Download Community Ecology - Dr. Mufti Sudibyo, M.Si

EKOLOGI KOMUNITAS
Apa itu komunitas?
 Komunitas merupakan kumpulan
populasi tanaman dan hewan yang
hidup di daerah tertentu atau habitat .
 Populasi dari berbagai spesies dalam
suatu komunitas berinteraksi dan
membentuk sebuah sistem dengan
sifat muncul sendiri.
Pola vs. Proses
 Pola adalah apa yang dapat diamati dengan mudah
mengamati langsung - vegetasi zonasi, daftar spesies,
aktivitas distribusi musiman, dan asosiasi spesies
tertentu.
 Proses berkecenderungan ke herbivora pola seperti
persaingan, risiko predasi, ketersediaan hara, pola
gangguan, aliran energi, sejarah, dan evolusi.
 Ekologi komunitas berusaha untuk menjelaskan
mekanisme yang mendasari penciptaan,
pemeliharaan, dan menentukan nasib komunitas
biologis.
 Biasanya, pola didokumentasikan dengan
observasi, dan digunakan untuk menghasilkan
hipotesis tentang proses yang diuji.
 Tidak semua ilmu pengetahuan eksperimental.
Hipotesis tes dapat melibatkan pengamatan
khusus, atau eksperimen.
Kekayaan yang muncul dari komunitas
 Skala
 Struktur tata ruang dan waktu
 Kekayaan spesies
 Keanekaragaman spesies
 struktur trofik
 Suksesi dan Gangguan
 Skala adalah ukuran komunitas.
 Asalkan daerah atau habitat didefinisikan
dengan baik, sebuah komunitas dapat menjadi
sistem hampir beberapa ukuran, dari setetes
air untuk log membusuk, sampai ke hutan, dan
ke permukaan Samudera Pasifik .
 Struktur ruang adalah cara spesies
terdistribusi secara relatif satu sama lain.
 Beberapa spesies menyediakan habitat bagi
spesies lain. pada gilirannya spesies inipun,
menciptakan habitat bagi populasi species lain,
dst
 Contoh : Pohon di hutan yang bertingkat-
tingkat menjadi beberapa tingkatan yang
berbeda, membentuk kanopi, beberapa
riwayat (sejarah), permukaan tanah, dan akar.
 Setiap tingkat adalah habitat dari spesies
tertentu.
 Beberapa tempat, seperti kolam air yang
terkumpul di dasar cabang-cabang pohon,
menjadi pelabuhan seluruh komunitas mereka
sendiri
 Temporal structure is the timing of the appearance
and activity of species. Some communities, i.e., arctic
tundra and the decay of a corpse, have pronounced
temporal species, other communities have less.
 Example: Many desert plants and animals are
dormant most of the year. They emerge, or germinate,
in response to seasonal rains. Other plants stick
around year round, having evolved adaptations to
resist drought.
 Species Richness - is the number
of species in a community. Clearly,
the number of species we can
observe is function of the area of the
sample. It also is a function of who
is looking. Thus, species richness is
sensitive to sampling procedure
 Diversity is the number of species in the
community, and their relative abundances.
 Species are not equally abundant, some
species occur in large percentage of samples,
others are poorly represented.
 Some communities, such as tropical
rainforests, are much more diverse than
others, such as the great basin desert.
 Species Diversity is often expressed using
Simpson’s diversity index: D=1-S (pi)2
Example Problem
 A community contains the following species:







Number of Individuals
Species A
104
Species B
71
Species C
19
Species D
5
Species E
3
What is the Simpson index value for this
community?
Answer:
 Total Individuals= (104+19+71+5+3)=202
 PA=104/202=.51 PB=19/202=.09
 PC=71/202=.35
PD=5/202=.03
PE=3/202=.02
 D=1{(.51)2+(.09)2+(.35)2+(.03)2+(.02)2}
 D=1-.40=.60
Clicker Question
In the example above, what was the species richness?
A. .60
B. 202 individuals
C. 5 species
D. .40
E. None of the above
Succession, Disturbance and
Change
 In terms of species and physical
structure, communities change with
time.

