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Introduction
Organisms select habitats to acquire and secure their living
essentials in various ways. Naturally different species of organisms
have their own organizational structures in a biotic community1 to
exploit the existing recourses.2–4 This ultimately leads to different
evolutionarily and ecological complexities, interactions, and
interdependencies among different species in a biotic community.
For example, species have different niche breadths which are affected
by the variability of the environment, and the relationship with other
species in the habitat,5,6 and therefore have different selectivity and
preference for habitats.5 Competition (i.e. intra–specic and inter–
specic), predation, mutualism, and commensalisms are the major
ecological interactions and interdependencies which inuence the
structure and the function of ecosystems.2,6,7 Species exhibit different
habitat preferences and thus are patchy in their distribution, diversity,
and hence the system is dynamic.8 Species distribution and abundance
depends on different factors. For example, competitively mediated
habitat selection creates the disturbing paradox that the competition
responsible for habitat segregation lurks as the ‘ghost of competition
past’,9–11 which is invisible at the point of equilibrium.
Understanding the process of habitat selection is of fundamental
importance in determining the extent and fate of population
interactions and distributions.8,12 Ecologists have long sought to link
behavior, population dynamics, and the rules of ecological community
organization by using optimal foraging theories.13–16 Density–
dependent habitat selection theory applies to all species independent
of their life–history characteristics or the number of habitats available
in the landscape.12,17–21 Most studies on habitat selection dealt with
how environmental variable,22 intra–specic and inter–specic
competitions,5,10 and predation7 affect habitat selection and preference
of species in their natural habitats. Many ecologists have proved that
the preference for one habitat among the many implies that the species
has higher tness in that habitat.23–25
A central challenge in ecology is to develop models that faithfully
capture those important mechanistic details of natural systems
that are required to make reliable predictions about population
dynamics.26 Many theories that deal with the different factors of
organisms’ habitat selection are developed based on the assumption
of IFD (Ideal Free Distribution).23 This is because IFD provides the
basis for understanding how individuals should distribute themselves
among different habitats in response to habitat quality and population
density.18,19,23 The IFD assumes that foragers can change habitats
without cost. Individuals choose the habitat that offers the highest
tness, and individuals can enter a habitat on an equal basis with those
already there. Moreover, the IFD assumes that suitability or tness of
individual in a habitat declines with the habitat’s population density
and species have full knowledge of their habitats, so they react in
Int J Avian & Wildlife Biol. 2018;3(5):358‒365. 358
© 2018 Tadesse. This is an open access article distributed under the terms of the Creative Commons Attribution License, which
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The effects of competition (intra–specic and inter–
specic) and predation on the distribution and
abundance of guppy sh (Poecilia reticulata)
Volume 3 Issue 5 - 2018
Solomon Ayele Tadesse
Department of Natural Resources Management, College of
Agriculture and Natural Resource Sciences, Ethiopia
Correspondence: Solomon Ayele Tadesse, Department of
Natural Resources Management, College of Agriculture and
Natural Resource Sciences, Debre Berhan University, PO Box
445, Debre Berhan, Ethiopia, Tel +2511 1168 1544 0 (ofce),
+2519 4670 3660 (mobile), Fax +2511 1168 1206 5,
Email solomon.ayele1972@gmail.com
Received: March 26, 2018 | Published: September 28, 2018
Abstract
Competition and predation are among the major evolutionarily and ecological forces
which play imperative role to determine the distribution, abundance, and population
dynamics of species in a biotic community. The objective of this study was to test
the effects of competition (i.e. intra–specific and interspecific) and predation on
the distribution, abundance, and fitness of guppy fish. The data were collected in
laboratory experiments where guppies were kept in homogenous aquarium with
different densities in each partition under the influence of goldfish as competitors
and predators. The experiment was conducted in three different stages: only guppies
were kept in the aquarium, goldfish were used as competitors, and different densities
of predatory fish (i.e. goldfish) were kept in both sides of the aquarium. Regression,
isocline, and isodar methods were employed to analyze the data to measure the
impacts of competition and predation on the distribution, abundance, and fitness of
guppies and later to determine which factor is more influential over the other. The
results revealed that both competition and predation were shown to be important
evolutionarily and ecological forces to affect the distribution, abundance, and fitness
of guppies. Competition coefficient was affected by the densities of both guppies
and goldfish; however, predation coefficient was affected only by the density of
goldfish. The results of the coefficients of competition and predation suggested that
the effect was density–dependent. Generally, predation had the strongest effect on
the distribution, abundance, and fitness of guppies followed by the effects of inter–
specific and intra–specific competitions, respectively.
