. diet without sinigrin, they die rather than eat. In this case, the secondary metabolite has become an
essential part of the diet.
53.Next beneficial Herbivory. In 1978 Daniel Simberloff and colleagues noted that the action of
isopod and other invertebrate root borers of mangroves in the Florida Keys tended to initiate new
prop roots at the point of attack. Because more prop roots meant greater stability to mangroves against
wave and storm action, root herbivory could in fact be beneficial. The article here by Brooks & Bell
published in 2002 confirms the same. Thus the herbivory has become beneficial to the mangrove,
hence called beneficial herbivory.
54. The fourth type of negative interaction is the parasitism which involves the interaction between a
prey called host and predator called parasite but the latter does not kill the former outright.
55. The major differences between a micro- & macroparasite, parasitoid and predator. Microparasite
includes microscopic parasites like virus. Macroparasites can be viewed with naked eyes like the
tapeworm. Parasitoids have size comaparable to that of hosts and they develop as internal parasites
of insect immature stages such as larvae or pupae of hosts.
56. Parasites can be divided into two types based on where they found in the host body. Ectoparasites,
such as ticks and fleas, live on the outside of the host’s body, while endoparasites, such as pathogenic
bacteria and tapeworms, live inside the host’s body.
57. Parasitic flowering plants may be classified as holoparasites or hemiparasites. Holoparasites lack
chlorophyll and are totally dependent on the host plant for their water and nutrients. Example
Rafflesia arnoldii. Hemiparasites generally photosynthesise, but they lack a root system to draw water
and thus depend on their hosts for that function. Mistletoe, Viscum album, is a hemiparasite.
Hemiparasites usually have a broader range of hosts than do holoparasites, which may be confined to
a single or a few host species.
58. Many species of macro-parasites cannot complete their life cycles without the presence of at least
two different host species. Such parasites are said to have complex life cycles. The definitive host is
the host in which parasites exhibit sexual reproduction. Intermediate hosts are species containing non-
reproducing forms of the parasite. Some parasites have a complex life cycle involving transmission
between several hosts. To facilitate transmission, many parasites induce changes in the behaviour or
colour of one host, making that host more susceptible to being eaten by a second host. The parasites
are called “enslaver parasites.” Plagiorhynchus cylindraceus is a parasitic worm that lives in the
intestines of songbirds, such as starlings. They produce eggs that exit with the host feces. Once on
the ground, the feces are eaten by foraging arthropods such as pillbugs. Here the eggs hatch into a
juvenile infective stage. Eventually, the infected pillbugs are eaten by birds and the life cycle
continues. Normally, pillbugs seek out areas of high humidity, for example, under leaf litter, and they
are concealed from predators. However, the behaviour of parasite-infected individuals is changed and
they wander more into open areas where they are more easily spotted by birds. Having two host
species facilitates the transmission of the parasite from one bird host to another.
59. Next Kleptoparasitism. Kleptoparasitism, means parasitism by theft. It is a form of feeding where
one animal takes food that another has caught. These interactions may be intraspecific or interspecific.
For example, some small spider species live as kleptoparasites in the webs of larger species, feeding
on prey remains of the larger spider. Some seagulls and frigatebirds steal food from other bird species
that dive into the ocean to catch it.
60. Brood parasitism is a specific kind of kleptoparasitism in which individuals manipulate others to
feed and look after their young. This is a video showing how brood parasitism occurs between Reed

9. Warbler & Cuckoo. Here the Cuckoo is the parasite and the Reed Warbler is the host. The Cuckoo
lays eggs in the nest of Reed Warbler which hatches out faster than the Reed Warbler.
61. Last type of negative interaction is Cannibalism. It is the practice of eating the flesh of individuals
of one’s own species. It has been recorded for more than 1,500 species in the animal Kingdom. The
rate of cannibalism increases in nutritionally poor environments as individuals turn to conspecifics as
an additional food source. Although it may benefit the individual, it has been shown that the presence
of cannibalism decreases the expected survival rate of the whole population and increases the risk of
consuming a relative. Other negative effects may include the increased risk of pathogen transmission
as the encounter rate of hosts increases. Human cannibalism is the act or practice of humans eating
the flesh or internal organs of other human beings. A person who practice cannibalism is called a
cannibal. In his book, The Gulag Archipelago Soviet writer Aleksandr Solzhenitsyn described cases
of cannibalism in 20th-century Soviet Union. The famine in Povolzhie was so horrible that it was up
to cannibalism, up to consuming children by their own parents. In India, Aghoris, a small group of
Shaiva Sadhus based in UP, believe that eating human flesh confers spiritual and physical benefits,
such as prevention of ageing.
The need to give the conservation of ecological processes an equal weighting to the conservation of
patterns is repeatedly stressed but rarely implemented. Species extinction is obviously what
conservation ecologists are trying to avoid, but an understanding of the community-level impact of
extinction is highly desirable. In this scenario, when we aim towards achieving global goals of
biodiversity conservation an understanding of the ecological interactions at different trophic levels
plays a beneficial role.