Ecological succession, the predictable change in species
over time, as each new set of species modifies the environment
to enable the establishment of other species, is virtually
ubiquitous.
 Example; a sphagnum bog community
may persist for only a few decades before
the process of ecological succession
changes transform it into the surrounding
Black Spruce Forest.
 A forest fire may destroy a large area of
trees, clearing the way for a meadow.
Eventually, the trees take over and the
meadow is replaced.
 Disturbances are events such as
floods, fire, droughts, overgrazing,
and human activity that damage
communities, remove organisms
from them, and alter resource
availability.
Some Agents of Disturbance
 Fire
 Floods
 Drought
 Large Herbivores
 Storms
 Volcanoes
 Human Activity
Disturbance, Invasion, Succession
 Disturbance creates opportunities for new species to
invade an area and establish themselves.
 These species modify the environment, and create
opportunities for other species to invade. The new
species eventually displace the original ones. Eventually,
they modify the environment enough to allow a new
series of invaders, which ultimately replace them, etc.
 Invasion:
 Disturbance creates an ecological vacuum that can be
filled from within, from outside, or both. For example,
forest fires clear away old brush and open up the
canopy, releasing nutrients into the soil at the same
time. Seeds that survive the fire germinate and rapidly
grow to take advantage of this opportunity. At the same
time, wind-borne and animal-dispersed seeds germinate
and seek to do the same thing.
 The best invaders have good dispersal powers and many
offspring, but they are often not the best competitors in
the long run.
Succession
 Disturbance of a community is usually
followed by recovery, called ecological
succession.
 The sequence of succession is driven by the interactions
among dispersal, ecological tolerances, and competitive
ability.
 Primary
succession-the sequence of species on newly
exposed landforms that have not previously been
influenced by a community, e.g., areas exposed by glacial
retreat.
 Secondary
succession occurs in cases which vegetation
of an area has been partially or completely removed, but
where soil, seeds, and spores remain.
 Early in succession, species are generally
excellent dispersers and good at tolerating
harsh environments, but not the best
interspecific competitors.
 As ecological succession progresses, they are
replaced with species which are superior
competitors, (but not as good at dispersing
and more specialized to deal with the
microenvironments created by other species
likely to be present with them).
 Early species modify their environment in
such a way as to make it possible for the next
round of species. These, in turn, make their
own replacement by superior competitors
possible.
A
climax community is a more or
less permanent and final stage of a
particular succession, often
characteristic of a restricted area.

Climax communities are characterized by
slow rates of change, compared with
more dynamic, earlier stages.

They are dominated by species tolerant of
competition for resources.
An Influential ecologist named F.E. Clements argued
that communities work like an integrated machine.
These “closed” communities had a predictable
composition.
According to Clements, there was only one true
climax in any given climatic region, which was the
endpoint of all successions.
Other influential ecologists, including Gleason,
hypothesized that random events determined the
composition of communities.
He recognized that a single climatic area could
contain a variety of specific climax types.
 Evidence suggests that for many habitats,
Gleason was right, many habitats never
return to their original state after being
disturbed beyond a certain point.
 For
example; very severe forest fires have
reduced spruce woodlands to a terrain of
rocks, shrubs and forbs.
 An incredibly rapid glacial retreat is occurring in Glacier
Bay, Alaska. In just 200 years, a glacier that once filled the
entire bay has retreated over 100km, exposing new
landforms to primary succession.


Clements would have predicted that succession today would follow
the sequence of ecological succession that has occurred in the past for
other parts of Alaska.
In fact, three different successional patterns seem to be occurring at
once, depending upon local conditions. Thus, Clements’ view of
succession is somewhat of an oversimplification.
Are Climax Communities Real?
 Succession

can take a long time.
For example, old-field succession may require
100-300 years to reach climax community. But
in this time frame, the probability that a
physical disturbance (fire, hurricane, flood) will
occur becomes so high, the process of
succession may never reach completion.
 Increasing evidence suggests that some amount of
disturbance and nonequilibrium resulting from
disturbance is the norm for most communities.
 One popular hypothesis is that communities are usually
in a state of recovery from disturbance.