Keywords: aquarium, biotic community, coefficients, density–dependent, fitness,
goldfish
International Journal of Avian & Wildlife Biology
Research Article Open Access
The effects of competition (intra–specic and inter–specic) and predation on the distribution and
abundance of guppy sh (Poecilia reticulata) 359
Copyright:
©2018 Tadesse
Citation: Tadesse SA. The effects of competition (intra–specic and inter–specic) and predation on the distribution and abundance of guppy sh (Poecilia
reticulata). Int J Avian & Wildlife Biol. 2018;3(5):358‒365. DOI: 10.15406/ijawb.2018.03.00121
response to changes in densities and resources.23 When there is more
than one habitat, at low densities, the most preferred habitat would be
taken rst. Then, as the density increases, the tness of the species
decreases to a point where it is better to move into the second best
habitat in order to increase its tness.18,19,24
In the present study, it is sought imperative to consider the combined
effects of different environmental variables, ecological complexities,
interdependencies, and interactions which signicantly affect the
mechanisms of habitat selection in guppies under the inuence of
competition (i.e. intra–specic and interspecic) and predation. Thus,
it is better to evaluate separately the impacts of competition and
predation to measure and compare their separate and combined effects
on the distribution, abundance, and tness of guppies. Moreover,
measuring the impact of intra–specic competition when competitors
or predators are present and the effect of competitors and predators
densities on their coefcients is imperative to evaluate and understand
whether all those factors equally affect the distribution, abundance,
and tness of guppies or there is some signicant difference among
those factors in affecting the distribution, abundance, and tness. Thus,
the objective of the study was to test the effects of competition (i.e.
intra–specic and inter–specic) and predation on the distribution,
abundance, and tness of guppies in an experimental aquarium under
laboratory condition.
Conceptual research background
The effect of competition and predation on the
distribution, abundance, and tness of guppies
Competition and predation are pervasive evolutionarily and
ecological forces which play imperative role to determine the
distribution, abundance, habitat selection, behavior, tness, and
population dynamics of different species in a biotic community.4,8,12–15
Thus, it is better to separately discuss how competition and predation
affect the distribution, abundance, and tness of organisms in a biotic
community.
Competition: is one of the evolutionarily and ecological complexities
which affects the real ecological niches of species in a biotic
community.4 Competition is often seen among individuals of the same
or different species which use similar habitat resources in a similar
way.5 For better understanding of this competition type (i.e. intra–
specic and interspecic), I briey discuss each type of competition
as followed.
Intra–specic competition: It is a kind of competition in which
individuals of the same species may compete for the same resources
due to either the scarcity of common habitat resources or due to higher
density.3–5 For example, according to the IFD assumptions, density
was demonstrated to have a paramount effect on the habitat selectivity
and resource utilization by individuals of a species.19–21,25 Several
ecological studies which were conducted on the habitat selections
of different species have clearly shown that habitat selection by
individuals of a species is affected by their own densities.19–21
For example, Abramsky et al.12 developed a dispersion method to
demonstrate how distribution and habitat selection in desert rodents
are affected by their own densities. Accordingly, Abramsky et al.12
studied desert rodent species whether they are more habitat selective,
density–dependent or randomly distributed between habitats. Thus,
the geometrical method that was developed by Rosenzweig and
Abramsky et al.12 was able to detect changes in selectivity level with
changes in species densities. Moreover, isodar theory19–21 and isocline
methodwere able to measure the effect of intra–specic competition
while competitors or predators are present. Thus, based on those
theories and methods, this study was conducted to test how density
and resource availability (i.e. food quantity) affect the distribution,
abundance, and tness of guppies.27
Inter–specic competition: Various ecological researchers proved
in their research works that inter–specic competition is one of the
natural selective forces that inuence the ecological niche breadth,
distribution, abundance, habitat selection, and resource utilization of
various species.3–5,12–14,28 For example, a number of theories have been
tested to measure the effects of inter–specic competition in the eld,
and different methods were employed to compute the effect of inter–
specic competition.5,7,17–19 Moreover, methods such as specic indices
of niche overlap,22 are based on the assumption that competition
coefcient between two species is constant and bi–directional. Other
methods such as Mac–Arthur & Levins6 measure of niche overlap are
based on different effect of each species on the other, but there is a
difculty in measuring those effects in nature, since it is difcult to
separate the impacts of different species and environmental variables.7
Competition coefcient is one of the important variables which help
explain the degree of inter–specic competition between individuals
of different species in a biotic community.5
However, Crowell & Pimm29 demonstrated that competition
coefcient is measurable among different species only in a
homogenous environment. Isoclines are also drawn from a set of
census data to measure the effects of inter–specic competition among
different competing species in a biotic community.5,7,30 For example;
Vandermeer31 demonstrated that once the slope of the isocline is
known, it is easy to compute the competition coefcients between
two competing species for the same habitat resource in a biotic
community. Multiple regression method is also another suggested
option to solve the problem of environmental heterogeneity in eld
experiments to compute inter–specic competition coefcients
between two competing species.5,29,30 All the aforementioned methods
of competition coefcient determining techniques used to and have
been still using species densities and variability of food resource
to measure the inter–specic competition between ecologically
competing species for similar habitat resources.
In the present study, guppies and goldsh were the two
competing species for the same food resource. Thus, the inter–
specic competition coefcients between these two sh species were
computed. A regression method was used to test whether competition
coefcients between the two sh species are affected by density
and food availability.5,17,30 Rosenzweig9 has theoretically shown that
habitat selection models promote the possibility of coexistence by
changing the shape of the species zero growth isoclines from linear
to non–linear. This study also looked into the effect of inter–specic
competition on the distribution, abundance, and tness of guppies in
an experimental aquarium
Predation: Predators directly affect their prey by killing and
consuming them. However, this is not the only way they can affect
them. Non–lethal effects, such as fear and apprehension generated
from the possibility of being attacked may be enough to change prey
behavior.5,26,31–36 Non–lethal effects affect the tness of prey individuals
because the prey’s options are constrained and the behavioral response
may be costly.26,35 and even physiologically stressful when it is at its
extreme case.36 For example, previous studies on invertebrates37–39 and
The effects of competition (intra–specic and inter–specic) and predation on the distribution and
abundance of guppy sh (Poecilia reticulata) 360
Copyright:
©2018 Tadesse
Citation: Tadesse SA. The effects of competition (intra–specic and inter–specic) and predation on the distribution and abundance of guppy sh (Poecilia
reticulata). Int J Avian & Wildlife Biol. 2018;3(5):358‒365. DOI: 10.15406/ijawb.2018.03.00121
amphibians40 have shown that non–lethal effects may be larger than
lethal effects in determining the habitat section, patch use, foraging
behavior, morphology, survival and reproductive rates, activity
density, time budgets, distribution, and abundance of animals over a
range of trophic levels.26,36
Due to the potentially high costs of avoiding predation and the
tendency for large portions of populations to respond to risk of
predation, the risk effects of predators can have impacts on prey
species and communities that may even surpass those of direct
predation,41 because effect of risks can exist even when direct rate of
predation is zero.42 So, to reduce the negative impacts of predation
risk, prey may avoid certain habitats, spend more time being vigilant
and less time feeding, feed in larger groups, use apprehension or
restrict their feeding to certain times.26,42,43 Ultimately, risk–sensitive
behavior resulted from non–lethal causes may affect the foraging
behavior, distribution, abundance, habitat selection, and patch use by
prey species.
Lima & Dill28 showed that predation has long been implicated as
a major selective force in the evolution of several morphological and
behavioral characteristic of prey species. Predation could affect the
tness of individuals of a species in a biotic community. Thus, prey
species need to protect themselves from risk of predation which adds
costs on the foraging efciency of the forager.7,15,44,46 For example,
Abramsky et al.5 and Kotler et al.7 demonstrated that predation was
stronger than competition in affecting the activity levels of two rodent
species (i.e. Gerbillus pyramidum and Gerbillus allenbyi) in the
sandy habitats of the Negev Desert, Israel. In this study, the impact of
predation on the distribution, abundance, and tness of guppies was
computed and later compared with the impacts of intra–specic and
inter–specic competitions. This helped to identify the strongest force
which signicantly affects the distribution, abundance, and tness of
guppies in an experimental aquarium under laboratory condition.