An area of habitat may form a patchwork of communities, each at
different stages of ecological succession. Thus, disturbance and
recovery potentially enable much greater biodiversity than is
possible without disturbance.
Are biological communities real
functional units?
 Do communities have a tightly prescribed organization
and composition, or are they merely a loose
assemblage of species?
 This is an unsolved problem in ecology.
 Clements argued that communities are stable,
functional units with a fixed composition-each
integrated part needs the others. Every area should
ultimately have the same species, given time.
 Gleason argued that their composition is unstable and
variable-they are more like assemblages of everything
that can live together in one place
The Kiddie Pool Experiment
 Jenkins and Buikema conducted an experiment to see
whether artificial ponds would develop predictable
assemblages of freshwater microorganisms.
 -if this were the case, it would support the notion that
communities are real, integrated units.
 -They set up 12 identical “ponds” and filled them with
sterile water. Came back in year to study the
composition of the resulting communities.
 Result-the ponds had very different compositions of
species.
 Accidents of dispersal, and different dispersal
capabilities affected which species ended up in each
pond.
 The early arrival of certain competitors, and
predators greatly affected the ability of later species
to colonize later.
 -Gleason’s view was supported. Composition of
communities is dictated largely by chance and
history.
 Trophic structure is the hierarchy of feeding. It
describes who eats whom
 (a trophic interaction is a transfer of energy: i.e.,
eating, decomposing, obtaining energy via
photosynthesis).
 For every community, a diagram of trophic
interactions called a food web.
 Energy flows from the bottom to the top.
A Simple Food Web
Killer Whales
Sharks
Harbor Seals
Yellowfin Tuna
Mackerel
Cod
Halibut
Zooplankton
Unicellular Algae and Diatoms
Killer Whales
Harbor Seals
Mackerel
Zooplankton
Phytoplankton
One path
through a
food web is a
food chain.
 The niche concept is very important in
community ecology.
 A niche is an organism’s habitat and
its way of making a living.
 An organism’s niche is reflected by its
place in a food web: i.e, what it eats,
what it competes with, what eats it.
 Each organism has the potential to
create niches for others.
 Keystone species are disproportionately important
in communities.
 Generally, keystone species act to maintain species
diversity.
 The extinction of a keystone species eliminates the
niches of many other species.
 Frequently, a keystone species modifies the
environment in such a way that other organisms are
able to live, in other cases, the keystone species is a
predator that maintains diversity at a certain trophic
level.
Examples of Keystone Species
 California Sea Otters: This species preys upon sea
urchins, allowing kelp forests to become established.
 Pisaster Starfish: Grazing by Pisaster prevents the
establishment of dense mussel beds, allowing other
species to colonize rocks on the pacific coast
 “Mangrove” trees: Actually, many species of trees
are called mangrove trees. Their seeds disperse in salt
water. They take root and form a dense forest in
saltwater shallows, allowing other species to thrive
Trophic Cascades
 Species at one trophic level influence species at other
levels; the addition or subtraction of species affects
the entire food web.

This causes positive effects for some species, and negative effects
for others. This is called a trophic cascade. For instance,
removing a secondary consumer might positively affect the
primary consumers they feed upon, and negatively affect the
producers that are food for primary consumers.
Top down vs. Bottom up
 Most biological communities have both top-down
and bottom-up effects on their structure and
composition.


In a well known study of ponds by Matthew Leibold, it was
demonstrated that the biomass of herbivores (zooplankton) was
positively correlated to the biomass of producers (algae),
indicating a top down effect.
He intentionally introduced fish to some ponds, The result was a
decrease in zooplankton and increase in producers, indicating a
top down effect.
Badly scanned from
Rose and Mueller (2006)
Types of Interspecific Interactions
Effect on

Species 1
 Neutralism
0
 Competition
 Commensalism +
 Amensalism
 Mutualism
+
 Predation,
 Parasitism, Herbivory