Materials and methods
Study species
Guppy
The guppy (Poecilia reticulata), also known as rainbow sh, is
one of the world’s most widely distributed tropical sh.47 It is also one
of the most popular freshwater aquarium sh species. Although not
typically found there, guppies also have tolerance to brackish water
and have colonized some brackish habitats.48 However, they tend to
be more abundant in smaller streams and pools than in large, deep
or fast–owing rivers.49 Guppies, whose natural range is in northeast
South America, were introduced to many habitats and are now found
all over the world.47,49 They are highly adaptable and thrive in many
different environmental and ecological conditions.47 Wild guppies
generally feed on a variety of food sources, including benthic algae
and aquatic insect larvae.50 Guppies have many predators, such as
large sh (e.g. goldsh) and birds, in their natural habitats.50,51 Like
many sh species, guppies often school together to avoid predation.
Schooling is more favored by evolution in populations of guppies
under high predation pressure, exerted either by predator type or
predator density. Coloration of guppies also evolves differentially in
response to predation.51 Guppies are used as a model organism in the
eld of ecology, evolution, and behavioral studies.47
Goldsh: Goldsh (Carassius auratus) is a freshwater sh species.
It is one of the most commonly kept aquarium sh. The goldsh
is native to East Asia.52 It was rst selectively bred in China more
than a thousand years ago, and several distinct breeds have since
been developed. Goldsh breeds vary greatly in size, body shape, n
conguration, and coloration.53 Goldsh are gregarious, displaying
schooling behavior, as well as displaying territorial behavior while
feeding.54 They are a generalist species with varied feeding and
breeding behaviors that contribute to their success. Goldsh are
opportunistic feeders and do not stop eating on their own accord.52–54
Experimental procedures
The data were collected from laboratory experiments where
guppies were kept in homogenous aquarium with different densities.
The aquarium was divided into two partitions with a string net as a
barrier. The dimension of each partition measures 50 cm×50cm. The
barriers made up of string nets were big enough to allow the free
movement and passage of the guppies between the two partitions
of the aquarium, but bigger sh (i.e. goldsh) could not. First, the
guppies were trained to recognize knocks in the aquarium glass as
a preliminary sign for food provision. Knocking was simultaneously
done in both sides of the aquarium before feeding, and guppies were
acquainted for such a response before the actual data collection was
started.
Experimental data collection
The experiment was conducted for 12 weeks in three different
stages. The experiment for each stage lasted within four weeks. The
data were collected as followed.
Only guppies were in the aquarium: Equal amount of food pellets
was added to both sides of the aquarium. This was done to test
whether guppies utilize the provisioned food pellets in both sides
similarly. Food pellet was given to the guppies in the amount of 0.5
pellets per sh in the beginning, but one pellet per sh was provided
later. Each pellet weighed 1 gm. The number of guppies in each side
of the aquarium was counted to measure their distribution and density.
Goldsh were used as competitors and kept in one side of the
aquarium in two different densities: Goldsh were unable to pass
through the small string nets so that they were not allowed to move
to the other side of the aquarium. Food was added to both sides of the
aquarium in equal quantity. Finally, the data were collected by counting
the number of guppies and goldsh in both sides of the aquarium.
This activity is important to measure the effect of the competitors (i.e.
goldsh) on the distribution, abundance, and competitive tness of
guppies. Food pellet was given to the sh (i.e. guppies and goldsh)
in an amount of 1 pellet per sh including the competitor goldsh.
Different densities of predatory sh were kept in both sides of
the aquarium: The goldsh were unable to pass from one side of
the aquarium to the other. Food pellet was added to both sides of the
aquarium in equal proportion. The data were collected by counting
the number of guppies on both sides of the aquarium. Moreover, the
number of the predatory sh (i.e. goldsh) was also counted. This
activity was important to measure the effect of predators on the
distribution, abundance, and tness of guppies in each partition of the
experimental aquarium.
Data analyses
First, I used one way ANOVA to analyze and measure the effect of
time on the distribution and abundance of guppies where competitors
(e.g. goldsh) were present in one side of the aquarium.
The effects of competition (intra–specic and inter–specic) and predation on the distribution and
abundance of guppy sh (Poecilia reticulata) 361
Copyright:
©2018 Tadesse
Citation: Tadesse SA. The effects of competition (intra–specic and inter–specic) and predation on the distribution and abundance of guppy sh (Poecilia
reticulata). Int J Avian & Wildlife Biol. 2018;3(5):358‒365. DOI: 10.15406/ijawb.2018.03.00121
The isodar method: According to Morris,18,19 the isodar method can
be employed to measure the tness of a single species so that it can
be computed with a simple linear regression technique by regressing
the densities of the study species in two adjacent habitats. Thus, for
species A when alone, the isodar is dened by the following equation:
NA1= C–b NA2
Where,
NA1 and NA2 = density of species A in habitat 1 and habitat 2,
respectively.
C = Intercept that reects the quantitative difference between the
two habitats.
B = slope that shows the qualitative difference of habitat 2
compared with habitat 1.
However, if both habitats are identical; then, C = 0 and b = 1.
Effects of inter–specic competition and predation: Competition
and predation coefcients were computed based on the method
developed by Abramsky et al.5 Accordingly, the different activity
densities of guppies were regressed to examine the preference of the
guppies and to draw the isoclines. Hence, the slopes of the isoclines
were measured at different densities. It helped determine competition
coefcients and evaluate its relation with the change in densities.
Moreover, different densities of guppies and the xed number of
competitors (i.e. goldsh) in one side of the aquarium were regressed.
The different densities of guppies were also regressed against the
densities of the predatory sh (i.e. goldsh).
I was able to draw one isocline from the average densities of
guppies and competitors and/or predators in each replicate of the
collected data from the aquarium experiment. This isocline was a line
between two points on a graph, where guppies’ density was in the Y
axis but competitor/predator density was in the X axis. The different
densities of the guppies allowed me to know the effect of guppies’
density on competition coefcients. Moreover, different densities
of the competitor and predatory sh (i.e. goldsh) allowed me to
know the effect of their density on the coefcient of competition or
predation.
Following Abramsky and Rosenzweig,30 drawing the slope of
every isocline was conducted by using the following general formula:
left right
guppy,gold
left right
guppys guppys
guppy
gold gold gold
α
−
∆
= =
∆−
For all analyses, I dened the alpha value to be 0.05 and performed
the analyses with SPSS version 16.
Results
As food pellet was equal in both sides of the experimental
aquarium, time did not have signicant effect (df = 1; F = 1.06; P =
0.86) on the distribution and abundance of guppies with the presence
of goldsh as competitors or without competitors. This suggested that
food does not have signicant effect on the distribution and abundance
of guppies, but the competitors (i.e. goldsh) signicantly affected the
distribution, abundance, and tness of guppies in the experimental
aquarium because goldsh seems to be territorial while acquiring
food.
Guppies’ isodar
The isodar was constructed by regressing the right side of guppies’
density as an independent variable whereas the left side of the guppies’
density as a dependent variable (Figure 1). The isodar equation
obtained by regressing the right side versus the left side densities
of guppies revealed that the intercept was not signicant because it
was less than 0. Moreover, the slope of the isodar was not signicant
because it was closer to 1 (Table 1), (Figure 1). This suggested that
guppies had equal tness in both sides of the experimental aquarium
because the two sides of the aquarium are identical in terms of food
availability and density of guppies.
Figure 1 Isodar of guppies when they were alone and food pellets were
provided in equal quantity in both sides of an experimental aquarium.
Table 1 The isodar equation obtained through the regression analysis of
right versus left density of guppies
Variable Coefcients P value -95.00% C.L +95.00%
C.L
Intercept 1.179 0.278 -0.963 3.322
Right 0.952 0.564 0.783 1.122
Isoclines and competition coefcients
Since the population size was less than 30; therefore, a student–t
test was used to measure the competitive difference between the right
versus left sides of the aquarium with and without competitors (i.e.
goldsh). The result revealed that goldsh had a signicant effect on
the competition coefcient, suggesting that inter–specic competition
signicantly affected the distribution, abundance, and tness of
guppies in an experimental aquarium (P<0.001) Figure 2.