Effect on
Species 2
0
0
0
+
+
Neutralism
 Neutralism the most common type of interspecific
interaction. Neither population affects the other.
Any interactions that do occur are indirect or
incidental.
 Example: the tarantulas living in a desert and the
cacti living in a desert
Competition
 Competition occurs when organisms in the same
community seek the same limiting resource.
This resource may be prey, water, light,
nutrients, nest sites, etc.
 Competition among members of the same
species is intraspecific.
 Competition among individuals of different
species is interspecific.
 Individuals experience both types of
competition, but the relative importance of the
two types of competition varies from population
to population and species to species
“Styles” of Competition
 Exploitation competition occurs when
individuals use the same limiting resource or
resources, thus depleting the amount available
to others.
 Interference competition occurs when
individuals interfere with the foraging, survival,
or reproduction of others, or directly prevent
their physical establishment in a portion of a
habitat.
Some specific types of competition
 Consumptive competition
 Preemptive competition
 Overgrowth competition
 Chemical composition
 Territorial competition
 Encounter competition
Example of Interference
Competition
 The confused flour beetle, Triboleum confusum, and
the red flour beetle, Triboleum castaneum cannibalize
the eggs of their own species as well as the other, thus
interfering with the survival of potential competitors.
 In mixed species cultures, one species always excludes
the other. Which species prevails depends upon
environmental conditions, chance, and the relative
numbers of each species at the start of the experiment.
Outcomes of Competition
 Exploitation competition may cause the
exclusion of one species. For this to occur, one
organism must require less of the limiting resource
to survive. The dominant species must also reduce
the quantity of the resource below some critical
level where the other species is unable to replace
its numbers by reproduction.
 Exploitation does not always cause the exclusion of
one species. They may coexist, with a decrease in
their potential for growth. For this to occur, they
must partition the resource.
 Interference competition generally results in the
exclusion of one of the two competitors.
The Competitive Exclusion Principle
 Early in the twentieth century, two mathematical
biologists, A.J. Lotka and V. Volterra developed a
model of population growth to predict the outcome
of competition.
 Their models suggest that two species cannot
compete for the same limiting resource for long.
Even a minute reproductive advantage leads to the
replacement of one species by the other.
 This is called the competitive exclusion
principal.
Evidence for Competitive Exclusion.
 A famous experiment by the Russian
ecologist, G.F. Gausse demonstrated that
Paramecium aurellia outcompetes and
displaces Paramecium caudatum in mixed
laboratory cultures, apparently confirming
the principle.
 (Interestingly, this is not always the case. Later studies
suggest that the particular strains involved affect the
outcome of this interaction).
Other experiments...
 Subsequent laboratory studies on other organisms,
have generally resulted in competitive exclusion,
provided that the environment was simple enough.
 Example: Thomas Park showed that, via
interference competition, the confused flour beetle
and the red flower beetle would not coexist. One
species always excluded the other.
Resource Partitioning
 Species that share the same
habitat and have similar needs
frequently use resources in
somewhat different ways - so that
they do not come into direct
competition for at least part of the
limiting resource. This is called
resource partitioning.
 Resource partitioning obviates competitive
exclusion, allowing the coexistence of several species
using the same limiting resource.
 Resource partitioning could be an evolutionary
response to interspecific competition, or it could
simply be that competitive exclusion eliminates all
situations where resource partitioning does not
occur.
 One of the best known cases of resource partitioning
occurs among Caribbean anoles.


As many as five different species of anoles may exist in the same
forest, but each stays restricted to a particular space: some occupy
tree canopies, some occupy trunks, some forage close to the ground.
When the brown anole was introduced to Florida from Cuba, it
excluded the green anole from the trunks of trees and areas near the
ground: the green anole is now restricted to the canopies of
trees:the resource (space, insects) has been partitioned among the
two species
 (for now at least, this interaction may not be stable in the long
run because the species eat each other’s young).
Character Displacement
 Sympatric populations of similar
species frequently have differences in
body structure relative to allopatric
populations of the same species.
 This tendency is called character
displacement.
 Character displacement is thought to
be an evolutionary response to
interspecific competition.
Example of Character Displacement
 The best known case of character displacement occurs
between the finches, Geospiza fuliginosa and
Geospiza fortis, on the Galapagos islands.
 When the two species occur together, G. fuliginosa has
a much narrower beak that G fortis. Sympatric
populations of G fuliginosa eats smaller seeds than G
fortis: they partition the resource.
 When found on separate islands, both species have
beaks of intermediate size, and exploit a wider variety
of seeds.
 These inter-population differences might have evolved
in response to interspecific competition.
Competition and the Niche
 An ecological niche can be thought of in terms of
competition.
 The fundamental niche is the set of resources and
habitats an organism could theoretically use under
ideal conditions.
 The realized niche is the set of resources and
habitats an organism actually used: it is generally
much more restricted due to interspecific competition
(or predation.)
Two organisms cannot occupy
exactly the same niche.
THIS IS SOMETIMES CALLED
GAUSSE’S RULE(ALTHOUGH
GAUSSE NEVER PUT IT
EXACTLY THAT WAY).
-EXPERIMENTS BY GAUSSE
(PARAMECIUM ), PETER FRANK
(DAPHNIA), AND THOMAS PARK
(TRIBOLEUM) HAVE CONFIRMED IT
FOR SIMPLE LABORATORY
SCENARIOS .
Amensalism
 Amensalism is when one species suffers and
the other interacting species experiences no
effect.
 Example: Redwood trees falling into the ocean
become floating battering-rams during storms,
killing large numbers of mussels and other
inter-tidal organisms.
 Allelopathy involves the production and
release of chemical substances by one species
that inhibit the growth of another. These
secondary substances are chemicals
produced by plants that seen to have no direct
use in metabolism.
 This same interaction can be seen as both
amensalism, and extremely one-sided
interference competition-in fact it is both.
Example: Allelopathy in the California
Chaparral
 Black Walnut (Juglans nigra) trees excrete an
antibiotic called juglone. Juglone is known to inhibit
the growth of trees, shrubs, grasses, and herbs found
growing near black walnut trees.
 Certain species of shrubs, notably Salvia leucophylla
(mint) and Artemisia californica (sagebrush) are
known to produce allelopathic substances that
accumulate in the soil during the dry season. These
substances inhibit the germination and growth of
grasses and herbs in an area up to 1 to 2 meters from
the secreting plants.
Commensalism
 Commensalism is an interspecific interaction where one