Figure 2 The isoclines of guppies where the density of goldsh is
independent variable and regressed against the guppies’ density as dependent
variable. The isocline slope represents the competition coefcient. However,
each line designates one isocline which was drawn by connecting two points
that represent the densities of goldsh versus guppies in each side of the
aquarium.
The effects of competition (intra–specic and inter–specic) and predation on the distribution and
abundance of guppy sh (Poecilia reticulata) 362
Copyright:
©2018 Tadesse
Citation: Tadesse SA. The effects of competition (intra–specic and inter–specic) and predation on the distribution and abundance of guppy sh (Poecilia
reticulata). Int J Avian & Wildlife Biol. 2018;3(5):358‒365. DOI: 10.15406/ijawb.2018.03.00121
Effect of guppies’ density on competition coefcient
As the value of P = 0.065, the result of the simple linear regression
revealed that guppies’ density did not have a signicant effect on
the competition coefcient (Figure 3). Furthermore, polynomial
regression was run to test the effect of guppies’ density on competition
coefcient (Table 2). The polynomial regression revealed that the
density of guppies signicantly affected the competition coefcient
because the value of P<0.001 (Table 2). Then, the following equation
was developed from the result of the polynomial regression (Table 2)
to explain how guppies’ density affected the competition coefcient.
Y = 17.47–2.15X + 0.05X2
Where Y = Competition coefcient
X = Guppies’ density
Now it is easy to nd the minimum value for the competition
coefcient using the above formula:
Y’ = –2.15+0.1X
Y’ = –2.15+0.1X = 0
Minimum point X = 21.5; Y = –5.71
Figure 3 The total density of guppies in both sides of the aquarium was
used as independent variable whereas competition coefcient was used as a
dependent variable.
Table 2 Multiple polynomial regression results for competition coefcients
measured against guppies’ density (X, X2)
Variable Coefcients P value Adjusted R2
Intercept 17.47 <0.001
0.39Guppies -2.15 <0.001
Guppies20.05 <0.001
The effect of goldsh’s density on competition coefcient
The result showed that the density of goldsh had a signicant
effect on the competition coefcient (Table 3), (Figure 4). However,
the result of the multiple regression obtained by regressing the
guppies’ density versus goldsh’s density did not signicantly affect
the competition coefcient because the value of P = 0.083. Thus,
the effect of goldsh’s density on competition coefcient can be
represented by simple linear regression equation using the following
formula:
Y = –7.75+1.31X
Where,
Y = Competition coefcient
X = Goldsh density
Figure 4 The density of goldsh was treated as independent variable whereas
competition coefcient was regressed as a dependent variable.
Table 3 The separate effect of goldsh density on competition coefcient
produced by employing simple regression technique
Variable Competition
Coefcient P value Adjusted R2
Goldsh (intercept) -7.75 <0.001 0.14
Goldsh (slope) 1.313 <0.001
Isoclines and predation coefcients
A similar method was employed to draw the isoclines like what
was used to draw the isoclines for the competition coefcient (Figure
5).
Figure 5 Isoclines of guppies where the density of the predator was treated
as independent variable whereas the density of guppies as dependent variable.
The Isocline slope represents the predation coefcient. Each line designates
one isocline which was drawn by connecting two points that represent
densities of predator versus guppies in each side of the aquarium.
The effect of guppies’ density on predation coefcient
Using simple linear regression, the result showed that guppies’
density did not show signicant effect on predation coefcient because
the value of P = 0.75. Similarly, the result of the polynomial regression
(X, X2) revealed that guppies’ density did not have signicant effect
on predation coefcient because the value of P = 0.170 (Figure 6).
The effect of predator’s density on predation coefcient
The result obtained by simple linear regression technique revealed
that predator’s density (i.e. goldsh as a predator) did not have a
signicant effect on predation coefcient because the value of P =
0.94. Furthermore, multiple polynomial regression technique was
employed to detect the effect of predator’s density on predation
coefcient. Fortunately, the result of the multiple polynomial
The effects of competition (intra–specic and inter–specic) and predation on the distribution and
abundance of guppy sh (Poecilia reticulata) 363
Copyright:
©2018 Tadesse
Citation: Tadesse SA. The effects of competition (intra–specic and inter–specic) and predation on the distribution and abundance of guppy sh (Poecilia
reticulata). Int J Avian & Wildlife Biol. 2018;3(5):358‒365. DOI: 10.15406/ijawb.2018.03.00121
regression revealed that predator’s density had a signicant effect at
(X, X2) including the intercept on the predation coefcient because
the value of P < 0.01 (Table 4), (Figure 7).