species benefits and the other is unaffected.
Commensalisms are ubiquitous in nature: birds nesting in
trees are commensal.
Commensal organisms frequently live in the nests, or on the
bodies, of the other species.
Examples of Commensalism:
Ant colonies harbor rove beetles as commensals. These
beetles mimic the ants behavior, and pass as ants. They eat
detritus and dead ants.
Anemonefish live within the tentacles of anemones. They
have specialized mucus membranes that render them immune
to the anemone’s stings. They gain protection by living in this
way.
Mutualism
 Mutualism in an interspecific interaction between
two species that benefits both members.
 Populations of each species grow, survive and/or
reproduce at a higher rate in the presence of the
other species.
 Mutualisms are widespread in nature, and occur
among many different types of organisms.
Examples of Mutualism
 Most rooting plants have mutualistic associations
with fungal mychorrhizae. Mychorrhizae increase
the capability of plant roots to absorb nutrients. In
return, the host provides support and a supply of
carbohydrates.
 Many corals have endosymbiotic organisms called
zooxanthellae (usually a dinoflagellate). These
mutualists provide the corals with carbohydrates
via photosynthesis. In return, they receive a
relatively protected habitat from the body of the
coral.
Mutualistic Symbiosis
 Mutualistic Symbiosis is a type of mutualism in which
individuals interact physically, or even live within the
body of the other mutualist. Frequently, the relationship
is essential for the survival of at least one member.
 Example: Lichens are a fungal-algal symbiosis (that
frequently includes a third member, a
cyanobacterium.) The mass of fungal hyphae provides
a protected habitat for the algae, and takes up water
and nutrients for the algae. In return, the algae (and
cynaobacteria) provide carbohydrates as a source of
energy for the fungus.
Facultative vs. Obligate Mutualisms
 Facultative Mutualisms are not essential for the
survival of either species. Individuals of each species
engage in mutualism when the other species is
present.
 Obligate mutualisms are essential for the survival of
one or both species.
Other Examples of Mutualisms
 Flowering plants and pollinators. (both facultative