Figure 6 Guppies’ density in both sides of the aquarium was treated as
independent variable whereas predation coefcient was treated as dependent
variable.
Figure 7 Predators’ density in both sides of the aquarium was treated as
independent variable whereas predation coefcient was assigned as dependent
variable. This was done to test the effect of predator’s density on predation
coefcient.
Table 4 The effect of predator’s density on predation coefcient produced by
polynomial regression (X, X2)
Variable Coefcients P value Adjusted R²
Intercept -54.486 0.004
0.362Predator 21.624 0.009
P2-2.239 0.008
The equation for the coefcient of predation and the isocline
could be developed for signicant factors. In this case, only predation
density had a signicant effect on predation coefcient. Thus, the
equation for the predation coefcient would be given by using:
Y = –54.486+21.624X–2.239X2
Where
Y = Predation coefcient
X = Density of predator
As the slope of the isocline changed with density, obtaining the
maximum value for the predation coefcient was important. This was
obtained by using the following equation:
Y’ = 21.624–4.486X
21.624–4.486X = 0
Maximum point would be when X = 4.832; and Y = –2.313 (i.e.
weakest predation coefcient)
Now it is easy to compute for the value of the isocline as followed:
Y’ = –54.486+21.624X–2.239X2
Y = C–54.486X+21.624X2/2–2.239X3/3
Y = C–54.486X+10.811X2–0.751X3
Thus, the value of C can be computed from the average values of
the densities of guppies and predators as followed.
Y (Guppies) =13.42, X (Predators) = 5
C = 13.42 + 54.48 × 5–10.81 × 52 + 0.75 × 53
C = 108.90
Therefore, the isocline equation was given by:
Y = 108.90–54.486X + 10.811X2 – 0.751X3
Discussion
Competition and predation are pervasive evolutionarily and
ecological forces which play imperative role to determine the
distribution, abundance, habitat selection, and population dynamics
of different species in a biotic community.4,8,12–15 This study was
conducted to test the effect of competition (i.e. intra–specic and
inter–specic) and predation on the distribution, abundance, and
tness of guppies in an experimental aquarium under laboratory
condition. The result showed that the movement of guppies in both
sides of the aquarium was signicantly affected by guppies’ density,
and the presence of goldsh as competitors and predators. Moreover,
goldsh had territorial behavior while feeding54 so that their impact
on the distribution, abundance, and tness of guppies was strongly
correlated with the effect of competition. Therefore, it is better
to separately discuss the effect of each factor on the distribution,
abundance, and tness of guppies as followed.
Effects of intra–specic competition
The result of the simple linear regression revealed that guppies’
density did not have a signicant effect on the intra–specic
competition coefcient (Figure 3). However, the result of the multiple
polynomial regression (Table 2) showed that guppies’ density had a
signicant effect on competition coefcient, suggesting that intra–
specic competition was important factor in affecting the distribution,
abundance, and tness of guppies in an experimental aquarium under
laboratory condition. Previous studies.5,30,55,56 also noted that intra–
specic competition is important to affect the distribution, abundance,
and tness of desert rodents.
Effects of inter–specic competition
Previous eld studies demonstrated that interference due to
inter–specic competition had a signicant effect on the distribution,
abundance, and tness of various species in a biotic community.5,7,46,57,58
The result of the simple linear regression revealed that the presence
of goldsh as a competitor signicantly affected (P<0.001) the inter–
specic competition coefcient, suggesting that the interference
of goldsh signicantly affected the distribution, abundance, and
tness of guppies (Table 3), (Figure 4). The territorial behavior of
goldsh might contribute to affect the free movement of guppies in
The effects of competition (intra–specic and inter–specic) and predation on the distribution and
abundance of guppy sh (Poecilia reticulata) 364
Copyright:
©2018 Tadesse
Citation: Tadesse SA. The effects of competition (intra–specic and inter–specic) and predation on the distribution and abundance of guppy sh (Poecilia
reticulata). Int J Avian & Wildlife Biol. 2018;3(5):358‒365. DOI: 10.15406/ijawb.2018.03.00121
an experimental aquarium so that the density of goldsh may have
a signicant effect on the inter–specic competition coefcient. For
example, Joseph54 noted that goldsh are naturally gregarious and
also displaying territorial behavior while feeding. However, the effect
of inter–specic competition due to the territorial behavior of the
competitor (i.e. the goldsh) is beyond the scope of this study. Thus, it
demands further studies just to investigate how the territorial behavior
of goldsh will signicantly contribute to affect the inter–specic
competition coefcient and ultimately the distribution, abundance,
and tness of guppies.