and obligate)
Parasitoid wasps and polydna viruses. (obligate)
Ants and aphids. (facultative)
Termites and endosymbiotic protozoa. (obligate)
Humans and domestic animals. (mostly facultative,
some obligate)
Predation, Parasitism, Herbivory
 Predators, parasites, parasitoids, and herbivores obtain
food at the expense of their hosts or prey.
 Predators tend to be larger than
their prey, and consume many prey
during their lifetimes.
 Parasites and pathogens are
smaller than their host. Parasites
may have one or many hosts during
their lifetime. Pathogens are
parasitic microbes-many
generations may live within the
same host. Parasites consume their
host either from the inside
(endoparasites) or from the
outside (ectoparasites).
 Parasitoids hunt their prey like predators, but
lay their eggs within the body of a host, where
they develop like parasites.
 Herbibores are animals that eat plants. This
interaction may resemble predation, or
parasitism.
Predator-Prey and Parasite-Host
Coevolution
 The relationships between predator
and prey, and parasites and hosts,
have coevolved over long periods of
time.
 About 50 years ago, an evolutionary biologist named
J.B.S. Haldane suggested that the interaction between
parasite and host (or predator and prey) should
resemble an evolutionary arms race:
 First a parasite (or predator) evolves a trait that allows it to
attack its host (or prey).
 Next, natural selection favors host individuals that are able to
defend themselves against the new trait.
 As the frequency of resistant host individuals increases, there
is natural selection for parasites with novel traits to subvert
the host defenses.
 This process continues as long as both species survive.
 Recent data on Plasmodium, the cause of malaria, support this
model.
Example of Parasite-Host Coevolution
 The common milkweed, Asclepias syriaca has leaves
that contain cardiac glycosides: they are very
poisonous to most herbivores. This renders them
virtually immune to herbivory by most species.
 Monarch butterfly larvae have evolved the ability to
tolerate these toxins, and sequester them within their
bodies. They are important specialist hervivores of
milkweeds.
 These sequestered compounds serve the additional
purpose of making monarch larvae virtually inedible to
vertebrate predators.
Predator-Prey Population Dynamics
 Predation may be a density-dependent mortality
factor to the host population-and prey may represent
a limiting resource to predators.
 The degree of prey mortality is a function of the
density of the predator population.
 The density of the prey population, in turn, affects the
birth and death rates of the predator population.
 i.e, when prey become particularly common,
predators increase in numbers until prey die back due
to increased predation, this, in turn, inhibits the
growth of prey.
 Typically, there is a time lag effect.
 There is often a dynamic balance
between predators and prey that is
necessary for the stability of both
populations.
 Feedback mechanisms may control the
densities of both species.
Example of Regulation of Host Population by a
Herbivore
 In the 19th century, prickly pear cactus, Opuntia sp. was
introduced into Australia from South America. Because no
Australian predator species existed to control the population
size of this cactus, it quickly expanded throughout millions of
acres of grazing land.
 The presence of the prickly pear cactus excluded cattle and
sheep from grazing vegetation and caused a substantial
economic hardship to farmers.
 A method of control of the prickly pear cactus was initiated
with the introduction of Cactoblastis cactorum, a cactus eating
moth from Argentina, in 1925. By 1930, densities of the prickly
pear cactus were significantly reduced.
 Sometimes predator species can drive their prey to
localized extinction.
 If there are no alternate prey, the predator then goes
extinct.
 If the environment is coarse grained, this makes
the habitat available for recolonization by the prey
species.
 Example: The parasitic wasp Dieratiella rapae is a
very efficient parasitoid. One female can oviposit into
several hundred aphids during its lifetime.
Frequently, aphids are driven locally extinct and the
adults must search for new patches when they
emerge. Once the aphid and the host are gone, the
host plants may become re-infested with aphids.
 In other cases, there are alternate
prey to support the predator and
the prey is permanently excluded.
 Example: Freshwater fish such as
bluegills and yellow perch
frequently exclude small
invertebrates such as Daphnia
pulex from ponds. The fish then
switch to other prey such as insects
larvae.
The time-lag effect may lead to predatorprey oscillations.
 Most predators do not respond instantaneously to the
availability of prey and adjust their reproduction
accordingly.
 If predator populations grow faster than prey
populations, they may overshoot the number of prey
that are able to support them
 This leads to a rapid decline in the prey, followed by a
rapid decline in the predator.
 Once the predator becomes rare, the prey population
may begin growing again.
 This pattern is called a predator-prey oscillation.
Cycles in the population dynamics of the snowshoe hare
and its predator the Canadian lynx (redrawn from
MacLulich 1937). Note that percent mortality is an elusive
measure, it may, or may not, be useful since mortality
varies with environment and time.
•In the 1920s, A. J. Lotka (1925) and V. Volterra (1926)
devised mathematical models representing host/prey
interaction.
•The Lotka-Volterra curve assumes that prey destruction is a
function not only of natural enemy numbers, but also of prey
density, i.e., related to the chance of encounter.
•This model predicts the predator-prey oscillations sometimes
seen in nature. Populations of prey and predator were
predicted to flucuate in a regular manner (Volterra termed
this "the law of periodic cycle").
•Lotka-Volterra model is an oversimplification of reality. In
nature, many different factors affect the densities of
predators and their prey.