However, the result obtained through the multiple polynomial
regression revealed that the density of guppies signicantly affected
the inter–specic competition coefcient, suggesting that the effect
of guppies density on the distribution, abundance, and tness of
goldsh was weaker than the counteract effect of the density of
goldsh as a competitor on the distribution, abundance, and tness
of guppies. Similarly, in a eld experiment conducted on two
competitive desert rodent species in the Negev Desert of Israel,
Abramsky et al.,5 found that the density of Gerbillus pyramidum
had a signicant effect on the inter–specic competition coefcient,
suggesting that interference of the dominant Gerbillus pyramidum
signicantly affected the distribution, abundance, and tness of the
co–dominant Gerbillus allenbyi. However, the density of Gerbillus
allenbyi did not signicantly affect the inter–specic competition
coefcient, suggesting that Gerbillus allenbyi had weaker effect on
the distribution, abundance, and tness of Gerbillus pyramidum.
Effects of predation
Different ecological researchers in their classical theories noted
that predation is one of the major and primary selective forces in nature
which has been continuously shaping the distribution, abundance,
habitat selection, population dynamics, behavior, and morphology
of different prey species more signicantly than the other natural
selective forces do (e.g. competition).3–5,7,15,44–46,57–59 The result of the
multiple polynomial regression revealed that predation had signicant
effect on the predation coefcient (Figure 7), suggesting that presence
of goldsh as a predator signicantly affected the distribution,
abundance, and tness of guppies in an experimental aquarium. One of
the possible reasons is that prey species are running for their lives, but
predators are running for their dinner, which suggests that predators
have stronger effect on their prey than preys do on their predators.
This is because unlike competition, predation results in fatal accidents
to prey species in a biotic community. However, predator density
affected the predation coefcient in a non–linear fashion (Table 4),
(Figure 7). Moreover, the result of this study revealed that predation
coefcient had only stronger effect in high and low predator densities,
but it had weak effect at the intermediate predator density (Figure
7). This result was in agreement with the results of many previous
researches conducted on the distribution, abundance, and tness of
prey species.3–5,7,46,57,58
Conclusion
Competition and predation are vital forces of evolution which
allow species coexistence in biotic community where resources are
limited in quantity and/or quality. The result of this study revealed
that the distribution, abundance, and tness of guppies’ were affected
by competition (i.e. intra–specic and inter–specic) and predation.
The results of the coefcients of competition and predation suggested
that the effect was density–dependent. Moreover, guppies’ density
affected the competition coefcient when goldsh were present as
a competitor. However, guppies’ density did not affect the predation
coefcient when goldsh were present as predators, suggesting that
guppies had weaker effect on the distribution, abundance, and tness
of their predators (i.e. goldsh). This is in contrast to the results of
Abramsky et al.,5 in which predation and inter–specic competition
between two desert rodent species (i.e. Gerbillus allenbyi and
Gerbillus allenbyi) was signicant, while intra–specic competition
was still important. The result of the present study would lead us to
conclude that the presence of goldsh as predators more strongly
affected the distribution, abundance, and tness of guppies than did
guppies as competitors on goldsh. This is supposed to be the effect
of predation may even result in fatal accident which is very unlikely
in the case of competition among individuals of different species in
a biotic community. With regard to the comparison made between
competition versus predation coefcients, it is difcult to decide
which coefcient had stronger effect than the other. This is because
both coefcients are affected by density as shown in the results of the
polynomial regression. To conclude, if all parameters are kept equal,
predation has the strongest effect on the distribution, abundance, and
tness of guppies followed by the effects of inter–specic and intra–
specic competitions, respectively.
Acknowledgement
None.
Conict of interest
Author declares that there is no conict of interest.
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